Patent Publication Number: US-2021195229-A1

Title: Coding method, device, system with merge mode

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2019/100209, filed on Aug. 12, 2019, which claims priority to U.S. provisional application No. 62/717,006, filed on Aug. 10, 2018, and U.S. provisional application No. 62/757,720, filed on Nov. 8, 2018, and U.S. provisional application No. 62/726,973, filed on Sep. 4, 2018, which claims priority to U.S. provisional application No. 62/726,424 filed on Sep. 3, 2018, All of the aforementioned patent applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The embodiments of the present application (disclosure) generally relates to the field of video coding and more particularly to the field of inter-prediction with merge mode. 
     BACKGROUND 
     The amount of video data needed to depict even a relatively short video can be substantial, which may result in difficulties when the data is to be streamed or otherwise communicated across a communications network with limited bandwidth capacity. Thus, video data is generally compressed before being communicated across modern day telecommunications networks. The size of a video could also be an issue when the video is stored on a storage device because memory resources may be limited. Video compression devices often use software and/or hardware at the source to code the video data prior to transmission or storage, thereby decreasing the quantity of data needed to represent digital video images. The compressed data is then received at the destination by a video decompression device that decodes the video data. With limited network resources and ever increasing demands of higher video quality, improved compression and decompression techniques that improve compression ratio with little to no sacrifice in image quality are desirable. High Efficiency Video Coding is the latest video compression issued by ISO/IEC Moving Picture Experts Group and ITU-T Video Coding Experts Group as ISO/IEC 23008-2 MPEG-H Part 2 or called ITU-T H.265, and offers about double the data compression ratio at the same level of video quality, or substantially improved video quality at the same bit rate. Several coding tools were developed and adopted by HEVC, and one of them is merge mode that is used in the inter-prediction to estimate a proper motion vector (MV) for a current prediction block from spatial or temporal candidate blocks. Specifically, the merge mode in Merge mode in HEVC is composed of two parts: 
     First Part: 
     Merge list construction which includes (for a current block to be predicted): 
     (1) inserting motion information of spatial candidates: up to four candidates are inserted in the merge list by sequentially checking candidates A1 (at the bottom of the left boundary of the current block), B1 (on the right side of the top boundary), B0 (diagonally adjacent at the top right), A0 (diagonally adjacent at the bottom left) and B2 (diagonally adjacent at the top left);
 
(2) one temporal merge candidate is derived from two temporal, co-located blocks;
 
(3) additional merge candidates including combined bi-predictive candidates; and
 
(4) zero motion vector candidates.
 
     Second Part: 
     Index signaling, one entry that in the merge list is selected as the motion information of the current block and signaled to a decoding side to deriving the MV of current prediction block correspondingly. 
     A parallel merge estimation level was introduced in HEVC that indicates the region in which merge candidate lists can be independently derived by checking whether a candidate block is located in that merge estimation region (MER). A candidate block that is in the same MER is not included in the merge candidate list. Hence, its motion data does not need to be available at the time of the list construction. When this level is e.g. 32, all prediction units in a 32×32 area can construct the merge candidate list in parallel since all merge candidates that are in the same 32×32 MER, are not inserted in the list. 
     As shown in  FIG. 6 , there is a CTU partitioning with seven CUs (square) and ten PUs (square or rectangular). All potential merge candidates for the first PU0 are available because they are outside the first 32×32 MER. For the second MER, merge candidate lists of PUs 2-6 cannot include motion data from these PUs when the merge estimation inside that MER should be independent. Therefore, when looking at a PU5 for example, no merge candidates are available and hence not inserted in the merge candidate list. In that case, the merge list of PU5 consists only of the temporal candidate (if available) and zero MV candidates. In order to enable an encoder to trade-off parallelism and coding efficiency, the parallel merge estimation level is adaptive and signaled as log2_parallel_merge_level_minus2 in the picture parameter set. 
     In HEVC, quad tree (QT) partitions are used, that always result in partitions that satisfy one of the following conditions (where N is 4, 8, 16, 32 or 64). All of the samples of a coding block are contained in an N×N region. All of the samples of an N×N region are contained in a coding block. However, in the newest developing of Versatile Video Coding (VVC), those conditions the merge mode relays on are not always satisfied because new partition patterns are used, for instance, Binary-Tree (BT) and Triple-Tree (TT) partitions are allowed with which non-square partition is allowed, and the checking of whether a candidate block belongs to a MER is not accurately applicable anymore and the coding performance is degenerated, especially the parallel processing the merge estimation will be severely impacted. 
     SUMMARY 
     Embodiments of the invention are defined by the features of the independent claims, and further advantageous implementations of the embodiments by the features of the dependent claims. 
     Throughout the present disclosure, the terms candidate block, potential candidate block, candidate coding block, potential candidate prediction block and potential candidate coding block are used synonymously. Similar applies for the terms current block, current prediction block and current coding block. Similar applies for the terms Coding Tree Unit (CTU) and Coding Tree Block (CTB). 
     The embodiments of the present application (or the present disclosure) provide inter prediction apparatuses and methods for encoding and decoding an image which can mitigate even eliminate the problem mentioned above. 
     According to an aspect of the present disclosure, an apparatus is provided for marking availability of a candidate coding block for merge estimation of a current coding block within a coding tree unit, CTU, wherein the apparatus comprises: a processing circuitry configured to: mark the candidate coding block as available; mark the candidate coding block as unavailable when a predefined location of the candidate coding block is included within an extended merge estimation region, MER, wherein the extended MER includes a current MER in which the current coding block is located and at least a portion of another MER, adjacent to the current MER. 
     This may provide an advantage of performing merge estimation for a candidate block even if a CTU is partitioned into irregular patterns (non-square coding blocks) as result of using BT and/or TT, so that a candidate block may be processed in parallel when marked as unavailable. Further, the use of an extended MER may provide an advantage that a candidate block in the extended MER may cover the current MER of the current block partially. This makes the merge estimation more flexible, in particular when QT is mixed with BT and/or TT partitioning. 
     In one exemplary implementation, the candidate coding block may be marked initially as available. This means that prior to the merge estimation, all candidate coding blocks are available for prediction of the current coding block (default setting/initialization). In other words, prior to a construction of a merge candidate list of the current coding block, the candidate block is marked as available. 
     In another exemplary implementation, the marking the candidate block as available relates to a conditional marking. This means that a condition for marking a candidate block as unavailable (MER condition(s)) is not satisfied, the candidate block is marked as available. 
     The above two exemplary implementations are alternatives for the order in which the marking of a candidate block as available or unavailable is performed. The first exemplary embodiment is an option to mark a candidate block as available by default before the subsequent check of the MER condition(s). The second exemplary embodiment is an option for making the available-unavailable marking of a candidate block in dependence of whether or not one or more MER condition(s) are satisfied. 
     In a third exemplary implementation, a candidate block may be marked initially as available or unavailable. In this case, an initially available-marked candidate block may be marked unavailable if the MER conditions(s) are satisfied. In turn, an initially unavailable-marked candidate block may be marked as available if the MER condition(s) are not satisfied. 
     According to an aspect of the present disclosure, the marking of the candidate coding block includes: obtain coordinates (X,Y) of a left-top pixel of the current coding block; obtain, as the predefined location, coordinates (X2,Y2) of a specific point in the candidate coding block; determine if the specific point is located within the extended MER by comparing the coordinates of the specific point and the coordinates of the left-top pixel, and mark the candidate coding block as unavailable, if the specific point is located within the extended MER. 
     The coordinates of the specific point and/or a corner of the candidate block and/or the current block may be along a horizontal axis (x direction/axis), going from left (negative x) to right (positive x) and a vertical axis (y direction/axis, gravity axis), going from up (negative y) to down (positive y). The coordinates x, y may be in units of pixels. A pixel refers also to a sample. This means that a value of x=10 and/or y=−5 corresponds to 10 pixels/samples along the positive x axis (right) and 5 pixels/samples along the negative y axis (upward). 
     According to an aspect of the present disclosure, the specific point is a top-left pixel of the candidate coding block, and the determining if the specific point is located within the extended MER includes: mark the candidate coding block as unavailable if any of the conditions is satisfied: if [X−1,Y] and [X,Y] are in the current MER, and if X2&lt;X and Y2&gt;=Y; or if [X,Y−1] and [X,Y] are in the current MER, and if Y2&lt;Y and X2&gt;=X; or if [X−1,Y−1] and [X,Y] are in the current MER, and if Y2&lt;Y and X2&lt;X. 
     According to an aspect of the present disclosure, the specific point is a bottom-right pixel of the candidate coding block, and the determining if the specific point is located within the extended MER includes: mark the candidate coding block as unavailable if any of the conditions is satisfied: if [X−1,Y] and [X,Y] are in the current MER, and if X2&lt;X and Y2&gt;=Y; or if [X,Y−1] and [X,Y] are in the current MER, and if Y2&lt;Y and X2&gt;=X; or if [X−1,Y−1] and [X,Y] are in the current MER, and if Y2&lt;Y and X2&lt;X. 
     This may provide an advantage of performing the merge estimation more accurately, since the MER condition(s) check not only the positional relation between the specific point and the current block corner, but also between the current block corner (X,Y) and its by one pixel/sample shifted position. Moreover, the use of the top-left or the bottom-right pixel as specific point may provide an advantage of making the merge estimation more flexible. 
     The same or similar advantages may be provided by any of the following aspects of the present invention. 
     According to an aspect of the present disclosure, the marking of the candidate coding block includes: obtain coordinates (x, y) of a corner of the current coding block; obtain, as the predefined location, coordinates of a specific point (x+a, y+b), wherein a∈(−1,0,1) and b∈(−1,0,1), and a and b are selected in dependence on the relationship of the relative position between the specific point and the corner, select, for the one candidate coding block, one value from (−1,0,1) as the a, and one value from the (−1,0,1) as the b; and mark the candidate coding block as unavailable, if floor((x+a)/mer_width) is equal to floor(x/mer_width); or if floor((y+b)/mer_width) is equal to floor(y/mer_height), wherein mer_width is a width and mer_height is a height of the current MER. 
     The floor function takes as input a real number X and gives as output the greatest integer less than or equal to X. 
     According to an aspect of the present disclosure, the candidate coding block neighbors the corner of the current coding block, and the corner of the current coding block is a bottom-left corner, and the candidate coding block is located on where there is left to the current coding block, a=−1, b=0; or the corner of the current coding block is a bottom-left corner, and the candidate coding block is located on where there is bottom-left to the current coding block, a=−1, b=1; or the corner of the current coding block is an upper left-corner, and the candidate coding block is located on where there is upper-left to the current coding block, a=−1, b=−1; or the corner of the current coding block is an upper-right corner, and the candidate coding block is located on where there is upper-right to the current coding block, a=1, b=−1; or the corner of the current coding block is an upper-right corner, and the candidate coding block located on where there is upper to the current coding block, a=0, b=−1. 
     According to an aspect of the present disclosure, the marking of the candidate coding block includes: obtain coordinates (x, y) of a corner of the current coding block; obtain, as the predefined location, coordinates (x+a, y+b) of a specific point, wherein the potential candidate coding block neighbors a corner of the current coding block and a∈(−1,0,1), b∈(−1,0,1), wherein a and b are not both equal to 0 or 1 and are selected in dependence on the relationship of the relative position between the specific point and the corner, select for the one candidate coding block, one value from (−1,0,1) as the a, and one value from the (−1,0,1) as the b; and mark the candidate coding block as unavailable if floor((x+a)/mer_width) is equal to floor(x/mer_width), and floor((y+b)/mer_height)&gt;=floor(y/mer_height), or if floor((y+b)/mer_height) is equal to floor(y/mer_height) and floor((x+a)/mer_width)&gt;=floor(x/mer_width), wherein mer_height is a height and mer_width is a width of the current MER. 
     This may provide an advantage of improving the accuracy of the merge estimation by selecting the values of a and/or b in dependence on the positional relation between the candidate block neighboring the current block. Moreover, the MER conditions in relation to the one or two axial directions may provide an advantage of making the merge estimation more flexible. This means that the merge estimation may be tuned, for example, whether or not a CTU is divided horizontally or vertically in a homogeneous or non-homogeneous manner, as relevant for BT and/or TT partitions. 
     According to an aspect of the present disclosure, the marking of the candidate coding block includes: obtain coordinates (x, y) of a corner of the current coding block; obtain, as the predefined location, coordinates of a specific point (x1, y1), wherein the specific point is a bottom-right corner or a top-left corner of the candidate coding block; and mark the candidate coding block as unavailable, if floor(x1/mer_width) is equal to floor(x/mer_width); or if floor(y1/mer_height) is equal to floor(y/mer_height), wherein mer_height is a height and mer_width is a width of the current MER. 
     According to an aspect of the present disclosure, the marking of the candidate coding block includes: obtain coordinates (x, y) of a corner of the current coding block; obtain, as the predefined location, coordinates of a specific point (x1, y1), wherein the specific point is a bottom-right corner or a top-left corner of the candidate coding block; and mark the candidate coding block as unavailable, if floor(x1/mer_width) is equal to floor(x/mer_width) and floor(y1/mer_height)&gt;=floor(y/mer_height); or if floor(y1/mer_height) is equal to floor(y/mer_height) and floor(x1/mer_width)&gt;=floor(x/mer_width), wherein mer_height is a height and mer_width is a width of the current MER. 
     According to an aspect of the present disclosure, the marking of the candidate coding block includes: obtain coordinates (X, Y) of a corner of the current coding block; obtain, as a predefined location, coordinates of a specific point (X2, Y2), wherein the specific point is a bottom-right corner of the candidate coding block; and mark the candidate coding block as unavailable, if any of the following condition is satisfied: if floor(X2/mer_width) is equal to floor(X/mer_width) and floor(Y2/mer_height)&gt;=floor(Y/mer_height); and/or if floor(Y2/mer_height) is equal to floor(Y/mer_height) and floor(X2/mer_width)&gt;=floor(X/mer_width); wherein mer_height is a height and mer_width is a width of the current MER. 
     According to an aspect of the present disclosure, the marking of the candidate coding block includes: obtain coordinates (X, Y) of a corner of the current coding block; obtain, a the predefined location, coordinates (X2, Y2) of a specific point, wherein the specific point is a bottom-right corner of the candidate coding block; and mark the candidate coding block as unavailable if any of the following condition is satisfied: if X2/mer_width is equal to X/mer_width and Y2/mer_height&gt;=Y/mer_height; and/or if Y2/mer_height is equal to Y/mer_height and X2/mer_width&gt;=X/mer_width; wherein mer_height is a height and mer_width is a width of the current MER. 
     According to an aspect of the present disclosure, the marking of the candidate coding block includes: obtain coordinates (X, Y) of a corner of the current coding block; obtain, as the predefined location, coordinates (X2, Y2) of a specific point, wherein the specific point is a bottom-right corner of the candidate coding block; and mark the candidate coding block as unavailable if any of the following condition is satisfied: if X2&gt;&gt;log2_mer_width is equal to X&gt;&gt;log2_mer_width and Y2&gt;&gt;log2_mer_height&gt;=Y&gt;&gt;log2_mer_height; and/or if Y2&gt;&gt;log2_mer_height is equal to Y&gt;&gt;log2_mer_height and X2&gt;&gt;log2_mer_width&gt;=X&gt;&gt;log2_mer_width; wherein log2_mer_height and log2_mer_width are the binary logarithm of a height and a width of the current MER. 
     The operator&gt;&gt;specifies the arithmetic right-shift operation. The various forms of MER conditions of the above different aspects of the present disclosure may provide an advantage of adapting and optimizing the merge estimation to the used partitioning pattern, using QT, TT, and/or BT in particular when there are used in a mixed manner. 
     According to an aspect of the present disclosure, an apparatus is provided for marking availability of a candidate coding block for merge estimation of a current coding block within a coding tree unit, CTU, wherein the apparatus comprises: a processing circuitry configured to: mark the candidate coding block as available; label coding blocks of a CTU, including the current coding block and the candidate coding block, based on a processing order; form a group of coding blocks by applying a sliding window with a length of K; determine if the candidate coding block and the current coding block belong to the same one group of coding blocks; and mark the candidate coding block as unavailable if the candidate coding block and the current coding block belong to the same one group of coding blocks. 
     The marking of a candidate block as available refers to marking the block initially as available. This means that all candidate blocks may be by default marked as available for prediction of the current coding block at the beginning of the merge estimation. 
     According to an aspect of the present disclosure, the labelling includes label the coding blocks incrementally using an integer number equal to or larger than zero, and K relates to the processing order. 
     For example, assuming a processing order of A-&gt;B-&gt;C-&gt;D-&gt;E-&gt;F, the six coding blocks may be labelled in increments of 1 as {0, 1, 2, 3, 4, 5} with increasing integer number. For a sliding window of length K=3, for example, the six coding blocks may be divided into two groups based on the integer labels and K, with the first group including coding blocks {0, 1, 2} and the second group including blocks {3, 4, 5}. 
     This may provide an advantage of performing the merge estimation for a candidate block in a fast manner by use of the processing order of the coding blocks. Hence, this is an alternative way of performing merge estimation for coding blocks in parallel in VVC, when a CTU is irregularly partitioned due to the use of BT and/or TT. 
     In this case, the MER region is based on a group comprising one or more coding blocks, which as a group form a MER region formed based on a processing order labeling. 
     According to an aspect of the present disclosure, the labelling includes label the coding blocks incrementally using the spanning area of the coding blocks, wherein the spanning area is counted based on the number of samples the coding blocks contain, and K relates to an area. 
     With reference to the above example, this means that the length of the sliding window K is now related to an area, for example, K=128 corresponding to the number of pixels/samples of an area. Using as an example the (pixel/sample) area as the labels of each of the coding blocks shown in  FIG. 18  for the coding blocks in conjunction with the processing order of A-&gt;B-&gt;C-&gt;D-&gt;E-&gt;F, the coding blocks with labels 64, 96, and 128 form the first group, and the blocks with labels 192, 224, and 256 form the second group. 
     In this case, the MER region is based on a group comprising one or more coding blocks, which as a group form a MER region formed based on (pixel) area labeling. This may provide an advantage that the MER regions are more balanced with regard to the covered areas. This means that by using the sliding window of length K with reference to a pixel area parallel processed regions are created which contain about the same number of samples. However, the number of samples in the regions may not be always exactly the same. Thus, the use of an “area” K may provide an advantage of a simpler and therefore, cheaper hardware implementation. 
     According to an aspect of the present disclosure, the processing circuitry is further configured to: derive motion vector candidates, MVCs, from the candidate coding block marked as available; and code the current coding block by referring to the MVCs. 
     According to an aspect of the present disclosure, an encoder is provided or encoding a current coding block within a coding tree unit, CTU, comprising a candidate list generator for generating a list of prediction candidates, including the apparatus for marking availability of a candidate coding block for merge estimation of the current coding block within the CTU according to any of the above aspects of the present disclosure; a prediction unit for determining prediction of the current coding block according to at least one prediction candidate out of the generated list; and a compression unit for encoding the current coding block by using the prediction of the current coding block. 
     According to an aspect of the present disclosure, a decoder is provided for decoding a current coding block within a coding tree unit, CTU, comprising a candidate list generator for generating a list of prediction candidates, including the apparatus for marking availability of a candidate coding block for merge estimation of the current coding block within the CTU according to any of the above aspects of the present disclosure; a prediction unit for determining prediction of the current coding block according to at least one prediction candidate out of the generated list; and a decompression unit for decoding the current coding block by using the prediction of the current coding block. 
     According to an aspect of the present disclosure, the encoder and/or decoder according to any of the above aspects of the present disclosure, the list of prediction candidates is a list of motion vectors, MVs. 
     The list may be a list of intra-prediction modes (directional with a certain direction, planar, and/or DC). 
     According to an aspect of the present disclosure, a method is provided or marking availability of a candidate coding block for merge estimation of a current coding block within a coding tree unit, CTU, comprising the steps of: marking the candidate coding block as available; marking the candidate coding block as unavailable when a predefined location of the candidate coding block is included within an extended merge estimation region, MER, wherein the extended MER includes a current MER in which the current coding block is located and at least a portion of another MER, adjacent to the current MER. 
     According to an aspect of the present disclosure, a method is provided or marking availability of a candidate coding block for merge estimation of a current coding block within a coding tree unit, CTU, comprising the steps of: marking the candidate coding block as available; labelling coding blocks of a CTU, including the current coding block and the candidate coding block, based on a processing order; forming a group of coding blocks by applying a slid window with a length of K; determining if the candidate coding block and the current coding block belong to the same one group of coding blocks; and marking the candidate coding block as unavailable if the candidate coding block and the current coding block belong to the same one group of coding blocks. 
     According to an aspect of the present disclosure, a computer-readable non-transitory medium is provided for storing a program, including instructions which when executed on a processor cause the processor to perform the method according to any of the previous methods. 
     By the present disclosure provided above, more coding blocks can be parallel processed during the merge estimation, therefore improving the performance of coding/decoding technology, especially, the VVC. 
     For the purpose of clarity, any one of the foregoing embodiments may be combined with any one or more of the other foregoing embodiments to create a new embodiment within the scope of the present disclosure. 
     These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts. 
         FIG. 1A  is a block diagram illustrating an example coding system that may implement embodiments of the invention. 
         FIG. 1B  is a block diagram illustrating another example coding system that may implement embodiments of the invention. 
         FIG. 2  is a block diagram illustrating an example video encoder that may implement embodiments of the invention. 
         FIG. 3  is a block diagram illustrating an example of a video decoder that may implement embodiments of the invention. 
         FIG. 4  is a schematic diagram of a network device. 
         FIG. 5  is a simplified block diagram of an apparatus  500  that may be used as either or both of the source device  12  and the destination device  14  from  FIG. 1A  according to an exemplary embodiment. 
         FIG. 6  illustrates an MER based candidate block availability status during a merge estimation. 
         FIG. 7  to  FIG. 9  are partition resulted based on the partition modes allowed in VVC. 
         FIG. 10  illustrates a diagram of an example of block partitioning using a quad-tree-binary-tree (QTBT) structure. 
         FIG. 11  illustrates a diagram of an example of tree structure corresponding to the block partitioning using the QTBT structure of  FIG. 10 . 
         FIG. 11 a    illustrates a diagram of an example of horizontal triple-tree partition types. 
         FIG. 11 b    illustrates a diagram of an example of vertical triple-tree partition types. 
         FIG. 12  illustrates potential merge estimation coding blocks in spatial and temporal domains. 
         FIG. 13  illustrates a diagram of an example of quadrant partitions for the present disclosure. 
         FIG. 14  illustrates a diagram of an example of block partitions an MER where the present disclosure applied. 
         FIG. 15  is a working flow showing availability checking for a potential merge estimation coding blocks according to the present disclosure. 
         FIG. 16  illustrates a diagram of an example of labeled block partitions where the availability checking  FIG. 15  is applied. 
         FIG. 17  is a working flow showing availability checking for a potential merge estimation coding blocks according to the present disclosure. 
         FIG. 18  illustrate a diagram of an example of labeled block partitions where the availability checking  FIG. 17  is applied. 
         FIG. 19  illustrates an example about a current block and its spatial neighbor blocks. 
         FIG. 20  illustrates an example about the sixth solution. 
         FIG. 20A  illustrates an example of where a neighbor blocks falls into around the current block will be marked unavailable. 
         FIG. 20B  illustrates another example of where a neighbor blocks falls into around the current block will be marked unavailable. 
         FIG. 21  illustrates an example of do merge estimation to remove the parallel processing restriction. 
         FIG. 22  illustrates an example of determine the availability of neighboring blocks 
         FIG. 23  illustrates an example of the flowchart of the solution 12. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the invention or specific aspects in which embodiments of the present invention may be used. It is understood that embodiments of the invention may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
     For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise. 
     It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents. 
     As mentioned before, when a coding block is no longer partitioned based on QT partitions as in HEVC, but rather on BT or TT as in VVC, the HEVC conditions for merge mode may be no longer suitable and/or may not be satisfied because the new partition patterns of the coding block resulting from the use of BT and/or TT are no longer consistent with the HEVC conditions which rely on square pattern partition of the coding block. In other words, the HEVC conditions are inconsistent with the non-square patterns, so that a check whether or not a candidate block (i.e. a candidate coding block) belongs to a MER can no longer be performed accurately or in the worst case may even be impossible. As a result, the coding performance may degenerate severely, in particular the parallel processing of the merge estimation. 
     In order to illustrate the above conflict in applying HEVC conditions in VVC in conjunction with BT and/or TT partitions, three different scenarios are chosen to show exemplarily how the MER-based merge estimation in HEVC impacts the parallelism of the merge estimation in Versatile Video Coding (VVC). 
     Scenario 1: 
       FIG. 7  illustrates a partition result based on partition modes allowed in VVC. If a top-left sample of blk1 (A) and a top-left sample of blk2 (B) are in the same MER (N×N grid), then motion information of blk1 is set as unavailable for the prediction by blk2 with a processing order blk1→blk2. Based on the MER based estimation in HEVC, the four prediction dependencies of coding blocks A, B, C, and D are: 
     C can be predicted from B.
 
