Patent Publication Number: US-2022217382-A1

Title: Reference picture resampling in video processing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Patent Application No. PCT/CN2020/116703, filed on Sep. 22, 2020, which claims the priority to and benefit of International Patent Application No. PCT/CN2019/107159, filed on Sep. 22, 2019. The entire disclosure of the aforementioned applications is incorporated by reference as part of the disclosure of this application. 
    
    
     TECHNICAL FIELD 
     This patent document relates to image and video coding and decoding techniques, devices, and systems. 
     BACKGROUND 
     Digital video accounts for the largest bandwidth use on the internet and other digital communication networks. As the number of connected user devices capable of receiving and displaying video increases, it is expected that the bandwidth demand for digital video usage will continue to grow. 
     SUMMARY 
     The disclosed techniques may be used by video decoder or encoder embodiments during video decoding or encoding using alternative temporal motion vector prediction. 
     In one example aspect, a video processing method is disclosed. The method includes determining, for a current video block, a motion vector for use in a sub-block based motion vector prediction (sbTMVP) process to locate a corresponding block in a collocated picture for a conversion between the current video block and a bitstream representation of the current video block, wherein the motion vector used in the sbTMVP process is computed in accordance with a scaling operation; and performing, based on using the motion vector, the conversion between the current video block and the bitstream representation of the visual media data. 
     In another example aspect, another video processing method is disclosed. The method includes determining, for a current video block, a motion vector for use in a sub-block based temporal motion vector prediction (sbTMVP) process to locate a corresponding block in a collocated picture for a conversion between the current video block and a bitstream representation ofthe currentvideoblock, whereinthe motion vector used in the sbTMVP process is computed with respect to a center point of the current video block; modifying the center point of the current video block by applying one or more operations; and performing, based on using the center point modified by applying the one or more operations, the conversion between the current video block and the bitstream representation of the visual media data. 
     In yet another example aspect, another video processing method is disclosed. The method includes determining, for a current video block, a motion vector for use in a sub-block based temporal motion vector prediction (sbTMVP) process to locate a corresponding block in a collocated picture for a conversion between the current video block and a bitstream representation ofthe currentvideoblock, whereinthe motion vector used in the sbTMVP process is computed with respect to a point in the corresponding block in the collocated picture; modifyingthe point in the correspondingblock in the collocated picture by applying one or more operations; and performing, based on usingthe point in the correspondingblockin the collocated picture modified by applying the one or more operations, the conversion between the current video block and the bitstream representation of the visual media data. 
     In yet another aspect, another method of video processing is disclosed. The method includes determining, for a conversion between a video picture included in visual media data and a bitstream representation of the visual media data using sub-pictures, that a rule related to one or more sub-pictures is satisfied by the conversion; and performingthe conversion according to the rule of constraint, wherein the rule specifies that a size of a sub-picture in the video picture is an integer multiple of a coding tree unit size associated with the video picture. 
     In yet another example aspect, another method of video processing is disclosed. The method includes determining, fora conversion between a video picture included in visual media data and a bitstream representation of the visual media data using sub-pictures, that a rule related to one or more sub-pictures is satisfied by the conversion; and performing the conversion according to the rule of constraint, wherein the rule specifies that all sub-pictures in the video picture are non-overlapping, and together the all sub-pictures in the video picture cover entirety of the video picture. 
     In yet another example aspect, another method of video processing is disclosed. The method includes making a determination, for a conversion between a video unit of a visual media and a bitstream representation of the visual media data, whether a reference picture resampling (RPR) technique is used during the conversion; performing the conversion based on the determination, wherein a flag corresponding to the determination is included in the bitstream representation at a sequence parameter set level. 
     In yet another example aspect, another method of video processing is disclosed. The method includes based on satisfying a condition, selecting an interpolation filter during a motion compensation process to derive a prediction block of a current block ofvisual mediadata, wherein the condition is based, at least in part, on determining that a resolution of a reference picture is different from a resolution of the current picture and/or that a dimension of a window associated with the reference picture is different from a dimension of a window associated with the current picture; and performing a conversion between the current block of visual media data and a bitstream representation of the current block. 
     In yet another example aspect, another method of video processing is disclosed. The method includes determining, for a conversion between a current block of a visual media data and a bitstream representation of the visual media data, that the current block is a combined intra and intra predicted (CIIP) block, wherein an intra prediction block for the CIIP block is generated using a size of a transform unit (TU), wherein, in the combined inter intra prediction (CIIP) block, a final prediction of the current block is based on a weighted sum of an inter prediction of the current block and an intra prediction of the current block; and performing the conversion based on the determining. 
     In yet another example aspect, a video encoder apparatus is disclosed. The video encoder apparatus includes a processor that is configured to implement a method described herein. 
     In yet another example aspect, a video decoder apparatus is disclosed. The video decoder apparatus includes a processor that is configured to implement a method described herein. 
     In yet another aspect, a computer readable medium having code stored thereupon is disclosed. The code, when executed by a processor, causes the processor to implement a method described in the present document. 
     These, and other, aspects are described in the present document. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
         FIG. 1  is an example of derivation process for merge candidates list construction. 
         FIG. 2  shows example positions of spatial merge candidates. 
         FIG. 3  shows an example of candidate pairs considered for redundancy check of spatial merge candidates. 
         FIG. 4A-4B  show example positions for the second PU of N×2N and 2N×N partitions. 
         FIG. 5  is an example illustration of motion vector scaling for temporal merge candidate. 
         FIG. 6  shows example candidate positions for temporal merge candidate, C0 and C1. 
         FIG. 7  shows an example of combined bi-predictive merge candidate. 
         FIG. 8  shows an example derivation process for motion vector prediction candidates. 
         FIG. 9  is an example illustration of motion vector scaling for spatial motion vector candidate. 
         FIG. 10  shows an example of alternative temporal motion vector prediction (ATMVP) motion prediction for a CU. 
         FIG. 11  shows an example of one CU with four sub-blocks (A-D) and its neighbouring blocks (ad). 
         FIG. 12  is a flowchart of an example of encoding with different MV precision 
         FIG. 13A-13B  show 135 degree partition type (splitting from top-left corner to bottom-right corner), and 45 degree splitting patterns. An illustration of splitting a CU into two triangular prediction units (two splitting patterns). 
         FIG. 14  shows an example of position of the neighboring blocks. 
         FIG. 15  shows examples of above and left blocks of a video block. 
         FIGS. 16A-16B  show examples of 2 control point motion vectors (CPMVs) and 3 CPMVs. 
         FIG. 17  shows an example of affine MVF per sub-block. 
         FIGS. 18A-18B  show examples of 4 and 6 parameter affine models. 
         FIG. 19  MVP for AF INTER for inherited affine candidates. 
         FIG. 20  shows an example of constructing affine motion predictors in AF_INTER. 
         FIG. 21A-21B  show examples of control point motion vectors in affine coding in AF_MERGE. 
         FIG. 22  shows examples of candidate positions for affine merge mode. 
         FIG. 23  shows an example of intra-picture block copy operation. 
         FIG. 24  shows an example of a valid corresponding region in the collocated picture. 
         FIG. 25  shows an example flowchart for history based motion vector prediction. 
         FIG. 26  shows modified merge list construction process. 
         FIG. 27  shows an example embodiment of the proposed valid region when the current block is inside a Basic Region. 
         FIG. 28  shows an example embodiment of a valid region when the current block is not inside a basic region. 
         FIG. 29  is a block diagram of an example of a video processing apparatus. 
         FIG. 30  is a flowchart for an example of a video processing method. 
         FIG. 31A  shows an example of locations for identification of default motion information in the current standards. 
         FIG. 31B  shows an example of locations for identification of default motion information in the proposed standards. 
         FIG. 32  is a block diagram of an example video processing system in which disclosed techniques may be implemented. 
         FIG. 33  is a flowchart for an example of a visual media processing method. 
         FIG. 34  is a flowchart for an example of a visual media processing method. 
         FIG. 35  is a flowchart for an example of a visual media processing method. 
         FIG. 36  is a flowchart for an example of a visual media processing method. 
         FIG. 37  is a flowchart for an example of a visual media processing method. 
         FIG. 38  is a flowchart for an example of a visual media processing method. 
         FIG. 39  is a flowchart for an example of a visual media processing method. 
         FIG. 40  is a flowchart for an example of a visual media processing method. 
         FIG. 41  is a block diagram that illustrates an example video coding system. 
         FIG. 42  is a block diagram that illustrates an encoder in accordance with some embodiments of the present disclosure. 
         FIG. 43  is a block diagram that illustrates a decoder in accordance with some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present document provides various techniques that can be used by a decoder of video bitstreams to improve the quality of decompressed or decoded digital video or images. Furthermore, a video encoder may also implement these techniques during the process of encoding in order to reconstruct decoded frames used for further encoding. 
     Section headings are used in the present document for ease of understanding and do not limit the embodiments and techniques to the corresponding sections. As such, embodiments from one section can be combined with embodiments from other sections. 
     1. Summary 
     This patent document is related to video coding technologies. Specifically, it is related to motion vector coding in video coding. It may be applied to the existing video coding standard like HEVC, or the standard (Versatile Video Coding) to be finalized. It may be also applicable to future video coding standards or video codec. 
     2. Introductory Remarks 
     Video coding standards have evolved primarily through the development of the well-known ITU-T and ISO/IEC standards. The ITU-T produced H.261 and H.263, ISO/IEC produced MPEG-1 and MPEG-4 Visual, and the two organizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4 Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, the video coding standards are based on the hybrid video coding structure wherein temporal prediction plus transform coding are utilized. To explore the future video coding technologies beyond HEVC, Joint Video Exploration Team (WET) was founded by VCEG and MPEG jointly in 2015. Since then, many new methods have been adopted by JVET and put into the reference software named Joint Exploration Model (JEM). In April 2018, the Joint Video Expert Team (JVET) between VCEG (Q6/16) and ISO/IEC JTC1 SC29/WG11 (MPEG) was created to work on the VVC standard targeting at 50% bitrate reduction compared to HEVC. 
     The latest version of VVC draft, i.e., Versatile Video Coding (Draft 3) can be found at http://phenix.it-sudparis.eu/jvet/doc_end_user/documents/12_Macao/wg11/JVET-L1001-v2.zip. The latest reference software of VVC, named VTM, can be found at: https://vcgit.hhi.fraunhofer.de/jvet/VVCSoftware_VTM/tagsNTM-3.0rc1 
     2.1 Inter Prediction in HEVC/H.265 
     Each inter-predicted PU has motion parameters for one or two reference picture lists. Motion parameters include a motion vector and a reference picture index. Usage of one of the two reference picture lists may also be signaled using inter_pred_idc. Motion vectors may be explicitly coded as deltas relative to predictors. 
     When a CU is coded with skip mode, one PU is associated with the CU, and there are no significant residual coefficients, no coded motion vector delta or reference picture index. A merge mode is specified whereby the motion parameters for the current PU are obtained from neighboring PUs, including spatial and temporal candidates. The merge mode can be applied to any inter-predicted PU, not only for skip mode. The alternative to merge mode is the explicit transmission of motion parameters, where motion vector (to be more precise, motion vector differences (MVD) compared to a motion vector predictor), corresponding reference picture index for each reference picture list and reference picture list usage are signaled explicitly per each PU. Such a mode is named Advanced motion vector prediction (AMVP) in this disclosure. 
     When signaling indicates that one of the two reference picture lists is to be used, the PU is produced from one block of samples. This is typically referred to as ‘uni-prediction’. Uni-prediction is available both for P-slices and B-slices. 
     When signaling indicates that both of the reference picture lists are to be used, the PU is produced from two blocks of samples. This is referred to as ‘bi-prediction’. Bi-prediction is available for B-slices only. 
     The following text provides the details on the inter prediction modes specified in HEVC. The description will start with the merge mode. 
     2.1.1 Reference Picture List 
     In HEVC, the term inter prediction is used to denote prediction derived from data elements (e.g., sample values or motion vectors) of reference pictures other than the current decoded picture. Like in H.264/AVC, a picture canbe predicted from multiple reference pictures. The reference pictures that are used for inter prediction are organized in one or more reference picture lists. The referenceindex identifies which of the reference pictures in the list can be used for creating the prediction signal. 
     A single reference picture list, List 0, is used for a P slice and two reference picture lists, List 0 and List 1 are used for B slices. Reference pictures included in List 0/1 can be from past and future pictures in terms of capturing/display order. 
     2.1.2 Merge Mode 
     2.1.2.1 Derivation of Candidates for Merge Mode 
     When a PU is predicted using merge mode, an index pointing to an entry in the merge candidates list is parsed from the bitstream and used to retrieve the motion information. The construction of this list is specified in the HEVC standard and can be summarized according to the following sequence of steps:
         Step 1: Initial candidates derivation
           Step 1.1: Spatial candidates derivation   Step 1.2: Redundancy check for spatial candidates   Step 1.3: Temporal candidates derivation   
           Step 2: Additional candidates insertion
           Step 2.1: Creation of bi-predictive candidates   Step 2.2: Insertion of zero motion candidates   
               

     These steps are also schematically depicted in  FIG. 1 . For spatial merge candidate derivation, a maximum of four merge candidates are selected among candidates that are located in five different positions. For temporal merge candidate derivation, a maximum of one merge candidate is selected among two candidates. Since constant number of candidates for each PU is assumed at decoder, additional candidates are generated when the number of candidates obtained from step 1 does not reach the maximum number of merge candidate (MaxNumMergeCand) which is signaled in slice header. Since the number of candidates is constant, index of best merge candidate is encoded using truncated unary binarization (TU). If the size of CU is equal to 8, all the PUs of the current CU share a single merge candidate list, which is identical to the merge candidate list of the 2N×2N prediction unit. 
     In the following, the operations associated with the aforementioned steps are detailed. 
     2.1.2.2 Spatial Candidates Derivation 
     In the derivation of spatial merge candidates, a maximum of four merge candidates are selected among candidates located in the positions depicted in  FIG. 2 . The order of derivation is A 1 , B 1 , B 0 , A 0  and B 2 . Position B 2  is considered only when any PU of position A 1 , B 1 , B 0 , A 0  is not available (e.g. because it belongs to another slice or tile) or is intra coded. After candidate at position A 1  is added, the addition of the remaining candidates is subject to a redundancy check which ensures that candidates with same motion information are excluded from the list so that coding efficiency is improved. To reduce computational complexity, not all possible candidate pairs are considered in the mentioned redundancy check. Instead only the pairs linked with an arrow in  FIG. 3  are considered and a candidate is only added to the list if the corresponding candidate used for redundancy check has not the same motion information. Another source of duplicate motion information is the “second PU” associated with partitions different from 2N×2N. As an example,  FIGS. 4A -4B depict the second PU for the case of N×2N and 2N×N, respectively. When the current PU is partitioned as N×2N, candidate at position A l  is not considered for list construction. In fact, by adding this candidate will lead to two prediction units having the same motion information, which is redundant to just have one PU in a coding unit. Similarly, position B 1  is not considered when the current PU is partitioned as 2N×N. 
     2.1.2.3 Temporal Candidates Derivation 
     In this step, only one candidate is added to the list. Particularly, in the derivation of this temporal merge candidate, a scaled motion vector is derived based on co-located PU belonging to the picture which has the smallest POC difference with current picture within the given reference picture list. The reference picture list to be used for derivation of the co-located PU is explicitly signaled in the slice header. The scaled motion vector for temporal merge candidate is obtained as illustrated by the dotted line in  FIG. 5 , which is scaled from the motion vector of the co-located PU using the POC distances, tb and td, where tb is defined to be the POC difference between the reference picture of the current picture and the current picture and td is defined to be the POC difference between the reference picture of the co-located picture and the co-located picture. The reference picture index of temporal merge candidate is set equal to zero. A practical realization of the scaling process is described in the HEVC specification. For a B-slice, two motion vectors, one is for reference picture list 0 and the other is for reference picture list 1, are obtained and combined to make the bi-predictive merge candidate. 
       FIG. 5  is an illustration of motion vector scaling for temporal merge candidate. 
     In the co-located PU (Y) belonging to the reference frame, the position for the temporal candidate is selected between candidates C 0  and C 1 , as depicted in  FIG. 6 . If PU at position C 0  is not available, is intra coded, or is outside of the current coding tree unit (CTU aka. LCU, largest coding unit) row, position C 1  is used. Otherwise, position C o  is used in the derivation of the temporal merge candidate. 
       FIG. 6  shows examples of candidate positions for temporal merge candidate, C0 and C1. 
     2.1.2.4 Additional Candidates Insertion 
     Besides spatial and temporal merge candidates, there are two additional types of merge candidates: combined bi-predictive merge candidate and zero merge candidate. Combined bi-predictive merge candidates are generated by utilizing spatial and temporal merge candidates. Combined bi-predictive merge candidate is used for B-Slice only. The combined bi-predictive candidates are generated by combining the first reference picture list motion parameters of an initial candidate with the second reference picture list motion parameters of another. If these two tuples provide different motion hypotheses, they will form a new bi-predictive candidate. As an example,  FIG. 7  depicts the case when two candidates in the original list (on the left), which have mvL0 and refIdxL0 or mvL0 and refIdxL1, are used to create a combined bi-predictive merge candidate added to the final list (on the right). There are numerous rules regarding the combinations which are considered to generate these additional merge candidates. 
     Zero motion candidates are inserted to fill the remaining entries in the merge candidates list and therefore hit the MaxNumMergeCand capacity. These candidates have zero spatial displacement and a reference picture index which starts from zero and increases every time a new zero motion candidate is added to the list. 
     More specifically, the following steps are performed in order till the merge list is full:
         1. Set variable numRef to either number of reference picture associated with list 0 for P slice, or the minimum number of reference pictures in two lists for B slice;   2. Add non-repeated zero motion candidates:
           For variable i being 0 . . . numRef-1, add a default motion candidate with MV set to (0, 0) and reference picture index set to i for list 0 (if P slice), or for both lists (if B slice).   
           3. Add repeated zero motion candidates with MV set to (0, 0), reference picture index of list 0 set to 0 (if P slice) and reference picture indices of both lists set to 0 (if B slice).       

     Finally, no redundancy check is performed on these candidates. 
     2.1.3 AMVP 
     AMVP exploits spatio-temporal correlation of motion vector with neighbouring PUs, which is used for explicit transmission of motion parameters. For each reference picture list, a motion vector candidate list is constructed by firstly checking availability of left, above temporally neighbouring PU positions, removing redundant candidates and adding zero vector to make the candidate list to be constant length. Then, the encoder can select the best predictor from the candidate list and transmit the corresponding index indicating the chosen candidate. Similarly with merge index signaling, the index of the best motion vector candidate is encoded using truncated unary. The maximum value to be encoded in this case is 2 (see  FIG. 8 ). In the following sections, details about derivation process of motion vector prediction candidate are provided. 
     2.1.3.1 Derivation of AMVP Candidates 
       FIG. 8  summarizes derivation process for motion vector prediction candidate. 
     In motion vector prediction, two types of motion vector candidates are considered: spatial motion vector candidate and temporal motion vector candidate. For spatial motion vector candidate derivation, two motion vector candidates are eventually derived based on motion vectors of each PU located in five different positions as depicted in  FIG. 2 . 
     For temporal motion vector candidate derivation, one motion vector candidate is selected from two candidates, which are derived based on two different co-located positions. After the first list of spatio-temporal candidates is made, duplicated motion vector candidates in the list are removed. If the number of potential candidates is larger than two, motion vector candidates whose reference picture index within the associated reference picture list is larger than 1 are removed from the list. If the number of spatio-temporal motion vector candidates is smaller than two, additional zero motion vector candidates is added to the list. 
     2.1.3.2 Spatial Motion Vector Candidates 
     In the derivation of spatial motion vector candidates, a maximum oftwo candidates are considered among five potential candidates, which are derived from PUs located in positions as depicted in  FIG. 2 , those positions being the same as those of motion merge. The order of derivation for the left side of the current PU is defined as A 0 , A 1 , and scaled A 0 , scaled A 1 . The order of derivation for the above side of the current PU is defined as B 0 , B 1 , B 2 , scaled B 0 , scaled B 1 , scaled B 2 . For each side there are therefore four cases that can be used as motion vector candidate, with two cases not required to use spatial scaling, and two cases where spatial scaling is used. The four different cases are summarized as follows.
         No spatial scaling
           (1) Same reference picture list, and same reference picture index (same POC)   (2) Different reference picture list, but same reference picture (same POC)   
           Spatial scaling
           (3) Same reference picture list, but different reference picture (different POC)   (4) Different reference picture list, and different reference picture (different POC)   
               

     The no-spatial-scaling cases are checked first followed by the spatial scaling Spatial scaling is considered when the POC is different between the reference picture of the neighbouring PU and that of the current PU regardless of reference picture list. If all PUs of left candidates are not available or are intra coded, scaling for the above motion vector is allowed to help parallel derivation of left and above MV candidates. Otherwise, spatial scaling is not allowed for the above motion vector. 
     In a spatial scaling process, the motion vector of the neighboring PU is scaled in a similar manner as for temporal scaling, as depicted in  FIG. 9 . The main difference is that the reference picture list and index of current PU is given as input; the actual scaling process is the same as that of temporal scaling. 
     2.1.3.3 Temporal Motion Vector Candidates 
     Apart for the reference picture index derivation, all processes for the derivation of temporal merge candidates are the same as for the derivation of spatial motion vector candidates (see  FIG. 6 ). The reference picture index is signaled to the decoder. 
     2.2 Sub-CU Based Motion Vector Prediction Methods in JEM 
     In the JEM with QTBT, each CU can have at most one set of motion parameters for each prediction direction. Two sub-CU level motion vector prediction methods are considered in the encoder by splitting a large CU into sub-CUs and deriving motion information for all the sub-CUs of the large CU. Alternative temporal motion vector prediction (ATMVP) method allows each CU to fetch multiple sets of motion information from multiple blocks smaller than the current CU in the collocated reference picture. In spatial-temporal motion vector prediction (STMVP) method motion vectors of the sub-CUs are derived recursively by using the temporal motion vector predictor and spatial neighboring motion vector. 
     To preserve more accurate motion field for sub-CU motion prediction, the motion compression for the reference frames is currently disabled. 
       FIG. 10  shows an example of ATMVP motion prediction for a CU. 
     2.2.1 Alternative Temporal Motion Vector Prediction 
     In the alternative temporal motion vector prediction (ATMVP) method, the motion vectors temporal motion vector prediction (TMVP) is modified by fetching multiple sets of motion information (including motion vectors and reference indices) from blocks smaller than the current CU. The sub-CUs are square N×N blocks (N is set to 4 by default). 
     ATMVP predicts the motion vectors of the sub -CUs within a CU in two steps. The first step is to identify the corresponding block in a reference picture with a so-called temporal vector. The reference picture is called the motion source picture. The second step is to split the current CU into sub-CUs and obtain the motion vectors as well as the reference indices of each sub-CU from the block corresponding to each sub-CU. 
     In the first step, a reference picture and the corresponding block is determined by the motion information of the spatial neighboring blocks of the current CU. To avoid the repetitive scanning process of neighboring blocks, the first merge candidate in the merge candidate list of the current CU is used. The first available motion vector as well as its associated reference index are set to be the temporal vector and the index to the motion source picture. This way, in ATMVP, the corresponding block may be more accurately identified, compared with TMVP, wherein the corresponding block (sometimes called collocated block) is always in a bottom-right or center position relative to the current CU. 
     In the second step, a corresponding block of the sub-CU is identified by the temporal vector in the motion source picture, by adding to the coordinate of the current CU the temporal vector. For each sub-CU, the motion information of its corresponding block (the smallest motion grid that covers the center sample) is used to derive the motion information for the sub-CU. After the motion information of a corresponding N×N block is identified, it is converted to the motion vectors and reference indices of the current sub-CU, in the same way as TMVP of HEVC, wherein motion scaling and other procedures apply. For example, the decoder checks whether the low-delay condition (i.e. the POCs of all reference pictures of the current picture are smaller than the POC of the current picture) is fulfilled and possibly uses motion vector MV x  ((the motion vector corresponding to reference picture list X) to predict motion vector MV y  (with X being equal to 0 or 1 and Y being equal to 1−X) for each sub-CU. 
     2.2.2 Spatial-Temporal Motion Vector Prediction (STMVP) 
     In this method, the motion vectors of the sub-CUs are derived recursively, following raster scan order.  FIG. 11  illustrates this concept. For example,  FIG. 11  shows a 8×8 CU with four 4×4 sub-CUs A, B, C, and D. The neighbouring 4×4 blocks in the current frame are labelled as a, b, c, and d. 
     The motion derivation for sub-CU A starts by identifying its two spatial neighbours. The first neighbour is the N×N block above sub-CU A (block c). If this block c is not available or is intra coded the other N×N blocks above sub-CU A are checked (from left to right, starting at block c). The second neighbour is a block to the left of the sub-CU A (block b). If block b is not available or is intra coded other blocks to the left of sub-CU A are checked (from top to bottom, staring at block b). The motion information obtained from the neighbouring blocks for each list is scaled to the first reference frame for a given list. Next, temporal motion vector predictor (TMVP) of sub-block A is derived by following the same procedure of TMVP derivation as specified in HEVC. The motion information of the collocated block at location D is fetched and scaled accordingly. Finally, after retrieving and scaling the motion information, all available motion vectors (up to 3) are averaged separately for each reference list. The averaged motion vector is assigned as the motion vector of the current sub-CU. 
     2.2.3 Sub-CU Motion Prediction Mode Signalling 
     The sub-CU modes are enabled as additional merge candidates and there is no additional syntax element required to signal the modes. Two additional merge candidates are added to merge candidates list of each CU to represent the ATMVP mode and STMVP mode. Up to seven merge candidates are used, if the sequence parameter set indicates that ATMVP and STMVP are enabled. The encoding logic of the additional merge candidates is the same as for the merge candidates in the HM, which means, for each CU in P or B slice, two more RD checks is needed for the two additional merge candidates. 
     In the JEM, all bins of merge index is context coded by CABAC. While in HEVC, only the first bin is context coded and the remaining bins are context by-pass coded. 
     2.3 Inter Prediction Methods in VVC 
     There are several new coding tools for inter prediction improvement, such as Adaptive motion vector difference resolution (AMVR) for signaling MVD, affine prediction mode, Triangular prediction mode (TPM), ATMVP, Generalized Bi-Prediction (GBI), Bi-directional Optical flow (BIO). 
     2.3.1 Adaptive Motion Vector Difference Resolution 
     In HEVC, motion vector differences (MVDs) (between the motion vector and predicted motion vector of a PU) are signalled in units of quarter luma samples when use_integer_mv_flag is equal to 0 in the slice header. In the VVC, a locally adaptive motion vector resolution (LAMVR) is introduced. In the VVC, MVD can be coded in units of quarter luma samples, integer luma samples or four luma samples (i.e., ¼-pel, 1-pel, 4-pel). The MVD resolution is controlled atthe codingunit (CU) level, and MVD resolution flags are conditionally signalled for each CU that has at least one non-zero MVD components. 
     For a CU that has at least one non-zero MVD components, a first flag is signalled to indicate whether quarter luma sample MV precision is used in the CU. When the first flag (equal to 1) indicates that quarter luma sample MV precision is not used, another flag is signalled to indicate whether integer luma sample MV precision or four luma sample MV precision is used. 
     When the first MVD resolution flag of a CU is zero, or not coded for a CU (meaning all MVDs in the CU are zero), the quarter luma sample MV resolution is used for the CU. When a CU uses integer-luma sample MV precision or four-luma-sample MV precision, the MVPs in the AMVP candidate list for the CU are rounded to the corresponding precision. 
     In the encoder, CU-level RD checks are used to determine which MVD resolution is to be used for a CU. That is, the CU-level RD check is performed three times for each MVD resolution. To accelerate encoder speed, the following encoding schemes are applied in the JEM.
         During RD check of a CU with normal quarter luma sample MVD resolution, the motion information of the current CU (integer luma sample accuracy) is stored. The stored motion information (after rounding) is used as the starting point for further small range motion vector refinement during the RD check for the same CU with integer luma sample and 4 luma sample MVD resolution so that the time-consuming motion estimation process is not duplicated three times.   RD check of a CU with 4 luma sample MVD resolution is conditionally invoked. For a CU, when RD cost integer luma sample MVD resolution is much larger than that of quarter luma sample MVD resolution, the RD check of 4 luma sample MVD resolution for the CU is skipped.       

