Method and apparatus for video coding

An apparatus for video decoding includes processing circuitry. The processing circuitry decodes prediction information of a current block from a coded video bitstream. The prediction information is indicative of an intra block copy mode, the current block is one of a plurality of coding blocks in a coding tree block (CTB) with a right to left coding order being allowed within the current CTB. The processing circuitry determines a block vector that points to a reference block in a same picture as the current block. Then, the processing circuitry ensures the reference block being buffered in a reference sample memory based on at least a determination that a sample that is right of a leftmost sample of the reference block is buffered in the reference sample memory. Further, the processing circuitry reconstructs at least a sample of the current block based on reconstructed samples of the reference block.

TECHNICAL FIELD

BACKGROUND

A video encoder and decoder can utilize techniques from several broad categories, including, for example, motion compensation, transform, quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding. In intra coding, sample values are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, the picture is spatially subdivided into blocks of samples. When all blocks of samples are coded in intra mode, that picture can be an intra picture. Intra pictures and their derivations such as independent decoder refresh pictures, can be used to reset the decoder state and can, therefore, be used as the first picture in a coded video bitstream and a video session, or as a still image. The samples of an intra block can be exposed to a transform, and the transform coefficients can be quantized before entropy coding. Intra prediction can be a technique that minimizes sample values in the pre-transform domain. In some cases, the smaller the DC value after a transform is, and the smaller the AC coefficients are, the fewer the bits that are required at a given quantization step size to represent the block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2 generation coding technologies, does not use intra prediction. However, some newer video compression technologies include techniques that attempt, from, for example, surrounding sample data and/or metadata obtained during the encoding/decoding of spatially neighboring, and preceding in decoding order, blocks of data. Such techniques are henceforth called “intra prediction” techniques. Note that in at least some cases, intra prediction is only using reference data from the current picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more than one of such techniques can be used in a given video coding technology, the technique in use can be coded in an intra prediction mode. In certain cases, modes can have submodes and/or parameters, and those can be coded individually or included in the mode codeword. Which codeword to use for a given mode/submode/parameter combination can have an impact in the coding efficiency gain through intra prediction, and so can the entropy coding technology used to translate the codewords into a bitstream.

A certain mode of intra prediction was introduced with H.264, refined in H.265, and further refined in newer coding technologies such as joint exploration model (JEM), versatile video coding (VVC), and benchmark set (BMS). A predictor block can be formed using neighboring sample values belonging to already available samples. Sample values of neighboring samples are copied into the predictor block according to a direction. A reference to the direction in use can be coded in the bitstream or may itself be predicted.

Referring toFIG. 1, depicted in the lower right is a subset of nine predictor directions known from H.265's 33 possible predictor directions (corresponding to the 33 angular modes of the 35 intra modes). The point where the arrows converge (101) represents the sample being predicted. The arrows represent the direction from which the sample is being predicted. For example, arrow (102) indicates that sample (101) is predicted from a sample or samples to the upper right, at a 45 degree angle from the horizontal. Similarly, arrow (103) indicates that sample (101) is predicted from a sample or samples to the lower left of sample (101), in a 22.5 degree angle from the horizontal.

Still referring toFIG. 1, on the top left there is depicted a square block (104) of 4×4 samples (indicated by a dashed, boldface line). The square block (104) includes 16 samples, each labelled with an “S”, its position in the Y dimension (e.g., row index) and its position in the X dimension (e.g., column index). For example, sample S21is the second sample in the Y dimension (from the top) and the first (from the left) sample in the X dimension. Similarly, sample S44is the fourth sample in block (104) in both the Y and X dimensions. As the block is 4×4 samples in size, S44is at the bottom right. Further shown are reference samples that follow a similar numbering scheme. A reference sample is labelled with an R, its Y position (e.g., row index) and X position (column index) relative to block (104). In both H.264 and H.265, prediction samples neighbor the block under reconstruction; therefore no negative values need to be used.

Intra picture prediction can work by copying reference sample values from the neighboring samples as appropriated by the signaled prediction direction. For example, assume the coded video bitstream includes signaling that, for this block, indicates a prediction direction consistent with arrow (102)—that is, samples are predicted from a prediction sample or samples to the upper right, at a 45 degree angle from the horizontal. In that case, samples S41, S32, S23, and S14are predicted from the same reference sample R05. Sample S44is then predicted from reference sample R08.

In certain cases, the values of multiple reference samples may be combined, for example through interpolation, in order to calculate a reference sample; especially when the directions are not evenly divisible by 45 degrees.

The number of possible directions has increased as video coding technology has developed. In H.264 (year 2003), nine different direction could be represented. That increased to 33 in H.265 (year 2013), and JEM/VVC/BMS, at the time of disclosure, can support up to 65 directions. Experiments have been conducted to identify the most likely directions, and certain techniques in the entropy coding are used to represent those likely directions in a small number of bits, accepting a certain penalty for less likely directions. Further, the directions themselves can sometimes be predicted from neighboring directions used in neighboring, already decoded, blocks.

FIG. 2shows a schematic (201) that depicts 65 intra prediction directions according to JEM to illustrate the increasing number of prediction directions over time.

The mapping of intra prediction directions bits in the coded video bitstream that represent the direction can be different from video coding technology to video coding technology; and can range, for example, from simple direct mappings of prediction direction to intra prediction mode, to codewords, to complex adaptive schemes involving most probable modes, and similar techniques. In all cases, however, there can be certain directions that are statistically less likely to occur in video content than certain other directions. As the goal of video compression is the reduction of redundancy, those less likely directions will, in a well working video coding technology, be represented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relate to techniques where a block of sample data from a previously reconstructed picture or part thereof (reference picture), after being spatially shifted in a direction indicated by a motion vector (MV henceforth), is used for the prediction of a newly reconstructed picture or picture part. In some cases, the reference picture can be the same as the picture currently under reconstruction. MVs can have two dimensions X and Y, or three dimensions, the third being an indication of the reference picture in use (the latter, indirectly, can be a time dimension).

In some video compression techniques, an MV applicable to a certain area of sample data can be predicted from other MVs, for example from those related to another area of sample data spatially adjacent to the area under reconstruction, and preceding that MV in decoding order. Doing so can substantially reduce the amount of data required for coding the MV, thereby removing redundancy and increasing compression. MV prediction can work effectively, for example, because when coding an input video signal derived from a camera (known as natural video) there is a statistical likelihood that areas larger than the area to which a single MV is applicable move in a similar direction and, therefore, can in some cases be predicted using a similar motion vector derived from MVs of neighboring area. That results in the MV found for a given area to be similar or the same as the MV predicted from the surrounding MVs, and that in turn can be represented, after entropy coding, in a smaller number of bits than what would be used if coding the MV directly. In some cases, MV prediction can be an example of lossless compression of a signal (namely: the MVs) derived from the original signal (namely: the sample stream). In other cases, MV prediction itself can be lossy, for example because of rounding errors when calculating a predictor from several surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec. H.265, “High Efficiency Video Coding”, December 2016). Out of the many MV prediction mechanisms that H.265 offers, described here is a technique henceforth referred to as “spatial merge”.

Referring toFIG. 3, a current block (301) comprises samples that have been found by the encoder during the motion search process to be predictable from a previous block of the same size that has been spatially shifted. Instead of coding that MV directly, the MV can be derived from metadata associated with one or more reference pictures, for example from the most recent (in decoding order) reference picture, using the MV associated with either one of five surrounding samples, denoted A0, A1, and B0, B1, B2(302through306, respectively). In H.265, the MV prediction can use predictors from the same reference picture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes receiving circuitry and processing circuitry. For example, processing circuitry decodes prediction information of a current block from a coded video bitstream. The prediction information is indicative of an intra block copy mode, the current block is one of a plurality of coding blocks in a coding tree block (CTB) with a right to left coding order being allowed within the CTB. The processing circuitry determines a block vector that points to a reference block in a same picture as the current block. Then, the processing circuitry ensures the reference block being buffered in a reference sample memory based on at least a determination that a sample that is right of a leftmost sample of the reference block is buffered in the reference sample memory. Further, the processing circuitry reconstructs at least a sample of the current block based on reconstructed samples of the reference block that are retrieved from the reference sample memory.

In some embodiments, the processing circuitry determines that a sample at a top right corner of the reference block is buffered in the reference sample memory. In an embodiment, the processing circuitry determines that a collocated region in the CTB that includes a collocated sample for the sample at the top right corner of the reference block has not been coded. In some examples, the processing circuitry determines that a top left corner of the collocated region in the CTB has not been coded. Further, in an example, the processing circuitry determines that a top right corner of the collocated region in the CTB has not been coded.

In some examples, a memory space that stores the sample at the top right corner of the reference block is allocated to store the collocated sample when the collocated region is coded.