D can be predicted from C.
 
B can be predicted from A.
 
C cannot be predicted from A.
 
     However, based on HEVC, none of the pair of those coding blocks can be processed in parallel with the proceeding order A→B→C→D. 
     According to the HEVC rule, two blocks are considered to be in the same MER if their top-left coordinates are in the same MER. Block B can be predicted from block A, since they are in different MER. Therefore, block B needs to wait for block A to be available, so that they cannot be processed in parallel. Block D can be predicted from block C, since they are in different MER. Hence they cannot be processed in parallel. Block C cannot be predicted from block A, since they are in the same MER. However, C and A still cannot be processed in parallel since block C can be predicted from block B, and block B can be predicted from block A. Therefore, in Scenario 1, a parallel processing of those coding block is impossible which will cost more coding time to do the merge estimation for each of those coding blocks. 
     Scenario 2: 
       FIG. 8  illustrates anther partition result based on partition modes allowed in VVC, where only coding blocks A and B can be processed in parallel with a processing order A→B→C→D→E→F. According to the HEVC rule, two blocks are considered to be in the same MER if their top-left coordinates are in the same MER. Therefore, coding blocks C and E are supposed to be processed in parallel. As contrast, in this scenario 2, coding blocks C and E cannot be processed in parallel although they are in the same MER because coding block E can be predicted from coding block D, and coding block D can be predicted from coding block C which results the later one coding block waiting until the prior one&#39;s MV according to the processing order is available. Therefore, in Scenario 2, a parallel processing of those coding blocks is limited which will still cost more coding time to do the merge estimation for those coding blocks. 
     Scenario 3: 
       FIG. 9  illustrates another partition result based on partition modes allowed in VVC, where none of the pair of coding blocks can be processed in parallel. Based on the HEVC rule, coding block C cannot be predicted from coding block A, but coding block C and coding block A still cannot be processed in parallel, since coding block C can be predicted from coding block B and coding block B can be predicted from coding block A. Based on the HEVC rule, coding block D cannot be predicted from coding block B, but coding block B and coding block D still cannot be processed in parallel, since coding block C can be predicted from coding block B and coding block D can be predicted from coding block C. Therefore, similar to Scenario 2, in Scenario 3, parallel processing of those coding block is impossible which will cost more coding time to do the merge estimation for each of those coding blocks. 
     The present disclosure provides a method of coding implemented by a decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block. The method includes, obtaining the coordination of a specific point in the potential candidate coding block, and the coordination of the left-top pixel of the current coding block; determining if the coordination of the specific point in the potential candidate coding block is located within a merge estimation region (MER) where the top-left pixel of the current coding block is located, by comparing the coordination of a specific point in the potential candidate coding block and the coordination of the left-top pixel of the current coding block, wherein the coordination is consisting of horizontal axis directing to right hand direction and labelled as X and a vertical axis directing to gravity direction and labelled as Y, the coordination of the specific point in the potential candidate coding block is indicated as (X2, Y2), and the coordination of the top-left pixel of the current coding block is indicated as (X, Y); and if the coordination of the specific point in the potential candidate coding block is located within the merge estimation region (MER), marking the potential candidate coding block is unavailable. 
     The specific point in the potential candidate coding block is the top-left pixel or the bottom-right pixel of the potential candidate coding block, and the determining if the coordination of the specific point in the potential candidate coding block is located within the MER is performed on any of the following rules: if [X−1,Y] and [X,Y] are in the MER, and if X2&lt;X and Y2&gt;=Y, the potential candidate coding block is set unavailable; if [X,Y−1] and [X,Y] are in the MER, and if Y2&lt;Y and X2&gt;=X, the potential candidate coding block is set unavailable; and if [X−1,Y−1] and [X,Y] are in the MER, and if Y2&lt;Y and X2&lt;X, the potential candidate coding block is set unavailable. 
     The present disclosure further provides a method of coding implemented by a decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, and the method comprises, incrementally labelling coding blocks based on a processing order; applying a slid window with a length of K to the coding blocks to form a group of coding blocks; determining if the potential candidate coding block and the current coding block belong to the same one group of coding blocks; and marking the potential candidate coding block as unavailable when the potential candidate coding block and the current coding block belong to the same one group of coding blocks. Alternatively, the incrementally labelling coding blocks can be performed by using natural number from Zero based on a processing order or by using the spanning area of the coding blocks based on a processing order, and the spanning area of the coding blocks is counted based on the number of pixels the coding blocks contain. 
     The present disclosure provides an apparatus and a method for marking the availability of a potential candidate coding block for merge estimation of a current coding block. 
     The method includes, based on a predefined principle which is made based on the closeness of two respective points within the potential candidate coding block and the current coding block, adaptively obtaining the coordinates (x, y) of the current coding block, and the coordinates of a specific point in the potential candidate coding block, wherein the coordinates of the specific point in the potential candidate coding block is (x1, y1), marking the potential candidate coding block as unavailable, if floor(x1/mer_width) is equal to floor(x/mer_width), or if floor(y1/mer_height) is equal to floor(y/mer_height), where the mer_width and mer_height are the width and height of a merge estimation region (MER), and the function that takes as input a real number X and gives as output the greatest integer less than or equal to X. 
     Specifically, the method comprises: obtaining the coordinates (x, y) of a corner of the current coding block, and the coordinates of a specific point in the potential candidate coding block, wherein the coordinates of the specific point in the potential candidate coding block is (x+a, y+b), a∈(−1,0,1), b∈(−1,0,1), and a and b are selected depending on the relationship of the relative position between the potential candidate coding block and the current coding block, and for one potential candidate coding block, one value from (−1,0,1) is selected as the a, and one value from the (−1,0,1) is selected as the b; marking the potential candidate coding block as unavailable, if floor((x+a)/mer_width) is equal to floor(x/mer_width), or if floor((y+b)/mer_height) is equal to floor(y/mer_height), where the mer_width and mer_height are the width and height of a merge estimation region (MER), and the function that takes as input a real number X and gives as output the greatest integer less than or equal to X. 
     Alternatively, the present disclosure further provides a method of coding implemented by a decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block. The method includes, obtaining the coordinates (x, y) of a corner of the current coding block, and the coordinates of a specific point in the potential candidate coding block, wherein the coordinates of the specific point in the potential candidate coding block are the coordinates (x1, y1) of the bottom right corner of the potential candidate coding block or the top-left corner of the potential candidate coding block; marking the potential candidate coding block as unavailable, if floor(x1/mer_width) is equal to floor(x/mer_width), or if floor(y1/mer_height) is equal to floor(y/mer_height), where the mer_width and mer_height are the width and height of a merge estimation region (MER), and the function that takes as input a real number X and gives as output the greatest integer less than or equal to X. 
     Alternatively, the condition used for marking the unavailability of the potential candidate coding block could be extended as if floor((x+a)/mer_width) is equal to floor(x/mer_width) and floor((y+b)/mer_height)&gt;=floor(y/mer_height) or if floor((y+b)/mer_height) is equal to floor(y/mer_height) and floor((x+a)/mer_width)&gt;=floor(x/mer_width). 
     Alternatively, the condition used for marking the unavailability of the potential candidate coding block could be extended as if floor(x1/mer_width) is equal to floor(x/mer_width) and floor(y1/mer_height)&gt;=floor(y/mer_height) or if floor(y1/mer_height) is equal to floor(y/mer_height) and floor(x1/mer_width)&gt;=floor(x/mer_width). 
     Alternatively, the present disclosure further provides a method of coding, implemented by a encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block. The method includes, obtaining the coordinates (x, y) of a corner of the current coding block, and the coordinates of a specific point in the potential candidate coding block, wherein the coordinates of the specific point in the potential candidate coding block is (x+a, y+b), a∈(−1,0,1), b∈(−1,0,1), and a and b are selected depending on the relationship of the relative position between the potential candidate coding block and the current coding block, and for one potential candidate coding block, one value from (−1,0,1) is selected as the a, and one value from the (−1,0,1) is selected as the b; marking the potential candidate coding block as unavailable, when the (x, y) and the (x+a, y+b) are located within one merge estimation region (MER), and the cqtDepth of the current coding block is greater or equal to a threshold, where the cqtDepth is a parameter that decide the quad-tree partition depth of a coding tree block to which the current coding block belongs. Alternatively, if the potential candidate coding block comes from a history list, then the coordinates of the specific point in the potential candidate coding block are the coordinates (x1, y1) of the top-left corner of the potential candidate coding block, or the bottom-right corner of the potential candidate coding block. 
       FIG. 1A  is a block diagram illustrating an example coding system  10  that may utilize bidirectional prediction techniques. As shown in  FIG. 1A , the coding system  10  includes a source device  12  that provides encoded video data to be decoded at a later time by a destination device  14 . In particular, the source device  12  may provide the video data to destination device  14  via a computer-readable medium  16 . Source device  12  and destination device  14  may comprise any of a wide range of devices, including desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, telephone handsets such as so-called “smart” phones, so-called “smart” pads, televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, or the like. In some cases, source device  12  and destination device  14  may be equipped for wireless communication. 
     Destination device  14  may receive the encoded video data to be decoded via computer-readable medium  16 . Computer-readable medium  16  may comprise any type of medium or device capable of moving the encoded video data from source device  12  to destination device  14 . In one example, computer-readable medium  16  may comprise a communication medium to enable source device  12  to transmit encoded video data directly to destination device  14  in real-time. The encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to destination device  14 . The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide-area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from source device  12  to destination device  14 . 
     In some examples, encoded data may be output from output interface  22  to a storage device. Similarly, encoded data may be accessed from the storage device by input interface. The storage device may include any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, digital video disks (DVDs), Compact Disc Read-Only Memories (CD-ROMs), flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data. In a further example, the storage device may correspond to a file server or another intermediate storage device that may store the encoded video generated by source device  12 . Destination device  14  may access stored video data from the storage device via streaming or download. The file server may be any type of server capable of storing encoded video data and transmitting that encoded video data to the destination device  14 . Example file servers include a web server (e.g., for a website), a file transfer protocol (FTP) server, network attached storage (NAS) devices, or a local disk drive. Destination device  14  may access the encoded video data through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., digital subscriber line (DSL), cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on a file server. The transmission of encoded video data from the storage device may be a streaming transmission, a download transmission, or a combination thereof. 
     The techniques of this disclosure are not necessarily limited to wireless applications or settings. The techniques may be applied to video coding in support of any of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, Internet streaming video transmissions, such as dynamic adaptive streaming over HTTP (DASH), digital video that is encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications. In some examples, coding system  10  may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and/or video telephony. 
     In the example of  FIG. 1A , source device  12  includes video source  18 , video encoder  20 , and output interface  22 . Destination device  14  includes input interface  28 , video decoder  30 , and display device  32 . In accordance with this disclosure, video encoder  200  of source device  12  and/or the video decoder  300  of the destination device  14  may be configured to apply the techniques for bidirectional prediction. In other examples, a source device and a destination device may include other components or arrangements. For example, source device  12  may receive video data from an external video source, such as an external camera. Likewise, destination device  14  may interface with an external display device, rather than including an integrated display device. 
     The illustrated coding system  10  of  FIG. 1A  is merely one example. Techniques for bidirectional prediction may be performed by any digital video encoding and/or decoding device. Although the techniques of this disclosure generally are performed by a video coding device, the techniques may also be performed by a video encoder/decoder, typically referred to as a “CODEC.” Moreover, the techniques of this disclosure may also be performed by a video preprocessor. The video encoder and/or the decoder may be a graphics processing unit (GPU) or a similar device. 
     Source device  12  and destination device  14  are merely examples of such coding devices in which source device  12  generates coded video data for transmission to destination device  14 . In some examples, source device  12  and destination device  14  may operate in a substantially symmetrical manner such that each of the source and destination devices  12 ,  14  includes video encoding and decoding components. Hence, coding system  10  may support one-way or two-way video transmission between video devices  12 ,  14 , e.g., for video streaming, video playback, video broadcasting, or video telephony. 
     Video source  18  of source device  12  may include a video capture device, such as a video camera, a video archive containing previously captured video, and/or a video feed interface to receive video from a video content provider. As a further alternative, video source  18  may generate computer graphics-based data as the source video, or a combination of live video, archived video, and computer-generated video. 
     In some cases, when video source  18  is a video camera, source device  12  and destination device  14  may form so-called camera phones or video phones. As mentioned above, however, the techniques described in this disclosure may be applicable to video coding in general, and may be applied to wireless and/or wired applications. In each case, the captured, pre-captured, or computer-generated video may be encoded by video encoder  20 . The encoded video information may then be output by output interface  22  onto a computer-readable medium  16 . 
     Computer-readable medium  16  may include transient media, such as a wireless broadcast or wired network transmission, or storage media (that is, non-transitory storage media), such as a hard disk, flash drive, compact disc, digital video disc, Blu-ray disc, or other computer-readable media. In some examples, a network server (not shown) may receive encoded video data from source device  12  and provide the encoded video data to destination device  14 , e.g., via network transmission. Similarly, a computing device of a medium production facility, such as a disc stamping facility, may receive encoded video data from source device  12  and produce a disc containing the encoded video data. Therefore, computer-readable medium  16  may be understood to include one or more computer-readable media of various forms, in various examples. 
     Input interface  28  of destination device  14  receives information from computer-readable medium  16 . The information of computer-readable medium  16  may include syntax information defined by video encoder  20 , which is also used by video decoder  30 , that includes syntax elements that describe characteristics and/or processing of blocks and other coded units, e.g., group of pictures (GOPs). Display device  32  displays the decoded video data to a user, and may comprise any of a variety of display devices such as a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device. 
     Video encoder  200  and video decoder  300  may operate according to a video coding standard, such as the High Efficiency Video Coding (HEVC) standard presently under development, and may conform to the HEVC Test Model (HM). Alternatively, video encoder  200  and video decoder  300  may operate according to other proprietary or industry standards, such as the International Telecommunications Union Telecommunication Standardization Sector (ITU-T) H.264 standard, alternatively referred to as Motion Picture Expert Group (MPEG)-4, Part 10, Advanced Video Coding (AVC), H.265/HEVC, or extensions of such standards. The techniques of this disclosure, however, are not limited to any particular coding standard. Other examples of video coding standards include MPEG-2 and ITU-T H.263. Although not shown in  FIG. 1A , in some aspects, video encoder  200  and video decoder  300  may each be integrated with an audio encoder and decoder, and may include appropriate multiplexer-demultiplexer (MUX-DEMUX) units, or other hardware and software, to handle encoding of both audio and video in a common data stream or separate data streams. If applicable, MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, or other protocols such as the user datagram protocol (UDP). 
     Video encoder  200  and video decoder  300  each may be implemented as any of a variety of suitable encoder circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware or any combinations thereof. When the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Each of video encoder  200  and video decoder  300  may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device. A device including video encoder  200  and/or video decoder  300  may comprise an integrated circuit, a microprocessor, and/or a wireless communication device, such as a cellular telephone. 
       FIG. 1B  is an illustrative diagram of an example video coding system  40  including encoder  200  of  FIG. 2  and/or decoder  300  of  FIG. 3  according to an exemplary embodiment. The system  40  can implement techniques of this present application, e.g. the merge estimation in the inter prediction. In the illustrated implementation, video coding system  40  may include imaging device(s)  41 , video encoder  20 , video decoder  300  (and/or a video coder implemented via logic circuitry  47  of processing unit(s)  46 ), an antenna  42 , one or more processor(s)  43 , one or more memory store(s)  44 , and/or a display device  45 . 
     As illustrated, imaging device(s)  41 , antenna  42 , processing unit(s)  46 , logic circuitry  47 , video encoder  20 , video decoder  30 , processor(s)  43 , memory store(s)  44 , and/or display device  45  may be capable of communication with one another. As discussed, although illustrated with both video encoder  200  and video decoder  30 , video coding system  40  may include only video encoder  200  or only video decoder  300  in various practical scenario. 
     As shown, in some examples, video coding system  40  may include antenna  42 . Antenna  42  may be configured to transmit or receive an encoded bitstream of video data, for example. Further, in some examples, video coding system  40  may include display device  45 . Display device  45  may be configured to present video data. As shown, in some examples, logic circuitry  54  may be implemented via processing unit(s)  46 . Processing unit(s)  46  may include application-specific integrated circuit (ASIC) logic, graphics processor(s), general purpose processor(s), or the like. Video coding system  40  also may include optional processor(s)  43 , which may similarly include application-specific integrated circuit (ASIC) logic, graphics processor(s), general purpose processor(s), or the like. In some examples, logic circuitry  54  may be implemented via hardware, video coding dedicated hardware, or the like, and processor(s)  43  may implemented general purpose software, operating systems, or the like. In addition, memory store(s)  44  may be any type of memory such as volatile memory (e.g., Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM), etc.) or non-volatile memory (e.g., flash memory, etc.), and so forth. In a non-limiting example, memory store(s)  44  may be implemented by cache memory. In some examples, logic circuitry  54  may access memory store(s)  44  (for implementation of an image buffer for example). In other examples, logic circuitry  47  and/or processing unit(s)  46  may include memory stores (e.g., cache or the like) for the implementation of an image buffer or the like. 
     In some examples, video encoder  200  implemented via logic circuitry may include an image buffer (e.g., via either processing unit(s)  46  or memory store(s)  44 )) and a graphics processing unit (e.g., via processing unit(s)  46 ). The graphics processing unit may be communicatively coupled to the image buffer. The graphics processing unit may include video encoder  200  as implemented via logic circuitry  47  to embody the various modules as discussed with respect to  FIG. 2  and/or any other encoder system or subsystem described herein. The logic circuitry may be configured to perform the various operations as discussed herein. 
     Video decoder  300  may be implemented in a similar manner as implemented via logic circuitry  47  to embody the various modules as discussed with respect to decoder  300  of  FIG. 3  and/or any other decoder system or subsystem described herein. In some examples, video decoder  300  may be implemented via logic circuitry may include an image buffer (e.g., via either processing unit(s)  46  or memory store(s)  44 )) and a graphics processing unit (e.g., via processing unit(s)  46 ). The graphics processing unit may be communicatively coupled to the image buffer. The graphics processing unit may include video decoder  300  as implemented via logic circuitry  47  to embody the various modules as discussed with respect to  FIG. 3  and/or any other decoder system or subsystem described herein. 
     In some examples, antenna  42  of video coding system  40  may be configured to receive an encoded bitstream of video data. As discussed, the encoded bitstream may include data, indicators, index values, mode selection data, or the like associated with encoding a video frame as discussed herein, such as data associated with the coding partition (e.g., transform coefficients or quantized transform coefficients, optional indicators (as discussed), and/or data defining the coding partition). Video coding system  40  may also include video decoder  300  coupled to antenna  42  and configured to decode the encoded bitstream. The display device  45  configured to present video frames. 
       FIG. 2  is a block diagram illustrating an example of video encoder  200  that may implement the techniques of the present application. Video encoder  200  may perform intra- and inter-coding of video blocks within video slices. Intra-coding relies on spatial prediction to reduce or remove spatial redundancy in video within a given video frame or picture. Inter-coding relies on temporal prediction to reduce or remove temporal redundancy in video within adjacent frames or pictures of a video sequence. Intra-mode (I mode) may refer to any of several spatial based coding modes. Inter-modes, such as uni-directional prediction (P mode) or bi-prediction (B mode), may refer to any of several temporal-based coding modes. 
       FIG. 2  shows a schematic/conceptual block diagram of an example video encoder  200  that is configured to implement the techniques of the present disclosure. In the example of  FIG. 2 , the video encoder  200  comprises a residual calculation unit  204 , a transform processing unit  206 , a quantization unit  208 , an inverse quantization unit  210 , and inverse transform processing unit  212 , a reconstruction unit  214 , a buffer  216 , a loop filter unit  220 , a decoded picture buffer (DPB)  230 , a prediction processing unit  260  and an entropy encoding unit  270 . The prediction processing unit  260  may include an inter estimation  242 , inter prediction unit  244 , an intra estimation  252 , an intra prediction unit  254  and a mode selection unit  262 . Inter prediction unit  244  may further include a motion compensation unit (not shown). A video encoder  200  as shown in  FIG. 2  may also be referred to as hybrid video encoder or a video encoder according to a hybrid video codec. 
     For example, the residual calculation unit  204 , the transform processing unit  206 , the quantization unit  208 , the prediction processing unit  260  and the entropy encoding unit  270  form a forward signal path of the encoder  200 , whereas, for example, the inverse quantization unit  210 , the inverse transform processing unit  212 , the reconstruction unit  214 , the buffer  216 , the loop filter  220 , the decoded picture buffer (DPB)  230 , prediction processing unit  260  form a backward signal path of the encoder, wherein the backward signal path of the encoder corresponds to the signal path of the decoder (see decoder  300  in  FIG. 3 ). 
     The encoder  200  is configured to receive, e.g. by input  202 , a picture  201  or a block  203  of the picture  201 , e.g. picture of a sequence of pictures forming a video or video sequence. The picture block  203  may also be referred to as current picture block or picture block to be coded, and the picture  201  as current picture or picture to be coded (in particular in video coding to distinguish the current picture from other pictures, e.g. previously encoded and/or decoded pictures of the same video sequence, i.e. the video sequence which also comprises the current picture). 
     Partitioning 
     Embodiments of the encoder  200  may comprise a partitioning unit (not depicted in  FIG. 2 ) configured to partition the picture  201  into a plurality of blocks, e.g. blocks like block  203 , typically into a plurality of non-overlapping blocks. The partitioning unit may be configured to use the same block size for all pictures of a video sequence and the corresponding grid defining the block size, or to change the block size between pictures or subsets or groups of pictures, and partition each picture into the corresponding blocks. 
     In HEVC and other video coding specifications, to generate an encoded representation of a picture, a set of coding tree units (CTUs) may be generated. Each of the CTUs may comprise a coding tree block of luma samples, two corresponding coding tree blocks of chroma samples, and syntax structures used to code the samples of the coding tree blocks. In monochrome pictures or pictures having three separate color planes, a CTU may comprise a single coding tree block and syntax structures used to code the samples of the coding tree block. A coding tree block may be an N×N block of samples. A CTU may also be referred to as a “tree block” or a “largest coding unit” (LCU). The CTUs of HEVC may be broadly analogous to the macroblocks of other standards, such as H.264/AVC. However, a CTU is not necessarily limited to a particular size and may include one or more coding units (CUs). A slice may include an integer number of CTUs ordered consecutively in a raster scan order. 
     In HEVC, a CTU is split into CUs by using a quad-tree structure denoted as coding tree to adapt to various local characteristics. The decision whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction is made at the CU level. A CU may comprise a coding block of luma samples and two corresponding coding blocks of chroma samples of a picture that has a luma sample array, a Cb sample array, and a Cr sample array, and syntax structures used to code the samples of the coding blocks. In monochrome pictures or pictures having three separate color planes, a CU may comprise a single coding block and syntax structures used to code the samples of the coding block. A coding block is an N×N block of samples. In some examples, a CU may be the same size of a CTU. Each CU is coded with one coding mode, which could be, e.g., an intra coding mode or an inter coding mode. Other coding modes are also possible. Encoder  200  receives video data. Encoder  200  may encode each CTU in a slice of a picture of the video data. As part of encoding a CTU, prediction processing unit  260  or another processing unit (Including but not limited to unit of encoder  200  shown in  FIG. 2 ) of encoder  200  may perform partitioning to divide the CTBs of the CTU into progressively-smaller blocks  203 . The smaller blocks may be coding blocks of CUs. 
     Syntax data within a bitstream may also define a size for the CTU. A slice includes a number of consecutive CTUs in coding order. A video frame or image or picture may be partitioned into one or more slices. As mentioned above, each tree block may be split into coding units (CUs) according to a quad-tree. In general, a quad-tree data structure includes one node per CU, with a root node corresponding to the treeblock (e.g., CTU). If a CU is split into four sub-CUs, the node corresponding to the CU includes four child nodes, each of which corresponds to one of the sub-CUs. The plurality of nodes in a quad-tree structure includes leaf nodes and non-leaf nodes. The leaf nodes have no child nodes in the tree structure (i.e., the leaf nodes are not further split). The, non-leaf nodes include a root node of the tree structure. For each respective non-root node of the plurality of nodes, the respective non-root node corresponds to a sub-CU of a CU corresponding to a parent node in the tree structure of the respective non-root node. Each respective non-leaf node has one or more child nodes in the tree structure. 
     Each node of the quad-tree data structure may provide syntax data for the corresponding CU. For example, a node in the quad-tree may include a split flag, indicating whether the CU corresponding to the node is split into sub-CUs. Syntax elements for a CU may be defined recursively, and may depend on whether the CU is split into sub-CUs. If a CU is not split further, it is referred as a leaf-CU. If a block of CU is split further, it may be generally referred to as a non-leaf-CU. As shown in  FIG. 2 , each level of partitioning is a quad-tree split into four sub-CUs. The black CU is an example of a leaf-node (i.e., a block that is not further split). 
     A CU has a similar purpose as a macroblock of the H.264 standard, except that a CU does not have a size distinction. For example, a tree block may be split into four child nodes (also referred to as sub-CUs), and each child node may in turn be a parent node and be split into another four child nodes. A final, unsplit child node, referred to as a leaf node of the quadtree, comprises a coding node, also referred to as a leaf-CU. Syntax data associated with a coded bitstream may define a maximum number of times a tree block may be split, referred to as a maximum CU depth, and may also define a minimum size of the coding nodes. Accordingly, a bitstream may also define a smallest coding unit (SCU). The term “block” is used to refer to any of a CU, PU, or TU, in the context of HEVC, or similar data structures in the context of other standards (e.g., macroblocks and sub-blocks thereof in H.264/AVC). 
     In HEVC, each CU can be further split into one, two or four PUs according to the PU splitting type. Inside one PU, the same prediction process is applied and the relevant information is transmitted to the decoder on a PU basis. After obtaining the residual block by applying the prediction process based on the PU splitting type, a CU can be partitioned into transform units (TUs) according to another quad-tree structure similar to the coding tree for the CU. One of key feature of the HEVC structure is that it has the multiple partition conceptions including CU, PU, and TU. PUs may be partitioned to be non-square in shape. Syntax data associated with a CU may also describe, for example, partitioning of the CU into one or more PUs. A TU can be square or non-square (e.g., rectangular) in shape, syntax data associated with a CU may describe, for example, partitioning of the CU into one or more TUs according to a quad-tree. Partitioning modes may differ between whether the CU is skip or direct mode encoded, intra-prediction mode encoded, or inter-prediction mode encoded. 
     While VVC (Versatile Video Coding) removes the separation of the PU and TU concepts, and supports more flexibility for CU partition shapes. A size of the CU corresponds to a size of the coding node and may be square or non-square (e.g., rectangular) in shape. The size of the CU may range from 4×4 pixels (or 8×8 pixels) up to the size of the tree block with a maximum of 128×128 pixels or greater (for example, 256×256 pixels). 
     After encoder  200  generates a predictive block (e.g., luma, Cb, and Cr predictive block) for CU, encoder  200  may generate a residual block for the CU. For instance, encoder  100  may generate a luma residual block for the CU. Each sample in the CU&#39;s luma residual block indicates a difference between a luma sample in the CU&#39;s predictive luma block and a corresponding sample in the CU&#39;s original luma coding block. In addition, encoder  200  may generate a Cb residual block for the CU. Each sample in the Cb residual block of a CU may indicate a difference between a Cb sample in the CU&#39;s predictive Cb block and a corresponding sample in the CU&#39;s original Cb coding block. Encoder  100  may also generate a Cr residual block for the CU. Each sample in the CU&#39;s Cr residual block may indicate a difference between a Cr sample in the CU&#39;s predictive Cr block and a corresponding sample in the CU&#39;s original Cr coding block. 
     In some examples, encoder  100  skips application of the transforms to the transform block. In such examples, encoder  200  may treat residual sample values in the same way as transform coefficients. Thus, in examples where encoder  100  skips application of the transforms, the following discussion of transform coefficients and coefficient blocks may be applicable to transform blocks of residual samples. 
     After generating a coefficient block (e.g., a luma coefficient block, a Cb coefficient block or a Cr coefficient block), encoder  200  may quantize the coefficient block to possibly reduce the amount of data used to represent the coefficient block, potentially providing further compression. Quantization generally refers to a process in which a range of values is compressed to a single value. After encoder  200  quantizes a coefficient block, encoder  200  may entropy encode syntax elements indicating the quantized transform coefficients. For example, encoder  200  may perform Context-Adaptive Binary Arithmetic Coding (CABAC) or other entropy coding techniques on the syntax elements indicating the quantized transform coefficients. 
     Encoder  200  may output a bitstream of encoded picture data  271  that includes a sequence of bits that forms a representation of coded pictures and associated data. Thus, the bitstream comprises an encoded representation of video data. 
     In J. An et al., “Block partitioning structure for next generation video coding”, International Telecommunication Union, COM16-C966, September 2015 (hereinafter, “VCEG proposal COM16-C966”), quad-tree-binary-tree (QTBT) partitioning techniques were proposed for future video coding standard beyond HEVC. Simulations have shown that the proposed QTBT structure is more efficient than the quad-tree structure in used HEVC. In HEVC, inter prediction for small blocks is restricted to reduce the memory access of motion compensation, such that bi-prediction is not supported for 4×8 and 8×4 blocks, and inter prediction is not supported for 4×4 blocks. In the QTBT of the JEM, these restrictions are removed. 
     In the QTBT, a CU can have either a square or rectangular shape. As shown in  FIG. 10 , a coding tree unit (CTU) is first partitioned by a quadtree structure. The quadtree leaf nodes can be further partitioned by a binary tree structure. There are two splitting types, symmetric horizontal splitting and symmetric vertical splitting, in the binary tree splitting. In each case, a node is split by dividing the node down the middle, either horizontally or vertically. The binary tree leaf nodes are called coding units (CUs), and that segmentation is used for prediction and transform processing without any further partitioning. This means that the CU, PU and TU have the same block size in the QTBT coding block structure. A CU sometimes consists of coding blocks (CBs) of different colour components, e.g. one CU contains one luma CB and two chroma CBs in the case of P and B slices of the 4:2:0 chroma format and sometimes consists of a CB of a single component, e.g., one CU contains only one luma CB or just two chroma CBs in the case of I slices.
         The following parameters are defined for the QTBT partitioning scheme.   CTU size: the root node size of a quadtree, the same concept as in HEVC   MinQTSize: the minimum allowed quadtree leaf node size   MaxBTSize: the maximum allowed binary tree root node size   MaxBTDepth: the maximum allowed binary tree depth   MinBTSize: the minimum allowed binary tree leaf node size       