     The encoding process is shown in  FIG. 12 . First, ¼ pel MV is tested and the RD cost is calculated and denoted as RDCost 0 , then integer MV is tested and the RD cost is denoted as RDCost 1 . If RDCost 1 &lt;th*RDCost 0  (wherein th is a positive value), then 4-pel MV is tested; otherwise, 4-pel MV is skipped. Basically, motion information and RD cost etc. are already known for 1/4 p el MV when checking integer or 4-pel MV, which can be reused to speed up the encoding process of integer or 4-pel MV. 
     2.3.2 Triangular Prediction Mode 
     The concept of the triangular prediction mode (TPM) is to introduce a new triangular partition for motion compensated prediction. As shown in  FIGS. 13A-13B , it splits a CU into two triangular prediction units, in either diagonal or inverse diagonal direction. Each triangular prediction unit in the CU is inter-predicted using its own uni-prediction motion vector and reference frame index which are derived from a single uni-prediction candidate list. An adaptive weighting process is performed to the diagonal edge after predicting the triangular prediction units. Then, the transform and quantization process are applied to the whole CU. This mode is only applied to merge mode, (skip mode is treated as a special merge mode). 
       FIG. 13A-13B  are illustrations of splitting a CU into two triangular prediction units (two splitting patterns). For example,  FIG. 13A  shows an example of a 135 degree partition type (splitting from top-left corner to bottom-right corner) and  FIG. 13B  shows an example of a 45 degree splitting pattern. 
     2.3.2.1 Uni-Prediction Candidate List for TPM 
     The uni-prediction candidate list, named TPM motion candidate list, consists of five uni-prediction motion vector candidates. It is derived from seven neighboring blocks including five spatial neighboring blocks (1 to 5) and two temporal co-located blocks (6 to 7), as shown in  FIG. 14 . The motion vectors of the seven neighboring blocks are collected and put into the uni-prediction candidate list according in the order of uni-prediction motion vectors, L0 motion vector of bi-prediction motion vectors, L1 motion vector of bi-prediction motion vectors, and averaged motion vector of the L0 and L1 motion vectors of bi-prediction motion vectors. If the number of candidates is less than five, zero motion vector is added to the list. Motion candidates added in this list for TPM are called TPM candidates, motion information derived from spatial/temporal blocks are called regular motion candidates. 
     More specifically, the following steps are involved:
         1) Obtain regular motion candidates from A 1 , B 1 , B 0 , A 0 , B 2 , Col and Col2 (corresponding to block  1 - 7  in  FIG. 14 ) with full pruning operations when adding a regular motion candidate from spatial neighboring blocks.   2) Set variable numCurrMergeCand=0   3) For each regular motion candidates derived from A 1 , B 1 , B 0 , A 0 , B 2 , Col and Col2, if not pruned and numCurrMergeCand is less than 5, if the regular motion candidate is uni-prediction (either from List 0 or List 1), it is directly added to the merge list as an TPM candidate with numCurrMergeCand increased by 1. Such a TPM candidate is named ‘originally uni-predicted candidate’.
           Full pruning is applied.   
           4) For each motion candidates derived from A 1 , B 1 , B 0 , A 0 , B 2 , Col and Col2, if not pruned, and numCurrMergeCand is less than 5, if the regular motion candidate is bi-prediction, the motion information from List 0 is added to the TPM merge list (that is, modified to be uni-prediction from List 0) as a new TPM candidate and numCurrMergeCand increased by 1. Such a TPM candidate is named ‘Truncated List0-predicted candidate’.
           Full pruning is applied.   
           5) For each motion candidates derived from A 1 , B 1 , B 0 , A 0 , B 2 , Col and Col2, if not pruned, and numCurrMergeCand is less than 5, if the regular motion candidate is bi-prediction, the motion information from List 1 is added to the TPM merge list (that is, modified to be uni-prediction from List 1) and numCurrMergeCand increased by 1. Such a TPM candidate is named ‘Truncated Listl-predicted candidate’.
 
Full pruning is applied.
   6) For each motion candidates derived from A 1 , B 1 , B 0 , A 0 , B 2 , Col and Col2, if not pruned, and numCurrMergeCand is less than 5, if the regular motion candidate is bi-prediction,   If List 0 reference picture&#39;s slice QP is smaller than List 1 reference picture&#39;s slice QP, the motion information of List 1 is firstly scaled to List 0 reference picture, and the average of the two MVs (one is from original List 0, and the other is the scaled MV from List 1) is added to the TPM merge list, such a candidate is called averaged uni-prediction from List 0 motion candidate and numCurrMergeCand increased by 1.   Otherwise, the motion information of List 0 is firstly scaled to List 1 reference picture, and the average of the two MVs (one is from original List 1, and the other is the scaled MV from List 0) is added to the TPM merge list, such a TPM candidate is called averaged uni-prediction from List 1 motion candidate and numCurrMergeCand increased by 1.
 
Full pruning is applied.
   7) If numCurrMergeCand is less than 5, zero motion vector candidates are added.       

     When inserting a candidate to the list, if it has to be compared to all previously added candidates to see whether it is identical to one of them, such a process is called full pruning 
     2.3.2.2 Adaptive Weighting Process 
     After predicting each triangular prediction unit, an adaptive weighting process is applied to the diagonal edge between the two triangular prediction units to derive the final prediction for the whole CU. Two weighting factor groups are defined as follows:
         1 st  weighting factor group: {7/8, 6/8, 4/8, 2/8, 1/8} and {7/8, 4/8, 1/8} are used for the luminance and the chrominance samples, respectively;   2 nd  weighting factor group: {7/8, 6/8, 5/8, 4/8, 3/8, 2/8, 1/8} and {6/8, 4/8, 2/8} are used for the luminance and the chrominance samples, respectively.       

     Weighting factor group is selected based on the comparison of the motion vectors of two triangular prediction units. The 2 nd  weighting factor group is used when the reference pictures of the two triangular prediction units are different from each other or their motion vector difference is larger than 16 pixels. Otherwise, the Pt weighting factor group is used. 
     2.3.2.3 Signaling of Triangular Prediction Mode (TPM) 
     One bit flag to indicate whether TPM is used may be firstly signaled. Afterwards, the indications of two splitting patterns (as depicted in  FIGS. 13A-13B ), and selected merge indices for each of the two partitions are further signaled. 
     2.3.2.3.1 Signaling of TPM Flag 
     If the width and height of a luma block is denoted by W and H, respectively, the, for W*H&lt;64, triangular prediction mode is disabled. 
     When one block is coded with affine mode, triangular prediction mode is also disabled. 
     When one block is coded with merge mode, one bit flag may be signaled to indicate whether the triangular prediction mode is enabled or disabled for the block. 
     The flag is coded with 3 contexts, based on the following equation: 
       Ctx index=((left block  L  available &amp;&amp;  L  is coded with TPM?)1:0)+((Above block A available &amp;&amp; A is coded with TPM?)1:0);
 
       FIG. 15  shows examples ofneighboringblocks (A and L) used for context selection in TPM flag coding. 
     2.3.2.3.2 Signaling of an Indication of Two Splitting Patterns (as depicted in  FIG. 13 ), and Selected Merge Indices for Each of the Two Partitions 
     It is noted that splitting patterns, merge indices of two partitions are jointly coded. Further, the merge indices are restricted so that the two partitions cannot use the same reference index. Therefore, there are 2 (splitting patterns)*N (maximum number of merge candidates)*(N−1) possibilities wherein N is set to 5. One indication is coded and the mapping between the splitting patterns, two merge indices and coded indication are derived from the array defined below:
         const uint8_t_g TriangleCombination[TRIANGLE_MAX_NUM_CANDS][3]={0, 1, 0}, {1, 0, 1}, {1, 0, 2}, {0, 0, 1}, {0, 2, 0}, {1, 0, 3}, {1, 0, 4}, {1, 1, 0}, {0, 3, 0}, {0, 4, 0}, {0, 0, 2}, {0, 1, 2}, {1, 1, 2}, {0, 0, 4}, {0, 0, 3}, {0, 1, 3}, {0, 1, 4}, {1, 1, 4}, {1, 1, 3}, {1, 2, 1}, {1, 2, 0}, {0, 2, 1}, {0, 4, 3}, {1, 3, 0}, {1, 3, 2}, {1, 3, 4}, {1, 4, 0}, {1, 3, 1}, {1, 2, 3}, {1, 4, 1}, {0, 4, 1}, {0, 2, 3}, {1, 4, 2}, {0, 3, 2}, {1, 4, 3}, {0, 3, 1}, {0, 2, 4}, {1, 2, 4}, {0, 4, 2}, {0, 3, 4}};       splitting patterns (45 degree or 135 degree)=g_TriangleCombination[signaledindication][0];   Merge index of candidate A=g_TriangleCombination[signaled indication][1];   Merge index of candidate B=g_TriangleCombination[signaled indication][2];   

     Once the two motion candidates A and B are derived, the two partitions&#39; (PU1 and PU2) motion information can be set either from A or B. Whether PU1 uses the motion information of merge candidate A or B is dependent on the prediction directions of the two motion candidates. Table 1 shows the relationship between two derived motion candidates A and B, with the two partitions. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Derivation of partitions&#39; motion information 
               
               
                 from derived two merge candidates (A, B) 
               
            
           
           
               
               
               
               
            
               
                 Prediction 
                 Prediction 
                 PU1&#39;s motion 
                 PU2&#39;s motion 
               
               
                 direction of A 
                 direction of B 
                 information 
                 information 
               
               
                   
               
               
                 L0 
                 L0 
                 A (L0) 
                 B (L0) 
               
               
                 L1 
                 L1 
                 B (L1) 
                 A (L1) 
               
               
                 L0 
                 L1 
                 A (L0) 
                 B (L1) 
               
               
                 L1 
                 L0 
                 B (L0) 
                 A (L1) 
               
               
                   
               
            
           
         
       
     
     2.3.2.3.3 Entropy Coding of the Indication (Denoted by Merge_Triangle_idx) 
     
         
         merge triangle idx is within the range [0, 39], inclusively. K-th order Exponential Golomb (EG) code is used for binarization of merge triangle idx wherein K is set to 1. 
       
    
     K-th Order EG 
     To encode larger numbers in fewer b its (at the expense ofu sing more bits to encode smaller numbers), this can be generalized using a nonnegative integer parameter k. To encode a nonnegative integer x in an order-k exp-Golomb code.
         1. Encode └x/2 x ┘ using order-0 exp-Golomb code described above, then   2. Encode x mod 2 k  in binary       

     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Exp-Golomb-k coding examples 
               
            
           
           
               
               
               
               
               
            
               
                   
                 x 
                 k = 0 
                 k = 1 
                 k = 2 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 0 
                 1 
                 10 
                 100 
               
               
                   
                 1 
                 010 
                 11 
                 101 
               
               
                   
                 2 
                 011 
                 0100 
                 110 
               
               
                   
                 3 
                 00100 
                 0101 
                 111 
               
               
                   
                 4 
                 00101 
                 0110 
                 01000 
               
               
                   
                 5 
                 00110 
                 0111 
                 01001 
               
               
                   
                 6 
                 00111 
                 001000 
                 01010 
               
               
                   
                 7 
                 0001000 
                 001001 
                 01011 
               
               
                   
                 8 
                 0001001 
                 001010 
                 01100 
               
               
                   
                 9 
                 0001010 
                 001011 
                 01101 
               
               
                   
                 10 
                 0001011 
                 001100 
                 01110 
               
               
                   
                 11 
                 0001100 
                 001101 
                 01111 
               
               
                   
                 12 
                 0001101 
                 001110 
                 0010000 
               
               
                   
                 13 
                 0001110 
                 001111 
                 0010001 
               
               
                   
                 14 
                 0001111 
                 00010000 
                 0010010 
               
               
                   
                 15 
                 000010000 
                 00010001 
                 0010011 
               
               
                   
                 16 
                 000010001 
                 00010010 
                 0010100 
               
               
                   
                 17 
                 000010010 
                 00010011 
                 0010101 
               
               
                   
                 18 
                 000010011 
                 00010100 
                 0010110 
               
               
                   
                 19 
                 000010100 
                 00010101 
                 0010111 
               
               
                   
                   
               
            
           
         
       
     
     2.3.3 Affine Motion Compensation Prediction 
     In HEVC, only translation motion model is applied for motion compensation prediction (MCP). While in the real world, there are many kinds of motion, e.g. zoom in/out, rotation, perspective motions and the other irregular motions. In VVC, a simplified affine transform motion compensation prediction is applied with 4-parameter affine model and 6-parameter affine model. As shown  FIGS. 16A-16B , the affine motion field of the block is described by two control point motion vectors (CPMVs) for the 4-parameter affine model ( FIG. 16A ) and 3 CPMVs for the 6-parameter affine model ( FIG. 16B ). 
     The motion vector field (MVF) of a block is described by the following equations with the 4-parameter affine model (wherein the 4-parameter are defined as the variables a, b, e and f) in equation (1) and 6-parameter affine model (wherein the 4-parameter are defined as the variables a, b, c, d, e and f) in equation (2) respectively: 
     
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             m 
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                                 ) 
                               
                             
                           
                           = 
                           
                             
                               
                                 a 
                                 ⁢ 
                                 x 
                               
                               - 
                               
                                 b 
                                 ⁢ 
                                 y 
                               
                               + 
                               e 
                             
                             = 
                             
                               
                                 
                                   
                                     ( 
                                     
                                       
                                         m 
                                         ⁢ 
                                         
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                                 ( 
                                 
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                           = 
                           
                             
                               
                                 b 
                                 ⁢ 
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                                 a 
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                               f 
                             
                             = 
                             
                               
                                 
                                   
                                     ( 
                                     
                                       
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                   { 
                   
                     
                       
                         
                           
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                           = 
                           
                             
                               
                                 a 
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                                 c 
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                               e 
                             
                             = 
                             
                               
                                 
                                   
                                     ( 
                                     
                                       
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                           = 
                           
                             
                               
                                 b 
                                 ⁢ 
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                                 d 
                                 ⁢ 
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                               f 
                             
                             = 
                             
                               
                                 
                                   
                                     ( 
                                     
                                       
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                                     ) 
                                   
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                                   h 
                                 
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                                 m 
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                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where (m vh   0 , m vh   0 ) is motion vector of the top-left corner control point, and (m vh   1 , m vh   1 ) is motion vector of the top-right corner control point and (m vh   2 , m vh   2 ) is motion vector of the bottom-left corner control point, all of the three motion vectors are called control point motion vectors (CPMV), (x, y) represents the coordinate of a representative point relative to the top-left sample within current block and (mv h (x,y), mv v (x,y)) is the motion vector derived for a sample located at (x, y). The CP motion vectors may be signaled (like in the affine AMVP mode) or derived on-the-fly (like in the affine merge mode). w and h are the width and height of the current block. In practice, the division is implemented by right-shift with a rounding operation. In VTM, the representative point is defined to be the center position of a sub-block, e.g., when the coordinate of the left-top corner of a sub-block relative to the top-left sample within current block is (xs, ys), the coordinate of the representative point is defined to be (xs+2, ys+2). For each sub-block (i.e., 4×4 in VTM), the representative point is utilized to derive the motion vector for the whole sub-block. 
     In order to further simplify the motion compensation prediction, sub-block based affine transform prediction is applied. To derive motion vector of each M×N (both M and N are set to 4 in current VVC) sub-block, the motion vector of the center sample of each sub-block, as shown in  FIG. 17 , is calculated according to Equation (1) and (2), and rounded to 1/16 fraction accuracy. Then the motion compensation interpolation filters for 1/16-pel are applied to generate the prediction of each sub-block with derived motion vector. The interpolation filters for 1/16-pel are introduced by the affine mode. 
     After MCP, the high accuracy motion vector of each sub-block is rounded and saved as the same accuracy as the normal motion vector. 
     2.3.3.1 Signaling of Affine Prediction 
     Similar to the translational motion model, there are also two modes for signaling the side information due affine prediction. They are AFFINE_INTER and AFFINE_MERGE modes. 
     2.3.3.2 AF_INTER Mode 
     For CUs with both width and height larger than 8, AF_INTER mode can be applied. An affine flag in CU level is signalled in the bitstream to indicate whether AF_INTER mode is used. 
     In this mode, for each reference picture list (List 0 or List 1), an affine AMVP candidate list is constructed with three types of affine motion predictors in the following order, wherein each candidate includes the estimated CPMVs of the current block. The differences of the best CPMVs found at the encoder side (such as mv 0  mv 1  mv 2  in  FIG. 20 ) and the estimated CPMVs are signalled. In addition, the index of affine AMVP candidate from which the estimated CPMVs are derived is further signalled. 
     1) Inherited Affine Motion Predictors 
     The checking order is similar to that of spatial MVPs in HEVC AMVP list construction. First, a left inherited affine motion predictor is derived from the first block in {A1, A0} that is affine coded and has the same reference picture as in currentblock. Second, an above inherited affine motion predictor is derived from the first block in {B1, B0, B2} that is affine coded and has the same reference picture as in current block. The five blocks A1, A0, B1, B0, B2 are depicted in  FIG. 19 . 
     Once a neighboring block is found to be coded with affine mode, the CPMVs of the codingunit covering the neighboringblock are used to derive predictors of CPMVs of current block. For example, if A1 is coded with non-affine mode and A0 is coded with 4-parameter affine mode, the left inherited affine MV predictor will be derived from A0. In this case, the CPMVs of a CU covering A0, as denoted by MV 0   N  for the top-left CPMV and MV 1   N  for the top-right CPMV in  FIG. 21B  are utilized to derive the estimated CPMVs of current block, denoted by MV 0   V , MV 1   C , MV 2   C  for the top-left (with coordinate (x0, y0)), top-right (with coordinate (x1, y1)) and bottom-right positions (with coordinate (x2, y2)) of current block. 
     2) Constructed Affine Motion Predictors 
     A constructed affine motion predictor consists of control-point motion vectors (CPMVs) that are derived from neighboring inter coded blocks, as shown in  FIG. 20 , that have the same reference picture. If the current affine motion model is 4-parameter affine, the number of CPMVs is 2, otherwise if the current affine motion model is 6-parameter affine, the number of CPMVs is 3. The top-left CPMV  mv   0  is derived by the MV at the first block in the group {A, B, C} that is inter coded and has the same reference picture as in current block. The top-right CPMV  mv   1  is derived by the MV at the first block in the group {D, E} that is inter coded and has the same reference picture as in current block. The bottom-left CPMV  mv   2  is derived by the MV at the first block in the group {F, G} that is inter coded and has the same reference picture as in current block.
         If the current affine motion model is 4-parameter affine, then a constructed affine motion predictor is inserted into the candidate list only if both  mv   0  and  mv   1  are founded, that is,  mv   0  and  mv   1  are used as the estimated CPMVs for top-left (with coordinate (x0, y0)), top-right (with coordinate (x1, y1)) positions of current block.   If the current affine motion model is 6-parameter affine, then a constructed affine motion predictor is inserted into the candidate list only if  mv   0 ,  mv   1  and  mv   2  are all founded, that is,  mv   0 ,  mv   1  and  mv   2  are used as the estimated CPMVs for top-left (with coordinate (x0, y0)), top-right (with coordinate (x1, y1)) and bottom-right (with coordinate (x2, y2)) positions of current block.       

     No pruning process is applied when inserting a constructed affine motion predictor into the candidate list. 
     3) Normal AMVP Motion Predictors 
     The following applies until the number of affine motion predictors reaches the maximum.
         1) Derive an affine motion predictor by setting all CPMVs equal to  mv   2  if available.   2) Derive an affine motion predictor by setting all CPMVs equal to  mv   1  if available.   3) Derive an affine motion predictor by setting all CPMVs equal to  mv   )  if available.   4) Derive an affine motion predictor by setting all CPMVs equal to HEVC TMVP if available.   5) Derive an affine motion predictor by setting all CPMVs to zero MV.       

     Note that  mv   1  is already derived in constructed affine motion predictor. 
       FIG. 18A  shows an example of a 4-parameter affine model.  FIG. 18B  shows an example of a 6-parameter affine model. 
       FIG. 19  shows an example of MVP for AF_INTER for inherited affine candidates. 
       FIG. 20  shows an example of MVP for AF_INTER for constructed affine candidates. 
     In AF_INTER mode, when 4/6-parameter affine mode is used, 2/3 control points are required, and therefore 2/3 MVD needs to be coded for these control points, as shown in  FIG. 18 . In JVET-K0337, it is proposed to derive the MV as follows, i.e., mvd 1  and mvd 2  are predicted from mvd 0 . 
     
       
      
       mv 
       0 
       = mv   
       0 
       +mvd 
       0  
      
     
     
       
      
       mv 
       1 
       = mv   
       1 
       +mvd 
       1 
       +mvd 
       0  
      
     
     
       
      
       mv 
       2 
       = mv   
       2 
       +mvd 
       2 
       +mvd 
       0  
      
     
     Wherein  mv   1 , mvd i  and mv 1  are the predicted motion vector, motion vector difference and motion vector of the top-left pixel (i=0), top-right pixel (i=1) or left-bottom pixel (i=2) respectively, as shown in  FIG. 18B . Please note that the addition of two motion vectors (e.g., mvA(xA, yA) and mvB(xB, yB)) is equal to summation of two components separately, that is, newMV=mvA+mvB and the two components of newMV is set to (xA+xB) and (yA+yB), respectively. 
     2.3.3.3 AF_MERGE Mode 
     When a CU is applied in AF_MERGE mode, it gets the first block coded with affine mode from the valid neighbor reconstructed blocks. And the selection order for the candidate block is from left, above, above right, left bottom to above left as shown in  FIG. 21A  (denoted by A, B, C, D, E in order). For example, if the neighbor left bottom block is coded in affine mode as denoted by A0 in  FIG. 21B , the Control Point (CP) motion vectors mv 0   N , mv 1   N  and mv 2   N  of the top left corner, above right corner and left bottom corner of the neighboring CU/PU which includes the block A are fetched. And the motion vector mv 0   C , mv 1   C  and mv 2   C  (which is only used for the 6-parameter affine model) of the top left corner/top right/bottom left on the current CU/PU is calculated based on mv 0   N , mv 1   N  and mv 2   N . In VTM-2.0, sub-block (e.g 4 ×4 block in VTM) located at the top-left corner stores mv0, the sub-block located at the top-right corner stores my 1 if the current block is affine coded. If the current block is coded with the 6-parameter affine model, the sub-block located at the bottom-left corner stores mv2; otherwise (with the 4-parameter affine model), LB stores mv2′. Other sub-blocks stores the MVs used for MC. 
     After the CPMV of the current CU mv 0   C , mv 1   C  and mv 2   C  are derived, according to the simplified affine motion model Equation (1) and (2), the MVF of the current CU is generated. In order to identify whether the current CU is coded with AF_MERGE mode, an affine flag is signaled in the bitstream when there is at least one neighbor block is coded in affine mode. 
     In JVET-L0142 and JVET-L0632, an affine merge candidate list is constructed with following steps: 
     1) Insert Inherited Affine Candidates 
     Inherited affine candidate means that the candidate is derived from the affine motion model of its valid neighbor affine coded block. The maximum two inherited affine candidates are derived from affine motion model of the neighboring blocks and inserted into the candidate list. For the left predictor, the scan order is {A0, A1}; for the above predictor, the scan order is {B0, B1, B2}. 
     2) Insert Constructed Affine Candidates 
     If the number of candidates in affine merge candidate list is less than MaxNumAffineCand (e.g., 5), constructed affine candidates are inserted into the candidate list Constructed affine candidate means the candidate is constructed by combining the neighbor motion information of each control point.
         a) The motion information forthe control points is derived firstly from the specified spatial neighbors and temporal neighbor shown in  FIG. 22 . CPk (k=1, 2, 3, 4) represents the k-th control point. A0, A1, A2, B0, B1, B2 and B3 are spatial positions for predicting CPk (k=1, 2, 3); T is temporal position for predicting CP4.       

     The coordinates of CP1, CP2, CP3 and CP4 is (0, 0), (W, 0), (H, 0) and (W, H), respectively, where W and H are the width and height of current block. 
     The motion information of each control point is obtained according to the following priority order:
         For CP1, the checking priority is B2-&gt;B3-&gt;A2. B2 is used if it is available. Otherwise, if B2 is available, B3 is used. If both B2 and B3 are unavailable, A2 is used. If all the three candidates are unavailable, the motion information of CP1 cannot be obtained.   For CP2, the checking priority is B1-&gt;B0.   For CP3, the checking priority is A1-&gt;A0.   For CP4, T is used.   b) Secondly, the combinations of controls points are used to construct an affine merge candidate.
           I. Motion information of three control points are needed to construct a 6-parameter affine candidate. The three control points can be selected from one of the following four combinations ({CP1, CP2, CP4}, {CP1, CP2, CP3}, {CP2, CP3, CP4}, {CP1, CP3, CP4}). Combinations {CP1, CP2, CP3}, {CP2, CP3, CP4}, {CP1, CP3, CP4} will be converted to a 6-parameter motion model represented by top-left, top-right and bottom-left control points.   II. Motion information of two control points are needed to construct a 4-parameter affine candidate. The two control points can be selected from one of the two combinations ({CP1, CP2}, {CP1, CP3}). The two combinations will be converted to a 4-parameter motion model represented by top-left and top-right control points.   III. The combinations of constructed affine candidates are inserted into to candidate list as following order:
               {CP1, CP2, CP3}, {CP1, CP2, CP4}, {CP1, CP3, CP4}, {CP2, CP3, CP4}, {CP1, CP2}, {CP1, CP3}   i. For each combination, the reference indices of list X for each CP are checked, if they are all the same, then this combination has valid CPMVs for list X. If the combination does not have valid CPMVs for both list 0 and list 1, then this combination is marked as invalid. Otherwise, it is valid, and the CPMVs are put into the sub-block merge list.
 
3) Padding with Xero Motion Vectors
   
               
               

     If the number of candidates in affine merge candidate list is less than 5, zero motion vectors with zero reference indices are insert into the candidate list, until the list is full. 
     More specifically, for the sub-block merge candidate list, a 4-parameter merge candidate with MVs set to (0, 0) and prediction direction set to uni-prediction from list 0 (for P slice) and bi-prediction (for B slice). 
     2.3.4 Current Picture Referencing 
     Intra block copy (a.k.a. IBC, or intra picture block compensation), also named current picture referencing (CPR) was adopted in HEVC screen content coding extensions (SCC). This tool is very efficient for coding of screen content video in that repeated patterns in text and graphics rich content occur frequently within the same picture. Having a previously reconstructed block with equal or similar pattern as a predictor can effectively reduce the prediction error and therefore improve coding efficiency. An example of the intra block compensation is illustrated in  FIG. 23 . 
     Similar to the design of CRP in HEVC SCC, In VVC, The use of the IBC mode is signaled at both sequence and picture level. When the IBC mode is enabled at sequence parameter set (SPS), it can be enabled at picture level. When the IBC mode is enabled at picture level, the current reconstructed picture is treated as a reference picture. Therefore, no syntax change on block level is needed on top of the existing VVC inter mode to signal the use of the IBC mode. 
     Main features:
         It is treated as a normal inter mode. Therefore, merge and skip modes are also available for the IBC mode. The merge candidate list construction is unified, including merge candidates from the neighboring positions that are either coded in the IBC mode or the HEVC inter mode. Depending on the selected merge index, the current block under merge or skip mode can merge into either an IBC mode coded neighbor or otherwise an normal inter mode coded one with different pictures as reference pictures.   Block vector prediction and coding schemes for the IBC mode reuse the schemes used for motion vector prediction and coding in the HEVC inter mode (AMVP and MVD coding).   The motion vector for the IBC mode, also referred as block vector, is codedwith integer-pel precision, but stored in memory in 1/16-pel precision after decoding as quarter-pel precision is used in interpolation and deblocking stages. When used in motion vector prediction for the IBC mode, the stored vector predictor will be right shifted by 4.   Search range: it is restricted to be within the current CTU.   CPR is disallowed when affine mode/triangular mode/GBI/weighted prediction is enabled.       

     2.3.5 Merge List Design in VVC 
     There are three different merge list construction processes supported in VVC:
         1) Sub-block merge candidate list: it includes ATMVP and affine merge candidates. One merge list construction process is shared for both affine modes and ATMVP mode. Here, the ATMVP and affine merge candidates may be added in order. Sub-block merge list size is signaled in slice header, and maximum value is 5.   2) Uni-Prediction TPM merge list: For triangular prediction mode, one merge list construction process for the two partitions is shared even two partitions can select their own merge candidate index. When constructing this merge list, the spatial neighbouring blocks and two temporal blocks of the block are checked. The motion information derived from spatial neighbours andtemporal blocks are called regular motion candidates in our IDF. These regular motion candidates are further utilized to derive multiple TPM candidates. Please note the transform is performed in the whole block level, even two partitions may use different motion vectors for generating their own prediction blocks. Uni-Prediction TPM merge list size is fixed to be 5.   3) Regular merge list: For remaining coding blocks, one merge list construction process is shared. Here, the spatial/temporal/HMVP, pairwise combined bi-prediction merge candidates and zero motion candidates may be inserted in order. Regular merge list size is signaled in slice header, and maximum value is 6.       