In an embodiment, the processing circuitry determines that a top right corner of a collocated region in the CBT that includes a collocated sample for a top left corner of the reference block has not been coded.

In another embodiment, the processing circuitry determines that a top right corner of the current block is not collocated with a top right corner of a reference region.

Aspects of the disclosure also provide a non-transitory computer-readable medium storing instructions which when executed by a computer for video decoding cause the computer to perform the method for video decoding.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 4illustrates a simplified block diagram of a communication system (400) according to an embodiment of the present disclosure. The communication system (400) includes a plurality of terminal devices that can communicate with each other, via, for example, a network (450). For example, the communication system (400) includes a first pair of terminal devices (410) and (420) interconnected via the network (450). In theFIG. 4example, the first pair of terminal devices (410) and (420) performs unidirectional transmission of data. For example, the terminal device (410) may code video data (e.g., a stream of video pictures that are captured by the terminal device (410)) for transmission to the other terminal device (420) via the network (450). The encoded video data can be transmitted in the form of one or more coded video bitstreams. The terminal device (420) may receive the coded video data from the network (450), decode the coded video data to recover the video pictures and display video pictures according to the recovered video data. Unidirectional data transmission may be common in media serving applications and the like.

In another example, the communication system (400) includes a second pair of terminal devices (430) and (440) that performs bidirectional transmission of coded video data that may occur, for example, during videoconferencing. For bidirectional transmission of data, in an example, each terminal device of the terminal devices (430) and (440) may code video data (e.g., a stream of video pictures that are captured by the terminal device) for transmission to the other terminal device of the terminal devices (430) and (440) via the network (450). Each terminal device of the terminal devices (430) and (440) also may receive the coded video data transmitted by the other terminal device of the terminal devices (430) and (440), and may decode the coded video data to recover the video pictures and may display video pictures at an accessible display device according to the recovered video data.

In theFIG. 4example, the terminal devices (410), (420), (430) and (440) may be illustrated as servers, personal computers and smart phones but the principles of the present disclosure may be not so limited. Embodiments of the present disclosure find application with laptop computers, tablet computers, media players and/or dedicated video conferencing equipment. The network (450) represents any number of networks that convey coded video data among the terminal devices (410), (420), (430) and (440), including for example wireline (wired) and/or wireless communication networks. The communication network (450) may exchange data in circuit-switched and/or packet-switched channels. Representative networks include telecommunications networks, local area networks, wide area networks and/or the Internet. For the purposes of the present discussion, the architecture and topology of the network (450) may be immaterial to the operation of the present disclosure unless explained herein below.

A streaming system may include a capture subsystem (513), that can include a video source (501), for example a digital camera, creating for example a stream of video pictures (502) that are uncompressed. In an example, the stream of video pictures (502) includes samples that are taken by the digital camera. The stream of video pictures (502), depicted as a bold line to emphasize a high data volume when compared to encoded video data (504) (or coded video bitstreams), can be processed by an electronic device (520) that includes a video encoder (503) coupled to the video source (501). The video encoder (503) can include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter as described in more detail below. The encoded video data (504) (or encoded video bitstream (504)), depicted as a thin line to emphasize the lower data volume when compared to the stream of video pictures (502), can be stored on a streaming server (505) for future use. One or more streaming client subsystems, such as client subsystems (506) and (508) inFIG. 5can access the streaming server (505) to retrieve copies (507) and (509) of the encoded video data (504). A client subsystem (506) can include a video decoder (510), for example, in an electronic device (530). The video decoder (510) decodes the incoming copy (507) of the encoded video data and creates an outgoing stream of video pictures (511) that can be rendered on a display (512) (e.g., display screen) or other rendering device (not depicted). In some streaming systems, the encoded video data (504), (507), and (509) (e.g., video bitstreams) can be encoded according to certain video coding/compression standards. Examples of those standards include ITU-T Recommendation H.265. In an example, a video coding standard under development is informally known as Versatile Video Coding (VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (520) and (530) can include other components (not shown). For example, the electronic device (520) can include a video decoder (not shown) and the electronic device (530) can include a video encoder (not shown) as well.

FIG. 6shows a block diagram of a video decoder (610) according to an embodiment of the present disclosure. The video decoder (610) can be included in an electronic device (630). The electronic device (630) can include a receiver (631) (e.g., receiving circuitry). The video decoder (610) can be used in the place of the video decoder (510) in theFIG. 5example.

The receiver (631) may receive one or more coded video sequences to be decoded by the video decoder (610); in the same or another embodiment, one coded video sequence at a time, where the decoding of each coded video sequence is independent from other coded video sequences. The coded video sequence may be received from a channel (601), which may be a hardware/software link to a storage device which stores the encoded video data. The receiver (631) may receive the encoded video data with other data, for example, coded audio data and/or ancillary data streams, that may be forwarded to their respective using entities (not depicted). The receiver (631) may separate the coded video sequence from the other data. To combat network jitter, a buffer memory (615) may be coupled in between the receiver (631) and an entropy decoder/parser (620) (“parser (620)” henceforth). In certain applications, the buffer memory (615) is part of the video decoder (610). In others, it can be outside of the video decoder (610) (not depicted). In still others, there can be a buffer memory (not depicted) outside of the video decoder (610), for example to combat network jitter, and in addition another buffer memory (615) inside the video decoder (610), for example to handle playout timing. When the receiver (631) is receiving data from a store/forward device of sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (615) may not be needed, or can be small. For use on best effort packet networks such as the Internet, the buffer memory (615) may be required, can be comparatively large and can be advantageously of adaptive size, and may at least partially be implemented in an operating system or similar elements (not depicted) outside of the video decoder (610).

The video decoder (610) may include the parser (620) to reconstruct symbols (621) from the coded video sequence. Categories of those symbols include information used to manage operation of the video decoder (610), and potentially information to control a rendering device such as a render device (612) (e.g., a display screen) that is not an integral part of the electronic device (630) but can be coupled to the electronic device (630), as was shown inFIG. 6. The control information for the rendering device(s) may be in the form of Supplemental Enhancement Information (SEI messages) or Video Usability Information (VUI) parameter set fragments (not depicted). The parser (620) may parse/entropy-decode the coded video sequence that is received. The coding of the coded video sequence can be in accordance with a video coding technology or standard, and can follow various principles, including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, and so forth. The parser (620) may extract from the coded video sequence, a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder, based upon at least one parameter corresponding to the group. Subgroups can include Groups of Pictures (GOPs), pictures, tiles, slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) and so forth. The parser (620) may also extract from the coded video sequence information such as transform coefficients, quantizer parameter values, motion vectors, and so forth.

The parser (620) may perform an entropy decoding/parsing operation on the video sequence received from the buffer memory (615), so as to create symbols (621).

A first unit is the scaler/inverse transform unit (651). The scaler/inverse transform unit (651) receives a quantized transform coefficient as well as control information, including which transform to use, block size, quantization factor, quantization scaling matrices, etc. as symbol(s) (621) from the parser (620). The scaler/inverse transform unit (651) can output blocks comprising sample values, that can be input into aggregator (655).

In some cases, the output samples of the scaler/inverse transform (651) can pertain to an intra coded block; that is: a block that is not using predictive information from previously reconstructed pictures, but can use predictive information from previously reconstructed parts of the current picture. Such predictive information can be provided by an intra picture prediction unit (652). In some cases, the intra picture prediction unit (652) generates a block of the same size and shape of the block under reconstruction, using surrounding already reconstructed information fetched from the current picture buffer (658). The current picture buffer (658) buffers, for example, partly reconstructed current picture and/or fully reconstructed current picture. The aggregator (655), in some cases, adds, on a per sample basis, the prediction information the intra prediction unit (652) has generated to the output sample information as provided by the scaler/inverse transform unit (651).

In other cases, the output samples of the scaler/inverse transform unit (651) can pertain to an inter coded, and potentially motion compensated block. In such a case, a motion compensation prediction unit (653) can access reference picture memory (657) to fetch samples used for prediction. After motion compensating the fetched samples in accordance with the symbols (621) pertaining to the block, these samples can be added by the aggregator (655) to the output of the scaler/inverse transform unit (651) (in this case called the residual samples or residual signal) so as to generate output sample information. The addresses within the reference picture memory (657) from where the motion compensation prediction unit (653) fetches prediction samples can be controlled by motion vectors, available to the motion compensation prediction unit (653) in the form of symbols (621) that can have, for example X, Y, and reference picture components. Motion compensation also can include interpolation of sample values as fetched from the reference picture memory (657) when sub-sample exact motion vectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (655) can be subject to various loop filtering techniques in the loop filter unit (656). Video compression technologies can include in-loop filter technologies that are controlled by parameters included in the coded video sequence (also referred to as coded video bitstream) and made available to the loop filter unit (656) as symbols (621) from the parser (620), but can also be responsive to meta-information obtained during the decoding of previous (in decoding order) parts of the coded picture or coded video sequence, as well as responsive to previously reconstructed and loop-filtered sample values.