     In one example of the QTBT partitioning structure, the CTU size is set as 128×128 luma samples with two corresponding 64×64 blocks of chroma samples, the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, the MinBTSize (for both width and height) is set as 4×4, and the MaxBTDepth is set as 4. The quadtree partitioning is applied to the CTU first to generate quadtree leaf nodes. The quadtree leaf nodes may have a size from 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). When the quadtree node has size equal to MinQTSize, no further quadtree is considered. If the leaf quadtree node is 128×128, it will not be further split by the binary tree since the size exceeds the MaxBTSize (i.e., 64×64). Otherwise, the leaf quadtree node could be further partitioned by the binary tree. Therefore, the quadtree leaf node is also the root node for the binary tree and it has the binary tree depth as 0. When the binary tree depth reaches MaxBTDepth (i.e., 4), no further splitting is considered. When the binary tree node has width equal to MinBTSize (i.e., 4), no further horizontal splitting is considered. Similarly, when the binary tree node has height equal to MinBTSize, no further vertical splitting is considered. The leaf nodes of the binary tree are further processed by prediction and transform processing without any further partitioning. In the JEM, the maximum CTU size is 256×256 luma samples. The leaf nodes of the binary-tree (CUs) may be further processed (e.g., by performing a prediction process and a transform process) without any further partitioning. 
       FIG. 10  illustrates an example of a block  30  (e.g., a CTB) partitioned using QTBT partitioning techniques. As shown in  FIG. 10 , using QTBT partition techniques, each of the blocks is split symmetrically through the center of each block. 
       FIG. 11  illustrates the tree structure corresponding to the block partitioning of  FIG. 11 . The solid lines in  FIG. 11  indicate quad-tree splitting and dotted lines indicate binary-tree splitting. In one example, in each splitting (i.e., non-leaf) node of the binary-tree, a syntax element (e.g., a flag) is signaled to indicate the type of splitting performed (e.g., horizontal or vertical), where 0 indicates horizontal splitting and 1 indicates vertical splitting. For the quad-tree splitting, there is no need to indicate the splitting type, as quad-tree splitting always splits a block horizontally and vertically into 4 sub-blocks with an equal size. 
     As shown in  FIG. 11 , at node  50 , block  30  is split into the four blocks  31 ,  32 ,  33 , and  34 , shown in  FIG. 10 , using QT partitioning. Block  34  is not further split, and is therefore a leaf node. At node  52 , block  31  is further split into two blocks using BT partitioning. As shown in  FIG. 11 , node  52  is marked with a 1, indicating vertical splitting. As such, the splitting at node  52  results in block  37  and the block including both blocks  35  and  36 . Blocks  35  and  36  are created by a further vertical splitting at node  54 . At node  56 , block  32  is further split into two blocks  38  and  39  using BT partitioning. 
     At node  58 , block  33  is split into 4 equal size blocks using QT partitioning. Blocks  43  and  44  are created from this QT partitioning and are not further split. At node  60 , the upper left block is first split using vertical binary-tree splitting resulting in block  40  and a right vertical block. The right vertical block is then split using horizontal binary-tree splitting into blocks  41  and  42 . The lower right block created from the quad-tree splitting at node  58 , is split at node  62  using horizontal binary-tree splitting into blocks  45  and  46 . As shown in  FIG. 11 , node  62  is marked with a 0, indicating horizontal splitting. 
     In addition, the QTBT scheme supports the ability for the luma and chroma to have a separate QTBT structure. Currently, for P and B slices, the luma and chroma CTBs in one CTU may share the same QTBT structure. However, for I slices, the luma CTB is partitioned into CUs by a QTBT structure, and the chroma CTBs may be partitioned into chroma CUs by another QTBT structure. This means that a CU in an I slice consists of a coding block of the luma component or coding blocks of two chroma components, and a CU in a P or B slice consists of coding blocks of all three colour components. 
     The encoder  200  applies a rate-distortion optimization (RDO) process for the QTBT structure to determine the block partitioning. 
     In addition, a block partitioning structure named multi-type-tree (MTT) is proposed in U.S. Patent Application Publication No. 20170208336 to replace QT, BT, and/or QTBT based CU structures. The MTT partitioning structure is still a recursive tree structure. In MTT, multiple different partition structures (e.g., three or more) are used. For example, according to the MTT techniques, three or more different partition structures may be used for each respective non-leaf node of a tree structure, at each depth of the tree structure. 
     The depth of a node in a tree structure may refer to the length of the path (e.g., the number of splits) from the node to the root of the tree structure. A partition structure may generally refer to in how many different blocks a block may be divided into. A Partition structure may be, for example, a quad-tree partitioning structure with a block being divided into four blocks, a binary-tree partitioning structure with a block being divided into two blocks, or a triple-tree partitioning structure with a block being divided into three blocks. Furthermore, a triple-tree partitioning structure may be without dividing the block through the center. A partition structure may have multiple different partition types. A partition type may additionally define how a block is divided, including symmetric or asymmetric partitioning, uniform or non-uniform partitioning, and/or horizontal or vertical partitioning. 
     In MTT, at each depth of the tree structure, encoder  200  may be configured to further split sub-trees using a particular partition type from among one of three more partitioning structures. For example, encoder  100  may be configured to determine a particular partition type from QT, BT, triple-tree (TT) and other partitioning structures. In one example, the QT partitioning structure may include square quad-tree or rectangular quad-tree partitioning types. Encoder  200  may partition a square block using square quad-tree partitioning by dividing the block, down the center both horizontally and vertically, into four equal-sized square blocks. Likewise, encoder  200  may partition a rectangular (e.g., non-square) block using rectangular quad-tree partition by dividing the rectangular block, down the center both horizontally and vertically, into four equal-sized rectangular blocks. 
     The BT partitioning structure may include at least one of horizontal symmetric binary-tree, vertical symmetric binary-tree, horizontal non-symmetric binary-tree, or vertical non-symmetric binary-tree partition types. For the horizontal symmetric binary-tree partition type, encoder  200  may be configured to split a block, down the center of the block horizontally, into two symmetric blocks of the same size. For the vertical symmetric binary-tree partition type, encoder  200  may be configured to split a block, down the center of the block vertically, into two symmetric blocks of the same size. For the horizontal non-symmetric binary-tree partition type, encoder  100  may be configured to split a block, horizontally, into two blocks of differing size. For example, one block may be ¼ the size of the parent block and the other block may be ¾ the size of the parent blocks, similar to the PART_2N×nU or PART_2N×nD partition type. For the vertical non-symmetric binary-tree partition type, encoder  100  may be configured to split a block, vertically, into two blocks of differing size. For example, one block may be ¼ the size of the parent block and the other block may be ¾ the size of the parent blocks, similar to the PART_nL×2N or PART_nR×2N partition type. In other examples, an asymmetric binary-tree partition type may divide a parent block into different size fractions. For example, one sub-block may be ⅜ of the parent block and the other sub-block may be ⅝ of the parent block. Of course, such a partition type may be either vertical or horizontal. 
     The TT partition structure differs from that of the QT or BT structures, in that the TT partition structure does not split a block down the center. The center region of the block remains together in the same sub-block. Different from QT, which produces four blocks, or binary tree, which produces two blocks, splitting according to a TT partition structure produces three blocks. Example partition types according to the TT partition structure include symmetric partition types (both horizontal and vertical), as well as asymmetric partition types (both horizontal and vertical). Furthermore, the symmetric partition types according to the TT partition structure may be uneven/non-uniform or even/uniform. The asymmetric partition types according to the TT partition structure are uneven/non-uniform. In one example, a TT partition structure may include at least one of the following partition types: horizontal even/uniform symmetric triple-tree, vertical even/uniform symmetric triple-tree, horizontal uneven/non-uniform symmetric triple-tree, vertical uneven/non-uniform symmetric triple-tree, horizontal uneven/non-uniform asymmetric triple-tree, or vertical uneven/non-uniform asymmetric triple-tree partition types. 
     In general, an uneven/non-uniform symmetric triple-tree partition type is a partition type that is symmetric about a center line of the block, but where at least one of the resultant three blocks is not the same size as the other two. One preferred example is where the side blocks are ¼ the size of the block, and the center block is ½ the size of the block. An even/uniform symmetric triple-tree partition type is a partition type that is symmetric about a center line of the block, and the resultant blocks are all the same size. Such a partition is possible if the block height or width, depending on a vertical or horizontal split, is a multiple of 3. An uneven/non-uniform asymmetric triple-tree partition type is a partition type that is not symmetric about a center line of the block, and where at least one of the resultant blocks is not the same size as the other two. 
       FIG. 11 a    is a conceptual diagram illustrating example horizontal triple-tree partition types.  FIG. 11 b    is a conceptual diagram illustrating example vertical triple-tree partition types. In both  FIG. 11 a    and  FIG. 11 b, h    represents the height of the block in luma or chroma samples and w represents the width of the block in luma or chroma samples. 
     Note that the respective center line of a block does not represent the boundary of the block (i.e., the triple-tree partitions do not spit a block through the center line). Rather, the center line is used to depict whether or not a particular partition type is symmetric or asymmetric relative to the center line of the original block. The center line is also along the direction of the split. 
     As shown in  FIG. 11 a   , block  71  is partitioned with a horizontal even/uniform symmetric partition type. The horizontal even/uniform symmetric partition type produces symmetrical top and bottom halves relative to the center line of block  71 . The horizontal even/uniform symmetric partition type produces three sub-blocks of equal size, each with a height of h/3 and a width of w. The horizontal even/uniform symmetric partition type is possible when the height of block  71  is evenly divisible by 3. 
     Block  73  is partitioned with a horizontal uneven/non-uniform symmetric partition type. The horizontal uneven/non-uniform symmetric partition type produces symmetrical top and bottom halves relative to the center line of block  73 . The horizontal uneven/non-uniform symmetric partition type produces two blocks of equal size (e.g., the top and bottom blocks with a height of h/4), and a center block of a different size (e.g., a center block with a height of h/2). In one example, according to the horizontal uneven/non-uniform symmetric partition type, the area of the center block is equal to the combined areas of the top and bottom blocks. In some examples, the horizontal uneven/non-uniform symmetric partition type may be preferred for blocks having a height that is a power of 2 (e.g., 2, 4, 8, 16, 32, etc.). 
     Block  75  is partitioned with a horizontal uneven/non-uniform asymmetric partition type. The horizontal uneven/non-uniform asymmetric partition type does not produce a symmetrical top and bottom half relative to the center line of block  75  (i.e., the top and bottom halves are asymmetric). In the example of  FIG. 11A , the horizontal uneven/non-uniform asymmetric partition type produces a top block a with height of h/4, a center block with a height of 3h/8, and a bottom block with a height of 3h/8. Of course, other asymmetric arrangements may be used. 
     As shown in  FIG. 11 b   , block  81  is partitioned with a vertical even/uniform symmetric partition type. The vertical even/uniform symmetric partition type produces symmetrical left and right halves relative to the center line of block  81 . The vertical even/uniform symmetric partition type produces three sub-blocks of equal size, each with a width of w/3 and a height of h. The vertical even/uniform symmetric partition type is possible when the width of block  81  is evenly divisible by 3. 
     Block  83  is partitioned with a vertical uneven/non-uniform symmetric partition type. The vertical uneven/non-uniform symmetric partition type produces symmetrical left and right halves relative to the center line of block  83 . The vertical uneven/non-uniform symmetric partition type produces symmetrical left and right halves relative to the center line of  83 . The vertical uneven/non-uniform symmetric partition type produces two blocks of equal size (e.g., the left and right blocks with a width of w/4), and a center block of a different size (e.g., a center block with a width of w/2). In one example, according to the vertical uneven/non-uniform symmetric partition type, the area of the center block is equal to the combined areas of the left and right blocks. In some examples, the vertical uneven/non-uniform symmetric partition type may be preferred for blocks having a width that is a power of 2 (e.g., 2, 4, 8, 16, 32, etc.). 
     Block  85  is partitioned with a vertical uneven/non-uniform asymmetric partition type. The vertical uneven/non-uniform asymmetric partition type does not produce a symmetrical left and right half relative to the center line of block  85  (i.e., the left and right halves are asymmetric). In the example of  FIG. 8 , the vertical uneven/non-uniform asymmetric partition type produces a left block with width of w/4, a center block with width of 3w/8, and a bottom block with a width of 3w/8. Of course, other asymmetric arrangements may be used. 
     In examples where a block (e.g., at a sub-tree node) is split to a non-symmetric triple-tree partition type, encoder  200  and/or decoder  300  may apply a restriction such that two of the three partitions have the same size. Such a restriction may correspond to a limitation to which encoder  200  must comply when encoding video data. Furthermore, in some examples, encoder  200  and decoder  300  may apply a restriction whereby the sum of the area of two partitions is equal to the area of the remaining partition when splitting according to a non-symmetric triple-tree partition type. 
     In some examples, encoder  200  may be configured to select from among all of the aforementioned partition types for each of the QT, BT, and TT partition structures. In other examples, encoder  200  may be configured to only determine a partition type from among a subset of the aforementioned partition types. For example, a subset of the above-discussed partition types (or other partition types) may be used for certain block sizes or for certain depths of a quadtree structure. The subset of supported partition types may be signaled in the bitstream for use by decoder  200  or may be predefined such that encoder  200  and decoder  300  may determine the subsets without any signaling. 
     In other examples, the number of supported partitioning types may be fixed for all depths in all CTUs. That is, encoder  200  and decoder  300  may be preconfigured to use the same number of partitioning types for any depth of a CTU. In other examples, the number of supported partitioning types may vary and may be dependent on depth, slice type, or other previously coded information. In one example, at depth 0 or depth 1 of the tree structure, only the QT partition structure is used. At depths greater than 1, each of the QT, BT, and TT partition structures may be used. 
     In some examples, encoder  200  and/or decoder  300  may apply preconfigured constraints on supported partitioning types in order to avoid duplicated partitioning for a certain region of a video picture or region of a CTU. In one example, when a block is split with non-symmetric partition type, encoder  200  and/or decoder  300  may be configured to not further split the largest sub-block that is split from the current block. For example, when a square block is split according to a non-symmetric partition type (similar to the PART_2N×nU partition type), the largest sub-block among all sub-blocks (similar to the largest sub-block of PART_2N×nU partition type) is the noted leaf node and cannot be further split. However, the smaller sub-block (similar to the smaller sub-block of PART_2N×nU partition type) can be further split. 
     As another example where constraints on supported partitioning types may be applied to avoid duplicated partitioning for a certain region, when a block is split with non-symmetric partition type, the largest sub-block that is split from the current block cannot be further split in the same direction. For example, when a square block is split with a non-symmetric partition type (similar to the PART_2N×nU partition type), encoder  200  and/or 3 encoder  200  may be configured to not split the large sub-block among all sub-blocks (similar to the largest sub-block of PART_2N×nU partition type) in the horizontal direction. 
     As another example where constraints on supported partitioning types may be applied to avoid difficulty in further splitting, encoder  200  and/or decoder  300  may be configured to not split a block, either horizontally or vertically, when the width/height of a block is not a power of 2 (e.g., when the width height is not 2, 4, 8, 16, etc.). 
     The above examples describe how encoder  200  may be configured to perform MTT partitioning. Decoder  300  may also then apply the same MTT partitioning as was performed by encoder  200 . In some examples, how a picture of video data was partitioned by encoder  200  may be determined by applying the same set of predefined rules at decoder  300 . However, in many situations, encoder  200  may determine a particular partition structure and partition type to use based on rate-distortion criteria for the particular picture of video data being coded. As such, in order for decoder  300  to determine the partitioning for a particular picture, encoder  200  may signal syntax elements in the encoded bitstream that indicate how the picture, and CTUs of the picture, are to be partitioned. Decoder  200  may parse such syntax elements and partition the picture and CTUs accordingly. 
     In one example, the prediction processing unit  260  of video encoder  200  may be configured to perform any combination of the partitioning techniques described above, especially, for the motion estimation, and the details will be described later. 
     Like the picture  201 , the block  203  again is or can be regarded as a two-dimensional array or matrix of samples with intensity values (sample values), although being of smaller dimension than the picture  201 . In other words, the block  203  may comprise, e.g., one sample array (e.g. a luma array in case of a monochrome picture  201 ) or three sample arrays (e.g. a luma and two chroma arrays in case of a color picture  201 ) or any other number and/or kind of arrays depending on the color format applied. The number of samples in the horizontal and vertical direction (or axis) of the block  203  define the size of block  203 . 
     Encoder  200  as shown in  FIG. 2  is configured to encode the picture  201  block by block, e.g. the encoding and prediction is performed per block  203 . 
     Residual Calculation 
     The residual calculation unit  204  is configured to calculate a residual block  205  based on the picture block  203  and a prediction block  265  (further details about the prediction block  265  are provided later), e.g. by subtracting sample values of the prediction block  265  from sample values of the picture block  203 , sample by sample (pixel by pixel) to obtain the residual block  205  in the sample domain. 
     Transform 
     The transform processing unit  206  is configured to apply a transform, e.g. a discrete cosine transform (DCT) or discrete sine transform (DST), on the sample values of the residual block  205  to obtain transform coefficients  207  in a transform domain. The transform coefficients  207  may also be referred to as transform residual coefficients and represent the residual block  205  in the transform domain. 
     The transform processing unit  206  may be configured to apply integer approximations of DCT/DST, such as the transforms specified for HEVC/H.265. Compared to an orthogonal DCT transform, such integer approximations are typically scaled by a certain factor. In order to preserve the norm of the residual block which is processed by forward and inverse transforms, additional scaling factors are applied as part of the transform process. The scaling factors are typically chosen based on certain constraints like scaling factors being a power of two for shift operation, bit depth of the transform coefficients, tradeoff between accuracy and implementation costs, etc. Specific scaling factors are, for example, specified for the inverse transform, e.g. by inverse transform processing unit  212 , at a decoder  300  (and the corresponding inverse transform, e.g. by inverse transform processing unit  212  at an encoder  20 ) and corresponding scaling factors for the forward transform, e.g. by transform processing unit  206 , at an encoder  200  may be specified accordingly. 
     Quantization 
     The quantization unit  208  is configured to quantize the transform coefficients  207  to obtain quantized transform coefficients  209 , e.g. by applying scalar quantization or vector quantization. The quantized transform coefficients  209  may also be referred to as quantized residual coefficients  209 . The quantization process may reduce the bit depth associated with some or all of the transform coefficients  207 . For example, an n-bit transform coefficient may be rounded down to an m-bit transform coefficient during quantization, where n is greater than m. The degree of quantization may be modified by adjusting a quantization parameter (QP). For example for scalar quantization, different scaling may be applied to achieve finer or coarser quantization. Smaller quantization step sizes correspond to finer quantization, whereas larger quantization step sizes correspond to coarser quantization. The applicable quantization step size may be indicated by a quantization parameter (QP). The quantization parameter may for example be an index to a predefined set of applicable quantization step sizes. For example, small quantization parameters may correspond to fine quantization (small quantization step sizes) and large quantization parameters may correspond to coarse quantization (large quantization step sizes) or vice versa. The quantization may include division by a quantization step size and corresponding or inverse dequantization, e.g. by inverse quantization  210 , may include multiplication by the quantization step size. Embodiments according to some standards, e.g. HEVC, may be configured to use a quantization parameter to determine the quantization step size. Generally, the quantization step size may be calculated based on a quantization parameter using a fixed point approximation of an equation including division. Additional scaling factors may be introduced for quantization and dequantization to restore the norm of the residual block, which might get modified because of the scaling used in the fixed point approximation of the equation for quantization step size and quantization parameter. In one example implementation, the scaling of the inverse transform and dequantization might be combined. Alternatively, customized quantization tables may be used and signaled from an encoder to a decoder, e.g. in a bitstream. The quantization is a lossy operation, wherein the loss increases with increasing quantization step sizes. 
     The inverse quantization unit  210  is configured to apply the inverse quantization of the quantization unit  208  on the quantized coefficients to obtain dequantized coefficients  211 , e.g. by applying the inverse of the quantization scheme applied by the quantization unit  208  based on or using the same quantization step size as the quantization unit  208 . The dequantized coefficients  211  may also be referred to as dequantized residual coefficients  211  and correspond—although typically not identical to the transform coefficients due to the loss by quantization—to the transform coefficients  207 . 
     The inverse transform processing unit  212  is configured to apply the inverse transform of the transform applied by the transform processing unit  206 , e.g. an inverse discrete cosine transform (DCT) or inverse discrete sine transform (DST), to obtain an inverse transform block  213  in the sample domain. The inverse transform block  213  may also be referred to as inverse transform dequantized block  213  or inverse transform residual block  213 . 
     The reconstruction unit  214  (e.g. Summer  214 ) is configured to add the inverse transform block  213  (i.e. reconstructed residual block  213 ) to the prediction block  265  to obtain a reconstructed block  215  in the sample domain, e.g. by adding the sample values of the reconstructed residual block  213  and the sample values of the prediction block  265 . 
     Optionally, the buffer unit  216  (or short “buffer”  216 ), e.g. a line buffer  216 , is configured to buffer or store the reconstructed block  215  and the respective sample values, for example for intra prediction. In further embodiments, the encoder may be configured to use unfiltered reconstructed blocks and/or the respective sample values stored in buffer unit  216  for any kind of estimation and/or prediction, e.g. intra prediction. 
     Embodiments of the encoder  200  may be configured such that, e.g. the buffer unit  216  is not only used for storing the reconstructed blocks  215  for intra prediction  254  but also for the loop filter unit  220  (not shown in  FIG. 2 ), and/or such that, e.g. the buffer unit  216  and the decoded picture buffer unit  230  form one buffer. Further embodiments may be configured to use filtered blocks  221  and/or blocks or samples from the decoded picture buffer  230  (both not shown in  FIG. 2 ) as input or basis for intra prediction  254 . 
     The loop filter unit  220  (or short “loop filter”  220 ), is configured to filter the reconstructed block  215  to obtain a filtered block  221 , e.g. to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit  220  is intended to represent one or more loop filters, such as a de-blocking filter, a sample-adaptive offset (SAO) filter or other filters, e.g. a bilateral filter or an adaptive loop filter (ALF) or a sharpening or smoothing filters or collaborative filters. Although the loop filter unit  220  is shown in  FIG. 2  as being an in-loop filter, in other configurations, the loop filter unit  220  may be implemented as a post-loop filter. The filtered block  221  may also be referred to as filtered reconstructed block  221 . Decoded picture buffer  230  may store the reconstructed coding blocks after the loop filter unit  220  performs the filtering operations on the reconstructed coding blocks. 
     Embodiments of the encoder  200  (respectively loop filter unit  220 ) may be configured to output loop filter parameters (such as sample adaptive offset information), e.g. directly or entropy encoded via the entropy encoding unit  270  or any other entropy coding unit, so that, e.g., a decoder  300  may receive and apply the same loop filter parameters for decoding. 
     The decoded picture buffer (DPB)  230  may be a reference picture memory that stores reference picture data for use in encoding video data by video encoder  20 . The DPB  230  may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The DPB  230  and the buffer  216  may be provided by the same memory device or separate memory devices. In some example, the decoded picture buffer (DPB)  230  is configured to store the filtered block  221 . The decoded picture buffer  230  may be further configured to store other previously filtered blocks, e.g. previously reconstructed and filtered blocks  221 , of the same current picture or of different pictures, e.g. previously reconstructed pictures, and may provide complete previously reconstructed, i.e. decoded, pictures (and corresponding reference blocks and samples) and/or a partially reconstructed current picture (and corresponding reference blocks and samples), for example for inter prediction. In some example, if the reconstructed block  215  is reconstructed but without in-loop filtering, the decoded picture buffer (DPB)  230  is configured to store the reconstructed block  215 . 
     The prediction processing unit  260 , also referred to as block prediction processing unit  260 , is configured to receive or obtain the block  203  (current block  203  of the current picture  201 ) and reconstructed picture data, e.g. reference samples of the same (current) picture from buffer  216  and/or reference picture data  231  from one or a plurality of previously decoded pictures from decoded picture buffer  230 , and to process such data for prediction, i.e. to provide a prediction block  265 , which may be an inter-predicted block  245  or an intra-predicted block  255 . 
     Mode selection unit  262  may be configured to select a prediction mode (e.g. an intra or inter prediction mode) and/or a corresponding prediction block  245  or  255  to be used as prediction block  265  for the calculation of the residual block  205  and for the reconstruction of the reconstructed block  215 . 
     Embodiments of the mode selection unit  262  may be configured to select the prediction mode (e.g. from those supported by prediction processing unit  260 ), which provides the best match or in other words the minimum residual (minimum residual means better compression for transmission or storage), or a minimum signaling overhead (minimum signaling overhead means better compression for transmission or storage), or which considers or balances both. The mode selection unit  262  may be configured to determine the prediction mode based on rate distortion optimization (RDO), i.e. select the prediction mode which provides a minimum rate distortion optimization or which associated rate distortion at least a fulfills a prediction mode selection criterion. 
     In the following, the prediction processing (e.g. prediction processing unit  260  and mode selection (e.g. by mode selection unit  262 ) performed by an example encoder  200  will be explained in more detail. 
     As described above, the encoder  200  is configured to determine or select the best or an optimum prediction mode from a set of (pre-determined) prediction modes. The set of prediction modes may comprise, e.g., intra-prediction modes and/or inter-prediction modes. 
     The set of intra-prediction modes may comprise 35 different intra-prediction modes, e.g. non-directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined in H.265, or may comprise 67 different intra-prediction modes, e.g. non-directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined in H.266 under development. 
     The set of (or possible) inter-prediction modes depend on the available reference pictures (i.e. previous at least partially decoded pictures, e.g. stored in DBP  230 ) and other inter-prediction parameters, e.g. whether the whole reference picture or only a part, e.g. a search window area around the area of the current block, of the reference picture is used for searching for a best matching reference block, and/or e.g. whether pixel interpolation is applied, e.g. half/semi-pel and/or quarter-pel interpolation, or not. 
     Additional to the above prediction modes, skip mode and/or direct mode may be applied. 
     The prediction processing unit  260  may be further configured to partition the block  203  into smaller block partitions or sub-blocks, e.g. iteratively using quad-tree-partitioning (QT), binary partitioning (BT) or triple-tree-partitioning (TT) or any combination thereof, and to perform, e.g. the prediction for each of the block partitions or sub-blocks, wherein the mode selection comprises the selection of the tree-structure of the partitioned block  203  and the prediction modes applied to each of the block partitions or sub-blocks. 
     The inter prediction unit  244  may include motion estimation (ME) unit and motion compensation (MC) unit (not shown in  FIG. 2 ). The motion estimation unit is configured to receive or obtain the picture block  203  (current picture block  203  of the current picture  201 ) and a decoded picture  331 , or at least one or a plurality of previously reconstructed blocks, e.g. reconstructed blocks of one or a plurality of other/different previously decoded pictures  331 , for motion estimation. E.g. a video sequence may comprise the current picture and the previously decoded pictures  331 , or in other words, the current picture and the previously decoded pictures  331  may be part of or form a sequence of pictures forming a video sequence. The encoder  200  may, e.g., be configured to select a reference block from a plurality of reference blocks of the same or different pictures of the plurality of other pictures and provide a reference picture (or reference picture index, . . . ) and/or an offset (spatial offset) between the position (x, y coordinates) of the reference block and the position of the current block as inter prediction parameters to the motion estimation unit (not shown in  FIG. 2 ). This offset is also called motion vector (MV). Merging is an important motion estimation tool used in HEVC and inherited to VVC. For performing the merge estimation, the first thing should be done is construct a merge candidate list where each of the candidate contains all motion data including the information whether one or two reference picture lists are used as well as a reference index and a motion vector for each list. 
     The merge candidate list is constructed based on the following candidates: (a) up to four spatial merge candidates that are derived from five spatial neighboring blocks; (b) one temporal merge candidate derived from two temporal, co-located blocks; (c) additional merge candidates including combined bi-predictive candidates and zero motion vector candidates. 
     The first candidates in the merge candidate list are the spatial neighbors. Up to four candidates are inserted in the merge list by sequentially checking A1, B1, B0, A0 and B2, in that order, according to the right part of  FIG. 12 . 
     Instead of just checking whether a coding block is available and contains motion information, some additional redundancy checks are performed before taking all the motion data of the coding block as a merge candidate. These redundancy checks can be divided into two categories for two different purposes: (a) avoid having candidates with redundant motion data in the list; (b) prevent merging two partitions that could be expressed by other means which would create redundant syntax. 
     When N is the number of spatial merge candidates, a complete redundancy check would consist of 
     