     2.3.5.1 Sub-Block Merge Candidate List 
     It is suggested that all the sub-block related motion candidates are put in a separate merge list in addition to the regular merge list for non-sub block merge candidates. 
     The sub-block related motion candidates are put in a separate merge list is named as ‘sub-block merge candidate list’. 
     In one example, the sub-block merge candidate list includes affine merge candidates, and ATMVP candidate, and/or sub-block based STMVP candidate. 
     2.3.5.1.1 JVET-L0278 
     In this contribution, the ATMVP merge candidate in the normal merge list is moved to the first position of the affine merge list. Such that all the merge candidates in the new list (i.e., sub-block based merge candidate list) are based on sub-block coding tools. 
     2.3.5.1.2 ATMVP in VTM-3.0 
     In VTM-3.0, a special merge candidate list, known as sub-block merge candidate list (a. k. a affine merge candidate list) is added besides the regular merge candidate list. The sub-block merge candidate list is filled with candidates in the following order:
         a. ATMVP candidate (maybe available or unavailable);   b. Inherited Affine candidates;   c. Constructed Affine candidates;   d. Padding as zero MV 4-parameter affine model       

     The maximum number of candidates (denoted as ML) in the sub-block merge candidate list derived as below:
         1) If the ATMVP usage flag (e.g. the flag may be named as “sps_sbtmvp_enabled_flag”) is on (equal to 1), but the affine usage flag (e.g. the flag may be named as “sps_affine_enabled_flag”) is off (equal to 0), then ML is set equal to 1.   2) If the ATMVP usage flag is off (equal to 0), and the affine usage flag is off (equal to 0), then ML is set equal to 0. In this case, the sub-block merge candidate list is not used.   3) Otherwise (the affine usage flag is on (equal to 1), the ATMVP usage flag is on or off), ML is signaled from the encoder to the decoder. Valid ML is 0&lt;=ML&lt;=5.       

     When construct the sub-block merge candidate list, ATMVP candidate is checked first. If any one of the following conditions is true, ATMVP candidate is skipped and not put into the sub-block merge candidate list.
         1) The ATMVP usage flag is off;   2) Any TMVP usage flag (e.g. the flag may be named as “slice_temporal_mvp_enabled_flag” when signaled at slice level) is off;   3) The reference picture with reference index 0 in reference list 0 is identical to the current picture (It is a CPR)       

     ATMVP in VTM-3.0 is much simpler than in JEM. When an ATMVP merge candidate is generated, the following process is applied:
         a. Check neighbouring blocks A1, B1, B0, A0 as shown in  FIG. 22  in order, to find the first inter-coded, but not CPR-coded block, denoted as block X;   b. Initialize TMV=(0,0). If there is a MV (denoted as MV′) of block X, referring to the collocated reference picture (as signaled in the slice header), TMV is set equal to MV′.   c. Suppose the center point of the current block is (x0, y0), then locate a corresponding position of (x0,y0) as M=(x0+MV′x, y0+MV′y) in the collocated picture. Find the block Z covering M.
           i. If Z is intra-coded, then ATMVP is unavailable;   ii. If Z is inter-coded, MVZ_0 and MVZ_1 for the two lists of block Z are scaled to (Reflist 0 index 0) and (Reflist 1 index 0) as MVdefault0, MVdefault1, and stored.   
           d. For each 8×8 sub-block, suppose its center point is (x0S, yOS), then locate a corresponding position of (x0S, y0S) as MS=(x0S+MV′x, y0S+MV′y) in the collocated picture. Find the block ZS covering MS.
           i. If ZS is intra-coded, MVdefault0, MVdefault1 are assigned to the sub-block;   ii. If ZS is inter-coded, MVZS_0 and MVZS_1 for the two lists of block ZS are scaled to (Reflist 0 index 0) and (Reflist 1 index 0) and are assigned to the sub-block;   
               

     MV clipping and masking in ATMVP: 
     When locating a corresponding position such as M or MS in the collocated picture, it is clipped to be inside a predefined region. The CTU size is S×S, S=128 in VTM-3 .0. Suppose the top-left position of the collocated CTU is (xCTU, yCTU), then the corresponding position M or MS at (xN, yN) will be clipped into the valid region xCTU&lt;=xN&lt;xCTU+S+4; yCTU&lt;=yN&lt;yCTU+S. 
     Besides Clipping, (xN, yN) is also masked as xN=xN&amp;MASK, yN=yN&amp;MASK, where MASK is an integer equal to ˜(2 N −1), and N=3, to set the lowest 3 bits to be 0. So xN and yN are numbers which are times of 8. (“” represents the bitwise complement operator). 
       FIG. 24  shows an example of a valid corresponding region in the collocated picture. 
     2.3.5.1.3 Syntax Design in Slice Header 
       
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                  if( sps_temporal_mvp_enabled_flag ) 
                   
               
               
                   
                   slice_temporal_mvp_enabled_flag 
                 u(1) 
               
               
                   
                  if( slice_type == B ) 
               
               
                   
                   mvd_l1_zero_flag 
                 u(1) 
               
               
                   
                  if( slice_temporal_mvp_enabled_flag ) { 
               
               
                   
                   if( slice_type == B ) 
               
               
                   
                    collocated_from_l0_flag 
                 u(1) 
               
               
                   
                  } 
               
               
                   
                 ... 
               
               
                   
                  if(!sps_affine_enabled_flag){ 
               
               
                   
                    if(!sps_sbtmvp_enabled_flag) 
               
               
                   
                     MaxSubBlockMergeListSize = 0 
               
               
                   
                    else 
               
               
                   
                     MaxSubBlockMergeListSize = 1 
               
               
                   
                  } 
               
               
                   
                  else{ 
               
               
                   
                    five_minus_max_num_affine_merge_cand 
                 ue(v) 
               
               
                   
                    MaxSubBlockMergeListSize = 5− 
               
               
                   
                 five_minus_max_num_affine_merge_cand 
               
               
                   
                  } 
               
               
                   
                   
               
            
           
         
       
     
     2.3.5.2 Regular Merge List 
     Different from the merge list design, in VVC, the history-based motion vector prediction (HMVP) method is employed. 
     In HMVP, the previously coded motion information is stored. The motion information of a previously coded block is defined as an HMVP candidate. Multiple HMVP candidates are stored in a table, named as the HMVP table, and this table is maintained during the encoding/decoding process on-the-fly. The HMVP table is emptied when starting coding/decoding a new slice. Whenever there is an inter-coded block, the associated motion information is added to the last entry of the table as a new HMVP candidate. The overall coding flow is depicted in  FIG. 25 . 
     HMVP candidates can be used in both AMVP and merge candidate list construction processes.  FIG. 26  depicts the modified merge candidate list construction process (shown with highlighted blocks in  FIG. 26 ). When the merge candidate list is not full after the TMVP candidate insertion, HMVP candidates stored in the HMVP table can be utilized to fill in the merge candidate list. Considering that one block usually has a higher correlation with the nearest neighbouring block in terms of motion information, the HMVP candidates in the table are inserted in a descending order of indices. The last entry in the table is firstly added to the list, while the first entry is added in the end. Similarly, redundancy removal is applied on the HMVP candidates. Once the total number of available merge candidates reaches the maximal number of merge candidates allowed to be signaled, the merge candidate list construction process is terminated. 
     2.4 MV Rounding 
     In VVC, when MV is right shifted, it is asked to be rounded toward zero. In a formulated way, for a MV(MVx, MVy) to be right shifted with N bits, the result MV′ (MVx′, MVy′) will be derived as: 
         MVx ′=( MVx +((1&lt;&lt; N )&gt;&gt;1)−( MVx&gt;= 0? 1:0))&gt;&gt; N;  
 
         MVy ′=( MVy +((1&lt;&lt; N )&gt;&gt;1)−( MVy&gt;= 0? 1:0))&gt;&gt; N;  
 
     2.5 RPR in JVET-O2001-v14 
     ARC, a.k.a. RPR (Reference Picture Resampling) is incorporated in WET-O2001-v14. 
     With RPR in JVET-O2001-v14, TMVP is disabled if the collocated picture has a different resolution to the current picture. Besides, BDOF and DMVR are disabled when the reference picture has a different resolution to the current picture. 
     To handle the normal MC when the reference picture has a different resolutionthan the current picture, the interpolation section is defined as below: 
     8.5.6.3 Fractional Sample Interpolation Process 
     8.5.6.3.1 General 
     Inputs to this process are:
     a luma location (xSb, ySb) specifying the top-left sample of the current coding subblock relative to the top-left luma sample of the current picture,   a variable sbWidth specifying the width of the current coding subblock,   a variable sbHeight specifying the height of the current coding subblock,   a motion vector offset mvOffset,   a refined motion vector refMvLX,   the selected reference picture sample array refPicLX,   the half sample interpolation filter index hpelIfIdx,   the bi-directional optical flow flag bdofFlag,   a variable cIdx specifying the colour component index of the current block.   

     Outputs of this process are:
     an (sbWidth+brdExtSize)×(sbHeight+brdExtSize) array predSamplesLX of prediction sample values.   

     The prediction block border extension size brdExtSize is derived as follows: 
         brd ExtSize=( bd ofFlag∥(inter_affine_flag[ xSb][ySb ]&amp;&amp;  sps _affine_prof_enabled_flag)) ? 2:0   (8-752)
 
     The variable fRefWidth is set equal to the PicOutputWidthL of the reference picture in luma samples. 
     The variable fRefHeight is set equal to PicOutputHeightL of the reference picture in luma samples. 
     The motion vector mvLX is set equal to (refMvLX−mvOffset).
     If cIdx is equal to 0, the following applies:
       The scaling factors and their fixed-point representations are defined as   
       

       hori_scale_ fp =(( f RefWidth&lt;&lt;14)+(PicOutputWidth L &gt;&gt;1))/PicOutputWidth L    (8-753)
 
       vert_scale_ fp =(( f RefHeight&lt;&lt;14)+(PicOutputHeight L &gt;&gt;1))/PicOutputHeight L    (8-754)
         Let (xIntL, yIntL) be a luma location given in full-sample units and (xFracL, yFracL) be an offset given in 1/16-sample units. These variables are used only in this clause for specifying fractional-sample locations inside the reference sample arrays refPicLX.   The top-left coordinate of the bounding block for reference sample padding (xSbInt L , ySbInt L ) is set equal to (xSb+(mvLX[0]&gt;&gt;4), ySb+(mvLX[1]&gt;&gt;4)).   For each luma sample location (x L =0..sbWidth−1+brdExtSize, y L =0..sbHeight−1+brdExtSize) inside the prediction luma sample array predSamplesLX, the corresponding prediction luma sample value predSamplesLX[x L ][y L ] is derived as follows:
           Let (refxSb L , refySb L ) and (refx L , refy L ) be luma locations pointed to by a motion vector (refMvLX[0], refMvLX[1]) given in 1/16-sample units. The variables refxSb L , refx L , refySb L , and refy L  are derived as follows:   
               

       ref xSb   L =(( xSb&lt;&lt; 4)+refMv LX[ 0])*hori_scale_ fp    (8-755)
 
       ref x   L =((Sign(ref xSb )*((Abs(ref xSb )+128)&gt;&gt;8)+ x   L *((hori_scale_ fp+ 8)&gt;&gt;4))+32)&gt;&gt;6   (8-756)
 
       ref ySb   L =(( ySb&lt;&lt; 4)+refMv LX[ 1])*vert_scale_ fp    (8-757)
 
       ref yL =((Sign(ref ySb )*((Abs(ref ySb )+128)&gt;&gt;8)+ yL * ((vert_scale_ fp+ 8)&gt;&gt;4))+32)&gt;&gt;6   (8-758)
             The variables xInt L , yInt L , xFrac L  and yFrac L  are derived as follows:           

       xInt L =refx L &gt;&gt;4   (8-759)
 
       yInt L =refy L &gt;&gt;4   (8-760)
 
       xFrac L =refx L &amp;15   (8-761)
 
       yFrac L =refy L &amp;15   (8-762)
         If bdofFlag is equal to TRUE or (sps affine_prof enabled flag is equal to TRUE and inter affine flag[xSb][ySb] is equal to TRUE), and one or more of the following conditions are true, the prediction luma sample value predSamplesLX[x L ][y L ] is derived by invoking the luma integer sample fetching process as specified in clause 8.5.6.3.3 with (xInt L +(xFrac L &gt;&gt;3)−1), yInt L +(yFrac L &gt;&gt;3)−1) and refPicLX as inputs.
           1. x L  is equal to 0.   2. x L  is equal to sbWidth+1.   3. yL is equal to 0.   
           4. y L  i s equal to sbHeight+1.   Otherwise, the prediction luma sample value predSamplesLX[xL][yL] is derived by invoking the luma sample 8-tap interpolation filtering process as specified in clause 8.5.6.3.2 with (xIntL−(brdExtSize&gt;0 ? 1:0), yIntL−(brdExtSize&gt;0 ? 1:0)), (xFracL, yFracL), (xSbInt L , ySbInt L ), refPicLX, hpelIfIdx, sbWidth, sbHeight and (xSb, ySb) as inputs.       Otherwise (cIdx is not equal to 0), the following applies:
       Let (xIntC, yIntC) be a chroma location given in full-sample units and (xFracC, yFracC) be an offset given in 1/32 sample units. These variables are used only in this clause for specifying general fractional-sample locations inside the reference sample arrays refPicLX.   The top-left coordinate of the bounding block for reference sample padding (xSbIntC, ySbIntC) is set equal to ((xSb/SubWidthC)+(mvLX[0]&gt;&gt;5), (ySb/SubHeightC)+(mvLX[1]&gt;&gt;5)).   For each chroma sample location (xC=0..sbWidth−1, yC=0.. sbHeight 1) inside the prediction chroma sample arrays predSamplesLX, the corresponding prediction chroma sample value predSamplesLX[xC][yC ] is derived as follows:
           Let (refx Sb C , refySb C ) and (refx C , refy C ) be chroma locations pointed to by a motion vector (mvLX[0], mvLX[1]) given in 1/32-sample units. The variables refxSb C , refySb C , refx C  and refy C  are derived as follows:   
           
       

       ref xSb   C =(( xSb/ SubWidth C&lt;&lt; 5)+mv LX[ 0])*hori_scale_ fp    (8-763)
 
       re fx   C =((Sign(ref xSb   C )*((Abs(ref xSb   C )+256)&gt;&gt;9)+ xC *((hori_scale_ fp+ 8)&gt;&gt;4))+16)&gt;&gt;5   (8-764)
 
       ref ySb   C =(( ySb/ SubHeight C&lt;&lt; 5)+mv LX[ 1])*vert_scale_ fp    (8-765)
 
       ref y   C =((Sign(ref ySb   C )*(Abs(ref ySb   C )+256)&gt;&gt;9)+ yC *((vert_scale  fp+ 8)&gt;&gt;4))+16)&gt;&gt;5   (8-766)
             The variables xInt C , yInt C , xFrac C  and yFrac C  are derived as follows:           

         x Int C =ref x   C &gt;&gt;5   (8-767)
 
         y Int C =ref y   C &gt;&gt;5   (8-768)
 
         x Frac C =ref y   C &amp; 31   (8-769)
 
         y Frac C =ref y   C &amp; 31 (8-770)
         The prediction sample value predSamplesLX[xC][yC] is derived by invoking the process specified in clause 8.5.6.3.4 with (xIntC, yIntC), (xFracC, yFracC), (xSbIntC, ySbIntC), sbWidth, sbHeight and refPicLX as inputs.       

     8.5.6.3.2 Luma Sample Interpolation Filtering Process 
     Inputs to this process are:
     a luma location in full-sample units (xInt L , yInt L ),   a luma location in fractional-sample units (xFrac L , yFrac L ),   a luma location in full-sample units (xSbInt L , ySbInt L ) specifying the top-left sample of the bounding block for reference sample padding relative to the top-left luma sample of the reference picture,   the luma reference sample array refPicLX L ,   the half sample interpolation filter index hpelIfIdx,   a variable sbWidth specifying the width of the current subblock,   a variable sbHeight specifying the height of the current subblock,   a luma location (xSb, ySb) specifying the top-left sample of the current subblock relative to the top-left luma sample of the current picture,   

     Output of this process is a predicted luma sample value predSampleLX L    
     The variables shiftl, shift2 and shift3 are derived as follows:
     The variable shiftl is set equal to Min(4, BitDepth Y −8), the variable shift2 is set equal to 6 and the variable shift3 is set equal to Max(2, 14−BitDepth Y ).   The variable picW is set equal to pic_width_in_luma_samples and the variable picH is set equal to pic_height_in_luma_samples.   

     The luma interpolation filter coefficients f L [p] for each 1/16 fractional sample position p equal to xFrac L  or yFrac L  are derived as follows:
     If MotionModelldc[xSb][ySb] is greater than 0, and sbWidth and sbHeight are both equal to 4, the luma interpolation filter coefficients f L [p] are specified in Table 8-12.   Otherwise, the luma interpolation filter coefficients f L [p] are specified in Table 8-11 depending on hpellfIdx.   

     The luma locations in full-sample units (xInt i , yInt i ) are derived as follows for i=0..7:
     If subpic treated as pic flag[SubPicIdx] is equal to 1, the following applies:   

         x Int i =Clip3(SubPicLeftBoundaryPos, SubPicRightBoundaryPos,  x Int L   +i− 3)   (8-771)
 
         y Int i =Clip3(SubPicTopBoundaryPos, SubPicBotBoundaryPos,  y Int L   +i− 3)   (8-772)
     Otherwise (subpic treated as_pic flag[ SubPicIdx ] is equal to 0), the following applies:   

         x Int i =Clip3 (0, pic W− 1, sps_ref_wraparound_enabled_flag ? Clip H (( sps _ref_wraparound_offset_minus1+1)*Min Cb Size Y,  pic W, x Int L   +i− 3   ):    (8-773)
 
         x Int L   +i− 3)  y Int i =Clip3(0, pic H− 1,  y Int L   +i− 3)   (8-774)
 
     The luma locations in full-sample units are further modified as follows for i=0..7: 
         x Int i =Clip3( xSb Int L −3,  xSb Int L   +sb Width+4,  x Int i )   (8-775)
 
         y Int i =Clip3( ySb Int L −3,  ySb Int L   +sb Height+4,  y Int i )   (8-776)
 
     The predicted luma sample value predSampleLX L  is derived as follows:
     If both xFrac L  and yFrac L  are equal to 0, the value of predSampleLX L  is derived as follows:   

       predSample LX   L =refPic LX   L   [x Int 3   ][y Int 3 ]&lt;&lt;shift3   (8-777)
     Otherwise, if xFrac L  is not equal to 0 and yFrac L  is equal to 0, the value of predSampleLX L  is derived as follows:   

       predSampleLX L =(Σ i=0   7   f   L   [x Frac L   ][i ]*refPic LX   L   [x Int i   ][y Int 3 ])&gt;&gt;shift1   (8-778)
     Otherwise, if xFrac L  is equal to 0 and yFrac L  is not equal to 0, the value of predSampleLX L  is derived as follows:   

       predSample LX   L =(Σ i=0   7   [f   L   ][y Frac L   ][i ]*refPic LX   L   [x Int 3 ][ y Int i ])&gt;&gt;shift1   (8-779)
     Otherwise, if xFrac L  is not equal to 0 and yFrac L  is not equal to 0, the value of predSampleLX L  is derived as follows:
       The sample array temp[n ] with n=0..7, is derived as follows:   
       

       temp[ n ]=(Σ i=0   7   f   L   [x Frac L   ][i ]*refPic LX   L   [x Int i   ][y Int n ])&gt;&gt;shift1   (8-780)
         The predicted luma sample value predSampleLX L  is derived as follows:       

       predSample LX   L =(Σ i=0   7   f   L   [y Frac L   ][i ]*temp[ i ])&gt;&gt;shift2   (8-781)
 
     
       
         
           
               
             
               
                 TABLE 8-11 
               
             
            
               
                   
               
               
                 Specification of the luma interpolation filter coefficients f L [p]  
               
               
                 for each 1/16 fractional sample position p. 
               
            
           
           
               
               
            
               
                 Fractional 
                   
               
               
                 sample 
                 interpolation filter coefficients 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 position p 
                 f L [p][0] 
                 f L [p][1] 
                 f L [p][2] 
                 f L [p][3] 
                 f L [p][4] 
                 f L [p][5] 
                 f L [p][6] 
                 f L [p][7] 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 0 
                 1 
                 −3 
                 63 
                 4 
                 −2 
                 1 
                 0 
               
               
                 2 
                 −1 
                 2 
                 −5 
                 62 
                 8 
                 −3 
                 1 
                 0 
               
               
                 3 
                 −1 
                 3 
                 −8 
                 60 
                 13 
                 −4 
                 1 
                 0 
               
               
                 4 
                 −1 
                 4 
                 −10 
                 58 
                 17 
                 −5 
                 1 
                 0 
               
               
                 5 
                 −1 
                 4 
                 −11 
                 52 
                 26 
                 −8 
                 3 
                 −1 
               
               
                 6 
                 −1 
                 3 
                 −9 
                 47 
                 31 
                 −10 
                 4 
                 −1 
               
               
                 7 
                 −1 
                 4 
                 −11 
                 45 
                 34 
                 −10 
                 4 
                 −1 
               
               
                 8 
                 −1 
                 4 
                 −11 
                 40 
                 40 
                 −11 
                 4 
                 −1 
               
               
                 (hpelIfIdx == 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 0) 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 8 
                 0 
                 3 
                 9 
                 20 
                 20 
                 9 
                 3 
                 0 
               
               
                 (hpelIfIdx == 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 1) 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 9 
                 −1 
                 4 
                 −10 
                 34 
                 45 
                 −11 
                 4 
                 −1 
               
               
                 10 
                 −1 
                 4 
                 −10 
                 31 
                 47 
                 −9 
                 3 
                 −1 
               
               
                 11 
                 −1 
                 3 
                 −8 
                 26 
                 52 
                 −11 
                 4 
                 −1 
               
               
                 12 
                 0 
                 1 
                 −5 
                 17 
                 58 
                 −10 
                 4 
                 −1 
               
               
                 13 
                 0 
                 1 
                 −4 
                 13 
                 60 
                 −8 
                 3 
                 −1 
               
               
                 14 
                 0 
                 1 
                 −3 
                 8 
                 62 
                 −5 
                 2 
                 −1 
               
               
                 15 
                 0 
                 1 
                 −2 
                 4 
                 63 
                 −3 
                 1 
                 0 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 8-12 
               
             
            
               
                   
               
               
                 Specification of the luma interpolation filter coefficients f L [p] 
               
               
                 for each 1/16 fractional sample position p for affine motion mode. 
               
            
           
           
               
               
            
               
                 Fractional 
                   
               
               
                 sample 
                 interpolation filter coefficients 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 position p 
                 f L [p][0] 
                 f L [p][1] 
                 f L [p][2] 
                 f L [p][3] 
                 f L [p][4] 
                 f L [p][5] 
                 f L [p][6] 
                 f L [p][7] 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 0 
                 1 
                 −3 
                 63 
                 4 
                 −2 
                 1 
                 0 
               
               
                 2 
                 0 
                 1 
                 −5 
                 62 
                 8 
                 −3 
                 1 
                 0 
               
               
                 3 
                 0 
                 2 
                 −8 
                 60 
                 13 
                 −4 
                 1 
                 0 
               
               
                 4 
                 0 
                 3 
                 −10 
                 58 
                 17 
                 −5 
                 1 
                 0 
               
               
                 5 
                 0 
                 3 
                 −11 
                 52 
                 26 
                 −8 
                 2 
                 0 
               
               
                 6 
                 0 
                 2 
                 −9 
                 47 
                 31 
                 −10 
                 3 
                 0 
               
               
                 7 
                 0 
                 3 
                 −11 
                 45 
                 34 
                 −10 
                 3 
                 0 
               
               
                 8 
                 0 
                 3 
                 −11 
                 40 
                 40 
                 −11 
                 3 
                 0 
               
               
                 9 
                 0 
                 3 
                 −10 
                 34 
                 45 
                 −11 
                 3 
                 0 
               
               
                 10 
                 0 
                 3 
                 −10 
                 31 
                 47 
                 −9 
                 2 
                 0 
               
               
                 11 
                 0 
                 2 
                 −8 
                 26 
                 52 
                 −11 
                 3 
                 0 
               
               
                 12 
                 0 
                 1 
                 −5 
                 17 
                 58 
                 −10 
                 3 
                 0 
               
               
                 13 
                 0 
                 1 
                 −4 
                 13 
                 60 
                 −8 
                 2 
                 0 
               
               
                 14 
                 0 
                 1 
                 −3 
                 8 
                 62 
                 −5 
                 1 
                 0 
               
               
                 15 
                 0 
                 1 
                 −2 
                 4 
                 63 
                 −3 
                 1 
                 0 
               
               
                   
               
            
           
         
       
     
     8.5.6.3.3 Luma Integer Sample Fetching Process 
     Inputs to this process are:
     a luma location in full-sample units (xInt L , yInt L ),   the luma reference sample array refPicLX L ,   

     Output of this process is a predicted luma sample value predSampleLX L    
     The variable shift is set equal to Max(2, 14−BitDepth Y ). 
     The variable picW is set equal to pic_width_in_luma_samples and the variable picH is set equal to pic_height_in_luma_samples. 
     The luma locations in full-sample units (xInt, yInt) are derived as follows: 
         x Int=Clip3(0, pic W− 1,  sps _ref_wraparound_enabled_flag?  (8-782)
 
       ClipH((sps_ref_wraparound_offset_minus1+1)*MinCbSizeY, picW, xInt L ): xInt L ) 
         y Int=Clip3(0, pic H− 1,  y Int L )   (8-783)
 
     The predicted luma sample value predSampleLX L  is derived as follows: 
       predSample LX   L =refPic LX   L   [x Int][ y Int]&lt;&lt;shift3   (8-784)
 
     8.5.6.3.4 Chroma Sample Interpolation Process 
     Inputs to this process are:
     a chroma location in full-sample units (xInt C , yint C ),   a chroma location in 1/32 fractional-sample units (xFrac C , yFrac C ),   a chroma location in full-sample units (xSbIntC, ySbIntC) specifying the top-left sample of the bounding block for reference sample padding relative to the top-left chroma sample of the reference picture,   a variable sbWidth specifying the width of the current subblock,   a variable sbHeight specifying the height of the current subblock,   the chroma reference sample array refPicLX C .   

     Output of this process is a predicted chroma sample value predSampleLX C    
     The variables shiftl, shift2 and shift3 are derived as follows:
     The variable shiftl is set equal to Min(4, BitDepth C −8), the variable shift2 is set equal to 6 and the variable shift3 is set equal to Max(2, 14−BitDepth C ).   The variable picW C  is set equal to pic_width_in_luma_samples/SubWidthC and the variable picH C  is set equal to pic_height_in_luma_samples/SubHeightC.   

     The chroma interpolation filter coefficients f C [p] for each 1/32 fractional sample position p equal to xFrac C  or yFrac C  are specified in Table 8-13. 
     The variable xOffset is set equal to (sps_ref_wraparound_offset_minus1+1)*MinCb SizeY)/Sub WidthC. 
     The chroma locations in full-sample units (xInt i , yInt i ) are derived as follows for i=0..3:
     If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the following applies:   

         x Int i =Clip3 (SubPicLeftBoundaryPos/SubWidth C,  SubPicRightBoundaryPos/SubWidth C, x Int L   +i )   (8-785)
 
         y Int i =Clip3(SubPicTopBoundaryPos/SubHeight C,  SubPicBotBoundaryPos/SubHeight C, y Int L   +i )   (8-786)
     Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0), the following applies:   

         x Int i =Clip3(0, picW C −1,  sps _ref_wraparound_enabled_flag ? Clip H ( x Offset, pic W   C   , x Int C   +i− 1):   (8-787)
 
         x Int C   +i− 1)  y Int i =Clip3(0, pic H   C −1,  y Int C   +i− 1)   (8-788)
 
     The chroma locations in full-sample units (xInt i , yInt i ) are further modified as follows for i=0..3: 
         x Int i =Clip3( xSb Int C− 1,  xSb Int C+sb Width+2,  x Int i )   (8-789)
 
         y Int i =Clip3( ySb Int C− 1,  ySb Int C+sb Height+2,  y Int i )   (8-790)
 
     The predicted chroma sample value predSampleLX C  is derived as follows:
     If both xFrac C  and yFrac C  are equal to 0, the value of predSampleLX C  is derived as follows:   

       predSample LX   C =refPic LX   C   [x Int 1   ][y Int 1 ]shift3   (8-791)
     Otherwise, if xFrac C  is not equal to 0 and yFrac C  is equal to 0, the value of predSampleLX C  is derived as follows:   

       predSample LX   C =(Σ i=0   3   f   C   [x Frac C   ][i* ]refPic LX   C   [x Int i ][ y Int 1 ])&gt;&gt;shift1    (8-792)
     Otherwise, if xFrac C  is equal to 0 and yFrac C  is not equal to 0, the value of predSampleLX C  is derived as follows:   

       predSample LX   C =(Σ i=0   3   f   C   [y Frac C   ][i ]*refPic LX   C   [x Int 1   ][y Int i ])&gt;&gt;shift1    (8-793)
     Otherwise, if xFrac C  is not equal to 0 and yFrac C  is not equal to 0, the value of predSampleLX C  is derived as follows:
       The sample array temp[n] with n=0..3, is derived as follows:   
       

       temp[ n ]=(Σ i=0   3   f   C   [x Frac C ][1]*refPic LX   C   [x Int i   ][y Int n ])&gt;&gt;shift1   (8-794)
         The predicted chroma sample value predSampleLX C  is derived as follows:       

       predSample LX   C =( f   C   [y Frac C ][0]*temp[0]+ f   C   [y Frac C ][1]*temp[1]+ f   C   [y Frac C ][2]*temp[2]+ f   C   [y Frac C ][3]*temp[3])&gt;&gt;shift2   (8-795)
 
     
       
         
           
               
             
               
                 TABLE 8-13 
               
             
            
               
                   
               
               
                 Specification of the chroma interpolation filter coefficients f C [ 
               
               
                 p ] for each 1/32 fractional sample position p. 
               