The output of the loop filter unit (656) can be a sample stream that can be output to the render device (612) as well as stored in the reference picture memory (657) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used as reference pictures for future prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture has been identified as a reference picture (by, for example, the parser (620)), the current picture buffer (658) can become a part of the reference picture memory (657), and a fresh current picture buffer can be reallocated before commencing the reconstruction of the following coded picture.

FIG. 7shows a block diagram of a video encoder (703) according to an embodiment of the present disclosure. The video encoder (703) is included in an electronic device (720). The electronic device (720) includes a transmitter (740) (e.g., transmitting circuitry). The video encoder (703) can be used in the place of the video encoder (503) in theFIG. 5example.

The video encoder (703) may receive video samples from a video source (701) (that is not part of the electronic device (720) in theFIG. 7example) that may capture video image(s) to be coded by the video encoder (703). In another example, the video source (701) is a part of the electronic device (720).

According to an embodiment, the video encoder (703) may code and compress the pictures of the source video sequence into a coded video sequence (743) in real time or under any other time constraints as required by the application. Enforcing appropriate coding speed is one function of a controller (750). In some embodiments, the controller (750) controls other functional units as described below and is functionally coupled to the other functional units. The coupling is not depicted for clarity. Parameters set by the controller (750) can include rate control related parameters (picture skip, quantizer, lambda value of rate-distortion optimization techniques, . . . ), picture size, group of pictures (GOP) layout, maximum motion vector search range, and so forth. The controller (750) can be configured to have other suitable functions that pertain to the video encoder (703) optimized for a certain system design.

In some embodiments, the video encoder (703) is configured to operate in a coding loop. As an oversimplified description, in an example, the coding loop can include a source coder (730) (e.g., responsible for creating symbols, such as a symbol stream, based on an input picture to be coded, and a reference picture(s)), and a (local) decoder (733) embedded in the video encoder (703). The decoder (733) reconstructs the symbols to create the sample data in a similar manner as a (remote) decoder also would create (as any compression between symbols and coded video bitstream is lossless in the video compression technologies considered in the disclosed subject matter). The reconstructed sample stream (sample data) is input to the reference picture memory (734). As the decoding of a symbol stream leads to bit-exact results independent of decoder location (local or remote), the content in the reference picture memory (734) is also bit exact between the local encoder and remote encoder. In other words, the prediction part of an encoder “sees” as reference picture samples exactly the same sample values as a decoder would “see” when using prediction during decoding. This fundamental principle of reference picture synchronicity (and resulting drift, if synchronicity cannot be maintained, for example because of channel errors) is used in some related arts as well.

The operation of the “local” decoder (733) can be the same as of a “remote” decoder, such as the video decoder (610), which has already been described in detail above in conjunction withFIG. 6. Briefly referring also toFIG. 6, however, as symbols are available and encoding/decoding of symbols to a coded video sequence by an entropy coder (745) and the parser (620) can be lossless, the entropy decoding parts of the video decoder (610), including the buffer memory (615), and parser (620) may not be fully implemented in the local decoder (733).

The local video decoder (733) may decode coded video data of pictures that may be designated as reference pictures, based on symbols created by the source coder (730). Operations of the coding engine (732) may advantageously be lossy processes. When the coded video data may be decoded at a video decoder (not shown inFIG. 7), the reconstructed video sequence typically may be a replica of the source video sequence with some errors. The local video decoder (733) replicates decoding processes that may be performed by the video decoder on reference pictures and may cause reconstructed reference pictures to be stored in the reference picture cache (734). In this manner, the video encoder (703) may store copies of reconstructed reference pictures locally that have common content as the reconstructed reference pictures that will be obtained by a far-end video decoder (absent transmission errors).

The predictor (735) may perform prediction searches for the coding engine (732). That is, for a new picture to be coded, the predictor (735) may search the reference picture memory (734) for sample data (as candidate reference pixel blocks) or certain metadata such as reference picture motion vectors, block shapes, and so on, that may serve as an appropriate prediction reference for the new pictures. The predictor (735) may operate on a sample block-by-pixel block basis to find appropriate prediction references. In some cases, as determined by search results obtained by the predictor (735), an input picture may have prediction references drawn from multiple reference pictures stored in the reference picture memory (734).

The controller (750) may manage coding operations of the source coder (730), including, for example, setting of parameters and subgroup parameters used for encoding the video data.

The transmitter (740) may buffer the coded video sequence(s) as created by the entropy coder (745) to prepare for transmission via a communication channel (760), which may be a hardware/software link to a storage device which would store the encoded video data. The transmitter (740) may merge coded video data from the video coder (703) with other data to be transmitted, for example, coded audio data and/or ancillary data streams (sources not shown).

The controller (750) may manage operation of the video encoder (703). During coding, the controller (750) may assign to each coded picture a certain coded picture type, which may affect the coding techniques that may be applied to the respective picture. For example, pictures often may be assigned as one of the following picture types:

The video encoder (703) may perform coding operations according to a predetermined video coding technology or standard, such as ITU-T Rec. H.265. In its operation, the video encoder (703) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancies in the input video sequence. The coded video data, therefore, may conform to a syntax specified by the video coding technology or standard being used.

In an embodiment, the transmitter (740) may transmit additional data with the encoded video. The source coder (730) may include such data as part of the coded video sequence. Additional data may comprise temporal/spatial/SNR enhancement layers, other forms of redundant data such as redundant pictures and slices, SEI messages, VUI parameter set fragments, and so on.

FIG. 8shows a diagram of a video encoder (803) according to another embodiment of the disclosure. The video encoder (803) is configured to receive a processing block (e.g., a prediction block) of sample values within a current video picture in a sequence of video pictures, and encode the processing block into a coded picture that is part of a coded video sequence. In an example, the video encoder (803) is used in the place of the video encoder (503) in theFIG. 5example.

In an HEVC example, the video encoder (803) receives a matrix of sample values for a processing block, such as a prediction block of 8×8 samples, and the like. The video encoder (803) determines whether the processing block is best coded using intra mode, inter mode, or bi-prediction mode using, for example, rate-distortion optimization. When the processing block is to be coded in intra mode, the video encoder (803) may use an intra prediction technique to encode the processing block into the coded picture; and when the processing block is to be coded in inter mode or bi-prediction mode, the video encoder (803) may use an inter prediction or bi-prediction technique, respectively, to encode the processing block into the coded picture. In certain video coding technologies, merge mode can be an inter picture prediction submode where the motion vector is derived from one or more motion vector predictors without the benefit of a coded motion vector component outside the predictors. In certain other video coding technologies, a motion vector component applicable to the subject block may be present. In an example, the video encoder (803) includes other components, such as a mode decision module (not shown) to determine the mode of the processing blocks.

In theFIG. 8example, the video encoder (803) includes the inter encoder (830), an intra encoder (822), a residue calculator (823), a switch (826), a residue encoder (824), a general controller (821), and an entropy encoder (825) coupled together as shown inFIG. 8.

The intra encoder (822) is configured to receive the samples of the current block (e.g., a processing block), in some cases compare the block to blocks already coded in the same picture, generate quantized coefficients after transform, and in some cases also intra prediction information (e.g., an intra prediction direction information according to one or more intra encoding techniques). In an example, the intra encoder (822) also calculates intra prediction results (e.g., predicted block) based on the intra prediction information and reference blocks in the same picture.

The general controller (821) is configured to determine general control data and control other components of the video encoder (803) based on the general control data. In an example, the general controller (821) determines the mode of the block, and provides a control signal to the switch (826) based on the mode. For example, when the mode is the intra mode, the general controller (821) controls the switch (826) to select the intra mode result for use by the residue calculator (823), and controls the entropy encoder (825) to select the intra prediction information and include the intra prediction information in the bitstream; and when the mode is the inter mode, the general controller (821) controls the switch (826) to select the inter prediction result for use by the residue calculator (823), and controls the entropy encoder (825) to select the inter prediction information and include the inter prediction information in the bitstream.

The residue calculator (823) is configured to calculate a difference (residue data) between the received block and prediction results selected from the intra encoder (822) or the inter encoder (830). The residue encoder (824) is configured to operate based on the residue data to encode the residue data to generate the transform coefficients. In an example, the residue encoder (824) is configured to convert the residue data from a spatial domain to a frequency domain, and generate the transform coefficients. The transform coefficients are then subject to quantization processing to obtain quantized transform coefficients. In various embodiments, the video encoder (803) also includes a residue decoder (828). The residue decoder (828) is configured to perform inverse-transform, and generate the decoded residue data. The decoded residue data can be suitably used by the intra encoder (822) and the inter encoder (830). For example, the inter encoder (830) can generate decoded blocks based on the decoded residue data and inter prediction information, and the intra encoder (822) can generate decoded blocks based on the decoded residue data and the intra prediction information. The decoded blocks are suitably processed to generate decoded pictures and the decoded pictures can be buffered in a memory circuit (not shown) and used as reference pictures in some examples.