       
         
           
             
               N 
               · 
               
                 ( 
                 
                   N 
                   - 
                   1 
                 
                 ) 
               
             
             2 
           
         
       
     
     motion data comparisons. In case of the five potential spatial merge candidates, ten motion data comparisons would be needed to assure that all candidates in the merge list have different motion data. During the development of HEVC, the checks for redundant motion data have been reduced to a subset in a way that the coding efficiency is kept while the comparison logic is significantly reduced. In the final design, no more than two comparisons are performed per candidate resulting in five overall comparisons. Given the order of {A1, B1, B0, A0, B2}, B0 only checks B1, A0 only A1 and B2 only A1 and B1. In an embodiment of the partitioning redundancy check, the bottom PU of a 2N×N partitioning is merged with the top one by choosing candidate B1. This would result in one CU with two PUs having the same motion data which could be equally signaled as a 2N×2N CU. Overall, this check applies for all second PUs of the rectangular and asymmetric partitions 2N×N, 2N×nU, 2N×nD, N×2N, nR×2N and nL×2N. It is noted that for the spatial merge candidates, only the redundancy checks are performed and the motion data is copied from the candidate blocks as it is. Hence, no motion vector scaling is needed here. 
     The derivation of the motion vectors for the temporal merge candidate is the same as for the TMVP. Since a merge candidate comprises all motion data and the TMVP is only one motion vector, the derivation of the whole motion data only depends on the slice type. For bi-predictive slices, a TMVP is derived for each reference picture list. Depending on the availability of the TMVP for each list, the prediction type is set to bi-prediction or to the list for which the TMVP is available. All associated reference picture indices are set equal to zero. Consequently for uni-predictive slices, only the TMVP for list 0 is derived together with the reference picture index equal to zero. 
     When at least one TMVP is available and the temporal merge candidate is added to the list, no redundancy check is performed. This makes the merge list construction independent of the co-located picture which improves error resilience. Consider the case where the temporal merge candidate would be redundant and therefore not included in the merge candidate list. In the event of a lost co-located picture, the decoder could not derive the temporal candidates and hence not check whether it would be redundant. The indexing of all subsequent candidates would be affected by this. 
     For parsing robustness reasons, the length of the merge candidate list is fixed. After the spatial and the temporal merge candidates have been added, it can happen that the list has not yet the fixed length. In order to compensate for the coding efficiency loss that comes along with the non-length adaptive list index signaling, additional candidates are generated. Depending on the slice type, up to two kind of candidates are used to fully populate the list: (a) Combined bi-predictive candidates; (b) Zero motion vector candidates. 
     In bi-predictive slices, additional candidates can be generated based on the existing ones by combining reference picture list 0 motion data of one candidate with and the list 1 motion data of another one. This is done by copying Δx0, Δy0, Δt0 from one candidate, e.g. the first one, and Δx1, Δy1, Δt1 from another, e.g. the second one. The different combinations are predefined and given in Table 1.1. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 1.1 
               
               
                   
               
               
                 Combination Order 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
                 10 
                 11 
               
               
                   
               
             
            
               
                 Δx 0 , Δy 0 , Δt 0  from Cand. 
                 0 
                 1 
                 0 
                 2 
                 1 
                 2 
                 0 
                 3 
                 1 
                 3 
                 2 
                 3 
               
               
                 Δx 1 , Δy 1 , Δt 1  from Cand. 
                 1 
                 0 
                 2 
                 0 
                 2 
                 1 
                 3 
                 0 
                 3 
                 1 
                 3 
                 2 
               
               
                   
               
            
           
         
       
     
     When the list is still not full after adding the combined bi-predictive candidates, or for uni-predictive slices, zero motion vector candidates are calculated to complete the list. All zero motion vector candidates have one zero displacement motion vector for uni-predictive slices and two for bi-predictive slices. The reference indices are set equal to zero and are incremented by one for each additional candidate until the maximum number of reference indices is reached. If that is the case and there are still additional candidates missing, a reference index equal to zero is used to create these. For all the additional candidates, no redundancy checks are performed as it turned out that omitting these checks will not introduce a coding efficiency loss. 
     For each PU coded in inter-picture prediction mode, a so called merge_flag indicates that block merging is used to derive the motion data. The merge_idx further determines the candidate in the merge list that provides all the motion data needed for the MCP. Besides this PU-level signaling, the number of candidates in the merge list is signaled in the slice header. Since the default value is five, it is represented as a difference to five (five_minus_max_num_merge_cand). That way, the five is signaled with a short codeword for the 0 whereas using only one candidate, is signaled with a longer codeword for the 4. Regarding the impact on the merge candidate list construction process, the overall process remains the same although it terminates after the list contains the maximum number of merge candidates. In the initial design, the maximum value for the merge index coding was given by the number of available spatial and temporal candidates in the list. When e.g. only two candidates are available, the index can be efficiently coded as a flag. But, in order to parse the merge index, the whole merge candidate list has to be constructed to know the actual number of candidates. Assuming unavailable neighboring blocks due to transmission errors, it would not be possible to parse the merge index anymore. 
     A crucial application of the block merging concept in HEVC is its combination with a skip mode. In previous video coding standards, the skip mode was used to indicate for a block that the motion data is inferred instead of explicitly signaled and that the prediction residual is zero, i.e. no transform coefficients are transmitted. In HEVC, at the beginning of each CU in an inter-picture prediction slice, a skip_flag is signaled that implies the following: (a). the CU only contains one PU (2N×2N partition type); (b). the merge mode is used to derive the motion data (merge_flag equal to 1); (c). no residual data is present in the bitstream. 
     A parallel merge estimation level was introduced in HEVC that indicates the region in which merge candidate lists can be independently derived by checking whether a candidate block is located in that merge estimation region (MER). A candidate block that is in the same MER is not included in the merge candidate list. Hence, its motion data does not need to be available at the time of the list construction. When this level is e.g. 32, all prediction units in a 32×32 area can construct the merge candidate list in parallel since all merge candidates that are in the same 32×32 MER, are not inserted in the list. As shown in  FIG. 6 , there is a CTU partitioning with seven CUs and ten PUs. All potential merge candidates for the first PU0 are available because they are outside the first 32×32 MER. For the second MER, merge candidate lists of PUs 2-6 cannot include motion data from these PUs when the merge estimation inside that MER should be independent. Therefore, when looking at a PU5 for example, no merge candidates are available and hence not inserted in the merge candidate list. In that case, the merge list of PU5 consists only of the temporal candidate (if available) and zero MV candidates. In order to enable an encoder to trade-off parallelism and coding efficiency, the parallel merge estimation level is adaptive and signaled as log2_parallel_merge_level_minus2 in the picture parameter set. 
     However, as discussed before, the parallel merge estimation level that is used in HEVC is not efficient anymore, because the VVC introduces more partition modes which results in irregular (no-square) coding blocks hindering the parallel processing for merge estimation of the coding blocks. 
     The present disclosure provides several solutions to resolve the problems discussed above. 
     According to a first embodiment, an apparatus is provided for marking availability of a candidate coding block for merge estimation of a current coding block within a coding tree unit, CTU. The candidate (coding) block is marked as available. The candidate block is marked as unavailable when a predefined location of the candidate coding block is included within an extended merge estimation region, MER, wherein the extended MER includes a current MER in which the current coding block is located and at least a portion of another MER, adjacent to the current MER. 
     This means that the respective block is marked as available for prediction of the current coding block initially, i.e. at the beginning of the merge estimation (e.g. by default). In other words, prior to a construction of a merge candidate list of the current coding block, the candidate block is marked as available. 
     The term “unavailable” means that an unavailable-marked candidate block is not used for prediction of a current coding block. As a result, there is or is no longer a dependence of the current coding block on the candidate block with respect to a processing order. Hence, by marking a candidate block as unavailable, the dependencies among a candidate and a current block is broken, and the candidate block may be parallel processed. 
     According to an embodiment, the marking of the candidate coding block includes to obtain the coordinates (X,Y) of a left-top pixel of the current coding block. As the predefined location, the coordinates (X2,Y2) of a specific point in the candidate coding block are obtained. It is then determined if the specific point is located within the extended MER by comparing the coordinates of the specific point and the coordinates of the left-top pixel. The candidate block is marked as unavailable, if the specific point is located within the extended MER. 
     In this embodiment, the top-left pixel position of the current coding block is used as reference position, as is common in HEVC and/or VVC. However, any other suitable position within the current coding block may be used as reference. 
     The predefined location of the candidate block may be located at specific positions/locations of the candidate block to optimize the merge estimation and in particular to increase the number of unavailable candidate blocks. This enhances the parallel processing, as discussed in the following embodiments (solutions). 
     Solution 1 
     According to an embodiment, the specific point is a top-left pixel of the candidate coding block. The determining if the specific point is located within the extended MER includes mark the candidate coding block as unavailable if any of the conditions is satisfied:
         if [X−1,Y] and [X,Y] are in the current MER, and if X2&lt;X and Y2&gt;=Y; or   if [X,Y−1] and [X,Y] are in the current MER, and if Y2&lt;Y and X2&gt;=X; or   if [X−1,Y−1] and [X,Y] are in the current MER, and if Y2&lt;Y and X2&lt;X.       