            
           
           
               
               
            
               
                 Fractional 
                   
               
               
                 sample 
                 interpolation filter coefficients 
               
            
           
           
               
               
               
               
               
            
               
                 position p 
                 f C [ p ][ 0 ] 
                 f C [ p ][ 1 ] 
                 f C [ p ][ 2 ] 
                 f C [ p ][ 3 ] 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 −1 
                 63 
                 2 
                 0 
               
               
                 2 
                 −2 
                 62 
                 4 
                 0 
               
               
                 3 
                 −2 
                 60 
                 7 
                 −1 
               
               
                 4 
                 −2 
                 58 
                 10 
                 −2 
               
               
                 5 
                 −3 
                 57 
                 12 
                 −2 
               
               
                 6 
                 −4 
                 56 
                 14 
                 −2 
               
               
                 7 
                 −4 
                 55 
                 15 
                 −2 
               
               
                 8 
                 −4 
                 54 
                 16 
                 −2 
               
               
                 9 
                 −5 
                 53 
                 18 
                 −2 
               
               
                 10 
                 −6 
                 52 
                 20 
                 −2 
               
               
                 11 
                 −6 
                 49 
                 24 
                 −3 
               
               
                 12 
                 −6 
                 46 
                 28 
                 −4 
               
               
                 13 
                 −5 
                 44 
                 29 
                 −4 
               
               
                 14 
                 −4 
                 42 
                 30 
                 −4 
               
               
                 15 
                 −4 
                 39 
                 33 
                 −4 
               
               
                 16 
                 −4 
                 36 
                 36 
                 −4 
               
               
                 17 
                 −4 
                 33 
                 39 
                 −4 
               
               
                 18 
                 −4 
                 30 
                 42 
                 −4 
               
               
                 19 
                 −4 
                 29 
                 44 
                 −5 
               
               
                 20 
                 −4 
                 28 
                 46 
                 −6 
               
               
                 21 
                 −3 
                 24 
                 49 
                 −6 
               
               
                 22 
                 −2 
                 20 
                 52 
                 −6 
               
               
                 23 
                 −2 
                 18 
                 53 
                 −5 
               
               
                 24 
                 −2 
                 16 
                 54 
                 −4 
               
               
                 25 
                 −2 
                 15 
                 55 
                 −4 
               
               
                 26 
                 −2 
                 14 
                 56 
                 −4 
               
               
                 27 
                 −2 
                 12 
                 57 
                 −3 
               
               
                 28 
                 −2 
                 10 
                 58 
                 −2 
               
               
                 29 
                 −1 
                 7 
                 60 
                 −2 
               
               
                 30 
                 0 
                 4 
                 62 
                 −2 
               
               
                 31 
                 0 
                 2 
                 63 
                 −1 
               
               
                   
               
            
           
         
       
     
     2.6 Sub-Pictures in JVET-O2001-v14 
     With the current syntax design of sub-pictures in JVET-O2001-vE, the locations and dimensions of sub-pictures are derived as below: 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 subpics_present_flag 
                 u(1) 
               
               
                   
                 if( subpics_present_flag ) { 
               
               
                   
                  max_subpics_minus1 
                 u(8) 
               
               
                   
                  subpic_grid_col_width_minus1 
                 u(v) 
               
               
                   
                  subpic_grid_row_height_minus1 
                 u(v) 
               
               
                   
                  for( i = 0; i &lt; NumSubPicGridRows; i++ ) 
               
               
                   
                   for( j = 0; j &lt; NumSubPicGridCols; j++ ) 
               
               
                   
                    subpic_grid_idx[ i ][ j ] 
                 u(v) 
               
               
                   
                  for( i = 0; i &lt;= NumSubPics; i++ ) { 
               
               
                   
                   subpic_treated_as_pic_flag[ i ] 
                 u(1) 
               
               
                   
                   loop_filter_across_subpic_enabled_flag[i ] 
                 u(1) 
               
               
                   
                  } 
               
               
                   
                 } 
               
               
                   
                   
               
            
           
         
       
         
         subpics_present_flag equal to 1 indicates that subpicture parameters are present in the present in the SPS RBSP syntax. subpics_present_flag equal to 0 indicates that subpicture parameters are not present in the present in the SPS RBSP syntax. 
       
    
     When a bitstream is the result of a sub-bitstream extraction process and includes only a subset of the subpictures of the input bitstream to the sub-bitstream extraction process, it might be required to set the value of subpics_present_flag equal to 1 in the RBSP of the SPSs.
     max_subpics_minus1 plus 1 specifies the maximum number of subpictures that may be present in the CVS. max_subpics_minus1 shall be in the range of 0 to 254. The value of 255 is reserved for future use by ITU-T|ISO/IEC.   subpic_grid_col_width_minus1 plus 1 specifies the width of each element of the subpicture identifier grid in units of 4 samples. The length of the syntax element is Ceil(Log 2(pic_width_max_in_luma_samples/4)) bits.   

     The variable NumSubPicGridCols is derived as follows: 
       NumSubPicGridCols=(pic_width_max_in_luma_samples+subpic_grid_col_width_minus1*4+3)/(subpic_grid_col_width_minus1*4+4)   (7-5)
     subpic_grid_row_height_minus1 plus 1 specifies the height of each element of the subpicture identifier grid in units of 4 samples. The length of the syntax element is Ceil(Log 2(pic_height_max_in_luma_samples/4)) bits.   

     The variable NumSubPicGridRows is derived as follows: 
       NumSubPicGridRows=(pic_height_max_in_luma_samples+subpic_grid_row_height_minus1*4+3)/(subpic_grid_row_height_minus1*4+4)   (7-6)
     subpic_grid_idx[i][j] specifies the subpicture index of the grid position (i, j). The length of the syntax element is Ceil(Log 2(max_subpics_minus1+1)) bits.   

     The variables SubPicTop[subpic_grid_idx[i][j]], SubPicLeft[subpic_grid_idx[i][j]], SubPicWidth[subpic_grid_idx [i][j]], SubPicHeight[subpic_grid_idx[i][j]], and NumSubPics are derived as follows: 
     
       
         
           
               
             
               
                   
               
             
            
               
                 NumSubPics = 0  
               
               
                 for( i = 0; i. &lt; NumSubPicGridRows; i++ ) { 
               
               
                  for( j = 0; j &lt; NumSubPicGridCols; j++ ) { 
               
               
                   if ( i = = 0)  
               
               
                     SubPicTop[ subpic_grid_idx[ i ][ j ] ] = 0  
               
               
                   else if( subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i − 1 ][ j ] ) { 
               
               
                     SubPicTop[ subpic_grid_idx[ i ][ j ] ] = i  
               
               
                    SubPicHeight[ subpic_grid_idx[ i − 1 ][ j ] ] =  
               
               
                 i − SubPicTop[ subpic_grid_idx[ i − 1 ][ j ] ]  
               
               
                   } 
               
               
                   if ( j = = 0)  
               
               
                     SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = 0     (7-7)  
               
               
                   else if (subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i ][ j − 1 ] ) { 
               
               
                     SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = j  
               
               
                     SubPicWidth[ subpic_grid_idx[ i ][ j ] ] =  
               
               
                 j − SubPicLeft[ subpic_grid_idx[ i ][ j − 1 ] ]  
               
               
                   }  
               
               
                   if( i = = NumSubPicGridRows − 1)  
               
               
                     SubPicHeight[ subpic_grid_idx[ i ][ j ] ] =  
               
               
                 i − SubPicTop[ subpic_grid_idx[ i − 1 ][ j ] ] + 1  
               
               
                   if (j = = NumSubPicGridRows − 1)  
               
               
                     SubPicWidth[ subpic_grid_idx[ i ][ j ] ] =  
               
               
                 j − SubPicLeft[ subpic_grid_idx[ i ][ j − 1 ] ] + 1  
               
               
                   if( subpic_grid_idx[ i ][ j ] &gt; NumSubPics)  
               
               
                      NumSubPics = subpic_grid_idx[ i ][ j ]  
               
               
                  } 
               
               
                 } 
               
               
                   
               
            
           
         
       
         
         subpic_treated_as_pic_flag[i] equal to 1 specifies that the i-th subpicture of each coded picture in the CVS is treated as a picture in the decoding process excluding in-loop filtering operations. subpic_treated_as_pic_flag[i] equal to 0 specifies that the i-th subpicture of each coded picture in the CVS is not treated as a picture in the decoding process excluding in-loop filtering operations. When not present, the value of subpic_treated_as_pic_flag[i] is inferred to be equal to 0. 
       
    
     2.7 CIIP in JVET-O2001-v14 
     Combined Inter-Intra Prediction (CIIP) is adopted into VVC as a special merge candidate. It can only be enabled for a W×H block with W&lt;=64 and H&lt;=64. 
     3. Examples of Problems Solved by Disclosed Techniques and Embodiments 
     In the current design of VVC, ATMVP has following problems:
         1) Whether to apply ATMVP is mismatched in slice level and in CU level;   2) In slice header, ATMVP may be enabled even if TMVP is disabled. Meanwhile, ATMVP flag is signaled before TMVP flag.   3) Masking is always done without considering whether MV is compressed;   4) The valid corresponding region may be too large;   5) The derivation of TMV is too complicated;   6) ATMVP may be unavailable in some cases and a better default MV is desirable.   7) The MV scaling methods in ATMVP may not be efficient;   8) ATMVP should consider the CPR cases;   9) A default zero affine merge candidate may be put into the list even when affineprediction is disabled.   10) Current picture is treated as a long-term reference picture while other pictures are treated as short-reference picture. For both ATMVP and TMVP candidates, the motion information from a temporal block in the collocated picture will be scaled to a reference picture with fixed reference index (i.e., 0 for each reference picture list in the current design). However, when CPR mode is enabled, the current picture is also treated as a reference picture and the current picture may be added to the reference picture list 0 (RefPicList0) with index equal to 0.
           a. For TMVP, if the temporal block is coded with CPR mode and reference picture of RefPicListO is a short reference picture, the TMVP candidate is set to be unavailable.   b. If the reference picture of the RefPicListO with index equal to 0 is the current picture and current picture is the Intra Random Access Point (IRAP) picture, ATMVP candidate is set to be unavailable.   c. For a ATMVP sub-block within a block, when deriving the sub-block&#39;s motion information from a temporal block, if the temporal block is coded with CPR mode, default ATMVP candidate (derived from a temporal block identified by the starting TMV and center position of the current block) is used to fill in the sub-block′ motion information.   
           11) MV is right shifted to the integer precision, but not following the rounding rule in VVC.   12) The MV(MVx, MVy) used in ATMVP to locate a corresponding block in a different picture (e.g., the TMV in 2.3.5.1.2) is directly used since it points to the collocated picture. This is based on the assumption that all pictures are in the same resolution. However, when RPR is enabled, different picture resolutions may be utilized. Similar issues are existing for identification of corresponding blocks in a collocate picture to derive sub-block motion information.   13) If one block width or height is greater than 32, and max transform unit size is 32, for a CIIP coded block, the intra prediction signal is generated with the coding unit (CU) size; while the inter prediction signal is generated with the transform unit (TU) size (recursively splitting current block to multiple 32×32 blocks). Using the CU to derive intra prediction signal results in less efficiency.       

     There are some problems with current design. Firstly, if the reference picture of the RefPicList0 with index equal to 0 is the current picture and current picture is not an TRAP picture, ATMVP procedure is still invoked, but the ATMVP procedure cannot locate any available ATMVP candidates since none of temporal motion vectors can be scaled to the current picture. 
     4. Examples of Embodiments and Techniques 
     The itemized list of techniques and embodiments below should be considered as examples to explain general concepts. These techniques should not be interpreted in a narrow way. Furthermore, these techniques can be combined in any manner in encoder or decoder embodiments.
     1. Whether TMVP is allowed and/or whether CPR is used should be considered to decide/parse the maximum number of candidates in the sub-block merge candidate list and/or to decide whether ATMVP candidate should be added to a candidate list. The maximum number of candidates in the sub-block merge candidate list is denoted as ML. Although some of the example embodiments are discussed below using alternative temporal motion vector prediction (ATMVP), in alternate embodiments, the technology disclosed in this document is applicable to sub-block based temporal motion vector prediction (sbTMVP).
       a) In one example, ATMVP is inferred to be not applicable if either ATMVP usage flag is off (equal to 0), or TMVP is disabled, in the determination of or parsing the maximum number of candidates in the sub-block merge candidate list.
           i. In one example, the ATMVP usage flag is on (equal to 1) and TMVP is disabled, the ATMVP candidate is not added to the sub-block merge candidate list or the ATMVP candidate list.   ii. In one example, the ATMVP usage flag is on (equal to 1) and TMVP is disabled, and the affine usage flag is off (equal to 0), then ML is set equal to 0, meaning that sub-block merge is not applicable.   iii. In one example, the ATMVP usage flag is on (equal to 1) and TMVP is enabled, and the affine usage flag is off (equal to 0), then ML is set equal to 1.   
           b) In one example, ATMVP is inferred to be not applicable if either ATMVP usage flag is off (equal to 0), or the collocated reference picture of the current picture is the current picture itself, when decide or parse the maximum number of candidates in the sub-block merge candidate list.
           i. In one example, the ATMVP usage flag is on (equal to 1) and the collocated reference picture of the current picture is the current picture itself, the ATMVP candidate is not added to the sub-block merge candidate list or the ATMVP candidate list.   ii. In one example, the ATMVP usage flag is on (equal to 1), and the collocated reference picture of the current picture is the current picture itself, and the affine usage flag is off (equal to 0), then ML is set equal to 0, meaning that sub-block merge is not applicable.   iii. In one example, the ATMVP usage flag is on (equal to 1), and the collocated reference picture ofthe current picture is not the current picture itself, and the affine usage flag is off (equal to 0), then ML is set equal to 1.   
           c) In one example, ATMVP is inferred to be not applicable if ATMVP usage flag is off (equal to 0), or the reference picture with reference picture index 0 in reference list 0 is the current picture itself, when decide or parse the maximum number of candidates in the sub-block merge candidate list.
           i. In one example, the ATMVP usage flag is on (equal to 1) and the collocated reference picture with reference picture index 0 in reference list 0 is the current picture itself, the ATMVP candidate is not added to the sub-block merge candidate list or the ATMVP candidate list.   ii. In one example, the ATMVP usage flag is on (equal to 1), and the reference picture with reference picture index 0 in reference list 0 is the current picture itself, and the affine usage flag is off (equal to 0), then ML is set equal to 0, meaning that sub-block merge is not applicable.   iii. In one example, the ATMVP usage flag is on (equal to 1) and the reference picture with reference picture index 0 in reference list 0 is not the current picture itself, and the affine usage flag is off (equal to 0), then ML is set equal to 1.   
           d) In one example, ATMVP is inferred to be not applicable if ATMVP usage flag is off (equal to 0), or the reference picture with reference picture index 0 in reference list 1 is the current picture itself, when decide or parse the maximum number of candidates in the sub-block merge candidate list.
           i. In one example, the ATMVP usage flag is on (equal to 1) and the collocated reference picture with reference picture index 0 in reference list 1 is the current picture itself, the ATMVP candidate is not added to the sub-block merge candidate list or the ATMVP candidate list.   ii. In one example, the ATMVP usage flag is on (equal to 1), and the reference picture with reference picture index 0 in reference list 1 is the current picture itself, and the affine usage flag is off (equal to 0), then ML is set equal to 0, meaning that sub-block merge is not applicable.   iii. In one example, the ATMVP usage flag is on (equal to 1) and the reference picture with reference picture index 0 in reference list 1 is not the current picture itself, and the affine usage flag is off (equal to 0), then ML is set equal to 1.   
           
       2. It is proposed that ATMVP is disabled implicitly and no ATMVP flag is signaled if TMVP is disabled at slice/tile/picture level.
       a) In one example, ATMVP flag is signaled after the TMVP flag in slice header/tile header/PPS.   b) In one example, ATMVP or/and TMVP flag may be not signaled in slice header/tile header/PPS and is only signaled in SPS header.   
       3. Whether and how to do mask the corresponding position in ATMVP depends on whether and how MVs are compressed. Suppose (xN, yN) is a corresponding position calculated with the coordinator of current block/sub-block and a starting motion vector (e.g., TMV) in the collocated picture
       a) In one example, (xN, yN) is not masked if MVs are not required to be compressed (e.g. sps_disable_motioncompression signaled in SPS is 1); Otherwise, (MVs can be compressed) (xN, yN) is masked as xN=xN&amp;MASK, yN=yN&amp; MASK, where MASK is an integer equal to ˜(2 M −1), and M can be integers such as 3 or 4.   b) Assume the MV compression method for MV storage result in each 2 K ×2 K  block share the same motion information and the mask in the ATMVP process is defined as ˜(2 M −1). It is proposed that K may be unequal to M, e.g., M=K+1.   c) The MASK used in ATMVP and TMVP may be the same, or they may be different.   
       4. In one example, the MV compression method can be flexible.
       a) In one example, the MV compression method can be selected between no compression, 8×8 compression (M=3 in Bullet 3.a), or 16 ×16 compression (M=4 in Bullet 3.a)   b) In one example, the MV compression method may be signaled in VPS/SPS/PPS/slice header/tile group header.   c) In one example, the MV compression method can be set differently in different standard profiles/levels/tiers.   
       5. The valid corresponding region in ATMVP may adaptive;
       a) For example, the valid corresponding region may depend on the width and height of the current block;   b) For example, the valid corresponding region may depend on the MV compression method;
           i. In one example, the valid corresponding region is smaller if MV compression method is not used; the valid corresponding region is larger if MV compression method is used.   
           
       6. The valid corresponding region in ATMVP may be based on a basic region with size M×N smaller than a CTU region. For example, the CTU size in VTM-3 .0 is 128 ×128, and the basic region size may be 64×64. Suppose the width and height of the current block is W and H.
       a) In one example, if W&lt;=M and H&lt;=N, meaning that the current block is inside a basic region, then the valid corresponding region in ATMVP is the collocated basic region and the extension in the collocated picture.  FIG. 27  shows an example.
           i. For example, suppose the top-left position of the collocated basic region is (xBR, yBR), then the corresponding position at (xN, yN) will be clipped into the valid region xBR&lt;=xN&lt;xBR+M+4; yBR&lt;=yN&lt;yBR+N.   
           
       

       FIG. 27  shows an example embodiment of the proposed valid region when the current block is inside a Basic Region (BR). 
       FIG. 28  shows an example embodiment of a valid region when the current block is not inside a basic region.
         b) In one example, if W&gt;M and H&gt;N, meaning that the current block is not inside a basic region, then the current block is divided into several parts. Each part has an individual valid corresponding region in ATMVP. For a position A in the current block, its corresponding position B in the collocated block should be within the valid corresponding region of the part in which the positionA locates.
           i. For example, the current block is divided into non-overlapped basic regions. The valid corresponding region for one basic region is its collocated basic region and the extension in the collocated picture.  FIG. 28  shows an example.
               1. For example, suppose position A in the current block is in one basic region R. The collocated basic region of R in the collocated picture is denoted as CR. The corresponding position of A in the collocated block is position B. The top-left position of CR is (xCR, yCR), then position B at (xN, yN) will be clipped into the valid region xCR&lt;=xN&lt;xCR+M+4; yCR&lt;=yN&lt;yCR+N.   
               
               7. It is proposed the motion vector used in ATMVP to locate a corresponding block in a different picture (e.g., the TMV in 2.3.5.1.2) can be derived as:
       a) In one example, TMV is always set equal to a default MV such as (0, 0).
           i. In one example, the default MV is signaled in VPS/SPS/PPS/slice header/tile group header/CTU/CU.   
           b) In one example, TMV is set to be one MV stored in the HMVP table with the following methods;
           i. If HMVP list is empty, TMV is set equal to a default MV such as (0, 0)   ii. Otherwise (HMVP list is not empty),
               1. TMV may be set to equal to the first element stored in the HMVP table;   2. Alternatively, TMV may be set to equal to the last element stored in the HMVP table;   3. Alternatively, TMV may only be set equal to a specific MV stored in the HMVP table;
                   a. In one example, the specific MV refers to reference list 0.   b. In one example, the specific MV refers to reference list 1.   c. In one example, the specific MV refers to a specific reference picture in reference list 0, such as the reference picture with index 0.   d. In one example, the specific MV refers to a specific reference picture in reference list 1, such as the reference picture with index 0.   e. In one example, the specific MV refers to the collocated picture.   
                   4. Alternatively, TMV may be set equal to the default MV if the specific MV (e.g., mentioned in bullet 3.) stored in the HMVP table cannot be found;
                   a. In one example, only the first element stored in the HMVP table is searched to find the specific MV.   b. In one example, only the last element stored in the HMVP table is searched to find the specific MV.   c. In one example, some or all elements stored in the HMVP table is searched to find the specific MV.   
                   5. Alternatively, furthermore, TMV obtained from the HMVP cannot refer to the current picture itself.   6. Alternatively, furthermore, TMV obtained from the HMVP table may be scaled to the collocated picture if it does not refer to it.   
               
           c) In one example, TMV is set to be one MV of one specific neighbouring block. No other neighbouring blocks are involved.
           i. The specific neighbouringblock may be block A0, A1, B0, B1, B2 in  FIG. 22 .   ii. TMV may be set equal to the default MV if
               1. The specific neighbouring block does not exist;   2. The specific neighbouring block is not inter-coded;   
               iii. TMV may only be set equal to a specific MV stored in the specific neighbouring block;
               1. In one example, the specific MV refers to reference list 0.   2. In one example, the specific MV refers to reference list 1.   3. In one example, the specific MV refers to a specific reference picture in reference list 0, such as the reference picture with index 0.   4. In one example, the specific MV refers to a specific reference picture in reference list 1, such as the reference picture with index 0.   5. In one example, the specific MV refers to the collocated picture.   6. TMV may be set equal to the defaultMV if the specific MV stored in the specific neighbouring block cannot be found;   
               iv. TMV obtained from the specific neighbouring block may be scaled to the collocated picture if it does not refer to it.   v. TMV obtained from the specific neighbouring block cannot refer to the current picture itself.   
           
       8. MVdefault0 and MVdefault1 used in ATMVP as disclosed in 2.3.5.1.2 may be derived as
       a) In one example, MVdefault0 and MVdefault1 are set equal to (0,0);   b) In one example, MVdefaultX (X=0 or 1) is derived from HMVP,
           i. If HMVP list is empty, MVdefaultX is set equal to a predefined default MV such as (0, 0).
               1. The predefined default MV may be signaled in VPS/SPS/PPS/slice header/tile group header/CTU/CU.   
               ii. Otherwise (HMVP list is not empty),
               1. MVdefaultX may be set to equal to the first element stored in the HMVP table;   2. MVdefaultX may be set to equal to the last element stored in the HMVP table;   3. MVdefaultX may only be set equal to a specific MV stored in the HMVP table;
                   a. In one example, the specific MV refers to reference list X.   b. In one example, the specific MV refers to a specific reference picture in reference list X, such as the reference picture with index 0.   
                   4. MVdefaultX may be set equal to the predefined default MV if the specific MV stored in the HMVP table cannot be found;
                   a. In one example, only the first element stored in the HMVP table is searched.   b. In one example, only the last element stored in the HMVP table is searched.   c. In one example, some or all elements stored in the HMVP table is searched.   
                   5. MVdefaultX obtained from the HMVP table may be scaled to the collocated picture if it does not refer to it.   6. MVdefaultX obtained from the HMVP cannot refer to the current picture itself.   
               
           c) In one example, MVdefaultX (X=0 or 1) is derived from a neighbouring block.
           i. The neighbouring blocks may include block A0, A1, B0, B1, B2 in  FIG. 22 .
               1. For example, only one of these blocks is used to derive MVdefaultX.   2. Alternatively, some or all of these blocks are used to derive MVdefaultX.
                   a. These blocks are checked in order until a valid MVdefaultX is found.   
                   3. If no valid MVdefaultX can be found from selected one or more neighbouring blocks, it is set equal to a predefined default MV such as (0, 0).
                   a. The predefined default MV may be signaled in VPS/SPS/PPS/slice header/tile group header/CTU/CU.   
                   
               ii. No valid MVdefaultX can be found from a specific neighbouring block if
               1. The specific neighbouring block does not exist;   2. The specific neighbouring block is not inter-coded;   
               iii. MVdefaultX may only be set equal to a specific MV stored in the specific neighbouring block;
               1. In one example, the specific MV refers to reference list X.   2. In one example, the specific MV refers to a specific reference picture in reference list X., such as the reference picture with index 0   
               iv. MVdefaultX obtained from the specific neighbouring block may be scaled to a specific reference picture, such as the reference picture with index 0 in reference list X.   v. MVdefaultX obtained from the specific neighbouring block cannot refer to the current picture itself.   
           
       9. For either sub-block or non-sub-block ATMVP candidate, if a temporal block for a sub-block/whole block in the collocated picture is coded with CPR mode, a default motion candidate may be utilized instead.
       a) In one example, the default motion candidate may be defined as the motion candidate associated with the center position of current block (e.g., MVdefault0 and/or MVdefault1 used in ATMVP as disclosed in 2.3.5.1.2).   b) In one example, the default motion candidate may be defined as (0, 0) motion vector and reference picture index equal to 0 for both reference picture lists, if available.   
       10. It is proposed that the default motion information for the ATMVP process (e.g., MVdefault0 and MVdefault1 used in ATMVP as disclosed in 2.3.5.1.2) may be derived based on the location of a position that is used in the sub-block motion information derivation process. With this proposed method, for that sub-block, there is no need to further derive motion information since the default motion information will be directly assigned.
       a) In one example, instead of using the center position of the current block, the center position of a sub-block (e.g., a center sub-block) within the current block may be utilized.   b) An example is given as depicted in  FIG. 31B .  FIG. 31A  shows an example of locations for identification of default motion information in the current standards.   
       11. It is proposed that the ATMVP candidate is always available with the following methods:
       a) Suppose the center point of the current block is (x0, y0), then locate a corresponding position of (x0,y0) as M=(x0+MV′x, y0+MV′y) in the collocated picture. Find the block Z covering M. If Z is intra-coded, then MVdefault0, MVdefault1 are derived by some methods proposed in Item 6.   b) Alternatively, Block Z is not located to get the motion information, somemethods proposed in Item 8 are directly applied to get MVdefault0 and MVdefault1.   c) Alternatively, the default motion candidate used in ATMVP process is always available. If it is set to unavailable based on current design (e.g., the temporal block is intra coded), other motion vectors may be utilized instead for the default motion candidate.
           i. In one example, the solutions in international application PCT/CN2018/124639, incorporated by reference herein, may be applied.   
           d) Alternatively, furthermore, whether ATMVP candidate is always available depend on other high-level syntax information.
           i. In one example, only when the ATMVP enabling flag at slice/tile/picture header or other video units is set to true is inferred to be true, the ATMVP candidate may be always set to be available.   ii. In one example, the ab ove methods may be only applicable when ATMVP enabling flag in slice header/picture header or other video units is set to true and current picture is not an TRAP picture and current picture is not inserted to RefPicListO with reference index equal to 0.   e) A fixed index or a fixed group of indices is assigned to ATMVP candidates. When ATMVP candidates are always unavailable, the fixed index/group index may be inferred to other kinds of motion candidates (such as affine candidates).   
           