FIG. 9shows a diagram of a video decoder (910) according to another embodiment of the disclosure. The video decoder (910) is configured to receive coded pictures that are part of a coded video sequence, and decode the coded pictures to generate reconstructed pictures. In an example, the video decoder (910) is used in the place of the video decoder (510) in theFIG. 5example.

In theFIG. 9example, the video decoder (910) includes an entropy decoder (971), an inter decoder (980), a residue decoder (973), a reconstruction module (974), and an intra decoder (972) coupled together as shown inFIG. 9.

The entropy decoder (971) can be configured to reconstruct, from the coded picture, certain symbols that represent the syntax elements of which the coded picture is made up. Such symbols can include, for example, the mode in which a block is coded (such as, for example, intra mode, inter mode, bi-predicted mode, the latter two in merge submode or another submode), prediction information (such as, for example, intra prediction information or inter prediction information) that can identify certain sample or metadata that is used for prediction by the intra decoder (972) or the inter decoder (980), respectively, residual information in the form of, for example, quantized transform coefficients, and the like. In an example, when the prediction mode is inter or bi-predicted mode, the inter prediction information is provided to the inter decoder (980); and when the prediction type is the intra prediction type, the intra prediction information is provided to the intra decoder (972). The residual information can be subject to inverse quantization and is provided to the residue decoder (973).

The inter decoder (980) is configured to receive the inter prediction information, and generate inter prediction results based on the inter prediction information.

The intra decoder (972) is configured to receive the intra prediction information, and generate prediction results based on the intra prediction information.

The residue decoder (973) is configured to perform inverse quantization to extract de-quantized transform coefficients, and process the de-quantized transform coefficients to convert the residual from the frequency domain to the spatial domain. The residue decoder (973) may also require certain control information (to include the Quantizer Parameter (QP)), and that information may be provided by the entropy decoder (971) (data path not depicted as this may be low volume control information only).

The reconstruction module (974) is configured to combine, in the spatial domain, the residual as output by the residue decoder (973) and the prediction results (as output by the inter or intra prediction modules as the case may be) to form a reconstructed block, that may be part of the reconstructed picture, which in turn may be part of the reconstructed video. It is noted that other suitable operations, such as a deblocking operation and the like, can be performed to improve the visual quality.

It is noted that the video encoders (503), (703), and (803), and the video decoders (510), (610), and (910) can be implemented using any suitable technique. In an embodiment, the video encoders (503), (703), and (803), and the video decoders (510), (610), and (910) can be implemented using one or more integrated circuits. In another embodiment, the video encoders (503), (703), and (703), and the video decoders (510), (610), and (910) can be implemented using one or more processors that execute software instructions.

Aspects of the disclosure provide encoding/decoding techniques for intra picture block compensation, especially techniques for reference search range constraints for intra picture block compensation with flexible coding order.

Block based compensation can be used for inter prediction and intra prediction. For the inter prediction, block based compensation from a different picture is known as motion compensation. For intra prediction, block based compensation can also be done from a previously reconstructed area within the same picture. The block based compensation from reconstructed area within the same picture is referred to as intra picture block compensation, current picture referencing (CPR) or intra block copy (IBC). A displacement vector that indicates the offset between the current block and the reference block in the same picture is referred to as a block vector (or BV for short). Different from a motion vector in motion compensation, which can be at any value (positive or negative, at either x or y direction), a block vector has a few constraints to ensure that the reference block is available and already reconstructed. Also, in some examples, for parallel processing consideration, some reference area that is tile boundary or wavefront ladder shape boundary is excluded.

The coding of a block vector could be either explicit or implicit. In the explicit mode (or referred to as advanced motion vector prediction (AMVP) mode in inter coding), the difference between a block vector and its predictor is signaled; in the implicit mode, the block vector is recovered from a predictor (referred to as block vector predictor), in a similar way as a motion vector in merge mode. The resolution of a block vector, in some implementations, is restricted to integer positions; in other systems, the block vector is allowed to point to fractional positions.

In some examples, the use of intra block copy at block level, can be signaled using a block level flag that is referred to as an IBC flag. In an embodiment, the IBC flag is signaled when the current block is not coded in merge mode. In other examples, the use of the intra block copy at block level is signaled by a reference index approach. The current picture under decoding is then treated as a reference picture. In an example, such a reference picture is put in the last position of a list of reference pictures. This special reference picture is also managed together with other temporal reference pictures in a buffer, such as decoded picture buffer (DPB).

There are also some variations for intra block copy, such as flipped intra block copy (the reference block is flipped horizontally or vertically before used to predict current block), or line based intra block copy (each compensation unit inside an M×N coding block is an M×1 or 1×N line).

FIG. 10shows an example of intra block copy according to an embodiment of the disclosure. Current picture (1000) is under decoding. The current picture (1000) includes a reconstructed area (1010) (doted area) and to-be-decoded area (1020) (white area). A current block (1030) is under reconstruction by a decoder. The current block (1030) can be reconstructed from a reference block (1040) that is in the reconstructed area (1010). The position offset between the reference block (1040) and the current block (1030) is referred to as a block vector (1050) (or BV (1050)).

In some examples (e.g., VVC), the search range of intra block copy mode is constrained to be within the current CTU. Then, the memory requirement to store reference samples for the intra block copy mode is 1 (largest) CTU size of samples. In an example, the (largest) CTU has a size of 128×128 samples. The CTU is divided into four block regions that each has a size of 64×64 samples, in some examples. Thus, in some embodiments, the total memory (e.g., cache memory with fast access speed than a main storage) is able to store samples for a size of 128×128, and the total memory includes an existing reference sample memory portion to store reconstructed samples in the current block, such as a 64×64 region, and additional memory portion to store samples of three other regions of the size 64×64. Thus, in some examples, the effective search range of the intra block copy mode is extended to some part of the left CTU while the total memory requirement for storing reference pixels are kept unchanged (e.g., 1 CTU size, 4 times of the 64×64 reference sample memory in total).

In some embodiments, an update process is performed to update the stored reference samples from the left CTU to the reconstructed samples from the current CTU. Specifically, in some examples, the update process is done on a 64×64 luma sample basis. In an embodiment, for each of the four 64×64 block regions in the CTU size memory, the reference samples in the regions from the left CTU can be used to predict the coding block in current CTU with CPR mode until any of the blocks in the same region of the current CTU is being coded or has been coded.

FIGS. 11A-11Dshow examples of effective search ranges for the intra block copy mode according to an embodiment of the disclosure. In some examples, an encoder/decoder includes a cache memory that is able to store samples of one CTU, such as 128×128 samples, and can be referred to as reference sample memory. In some embodiments, the reference sample memory is updated based on units of block regions. A CTU can include a plurality of block regions. Before a reconstruction of a block region, a memory space in the reference sample memory is allocated and reset to store the reconstructed samples of the block region. In theFIGS. 11A-11Dexamples, a block region for prediction has a size of 64×64 samples. It is noted that the examples can be suitably modified for block region of other suitable sizes.

Each ofFIGS. 11A-11Dshows a current CTU (1120) and a left CTU (1110). The left CTU (1110) includes four block regions (1111)-(1114), and each block region has a sample size of 64×64 samples. The current CTU (1120) includes four block regions (1121)-(1124), and each block region has a sample size of 64×64 samples. The current CTU (1120) is the CTU that includes a current block region (as shown with vertical stripe pattern) under reconstruction. The left CTU (1110) is the immediate neighbor on the left side of the current CTU (1120). It is noted inFIGS. 11A-11D, the grey blocks are block regions that are already reconstructed, and the white blocks are block regions that are to be reconstructed.

InFIG. 11A, the current block region under reconstruction is the block region (1121). The cache memory stores reconstructed samples in the block regions (1112), (1113) and (1114), and the cache memory will be used to store reconstructed samples of the current block region (1121). In theFIG. 11Aexample, the effective search range for the current block region (1121) includes the block regions (1112), (1113) and (1114) in the left CTU (1110) with reconstructed samples stored in the cache memory. It is noted that, in an embodiment, the reconstructed samples of the block region (1111) are stored in a main memory (e.g., are copied from the cache memory to the main memory before the reconstruction of the block region (1121)) that has a slower access speed than the cache memory.

InFIG. 11B, the current block region under reconstruction is the block region (1122). The cache memory stores reconstructed samples in the block regions (1113), (1114) and (1121), and the cache memory will be used to store reconstructed samples of the current block region (1122). In theFIG. 11Bexample, the effective search range for the current block region (1122) includes the block regions (1113) and (1114) in the left CTU (1110) and (1121) in the current CTU (1020) with reconstructed samples stored in the cache memory. It is noted that, in an embodiment, the reconstructed samples of the block region (1112) are stored in a main memory (e.g., are copied from the cache memory to the main memory before the reconstruction of the block region (1122)) that has a slower access speed than the cache memory.