     This is illustrated in  FIG. 13 , showing a scenario where the above embodiment is applied. The block shown in the  FIG. 13  is a current coding block to be merge estimated. The bold dash line is the boundary of a MER for the current coding block, and the thin dash lines are auxiliary lines used for easily referring the locations in that  FIG. 13 . In the solution 1, a set of new MER conditions is provided. Before the new MER conditions are applied, it is assumed that the top-left coordinate of the current block is [X, Y], and the top-left coordinate of a second block is [X2, Y2]. The second block is referred also to the candidate (coding) block. The second block is initially marked/set as available for prediction, which means the second block is in the same picture as the current block, and in the same slice, and is an inter-predicted block. This means that the second block/candidate block may be used in general for prediction of the current (coding) block. Then, the above MER conditions are: 
     Assume that the [X,Y] are the top-left coordinate of the current block. 
     Assume [X2, Y2] are the top-left coordinate of a second block. 
     First set second block “available for prediction”. 
     If [X−1,Y] and [X,Y] are in the same MER, and if X2&lt;X and Y2&gt;=Y, motion information candidates of second block are set unavailable for prediction (quadrant 1). 
     If [X,Y−1] and [X,Y] are in the same MER, and if Y2&lt;Y and X2&gt;=X, motion information candidates of second block are set unavailable for prediction (quadrant 2). 
     If [X−1,Y−1] and [X,Y] are in the same MER, and if Y2&lt;Y and X2&lt;X, motion information candidates of second block are set unavailable for prediction (quadrant 3). 
     The word “same” refers to the current MER, i.e. the MER which includes the current coding block. Further, the quadrants 1, 2, and 3 correspond to the extended MER, and the above conditions test whether or not the candidate/second block is within the extended MER. 
     It is noted that throughout the application it is assumed that the value of x increases from left to right along the horizontal x-axis. Moreover, the value of y increases from top to bottom along the vertical y-axis (i.e. gravity axis). 
     By these new MER conditions the dependency with respect to a processing order between the current block and the second block (i.e. candidate) can be broken by setting the second block as unavailable for prediction if one the conditions is met. This allows the current block and the second block to be processed in a parallel way thereby, overcoming the technical problem discussed above. 
     It is noted that the new MER condition breaks both direct and indirect dependencies between the current block and the second block. In other words, if the processing order of blocks is given by second block→a third block→current block, the new MER condition not only breaks the prediction dependency between the current block and the second block, but breaks also the dependency between the third block and the current block. The following embodiment can exemplify how the new MER conditions work. 
     In VVC, the merge estimation scheme is mostly inherited from HEVC, and the potential candidate coding blocks in the spatial domain (in the other words, the blocks within the same picture) to be used to derive MVs therefrom to construct a MV candidate list for the inter prediction of a current coding block are substantially the same as those blocks shown in  FIG. 12 . Namely, during the merge estimation of a current block, blocks A1, A0, B1, B0, and B2 will be checked in turn to construct a candidate list. The basic rule to construct a candidate list for a current block is first constructing a spatial candidate list, then a temporal candidate list, and finally additional merge candidates. 
     The spatial candidate list is constructed by sequentially checking the blocks A1, B1, B0, A0 and B2, in that order, and up to four spatial merge candidates that are derived from A1, B1, B0, A0 and B2. 
     More specifically, the spatial candidates list is constructed based on the following rule. 
     (a). When the current candidate coding block is the coding block A1, check the availability of the coding block A1 based on the solution 1 or the following solutions 2˜4, and when the coding block A1 is not marked as unavailable (i.e. A1 is marked as being available), then add the MV of the coding block A1 to the motion vector list; 
     (b). when the current candidate coding block is the coding block B1, check the availability of the coding block B1 based on the solution 1 or the following solutions 2˜4, and when the coding block B1 is not marked as unavailable (i.e. B1 is marked as being available), add the MV of the coding block B1 to the motion vector list; 
     (c). when the current candidate coding block is the coding block B0, check the availability of the coding block B0 based on the solution 1 or the following solutions 2˜4, and when the coding block B0 is not marked as unavailable (i.e. B0 is marked as being available), and the MV is different from the MV of the coding block B1 that has been added to the motion vector list, add the motion vector predictor of the coding block B0 to the motion vector list; 
     (d). when the current candidate coding block is the coding block A0, check the availability of the coding block A0 based on the solution 1 or the following solutions 2˜4, and when the coding block A0 is not marked as unavailable (i.e. A0 is marked as being available), and the MV is different from the MV of the coding block A1 that has been added to the motion vector list, add the MV of the coding block A0 to the motion vector list; and 
     (e). when the current candidate coding block is the coding block B2, check the availability of the coding block B2 based on the solution 1 or the following solutions 2˜4, and when the coding block B2 is not marked as unavailable (i.e. B2 is marked as being available), and the MV is different from both the MV of the coding block A1 that has been added to the motion vector list, and the MV of the coding block B1 that has been added to the motion vector list, add MV of the coding block B2 to the motion vector list. 
     The spatial candidates list is derived from two temporal, co-located blocks. 
     The additional merge candidates includes combined bi-predictive candidates and zero motion vector candidates. 
     As long as the merge candidate list is built, a merge estimation is carried based on each of the MV included in the candidate list by using an RDO (Rate Distortion Optimization) rule or an other measure to find the optimal MV as the MV or MV predictor of a current coding block, and the index of the MV within the merge candidate list will be added into the bit-stream to have the decoding side know which MV is the one used for inter-predicting the current block. It should be noted that the number of the spatial merge candidates is not limited to 4 as used in HEVC, it can be changed and signaled in the bit stream to the decoding side. Besides, the potential candidate coding blocks used to build the spatial candidate list for a current coding block is not fixed, it can be changed based on any positive gain observed. 
       FIG. 14  shows a partition result of a picture block with a size of 16×16, the dashed line indicate the MER grid which is a size of 8×8. The picture block is partitioned into A˜F coding blocks with a processing order of the blocks as A→B→C→D→F). The top-left coordinates of blocks A, B and F are respectively marked in the  FIG. 14  as (0, 0), (4, 0), (12, 8). The bottom right coordinate of block A is also marked (3, 15). The widths and heights are also shown in the figure. Based on the new MER conditions of the present disclosure, block B can be now processed in parallel with block A, as the top-left coordinates are in the same MER. This is guaranteed by the fact that the motion information of block A is marked as unavailable for prediction of block B by using the new MER condition. Therefore, the processing of block B does not need to wait for the motion information of block A to become available, so that both blocks can be processed at the same time. 
     Moreover the blocks C and E can also be processed in parallel according to the rule: “If [X−1,Y] and [X,Y] are in the same MER, and if X2&lt;X and Y2&gt;=Y, motion information candidates of second block are set unavailable for prediction (quadrant 1).” In the rule, due to the processing order, block E is the current block and block C is the second block. Accordingly, both blocks C and D are set unavailable for prediction of block E. Which means block E can now be processed in parallel with block C, since no direct and indirect dependency exists. As a result, several pairs of the blocks A to F can be processed in parallel, which can save the time consumed for the motion estimation, especially, the candidate list construction. 
     An alternative implementation of the solution 1 can be formulated as follows. The new MER conditions are: 
     Assume that the [X,Y] are the top-left coordinate of the current block. 
     Assume [X2, Y2] are the top-left coordinate of a second block. 
     First set second block “available for prediction”. 
     If [X−1,Y] and [X,Y] are in the same MER, and if X2&lt;X and Y2&gt;=Y, motion information candidates of second block are set unavailable for prediction. 
     If [X,Y−1] and [X,Y] are in the same MER, and if Y2&lt;Y and X2&gt;=X, motion information candidates of second block are set unavailable for prediction. 
     If [X−1,Y−1] and [X,Y] are in the same MER, motion information candidates of second block are set unavailable for prediction. 
     This alternative implementation is logically identical to the previous implementation and results in the same neighboring blocks marked as unavailable for prediction. The reason is, since a neighbor block always precedes a current block, therefore since the conditions Y2&gt;=Y and X2&gt;=X cannot hold true at the same time, this alternative implementation results in the same logical outcome for all possible values of X, X2, Y and Y2. 
     A third alternative implementation of the solution 1 can be formulated as follows. The new MER conditions are: 
     Assume that the [X,Y] are the top-left coordinate of the current block. 
     Assume [X2, Y2] are the top-left coordinate of a second block. 
     First set second block “available for prediction”. 
     If floor(X2/mer_width) is equal to floor(X/mer_width) and floor(Y2/mer_height)&gt;=floor(Y/mer_height), motion information candidates of second block are set unavailable for prediction. 
     If floor(Y2/mer_height) is equal to floor(Y/mer_height) and floor(X2/mer_width)&gt;=floor(X/mer_width), motion information candidates of second block are set unavailable for prediction. 
     The mer_width and mer_height are the width and the height of the merge estimation region. The floor function is a function that takes as input a real number x and gives as output the greatest integer less than or equal to x. 
     It should be noted that the third alternative implementation is not identical to first two implementations. 
     Solution 2 
     According to an embodiment, the specific point is a bottom-right pixel of the candidate coding block, and the determining if the specific point is located within the extended MER includes mark the candidate coding block as unavailable if any of the conditions is satisfied:
         if [X−1,Y] and [X,Y] are in the current MER, and if X2&lt;X and Y2&gt;=Y; or   if [X,Y−1] and [X,Y] are in the current MER, and if Y2&lt;Y and X2&gt;=X; or   if [X−1,Y−1] and [X,Y] are in the current MER, and if Y2&lt;Y and X2&lt;X.       

     Based on the same partition as shown in the  FIG. 13 , solution 2 can provide more parallel processing blocks. The new MER conditions are:
         Assume that the [X,Y] are the top-left coordinate of the current block.   Assume [X2, Y2] are the bottom-right coordinate of a second block.   First set second neighbor available for prediction.   If [X−1,Y] and [X,Y] are in the same MER, and if X2&lt;X and Y2&gt;=Y, motion information candidates of second block are set unavailable for prediction.   If [X,Y−1] and [X,Y] are in the same MER, and if Y2&lt;Y and X2&gt;=X, motion information candidates of second block are set unavailable for prediction.   If [X−1,Y−1] and [X,Y] are in the same MER, and if Y2&lt;Y and X2&lt;X, motion information candidates of second block are set unavailable for prediction.       

     As compared with solution 1, the solution 2 uses the bottom-right coordinate of a second block rather than the top-left coordinate of the second block to perform the availability marking, which can increase the number of blocks which can be parallel processed. 
     An embodiment based on the solution 2 can be elaborated based on the same partitions as shown in  FIG. 14 . Based on the new MER of solution 2 of the present disclosure, in addition to A-B and C-E can be processed in a parallel way, A-D, and D-F can also be processed in parallel since the bottom-right coordinates cover more regions as compared with the top-left coordinates of the second block. It should be noted that the pairs of B&amp;D, C&amp;D, C&amp;F, B&amp;C, E&amp;F cannot be processed in parallel, since they do not belong to the same MER. 
     The solutions 1 and 2 can be summarized as a method for marking the availability of a potential candidate coding block used for the prediction of a current coding block, which includes: determining if a specific reference point (the coordinates of a specific point in the second block) in a potential candidate block is located in a same MER as the current block; 
     if yes, the potential candidate block is marked as unavailable for the inter-prediction of the current block;
 
encoding/decoding the current block independent of the potential candidate block.
 
     In summary, it should be noted that the specific reference point can be chosen based on different requirement, for example, in solution 1, the specific reference point is the top-left coordinates of the second block, but in solution 2, the specific reference point is the bottom-right coordinates of the second block. Alternatively, it can also be the middle point of the second block, the top-right coordinates of the second block, or the bottom-left coordinates of the second block. 
     An alternative implementation of the solution 2 can be formulated as follows. The new MER conditions are: 
     Assume that the [X,Y] are the top-left coordinates of the current block. 
     Assume [X2, Y2] are the bottom-right coordinates of a second block. 
     First, set the second block “available for prediction”. 
     If [X−1,Y] and [X,Y] are in the same MER, and if X2&lt;X and Y2&gt;=Y, motion information candidates of the second block are set unavailable for prediction. 
     If [X,Y−1] and [X,Y] are in the same MER, and if Y2&lt;Y and X2&gt;=X, motion information candidates of the second block are set unavailable for prediction. 
     If [X−1,Y−1] and [X,Y] are in the same MER, motion information candidates of the second block are set unavailable for prediction. 
     This alternative implementation is logically identical to the previous implementation and results in the same neighboring blocks marked as unavailable for prediction. The reason is that, since a neighbor block always precedes a current block, the conditions Y2&gt;=Y and X2&gt;=X therefore cannot hold true at the same time. Hence, this alternative implementation results in the same logical outcome for all possible values of X, X2, Y and Y2. 
     A third alternative implementation of the solution 2 can be formulated as follows. The new MER conditions are: 
     Assume that the [X,Y] are the top-left coordinate of the current block. 
     Assume [X2, Y2] are the bottom-right coordinate of a second block. 
     First, set second block “available for prediction”. 
     If floor(X2/mer_width) is equal to floor(X/mer_width) and floor(Y2/mer_height)&gt;=floor(Y/mer_height), motion information candidates of second block are set unavailable for prediction. 
     If floor(Y2/mer_height) is equal to floor(Y/mer_height) and floor(X2/mer_width)&gt;=floor(X/mer_width), motion information candidates of second block are set unavailable for prediction. 
     Where mer_width and mer_height are the width and the height of the merge estimation region, and with floor being a function taking as input a real number x and gives as output the greatest integer less than or equal to x. 
     The third alternative is identical to the first two alternatives of solution 2 if a neighbor block must be spatially adjacent to the current block. This is the case, for instance, in the H.265/HEVC video coding standard. If, however, it is possible for the current block to predict motion vectors from a neighbor block that is not spatially adjacent, then the third alternative implementation can provide superior compression performance w.r.t. the first two alternatives of solution 2. This case of being able to predict motion information from neighbor blocks is exemplified in prior art document JVET-K0104, which is an input document to Joint Video Experts Team (WET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 11th Meeting: Ljubljana, SI, 10-18 Jul. 2018. The technique presented in the prior art is explained later on in this application. 
     Solution 3 
     According to an embodiment, an apparatus is provided for marking availability of a candidate coding block for merge estimation of a current coding block within a coding tree unit, CTU. The candidate coding block is (initially) marked as available. Coding blocks of the CTU, which include the current block and the candidate block, are labelled based on a processing order. A group of coding blocks is formed by applying a sliding window with a length of K. It is determined if the candidate coding block and the current coding block belong to the same one group of coding blocks; and the candidate coding block is marked as unavailable, if the candidate coding block and the current coding block belong to the same one group of coding blocks. 
     In the embodiments of the present application, the initial marking of the candidate coding block as available is an optional step, which is included in order to describe the process when a candidate block is not marked unavailable. The embodiments of the present application describe the conditions for marking a candidate coding block as unavailable, and if a coding block is not marked as unavailable it is marked as available (a candidate coding block is either marked available or unavailable). In other words, the order of the processing steps of marking a coding block as available might be before (initially) or after a coding block is marked unavailable. If the candidate coding block is initially marked as available, then if it belongs to the same extended MER (or MER) as the current coding block, the marking of the candidate block is changed (from available to unavailable). This order of steps generates an identical result when a candidate coding block is marked as available after it is determined that it does not belong to the same extended MER (or MER) as the current block (hence not marked as unavailable). 
     Solution 3 is a different method to mark the availability of a (potential) candidate bock in so far as no direct test related to a positional location of the candidate block with respect to the current block is used here. However, the MER may be interpreted to be formed as a result of the grouping of the coding blocks, where the blocks within each group create a MER for this group. The MER is therefore here to be understood in terms of a membership to a group, i.e. the MER. 
     The method includes, grouping K coding blocks together according to the processing order in the encoder and decoder, wherein K is an integer bigger than or equal to 2; marking a potential candidate coding block as unavailable for prediction of a current coding block, if the potential candidate coding block and the current coding block are grouped into one (i.e. same) group; encoding/decoding the current coding block independent to the potential candidate coding block. 
     A specific working flow chart of solution 4 is illustrated in  FIG. 15 . The floor function in the inequality “floor(Label(blk_current)/K)&gt;floor(Label(blk_neighbor)/K)” in step S 3  is a function that takes as input a real number x and gives as output the greatest integer less than or equal to x. K describes a window size for group the coding blocks. The inequality condition groups the blocks into groups of K blocks. Based on the floor function, a potential candidate coding block (blk_neighbor) can be marked as unavailable or available for prediction of a current coding block. 
     According to an embodiment, the labelling includes label the coding blocks incrementally using an integer number equal to or larger than zero. In this case, the length K of the sliding window relates to the processing order. 
     This is illustrated further by the following example. For instance, the right branch in  FIG. 15  is selected if the current block and the neighbor block are in the different groups. The left branch is selected if the 2 blocks are in the same group. As an example, assume K=5, Label (blk_current)=33 and Label(blk_neigbour)=32. In this case, the inequality of the floor function used in the previous step is evaluated as false and left right branch is selected. The computation steps are as follows: 
     Floor ((33−1)/5)&gt;? Floor ((32−1)/5) 
     Floor (6.4)&gt;? Floor (6.2) 
     6&gt;?6 
     No. 
     Then, the current coding block can be processed independently of the unavailable potential candidate coding blocks, after the marking of the non availability of the potential candidate coding blocks in step S 4 . Because, the dependency between the current coding block and the unavailable potential candidate coding block is broken by the solution 3. If the candidate block and the current block are in different groups, the candidate block is marked as available (step S 5 ). 
     Finally, the counter C is incremented by one, C=C+1 (step S 7 ), after the processing of each block (current coding block) in step S 6 . As a result, the coding blocks are labeled in step S 8  according to processing order in the encoder and decoder, since the processing order is identical both in the encoder and decoder, labelling will be the same in both the encoder and decoder. In step S 1 , a next candidate block is taken and the above steps a repeated for all the candidate blocks. 
     An exemplary embodiment according to solution 3 is elaborated as follows accompanying with  FIG. 16 . According to the solution 3, all of the coding blocks are labeled according to their processing order as 0˜5. The processing window (defined by length K) groups together the coding blocks according to a processing order in the encoder and decoder. For instance, if K is equal to 3, then the blocks {0,1, 2} and blocks {3,4,5} are grouped together. According to the present disclosure, if a current block and a neighbor block belong to the same group, the neighbor block is marked as unavailable for prediction during the processing of the current block. This means that the motion information of the neighbor block is not used to predict the motion information of the current block. On the other hand, if the current block and the coding block do not belong to the same group, then the neighbor block is set available for the prediction of the current block. 
     In the example above (K=3), block 5 cannot be predicted from blocks 3 and 4. However, it can be predicted from block 2, for example. It must be noted that the rule in solution 3 also allows the prediction of block 5 from blocks 1 and 0. However, blocks 1 and 0 are normally not candidates for the prediction according to the merge list construction rules, which was explained with respect to  FIG. 12 . 
     By solution 3, a new availability marking method is provided to mark coding blocks by checking if any of the coding blocks is grouped into the same group of a current coding blocks, which is an alternative way to eliminate the technical problem discussed above. 
     Solution 4 
     According to an embodiment, the labelling includes label the coding blocks incrementally using the spanning area of the coding blocks, wherein the spanning area is counted based on the number of pixels/samples the coding blocks contain. In this case, the length K of the sliding window relates to an area. 
     Solution 4 is similar to solution 3, and the difference is that the labeling of each coding block is based on the processing order of the coding blocks and the area spanned by the coding block. A specific working flow chart of solution 4 is illustrated in  FIG. 17 . The working flow in  FIG. 17  is the same as the working flow in  FIG. 15 , so that the same steps are not repeated here. Solution 4 and 3 differ in the counter step (step S 7 ), specifically, the step “Increase counter, C=C+w*h” which means the coding block is labeled by its spanning region, the pixels/samples it contains. 
     By referring  FIG. 18 , the first block in the processing order has a width equal to 4 and height equal to 16. Therefore, it is labeled C=0+w*h=64, assuming the counter is at C=0 at the beginning. Given K is equal to 128, the blocks labeled 64, 96, and 128 are grouped together and the block 192, 224, and 256 are grouped to in the second group together. After that as in solution 3, a current block cannot be predicted from motion information of a neighbor block, if they are in the same group. 
     As compared to solution 3, solution 4 results in merge estimation regions that are more balanced in terms of area covered. In other words, in solution 4 the sliding window creates parallel processing regions that contain more or less the same number of samples. Please note that the number of samples in the regions are not always exactly same. As a result, the hardware implementations for solution 4 are easier than for solution 3. 
     MER Determination 
     According to solutions 1 and 2, the merge estimation region can be determined as a fixed grid of partitions with size N×M in the −x and −y directions. In other words, the video picture can be partitioned with same-sized N×M rectangles each of which represents a merge estimation region. 
     According to solutions 3 and 4, the merge estimation region can be determined as a positive integer number K, which represents either the number of coding blocks or the amount of samples inside a Merge estimation region. 
     The positive integer numbers N, M, and K can be numbers that are encoded into bitstream, preferably in a parameter set, such as a sequence parameter set or a picture parameter set. 
     The numbers N, M, and K can be encoded in the bitstream using a transformation operation, whose inverse exists and known to the decoder. For example, the numbers can be encoded using a logarithm operation in base two and whose inverse is defined as exponentiation of base two. 
     Alternatively, the numbers N, M, and K might have predetermined values. In this case, an indication can be encoded in the bitstream that selects between predetermined values of N, M, and K according to a table of predetermined values. 
     Solution 5 
     Solution 5 provides an option to harmonize the solutions 1˜4 with the history-based motion vector prediction. The history based motion vector prediction is proposed in JVET-K0104 which is an input document to Joint Video Experts Team (WET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 11th Meeting: Ljubljana, SI, 10-18 Jul. 2018. The history-based MVP (HMVP) method is proposed wherein a HMVP candidate is defined as the motion information of a previously coded block. 
     A table with multiple HMVP candidates is maintained during the encoding/decoding process. The table is emptied when a new slice is encountered. 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 the figure above. HMVP candidates could be used in the merge candidate list construction process. All HMVP candidates from the last entry to the first entry in the table are inserted after the TMVP candidate. Pruning is applied on the HMVP candidates. 
     Once the total number of available merge candidates reaches the signaled maximally allowed merge candidates, the merge candidate list construction process is terminated. Similarly, HMVP candidates could also be used in the AMVP candidate list construction process. The motion vectors of the last K HMVP candidates in the table are inserted after the TMVP candidate. Only HMVP candidates with the same reference picture as the AMVP target reference picture are used to construct the AMVP candidate list. Pruning is applied on the HMVP candidates. K preferably is set to 4. 
     The HMVP allows for motion vector prediction from non-adjacent spatial neighbor blocks. As an example according to HMVP, it would be possible that block F as shown in  FIG. 14  can predict the motion information from block A, since the motion information of block A would be stored in the aforementioned table with HMVP candidates. In this case, the solutions 1-4 apply without a change to the candidates that are stored in the table. 
     As an embodiment, in addition to the motion information, top-left or bottom right coordinate of the block must also be stored in association with the table entries, in order to apply the rules given in solutions 1 and 2. 
     Alternatively, the present disclosure discloses further the following embodiments (solutions) which allow more flexibility in parallel processing of merge estimation. 
     Similar to the previous embodiments, different forms of MER conditions may be used to check whether a specific point of the candidate block is located in the extended MER. This check or the outcome of the respective MER test depends on the positional relation between the specific point and a position (e.g. a corner) of the current coding block. The candidate block is then marked as unavailable depending on whether or not the condition(s) is satisfied. This is further exemplified by the following embodiments. 
     According to an embodiment, the marking of the candidate coding block includes: obtain coordinates (x, y) of a corner of the current coding block; obtain, as the predefined location, coordinates of a specific point (x+a, y+b), wherein a∈(−1,0,1) and b∈(−1,0,1), and a and b are selected in dependence on the relationship of the relative position between the specific point and the corner; select, for the one candidate coding block, one value from (−1,0,1) as the a, and one value from the (−1,0,1) as the b; and mark the candidate coding block as unavailable, if floor((x+a)/mer_width) is equal to floor(x/mer_width); or if floor((y+b)/mer_width) is equal to floor(y/mer_height), wherein mer_width is a width and mer_height is a height of the current MER. 
     This means that current and candidate block are spatial neighbors, with reference to one of a corner of the current block and a (a,b)-parametrized position of the candidate block. 
     According to an embodiment, the candidate coding block neighbors the corner of the current coding block, and
         the corner of the current coding block is a bottom-left corner, and the candidate coding block is located on where there is left to the current coding block, a=−1, b=0; or   the corner of the current coding block is a bottom-left corner, and the candidate coding block is located on where there is bottom-left to the current coding block, a=−1, b=1; or   the corner of the current coding block is an upper left-corner, and the candidate coding block is located on where there is upper-left to the current coding block, a=−1, b=−1; or   the corner of the current coding block is an upper-right corner, and the candidate coding block is located on where there is upper-right to the current coding block, a=1, b=−1; or       