       12. It is proposed that whether the Zero motion affine merge candidate is put into the sub-block merge candidate list should depend on whether affine prediction is enabled.
       a) For example, if affine usage flag is off (sps_affine_enabled_flag is equal to 0), the Zero motion affine merge candidate is not put into the sub-block merge candidate list.   b) Alternatively, furthermore, default motion vector candidates which are non-affine candidate are added instead.   
       13. It is proposed that non-affine padding candidate may be put into the sub-block merge candidate list.
       a) Zero motion non-affine padding candidate may be added if the sub-block merge candidate list is not fulfilled.   b) When such a padding candidate is chosen, the affine flag of the current block should be set to be 0.   c) Alternatively, Zero motion non-affine padding candidate is put into the sub-block merge candidate list if the sub-block merge candidate list is not fulfilled and affine usage flag is off.   
       14. Suppose MV0 and MV1 represent the MVs in reference list 0 and reference list 1 of the block covering a corresponding position (e.g., MV0 and MV1 may be MVZ_0 and MVZ_1 or MVZS_0 and MVZS_1 described in section 2.3.5.1.2). MV0′ and MV1′ represent the MVs in reference list 0 and reference list 1 to be derived for the current block or sub-block. Then the MV0′ and MV1′ should be derived by scaling.
       a) MV0, if the collocated picture is in reference list 1;   b) MV1, if the collocated picture is in reference list 0.   
       15. The ATMVP and/or TMVP enabling/disabling flag may be inferred to be false for a slice/tile or other kinds of video units when current picture is treated as a reference picture with index set to M (e.g., 0) in a reference picture list X (PicRefListX, e.g., X=0). Here, M may be equal to the target reference picture index that motion information of a temporal block shall be scaled to for PicRefListX during ATMVP/TMVP processes.
       a) Alternatively, furthermore, the above method is only applicable when the current picture is an Intra Random Access Point (IRAP) picture.   b) In one example, ATMVP and/or TMVP enabling/disabling flag may be inferred to be false when current picture is treated as a reference picture with index set to M (e.g., 0) in a PicRefListX and/or current picture is treated as a reference picture with index set to N (e.g., 0) in a PicRefListY. The variable M and N represent the target reference picture index used in TMVP or ATMVP process.   c) For the ATMVP process, it is restricted that a confirming bitstream shall follow the rule that the collocated picture wherein motion information of current block is derived from shall not be the current picture.   d) Alternatively, when the above conditions are true, the ATMVP or TMVP process is not invoked.   
       16. It is proposed that if a reference picture with index set to M (e.g., 0) in a reference picture list X (PicRefListX, e.g., X=0) for the current block is the current picture, ATMVP may be still enabled for this block.
       a) In one example, all sub-blocks&#39; motion information are point to the current picture.   b) In one example, when obtaining the sub-block&#39;s motion information from a temporal block, the temporal block shall be coded with at least one reference picture pointing to the current picture of the temporal block.   c) In one example, when obtaining the sub-block&#39;s motion information from a temporal block, no scaling operations are applied.   
       17. Coding methods of sub-block merge index are aligned regardless the usage of ATMVP or not.
       a) In one example, for the first L bins, they are context coded. For the remaining bins, they are bypass coded. In one example, L is set to 1.   b) Alternatively, for all bins, they are context coded.   
       18. The MV(MVx, MVy) used in ATMVP to locate a corresponding block in a different picture (e.g., the TMV in 2.3.5.1.2) may be right-shifted to the integer precision (denoted as (MVx′, MVy′) with the same rounding method as in the MV scaling process.
       a) Alternatively, the MV used in ATMVP to locate a corresponding block in a different picture (e.g., the TMV in 2.3.5.1.2) may be right-shifted to the integer precision with the same rounding method as in the MV averaging process.   b) Alternatively, the MV used in ATMVP to locate a corresponding block in a different picture (e.g., the TMV in 2.3.5.1.2) may be right-shifted to the integer precision with the same rounding method as in the adaptive MV resolution (AMVR) process.   
       19. The MV(MVx, MVy) used in ATMVP to locate a corresponding block in a different picture (e.g., the TMV in 2.3.5.1.2) may be right-shifted to the integer precision (denoted as (MVx′, MVy′) by rounding toward zero.
       a) For example, MVx′=(MVx+((1&lt;&lt;N)&gt;&gt;1)−(MVx&gt;=0? 1:0))&gt;&gt;N; N is an integer presenting the MV resolution, e.g. N=4.
           i. For example, MVx′=(MVx+(MVx&gt;=0 ? 7:8))&gt;&gt;4.   
           b) For example, MVy′=(MVy+((1&lt;&lt;N)&gt;&gt;1)−(MVy&gt;=0? 1:0))&gt;&gt;N; N is an integer presenting the MV resolution, e.g. N=4.
           i. For example, MVy′=(MVy+(MVy&gt;=0 ? 7:8))&gt;&gt;4.   
           
       20. In one example, MV(MVx, MVy) in bullet 18 and bullet 19 is used to locate a corresponding block to derive the default motion information used in ATMVP, such as using the center position of the sub-block and the shifted MV, or using the top-left position of current block and the shifted MV.
       a) In one example, MV(MVx, MVy) is used to locate a corresponding block to derive the motion information of a sub-block in currentblock duringthe ATMVP process, such as using the center position of the sub-block and the shifted MV.   
       21. The proposed methods in bullet 18, 19, 20 may be also applied to other coding tools associated with locating a reference block in a different picture or current picture with a motion vector.   22. The MV(MVx, MVy) used in ATMVP to locate a corresponding block in a different picture (e.g., the TMV in 2.3.5.1.2) may be scaled even if it points to the collocated picture.
       a) In one example, if the width and/or height of the collocated picture (or the conformance window in it) is different from that of the current picture (or the conformance window in it), the MV may be scaled.   b) Suppose the width and height of (the conformance window) of the collocated picture are denoted as W1 and H1, respectively. The width and height of (the conformance window of) the current picture are denoted as W2 and H2, respectively. Then MV(MVx, MVy) may be scaled as MVx′=MVx*W1/W2 and MVy′=MVy*H1/H2.   
       23. The center point of the currentblock (such as position (x0, y0) in 2.3.5.1.2) used to derive motion information in the ATMVP process may be further modified by scaling and/or adding offsets.
       a) In one example, if the width and/or height of the collocated picture (or the conformance window in it) is different from that of the current picture (or the conformance window in it), the center point may be further modified.   b) Suppose the top-left position of the conformance window in the collocated picture are denoted as X1 and Y1. The top-left position of the conformance window defined in the current picture are denoted as X2 and Y2. The width and height of (the conformance window of) the collocated picture are denoted as W1 and H1, respectively. The width and height of (the conformance window) of the current picture are denoted as W2 and H2, respectively. Then (x0, y0) may be modified as x0′=(x0−X2)*W1/W2+×1 and y0′=(y0−Y2)*H1/H2+Y1.
           i. Alternatively, x0′=x0*W1/W2, y0′=y0*H1/H2.   
           
       24. The corresponding position (such as position M in 2.3.5.1.2) used to derive motion information in the ATMVP process may be further modified by scaling and/or adding offsets
       a) In one example, if the width and/or height of the collocated picture (or the conformance window in it) is different from that of the current picture (or the conformance window in it), the corresponding position may be further modified.   b) Suppose the top-left position of the conformance window in the collocated picture are denoted as X1 and Y1. The top-left position of the conformance window defined in the current picture are denoted as X2 and Y2. The width and height of (the conformance window of) the collocated picture are denoted as W1 and H1, respectively. The width and height of (the conformance window) of the current picture are denoted as W2 and H2, respectively. Then M(x, y) may be modified as x′=(x−X2)*W1/W2+X 1 and y′=(y−Y2)*H1/H2+Y1.
           i. Alternatively, x′=x*W1/W2, y′=y*H1/H2.   
           
       

     Sub-Picture Related 
     
         
         25. In one example, the width of a sub-picture S ending at the (j−1) column may be set equal to j minus the left-most column of the sub-picture S, if the position (i, j) and (i, j−1) belong to different sub-pictures.
       a) An embodiment based on JVET-O2001-vE is highlighted below in bold, italicized font.   
     
       
    
     
       
         
           
               
             
               
                   
               
             
            
               
                 NumSubPics = 0  
               
               
                 for( i = 0; i. &lt; NumSubPicGridRows; i++ ) { 
               
               
                  for( j = 0; j &lt; NumSubPicGridCols; j++ ) { 
               
               
                   if ( i = = 0)  
               
               
                     SubPicTop[ subpic_grid_idx[ i ][ j ] ] = 0  
               
               
                   else if( subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i − 1 ][ j ] ) { 
               
               
                     SubPicTop[ subpic_grid_idx[ i ][ j ] ] = i  
               
               
                    SubPicHeight[ subpic_grid_idx[ i − 1][ j ] ] =  
               
               
                 i − SubPicTop[ subpic_grid_idx[ i − 1 ][ j ] ]  
               
               
                   } 
               
               
                   if ( j = = 0)  
               
               
                     SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = 0    (7-7)  
               
               
                   else if (subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i ][ j − 1 ] ) { 
               
               
                     SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = j  
               
               
                         
               
               
                      
               
               
                   } 
               
               
                   if( i = = NumSubPicGridRows − 1)  
               
               
                     SubPicHeight[ subpic_grid_idx[ i ][ j ] ] =  
               
               
                 i − SubPicTop[ subpic_grid_idx[ i − 1 ][ j ] ] + 1  
               
               
                   if (j = = NumSubPicGridRows − 1)  
               
               
                     SubPicWidth[ subpic_grid_idx[ i ][ j ] ] =  
               
               
                 j − SubPicLeft[ subpic_grid_idx[ i ][ j − 1 ] ] + 1  
               
               
                   if( subpic_grid_idx[ i ][ j ] &gt; NumSubPics)  
               
               
                     NumSubPics = subpic_grid_idx[ i ][ j ]  
               
               
                  } 
               
               
                 } 
               
               
                   
               
            
           
         
       
         
         26. In one example, the height of a sub-picture S ending at the (NumSubPicGridRows−1) row may be set equal to (NumSubPicGridRows−1) minus the top-most row of the sub-picture S then plus one.
       a) An embodiment based on JVET-O2001-vE is highlighted below.   
     
       
    
     
       
         
           
               
             
               
                   
               
             
            
               
                 NumSubPics = 0  
               
               
                 for( i = 0; i. &lt; NumSubPicGridRows; i++ ) { 
               
               
                  for( j = 0; j &lt; NumSubPicGridCols; j++ ) { 
               
               
                   if ( i = = 0)  
               
               
                     SubPicTop[ subpic_grid_idx[ i ][ j ] ] = 0  
               
               
                   else if( subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i − 1 ][ j ] ) { 
               
               
                     SubPicTop[ subpic_grid_idx[ i ][ j ] ] = i  
               
               
                     SubPicHeight[ subpic_grid_idx[ i − 1][ j ] ] =  
               
               
                 i − SubPicTop[ subpic_grid_idx[ i − 1 ][ j ] ]  
               
               
                   } 
               
               
                   if ( j = = 0)  
               
               
                     SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = 0  
               
               
                    (7-7)  
               
               
                   else if (subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i ][ j − 1 ] ) { 
               
               
                     SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = j  
               
               
                     SubPicWidth[ subpic_grid_idx[ i ][ j ] ] =  
               
               
                 j − SubPicLeft[ subpic_grid_idx[ i ][ j − 1 ] ]  
               
               
                   } 
               
               
                   if( i = = NumSubPicGridRows − 1)  
               
               
                          
               
               
                      
               
               
                   if (j = = NumSubPicGridRows − 1)  
               
               
                     SubPicWidth[ subpic_grid_idx[ i ][ j ] ] =  
               
               
                 j − SubPicLeft[ subpic_grid_idx[ i ][ j − 1 ] ] + 1  
               
               
                   if( subpic_grid_idx[ i ][ j ] &gt; NumSubPics)  
               
               
                     NumSubPics = subpic_grid_idx[ i ][ j ]  
               
               
                   
               
            
           
         
       
         
         27. In one example, the width of a sub-picture S ending atthe (Num SubPicGridColumns−1) column may be set equal to (Num SubPicGridColumns−1) minus the left-most column of the sub-picture S then plus 1.
       a) An embodiment based on JVET-O2001-vE is highlighted below.   
     
       
    
     
       
         
           
               
             
               
                   
               
             
            
               
                 NumSubPics = 0  
               
               
                 for( i = 0; i. &lt; NumSubPicGridRows; i++ ) { 
               
               
                  for( j = 0; j &lt; NumSubPicGridCols; j++ ) { 
               
               
                   if ( i = = 0)  
               
               
                    SubPicTop[ subpic_grid_idx[ i ][ j ] ] = 0  
               
               
                   else if( subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i − 1 ][ j ] ) { 
               
               
                    SubPicTop[ subpic_grid_idx[ i ][ j ] ] = i  
               
               
                    SubPicHeight[ subpic_grid_idx[ i − 1][ j ] ] =  
               
               
                 i − SubPicTop[ subpic_grid_idx[ i − 1 ][ j ] ]  
               
               
                   } 
               
               
                   if ( j = = 0)  
               
               
                    SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = 0     (7-7)  
               
               
                   else if (subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i ][ j − 1 ] ) { 
               
               
                    SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = j  
               
               
                    SubPicWidth[ subpic_grid_idx[ i ][ j ] ] =  
               
               
                 j − SubPicLeft[ subpic_grid_idx[ i ][ j − 1 ] ]  
               
               
                   } 
               
               
                   if( i = = NumSubPicGridRows − 1)  
               
               
                    SubPicHeight[ subpic_grid_idx[ i ][ j ] ] =  
               
               
                 i − SubPicTop[ subpic_grid_idx[ i − 1 ][ j ] ] + 1  
               
               
                        
               
               
                         
               
               
                      
               
               
                   if( subpic_grid_idx[ i ][ j ] &gt; NumSubPics)  
               
               
                    NumSubPics = subpic_grid_idx[ i ][ j ]  
               
               
                   
               
            
           
         
       
         
         28. The sub-picture grid can be integer times of the CTU size.
       a) An embodiment based on JVET-O2001-vE is highlighted below   
     
         subpic_grid_col_width_minus1 plus 1 specifies the width of each element of the subpicture identifier grid in units of CtbSizeY. The length of the syntax element is Ceil(Log 2(pic_width_max_in_luma_samples/CtbSizeY)) bits. 
       
    
     The variable NumSubPicGridCols is derived as follows: 
       NumSubPicGridCols=(pic_width_max_in_luma_samples+subpic_grid_col_width_minus1* Ctb Size Y+Ctb Size Y− 1)/(subpic_grid_col_width_minus1* Ctb Size Y+Ctb Size Y )   (7-5)
     subpic_grid_row_height_minus1 plus 1 specifies the height of each element of the subpicture identifier grid in units of 4 samples. The length of the syntax element is Ceil(Log 2(pic_height_max_in_luma_samples/CtbSizeY)) bits.   

     The variable NumSubPicGridRows is derived as follows: 
       NumSubPicGridRows=(pic_height_max_in_luma_samples+subpic_grid_row_height_minus1* Ctb Size Y+Ctb Size Y− 1)/(subpic_grid_row_height_minus1* Ctb Size Y+Ctb Size Y )   (7-6)
     29. A conformance constraint is added to guarantee that sub-pictures cannot be overlapped with each other, and all the sub-pictures can cover the whole picture.
       a) An embodiment based on JVET-O2001-vE is indicated below.   
       

     Any subpic grid_idx[i][j] must be equal to idx if the following conditions are both satisfied: 
         i &gt;=SubPicTop[idx] and  i &lt;SubPicTop[idx]+SubPicHeight[idx]. 
         j &gt;=SubPicLeft[idx] and  j &lt;SubPicLeft[idx]+SubPicWidth[idx]. 
     Any subpic_grid_idx[i][j] must be different to idx if the following conditions are not both satisfied: 
         i &gt;=SubPicTop[idx] and  i &lt;SubPicTop[idx]+SubPicHeight[idx]. 
         j &gt;=SubPicLeft[idx] and  j &lt;SubPicLeft[idx]+SubPicWidth[idx]. 
     RPR Related 
     
         
         30. A syntax element (such as a flag), denoted as RPR_flag, is signaled to indicate whether RPR may be used or not in a video unit (e.g., sequence). RPR_flag may be signaled in SPS, VPS, or DPS.
       a) In one example, if RPR is signaled not to be used (e.g. RPR_flag is 0) all width/height signaled in picture parameter set (PPS) can be the same to the maximum width/maximum height signaled in sequence parameter set (SPS).   b) In one example, if RPR is signaled not to be used (e.g. RPR_flag is 0) all width/height in PPS is not signaled and inferred to be the maximum width/maximum height signaled in SPS.   c) In one example, if RPR is signaled not to be used (e.g. RPR_flag is 0), conformance window information is notused in the decoding process. Otherwise (RPR is signaled to be used), conformance window information may be used in the decoding process.   
     
         31. It is proposed that the interpolation filters used in the motion compensation process to derive the prediction block of a current block may be selected depending on whether the resolution of the reference picture is different to the current picture, or whether the width and/or height of the reference picture is larger that of the current picture.
       a. In one example, the interpolation filters with less taps may be applied when condition A is satisfied, wherein condition A depends on the dimensions of the current picture and/or the reference picture.
           i. In one example, condition A is the resolution of the reference picture is different to the current picture.   ii. In one example, condition A is the width and/or height of the reference picture is larger than that of the current picture.   
           iii. In one example, condition A is W1&gt;a*W2 and/or H1&gt;b*H2, wherein (W1, H1) represents the width and height of the reference picture and (W2, H2) represents the width and height of the current picture, a and b are two factors, e.g. a=b=1.5.
           iv. In one example, condition A may also depend on whether bi-prediction is used.
               1) Condition A is satisfied is satisfied only when bi-prediction is used for the current block.   
               v. In one example, condition A may depend on M and N, where M and N represent the width and height of the current block.
               1) For example, condition A is satisfied only when M*N&lt;=T, where T is an integer such as 64.   2) For example, condition A is satisfied only when M&lt;=T1 or N&lt;=T2, where T1 and T2 are integers, e.g. T1=T2=4.   3) For example, condition A is satisfied only when M&lt;=T1 and N&lt;=T2, where T1 and T2 are integers, e.g. T1=T2=4.   4) For example, condition A is satisfied only when M*N &lt;=T, or M&lt;=T1 or N&lt;=T2, where T, T1 and T2 are integers, e.g. T=64, T1=T2=4.   5) In one example, the smaller condition in above sub-bullets may be replaced by greater.   
               vi. In one example, 1-tap filters are applied. In other words, an integer pixel without filtering is output as the interpolation result.   vii. In one example, bi-linear filters are applied when the resolution of the reference picture is different to the current picture.   viii. In one example, 4-tap filters or 6-tap filters are applied when the resolution of the reference picture is different to the current picture, or the width and/or height of the reference picture is larger than that of the current picture.
               1) The 6-tap filters may also be used for the affine motion compensation.   2) The 4-tap filters may also be used for interpolation for chroma samples.   
               
           b. Whether to and/or how to apply the methods disclosed in bullet 31 may depend on the color components.
           i. For example, the methods are only applied on the luma component.   
           c. Whether to and/or how to apply the methods disclosed in bullet 31 may depend on the interpolation filtering direction.
           i. For example, the methods are only applied on horizontal filtering.   ii. For example, the methods are only applied on vertical filtering.   
           
     
       
    
     CIIP Related 
     
         
         32. Intra prediction signal used in CIIP process may be done in TU level instead of CU level (e.g., using reference samples outside the TU instead of CU).
       a) In one example, if either CU width or height is greater than the max transform unit size, the CU may be split to multiple TUs and intra/inter prediction may be generated for each TU, e.g., using reference samples outside the TU.   b) In one example, if the maximum transform size K is smaller than 64 (such as K=32), then the intra-prediction used in CIIP is performed in a recursive way like in a normal intra-code block.   c) For example, a KM×KN CIIP coded block where M and N are integers are split into MN of K×K blocks, Intra-prediction is done for each K×K block. The intra-prediction for a later coded/decoded K×K block may depend on the reconstruction samples of a previously coded/decoded K×K block.   
     
       
    
     5. Additional Example Embodiments 
     5.1 Embodiment #1: An example of Ssyntax Design in SPS/PPS/Slice Header/Tile Group Header 
     The changes compared to the VTM3.0.1rc1 reference software is highlighted in large size bold face font as follow: 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                  if( sps_temporal_mvp_enabled_flag ) 
                   
               
               
                   
                   slice_temporal_mvp_enabled_flag 
                 u(1) 
               
               
                   
                  if( slice_type == B ) 
               
               
                   
                   mvd_l1_zero_flag 
                 u(1) 
               
               
                   
                  if( slice_temporal_mvp_enabled_flag ) { 
               
               
                   
                   if( slice_type == B ) 
               
               
                   
                    collocated_from_l0_flag 
                 u(1) 
               
               
                   
                  } 
               
               
                   
                 ... 
               
               
                   
                  if(!sps_affine_enabled_flag){ 
               
               
                   
                    if(!(sps_sbtmvp_enabled_flag &amp;&amp; 
               
               
                   
                 slice_temporal_mvp_enabled_flag )) 
               
               
                   
                     MaxSubBlockMergeListSize = 0 
               
               
                   
                    else 
               
               
                   
                     MaxSubBlockMergeListSize = 1 
               
               
                   
                  } 
               
               
                   
                  else{ 
               
               
                   
                    five_minus_max_num_affine_merge_cand 
                 ue(v) 
               
               
                   
                    MaxSubBlockMergeListSize = 5− 
               
               
                   
                 five_minus_max_num_affine_merge_cand 
               
               
                   
                  } 
               
               
                   
                   
               
            
           
         
       
     
     5.2 Embodiment #2: An Example of Syntax Design in SPS/PPS/Slice Header/Tile Group Header 
     7.3.2.1 Sequence Parameter Set RBSP Syntax 
       
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 seq_parameter_set_rbsp( ) { 
                   
               
               
                   
                  sps_seq_parameter_set_id 
                 ue(v) 
               
               
                   
                  chroma_format_idc 
                 ue(v) 
               
               
                   
                 ... 
               
               
                   
                  sps_ref_wraparound_enabled_flag 
                 u(1) 
               
               
                   
                  if( sps_ref_wraparound_enabled_flag ) 
               
               
                   
                   sps_ref_wraparound_offset 
                 ue(v) 
               
               
                   
                  sps_temporal_mvp_enabled_flag 
                 u(1) 
               
               
                   
                  if( sps_temporal_mvp_enabled_flag ) 
               
               
                   
                   sps_sbtmvp_enabled_flag 
                 u(1) 
               
               
                   
                  sps_amvr_enabled_flag 
                 u(1) 
               
               
                   
                 ... 
               
               
                   
                  } 
               
               
                   
                  rbsp_trailing_bits( ) 
               
               
                   
                 } 
               
               
                   
                   
               
            
           
         
       
     
     sps_sbtmvp_enabled_flag equal to 1 specifies that subblock-based temporal motion vector predictors may be used in decoding of pictures with all slices having slice_type not equal to I in the CVS. sps_sbtmvp_enabled_flag equal to 0 specifies that subblock-based temporal motion vector predictors are not used in the CVS. When sps_sbtmvp_enabled_flag is not present, it is inferred to be equal to 0. 
     five_minus_max_num_subblock_merge_cand specifies the maximum number of subblock-based merging motion vector prediction (MVP) candidates supported in the slice subtracted from 5. When five_minus_max_num_subblock_merge_cand is not present, it is inferred to be equal to 5−sps_sbtmvp_enabled_flag. The maximum number of subblock-based merging MVP candidates, MaxNumSubblockMergeCand is derived as follows: 
       MaxNumSubblockMergeCand=5−five_minus_max_num_subblock_merge_cand   (7-45)
 
     The value of MaxNumSubblockMergeCand shall be in the range of 0 to 5, inclusive. 
     8.3.4.2 Derivation Process for Motion Vectors and Reference Indices in Subblock Merge Mode 
     Inputs to this process are: 
     .. [No changes to the current VVC specification draft]. 
     Outputs of this process are: 
     ... [No changes to the current VVC specification draft]. 
     The variables numSbX, numSbY and the subblock merging candidate list, subblockMergeCandList are derived by the following ordered steps: 
     When sps_sbtmvp_enabled_flag is equal to 1 and (current picture is an IRAP and index 0 of reference picture list 0 is the current picture) is not true, the following applies: 
     The derivation process for merging candidates from neighbouring coding units as specified in clause 8.3.2.3 is invoked with the luma coding block location (xCb, yCb), the luma coding block width cbWidth, the luma coding block height cbHeight and the luma coding block width as inputs, and the output being the availability flags availableFlagA0, availableFlagA1, availableFlagB0, availableFlagB1 and availableFlagB2, the reference indices refIdxLXA0, refIdxLXA1, refIdxLXB0, refIdxLXB1 and refIdxLXB2, the prediction list utilization flags predFlagLXA0, predFlagLXA1, predFlagLXB0, predFlagLXB1 and predFlagLXB2, and the motion vectors mvLXA0, mvLXA1, mvLXB0, mvLXB1 and mvLXB2, with X being 0 or 1. 
     The derivation process for subblock-based temporal merging candidates as specified in clause 8.3.4.3 is invoked with the luma location (xCb, yCb), the luma coding block width cbWidth, the luma coding block height cbHeight, the availability flags availableFlagA0, availableFlagA1, availableFlagB0, availableFlagB1, the reference indices refIdxLXA0, refIdxLXA1, refIdxLXB0, refIdxLXB1, the prediction list utilization flags predFlagLXA0, predFlagLXA1, predFlagLXB0, predFlagLXB1 and the motion vectors mvLXA0, mvLXA1, mvLXB0, mvLXB1 as inputs and the output being the availability flag availableFlagSbCol, the number of luma coding subblocks in horizontal direction numSbX and in vertical direction numSbY, the reference indices refIdxLXSbCol, the luma motion vectors mvLXSbCol[xSbIdx][ySbIdx] and the prediction list utilization flags predFlagLXSbCol[xSbIdx][ySbIdx] with xSbIdx=0..numSbX−1, ySbIdx=0 numSbY−1 and X being 0 or 1. 
     When sps_affine_enabled_flag is equal to 1, the sample locations (xNbA0, yNbA0), (xNbA1, yNbA1), (xNbA2, yNbA2), (xNbB0, yNbB0), (xNbB1, yNbB1), (xNbB2, yNbB2), (xNbB3, yNbB3), and the variables numSbX and numSbY are derived as follows: 
     [No changes to the current VVC specification draft]. 
     5.3 Embodiment #3 An Example of MV Rounding 
     The syntax changes are based on JVET-O2001-vE. 
     8.5.5.3 Derivation Process for Subblock-Based Temporal Merging Candidates 
     
         
         
           
             The location (xColSb, yColSb) of the collocated subblock inside ColPic is derived as follows.
           1. The following applies:   
         
           
         
       
    
         y ColSb=Clip3( yCtb, Min(CurPicHeightInSamples Y− 1,  yCtb +(1&lt;&lt; Ctb  Log 2Size Y )−1),  ySb +((tempMv[1]+8−(tempMv[1]&gt;=0))&gt;&gt;4))
             If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the following applies:           

         x Col Sb =Clip3( xCtb, Min(SubPicRightBoundaryPos,  xCtb +(1&lt;&lt; Ctb  Log 2 Size Y )+3),  xSb +((tempMv[0]+8+(tempMV[0]&gt;=0))&gt;&gt;4))             Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0), the following applies:           
         x Col Sb =Clip3( xCtb, Min(CurPicWidthInSamples Y− 1,  xCtb +(1&lt;&lt; Ctb  Log 2 Size Y )+3),  xSb +(tempMv[0]+8+(tempMV[0]&gt;=0))&gt;&gt;4)) 
     8.5.5.4 Derivation Process for Subblock-Based Temporal Merging Base Motion Data 
     The location (xColCb, yColCb) of the collocated block inside ColPic is derived as follows.
         The following applies:       

         y Col Cb =Clip3( yCtb, Min(CurPicHeightInSamples Y− 1,  yCtb +(1&lt;&lt; Ctb  Log 2Size Y )−1),  y ColCtr Cb +((tempMv[1]+8−(tempMv[1]&gt;=0))&gt;&gt;4))
         If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the following applies:       

         x Col Cb =Clip3( xCtb, Min(SubPicRightBoundaryPos,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3), x Col CtrCb +((tempMv[0]+8+(tempMV[0]&gt;=0))&gt;&gt;4))         Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0, the following applies:       
         x ColCb=Clip3( xCtb, Min(CurPicWidthInSamples Y− 1,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3),  x Col CtrCb +((tempMv[0]+8+(tempMV[0]&gt;=0))&gt;&gt;4)) 
     5.3 Embodiment #3: An Example of MV Rounding 
     The syntax changes are based on JVET-O2001-vE. 
     8.5.5.3 Derivation Process for Subblock-Based Temporal Merging Candidates 
     
         
         The location (xColSb, yColSb) of the collocated subblock inside ColPic is derived as follows.
       1. The following applies:   
     
       
    
         y Col Sb =Clip3( yCtb, Min(CurPicHeightInSamples Y− 1,  yCtb +(1&lt;&lt; Ctb  Log 2Size Y )−1), ySb +((tempMv[1]+8−(tempMv[1]&gt;=0))&gt;&gt;4))
         If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the following applies:       

         x Col Sb =Clip3( xCtb, Min(SubPicRightBoundaryPos,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3),  xSb +((tempMv[0]+8+(tempMV[0]&gt;=0))&gt;&gt;4))         Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0), the following applies:       
         x Col Sb =Clip3( xCtb, Min(CurPicWidthInSamples Y− 1,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3),  xSb +(tempMv[0]+8+(tempMV[0]&gt;=0))&gt;&gt;4)) 
     8.5.5.4 Derivation Process for Subblock-Based Temporal Merging Base Motion Data 
     The location (xColCb, yColCb) of the collocated block inside ColPic is derived as follows.
         The following applies:       

         y Col Cb =Clip3( yCtb, Min(CurPicHeightInSamples Y− 1,  yCtb +(1&lt;&lt; Ctb  Log 2Size Y )−1), y Col CtrCb +((tempMv[1]+8−(tempMv[1]&gt;=0))&gt;&gt;4))
         If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the following applies:       

         x Col Cb =Clip3( xCtb, Min(SubPicRightBoundaryPos,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3), x ColCtr Cb +((tempMv[0]+8+(tempMV[0]&gt;=0))&gt;&gt;4))         Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0, the following applies:       
         x Col Cb =Clip3( xCtb, Min(CurPicWidthInSamples Y− 1,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3),  x Col CtrCb +((tempMv[0]+8+(tempMV[0]&gt;=0))&gt;&gt;4)) 
     5.4 Embodiment #4: A Second Example of MV Rounding 
     8.5.5.3 Derivation Process for Subblock-Based Temporal Merging Candidates 
     Inputs to this process are:
     a luma location (xCb, yCb) of the top-left sample of the current luma coding block relative to the top-left luma sample of the current picture,   a variable cbWidth specifying the width of the current coding block in luma samples,   a variable cbHeight specifying the height of the current coding block in luma samples.   the availability flag availableFlagA 1  of the neighbouring coding unit,   the reference index refIdxLXA 1  of the neighbouring coding unit with X being 0 or 1,   the prediction list utilization flag predFlagLXA 1  of the neighbouring coding unit with X being 0 or 1,   the motion vector in 1/16 fractional-sample accuracy mvLXA 1  of the neighbouring coding unit with X being 0 or 1.   