InFIG. 11C, the current block region under reconstruction is the block region (1123). The cache memory stores reconstructed samples in the block regions (1114), (1121) and (1122), and the cache memory will be used to store reconstructed samples of the current block region (1123). In theFIG. 11Cexample, the effective search range for the current block (1123) includes the block regions (1114) in the left CTU (1110) and (1121) and (1122) in the current CTU (1120) with reconstructed samples stored in the cache memory. It is noted that, in an embodiment, the reconstructed samples of the block region (1113) are stored in a main memory (e.g., are copied from the cache memory to the main memory before the reconstruction of the block region (1023)) that has a slower access speed than the cache memory.

InFIG. 11D, the current block region under reconstruction is the block region (1124). The cache memory stores reconstructed samples in the block regions (1121), (1122) and (1123), and the cache memory will be used to store reconstructed samples of the current block region (1124). In theFIG. 11Dexample, the effective search range for the current block region (1124) includes the blocks (1121), (1122) and (1123) in the current CTU (1120) with reconstructed samples stored in the cache memory. It is noted that, in an embodiment, the reconstructed samples of the block region (1114) are stored in a main memory (e.g., are copied from the cache memory to the main memory before the reconstruction of the block region (1124)) that has a slower access speed than the cache memory.

In some embodiments, the designated memory to store reference samples of previously coded CUs for future intra block copy reference is referred as reference sample memory. In an example, such as VVC standard, one CTU size of reference samples is considered as the designated memory size. In some examples, the cache memory has a total memory space for 1 (largest) CTU size. The examples can be suitably adjusted for other suitable CTU sizes. It is noted that the cache memory that is designated to store reference samples of previously coded CUs for future intra block copy reference is referred to as reference sample memory in some examples.

According to an aspect of the disclosure, collocated blocks in the present disclosure refer to a pair of blocks that have the same sizes, one of the collocated blocks is in the previously coded CTU, the other of the collocated blocks is in the current CTU, and one block in the pair is referred to as a collated block of the other block in the pair. Further, when the memory buffer size is designed to store a CTU of the maximum size (e.g., 128×128), then the previous CTU refers to the CTU that has one CTU width luma sample offset to the left of current CTU in an example. In addition, these two collocated blocks have the same location offset values relative to the top left corner of their own CTU, respectively. Or in other words, collocated blocks are those two that have the same y coordinate relative to the top left corner of a picture, but with a CTU width difference in x coordinates to one another in some examples.

FIG. 12shows examples of collocated blocks according to some embodiments of the disclosure. In theFIG. 12example, a current CTU and a left CTU during decoding are shown. The area that has been reconstructed is shown in grey color, and the area to be reconstructed is shown in white color.FIG. 12shows three examples of reference blocks in the left CTU for the current block in the intra block copy mode during decoding. The three examples are shown as reference block1, reference block2and reference block3.FIG. 12also shows the collocated block1for the reference block1, collocated block2for the reference block2and collocated block3for the reference block3. In theFIG. 12example, the reference sample memory size is a CTU size. Reconstructed samples of the current CTU and the left CTU are stored in the reference sample memory in a complementary manner. When a reconstructed sample of the current CTU is written to the reference sample memory, the reconstructed sample is written in the place of a collocated sample in the left CTU. In an example, for the reference block3, because the collocated block3in the current CTU has not yet been reconstructed, thus the reference block3can be found from the reference sample memory. The reference sample memory still stores samples of the reference block3from the left CTU and can be accessed with fast speed to retrieve the samples of the reference block3, and the reference block3can be used to reconstruct the current block in the intra block copy mode in an example.

In another example, for the reference block1, the collocated block1in the current CTU has been reconstructed completed, thus the reference sample memory stores samples of the collocated block1, and the samples of the reference block1have been stored in, for example, an off-chip storage that has relative high delay compared to the reference sample memory. Thus, in an example, the reference block1cannot be found in the reference sample memory, and the reference block1cannot be used to reconstruct the current block in the intra block copy mode in an example.

Similarly, in another example, for the reference block2, even if the collocated block2in the current CTU has not yet been reconstructed, because the 64×64 block region that includes the collocated blocks2is considered as a whole in a memory update example, then the reference block2is not a valid reference block for reconstructing the current block in the intra block copy mode.

Generally, in the intra block copy mode, for a reference block in the previously decoded CTU, when the collocated block in the current CTU has not yet been reconstructed, then samples of the reference block are available in the reference sample memory, and the reference sample memory can be accessed to retrieve the samples of the reference block to use as reference for reconstruction in the intra block copy mode.

It is noted that, in the above examples, the top left corner sample of the collocated block in the current CTU, which is also referred to as the collocated sample of the top left corner of the reference block, is checked. When the collocated sample in the current CTU has not yet been reconstructed, the rest of samples for the reference block will all be available for use as reference in the intra block copy.

In some embodiments, a CTU may be divided into block regions to determine valid reference block regions. For example, a CTU of 128×128 is divided into four 64×64 block regions. In an example, for the reference block2, even if the collocated block2in the current CTU has not yet been reconstructed, the reference block2may not become a valid reference block if the entire 64×64 block region (1201) of the collocated block2is considered as a whole. For example, by checking the top left corner (1202) of the 64×64 block region (1201) (top right 64×64 region of current CTU) where the collocated block2belongs to, that top left corner (1202) is considered being reconstructed therefore the entire of the 64×64 block region (1203) where reference block2belongs to cannot be used as reference block region.

When reference sample memory size is larger than the CTU size, more than 1 CTU to the left may be used to store reference samples for intra block copy. For example, when the CTU size is 64×64 while the reference memory size is 128×128, in addition to current CTU, 3 left CTUs may be considered as the valid reference area for intra block copy.

It is also noted that, in the above examples, the memory size of the reference sample memory is the size of one CTU, then the previously decoded CTU means the CTU immediate to the left of current CTU.

According to an aspect of the disclosure, the memory size of the reference sample memory can be larger than the size of one CTU.

According to some aspects of the disclosure, for a valid search range, the bitstream conformance requires the luma block vector mvL to obey the certain constraints. In an example, a current CTB is a luma CTB including a plurality of luma samples and a block vector mvL satisfies the following constraints for bitstream conformance.

In some examples, first constraints are used to make sure that the reference block for the current block has to be reconstructed. When the reference block has a rectangular shape, a reference block availability checking process can be implemented to check whether a top left sample and a bottom right sample of the reference block are reconstructed. When both the top left sample and the bottom right sample of the reference block are reconstructed, the reference block is determined to have been reconstructed.

For example, a reconstructed top left sample of the reference block should be available. In some examples, a derivation process for block availability can be invoked, the derivation process can receive a current luma location and a neighboring luma position as inputs, and generate an output that indicates whether a sample at the neighboring luma position has been reconstructed. For example, when the output is TRUE, the sample at the input position has been reconstructed; and when the output is FALSE, the sample at the input position hasn't been reconstructed yet.

Generally, the current luma position is set to (xCb, yCb), which is the position of the top left sample of the current block. Further, mvL denotes block vector, mvL[0] denotes the x component and mvL[1] denotes the y component of the block vector. In some examples, the x component and y component are stored in 1/16 inter sample accuracy, thus the x component and the y component can have 4-bit for fractional parts of a pixel. Then, to get the inter part, the x component and y component can be right shift by 4. The current luma location (xCurr, yCurr) is set to be the top left sample of the current block (xCb, yCb), the neighboring luma location can be represented by (xCb+(mvL[0]>>4), yCb+(mvL[1]>>4)) which is the position of the top left sample of the reference block. In an example, a derivation process for reference block availability is invoked, the position of the top left sample of the reference block is used as an input, when an output is equal to TRUE, the top left sample of the reference block is reconstructed.

Similarly, the reconstructed bottom right sample of the reference block should be available. In some examples, a derivation process for block availability can be invoked, and the input to the derivation process includes the position of the bottom right sample of the reference block. For example, the current luma position is set to be (xCb, yCb), and width of the current block and the reference block is denoted by cbWidth, the height of the current block and the reference block is denoted by cbHeight. Then, the position of the bottom right sample of the reference block is (xCb+(mvL[0]>>4)+cbWidth−1, yCb+(mvL[1]>>4)+cbHeight−1). The position of the bottom right sample is input to the derivation process for block availability, when the output is TRUE, the bottom right sample of the reference block is reconstructed.