     the corner of the current coding block is an upper-right corner, and the candidate coding block located on where there is upper to the current coding block, a=0, b=−1. 
     The values of (a,b) of the candidate depend therefore on whether the position of the current block is the bottom-left or upper-right corner and how the candidate block is located relative to that corner. 
     The various positional relations between the candidate and current block may be illustrated as shown in the following. As a common basis, the following assumption is made for easily understanding the present disclosure by exemplifying embodiments. 
     As shown in  FIG. 19 , a current block and its spatial neighbors are illustrated as an example. The formal definitions of the spatial neighboring blocks are as follows. Note that here Coord1 refers to the current coding block and Coord2 refers to the candidate block. 
     Assume that the top-left (top-left corner), top-right (top-right corner) and bottom-left (bottom-left corner) coordinate of the current block are denoted by Pos1=(x1, y1), Pos2=(x2, y2) and Pos3=(x3, y3) respectively, wherein (x,y) are the coordinates in the −x and −y direction. Pos1.x denotes the −x coordinate of Pos1 and Pos1.y denotes the −y coordinate of Pos1. 
     The left spatial neighbor block (A1) is defined as the block that contains the point PosA1=(x3−1, y3). The left-bottom spatial neighbor block (A0) is defined as the block that contains the point PosA0=(x3−1, y3+1). The above-left spatial neighbor block (B2) is defined as the block that contains the point PosB2=(x1−1, y1−1). The above spatial neighbor block (B1) is defined as the block that contains the point PosB1=(x2, y2−1). The above-right spatial neighbor block (B0) is defined as the block that contains the point PosB0=(x2+1, y2−1). 
     According to an embodiment, the marking of the candidate coding block includes: obtain coordinates (x, y) of a corner of the current coding block; obtain, as the predefined location, coordinates (x+a, y+b) of a specific point, wherein the potential candidate coding block neighbors a corner of the current coding block and a∈(−1,0,1), b∈(−1,0,1), wherein a and b are not both equal to 0 or 1 and are selected in dependence on the relationship of the relative position between the specific point and the corner; select for the one candidate coding block, one value from (−1,0,1) as the a, and one value from the (−1,0,1) as the b; and mark the candidate coding block as unavailable
         if floor((x+a)/mer_width) is equal to floor(x/mer_width), and floor((y+b)/mer_height)&gt;=floor(y/mer_height), or   if floor((y+b)/mer_height) is equal to floor(y/mer_height) and floor((x+a)/mer_width)&gt;=floor(x/mer_width),
 
wherein mer_height is a height and mer_width is a width of the current MER.
       

     Based on the assumption shown in  FIG. 19 , the sixth solution is as follows accompanying with  FIG. 20 . 
     Solution 6 
     Mer_width and Mer_height define the width and height of the MER region. 
     New MER condition: 
     Depending on the neighboring block that is going to be checked; 
     If neighbor block is A 1 , Coord1 is set equal to Pos3, Coord2 is set equal to PosA 1 . 
     If neighbor block is A 0 , Coord1 is set equal to Pos3, Coord2 is set equal to PosA 0 . 
     If neighbor block is B 0 , Coord1 is set equal to Pos2, Coord2 is set equal to PosB 0 . 
     If neighbor block is B 1 , Coord1 is set equal to Pos2, Coord2 is set equal to PosB 1 . 
     If neighbor block is B 2 , Coord1 is set equal to Pos1, Coord2 is set equal to PosB 2 . 
     If both of the following conditions are true, the neighboring block is set unavailable for prediction by current block.
         floor(Coord2.x/mer_width) is equal to floor(Coord1.x/mer_width)   floor(Coord2.y/mer_height)&gt;=floor(Coord1.y/mer_height)       

     Alternatively, If both of the following conditions are true, the neighboring block is set unavailable for prediction by current block.
         floor(Coord2.y/mer_height) is equal to floor(Coord1.y/mer_height)   floor(Coord2.x/mer_width)&gt;=floor(Coord1.x/mer_width)       

     Note: the floor function is the function that takes as input a real number X and gives as output the greatest integer less than or equal to X. 
     Note: Throughout the present disclosure, coordinate x increases from left to right. Coordinate y increases from top to bottom. 
     Note: it is assumes that a process precedes the current invented process that sets the neighbor block available for prediction by current block. For example, the process that precedes the current invention might check whether the neighbor block is inside the picture boundaries, or whether it is inside the same slice, whether the neighbor block precedes the current block in coding order etc. 
     Neighbor blocks A0, . . . B2 are exemplary spatial neighbor positions. The present invention is applicable to any other spatial neighbor arrangements and also spatial non-neighbor arrangements. 
     It is possible to have implementations logically identical to solution 6 keeping in mind that the conditions Coord2.x&gt;=Coord1.x and Coord2.y&gt;=Coord1.y cannot hold true at the same time. One alternative implementation of solution 6 can be formulated as follows: 
     New MER condition: 
     Depending on the neighboring block that is going to be checked; 
     If neighbor block is A 1 , Coord1 is set equal to Pos3, Coord2 is set equal to PosA 1 . 
     If neighbor block is A 0 , Coord1 is set equal to Pos3, Coord2 is set equal to PosA 0 . 
     If neighbor block is B 0 , Coord1 is set equal to Pos2, Coord2 is set equal to PosB 0 . 
     If neighbor block is B 1 , Coord1 is set equal to Pos2, Coord2 is set equal to PosB 1 . 
     If neighbor block is B 2 , Coord1 is set equal to Pos1, Coord2 is set equal to PosB 2 .
         a. If both of the following conditions are true, the neighboring block is set unavailable for prediction by current block.   floor(Coord2.x/mer_width) is equal to floor(Coord1.x/mer_width),   Coord2.y/mer_height&gt;=Coord1.y/mer_height       

     Alternatively, if both of the following conditions are true, the neighboring block is set unavailable for prediction of the current block:
         floor(Coord2.y/mer_height) is equal to floor(Coord1.y/mer_height)   Coord2.x/mer_width&gt;=Coord1.x/mer_width       

     Alternatively, if the following condition is true, the neighboring block is set unavailable for prediction of the current block:
         Coord2 is inside the same merge estimation region as Coord1.       

       FIGS. 20A and 20B  show examples where a neighbor blocks falls into around the current block and will be hence marked unavailable. 
     Solution 7 
     Solution 7 is a harmonizing solution to have solution 6 being adopted to the history-based motion vector prediction, as disclosed in “CE4-related: History-based Motion Vector Prediction”, it might be possible that some of the neighbor blocks might not be spatially adjacent to the current block. In other words, the method as described in the referenced technology constructs a list of motion vectors from blocks that might not be adjacent to the current block. 
     In this case, solution 7 is made as follows: 
     Mer_width and Mer_height define the width and height of the MER region. 
     New MER conditions, depending on the neighboring block that is going to be checked; 
     If neighbor block belongs to the history-based candidate list, Coord2 is set equal to the bottom-right coordinate of the neighbor block, Coord1 is set equal to the top-left coordinate of the current block. As an alternative, instead of the bottom-right coordinate of the neighbor block, the top-left coordinate of the neighbor block can be used. More specifically, Coord2 is set equal to the top-left coordinate of the neighbor block, Coord1 is set equal to the top-left coordinate of the current block. 
     If both of the following conditions are true, the neighboring block is set unavailable for prediction of the current block.
         floor(Coord2.x/mer_width) is equal to floor(Coord1.x/mer_width)   floor(Coord2.y/mer_height)&gt;=floor(Coord1.y/mer_height)       

     If both of the following conditions are true, the neighboring block is set unavailable for prediction of the current block.
         floor(Coord2.y/mer_height) is equal to floor(Coord1.y/mer_height)   floor(Coord2.x/mer_width)&gt;=floor(Coord1.x/mer_width)       

     Solution 8 
     To further improve the parallelism as doing merge estimation to remove the parallel processing restriction as shown in  FIG. 21 . In  FIG. 21 , Block A is both the left (A1) and top-left (B2) neighbor of the current block. According to the previous solution, block A is set unavailable for prediction when it is considered as a left-neighbor (using Pos3, PosA1 pair). However, it is set available for prediction, when it is considered as a left-top neighbor (using Pos1, PosB2 pair). Δt the end, block A and current block cannot be processed in parallel, since motion information of block A is used as predictor for the current block. 
     The solution 8 is shown in  FIG. 22 , a new rule of determining the availability of neighboring blocks is shown, which is elaborated as follows. 
     Mer_width and Mer_height define the width and height of the MER region. 
     New MER Conditions: 
     Depending on the neighboring block that is going to be checked; 
     If neighbor block is A 1 , Coord1 is set equal to pos3, Coord2 is set equal to PosA 1 . 
     If neighbor block is A 0 , Coord1 is set equal to pos3, Coord2 is set equal to PosA 0 . 
     If neighbor block is B 0 , Coord1 is set equal to pos2, Coord2 is set equal to PosB 0 . 
     If neighbor block is B 1 , Coord1 is set equal to pos2, Coord2 is set equal to PosB 1 . 
     If neighbor block is B 2 , Coord1 is set equal to pos1, Coord2 is set equal to PosB 2 . 
     If the following condition is true, the neighboring block is set unavailable for prediction of the current block.
         floor(Coord2.x/mer_width) is equal to floor(Coord1.x/mer_width)
 
If the following condition is true, the neighboring block is set unavailable for prediction of the current block.
   floor(Coord2.y/mer_height) is equal to floor(Coord1.y/mer_height)       

     Solution 9 
     Solution 9 comes for adopt the restriction of CTU (coding tree unit) partitions. According to the draft video coding standard “Versatile Video Coding (Draft 2)”, it is possible to partition a picture frame into blocks using quadtree split, binary split, or ternary split (document: JVET-K1001-v4 which is accessible @ http://phenix.it-sudparis.eu/jvet). The split operation starts with a CTB (Coding Tree Block) and the CTB is hierarchically partitioned into coding blocks using quadtree split, binary split, or ternary split. Definitions are as follows: 
     quadtree: A tree in which a parent node can be split into four child nodes, each of which may become parent node for another split.
 
multi-type tree: A tree in which a parent node can be split either into two child nodes using a binary split or into three child nodes using a ternary split, each of which may become parent node for another split into either two or three child nodes.
 
     A restriction is imposed in the document that a binary split or a ternary split cannot be followed by a quadtree split in the child node. 
     Quadtree partition depth, or cqtDepth is incremented in the child node of a parent node, if quadtree splitting is performed to generate the child node. Similarly, mttDepth is incremented if binary or ternary split is performed. 
     In the solution 9, the following is new neighboring block availability checking rule is provided. 
     New MER Conditions: 
     Depending on the neighboring block that is going to be checked; 
     If neighbor block is A 1 , Coord1 is set equal to pos3, Coord2 is set equal to PosA 1 . 
     If neighbor block is A 0 , Coord1 is set equal to pos3, Coord2 is set equal to PosA 0 . 
     If neighbor block is B 0 , Coord1 is set equal to pos2, Coord2 is set equal to PosB 0 . 
     If neighbor block is B 1 , Coord1 is set equal to pos2, Coord2 is set equal to PosB 1 . 
     If neighbor block is B 2 , Coord1 is set equal to pos1, Coord2 is set equal to PosB 2 . 
     If both of the following conditions are true, the neighboring block is set unavailable for prediction by current block.
         Coord2 and Coord 1 are inside the same MER.   cqtDepth of the current block is greater than or equal to a threshold (qtDepthThr).       

     Note: threshold is an integer number such as 0, 1, 2. 
     An exemplary embodiment of solution 9 is provided as follows accompanying  FIG. 22 . For blocks A and B, cqtDepth is equal to 1 and mttdepth is equal to 3, since 1 quadtree split followed by 3 binary split are performed to generate blocks A and B. For block C, cqtDepth is equal to 2 and mttdepth is equal to 1, since 2 quadtree splits followed by 1 binary split are performed to generate block C. For blocks D and E, cqtDepth is equal to 2 and mttdepth is equal to 2, since 2 quadtree splits followed by 2 binary split are performed to generate blocks D and E. 
     According to the example, the threshold is set equal to 2. This means that at least 2 quadtree splits need to be performed (cqtDepth&gt;=2) in order for the current block and a neighbor block to be processed in parallel. 
     In the example on the left, block B (current block) cannot be processed in parallel to block A (neighbor block) although cqtDepth of block B is 1, since blocks A and B are inside the same MER. 
     Block E (current block) can be processed in parallel to block C and D (neighbor blocks), since the cqtDepth of block E is equal to 2, which is equal to the threshold. Note: As mentioned earlier, the JVET-K1001 prohibits quadtree splits after binary or ternary split. 
     Solution 10 is a harmonizing solution to have the solution 9 adapted to history-based motion vector prediction as disclosed in “CE4-related: History-based Motion Vector Prediction”, it might be possible that some of the neighbor blocks might not be spatially adjacent to the current block. In other words, the method described in the referenced technology constructs a list of motion vectors from blocks that might not be adjacent to the current block. 
     Solution 10, 
     New MER Conditions: 
     Depending on the neighboring block that is going to be checked; 
     If neighbor block belongs to the history-based candidate list, Coord2 is set equal to the top-left coordinate of the neighbor block, Coord1 is set equal to the top-left coordinate of the current block. Alternatively, Coord2 is set equal to the bottom-right coordinate of the neighbor block, Coord1 is set equal to the top-left coordinate of the current block. 
     If the following conditions are true, the neighboring block is set unavailable for prediction of the current block.
         Coord2 and Coord 1 are inside the same MER.   cqtDepth of the current block is greater than or equal to a threshold (qtDepthThr).       

     Advantageously in solutions 9 and 10, the quadtree depth threshold (qtDepthThr) and the size of the MER (Merge Estimation Region) are preferably obey the following equations: 
       Width of MER=(width of CTB)/2 qtDepthThr    
       Height of MER=(height of CTB)/2 qtDepthThr    
     Advantageously, the width and height of the MER is equal to each other according to the above equations in solutions 1 to 10, since the width and height of the Coding Tree Block are defined to be equal in the prior art document WET-K1001-v4. 
     Advantageously in solutions 9 and 10: 
     qtDepthThr and/or size of the MER can be signaled in a parameter set such as Sequence Parameter Set, Picture Parameter Set, slice header etc. 
     Advantageously, in the solutions 1 to 10, a neighbor block is set unavailable for prediction by the current block, if the current block is coded using merge mode. 
     Advantageously, in the solutions 1 to 10, a neighbor block is set unavailable for prediction by the current block, if the current block is coded using affine merge mode. 
     Advantageously in the solutions 1 to 10, a neighbor block is set unavailable for prediction by the current block, if the current block is coded using an inter prediction mode where motion vector difference is not signaled. Please note that the motion vector used for inter prediction of a current block is given by the summation of a motion vector predictor and motion vector difference. According to present invention, a neighbor block is set unavailable for prediction by the current block if the current block is coded using an inter prediction mode where motion vector difference is not signaled and inferred to be zero in length. 
     Advantageously in the solutions 1 to 10, a neighbor block is set unavailable for prediction by the current block if the current block is coded using an inter prediction mode where the motion vector difference can only have predefined values. For example, one such inter prediction mode is exemplified in document JVET-K0115, “CE4 Ultimate motion vector expression in J0024 (Test 4.2.9)” of Joint Video Experts Team (WET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 11th Meeting: Ljubljana, SI, 10-18 Jul. 2018. In this document, an inter prediction mode is exemplified where the motion vector difference cannot have any arbitrary value. Instead, the motion vector difference can only assume specific predefined values. If the current coding block is coded using this inter prediction mode, it is advantageous to apply solutions 1 to 10. In the document JVET-K0115 it is also mentioned that the proposed method is applied when the current block is coded using merge mode. 
     Solution 11 
     According to an embodiment, the marking of the candidate coding block includes: obtain coordinates (x, y) of a corner of the current coding block; obtain, as the predefined location, coordinates of a specific point (x1, y1), wherein the specific point is a bottom-right corner or a top-left corner of the candidate coding block; and mark the candidate coding block as unavailable,
         if floor(x1/mer_width) is equal to floor(x/mer_width); or   if floor(y1/mer_height) is equal to floor(y/mer_height),
 
wherein mer_height is a height and mer_width is a width of the current MER.
       

     Each of the two MER conditions may be extended/modified further as shown by the embodiment below. 
     According to an embodiment, the marking of the candidate coding block includes: obtain coordinates (x, y) of a corner of the current coding block; obtain, as the predefined location, coordinates of a specific point (x1, y1), wherein the specific point is a bottom right corner or a top-left corner of the candidate coding block; and mark the candidate coding block as unavailable,
         if floor(x1/mer_width) is equal to floor(x/mer_width) and floor(y1/mer_height)&gt;=floor(y/mer_height); or   if floor(y1/mer_height) is equal to floor(y/mer_height) and floor(x1/mer_width)&gt;=floor(x/mer_width);
 
wherein mer_height is a height and mer_width is a width of the current MER.
       

     New MER Conditions: 
     According to an embodiment, the marking of the candidate coding block includes: obtain coordinates (X, Y) of a corner of the current coding block; obtain, as a predefined location, coordinates of a specific point (X2, Y2), wherein the specific point is a bottom-right corner of the candidate coding block; and mark the candidate coding block as unavailable, if any of the following condition is satisfied:
         if floor(X2/mer_width) is equal to floor(X/mer_width) and floor(Y2/mer_height)&gt;=floor(Y/mer_height); and/or   if floor(Y2/mer_height) is equal to floor(Y/mer_height) and floor(X2/mer_width)&gt;=floor(X/mer_width);
 
wherein mer_height is a height and mer_width is a width of the current MER.
       

     Assume that the [X,Y] are the top-left coordinate of the current block. 
     Assume [X2, Y2] are the bottom-right coordinate of a second block. 
     Assume that the width and height of the MER region given by MER_width and MER_height. 
     If floor(X2/MER_width) is equal to floor(X/MER_width) and Y2&gt;=Y, motion information candidates of second block are set unavailable for prediction. 
     If floor(Y2/MER_height) is equal to floor(Y/MER_height) and X2&gt;=X, motion information candidates of second block are set unavailable for prediction. 
     If floor(Y2/MER_height) is equal to floor(Y/MER_height) and floor(X2/MER_width) is equal to floor(X/MER_width), motion information candidates of second block are set unavailable for prediction. 
     Solution 11 can be implemented in an alternative way as follows: 
     If floor(X2/MER_width) is equal to floor(X/MER_width) and floor(Y2/MER_height)&gt;=floor(Y/MER_height), motion information candidates of second block are set unavailable for prediction. 
     If floor(X2/MER_width) is equal to floor(X/MER_width) and floor(Y2/MER_Height)&gt;=floor(Y/MER_height), motion information candidates of second block are set unavailable for prediction. 
     The neighboring block might have been set available/unavailable for prediction by a preceding process. The invention modifies the setting. This solution is actually identical to solution 2, if only adjacent spatial neighbor blocks are used for motion vector prediction (like in the case of H.265/HEVC video coding standard). However, if non-adjacent spatial neighbors are used, such as in prior art “CE4-related: History-based Motion Vector Prediction”, then the present solution 10 would increase the coding gain with respect to solution 2. 
     As an example, solution 11 is applied to the VVC with the following form. 
     Derivation process for neighboring block availability according to parallel merge estimation 
     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 luma location (xNb, yNb) inside the neighbouring luma coding block relative to the top-left luma sample of the current picture, a variable availableFlag indicating the availability of the neighbouring block.
 
Output of this process is the modified availableFlag. xNbBR and yNbBR are set equal to CbPosX[xNb][yNb]+CbWidth[xNb][yNb]−1 and CbPosY[xNb][yNb]+CbHeight[xNb][yNb]−1, which means the bottom right pixel of the neighbouring block.
 