     Outputs of this process are:
     the availability flag availableFlagSbCol,   the number of luma coding subblocks in horizontal direction numSbX and in vertical direction numSbY,   the reference indices refIdxL0SbCol and refIdxL1SbCol,   the luma motion vectors in 1/16 fractional-sample accuracy mvLOSbCol[xSbIdx][ySbIdx] and mvL1SbCol[xSbIdx][ySbIdx] with xSbIdx=0..numSbX−1, ySbIdx=0..numSbY−1,   the prediction list utilization flags predFlagLOSbCol[xSbIdx][ySbIdx] and predFlagL1SbCol[xSbIdx][ySbIdx] with xSbIdx=0..numSbX−1, ySbIdx=0 numSbY−1.   

     The availability flag availableFlagSbCol is derived as follows.
     If one or more of the following conditions is true, availableFlagSb Col is set equal to 0.   slice temporal mvp enabled flag is equal to 0.   sps sbtmvp enabled flag is equal to 0.   cbWidth is less than 8.   cbHeight is less than 8.   Otherwise, the following ordered steps apply:
       1. The location (xCtb, yCtb) of the top-left sample of the luma coding tree block that contains the current coding block and the location (xCtr, yCtr) of the below-right center sample of the current luma coding block are derived as follows:   
       

         xCtb =( xCb&gt;&gt;Ctu  Log 2Size)&lt;&lt; Ctu  Log2Size   (8-542)
 
         yCtb =( yCb&gt;&gt;Ctu  Log 2Size)&lt;&lt; Ctu  Log2Size   (8-543)
 
         xCtr=xCb +( cb Width/2)   (8-544)
 
         yCtr=yCb +( cb Height/2)   (8-545)
         2. The luma location (xColCtrCb, yColCtrCb) is set equal to the top-left sample of the collocated luma coding block covering the location given by (xCtr, yCtr) inside ColPic relative to the top-left luma sample of the collocated picture specified by ColPic.   3. The derivation process for subblock-based temporal merging base motion data as specified in clause 8.5.5.4 is invoked with the location (xCtb, yCtb), the location (xColCtrCb, yColCtrCb), the availability flag availableFlagA 1 , and the prediction list utilization flag predFlagLXA 1 , and the reference index refIdxLXA 1 , and the motion vector mvLXA 1 , with X being 0 and 1 as inputs and the motion vectors ctrMvLX, and the prediction list utilization flags ctrPredFlagLX of the collocated block, with X being 0 and 1, and the temporal motion vector tempMv as outputs.   4. The variable availableFlagSbCol is derived as follows:
           If both ctrPredFlagL0 and ctrPredFlagL1 are equal to 0, availableFlagSbCol is set equal to 0.   Otherwise, availableFlagSbCol is set equal to 1.   
               

     When availableFlagSbCol is equal to 1, the following applies:
     The variables numSbX, numSbY, sbWidth, sbHeight and refIdxLXSbCol are derived as follows:   

       num SbX=cb Width&gt;&gt;3   (8-546)
 
       num SbY=cb Height&gt;&gt;3   (8-547)
 
         sb Width= cb Width/num SbX    (8-548)
 
         sb Height= cb Height/num SbY    (8-549)
 
       refIdxLXSbCol=0   (8-550)
     For xSbIdx=0..numSbX−1 and ySbIdx=0..numSbY−1, the motion vectors mvLXSbCol[xSbIdx][ySbIdx] and prediction list utilization flags predFlagLXSbCol[xSbIdx][ySbIdx] are derived as follows:
       The luma location (xSb, ySb) specifying the top-left sample of the current coding subblock relative to the top-left luma sample of the current picture is derived as follows:   
       

         xSb=xCb+xSb Idx* sb Width+ sb Width/2   (8-551)
 
         ySb=yCb+ySb Idx* sb Height+ sb Height/2   (8-552)
         The location (xColSb, yColSb) of the collocated subblock inside ColPic is derived as follows.
           1. The following applies:   
               

         y Col Sb =Clip3( yCtb,  Min(CurPicHeightInSamples Y− 1,  yCtb +(1&lt;&lt; Ctb  Log 2Size Y )−1),  ySb +((tempMv[1]+8−(tempMv[1]&gt;=0 ? 1:0))&gt;&gt;4))    (8-553)
             If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the following applies:           

         x Col Sb =Clip3( xCtb,  Min(SubPicRightBoundaryPos,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3),  xSb +((tempMv[0]+8−(tempMv[0]&gt;=0 ? 1:0))&gt;&gt;4))    (8-554)
             Otherwise (subpic treated as pic flag[SubPicIdx] is equal to 0), the following applies:           

         x Col Sb =Clip3( xCtb,  Min(CurPicWidthInSamples Y− 1,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3),  xSb +((tempMv[0]+8−(tempMv[0]&gt;=0 ? 1:0))&gt;&gt;4))   (8-555)
         The variable currCb specifies the luma coding block covering the current coding subblock inside the current picture.   The variable colCb specifies the luma coding block covering the modified location given by ((xColSb&gt;&gt;3)&lt;&lt;3, (yColSb&gt;&gt;3)&lt;&lt;3) inside the ColPic.   The luma location (xColCb, yColCb) is set equal to the top-left sample of the collocated luma coding block specified by colCb relative to the top-left luma sample of the collocated picture specified by ColPic.   The derivation process for collocated motion vectors as specified in clause 8.5.2.12 is invoked with currCb, colCb, (xColCb, yColCb), refIdxL0 set equal to 0 and sbFlag set equal to 1 as inputs and the output being assigned to the motion vector of the subblock mvL0SbCol[xSbIdx][ySbIdx] and availableFlagLOSbCol.   The derivation process for collocated motion vectors as specified in clause 8.5.2.12 is invoked with currCb, colCb, (xColCb, yColCb), refIdxL1 set equal to 0 and sbFlag set equal to 1 as inputs and the output being assigned to the motion vector of the subblock mvL1SbCol[xSbIdx][ySbIdx] and availableFlagL1SbCol.   When availableFlagL0SbCol and availableFlagL1SbCol are both equal to 0, the following applies for X being 0 and 1:       

       mv LXSb Col[ xSb Idx][ ySb Idx]= ctr Mv LX    (8-556)
 
       predFlag LXSb Col[ xSb Idx][ ySb Idx]=ctrPredFlag LX    (8-557)
 
     8.5.5.4 Derivation Process for Subblock-Based Temporal Merging Base Motion Data 
     Inputs to this process are:
     the location (xCtb, yCtb) of the top-left sample of the luma coding tree block that contains the current coding block,   the location (xColCtrCb, yColCtrCb) of the top-left sample of the collocated luma coding block that covers the below-right center sample.   the availability flag availableFlagA 1  of the neighbouring coding unit,   the reference index refIdxLXA 1  of the neighbouring coding unit,   the prediction list utilization flag predFlagLXA i  of the neighbouring coding unit,   the motion vector in 1/16 fractional-sample accuracy mvLXA 1  of the neighbouring coding unit.   

     Outputs of this process are:
     the motion vectors ctrMvL0 and ctrMvL1,   the prediction list utilization flags ctrPredFlagL0 and ctrPredFlagL1,   the temporal motion vector tempMv.   

     The variable tempMv is set as follows: 
       tempMv[0]=0   (8-558)
 
       tempMv[1]=0   (8-559)
 
     The variable currPic specifies the current picture. 
     When availableFlagA i  is equal to TRUE, the following applies:
     If all of the following conditions are true, tempMv is set equal to mvL0A 1 :
       predFlagL0A 1  is equal to 1,   DiffPicOrderCnt(ColPic, RefPicList[0][refIdxL0A 1 ]) is equal to 0,   
       Otherwise, if all of the following conditions are true, tempMv is set equal to mvL1A 1 :
       slice_type is equal to B,   predFlagL1A 1  is equal to 1,   DiffPicOrderCnt(ColPic, RefPicList[1][refIdxL1A 1 ]) is equal to 0.   
       

     The location (xColCb, yColCb) of the collocated block inside ColPic is derived as follows.
         The following applies:       

         y Col Cb =Clip3( yCtb,  Min(CurPicHeightInSamples Y− 1,  yCtb +(1&lt;&lt; Ctb  Log 2Size Y ) −1),  y ColCtr Cb +((tempMv[1]+8−(tempMv[1]&gt;=0 ? 1:0))&gt;&gt;4))   (8-560)
         If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the following applies:       

         x Col Cb =Clip3( xCtb,  Min(SubPicRightBoundaryPos,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3),  x Col CtrCb +((tempMv[0]+8−(tempMv[0]&gt;=0 ? 1:0))&gt;&gt;4))   (8-561)
         Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to o, the following applies:       

         x Col Cb =Clip3( xCtb,  Min(CurPicWidthInSamples Y− 1,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3),  x Col CtrCb +((tempMv[0]+8−(tempMv[0]&gt;=0 ? 1:0))&gt;&gt;4))   (8-562)
 
     The array colPredMode is set equal to the prediction mode array CuPredMode[0] of the collocated picture specified by ColPic. 
     The motion vectors ctrMvL0 and ctrMvL1, and the prediction list utilization flags ctrPredFlagL0 and ctrPredFlagL1 are derived as follows:
         If colPredMode[xColCb][yColCb] is equal to MODE INTER, the following applies:
           The variable currCb specifies the luma coding block covering (xCtrCb,yCtrCb) inside the current picture.   The variable colCb specifies the luma coding block covering the modified location given by ((xColCb&gt;&gt;3)&lt;&lt;3, (yColCb&gt;&gt;3)&lt;&lt;3) inside the ColPic.   The luma location (xColCb, yColCb) is set equal to the top-left sample of the collocated luma coding block specified by colCb relative to the top-left luma sample of the collocated picture specified by ColPic.   The derivation process for collocated motion vectors specified in clause 8.5.2.12 is invoked with currCb, colCb, (xColCb, yColCb), refIdxL0 set equal to 0, and sbFlag set equal to 1 as inputs and the output being assigned to ctrMvL0 and ctrPredFlagL0.   The derivation process for collocated motion vectors specified in clause 8.5.2.12 is invoked with currCb, colCb, (xColCb, yColCb), refIdxL1 set equal to 0, and sbFlag set equal to 1 as inputs and the output being assigned to ctrMvL1 and ctrPredFlagL1.   
           Otherwise, the following applies:       

       ctrPredFlagL0=0   (8-563)
 
       ctrPredFlagL1=0   (8-564)
 
     5.5 Embodiment #5: A Third Example of MV Rounding 
     8.5.5.3 Derivation Process for Subblock-Based Temporal Merging Candidates 
     Inputs to this process are:
     a luma location (xCb, yCb) of the top-left sample of the current luma coding block relative to the top-left luma sample of the current picture,   a variable cbWidth specifying the width of the current coding block in luma samples,   a variable cbHeight specifying the height of the current coding block in luma samples.   the availability flag availableFlagA 1  of the neighbouring coding unit,   the reference index refIdxLXA 1  of the neighbouring coding unit with X being 0 or 1,   the prediction list utilization flag predFlagLXA 1  of the neighbouring coding unit with X being 0 or 1,   the motion vector in 1/16 fractional-sample accuracy mvLXA 1  of the neighbouring coding unit with X being 0 or 1.   

     Outputs of this process are:
     the availability flag availableFlagSbCol,   the number of luma coding subblocks in horizontal direction numSbX and in vertical direction num SbY,   the reference indices refIdxL0SbCol and refIdxL1SbCol,   the luma motion vectors in 1/16 fractional-sample accuracy mvL0SbCol[xSbIdx][ySbIdx] and myL1SbCol[xSbIdx][ySbIdx] with xSbIdx=0..numSbX−1, ySbIdx=0..num SbY−1,   the prediction list utilization flags predFlagL0SbCol[xSbIdx][ySbIdx] and predFlagL1SbCol[xSbIdx][ySbIdx] with xSbIdx=0..numSbX−1, ySbIdx=0..numSbY−1.   

     The availability flag availableFlagSbCol is derived as follows.
     If one or more of the following conditions is true, availableFlagSbCol is set equal to 0.   slice temporal mvp enabled flag is equal to 0.   sps sbtmvp enabled flag is equal to 0.   cbWidth is less than 8.   cbHeight is less than 8.   Otherwise, the following ordered steps apply:
       1. The location (xCtb, yCtb) of the top-left sample of the luma coding tree block that contains the current coding block and the location (xCtr, yCtr) of the below-right center sample of the current luma coding block are derived as follows:   
       

         xCtb =( xCb&gt;&gt;Ctu  Log 2 Size)&lt;&lt; Ctu  Log2 Size   (8-542)
 
         yCtb =( yCb&gt;&gt;Ctu  Log 2Size)&lt;&lt; Ctu  Log2 Size   (8-543)
 
         xCtr=xCb +( cb Width/2)   (8-544)
 
         yCtr=yCb +( cb Height/2)   (8-545)
         2. The luma location (xColCtrCb, yColCtrCb) is set equal to the top-left sample of the collocated luma coding block covering the location given by (xCtr, yCtr) inside ColPic relative to the top-left luma sample of the collocated picture specified by ColPic.   3. The derivation process for subblock-based temporal merging base motion data as specified in clause 8.5.5.4 is invoked with the location (xCtb, yCtb), the location (xColCtrCb, yColCtrCb), the availability flag availableFlagA 1 , and the prediction list utilization flag predFlagLXA 1 , and the reference index refIdxLXA 1 , and the motion vector mvLXA 1 , with X being 0 and 1 as inputs and the motion vectors ctrMvLX, and the prediction list utilization flags ctrPredFlagLX of the collocated block, with X being 0 and 1, and the temporal motion vector tempMv as outputs.   4. The variable availableFlagSbCol is derived as follows:
           If both ctrPredFlagL0 and ctrPredFlagL1 are equal to 0, availableFlagSbCol is set equal to 0.   Otherwise, availableFlagSbCol is set equal to 1.   
               

     When availableFlagSbCol is equal to 1, the following applies:
         The variables numSbX, numSbY, sbWidth, sbHeight and refIdxLXSbCol are derived as follows:       

       numSbX=cbWidth&gt;&gt;3   (8-546)
 
       numSbY=cbHeight&gt;&gt;3   (8-547)
 
         sb Width= cb Width/num SbX    (8-548)
 
         sb Height= cb Height/num SbY    (8-549)
 
       refIdxLXSbCol=0   (8-550)
         For xSbIdx=0..numSbX−1 and ySbIdx=0..numSbY−1, the motion vectors mvLXSbCol[xSbIdx][ySbIdx] and prediction list utilization flags predFlagT XSbCol[xSbIdx][ySbIdx] are derived as follows:
           The luma location (xSb, ySb) specifying the top-left sample of the current coding subblock relative to the top-left luma sample of the current picture is derived as follows:   
               

         xSb=xCb+xSb Idx* sb Width+ sb Width/2   (8-551)
 
         ySb=yCb+ySb Idx* sb Height+ sb Height/2   (8-552)
         The location (xColSb, yColSb) of the collocated subblock inside ColPic is derived as follows.   1. The following applies:       

         y Col Sb =Clip3( yCtb,  Min(CurPicHeightInSamples Y− 1,  yCtb +(1&lt;&lt; Ctb  Log 2Size Y )−1),  ySb +((tempMv[1]+(tempMv[1]&gt;=0 ? 7:8))&gt;&gt;4))   (8-553)
         If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the following applies:       

         x Col Sb =Clip3( xCtb,  Min(SubPicRightBoundaryPos,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3),  xSb +((tempMv[0]+(tempMv[0]&gt;=0 ? 7:8))&gt;&gt;4))   (8-554)
         Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0), the following applies:       

         x Col Sb =Clip3( xCtb,  Min(CurPicWidthInSamples Y− 1,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3),  xSb +((tempMv[0]+(tempMv[0]&gt;=0 ? 7:8))&gt;&gt;4))   (8-555)
         The variable currCb specifies the luma coding block covering the current coding subblock inside the current picture.   The variable colCb specifies the luma coding block covering the modified location given by ((xColSb&gt;&gt;3)&lt;&lt;3, (yColSb&gt;&gt;3)&lt;&lt;3) inside the ColPic.   The luma location (xColCb, yColCb) is set equal to the top-left sample of the collocated luma coding block specified by colCb relative to the top-left luma sample of the collocated picture specified by ColPic.   The derivation process for collocated motion vectors as specified in clause 8.5.2.12 is invoked with currCb, colCb, (xColCb, yColCb), refIdxL0 set equal to 0 and sbFlag set equal to 1 as inputs and the output being assigned to the motion vector of the subblock mvL0 Sb Col[xSbIdx][ySbIdx] and availableFlagL0SbCol.   The derivation process for collocated motion vectors as specified in clause 8.5.2.12 is invoked with currCb, colCb, (xColCb, yColCb), refIdxL1 set equal to 0 and sbFlag set equal to 1 as inputs and the output being assigned to the motion vector of the subblock mvL1SbCol[xSbIdx][ySbIdx] and availableFlagL1SbCol.   When availableFlagLOSbCol and availableFlagL1 SbCol are both equal to 0, the following applies for X being 0 and 1:       

       mv LXSb Col[ xSb Idx][ ySb Idx]= ctr Mv LX    (8-556)
 
       predFlag LXSb Col[ xSb Idx][ ySb Idx]=ctrPredFlag LX    (8-557)
 
     8.5.5.4 Derivation Process for Subblock-Based Temporal Merging Base Motion Data 
     Inputs to this process are:
     the location (xCtb, yCtb) of the top-left sample of the luma coding tree block that contains the current coding block,   the location (xColCtrCb, yColCtrCb) of the top-left sample of the collocated luma coding block that covers the below-right center sample.   the availability flag availableFlagA 1  of the neighbouring coding unit,   the reference index refIdxLXA 1  of the neighbouring coding unit,   the prediction list utilization flag predFlagLXA 1  of the neighbouring coding unit,   the motion vector in 1/16 fractional-sample accuracy mvLXA 1  of the neighbouring coding unit.   

     Outputs of this process are:
     the motion vectors ctrMvL0 and ctrMvL1,   the prediction list utilization flags ctrPredFlagL0 and ctrPredFlagL1,   the temporal motion vector tempMv.   

     The variable tempMv is set as follows: 
       tempMv[0]=0   (8-558)
 
       tempMv[1]=0   (8-559)
 
     The variable currPic specifies the current picture. 
     When availableFlagA 1  is equal to TRUE, the following applies:
     If all of the following conditions are true, tempMv is set equal to mvL0A 1 :
       predFlagL0A 1  is equal to 1,   DiffPicOrderCnt(ColPic, RefPicList[0][refIdxL0A 1 ]) is equal to 0,   
       Otherwise, if all of the following conditions are true, tempMv is set equal to mvLlA 1 :
       slice type is equal to B,   predFlagL1A 1  is equal to 1,   DiffPicOrderCnt(ColPic, RefPicList[1][refIdxL1A 1 ]) is equal to 0.   
       

     The location (xColCb, yColCb) of the collocated block inside ColPic is derived as follows.
         The following applies:       

         y Col Cb =Clip3( yCtb,  Min(CurPicHeightInSamples Y− 1,  yCtb +(1&lt;&lt; Ctb  Log 2Size Y )−1),  y Col CtrCb +((tempMv[1]+(tempMv[1]&gt;=0 ? 7:8))&gt;&gt;4))   (8-560)
         If subpic treated as pic flag[SubPicIdx] is equal to 1, the following applies:       

         x Col Cb =Clip3( xCtb,  Min(SubPicRightBoundaryPos,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3),  x Col CtrCb +((tempMv[0]+(tempMv[0]&gt;=0 ? 7:8))&gt;&gt;4))   (8-561)
         Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to o, the following applies:       

         x Col Cb =Clip3( xCtb,  Min(CurPicWidthInSamples Y− 1,  xCtb +(1&lt;&lt; Ctb  Log 2Size Y )+3),  x Col CtrCb +((tempMv[0]+(tempMv[0]&gt;=0 ? 7:8))&gt;&gt;4))   (8-562)
 
     The array colPredMode is set equal to the prediction mode array CuPredMode[0] of the collocated picture specified by ColPic. 
     The motion vectors ctrMvL0 and ctrMvLl, and the prediction list utilization flags ctrPredFlagL0 and ctrPredFlagL1 are derived as follows:
     If colPredMode[xColCb][yColCb] is equal to MODE INTER, the following applies:
       The variable currCb specifies the luma coding block covering (xCtrCb ,yCtrCb) inside the current picture.   The variable colCb specifies the luma coding block covering the modified location given by ((xColCb&gt;&gt;3)&lt;&lt;3, (yColCb&gt;&gt;3)&lt;&lt;3) inside the ColPic.   The luma location (xColCb, yColCb) is set equal to the top-left sample of the collocated luma coding block specified by colCb relative to the top-left luma sample of the collocated picture specified by ColPic.   The derivation process for collocated motion vectors specified in clause 8.5.2.12 is invoked with currCb, colCb, (xColCb, yColCb), refIdxL0 set equal to 0, and sbFlag set equal to 1 as inputs and the output being assigned to ctrMvL0 and ctrPredFlagL0.   The derivation process for collocated motion vectors specified in clause 8.5.2.12 is invoked with currCb, colCb, (xColCb, yColCb), refIdxL1 set equal to 0, and sbFlag set equal to 1 as inputs and the output being assigned to ctrMvL1 and ctrPredFlagT 1.   
       Otherwise, the following applies:   

       ctrPredFlagL0=0   (8-563)
 
       ctrPredFlagL1=0   (8-564)
 
     8.5.6.3 Fractional Sample Interpolation Process 
     8.5.6.3.1 General 
     Inputs to this process are:
     a luma location (xSb, ySb) specifying the top-left sample of the current coding subblock relative to the top-left luma sample of the current picture,   a variable sbWidth specifying the width of the current coding subblock,   a variable sbHeight specifying the height of the current coding subblock,   a motion vector offset mvOffset,   a refined motion vector refMvLX,   the selected reference picture sample array refPicLX,   the half sample interpolation filter index hpelIfIdx,   the bi-directional optical flow flag bdofFlag,   a variable cIdx specifying the colour component index of the current block.   

     Outputs of this process are:
     an (sbWidth+brdExtSize)×(sbHeight+brdExtSize) array predSamplesLX of prediction sample values.   

     The prediction block border extension size brdExtSize is derived as follows: 
         brd ExtSize=( bd ofFlag∥(inter_affine_flag[ xSb][ySb ] &amp;&amp;  sps _affine_prof_enabled_flag)) ? 2:0    (8-752)
 
     The variable fRefWidth is set equal to the PicOutputWidthL of the reference picture in luma samples. 
     The variable fRefHeight is set equal to PicOutputHeightL of the reference picture in luma samples. 
     The motion vector mvLX is set equal to (refMvLX−mvOffset).
     If cIdx is equal to 0, the following applies:
       The scaling factors and their fixed-point representations are defined as   
       

       hori_scale_ fp =(( f RefWidth&lt;&lt;14)+(PicOutputWidth L&gt;&gt; 1))/PicOutputWidth L    (8-753)
 
       vert_scale_ fp =(( f RefHeight&lt;&lt;14)+(PicOutputHeight L&gt;&gt; 1))/PicOutputHeight L    (8-754)
         Let (xIntL, yIntL) be a luma location given in full-sample units and (xFracL, yFracL) be an offset given in 1/16-sample units. These variables are used only in this clause for specifying fractional-sample locations inside the reference sample arrays refPicLX.   The top-left coordinate of the bounding block for reference sample padding (xSbInt L , ySbInt L ) is set equal to (xSb+(mvLX[0]&gt;&gt;4), ySb+(mvLX[1]&gt;&gt;4)).   For each luma sample location (x L =0..sbWidth−1+brdExtSize, y L =0..sbHeight−1+brdExtSize) inside the prediction luma sample array predSamplesLX, the corresponding prediction luma sample value predSamplesLX[x L ][y L ] is derived as follows:
           Let (refxSb L , refySb L ) and (refx L , refy L ) be luma locations pointed to by a motion vector (refMvLX[0], refMvLX[1])given in 1/16-sample units. The variables refxSb L , refx L , refySb L , and refy L  are derived as follows:   
               

       ref xSb   L =(( xSb&lt;&lt; 4)+refMv LX[ 0])*hori_scale_ fp    (8-755)
 
       ref x   L =((Sign(ref xSb )*((Abs(ref xSb )+128)&gt;&gt;8)+ x   L *((hori_scale_ fp+ 8)&gt;&gt;4))+32)&gt;&gt;6   (8-756)
 
       ref y Sb L =(( ySb&lt;&lt; 4)+refMv LX[ 1])*vert_scale_ fp    (8-757)
 
       ref yL =((Sign(ref ySb )*((Abs(ref ySb )+128)&gt;&gt;8)+ yL* ((vert_scale_ fp+ 8)&gt;&gt;4))+32)&gt;&gt;6   (8-758)
         The variables xInt L , yInt L , xFrac L  and yFrac L  are derived as follows:       

       xInt L =refx L &gt;&gt;4   (8-759)
 
       yInt L =refy L &gt;&gt;4   (8-760)
 
       xFrac L =refx L  &amp; 15   (8-761)
 
       yFrac L =refy L  &amp; 15   (8-762)
     using6TapFlag is set to be 1 if all the conditions below are satisfied:   

         cb Width[0][ xSb][ySb]&lt;= 4∥ cb Height[0][ xSb][ySb]&lt;= 4∥ cb Width[0][ xSb][ySb]*cb Height[0][ xSb][ySb]&lt;= 64.
 