In some examples, second constraints ensure that the reference block is to the left and/or above of the current block and does not overlap with the current block. The second constraints can also include at least one of the following two conditions: 1) a value of (mvL[0]>>4)+cbWidth is less than or equal to 0, which indicates that the reference block is to the left of the current block and does not overlap with the current block; 2) a value of (mvL[1]>>4)+cbHeight is less than or equal to 0, which indicates that the reference block is above the current block and does not overlap with the current block.

The third constraints ensure the reference block is in an appropriate search range. In some examples, the third constrains can include that the following conditions are satisfied by the block vector mvL:
(yCb+(mvL[1]>>4))>>CtbLog2SizeY=yCb>>CtbLog2SizeY(Eq. 1)
(yCb+(mvL[1]>>4+cbHeight−1)>>CtbLog2SizeY=yCb>>CtbLog2SizeY(Eq. 2)
(xCb+(mvL[0]>>4))>>CtbLog2SizeY>=(xCb>>CtbLog2SizeY)−(1<<((7−CtbLog2SizeY)<<1)))+Min(1,7−CtbLog2SizeY)  (Eq. 3)
(xCb+(mvL[0]>>4)+cbWidth−1)>>CtbLog2SizeY<=(xCb>>CtbLog2SizeY)  (Eq. 4)
where the parameters CtbLog2SizeY denotes the CTB size (e.g., height or width) in log 2 form. For example, when the CTB height is 128 samples, CtbLog2SizeY is 7. Eq. 1 and Eq. 2 specify that a CTB including the reference block is in a same CTB row as the current CTB (i.e., the previously reconstructed CTB is in a same row as the current CTB when the reference block is in the previously reconstructed CTB). Eq. 3 and Eq. 4 specify that the CTB including the reference block is either in a left CTB column of the current CTB or a same CTB column as the current CTB. The conditions as described by Eq. 1-Eq. 4 specify that the CTB including the reference block is either the current CTB, or a left neighbor, such as the previously reconstructed CTB, of the current CTB.

The fourth constraints ensure the reference block is stored in the reference sample memory, in other words, the collocated block of the reference block has not been reconstructed. In some examples, the fourth constraints can include following conditions: when the reference block is in the left neighbor of the current CTB, a collocated region for the reference block is not reconstructed (i.e., no samples in the collocated region have been reconstructed). Further, the collocated region for the reference block is in the current CTB.

In an example, the above conditions can be specified as below: when (xCb+(mvL[0]>>4))>>CtbLog2SizeY is equal to (xCb>>CtbLog2SizeY)−1, and CtbLog2SizeY is 7, the derivation process for reference block availability is invoked. The input for the current luma location (xCurr, yCurr) is set to be (xCb, yCb) and the input for the neighboring luma location is (((xCb+(mvL[0]>>4)+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1), ((yCb+(mvL[1]>>4))>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)). When an output of the derivation process is FALSE, the collocated region has not been reconstructed. Also, the luma location (((xCb+(mvL[0]>>4)+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1), ((yCb+(mvL[1]>>4))>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)) shall not be equal to (xCb, yCb).

According to some aspects of the disclosure, flexible coding order can be used in some coding techniques. In some embodiments, a CTU is recursively partitioned by quad-tree structure, binary tree structure or triple tree structure. The units in the partitioning process, which are further split into two, three, or four units are named split units (SUs). Usually the coding order of a split unit is from left to right and from above to bottom because of z scanning order of quad tree structure and raster scan of CTUs in a picture. However, normal left to right coding order is more beneficial to left inclined features than right inclined features. Not limited to intra prediction, even in inter prediction blocks with right inclined features cannot find similar motion information from left and above neighborhood.

In some examples, a technique that is referenced to as split unit coding order (SUCO) can be used. SUCO enables more flexible coding order, such as left to right (L2R) and right to left (R2L), to allow intra prediction from right reference pixels and inter prediction with right motion vector predictors. In some examples, if a SU is partitioned vertically, a flag is signaled to indicate L2R or R2L coding order. Further, if a SU is partitioned by quad tree structure, a flag is shared for above two units and bottom two units. If no flag is signaled for the coding order of a SU, the following coding orders of that SU implicitly inherit from previous level SU.

FIG. 13shows examples for splits and coding orders. For example, a split unit (1310) can be partitioned according to binary tree (BT) structure, triple tree (TT) structure, and quad-tree (QT) structure, and can be suitable coded in a left to right (L2R) order or a right to left (R2L) order.

For example, the split unit (1310) is vertically partitioned into units (1321) and (1322) according to BT structure. The units1321and1322can be coded in an L2R order or an R2L order. The split unit (1310) is horizontally partitioned into units (1331) and (1332) according to BT structure. The units (1331) and (1332) are coded generally in an above to bottom order.

In another example, the split unit (1310) is vertically partitioned into units (1341)-(1343) according to TT structure. The units (1341)-(1343) can be coded in an L2R order or an R2L order. The split unit (1310) is horizontally partitioned into units (1351)-(1352). The units (1351)-(1353) are coded generally in an above to bottom order.

In another example, the split unit (1310) is partitioned into units (1361)-(1364) according to QT structure. For L2R order, the units (1361)-(1364) can be coded following (1361), (1362), (1363) and (1364). For R2L order, the units (1361)-(1364) can be coded following (1362), (1361), (1364) and (1363).

FIG. 14shows an example of SUCO in a CTU. In theFIG. 14examples, a CTU (1410) is partitioned according to a tree structure (1450). The CTU (1410) is also referred to as a unit S1. The unit S1is partitioned into units S21-S24according to QT structure, and coded in the R2L order. The unit S21is horizontally partitioned into units S31-S32according to BT structure. The unit S31is vertically partitioned into units S41-S43according to TT structure, and coded in the R2L order. The unit S32is vertically partitioned into units S44-S45according to BT structure and coded in the L2R order. The unit S45is horizontally partitioned into units S51-S52according to BT structure. The unit S52is vertically partitioned into units S61-S62according to BT structure and coded in the L2R order. In theFIG. 14example, when a unit is further partitioned, the unit can be referred to as a split unit (SU). When a unit is not further partitioned, the unit can be referred to as a leaf CU.

In theFIG. 14example, due to the flexible coding order in SU level, the neighboring availability of a leaf CU become more diverse than common left and above neighbors in HEVC. For example, there are four availability cases if only left and right neighboring blocks are considered. Specifically, for the first case that is referred to as LR_10, the left neighboring block is available and the right neighboring block is not available; for the second case that is referred to as LR_01, the left neighboring block is not available and the right neighboring block is available; for the third case that is referred to as LR_11, both of the left neighboring block and the right neighboring block are available; and for the fourth case that is referred to as LR_00, both of the left neighboring block and the right neighboring block are not available. The above block is always available unless the current CU lies on the top boundary of a slice. Availability of the above left or above right corner block depends on the corresponding left or right neighbor availability.

When SUCO is used, the coding order and neighboring pixel availability become more complex. Aspects of the disclosure provide techniques to specify the search range of intra block copy when SUCO is used, given a specific reference sample memory size is allocated for intra block copy usage.

The proposed methods may be used separately or combined in any order. Further, each of the methods (or embodiments), encoder, and decoder may be implemented by processing circuitry (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program that is stored in a non-transitory computer-readable medium. In the following, the term block may be interpreted as a prediction block, a coding block, or a coding unit, i.e. CU.

It is noted that, in the following discussion, an update of reference sample memory is based on 64×64 block region. However, the disclosed techniques are not limited to such a size, other patterns of reference sample memory arrangements can be applied as well.

When SUCO is used, for a current coding block, the right neighboring blocks of the current block may be coded prior to the left neighboring blocks. To check whether a 64×64 block region has not yet been coded, both its top left corner and top right corner need to be checked. In some examples, a 64×64 block region has not yet been reconstructed only when none of its top left and top right corners have not yet been reconstructed.

For a general availability condition of a reference block, the reference block should be outside of current coding block. For example, the reference block is above the current block, or the reference block is to the left of current block, or the reference block is to the right of current block when SUCO is used.

For naming purpose, the 64×64 block region that has 1 CTU offset leftward as compared to current 64×64 block region is referred to as the collocated 64×64 region. In some embodiments, when the reference sample memory size is 1 CTU large, to check whether a reference block coming from the left CTU is valid, the top left corner of the corresponding collocated 64×64 block region in the current CTU (where a collocated location of that reference block's top left corner belongs to) is checked to have not yet been coded, and the top right corner of the same collocated 64×64 block region in the current CTU should be checked as well to have not yet been coded.

In some embodiments, considering that the reference block's top right corner may be located in a different 64×64 block region in the left CTU, compared with the reference block's top left corner, similar checks should be performed for the reference block's top right corner to make sure that the collocated 64×64 block region (for the reference block's top right corner) in the current CTU has not been coded. To do that, both the top left and top right corner of the collocated 64×64 region in current CTU may need to be checked.