     If the variable availableFlag is equal to 1 and if any of the following conditions are true, the availableFlag is set equal to 0 which means the neighbouring luma coding block is not available: 
     xCb&gt;&gt;Log2ParMrgLevel is equal to xNbBR&gt;&gt;Log2ParMrgLevel and yNbBR&gt;&gt;Log2ParMrgLevel is greater than or equal to yCb&gt;&gt;Log2ParMrgLevel,
 
yCb&gt;&gt;Log2ParMrgLevel is equal to yNbBR&gt;&gt;Log2ParMrgLevel and xNbBR&gt;&gt;Log2ParMrgLevel is greater than or equal to xCb&gt;&gt;Log2ParMrgLevel.
 
     The MER condition(s) may be also formulated without the floor function. 
     According to an embodiment, the marking of the candidate coding block includes: obtain coordinates (X, Y) of a corner of the current coding block; obtain, a the predefined location, coordinates (X2, Y2) of a specific point, wherein the specific point is a bottom-right corner of the candidate coding block; and mark the candidate coding block as unavailable if any of the following condition is satisfied:
         if X2/mer_width is equal to X/mer_width and Y2/mer_height&gt;=Y/mer_height; and/or   if Y2/mer_height is equal to Y/mer_height and X2/mer_width&gt;=X/mer_width,
 
wherein mer_height is a height and mer_width is a width of the current MER.
       

     According to an embodiment, the marking of the candidate coding block includes: obtain coordinates (X, Y) of a corner of the current coding block; obtain, as the predefined location, coordinates (X2, Y2) of a specific point, wherein the specific point is a bottom-right corner of the candidate coding block; and mark the candidate coding block as unavailable if any of the following condition is satisfied:
         if X2&gt;&gt;log2_mer_width is equal to X&gt;&gt;log2_mer_width and Y2&gt;&gt;log2_mer_height&gt;=Y&gt;&gt;log2_mer_height; and/or   if Y2&gt;&gt;log2_mer_height is equal to Y&gt;&gt;log2_mer_height and X2&gt;&gt;log2_mer_width&gt;=X&gt;&gt;log2_mer_width;
 
wherein log2_mer_height and log2_mer_width are the binary logarithm of a height and a width of the current MER.
       

     In VVC, a coding tree block (CTB) can be recursively split into progressively smaller coding blocks using binary tree, ternary tree, and quadtree splitting. If a coding block (parent) is split using quadtree split, 4 child blocks are generated. If a coding block (parent) is split using ternary split, 3 child blocks are generated. Similarly, 2 child blocks are generated after a binary split. The block that is split is called a parent block and the resulting partitions are called child blocks. The child-parent block relationships are established recursively until the child block is decided to be not further split. In this case, the resulting child block is called a leaf block (or can be called a leaf node). The splitting decisions are inserted in the bitstream. As a result of the splitting process, a CTB is split into one or more leaf nodes that have different sizes and shapes. The total number of splitting operations (starting from a CTB) might be different for different child blocks. 
     Solution 12: 
     According to solution 12, two leaf blocks are considered to be in the same merge estimation region if both of the following conditions are satisfied: 
     two leaf blocks belong to a same parent block (or parent of a parent block, or parent of a parent of a parent block etc.) and
 
the same parent block is smaller in size than a threshold.
 
     If the two leaf blocks are considered to be in the same merge estimation region, motion information of the first leaf block in coding order is set unavailable for prediction by the second block. Otherwise, the motion information of the first leaf block is set available for prediction by the first block. 
     It is noted that due to the recursive splitting process, a leaf block might have more than one parent block at different hierarchy levels (direct parent, parent of parent etc.). According to solution 12, if there is at least one parent block (at any hierarchy level) that contains the two leaf blocks, they (the two leaf blocks) are considered to belong to the same parent block. Moreover, the hierarchy level might be different for the two leaf blocks, meaning that the number of splitting operations starting from the parent block to obtain the leaf block might be different for the two leaf blocks. 
     According to one specific implementation, the size threshold is computed as the number of pixel samples inside a parent coding block, which is computed as width multiplied by height of that coding block. According to another implementation of solution 12, the threshold is a positive integer number and the size of a block is computed based on the width of the block. According to a third specific implementation of solution 12, the threshold is a positive integer number and the size of a block is computed based on the height of the block. In general the size of a block is computed based on the width and the height of the block, taking both of them into account. 
     Solution 13: 
     According to solution 13, two leaf blocks are considered to be in the same merge estimation region if both of the following conditions are satisfied: 
     they belong to a same parent block (or recursively parent of a parent block, or parent of a parent of a parent block etc.) and
 
the number of splitting operations that are performed in order to obtain the parent block are greater than a threshold.
 
     If the two leaf blocks are considered to be in the same merge estimation region, motion information of the first block in coding order is set unavailable for prediction by the second block. Otherwise, the motion information of the first block is set available for prediction by the first block. 
     According to solution 13, the threshold comparison is performed based on the number of quadtree, binary tree, and ternary tree splitting operations that were performed in order to obtain the parent block. As an example, assume that the number of quadtree splitting operations that are performed to obtain the parent block is represented by qtDepthThr and the number of binary and ternary tree splitting operations that are performed are represented collectively by mttDepth (the terms qtDepth and mttDepth are used according to the document NET-L1001-v1, Versatile Video Coding (Draft 3), which can be obtained from the website http://phenix.it-sudparis.eu/jvet. qtDepth denotes the quadtree partition depth, which is equivalent to number of quadtree splitting operations that are performed to obtain a block. mttDepth denotes the multi-type tree partition depth, which is equivalent to number of binary tree and ternary tree splitting operations that are performed to obtain a block). Then, according to solution 13, any two leaf blocks that belong to the same parent block are considered to be in the same MER, if the qtDepth plus K multiplied by mttDepth is greater than a specified threshold value (qtDepth+K×mttDepth&gt;Thr). 
     K and Thr can be an integer number 0, 1, 2, . . . K and the threshold value can be predetermined or signalled in the bitstream. In one preferred implementation, K has a predetermined value of 2. In other words, Thr may be included into the bitstream and K may be a positive integer number or be zero. 
     The counting of number of quadtree, binary tree, and ternary tree splitting operations can be explained using  FIG. 10  and  FIG. 11 . As an example, block  34  has been obtained by one quadtree splitting of block  50 . According to  FIG. 11 , block  34  is a leaf block, which was obtained by one quadtree splitting operation and zero ternary and zero binary splitting operations. 
     According to  FIG. 11 , block  45  has been obtained by two quadtree splitting operations and one binary tree splitting operation. Block  50  (which is the CTB) is first split using quadtree splitting to obtain block  58 , block  58  is split using quadtree splitting to obtain block  62  and finally block  62  is split using binary splitting to obtain block  45 . 
     It is noted that the number of splitting operations are counted w.r.t. the coding tree block (CTB) which is considered as the starting point of the splitting operation. 
     Explanation of Solution 12: Accompanying figure  FIG. 23  presents the flowchart of the solution 12. It is noted that Block 1 is assumed to precede Block 2 in coding order. According to solution 12, first the parent blocks that are smaller than a specified threshold “Thr” of Block 1 and Block 2 are determined in a recursive manner in steps (S 3 , S 5 ) and in steps (S 4 , S 6 ), respectively. Parent1.1 represents the parent block of Block 1 and parent1.2 represents the parent block of parent1.1, and so on. Similarly, parent 2.1 represents the parent block of Block 2. 
     If, as a result of the test in step S 7 , a parent block of Block1 is the same block of a parent block of Block 2 (step S 8 ) and if the parent block is smaller than Thr in size, then the motion information of Block 1 is set unavailable for prediction of Block 2 (step S 10 ). If a parent block of Block1 is different from a parent block of Block1 (step S 9 ), the motion information of Block1 is then set as available for prediction of Block 2 (step S 11 ). 
     Similarly,  FIG. 23  can also be used to explain the Solution 13, where the size comparison is replaced by a comparison based on the number of quadtree, binary tree, and ternary tree splitting operations that were performed in order to obtain the parent block. 
     In an example, the function of splitting operations to obtain parentCand block greater than a threshold is implemented by qtDepth+K×mttDepth&gt;Thr, the qtDepth indicates the number of quadtree split operations that had been performed to obtain the parentCand, mttDepth indicates the number of binary split and ternary split operations that had been performed to obtain parentCand, Thr is the threshold. 
     In a second example, the function of splitting operations to obtain parentCand block greater than a threshold is implemented by number of “quadtree splitting+K×number of binary tree splitting+M×number of ternary tree splitting&gt;Thr”, Thr is the threshold 
     The motion information of the candidate block, which is marked as unavailable when current and candidate block have the same parent block, is not used in the prediction of the current block. 
     Similarly, the motion information of the candidate block is not used for the prediction, if the candidate is marked as unavailable and the current block is predicted using the merge prediction mode. 
     According to an embodiment, motion vector candidates, MVCs, are derived from the candidate coding block marked as available; and the current coding block is coded by referring to the MVCs. 
     According to an embodiment, an encoder is provided for encoding a current coding block within a coding tree unit, CTU, comprising a candidate list generator for generating a list of prediction candidates, including the apparatus for marking availability of a candidate coding block for merge estimation of the current coding block within the CTU according to any of the previous embodiments; a prediction unit for determining prediction of the current coding block according to at least one prediction candidate out of the generated list; and a compression unit for encoding the current coding block by using the prediction of the current coding block. 
     According to an embodiment, a decoder is provided for decoding a current coding block within a coding tree unit, CTU, comprising a candidate list generator for generating a list of prediction candidates, including the apparatus for marking availability of a candidate coding block for merge estimation of the current coding block within the CTU according to any of the previous embodiments; a prediction unit for determining prediction of the current coding block according to at least one prediction candidate out of the generated list; and a decompression unit for decoding the current coding block by using the prediction of the current coding block. 
     According to the encoder and/or decoder according to any of the previous embodiments, the list of prediction candidates is a list of motion vectors, MVs. 
     According to an embodiment, a method is provided for marking availability of a candidate coding block for merge estimation of a current coding block within a coding tree unit, CTU, comprising the steps of: marking the candidate coding block as available marking the candidate coding block as unavailable when a predefined location of the candidate coding block is included within an extended merge estimation region, MER, wherein the extended MER includes a current MER in which the current coding block is located and at least a portion of another MER, adjacent to the current MER. 
     According to an embodiment, a method is provided for marking availability of a candidate coding block for merge estimation of a current coding block within a coding tree unit, CTU, comprising the steps of: marking the candidate coding block as available labelling coding blocks of a CTU, including the current coding block and the candidate coding block, based on a processing order; forming a group of coding blocks by applying a slid window with a length of K; determining if the candidate coding block and the current coding block belong to the same one group of coding blocks; and marking the candidate coding block as unavailable if the candidate coding block and the current coding block belong to the same one group of coding blocks. 
     According to an embodiment, a computer-readable non-transitory medium is provided for storing a program, including instructions which when executed on a processor cause the processor to perform the method according to any of the above embodiments. 
     The motion compensation unit is configured to obtain, e.g. receive, an inter prediction parameter and to perform inter prediction based on or using the inter prediction parameter to obtain an inter prediction block  245 . Motion compensation, performed by motion compensation unit (not shown in  FIG. 2 ), may involve fetching or generating the prediction block based on the motion/block vector determined by motion estimation, possibly performing interpolations to sub-pixel precision. Interpolation filtering may generate additional pixel samples from known pixel samples, thus potentially increasing the number of candidate prediction blocks that may be used to code a picture block. Upon receiving the motion vector for the PU of the current picture block, the motion compensation unit  246  may locate the prediction block to which the motion vector points in one of the reference picture lists. Motion compensation unit  246  may also generate syntax elements associated with the blocks and the video slice for use by video decoder  300  in decoding the picture blocks of the video slice. 
     The intra prediction unit  254  is configured to obtain, e.g. receive, the picture block  203  (current picture block) and one or a plurality of previously reconstructed blocks, e.g. reconstructed neighbor blocks, of the same picture for intra estimation. The encoder  200  may, e.g., be configured to select an intra prediction mode from a plurality of (predetermined) intra prediction modes. 
     The arithmetic right shift operation is defined as follows: 
     x&gt;&gt;y Arithmetic right shift of a two&#39;s complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y. Bits shifted into the most significant bits (MSBs) as a result of the right shift have a value equal to the MSB of x prior to the shift operation. 
     The binary logarithm can be defined as follows: 
     the binary logarithm log 2 (n) is the power to which the number 2 must be raised to obtain the value n.
 
If x=log 2 (n), then 2 x =n
 
     According to above definitions, the following equality holds: 
     floor (X/mer_width)=X&gt;log2_mer_width, where log2_mer_width is the binary logarithm of mer_width. 
     Embodiments of the encoder  200  may be configured to select the intra-prediction mode based on an optimization criterion, e.g. minimum residual (e.g. the intra-prediction mode providing the prediction block  255  most similar to the current picture block  203 ) or minimum rate distortion. 
     The intra prediction unit  254  is further configured to determine based on intra prediction parameter, e.g. the selected intra prediction mode, the intra prediction block  255 . In any case, after selecting an intra prediction mode for a block, the intra prediction unit  254  is also configured to provide intra prediction parameter, i.e. information indicative of the selected intra prediction mode for the block to the entropy encoding unit  270 . In one example, the intra prediction unit  254  may be configured to perform any combination of the intra prediction techniques described later. 
     The entropy encoding unit  270  is configured to apply an entropy encoding algorithm or scheme (e.g. a variable length coding (VLC) scheme, an context adaptive VLC scheme (CALVC), an arithmetic coding scheme, a context adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy encoding methodology or technique) on the quantized residual coefficients  209 , inter prediction parameters, intra prediction parameter, and/or loop filter parameters, individually or jointly (or not at all) to obtain encoded picture data  21  which can be output by the output  272 , e.g. in the form of an encoded bitstream  21 . The encoded bitstream  21  may be transmitted to video decoder  30 , or archived for later transmission or retrieval by video decoder  30 . The entropy encoding unit  270  can be further configured to entropy encode the other syntax elements for the current video slice being coded. 
     Other structural variations of the video encoder  200  can be used to encode the video stream. For example, a non-transform based encoder  200  can quantize the residual signal directly without the transform processing unit  206  for certain blocks or frames. In another implementation, an encoder  200  can have the quantization unit  208  and the inverse quantization unit  210  combined into a single unit. 
       FIG. 3  shows an exemplary video decoder  300  that is configured to implement the techniques of this present application. The video decoder  300  configured to receive encoded picture data (e.g. encoded bitstream)  271 , e.g. encoded by encoder  200 , to obtain a decoded picture  331 . During the decoding process, video decoder  300  receives video data, e.g. an encoded video bitstream that represents picture blocks of an encoded video slice and associated syntax elements, from video encoder  200 . 
     In the example of  FIG. 3 , the decoder  300  comprises an entropy decoding unit  304 , an inverse quantization unit  310 , an inverse transform processing unit  312 , a reconstruction unit  314  (e.g. a summer  314 ), a buffer  316 , a loop filter  320 , a decoded picture buffer  330  and a prediction processing unit  360 . The prediction processing unit  360  may include an inter prediction unit  344 , an intra prediction unit  354 , and a mode selection unit  362 . Video decoder  300  may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder  200  from  FIG. 2 . 
     The entropy decoding unit  304  is configured to perform entropy decoding to the encoded picture data  271  to obtain, e.g., quantized coefficients  309  and/or decoded coding parameters (not shown in  FIG. 3 ), e.g. (decoded) any or all of inter prediction parameters, intra prediction parameter, loop filter parameters, and/or other syntax elements. Entropy decoding unit  304  is further configured to forward inter prediction parameters, intra prediction parameter and/or other syntax elements to the prediction processing unit  360 . Video decoder  300  may receive the syntax elements at the video slice level and/or the video block level. 
     The inverse quantization unit  310  may be identical in function to the inverse quantization unit  110 , the inverse transform processing unit  312  may be identical in function to the inverse transform processing unit  112 , the reconstruction unit  314  may be identical in function reconstruction unit  114 , the buffer  316  may be identical in function to the buffer  116 , the loop filter  320  may be identical in function to the loop filter  120 , and the decoded picture buffer  330  may be identical in function to the decoded picture buffer  130 . 
     The prediction processing unit  360  may comprise an inter prediction unit  344  and an intra prediction unit  354 , wherein the inter prediction unit  344  may resemble the inter prediction unit  144  in function, and the intra prediction unit  354  may resemble the intra prediction unit  154  in function. The prediction processing unit  360  are typically configured to perform the block prediction and/or obtain the prediction block  365  from the encoded data  21  and to receive or obtain (explicitly or implicitly) the prediction related parameters and/or the information about the selected prediction mode, e.g. from the entropy decoding unit  304 . 
     When the video slice is coded as an intra coded (I) slice, intra prediction unit  354  of prediction processing unit  360  is configured to generate prediction block  365  for a picture block of the current video slice based on a signaled intra prediction mode and data from previously decoded blocks of the current frame or picture. When the video frame is coded as an inter coded (i.e., B, or P) slice, inter prediction unit  344  (e.g. motion compensation unit) of prediction processing unit  360  is configured to produce prediction blocks  365  for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit  304 . For inter prediction, the prediction blocks may be produced from one of the reference pictures within one of the reference picture lists. Video decoder  300  may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference pictures stored in DPB  330 . 
     Prediction processing unit  360  is configured to determine prediction information for a video block of the current video slice by parsing the motion vectors and other syntax elements, and uses the prediction information to produce the prediction blocks for the current video block being decoded. For example, the prediction processing unit  360  uses some of the received syntax elements to determine a prediction mode (e.g., intra or inter prediction) used to code the video blocks of the video slice, an inter prediction slice type (e.g., B slice, P slice, or GPB slice), construction information for one or more of the reference picture lists for the slice, motion vectors for each inter encoded video block of the slice, inter prediction status for each inter coded video block of the slice, and other information to decode the video blocks in the current video slice. 
     Inverse quantization unit  310  is configured to inverse quantize, i.e., de-quantize, the quantized transform coefficients provided in the bitstream and decoded by entropy decoding unit  304 . The inverse quantization process may include use of a quantization parameter calculated by video encoder  100  for each video block in the video slice to determine a degree of quantization and, likewise, a degree of inverse quantization that should be applied. 
     Inverse transform processing unit  312  is configured to apply an inverse transform, e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process, to the transform coefficients in order to produce residual blocks in the pixel domain. 
     The reconstruction unit  314  (e.g. Summer  314 ) is configured to add the inverse transform block  313  (i.e. reconstructed residual block  313 ) to the prediction block  365  to obtain a reconstructed block  315  in the sample domain, e.g. by adding the sample values of the reconstructed residual block  313  and the sample values of the prediction block  365 . 
     The loop filter unit  320  (either in the coding loop or after the coding loop) is configured to filter the reconstructed block  315  to obtain a filtered block  321 , e.g. to smooth pixel transitions, or otherwise improve the video quality. In one example, the loop filter unit  320  may be configured to perform any combination of the filtering techniques described later. The loop filter unit  320  is intended to represent one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or other filters, e.g. a bilateral filter or an adaptive loop filter (ALF) or a sharpening or smoothing filters or collaborative filters. Although the loop filter unit  320  is shown in  FIG. 3  as being an in loop filter, in other configurations, the loop filter unit  320  may be implemented as a post loop filter. 
     The decoded video blocks  321  in a given frame or picture are then stored in decoded picture buffer  330 , which stores reference pictures used for subsequent motion compensation. 
     The decoder  300  is configured to output the decoded picture  311 , e.g. via output  312 , for presentation or viewing to a user. 
     Other variations of the video decoder  300  can be used to decode the compressed bitstream. For example, the decoder  300  can produce the output video stream without the loop filtering unit  320 . For example, a non-transform based decoder  300  can inverse-quantize the residual signal directly without the inverse-transform processing unit  312  for certain blocks or frames. In another implementation, the video decoder  300  can have the inverse-quantization unit  310  and the inverse-transform processing unit  312  combined into a single unit. 
       FIG. 4  is a schematic diagram of a network device  400  (e.g., a coding device) according to an embodiment of the disclosure. The network device  400  is suitable for implementing the disclosed embodiments as described herein. In an embodiment, the network device  400  may be a decoder such as video decoder  300  of  FIG. 1A  or an encoder such as video encoder  200  of  FIG. 1A . In an embodiment, the network device  400  may be one or more components of the video decoder  300  of  FIG. 1A  or the video encoder  200  of  FIG. 1A  as described above. 
     The network device  400  comprises ingress ports  410  and receiver units (Rx)  420  for receiving data; a processor, logic unit, or central processing unit (CPU)  430  to process the data; transmitter units (Tx)  440  and egress ports  450  for transmitting the data; and a memory  460  for storing the data. The network device  400  may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the ingress ports  410 , the receiver units  420 , the transmitter units  440 , and the egress ports  450  for egress or ingress of optical or electrical signals. 
     The processor  430  is implemented by hardware and software. The processor  430  may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), FPGAs, ASICs, and DSPs. The processor  430  is in communication with the ingress ports  410 , receiver units  420 , transmitter units  440 , egress ports  450 , and memory  460 . The processor  430  comprises a coding module  470 . The coding module  470  implements the disclosed embodiments described above. For instance, the coding module  470  implements, processes, prepares, or provides the various coding operations. The inclusion of the coding module  470  therefore provides a substantial improvement to the functionality of the network device  400  and effects a transformation of the network device  400  to a different state. Alternatively, the coding module  470  is implemented as instructions stored in the memory  460  and executed by the processor  430 . 
     The memory  460  comprises one or more disks, tape drives, and solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory  460  may be volatile and/or non-volatile and may be read-only memory (ROM), random access memory (RAM), ternary content-addressable memory (TCAM), and/or static random-access memory (SRAM). 
       FIG. 5  is a simplified block diagram of an apparatus  500  that may be used as either or both of the source device  12  and the destination device  14  from  FIG. 1A  according to an exemplary embodiment. The apparatus  500  can implement techniques of this present application. The apparatus  500  can be in the form of a computing system including multiple computing devices, or in the form of a single computing device, for example, a mobile phone, a tablet computer, a laptop computer, a notebook computer, a desktop computer, and the like. 
     A processor  502  in the apparatus  500  can be a central processing unit. Alternatively, the processor  502  can be any other type of device, or multiple devices, capable of manipulating or processing information now-existing or hereafter developed. Although the disclosed implementations can be practiced with a single processor as shown, e.g., the processor  502 , advantages in speed and efficiency can be achieved using more than one processor. 
     A memory  504  in the apparatus  500  can be a read only memory (ROM) device or a random access memory (RAM) device in an implementation. Any other suitable type of storage device can be used as the memory  504 . The memory  504  can include code and data  506  that is accessed by the processor  502  using a bus  512 . The memory  504  can further include an operating system  508  and application programs  510 , the application programs  510  including at least one program that permits the processor  502  to perform the methods described here. For example, the application programs  510  can include applications  1  through N, which further include a video coding application that performs the methods described here. The apparatus  500  can also include additional memory in the form of a secondary storage  514 , which can, for example, be a memory card used with a mobile computing device. Because the video communication sessions may contain a significant amount of information, they can be stored in whole or in part in the secondary storage  514  and loaded into the memory  504  as needed for processing. 
     The apparatus  500  can also include one or more output devices, such as a display  518 . The display  518  may be, in one example, a touch sensitive display that combines a display with a touch sensitive element that is operable to sense touch inputs. The display  518  can be coupled to the processor  502  via the bus  512 . Other output devices that permit a user to program or otherwise use the apparatus  500  can be provided in addition to or as an alternative to the display  518 . When the output device is or includes a display, the display can be implemented in various ways, including by a liquid crystal display (LCD), a cathode-ray tube (CRT) display, a plasma display or light emitting diode (LED) display, such as an organic LED (OLED) display. 
     The apparatus  500  can also include or be in communication with an image-sensing device  520 , for example a camera, or any other image-sensing device  520  now existing or hereafter developed that can sense an image such as the image of a user operating the apparatus  500 . The image-sensing device  520  can be positioned such that it is directed toward the user operating the apparatus  500 . In an example, the position and optical axis of the image-sensing device  520  can be configured such that the field of vision includes an area that is directly adjacent to the display  518  and from which the display  518  is visible. 
     The apparatus  500  can also include or be in communication with a sound-sensing device  522 , for example a microphone, or any other sound-sensing device now existing or hereafter developed that can sense sounds near the apparatus  500 . The sound-sensing device  522  can be positioned such that it is directed toward the user operating the apparatus  500  and can be configured to receive sounds, for example, speech or other utterances, made by the user while the user operates the apparatus  500 . 
     Although  FIG. 5  depicts the processor  502  and the memory  504  of the apparatus  500  as being integrated into a single unit, other configurations can be utilized. The operations of the processor  502  can be distributed across multiple machines (each machine having one or more of processors) that can be coupled directly or across a local area or other network. The memory  504  can be distributed across multiple machines such as a network-based memory or memory in multiple machines performing the operations of the apparatus  500 . Although depicted here as a single bus, the bus  512  of the apparatus  500  can be composed of multiple buses. Further, the secondary storage  514  can be directly coupled to the other components of the apparatus  500  or can be accessed via a network and can comprise a single integrated unit such as a memory card or multiple units such as multiple memory cards. The apparatus  500  can thus be implemented in a wide variety of configurations. 
     In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium. 
     By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
     Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements. 
     The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware. 
     While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented. 
     In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein. 
     Summarizing, the present disclosure relates to an apparatus and method for marking availability of a candidate coding block for merge estimation of a current coding block within a coding tree unit, CTU, which includes multiple coding blocks. Initially, the candidate coding block is marked as available. The candidate coding block is marked as unavailable when a predefined location of the candidate coding block is included within an extended merge estimation region, MER. The extended MER includes a current MER in which the current coding block is located and at least a portion of another MER, adjacent to the current MER. The predefined location may be a top-left or bottom-right (pixel) position of a corner of the candidate coding block. Whether the candidate coding block is located within the extended MER is determined in dependence on the positional relation between the predefined location and a position of a corner of the current coding block, with the corner being any of the upper-left, bottom-left, or bottom-right. The coding blocks may be labelled based on a processing order and grouped using a slid window. When the candidate and current coding blocks are in the same group, the candidate coding block is marked as unavailable. 
     Additional embodiments are summarized in the following clauses. 
     Clause 1: A method of coding implemented by an encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising:
         obtaining the coordination (x, y) of a corner of the current coding block, and the coordination of a specific point in the potential candidate coding block, wherein the coordination of the specific point in the potential candidate coding block is (x+a, y+b), a∈(−1,0,1), b∈(−1,0,1), and a and b are selected depends on the relationship of the relative position between the potential candidate coding block and the current coding block, and for one potential candidate coding block, one value from (−1,0,1) is selected as the a, and one value from the (−1,0,1) is selected as the b;   marking the potential candidate coding block as unavailable, if floor((x+a)/mer_width) is equal to floor(x/mer_width), where the mer_width is the width of a merge estimation region (MER), or if floor((y+b)/mer_width) is equal to floor(y/mer_height), where the mer_height is the height of the merge estimation region (MER), and the floor function that takes as input a real number X and gives as output the greatest integer less than or equal to X.       