       PredFlagL0[ xSb][ySb]== 1 &amp;&amp; PredFlagL1[ xSb][ySb] 1.
     If bdofFlag is equal to TRUE or (sps_affine_prof_enabled_flag is equal to TRUE and inter_affine_flag[xSb][ySb] is equal to TRUE), and one or more of the following conditions are true, the prediction luma sample value predSamplesLX[x L ][y L ] is derived by invoking the luma integer sample fetching process as specified in clause 8.5.6.3.3 with (xInt L +(xFrac L &gt;&gt;3)−1), yInt L +(yFrac L &gt;&gt;3)−1) and refPicLX as inputs.
       1. x L  is equal to 0.   2. x L  is equal to sbWidth+1.   3. y L  is equal to 0.   4. y L  is equal to sbHeight+1.   
       Otherwise, the prediction luma sample value predSamplesLX[xL][yL] is derived by invoking the luma sample 8-tap interpolation filtering process as specified in clause 8.5.6.3.2 with (xIntL−(brdExtSize&gt;0 ? 1:0), yIntL−(brdExtSize&gt;0 ? 1:0)), (xFracL, yFracL), (xSbInt L , ySbInt L ), refPicLX, hpelIfIdx, sbWidth, sbHeight and (xSb, ySb) and using6TapFlag as inputs.   Otherwise (cIdx is not equal to 0), the following applies:
       Let (xIntC, yIntC) be a chroma location given in full-sample units and (xFracC, yFracC) be an offset given in 1/32 sample units. These variables are used only in this clause for specifying general fractional-sample locations inside the reference sample arrays refPicLX.   The top-left coordinate of the bounding block for reference sample padding (xSbIntC, ySbIntC) is set equal to ((xSb/SubWidthC)+(mvLX[0]&gt;&gt;5), (ySb/SubHeightC)+(mvLX[1]&gt;&gt;5)).   For each chroma sample location (xC=0..sbWidth−1, yC=0..sbHeight−1) inside the prediction chroma sample arrays predSamplesLX, the corresponding prediction chroma sample value predSamplesLX[xC][yC] is derived as follows:
           Let (refxSb C , refy Sb C ) and (refx C , refy C ) be chroma locations pointed to by a motion vector (mvLX[0], mvLX[1]) given in 1/32-sample units. The variables refxSb C , refySb C , refx C  and refy C  are derived as follows:   
           
       

       ref xSb   C =(( xSb/ SubWidth C&lt;&lt; 5)+mv LX[ 0])*hori_scale_ fp    (8-763)
 
       ref x   C =((Sign(ref xSb   C )*((Abs(ref xSb   C )+256)&gt;&gt;9)+ xC *((hori_scale_ fp+ 8)&gt;&gt;4))+16)&gt;&gt;5   (8-764)
 
       ref ySb   C =(( ySb/ SubHeight C&lt;&lt; 5)+mv LX[ 1])*vert_scale_ fp    (8-765)
 
       ref y   C =((Sign(ref ySb   C )*((Abs(ref ySb   C )+256)&gt;&gt;9)+ yC* ((vert_scale_ fp+ 8)&gt;&gt;4))+16)&gt;&gt;5   (8-766)
             The variables xInt C , yInt C , xFrac C  and yFrac C  are derived as follows:           

       xInt C =refx C &gt;&gt;5   (8-767)
 
       yInt C =refy C &gt;&gt;5   (8-768)
 
       xFrac C =refy C  &amp; 31   (8-769)
 
       yFrac C =refy C  &amp; 31   (8-770)
         The prediction sample value predSamplesLX[xC][yC] is derived by invoking the process specified in clause 8.5.6.3.4 with (xIntC, yIntC), (xFracC, yFracC), (xSbIntC, ySbIntC), sbWidth, sbHeight and refPicLX as inputs.       

     8.5.6.3.2 Luma Sample Interpolation Filtering Process 
     Inputs to this process are:
     a luma location in full-sample units (xInt L , yInt L ),   a luma location in fractional-sample units (xFrac L , yFrac L ),   a luma location in full-sample units (xSbInt L , ySbInt L ) specifying the top-left sample of the bounding block for reference sample padding relative to the top-left luma sample of the reference picture,   the luma reference sample array refPicLX L ,   the half sample interpolation filter index hpelIfIdx,   a variable sbWidth specifying the width of the current subblock,   a variable sbHeight specifying the height of the current subblock,   a luma location (xSb, ySb) specifying the top-left sample of the current subblock relative to the top-left luma sample of the current picture,   a flag using6TapFlag specifying whether the 6-tap interpolation filter used.   

     Output of this process is a predicted luma sample value predSampleLX L    
     The variables shift1, shift2 and shift3 are derived as follows:
     The variable shiftl is set equal to Min(4, BitDepth Y −8), the variable shift2 is set equal to 6 and the variable shift3 is set equal to Max(2, 14−BitDepth Y ).   The variable picW is set equal to pic_width_in_luma_samples and the variable picH is set equal to pic_height_in_luma_samples.   

     The luma interpolation filter coefficients f L [p] for each 1/16 fractional sample position p equal to xFrac L  or yFrac L  are derived as follows: 
       0  If at least one of the following conditions are satisfied, the luma interpolation filter coefficients f L [p] are specified in Table 8-12.
         MotionModelIdc[xSb][ySb] is greater than 0, and sbWidth and sbHeight are both equal to 4,   using6TapFlag is equal to 1.       Otherwise, the luma interpolation filter coefficients f L [p] are specified in Table 8-11 depending on hpellfIdx.   

     The luma locations in full-sample units (xInt i , yInt i ) are derived as follows for i=0..7:
     If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the following applies:   

         x Int i =Clip3(SubPicLeftBoundaryPos, SubPicRightBoundaryPos,  x Int L   +i− 3)   (8-771)
 
         y Int i =Clip3(SubPicTopBoundaryPos, SubPicBotBoundaryPos,  y Int L   +i− 3)   (8-772)
     Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0), the following applies:   

         x Int i =Clip3(0, pic W− 1,  sps _ref_wraparound_enabled_flag ? Clip H (( sps _ref_wraparound_offset_minus1+1)*Min Cb Size Y,  pic W, x Int L   +i− 3):  x Int L   +i− 3)   (8-773)
 
         y int i =Clip3(0, pic H− 1,  y Int L   +i− 3)    (8-774)
 
     The luma locations in full-sample units are further modified as follows for i=0..7: 
         x Int i =Clip3( xSb Int L −3,  xSb Int L   +sb Width+4,  x Int i )   (8-775)
 
         y Int i =Clip3( ySb Int L −3,  ySb Int L   +sb Height+4,  y Int i )   (8-776)
 
     The predicted luma sample value predSampleLX L  is derived as follows:
     If both xFrac L  and yFrac L  are equal to 0, the value of predSampleLX L  is derived as follows:   

       predSample LX   L =refPic LX   L   [x Int 3   ][y Int 3 ]&lt;&lt;shift3   (8-777)
     Otherwise, if xFrac L  is not equal to 0 and yFrac L  is equal to 0, the value of predSampleLX L  is derived as follows:   

       predSample LX   L =(Σ i=0   7   f   L   [x Frac L   ][i ]*refPic LX   L   [x Int i   ][y Int 3 ])&gt;&gt;shift1    (8-778)
     Otherwise, if xFrac L  is equal to 0 and yFrac L  is not equal to 0, the value of predSampleLX L  is derived as follows:   

       predSample LX   L =(Σ i=   7   [y Frac L   ][i ]*refPic LX   L   [x Int 3   ][y Int])&gt;&gt;shift1    (8-779)
     Otherwise, if xFrac L  is not equal to 0 and yFrac L  is not equal to 0, the value of predSampleLX L  is derived as follows:
       The sample array temp[n] with n=0..7, is derived as follows:   
       

       temp[ n ]=(Σ i=0   7   f   L   [x Frac L   ][i ]*refPic LX   L   [x Int i   ][y Int n ])&gt;&gt;shift1   (8-780)
         The predicted luma sample value predSampleLX L  is derived as follows:       

       predSample LX   L =(Σ i=0   7   f   L   [y Frac L   ][i ]*temp[ i ])&gt;&gt;shift2   (8-781)
 
     
       
         
           
               
             
               
                 TABLE 8-11 
               
             
            
               
                   
               
               
                 Specification of the luma interpolation filter coefficients f L [p] 
               
               
                 for each 1/16 fractional sample position p. 
               
            
           
           
               
               
            
               
                 Fractional 
                   
               
               
                 sample 
                 interpolation filter coefficients 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 position 
                 f L [p][0] 
                 f L [p][1] 
                 f L [p][2] 
                 f L [p][3] 
                 f L [p][4] 
                 f L [p][5] 
                 f L [p][6] 
                 f L [p][7] 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 0 
                 1 
                 −3 
                 63 
                 4 
                 −2 
                 1 
                 0 
               
               
                 2 
                 −1 
                 2 
                 −5 
                 62 
                 8 
                 −3 
                 1 
                 0 
               
               
                 3 
                 −1 
                 3 
                 −8 
                 60 
                 13 
                 −4 
                 1 
                 0 
               
               
                 4 
                 −1 
                 4 
                 −10 
                 58 
                 17 
                 −5 
                 1 
                 0 
               
               
                 5 
                 −1 
                 4 
                 −11 
                 52 
                 26 
                 −8 
                 3 
                 −1 
               
               
                 6 
                 −1 
                 3 
                 −9 
                 47 
                 31 
                 −10 
                 4 
                 −1 
               
               
                 7 
                 −1 
                 4 
                 −11 
                 45 
                 34 
                 −10 
                 4 
                 −1 
               
               
                 8 
                 −1 
                 4 
                 −11 
                 40 
                 40 
                 −11 
                 4 
                 −1 
               
               
                 (hpelIfIdx == 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 0) 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 8 
                 0 
                 3 
                 9 
                 20 
                 20 
                 9 
                 3 
                 0 
               
               
                 (hpelIfIdx == 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 1) 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 9 
                 −1 
                 4 
                 −10 
                 34 
                 45 
                 −11 
                 4 
                 −1 
               
               
                 10 
                 −1 
                 4 
                 −10 
                 31 
                 47 
                 −9 
                 3 
                 −1 
               
               
                 11 
                 −1 
                 3 
                 −8 
                 26 
                 52 
                 −11 
                 4 
                 −1 
               
               
                 12 
                 0 
                 1 
                 −5 
                 17 
                 58 
                 −10 
                 4 
                 −1 
               
               
                 13 
                 0 
                 1 
                 −4 
                 13 
                 60 
                 −8 
                 3 
                 −1 
               
               
                 14 
                 0 
                 1 
                 −3 
                 8 
                 62 
                 −5 
                 2 
                 −1 
               
               
                 15 
                 0 
                 1 
                 −2 
                 4 
                 63 
                 −3 
                 1 
                 0 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 8-12 
               
             
            
               
                   
               
               
                 Specification of the luma interpolation filter coefficients f L [p] 
               
               
                 for each 1/16 fractional sample position p for affine motion mode. 
               
            
           
           
               
               
            
               
                 Fractional 
                   
               
               
                 sample position 
                 interpolation filter coefficients 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 p 
                 f L [p][0] 
                 f L [p][1] 
                 f L [p][2] 
                 f L [p][3] 
                 f L [p][4] 
                 f L [p][5] 
                 f L [p][6] 
                 f L [p][7] 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 0 
                 1 
                 −3 
                 63 
                 4 
                 −2 
                 1 
                 0 
               
               
                 2 
                 0 
                 1 
                 −5 
                 62 
                 8 
                 −3 
                 1 
                 0 
               
               
                 3 
                 0 
                 2 
                 −8 
                 60 
                 13 
                 −4 
                 1 
                 0 
               
               
                 4 
                 0 
                 3 
                 −10 
                 58 
                 17 
                 −5 
                 1 
                 0 
               
               
                 5 
                 0 
                 3 
                 −11 
                 52 
                 26 
                 −8 
                 2 
                 0 
               
               
                 6 
                 0 
                 2 
                 −9 
                 47 
                 31 
                 −10 
                 3 
                 0 
               
               
                 7 
                 0 
                 3 
                 −11 
                 45 
                 34 
                 −10 
                 3 
                 0 
               
               
                 8 
                 0 
                 3 
                 −11 
                 40 
                 40 
                 −11 
                 3 
                 0 
               
               
                 9 
                 0 
                 3 
                 −10 
                 34 
                 45 
                 −11 
                 3 
                 0 
               
               
                 10 
                 0 
                 3 
                 −10 
                 31 
                 47 
                 −9 
                 2 
                 0 
               
               
                 11 
                 0 
                 2 
                 −8 
                 26 
                 52 
                 −11 
                 3 
                 0 
               
               
                 12 
                 0 
                 1 
                 −5 
                 17 
                 58 
                 −10 
                 3 
                 0 
               
               
                 13 
                 0 
                 1 
                 −4 
                 13 
                 60 
                 −8 
                 2 
                 0 
               
               
                 14 
                 0 
                 1 
                 −3 
                 8 
                 62 
                 −5 
                 1 
                 0 
               
               
                 15 
                 0 
                 1 
                 −2 
                 4 
                 63 
                 −3 
                 1 
                 0 
               
               
                   
               
            
           
         
       
     
       FIG. 29  is a block diagram of a video processing apparatus  2600 . The apparatus  2600  may be used to implement one or more of the methods described herein. The apparatus  2600  may be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, and so on. The apparatus  2600  may include one or more processors  2602 , one or more memories  2604  and video processing hardware  2606 . The processor(s)  2602  may be configured to implement one or more methods described in the present document. The memory (memories)  2604  may be used for storing data and code used for implementing the methods and techniques described herein. The video processing hardware  2606  may be used to implement, in hardware circuitry, some techniques described in the present document. 
       FIG. 30  is a flowchart for an example method  3000  of video processing. The method includes determining ( 3002 ), for a current video block, a maximum number of candidates ML in a sub-block merge candidate list or enabling a use of alternative temporal motion vector prediction (ATMVP) candidates based on a state of use of temporal motion vector prediction (TMVP) or current picture referencing coding (CPR) for the current video block, wherein the state is one of enabled or disabled and performing ( 3004 ), based on a result of the determining, a conversion between the current video block and a bitstream representation of the current video block. 
     It will be appreciated that several techniques have been disclosed that will benefit video encoder and decoder embodiments incorporated within video processing devices such as smartphones, laptops, desktops, and similar devices by allowing the use of ATMVP coding tool in encoding or decoding of video or images. Various embodiments and techniques may be described using the following clause-based description. 
     1. A method of video processing, comprising: determining, for a current video block, a maximum number of candidates ML in a sub-block merge candidate list or enabling a use of alternative temporal motion vector prediction (ATMVP) candidates based on a state of use of temporal motion vector prediction (TMVP) or a state of current picture referencing coding (CPR) for the current video block, wherein the state is one of enabled or disabled, and performing, based on a result of the determining, a conversion between the current video block and a bitstream representation of the current video block. 
     2. The method of clause 1, wherein the enabling the use of ATMVP candidates is further based on a state of ATMVP usage for the current video block. 
     3. The method of any of claims 1-2, wherein the determining ML includes: determining that ATMVP and TMVP are disabled; and determining ML by excluding ATMVP candidates from the sub-block merge candidate list. 
     4. The method of any of claims 1-2, wherein the determining ML includes:
         concluding that ATMVP is enabled for the current video block, TMVP is disabled for the current video block and affine coding is disabled for the current video block; and   based on the concluding, setting ML to zero.       

     5 The method of any of claims 1-2, wherein the determining ML includes:
         concluding that ATMVP is enabled for the current video block, TMVP is enabled for the current video block and affine coding is disabled for the current video block; and   based on the concluding, setting ML to 1.       

     6. The method of any of claims 1-2, wherein the determining ML is based on the state of ATMVP usage for the current block, and whether a collocated reference picture of a current picture of the current video block is the current picture. 
     7. The method of any of claims 1-2, wherein the determining ML is based on the state of ATMVP, and whether a reference picturewith reference index 0 in a reference picture list of a current picture of the current video block is the current picture. 
     8. The method of clause 7, wherein the reference picture list is either list 0 or list 1. 
     Additional description of clauses 1-8 can be found in the items 1-2 listed in Section 4. 
     9. A method of video processing, comprising:
         determining, fora conversion between a bitstream representing a sequence of video pictures and pixel values of the video picture using a block-based encoding in which blocks of a video picture are organized as slices or tiles, a relationship between a temporal motion vector prediction (TMVP) coding tool and an alternative TMVP (ATMVP) coding tool, and   performing, based on the determining, the conversion;   wherein the relationship specifies the applicability as one or more of the following:   (a) in case that the TMVP is not allowed at a slice or a tile or a picture level, then ATMVP is disabled at the slice or the tile or the picture level;   (b) in case that the TMVP is signaled at the slice or the tile or the picture level, then ATMVP is signaled at the slice or the tile or the picture level after the TMVP;   (c) the relationship is specified only at a sequence level and not included at the slice or the tile or the picture level.       

     10. The method of clause 9, wherein the relationship is signaled in a single bit in the bitstream representation. 
     Additional description of clauses 9-10 can be found in the items 3-4 listed in Section 4. 
     11. A method of video coding, comprising:
         determining, for a conversion between a video region and a bitstream representation, an amount of masking to be applied to a position of a coordinated of a current block or a current sub-block of the video region for temporal motion vector prediction (TMVP) or advanced temporal motion vector prediction (ATMVP) coding; and   performing, by applying the masking based on the amount, the conversion between the video region and the corresponding bitstream representation.       

     12. The method of clause 11, wherein the amount of masking is signaled in the bitstream representation. 
     13. The method of claims 11-12, wherein the amount of masking is set to no-masking in case that an indication in a signal parameter set of the bitstream representation indicates that motion compression is disabled. 
     14. The method of any of claims 11-13, wherein the masking is applied by a bit-wise AND operation with an integer MASK whose value is equal to ˜(2 M −1), where M is an integer, “˜” represents the bitwise complement operator. 
     15. The method of any of claims 11-14, wherein the applying the masking includes applying the masking resulting in 2K×2K blocks of the video region share a same motion information, wherein K and M are different integers. 
     16. The method of any of claims 11-15, wherein M=3 or M=4. 
     17. The method of any of claims 11-16, wherein M is signaled in the bitstream representation. 
     Additional description of clauses 11-17 can be found in the items 3-4 listed in Section 4. 
     18. A method of video processing, comprising:
         determining, during a conversion between a current video region and a bitstream representation, a valid corresponding region for alternative temporal motion vector prediction (ATMVP) of the current video region, and   performing the conversion based on the valid corresponding region,   wherein the determining is based on one or more of:   (a) an adaptive determination based on a characteristic of the current video region;   (b) a basic region having a size M×N pixels, where M and N are integers;   (c) determining a motion vector used for locating the valid corresponding region, wherein the determining the motion vector is based on a rule; or   (d) determining default motion vectors for the ATMVP coding.       

     19. The method of clause 18, wherein the current video region is the valid corresponding region is a function of (a) a width or a height of the current video region, or (b) a motion vector compression tool applied to the current video region. 
     20. The method of any of claims  18 - 19 , wherein the current video region corresponds to a basic region of size M×N that is smaller than a coding tree unit (CTU) region. 
     21. The method of clause 20, wherein a current video block is inside the basic region, and wherein the valid corresponding region is a collocated basic region. 
     22. The method of clause 20, wherein a current video block is inside the basic region, and wherein the valid corresponding region is at least partly non-overlapping with a collocated basic region. 
     23. The method of clause 18, wherein the valid corresponding region is in a different picture than a current picture that includes the current video region. 
     24. The method of clause 23, wherein the current video region is a current video block and a temporal motion vector (TMV) corresponding to the current video block is (1) set to a default value, or (2) set to a motion vector in a history based motion vector predictor table. 
     25. The method of clause 23, wherein the determining the default motion vectors for ATMVP coding includes (1) setting the default motion vectors to a value (0,0), or (2) deriving the default motion vectors from a history based motion vector predictor table, or (3) deriving the default motion vectors from a neighboring block. 
     Additional description of clauses 18-25 can be found in the items 7-10 listed in Section 4. 
     26. A method of video processing, comprising:
         generating a candidate list or motion vectors for a video region using a rule; and   performing a conversion between the video region and a bitstream representation of the video region using the candidate list, wherein the rule includes one or more of:   (a) rule 1: a candidate corresponding to alternative temporal motion vector prediction (ATMVP) mode is always considered during the conversion;   (b) rule 2: enablement status of affine mode for the video region is used in determining availability of zero motion affine merge candidate in a sub-block merge candidate list for sub-blocks of the video region;   (c) rule 3: using a non-affine padding candidate to a sub-block merge candidate list for a sub-block of the video region; or   (d) rule 4: motion vectors for the video region are derived from motion vectors of a block covering a corresponding position accordingto an alternative temporal motion vector predictor method.       

     27. The method of clause 26, wherein the video region is a current video block and rule 1 further specifies to determine ATMVP default motion vectors by determining a block at a corresponding position that covers a corresponding position of a center point of the current video block. 
     28. The method of clause 26, wherein rule 2 further specifies to refrain from adding the zero motion affine merge candidate into the sub-block merge candidate list in case that enablement of affine mode status indicates that affine mode is turned off for the current video block. 
     Additional description of clauses 26-28 can be found in the items 11-12 listed in Section 4. 
     29. The method of any of claims 1-28, wherein the conversion includes generating the bitstream from the current video block or the current video region. 
     30. The method of any of claims 1-28, wherein the conversion includes generating pixel values of the current video block or the current video region from the bitstream representation. 
     31. The method of any of clauses 1-28, further comprising: determining that a temporal block in a collocated picture related with the current video block is coded with CPR mode, and wherein a default motion candidate is used rather than an ATMVP candidate based on the determination that the temporal block is coded with CPR mode. 
     32. The method of clause 31, whereinthe default motion candidate is indicative of a center position of the current video block. 
     33. The method of clause 31, wherein the default motion candidate is a (0,0) motion vector, and a reference picture index is equal to zero for both reference picture lists. 
     34. The method of any of clauses 1-28, further comprising: determining a position of the current video block, wherein default motion information for use of the ATMVP candidates is based on the determination of the position of the current video block. 
     35. The method of clause 34, wherein the position is based on a position of a sub-block of the current video block. 
     36. The method of any of clauses 1-28, wherein use of the ATMVP candidates is based on a flag indicatinguse of the ATMVP candidates providedby a slice, a tile, or a picture header. 
     37. The method of clause 36, wherein a current picture including the current video block is not an Intra Random Access Point (IRAP) picture, and wherein the current picture is not inserted into RefPicListO with a reference index equal to zero. 
     38. The method of any of clauses 1-28, wherein ATMVP or TMVP is enabled or disabled based on a flag that is inferred to be false for a slice or a tile based on a current picture includingthe currentvideo block being a reference picture with an index setto M and a reference picture list X. 
     39. The method of any of clauses 1-28, further comprising: determining that a reference picture with an index set to M in a reference picture list X for the current video block is a current picture, and wherein ATMVP is enabled based on the determination that the reference picture with the index set to M in the reference picture list X for the current video block is the current picture. 
     40. The method of clause 39, wherein sub-block motion information are defined to point to the current picture. 
     41. The method of clause 39, further comprising: determining that a sub-block motion information is from a temporal block, wherein the temporal block is coded with a reference picture pointing to the current picture of the temporal block. 
     42. The method of clause 41, wherein the sub-block motion information is not scaled. 
     43. The method of any clauses 1-28, wherein performing the conversion includes aligning a sub-block merge index for coding. 
     44. The method of clause 43, wherein a first number of bins are context coded, and a second number of bins are bypass coded, the second number of bins not context coded. 
     45. The method of clause 43, wherein bins are context coded. 
     46. A method of video processing, comprising: determining, for a current video block, a motion vector used in an alternative temporal motion vector prediction (ATMVP) process to locate a correspondingblockin a different picturefor a conversion between the current video block and a coded representation of the current video block based on a right-shifting rounding process, and performing, based on a result of the determining, the conversion between the current video block and the coded representation of the current video block. 
     47. The method of clause 46, wherein the right-shifted rounding process is identical to that used for motion vector scaling during the conversion. 
     48. The method of clause 46, wherein the right-shifted rounding process results in a rounding to integer value by rounding towards zero. 
     49. The method of any of clauses 46-48, wherein the motion vector used in the ATMVP process is used to derive a default motion information. 
     The following clauses provide some example solutions of techniques described in items in the previous section (e.g., items 24-29). 
     50. A method of video processing, comprising determining, for a conversion between a video picture of a video and a coded representation of the video segment using sub-pictures, that a rule of constraint related to sub-blocks is satisfied by the conversion; and performing the conversion according to the rule of constraints. 
     51. The method of clause 50, wherein the rule of constraint specifies that a width of a sub-picture S ending at the (j−1) column is set equal to j minus a left-most column of the sub-picture S, due to positions (i, j) and (i, j−1) belonging to different sub-pictures within the video picture. 
     52. The method of any of clauses 50-51, whereinthe rule of constraint specifies that a height of a sub-picture S ending at the (NumSubPicGridRows−1) row is set equal to (NumSubPicGridRows −1) minus a top-most row of the sub-picture S plus one. 
     53. The method of any of clauses 50-52, whereinthe rule of constraint specifies that a width of a sub-picture S ending at the (Num SubPicGridColumns−1) column is set equal to (Num SubPicGridColumns−1) minus a left-most column of the sub-picture S plus 1. 
     54. The method of any of clauses 50-53, whereinthe rule of constraint specifies that a size of a sub-picture grid in the video picture is an integer multiple of a coding tree unit size used during the conversion. 
     55. The method of any of clauses 50-54, whereinthe rule of constraint specifies that all sub-pictures in the video picture are non-overlapping, and together cover entirety of the video picture. 
     The following clauses provide some example solutions of techniques described in items in the previous section (e.g., items 30-34). 
     56. A method of video processing, comprising determining, for a conversion between a video unit of a video and a coded representation of the video, whether a reference picture resampling (RPR) mode is used during the conversion, and performing the conversion based on the determining. 
     57. The method of clause 56, wherein a flag in the coded representation indicates use of the RPR mode. 
     58. The method of any of clauses 56-57, wherein the RPR mode is indicated at a sequence level or a video parameter set level. 
     59. The method of any of clauses 56-59, wherein the RPR mode comprises using interpolation filters during a motion compensation process to derive a prediction block of a current block of the video unit during the conversion based on whether a resolution of a reference picture is different to the current picture, or whether a width and/or a height of the reference picture is larger that of the current picture. 
     60. The method of any of clause 1 to 59, wherein the conversion includes generating the coded representation from pixel values of the current video block. 
     61. The method of any of clauses 1 to 59, wherein the conversion includes pixels values of the current video block from the coded representation. 
     62. A video encoder apparatus comprising a processor configured to implement a method recited in any of clauses 1 to 61. 
     63. A video decoder apparatus comprising a processor configured to implement a method recited in any of clauses 1 to 61. 
     64. A computer readable medium having code stored thereon, the code, when executed by a processor, causing the processor to implement a method recited in any of clauses 1 to 61. 
       FIG. 32  is a block diagram showing an example video processing system  3200  in which various techniques disclosed herein may be implemented. Various implementations may include some or all of the components of the system  3200 . The system  3200  may include input  3202  for receiving video content. The video content may be received in a raw or uncompressed format, e.g., 8 or 10 bit multi-component pixel values, or may be in a compressed or encoded format. The input  3202  may represent a network interface, a peripheral bus interface, or a storage interface. Examples of network interface include wired interfaces such as Ethernet, passive optical network (PON), etc. and wireless interfaces such as Wi-Fi or cellular interfaces. 
     The system  3200  may include a coding component  3204  that may implement the various coding or encoding methods described in the present document. The coding component  3204  may reduce the average bitrate of video from the input  3202  to the output of the coding component  3204  to produce a coded representation of the video. The coding techniques are therefore sometimes called video compression or video transcoding techniques. The output of the coding component  3204  may be either stored, or transmitted via a communication connected, as represented by the component  3206 . The stored or communicated bitstream (or coded) representation of the video received at the input  3202  may be used by the component  3208  for generating pixel values or displayable video that is sent to a display interface  3210 . The process of generating user-viewable video from the bitstream representation is sometimes called video decompression. Furthermore, while certain video processing operations are referred to as “coding” operations or tools, it will be appreciated that the coding tools or operations are used at an encoder and corresponding decoding tools or operations that reverse the results of the coding will be performed by a decoder. 
     Examples of a peripheral bus interface or a display interface may include universal serial bus (USB) or high definition multimedia interface (HDMI) or Displayport, and so on. Examples of storage interfaces include SATA (serial advanced technology attachment), PCI, IDE interface, and the like. The techniques described in the present document may be embodied in various electronic devices such as mobile phones, laptops, smartphones or other devices that are capable of performing digital data processing and/or video display. 
     Some embodiments of the disclosed technology are discussed in clause-based format. 
     Some example embodiments of techniques described in item 22 of section 4 include: 
     A1. A method of visual media processing (e.g., method  3300  depicted in  FIG. 33 ), comprising: determining ( 3302 ), for a current video block, a motion vector for use in a sub-block based motion vector prediction (sbTMVP) process to locate a corresponding block in a collocated picture for a conversion between the current video block and a bitstream representation ofthe currentvideoblock, whereinthe motion vector used in the sbTMVP process is computed in accordance with a scaling operation; and performing ( 3304 ), based on using the motion vector, the conversion between the current video block and the bitstream representation of the visual media data. 
     A2. The method of clause Al, wherein the scaling operation comprises at least one of: a right-shifting operation, a left-shifting operation, and/or a rounding operation applied on the motion vector used in the sbTMVP process. 
     A3. The method of clause A2, wherein the right-shifted rounding operation results in a rounding of the motion vector to an integer value by rounding towards zero. 
     A4. The method of clause Al, further comprising: 
     upon determining that a dimension of a collocated picture or a dimension of a window associated with the collocated picture is different from a dimension of a current picture associated with the currentblock or a dimension of a window associated with the current picture, applying a scaling operation on the motion vector used in the sbTMVP process. 
     A5. The method of clause A4, wherein a result of the scaling operation on the motion vector for the use in the sbTMVP process is expressed as: 
     MVx′=MVx*W1/W2 and MVy′=MVy*H1/H2, wherein MVx, MVy are motion vectors to locate a block corresponding to the current video block, wherein MVx′, MVy′ are scaled motion vectors of the currentvideoblock, wherein the dimension ofthe collocated picture or the dimension of the window associated with the collocated picture is denoted as W1, H1, and wherein the dimension of the current picture or the dimension of the window associated with the current picture is denoted as W2, H2 respectively. 
     Some example embodiments of techniques described in item 23 of section 4 include: 
     B1. A method of visual media processing (e.g., method  3400  depicted in  FIG. 34 ), comprising: determining ( 3402 ), for a current video block, a motion vector for use in a sub-block based temporal motion vector prediction (sbTMVP) process to locate a corresponding block in a collocated picture for a conversion between the current video block and a bitstream representation ofthe currentvideoblock, whereinthe motion vector used in the sbTMVP process is computed with respect to a center point of the currentvideoblock; modifying ( 3406 ) the center point of the current video block by applying one or more operations; and performing ( 3408 ), based on using the center point modified by applying the one or more operations, the conversion between the current video block and the bitstream representation of the visual media data. 
     B2. The method of clause B1, wherein the one or more operations include a scaling operation and/or an operation corresponding to addition of an offset to the center point. 
     B3. The method of clause B1, further comprising: 
     upon determining that a dimension of a collocated picture or a dimension of a window associated with the collocated picture is different from a dimension of a current picture associated with the currentblock or a dimension of a window associated with the current picture, performing additional modifications of the center point of the current video block. 
     B4. The method of clause B3, wherein the additional modifications of the center point of the current video block are expressed as: 
         x 0′=( x 0 −X 2)* W 1/ W 2+ X 1 and  y 0′=( y 0− Y 2)* H 1/ H 2+Y1,
 