Separately, to avoid the first coded block of a current 64×64 region in the current CTU can refer to its collocated 64×64 block region in the left CTU, the coordinates of the 64×64 block region where the reference block in the left CTU belongs to should be checked. In addition to checking that the current block's top left position shall not be collocated with the reference 64×64 block region's top left corner, the current block's top right position shall not be collocated with the reference 64×64 block region's top right corner either.

FIG. 15shows an example of reference search range constraints for intra picture block compensation. Without using SUCO, the coding order is from left to right, top to bottom. Thus, when a block's top left location is not coded, the rest of the block has not been coded either. Without using SUCO, to check whether a reference block's location in left CTU is valid (samples of the reference block are stored in the reference sample memory), the reference block's top left position is checked by a checking process. For example, the reference block's top left position is right shifted by a CTU width, such as 128, to a collocated point in the current CTU, and a collocated 64×64 block region (corresponding to an update of reference sample memory) that includes the collocated point is determined. Then, the top left position of the collocated 64×64 block region is checked. When the top left position of the collocated 64×64 block region has not been coded, the reference block is valid in the situation without using SUCO.

With SUCO, more checks are performed. In theFIG. 15example, the left CTU includes a plurality of update units for reference sample memory, such as four 64×64 block regions that are labeled as A′, B′, C′ and D′, and the current CTU includes a plurality of update units for reference sample memory, such as four 64×64 block regions that are labeled as A, B, C and D. In an example, the top right 64×64 block region B of the current CTU is coded first, thus, the reference sample memory stores samples for regions of A′, C′, D′ and B. The current block is the first coding block in top left 64×64 block region A of current CTU. According to the requirement of memory update process, the memory space for storing the entire top left 64×64 block region will be reset, so the reference samples in the top left 64×64 block region A′ in the left CTU cannot be used anymore.

In an example, using the checking process without SUCO, the top left position of the reference block1is right shifted, for example by 128, to determine the block region A as the collocated 64×64 block region. Then, the top left position of the block region A, as shown by (1501) inFIG. 5, is checked. In an example, since the top left position of region A has not been coded yet, a wrong decision (the reference block1is valid) may be made using only checking process without SUCO.

To overcome such issue, a few more checks can be added. For example, the top right corner of the region A, shown by (1502) inFIG. 15can be checked, and the top right corner of the region A needs to be not coded for the decision that the reference block1is valid. In another example, the top right corner of the block region A is checked not to be the collocated position of the reference block's 64×64 region's (A′) top right corner in order to make the decision that the reference block1is valid. Because the top right corner of the region A is the collocated position of the reference block's 64×64 region's (A′) top right corner, the decision cannot be made.

In some examples, the reference block may be positioned across 64×64 regions, and similar checks are performed on the top right corner of the reference block. For example, the reference block2is positioned across C′ and D′. The top left of the corner of reference block2is in the block region C′, and the top right corner of the reference block2is in the block region D′. The top left corner of the reference block2is used to find the collocated block region C. Then, the top left corner (shown by (1503) inFIG. 15) and the top right corner of the region C (shown by (1504) inFIG. 15) are checked for reference block validity. The reference block2can be valid when the top left corner (shown by (1503) inFIG. 15) and the top right corner of the region C (shown by (1504) inFIG. 15) have not been coded yet. The top right corner of the reference block2is used to find the collocated region D. Then, the top left corner (shown by (1505) inFIG. 15) and the top right corner (shown by (1506) inFIG. 15) of the region D are checked for reference block validity. The reference block2can be valid when the top left corner (1505) and the top right corner (1506) of the region D have not been coded yet.

According to some aspects of the disclosure, when SUCO is used, for a valid search range, the bitstream conformance requires the luma block vector mvL to obey the certain constraints. In an example, a current CTB is a luma CTB including a plurality of luma samples and a block vector mvL satisfies the following constraints for bitstream conformance when SUCO is used.

In some examples, first constraints are used to make sure that the reference block for the current block has been reconstructed. When the reference block has a rectangular shape, a reference block availability checking process can be implemented to check whether a top left sample and a bottom right sample of the reference block are reconstructed. When both the top left sample and the bottom right sample of the reference block are reconstructed, the reference block is determined to have been reconstructed.

For example, a reconstructed top left sample of the reference block should be available. In some examples, a derivation process for block availability can be invoked, the derivation process can receive a current luma location and a neighboring luma position as inputs, and generate an output that indicates whether a sample at the neighboring luma position has been reconstructed. For example, when the output is TRUE, the sample at the input position has been reconstructed; and when the output is FALSE, the sample at the input position hasn't been reconstructed yet.

Generally, the current luma position (xCurr, yCurr) is set to (xCb, yCb), which is the position of the top left sample of the current block. Further, mvL denotes block vector, mvL[0] denotes the x component and mvL[1] denotes the y component of the block vector, and the x component and the y component can have 4-bit for fractional parts of resolution in pixel. The current luma location (xCurr, yCurr) is set to be the top left sample of the current block (xCb, yCb), the neighboring luma location can be represented by (xCb+(mvL[0]>>4), yCb+(mvL[1]>>4)) which is the position of the top left sample of the reference block. In an example, a derivation process for reference block availability is invoked, the position of the top left sample of the reference block is used as an input, when an output is equal to TRUE, the top left sample of the reference block is reconstructed.

Similarly, the reconstructed bottom right sample of the reference block should be available. In some examples, a derivation process for block availability can be invoked, and the input to the derivation process includes the position of the bottom right sample of the reference block. For example, the current luma position is set to be (xCb, yCb), and width of the current block and the reference block is denoted by cbWidth, the height of the current block and the reference block is denoted by cbHeight. Then, the position of the bottom right sample of the reference block is (xCb+(mvL[0]>>4)+cbWidth−1, yCb+(mvL[1]>>4)+cbHeight−1). The position of the bottom right sample is input to the derivation process for block availability, when the output is TRUE, the bottom right sample of the reference block is reconstructed.

In some examples, second constraints ensure that the reference block is to the left and/or above of the current block and/or to the right of the current block, does not overlap with the current block. The second constraints can also include at least one of the following three conditions: 1) the value of (mvL[0]>>4)+cbWidth is less than or equal to 0, which indicates that the reference block is to the left of the current block and does not overlap with the current block; 2) the value of (mvL[1]>>4)+cbHeight is less than or equal to 0, which indicates that the reference block is above the current block and does not overlap with the current block; and 3) the value of (mvL[0]>>4) is greater than or equal to cbWidth, which indicates that the reference block is to the right of the current block and does not overlap with the current block.

The third constraints ensure the reference block is in an appropriate search range. In some examples, the third constrains can also include that the conditions in (Eq. 1)-(Eq. 4) are satisfied by the block vector mvL. Eq. 1 and Eq. 2 specify that a CTB including the reference block is in a same CTB row as the current CTB (i.e., the previously reconstructed CTB is in a same row as the current CTB when the reference block is in the previously reconstructed CTB). Eq. 3 and Eq. 4 specify that the CTB including the reference block is either in a left CTB column of the current CTB or a same CTB column as the current CTB. The conditions as described by Eq. 1-Eq. 4 specify that the CTB including the reference block is either the current CTB, or a left neighbor, such as the previously reconstructed CTB, of the current CTB (“left CTB”).

The fourth constraints ensure that the reference block is stored in the reference sample memory, in other words, the collocated block of the reference block has not been reconstructed. In some examples, the fourth constraints can include following conditions: when the reference block is in the left neighbor of the current CTB, a collocated region for the reference block is not reconstructed (i.e., no samples in the collocated region have been reconstructed). Further, the collocated region for the reference block is in the current CTB.

In an example, the above conditions can be specified as below: when (xCb+(mvL[0]>>4))>>CtbLog2SizeY is equal to (xCb>>CtbLog2SizeY)−1, and CtbLog2SizeY is 7, the derivation process for reference block availability is invoked. The input for the current luma location (xCurr, yCurr) is set to be (xCb, yCb) and the input for the neighboring luma location is (((xCb+(mvL[0]>>4)+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1), ((yCb+(mvL[1]>>4))>>(CtbLog2SizeY−1))>>(CtbLog2SizeY−1)). When an output of the derivation process is FALSE, the collocated region has not been reconstructed. Also, the luma location (((xCb+(mvL[0]>>4)+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1), ((yCb+(mvL[1]>>4))>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)) shall not be equal to (xCb, yCb).

The fifth constraints ensure that, when SUCO is used, the reference block is stored in the reference sample memory, in other words, the collocated block region (e.g., 64×64 block region in some examples) for the reference block has not been reconstructed. In some examples, the fifth constraints can include following conditions: when the reference block is in the left neighbor of the current CTB, a collocated block region for the reference block is not reconstructed (i.e., no samples in the collocated block region have been reconstructed). Further, the collocated block region for the reference block is in the current CTB.