     Clause 2: The method of clause 1, wherein, the potential candidate coding block neighbors to the corner of the current coding block, and
         the corner of the current coding block is bottom left corner, and the potential candidate coding block located on where there is left to the current coding block, a=−1, b=0; or   the corner of the current coding block is bottom left corner, and the potential candidate coding block located on where there is bottom-left to the current coding block, a=−1, b=1; or   the corner of the current coding block is upper left corner, and the potential candidate coding block located on where there is upper-left to the current coding block, a=−1, b=−1; or   the corner of the current coding block is upper right corner, and the potential candidate coding block located on where there is upper-right to the current coding block, a=1, b=−1; or   the corner of the current coding block is upper right corner, and the potential candidate coding block located on where there is upper to the current coding block, a=0, b=−1.       

     Clause 3: A method of coding implemented by a encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising:
         obtaining the coordination (x, y) of a corner of the current coding block, and the coordination of a specific point in the potential candidate coding block, wherein the potential candidate coding block neighbors to the corner of the current coding block and the coordination of the specific point in the potential candidate coding block is (x+a, y+b), a∈(−1,0,1), b∈(−1,0,1), and a and b are not both equal to 0 or 1 and selected depends on the relationship of the relative position between the potential candidate coding block and the current coding block, and for one potential candidate coding block, one value from (−1,0,1) is selected as the a, and one value from the (−1,0,1) is selected as the b;   marking the potential candidate coding block as unavailable, when floor((x+a)/mer_width) is equal to floor(x/mer_width), and floor((y+b)/mer_height)&gt;=floor(y/mer_height), or when floor((y+b)/mer_height) is equal to floor(y/mer_height) and floor((x+a)/mer_width)&gt;=floor(x/mer_width), where the mer_height and mer_width are the height and the width of the merge estimation region (MER), and the function that takes as input a real number X and gives as output the greatest integer less than or equal to X.       

     Clause 4: The method of clause 3, wherein,
         the corner of the current coding block is bottom left corner, and the potential candidate coding block located on where there is left to the current coding block, a=−1, b=0;   or the corner of the current coding block is bottom left corner, and the potential candidate coding block located on where there is bottom-left to the current coding block, a=−1, b=1;   or the corner of the current coding block is upper left corner, and the potential candidate coding block located on where there is upper-left to the current coding block, a=−1, b=−1;   or the corner of the current coding block is upper right corner, and the potential candidate coding block located on where there is upper-right to the current coding block, a=1, b=−1;   or the corner of the current coding block is upper right corner, and the potential candidate coding block located on where there is upper to the current coding block, a=0, b=−1.       

     Clause 5: A method of coding implemented by a encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising:
         obtaining the coordination (x, y) of a corner of the current coding block, and the coordination of a specific point in the potential candidate coding block, wherein the coordination of the specific point in the potential candidate coding block is the coordination (x1, y1) of the bottom right corner of the potential candidate coding block or the top-left corner of the potential candidate coding block;   marking the potential candidate coding block as unavailable, if floor(x1/mer_width) is equal to floor(x/mer_width), or floor(y1/mer_height) is equal to floor(y/mer_height), the mer_height and mer_width are the height and the width of the merge estimation region (MER), and the function that takes as input a real number X and gives as output the greatest integer less than or equal to X.       

     Clause 6: A method of coding implemented by a encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising:
         obtaining the coordination (x, y) of a corner of the current coding block, and the coordination of a specific point in the potential candidate coding block, wherein the coordination of the specific point in the potential candidate coding block is the coordination (x1, y1) of the bottom right corner of the potential candidate coding block or the top-left corner of the potential candidate coding block;   marking the potential candidate coding block as unavailable, if floor(x1/mer_width) is equal to floor(x/mer_width) and floor(y1/mer_height)&gt;=floor(y/mer_height), or floor(y1/mer_height) is equal to floor(y/mer_height) and floor(x1/mer_width)&gt;=floor(x/mer_width), the mer_height and mer_width are the height and the width of the merge estimation region (MER), and the function that takes as input a real number X and gives as output the greatest integer less than or equal to X.       

     Clause 7: A method of coding implemented by a encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising:
         obtaining the coordination (x, y) of a corner of the current coding block, and the coordination of a specific point in the potential candidate coding block, wherein the coordination of the specific point in the potential candidate coding block is (x+a, y+b), a∈(−1,0,1), b∈(−1,0,1), and a and b are selected depends on the relationship of the relative position between the potential candidate coding block and the current coding block, and for one potential candidate coding block, one value from (−1,0,1) is selected as the a, and one value from the (−1,0,1) is selected as the b;   marking the potential candidate coding block as unavailable, when the (x, y) and the (x+a, y+b) are located within one merge estimation region (MER), and the cqtDepth of the current coding block is greater or equal to a threshold, where the cqtDepth is a parameter that decide the quad-tree partition depth of a coding tree block to which the current coding block belongs.       

     Clause 8: The method of clause 7, wherein,
         the corner of the current coding block is bottom left corner, and the potential candidate coding block located on where there is left to the current coding block, a=−1, b=0;   or the corner of the current coding block is bottom left corner, and the potential candidate coding block located on where there is bottom-left to the current coding block, a=−1, b=1;   or the corner of the current coding block is upper left corner, and the potential candidate coding block located on where there is upper-left to the current coding block, a=−1, b=−1;   or the corner of the current coding block is upper right corner, and the potential candidate coding block located on where there is upper-right to the current coding block, a=1, b=−1;   or the corner of the current coding block is upper right corner, and the potential candidate coding block located on where there is upper to the current coding block, a=0, b=−1.       

     Clause 9: A method of coding implemented by a encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising: 
     obtaining the coordination (x, y) of a corner of the current coding block, and the coordination of a specific point in the potential candidate coding block, wherein the coordination of the specific point in the potential candidate coding block is the coordination (x1, y1) of the top-left corner of the potential candidate coding block, or the bottom-right corner of the potential candidate coding block;
 
when the (x, y) and the (x1, y1) are located within one merge estimation region (MER), and the cqtDepth of the current coding block is greater or equal to a threshold, qtDepthThr, where the cqtDepth is a parameter that decide the quad-tree partition depth of a coding tree block to which the current coding block belongs.
 
     Clause 10: The method of clause 9, where in the width of MER=(width of CTB)/2 qtDepthThr , the height of MER=(height of CTB)/2 qtDepthThr . 
     Clause 11: A device for coding image, which comprises a processer and a memory storing a series of instructions and coupling with the processor, the processor implementing the instructions for performing any of clauses 1 to 10. 
     Clause 12: An encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising:
         coordination obtaining module, configured for, obtaining the coordination (x, y) of a corner of the current coding block, and the coordination of a specific point in the potential candidate coding block, wherein the coordination of the specific point in the potential candidate coding block is (x+a, y+b), a∈(−1,0,1), b∈(−1,0,1), and a and b are selected depends on the relationship of the relative position between the potential candidate coding block and the current coding block, and for one potential candidate coding block, one value from (−1,0,1) is selected as the a, and one value from the (−1,0,1) is selected as the b; and   marking module, configured for, marking the potential candidate coding block as unavailable, if floor((x+a)/mer_width) is equal to floor(x/mer_width), where the mer_width is the width of a merge estimation region (MER), or floor((y+b)/mer_height) is equal to floor(y/mer_height), where the mer_height is the height of the merge estimation region (MER), and the function that takes as input a real number X and gives as output the greatest integer less than or equal to X.       

     Clause 13: The method of clause 12, wherein, the potential candidate coding block neighbors to the corner of the current coding block, and
         the corner of the current coding block is bottom left corner, and the potential candidate coding block located on where there is left to the current coding block, a=−1, b=0; or   the corner of the current coding block is bottom left corner, and the potential candidate coding block located on where there is bottom-left to the current coding block, a=−1, b=1; or   the corner of the current coding block is upper left corner, and the potential candidate coding block located on where there is upper-left to the current coding block, a=−1, b=−1; or   the corner of the current coding block is upper right corner, and the potential candidate coding block located on where there is upper-right to the current coding block, a=1, b=−1; or   the corner of the current coding block is upper right corner, and the potential candidate coding block located on where there is upper to the current coding block, a=0, b=−1.       

     Clause 14: An encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising:
         coordination obtaining module, configured for, obtaining the coordination (x, y) of a corner of the current coding block, and the coordination of a specific point in the potential candidate coding block, wherein the potential candidate coding block neighbors to the corner of the current coding block and the coordination of the specific point in the potential candidate coding block is (x+a, y+b), a∈(−1,0,1), b∈(−1,0,1), and a and b are not both equal to 0 or 1 and selected depends on the relationship of the relative position between the potential candidate coding block and the current coding block, and for one potential candidate coding block, one value from (−1,0,1) is selected as the a, and one value from the (−1,0,1) is selected as the b;   marking module, configured for, marking the potential candidate coding block as unavailable, when floor((x+a)/mer_width) is equal to floor(x/mer_width) and floor ((y+b)/mer_height)&gt;=floor(y/mer_height), or floor((y+b)/mer_height) is equal to floor(y/mer_height) and floor((x+a)/mer_width)&gt;=floor(x/mer_width), where the mer_height and mer_width are the height and the width of the merge estimation region (MER), and the function that takes as input a real number X and gives as output the greatest integer less than or equal to X and when where the mer_height is the height of the merge estimation region.       

     Clause 15: The device of clause 14, wherein,
         the corner of the current coding block is bottom left corner, and the potential candidate coding block located on where there is left to the current coding block, a=−1, b=0;   or the corner of the current coding block is bottom left corner, and the potential candidate coding block located on where there is bottom-left to the current coding block, a=−1, b=1;   or the corner of the current coding block is upper left corner, and the potential candidate coding block located on where there is upper-left to the current coding block, a=−1, b=−1;   or the corner of the current coding block is upper right corner, and the potential candidate coding block located on where there is upper-right to the current coding block, a=1, b=−1;   or the corner of the current coding block is upper right corner, and the potential candidate coding block located on where there is upper to the current coding block, a=0, b=−1.       

     Clause 16: A encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising:
         coordination obtaining module, configured for, obtaining the coordination (x, y) of a corner of the current coding block, and the coordination of a specific point in the potential candidate coding block, wherein the coordination of the specific point in the potential candidate coding block is the coordination (x1, y1) of the bottom right corner of the potential candidate coding block or the top-left corner of the potential candidate coding block; and   marking module, configured for, marking the potential candidate coding block as unavailable, if floor(x1/mer_width) is equal to floor(x/mer_width) and floor(y1/mer_height)&gt;=floor(y/mer_height), or floor(y1/mer_height) is equal to floor(y/mer_height) and floor (x1/mer_width)&gt;=floor(x/mer_width), where the mer_width and mer_height are the width and the height of a merge estimation region (MER), and the function that takes as input a real number X and gives as output the greatest integer less than or equal to X,       

     Clause 17: An encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising:
         obtaining the coordination (x, y) of a corner of the current coding block, and the coordination of a specific point in the potential candidate coding block, wherein the coordination of the specific point in the potential candidate coding block is the coordination (x1, y1) of the bottom right corner of the potential candidate coding block or the top-left corner of the potential candidate coding block; and   marking module, configured for, marking the potential candidate coding block as unavailable, if floor(x1/mer_width) is equal to floor(x/mer_width) and floor((y+b)/mer_height)&gt;=floor(y/mer_height), or floor((y+b)/mer_height) is equal to floor(y/mer_height) and floor ((x+a)/mer_width)&gt;=floor(x/mer_width), where the mer_width and mer_height are the width and the height of a merge estimation region (MER), and the function that takes as input a real number X and gives as output the greatest integer less than or equal to X.       

     Clause 18: An encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising:
         coordination obtaining module, configured for, obtaining the coordination (x, y) of a corner of the current coding block, and the coordination of a specific point in the potential candidate coding block, wherein the coordination of the specific point in the potential candidate coding block is (x+a, y+b), a∈(−1,0,1), b∈(−1,0,1), and a and b are selected depends on the relationship of the relative position between the potential candidate coding block and the current coding block, and for one potential candidate coding block, one value from (−1,0,1) is selected as the a, and one value from the (−1,0,1) is selected as the b; and   marking module, configured for, marking the potential candidate coding block as unavailable, when the (x, y) and the (x+a, y+b) are located within one merge estimation region (MER), and the cqtDepth of the current coding block is greater or equal to a threshold, where the cqtDepth is a parameter that decide the quad-tree partition depth of a coding tree block to which the current coding block belongs.       

     Clause 19: The device of clause 18, wherein,
         the corner of the current coding block is bottom left corner, and the potential candidate coding block located on where there is left to the current coding block, a=−1, b=0;   or the corner of the current coding block is bottom left corner, and the potential candidate coding block located on where there is bottom-left to the current coding block, a=−1, b=1;   or the corner of the current coding block is upper left corner, and the potential candidate coding block located on where there is upper-left to the current coding block, a=−1, b=−1;   or the corner of the current coding block is upper right corner, and the potential candidate coding block located on where there is upper-right to the current coding block, a=1, b=−1;   or the corner of the current coding block is upper right corner, and the potential candidate coding block located on where there is upper to the current coding block, a=0, b=−1.       

     Clause 20: An encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising:
         coordination obtaining module, configured for, obtaining the coordination (x, y) of a corner of the current coding block, and the coordination of a specific point in the potential candidate coding block, wherein the coordination of the specific point in the potential candidate coding block is the coordination (x1, y1) of the top-left corner of the potential candidate coding block, or the bottom-right corner of the potential candidate coding block; and   marking module, configured for, when the (x, y) and the (x1, y1) are located within one merge estimation region (MER), and the cqtDepth of the current coding block is greater or equal to a threshold, qtDepthThr, where the cqtDepth is a parameter that decide the quad-tree partition depth of a coding tree block to which the current coding block belongs.       

     Clause 21: The device of clause 20, where in the width of MER=(width of CTB)/2 qtDepthThr , the height of MER=(height of CTB)/2 qtDepthThr . 
     Clause 22: A method of coding implemented by an encoding/decoding device for marking the availability of a potential candidate coding block for merge estimation of a current coding block, comprising:
         obtaining the coordination of a specific point in the potential candidate coding block, and the coordination of the left-top pixel of the current coding block;   determining if the coordination of the specific point in the potential candidate coding block is located within a merge estimation region (MER) where the top-left pixel of the current coding block is located, by comparing the coordination of a specific point in the potential candidate coding block and the coordination of the left-top pixel of the current coding block, wherein the coordination is consisting of horizontal axis directing to right hand direction and labelled as X and a vertical axis directing to gravity direction and labelled as Y, the coordination of the specific point in the potential candidate coding block is indicated as (X2, Y2), and the coordination of the top-left pixel of the current coding block is indicated as (X, Y); and if the coordination of the specific point in the potential candidate coding block is located within the merge estimation region (MER), marking the potential candidate coding block as unavailable.       

     Clause 23: The method of clause 22, wherein, the specific point in the potential candidate coding block is the bottom-right pixel of the potential candidate coding block, and the determining if the coordination of the specific point in the potential candidate coding block is located within the MER is performed on any of the following rules:
         if [X−1, Y] and [X, Y] are in the same MER, and if X2&lt;X and Y2&gt;=Y, the potential candidate coding block is set unavailable;   if [X, Y−1] and [X, Y] are in the same MER, and if Y2&lt;Y and X2&gt;=X, the potential candidate coding block is set unavailable; and   if [X−1, Y−1] and [X, Y] are in the same MER, the potential candidate coding block is set unavailable.       

     Clause 24: The method of clause 22, wherein, the specific point in the potential candidate coding block is the bottom-right pixel of the potential candidate coding block, and the determining if the coordination of the specific point in the potential candidate coding block is located within the MER is performed on any of the following rules:
         if floor(X2/mer_width) is equal to floor(X/mer_width) and floor(Y2/mer_height)&gt;=floor(Y/mer_height), the potential candidate coding block is set unavailable; and   if floor(Y2/mer_height) is equal to floor(Y/mer_height) and floor(X2/mer_width)&gt;=floor(X/mer_width), the potential candidate coding block is set unavailable;
 
where the mer_height and mer_width are the height and the width of the merge estimation region (MER), and the function that takes as input a real number X and gives as output the greatest integer less than or equal to X.
       

     LIST OF REFERENCE SIGNS 
     
       FIG. 1A 
         
           10  video coding system 
           12  source device 
           13  communication channel 
           14  destination device 
           16  picture source 
           17  picture data 
           18  pre-processor 
           19  pre-processed picture data 
           20  video encoder 
           21  encoded picture data 
           22  communication interface 
           28  communication interface 
           30  video decoder 
           31  decoded picture data 
           32  post processor 
           33  post-processed picture data 
           34  display device 
       
    
     
       FIG. 1B 
         
           40  video coding system 
           41  imaging device(s) 
           42  antenna 
           43  processor(s) 
           44  memory store(s) 
           45  display device 
           46  processing circuitry 
           20  video encoder 
           30  video decoder 
       
    
     
       FIG. 2 
         
           17  picture (data) 
           19  pre-processed picture (data) 
           20  encoder 
           21  encoded picture data 
           201  input (interface) 
           204  residual calculation [unit or step] 
           206  transform processing unit 
           208  quantization unit 
           210  inverse quantization unit 
           212  inverse transform processing unit 
           214  reconstruction unit 
           220  loop filter unit 
           230  decoded picture buffer (DPB) 
           260  mode selection unit 
           270  entropy encoding unit 
           272  output (interface) 
           244  inter prediction unit 
           254  intra prediction unit 
           262  partitioning unit 
           203  picture block 
           205  residual block 
           213  reconstructed residual block 
           215  reconstructed block 
           221  filtered block 
           231  decoded picture 
           265  prediction block 
           266  syntax elements 
           207  transform coefficients 
           209  quantized coefficients 
           211  dequantized coefficients 
       
    
     
       FIG. 3 
         
           21  encoded picture data 
           30  video decoder 
           304  entropy decoding unit 
           309  quantized coefficients 
           310  inverse quantization unit 
           311  dequantized coefficients 
           312  inverse transform processing unit 
           313  reconstructed residual block 
           314  reconstruction unit 
           315  reconstructed block 
           320  loop filter 
           321  filtered block 
           330  decoded picture buffer DBP 
           331  decoded picture 
           360  mode application unit 
           365  prediction block 
           366  syntax elements 
           344  inter prediction unit 
           354  intra prediction unit 
       
    
     
       FIG. 4 
         
           400  video coding device 
           410  ingress ports/input ports 
           420  receiver units Rx 
           430  processor 
           440  transmitter units Tx 
           450  egress ports/output ports 
           460  memory 
           470  coding module 
       
    
     
       FIG. 5 
         
           500  source device or destination device 
           502  processor 
           504  memory 
           506  code and data 
           508  operating system 
           510  application programs 
           512  bus 
           518  display