     wherein the center point of the current video block is (x0, y0), and the coordinates of the center point of the current video block after the additional modifications are (x0′, y0′), wherein the dimension of the collocated picture or the dimension of the window associated with the collocated picture is denoted as W1, H1, and wherein the dimension of the current picture or the dimension of the window associated with the current picture is denoted as W2, H2 respectively, a top-left position of the window associated with the current picture is denoted as (X2, Y2), and a top-left position of the window associated with the collocated picture is denoted as (X1, Y1). 
     B5. The method of clause B3, wherein the additional modifications of the center point of the current video block are expressed as: 
         x 0′=( x 0− X 2)* W 1/ W 2 and  y 0′=( y 0 −Y 2)* H 1/ H 2,
 
     wherein the center point of the current video block is (x0, y0), and the coordinates of the center point of the current video block after the additional modifications are (x0′, y0′), wherein the dimension of the collocated picture or the dimension of the window associated with the collocated picture is denoted as W1, H1, a top-left position of the window associated with the current picture is denoted as (X2, Y2), and wherein the dimension of the current picture or the dimension of the window associated with the current picture is denoted as W2, H2 respectively. 
     Some example embodiments of techniques described in item 24 of section 4 include: 
     C1. A method of visual media processing (e.g., method  3500  depicted in  FIG. 35 ), comprising: determining ( 3502 ), for a current video block, a motion vector for use in a sub-block based temporal motion vector prediction (sbTMVP) process to locate a corresponding block in a collocated picture for a conversion between the current video block and a bitstream representation ofthe current videoblock, whereinthe motion vector used in the sbTMVP process is computed with respect to a point in the corresponding block in the collocated picture; modifying ( 3504 ) the point in the corresponding block in the collocated picture by applying one or more operations; and performing ( 3506 ), based on using the point in the corresponding block in the collocated picture modified by applying the one or more operations, the conversion between the current video block and the bitstream representation of the visual media data. 
     C2. The method of clause C1, wherein the one or more operations include a scaling operation and/or an operation corresponding to addition of an offset to the point in the corresponding block in the collocated picture. 
     C3. The method of clause C1, further comprising: 
     upon determining that a dimension of a collocated picture or a dimension of a window associated with the collocated picture is different from a dimension of a current picture associated with the current video block or a dimension of a window associated with the current picture, performing additional modifications of the point in the corresponding block in the collocated picture. 
     C4. The method of clause C3, wherein the additional modifications of the point in the corresponding block in the collocated picture are expressed as: 
         x ′=( x−X 2)* W 1/ W 2+×1 and  y ′=( y−Y 2)* H 1/ H 2+ Y 1,
 
     wherein the point in the corresponding block in the collocated picture is (x, y), and the coordinates of the point in the corresponding block in the collocated picture after the additional modifications are (x′, y′), wherein a width and a height of a window associated with the current picture are denoted as W2 and H2 respectively, a width and a height of a window associated with the collocated picture are denoted as W1 and H1 respectively, a top-left position of the window associated with the current picture is denoted as (X2, Y2), and a top-left position of the window associated with the collocated picture is denoted as (X1, Y1). 
     C5. The method of clause C3, wherein the additional modifications of the point in the corresponding block in the collocated picture are expressed as: 
     x′=(x−X2)*W1/W2 and y′=(y−Y2)*H1/H2, wherein the point in the corresponding block in the collocated picture is (x, y), and the coordinates of the point in the corresponding block in the collocated picture after the additional modifications are (x′, y′), wherein a width and a height of a window associated with the current picture are denoted as W2 and H2 respectively, a width and a height of a window associated with the collocated picture are denoted as W1 and H1 respectively and a top-left position of the window associated with the current picture is denoted as (X2, Y2). 
     Some example embodiments of techniques described in item 28 of section 4 include: 
     D1. A method of visual media processing (e.g., method  3600  depicted in  FIG. 36 ), comprising: determining ( 3602 ), for a conversion between a video picture included in visual media data and a bitstream representation of the visual media data using sub-pictures, that a rule related to one or more sub-pictures is satisfied by the conversion; and performing ( 3604 ) the conversion according to the rule of constraint, wherein the rule specifies that a size of a sub-picture in the video picture is an integer multiple of a coding tree unit size associated with the video picture. 
     D2. The method of clause D1, wherein the rule specifies that the bitstream representation includes a variable corresponding to a width of the sub-picture. 
     D3. The method of clause D1, wherein the rule specifies that the bitstream representation includes a variable corresponding to a height of the sub-picture. 
     D4. The method of any one or more of clauses D2-D3, wherein the variable corresponding to the height of the sub-picture and/or the variable corresponding to the width of the sub-picture is expressed in units of luma coding tree unit size. 
     D5. The method of any one or more of clauses D2 and D4, wherein the variable corresponding to the width of the sub-picture is equal to a difference between the width of the sub-picture in units of luma coding tree block size and 1. 
     D6. The method of any one or more of clauses D3 and D4, wherein the variable correspondingto the height of the sub-picture is equal to a differencebetweenthe height of the sub-picture in units of luma coding tree unit size and 1. 
     D7. The method of clause D4, wherein the luma coding tree unit size is defined as a width or a height of a luma coding tree block array. 
     D8. The method of clause D4, wherein the luma coding tree unit size for a coding tree unit is defined as a variable CtbSizeY expressed as: 
         Ctb Size Y =(1&lt;&lt;( sps _log 2_ ctu _size_minus5+5)), wherein  sps _log 2_ ctu _size_minus5 denotes a size of a syntax element. 
     D9. The method of clause D8, wherein the variable correspondingto the width of the sub-picture is computed as the width of the subpicture width multiplied by CtbSizeY. 
     D10. The method of clause D8, wherein the variable corresponding to the height of the sub-picture is computed as the height of the subpicture width multiplied by CtbSizeY. 
     D11. The method of clause D1, wherein the rule specifies that a value of a flag indicates a use of sub-pictures during the conversion. 
     D12. The method of clause D11, wherein the flag is a Boolean variable. 
     D13. The method of clause D12, wherein, the use of sub-pictures is indicated when the flag takes a value 1 and a non-use of sub-pictures is indicated when the flag takes a value 0. 
     Some example embodiments of techniques described in item 29 of section 4 include: 
     E1. A method of video processing (e.g., method  3700  depicted in  FIG. 37 ), comprising: determining ( 3702 ), for a conversion between a video picture included in visual media data and a bitstream representation of the visual media data using sub-pictures, that a rule related to one or more sub-pictures is satisfied by the conversion; and performing ( 3704 ) the conversion according to the rule of constraint, wherein the rule specifies that all sub-pictures in the video picture are non-overlapping, and together the all sub-pictures in the video picture cover entirety of the video picture. 
     Some example embodiments of techniques described in item 30 of section 4 include: 
     F1. A method of visual media processing (e.g., method  3800  depicted in  FIG. 38 ), comprising: making ( 3802 ) a determination, for a conversion between a video unit of a visual media and a bitstream representation of the visual media data, whether a reference picture resampling (RPR) technique is used during the conversion; and performing ( 3804 ) the conversion based on the determination, wherein a flag corresponding to the determination is included in the bitstream representation at a sequence parameter set level. 
     F2. The method of clause F1, wherein the flag indicates a use of the RPR technique, and wherein the flag takes Boolean values. 
     F3. The method of clauses F2, wherein the flag equal to 1 specifies that spatial resolutions of coded pictures with respect to the sequence parameter set are inferred to be changeable, and the flag equal to 0 specifies that the spatial resolutions of the coded pictures with respect to the sequence parameter set are inferred to be unchanged. 
     F4. The method of clause F2, wherein the flag equal to 1 specifies that picture spatial resolution is changeable within a coded layer video sequence that refers to the sequence parameter set, and the flag equal to 0 specifies that the picture spatial resolution does not change within a coded layer video sequence that refers to the sequence parameter set. 
     F5. The method of any one or more of clauses F1-F4, wherein, whether a window information of a picture associated with the video unit is included in the bitstream representation is irrespective of the RPR technique being used or not. 
     F6. The method of any one or more of clauses F1-F4, wherein a height and/or a width of the video unit indicated in the picture parameter set (PPS) is inferred to be same as a height and/or a width of the video unit in another picture parameter set (PPS) associated with a same sequence parameter set. 
     F7. The method of any one or more of clauses F1-F6, wherein the bitstream representation is configured to include a window information of a picture associated with the video unit irrespective of a value of the flag. 
     F8. The method of any one or more of clauses F1 -F6, wherein the bitstream representation is configured to include a window information of a picture associated with the video unit, and wherein the flag is indicative of whether the window information is used during the conversion. 
     F9. The method of any one or more of clauses F1-F4, wherein a height and/or a width of the video unit indicated in the picture parameter set (PPS) is inferred to be same as a height and/or a width of the video unit in another picture parameter set (PPS) associated with a same sequence parameter set. 
     F10. The method of any one or more of clauses F1-F4, further comprising: 
     upon determining that the RPR technique is not used during the conversion, a height and/or a width of the video unit indicated in the picture parameter set (PPS) is inferred to be a default value of the height and/or a default value of the width of the video unit s 
     F11. The method of clause F10, wherein the default value of the height and/or the default value of the width of the video unit is inferred as a maximum height and/or a maximum width of video units indicated in a sequence parameter set (SPS) associated with the video unit. 
     Some example embodiments of techniques described in item 31 of section 4 include: 
     G1. A method of visual media processing (e.g., method  3900  depicted in  FIG. 39 ), comprising: based on satisfying a condition, selecting ( 3902 ) an interpolation filter during a motion compensation process to derive a prediction block of a current block of visual media data, wherein the condition is based, at least in part, on determining that a resolution of a reference picture is different from a resolution of the current picture and/or that a dimension of a window associated with the reference picture is different from a dimension of a window associated with the current picture; and performing ( 3904 ) a conversion between the current block of visual media data and a bitstream representation of the current block. 
     G2. The method of clause G1, further comprising: 
     upon determining that the resolution of the reference picture is different than the resolution of the current picture or a dimension of a window associated with the reference picture is different than a dimension of a window associated with the current picture, using an interpolation filter different than another filter used when the reference picture has a same resolution as the current picture. 
     G3. The method of clause G1, wherein the condition is based on determining that W1&gt;a*W2 and/or H1&gt;b*H2, wherein (W1, H1) represents the width and height of the reference picture or a window associated with the reference picture, and (W2, H2) represents the width and height of the current picture, or a window associated with the reference picture, and a and b are scaling factors. 
     G4. The method of clause G3, wherein a=b=1.5. 
     G5. The method of clause G1, wherein the condition is further based on a height and/or a width of the current block. 
     G6. The method of clause G5, wherein the height and/or the width of the current block individually achieves one or more threshold conditions. 
     G7. The method of clause G5, wherein a mathematical combination of the height and/or the width of the current block achieves one or more threshold conditions. 
     G8. The method of clause G6, wherein achieving the one or more threshold conditions includes the height and/or the width of the current block exceeding the one or more threshold conditions. 
     G9. The method of clause G6, wherein achieving the one or more threshold conditions includes the height and/or the width of the current block missing the one or more threshold conditions. 
     G10. The method of clause G7, wherein achieving the one or more threshold conditions includes the mathematical combination of the height and/or the width of the current block exceeding the one or more threshold conditions. 
     G11. The method of clause G7, wherein achieving the one or more threshold conditions includes the mathematical combination of the height and/or the width of the current block missing the one or more threshold conditions. 
     G12. The method of any one or more of clauses G1-G11, wherein the interpolation filter selected is applied exclusively on chroma color components of the current video block. 
     G13. The method of any one or more of clauses G1-G11, wherein the interpolation filter selected is applied exclusively on luma color components of the current video block. 
     G14. The method of any one or more of clauses G1-G11, wherein the interpolation filter selected is applied exclusively on a horizontal filtering direction. 
     G15. The method of any one or more of clauses G1-G11, wherein the interpolation filter selected is applied exclusively on a vertical filtering direction. 
     G16. The method of any one or more of clauses GI-Gil, wherein a single tap filter is selected as the interpolation filter such that a result of applying the interpolation filter is equivalent to copying integer samples. 
     G17. The method of any one or more of clauses GI-Gil, wherein a 4-tap interpolation filter or a 6-tap interpolation filter is selected when the condition is satisfied. 
     G18. The method of any one or more of clauses GI-Gil, wherein a bi-linear filter is selected as the interpolation filter when the condition is satisfied. 
     Some example embodiments of techniques described in item 32 of section 4 include: 
     H1. A method of visual media processing (e.g., method  4000  depicted in  FIG. 40 ), comprising: determining ( 4002 ), for a conversion between a current block of a visual media data and a bitstream representation of the visual media data, that the current block is a combined intra and intra predicted (CIIP) block, wherein an intra prediction block for the CIIP block is generated using a size of a transform unit (TU), wherein, in the combined inter intra prediction (CIIP) block, a final prediction of the current block is based on a weighted sum of an inter prediction of the currentblock and an intra prediction of the currentblock; and performing ( 4004 ) the conversion based on the determining. 
     H2. The method of clause H1, further comprising: 
     upon determining that a dimension of a coding unit associated with the current block exceeds a maximum size of a transform unit, splitting the coding unit into multiple transform units; and 
     generating intra prediction blocks and inter prediction blocks for each transform unit included in the multiple transform units. 
     H3. The method of clause H2, further comprising: 
     upon determining that a maximum size of a transform unit is smaller than a threshold value and a dimension of the coding unit associated with the current block exceeds a maximum size of a transform unit, recursively splitting the coding unit into multiple transform units; and 
     generating intra prediction blocks and inter prediction blocks for each transform unit included in the multiple transform units. 
     H4. The method of clause H3, wherein a first intra-predicted block is based on reconstructed samples of a second intra-predicted block, wherein the first intra-predicted block and the second intra-predicted block are generated based on splitting the current block. 
     I1. The method of any one or more of clauses A1 to H4, wherein the conversion includes generating the bitstream representation from the current video block. 
     12. The method of any one or more of clauses A1 to H4, wherein the conversion includes generating samples of the current video block from the bitstream representation. 
     13. A video encoder apparatus comprising a processor configured to implement a method recited in any one or more of clauses A1 to H4. 
     14. A video decoder apparatus comprising a processor configured to implement a method recited in any one or more of clauses A1 to H4. 
     15. A computer readable medium having code stored thereon, the code, when executed by a processor, causing the processor to implement a method recited in any one or more of clauses A1 to H4. 
     16. A computer readable storage medium that stores a bitstream representation generated according to a method described in any one or more of claims A1 to H4. 
       FIG. 41  is a block diagram that illustrates an example video coding system  100  that may utilize the techniques of this disclosure. 
     As shown in  FIG. 41 , video coding system  100  may include a source device  110  and a destination device  120 . Source device  110  generates encoded video data which may be referred to as a video encoding device. Destination device  120  may decode the encoded video data generated by source device  110  which may be referred to as a video decoding device. 
     Source device  110  may include a video source  112 , a video encoder  114 , and an input/output (I/O) interface  116 . 
     Video source  112  may include a source such as a video capture device, an interface to receive video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of such sources. The video data may comprise one or more pictures. Video encoder  114  encodes the video data from video source  112  to generate a bitstream. The bitstream may include a sequence of bits that form a coded representation of the video data. The bitstream may include coded pictures and associated data. The coded picture is a coded representation of a picture. The associated data may include sequence parameter sets, picture parameter sets, and other syntax structures. I/O interface  116  may include a modulator/demodulator (modem) and/or a transmitter. The encoded video data may be transmitted directly to destination device  120  via I/O interface  116  through network  130   a.  The encoded video data may also be stored onto a storage medium/server  130 b for access by destination device  120 . 
     Destination device  120  may include an I/O interface  126 , a video decoder  124 , and a display device  122 . 
     I/O interface  126  may include a receiver and/or a modem. I/O interface  126  may acquire encoded video data from the source device  110  or the storage medium/server  130   b.  Video decoder  124  may decode the encoded video data. Display device  122  may display the decoded video data to a user. Display device  122  may be integrated with the destination device  120 , or may be external to destination device  120  which be configured to interface with an external display device. 
     Video encoder  114  and video decoder  124  may operate according to a video compression standard, such as the High Efficiency Video Coding (HEVC) standard, Versatile Video Coding (VVC) standard and other current and/or further standards. 
       FIG. 42  is a block diagram illustrating an example of video encoder  200 , which may be video encoder  114  in the system  100  illustrated in  FIG. 41 . 
     Video encoder  200  may be configured to perform any or all of the techniques of this disclosure. In the example of  FIG. 42 , video encoder  200  includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of video encoder  200 . In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure. 
     The functional components of video encoder  200  may include a partition unit  201 , a predication unit  202  which may include a mode select unit  203 , a motion estimation unit  204 , a motion compensation unit  205  and an intra prediction unit  206 , a residual generation unit  207 , a transform unit  208 , a quantization unit  209 , an inverse quantization unit  210 , an inverse transform unit  211 , a reconstruction unit  212 , a buffer  213 , and an entropy encoding unit  214 . 
     In other examples, video encoder  200  may include more, fewer, or different functional components. In an example, predication unit  202  may include an intra block copy (IBC) unit. The IBC unit may perform predication in an IBC mode in which at least one reference picture is a picture where the current video block is located. 
     Furthermore, some components, such as motion estimation unit  204  and motion compensation unit  205  may be highly integrated, but are represented in the example of  FIG. 5  separately for purposes of explanation. 
     Partition unit  201  may partition a picture into one or more video blocks. Video encoder  200  and video decoder  300  may support various video block sizes. 
     Mode select unit  203  may select one of the coding modes, intra or inter, e.g., based on error results, and provide the resulting intra- or inter-coded block to a residual generation unit  207  to generate residual block data and to a reconstruction unit  212  to reconstruct the encoded block for use as a reference picture. In some example, Mode select unit  203  may select a combination of intra and inter predication (CIIP) mode in which the predication is based on an inter predication signal and an intra predication signal. Mode select unit  203  may also select a resolution for a motion vector (e.g., a sub-pixel or integer pixel precision) for the block in the case of inter-predication. 
     To perform inter prediction on a current video block, motion estimation unit  204  may generate motion information for the current video block by comparing one or more reference frames from buffer  213  to the current video block. Motion compensation unit  205  may determine a predicted video block for the current video block based on the motion information and decoded samples of pictures from buffer  213  other than the picture associated with the current video block. 
     Motion estimation unit  204  and motion compensation unit  205  may perform different operations for a current video block, for example, depending on whether the current video block is in an I slice, a P slice, or a B slice. 
     In some examples, motion estimation unit  204  may perform uni-directional prediction for the current video block, and motion estimation unit  204  may search reference pictures of list 0 or list 1 for a reference video block for the current video block. Motion estimation unit  204  may then generate a reference index that indicates the reference picture in list 0 or list 1 that contains the reference video block and a motion vector that indicates a spatial displacement between the current video block and the reference video block. Motion estimation unit  204  may output the reference index, a prediction direction indicator, and the motion vector as the motion information of the current video block. Motion compensation unit  205  may generate the predicted video block of the current block based on the reference video block indicated by the motion information of the current video block. 
     In other examples, motion estimation unit  204  may perform bi-directional prediction for the current video block, motion estimation unit  204  may search the reference pictures in list 0 for a reference video block for the current video block and may also search the reference pictures in list 1 for another reference video block for the current video block. Motion estimation unit  204  may then generate reference indexes that indicate the reference pictures in list 0 and list 1 containing the reference video blocks and motion vectors that indicate spatial displacements between the reference video blocks and the current video block. Motion estimation unit  204  may output the reference indexes and the motion vectors of the currentvideo block as the motion information of the current video block. Motion compensation unit  205  may generate the predicted video block ofthe current video blockbased on the reference video blocks indicated by the motion information of the current video block. 
     In some examples, motion estimation unit  204  may output a full set of motion information for decoding processing of a decoder. 
     In some examples, motion estimation unit  204  may do not output a full set of motion information for the current video. Rather, motion estimation unit  204  may signal the motion information of the current video block with reference to the motion information of another video block. For example, motion estimation unit  204  may determine that the motion information of the current video block is sufficiently similar to the motion information of a neighboring video block. 
     In one example, motion estimation unit  204  may indicate, in a syntax structure associated with the current video block, a value that indicates to the video decoder  300  that the current video block has the same motion information as the another video block. 
     In another example, motion estimation unit  204  may identify, in a syntax structure associated with the current video block, another video block and a motion vector difference (MVD). The motion vector difference indicates a difference between the motion vector of the current video block and the motion vector of the indicated video block. The video decoder  300  may use the motion vector of the indicated video block and the motion vector difference to determine the motion vector of the current video block. 
     As discussed above, video encoder  200  may predictively signal the motion vector. Two examples of predictive signaling techniques that may be implemented by video encoder  200  include advanced motion vector predication (AMVP) and merge mode signaling. 
     Intra prediction unit  206  may perform intra prediction on the current video block. When intra prediction unit  206  performs intra prediction on the current video block, intra prediction unit  206  may generate prediction data for the current video block based on decoded samples of other video blocks in the same picture. The prediction data for the current video block may include a predicted video block and various syntax elements. 
     Residual generation unit  207  may generate residual data for the current video block by subtracting (e.g., indicated by the minus sign) the predicted video block(s) of the current video block from the current video block. The residual data of the current video block may include residual video blocks that correspond to different sample components of the samples in the current video block. 
     In other examples, there may be no residual data for the current video block for the current video block, for example in a skip mode, and residual generation unit  207  may not perform the subtracting operation. 
     Transform processing unit  208  may generate one or more transform coefficient video blocks for the current video block by applying one or more transforms to a residual video block associated with the current video block. 
     After transform processing unit  208  generates a transform coefficient video block associated with the current video block, quantization unit  209  may quantize the transform coefficient video block associated with the current video block based on one or more quantization parameter (QP) values associated with the current video block. 
     Inverse quantization unit  210  and inverse transform unit  211  may apply inverse quantization and inverse transforms to the transform coefficient video block, respectively, to reconstruct a residual video block from the transform coefficient video block. Reconstruction unit  212  may add the reconstructed residual video block to corresponding samples from one or more predicted video blocks generated by the predication unit  202  to produce a reconstructed video block associated with the current block for storage in the buffer  213 . 
     After reconstruction unit  212  reconstructs the video block, loop filtering operation may be performed reduce video blocking artifacts in the video block. 
     Entropy encoding unit  214  may receive data from other functional components of the video encoder  200 . When entropy encodingunit  214  receives the data, entropy encodingunit  214  may perform one or more entropy encoding operations to generate entropy encoded data and output a bitstream that includes the entropy encoded data. 
       FIG. 43  is a block diagram illustrating an example of video decoder  300  which may be video decoder  114  in the system  100  illustrated in  FIG. 41 . 
     The video decoder  300  may be configured to perform any or all of the techniques of this disclosure. In the example of  FIG. 43 , the video decoder  300  includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of the video decoder  300 . In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure. 
     In the example of  FIG. 43 , video decoder  300  includes an entropy decoding unit  301 , a motion compensation unit  302 , an intra prediction unit  303 , an inverse quantization unit  304 , an inverse transformation unit  305 , and a reconstruction unit  306  and a buffer  307 . Video decoder  300  may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder  200  (e.g.,  FIG. 42 ). 
     Entropy decoding unit  301  may retrieve an encoded bitstream. The encoded bitstream may include entropy coded video data (e.g., encoded blocks of video data). Entropy decoding unit  301  may decode the entropy codedvideo data, and from the entropy decoded video data, motion compensationunit  302  may determinemotion information including motion vectors, motion vector precision, reference picture list indexes, and other motion information. Motion compensation unit  302  may, for example, determine such information by performing the AMVP and merge mode. 
     Motion compensation unit  302  may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used with sub-pixel precision may be included in the syntax elements. 
     Motion compensation unit  302  may use interpolation filters as used by video encoder  20  during encoding of the video block to calculate interpolated values for sub-integer pixels of a reference block. Motion compensation unit  302  may determine the interpolation filters used by video encoder  200  according to received syntax information and use the interpolation filters to produce predictive blocks. 
     Motion compensation unit  302  may uses some of the syntax information to determine sizes of blocks used to encode frame(s) and/or slice(s) of the encoded video sequence, partition information that describes how each macroblock of a picture of the encoded video sequence is partitioned, modes indicating how each partition is encoded, one or more reference frames (and reference frame lists) for each inter-encoded block, and other information to decode the encoded video sequence. 
     Intra prediction unit  303  may use intra prediction modes for example received in the bitstream to form a prediction block from spatially adjacent b locks. Inverse quantization unit  303  inverse quantizes, i.e., de-quantizes, the quantized video block coefficients provided in the bitstream and decoded by entropy decoding unit  301 . Inverse transform unit  303  applies an inverse transform. 
     Reconstruction unit  306  may sum the residual blocks with the corresponding prediction blocks generated by motion compensation unit  202  or intra-prediction unit  303  to form decoded blocks. If desired, a deblocking filter may also be applied to filter the decoded blocks in order to remove blockiness artifacts. The decodedvideoblocks are then stored in buffer  307 , which provides reference blocks for subsequent motion compensation. 
     In the present document, the term “video processing” or “visual media processing” may refer to video encoding, video decoding, video compression or video decompression. For example, video compression algorithms may be applied during conversion from pixel representation of a video to a corresponding bitstream representation or vice versa. The bitstream representation of a current video block may, for example, correspond to bits that are either co-located or spread in different places within the bitstream, as is defined by the syntax. For example, a macroblock may be encoded in terms of transformed and coded error residual values and also using bits in headers and other fields in the bitstream. Furthermore, during conversion, a decoder may parse a bitstream with the knowledge that some fields may be present, or absent, based on the determination, as is described in the above solutions. Similarly, an encoder may determine that certain syntax fields are or are not to be included and generate the coded representation accordingly by including or excluding the syntax fields from the coded representation. 
     The disclosed and other solutions, examples, embodiments, modules and the functional operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this document and their structural equivalents, or in combinations of one or more of them. The disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for executionby, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them. The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus. 
     A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for u se in a computing environment A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network. 
     The processes and logic flows described in this document can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit). 
     Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random-access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. 
     While this patent document includes many specifics, these should not be construed as limitations on the scope of any subject matter or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular techniques. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a sub combination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments. 
     Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document.