In some embodiments, when SUCO is used and (xCb+(mvL[0]>>4))>>CtbLog2SizeY is equal to (xCb>>CtbLog2SizeY)−1 (which means the reference block is in the left CTB of the current CTB), the following conditions shall be true. It is noted that while the following description is based on that CtbLog2SizeY is equal to 7, the disclosed technique can be used for other suitable CTB size.

The fifth constraints include a condition to ensure the top right corner of the collocated 64×64 block region for the top left corner of the reference block has not been coded. For example, the derivation process for block availability is invoked. The inputs include the current luma location(xCurr, yCurr) that is set to (xCb, yCb) and the neighboring luma location that is the top right corner of the collocated 64×64 block region for the top left corner of the reference block (e.g., (1504) for the reference block2inFIG. 15) and represented by (((xCb+(mvL[0]>>4)+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)+CtbSizeY/2−1, ((yCb+(mvL[1]>>4))>>(CtbLog2SizeY−1)) (CtbLog2SizeY−1)). When the output of the derivation process is FALSE, the top right corner of the collocated 64×64 region for the top left corner of the reference block has not been coded.

The fifth constraints include a condition to ensure the top right corner of the collocated 64×64 block region for the top left corner of the reference block is not the top right corner of the current block. For example, the luma location (((xCb+(mvL[0]>>4)+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)+CtbSizeY/2−1, ((yCb+(mvL[1]>>4))>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)), which is the top right corner of the collocated 64×64 region for the top left corner of the reference block, shall not be equal to (xCb+cbWidth−1, yCb) which is the top right corner of the current block.

The fifth constrains include a condition to ensure the top left corner of the collocated 64×64 block region for the top right corner of the reference block has not been coded. In an example, the derivation process for block availability is invoked. The inputs to the derivation process include the current luma location (xCurr, yCurr) that is set equal to (xCb, yCb) and the neighboring luma location, that is set to the top left corner of the collocated 64×64 region for the top right corner of the reference block (e.g., (1505) for the reference block2inFIG. 15) the which can be represented by (((xCb+(mvL[0]>>4)+cbWidth−1+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1), ((yCb+(mvL[1]>>4))>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)). When the output of the derivation process is FALSE, the top left corner of the collocated 64×64 region for the top right corner of the reference block has not been coded.

The fifth constraints include a condition to ensure the top left corner of the collocated 64×64 region for the top right corner of the reference block is not the top right of the current block. For example, the luma location (((xCb+(mvL[0]>>4)+cbWidth−1+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1), ((yCb+(mvL[1]>>4))>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)) shall not be equal to (xCb+cbWidth−1, yCb).

The fifth constraints include a condition to ensure the top right corner of the collocated 64×64 block region for the top right corner of the reference block has not been coded. For example, the derivation process for block availability is invoked. The inputs to the derivation process include the current luma location (xCurr, yCurr) that is set equal to (xCb, yCb) and the neighboring luma location that is the top right corner of the collocated 64×64 block region for the top right corner of the reference block (e.g., (1506) for the reference block2), which can be represented by (((xCb+(mvL[0]>>4)+cbWidth−1+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)+CtbSizeY/2−1, ((yCb+(mvL[1]>>4))>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)). When the output is FALSE, the top right corner of the collocated 64×64 region for the top right corner of the reference block has not been coded.

The fifth constraints include a condition to ensure the top right corner of the collocated 64×64 region for the top right corner of the reference block is not the top right of the current block. For example, the luma location (((xCb+(mvL[0]>>4)+cbWidth−1+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)+CtbSizeY/2−1, ((yCb+(mvL[1]>>4))>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1)) shall not be equal to (xCb+cbWidth−1, yCb).

In the above description, the block vector components (e.g., mvL[0] and mvL[1]) include four bits to represent the fractional part of a pixel for the 1/16 integer sample accuracy, thus the block vector components are right shifted by 4. When the block vectors are stored in 1 integer sample accuracy, the shift operation is not needed. Also, the detail operations can be adjusted for other sample accuracy.

In some embodiments, the maximum block size for which SUCO is allowed is constrained to be no larger than 64×64 when IBC is enabled.

In some embodiments, the current CTU size is smaller than the allowed maximum reference memory buffer size (in the present disclosure, this maximum size is assumed to be the maximum allowed CTU size, such as 128×128 luma samples), then the reference sample memory can store multiple CTU sizes of reference samples.

FIG. 16shows an example with multiple CTUs in the reference sample memory. In theFIG. 16example, the reference sample memory size is 128×128 and the CTU size is 64×64. Then, in addition to current CTU, the left 3 CTU of reference samples can be fully available in the reference sample memory without additional condition check. Furthermore, the 4th left CTU may be conditionally available, using the similar logic as the above discussion (checking whether the memory to store samples from the 4th left CTU have been updated by the samples from current CTU).

FIG. 17shows a flow chart outlining a process (1700) according to an embodiment of the disclosure. The process (1700) can be used in the reconstruction of a block, so to generate a prediction block for the block under reconstruction. In various embodiments, the process (1700) are executed by processing circuitry, such as the processing circuitry in the terminal devices (410), (420), (430) and (440), the processing circuitry that performs functions of the video encoder (503), the processing circuitry that performs functions of the video decoder (510), the processing circuitry that performs functions of the video decoder (610), the processing circuitry that performs functions of the video encoder (703), and the like. In some embodiments, the process (1700) is implemented in software instructions, thus when the processing circuitry executes the software instructions, the processing circuitry performs the process (1700). The process starts at (S1701) and proceeds to (S1710).

At (S1710), prediction information of a current block is decoded from a coded video bitstream. The prediction information is indicative of intra block copy mode. The current block is one of a plurality of coding blocks in a CTB with a right to left coding order being allowed within the current CTB. For example, SUCO is used to enable flexible coding order in the current CTB.

At (S1720), a block vector is determined. The block vector points to a reference block in a same picture as the current block.

At (S1730), the reference block is ensured to be buffered in a reference sample memory based on at least a determination that a sample that is right of a leftmost sample of the reference block is buffered in the reference sample memory. In some examples, the fifth constraints are applied to ensure that reference block is buffered in the reference sample memory. In some embodiments, a sample at a top right corner of the reference block is determined to be buffered in the reference sample memory. In an embodiment, a collocated region in the current CTB is determined. The collocated region includes a collocated sample for the sample at the top right corner of the reference block in a left CTB. Then, the collocated region is checked to be not coded. In an example, a top left corner of the collocated region in the current CTB is checked to be not coded. Further, a top right corner of the collocated region in the current CTB is checked to be not coded. Other suitable conditions may be checked to ensure that the reference block is valid.

At (S1740), samples of the current block are reconstructed based on the reconstructed samples of the reference block. The reconstructed samples are retrieved from the reference sample memory. Then the process proceeds to (S1799) and terminates.

The techniques described above, can be implemented as computer software using computer-readable instructions and physically stored in one or more computer-readable media. For example,FIG. 18shows a computer system (1800) suitable for implementing certain embodiments of the disclosed subject matter.

Input human interface devices may include one or more of (only one of each depicted): keyboard (1801), mouse (1802), trackpad (1803), touch screen (1810), data-glove (not shown), joystick (1805), microphone (1806), scanner (1807), camera (1808).

Computer system (1800) can also include human accessible storage devices and their associated media such as optical media including CD/DVD ROM/RW (1820) with CD/DVD or the like media (1821), thumb-drive (1822), removable hard drive or solid state drive (1823), legacy magnetic media such as tape and floppy disc (not depicted), specialized ROM/ASIC/PLD based devices such as security dongles (not depicted), and the like.

Aforementioned human interface devices, human-accessible storage devices, and network interfaces can be attached to a core (1840) of the computer system (1800).

The core (1840) can include one or more Central Processing Units (CPU) (1841), Graphics Processing Units (GPU) (1842), specialized programmable processing units in the form of Field Programmable Gate Areas (FPGA) (1843), hardware accelerators for certain tasks (1844), and so forth. These devices, along with Read-only memory (ROM) (1845), Random-access memory (1846), internal mass storage such as internal non-user accessible hard drives, SSDs, and the like (1847), may be connected through a system bus (1848). In some computer systems, the system bus (1848) can be accessible in the form of one or more physical plugs to enable extensions by additional CPUs, GPU, and the like. The peripheral devices can be attached either directly to the core's system bus (1848), or through a peripheral bus (1849). Architectures for a peripheral bus include PCI, USB, and the like.

CPUs (1841), GPUs (1842), FPGAs (1843), and accelerators (1844) can execute certain instructions that, in combination, can make up the aforementioned computer code. That computer code can be stored in ROM (1845) or RAM (1846). Transitional data can be also be stored in RAM (1846), whereas permanent data can be stored for example, in the internal mass storage (1847). Fast storage and retrieve to any of the memory devices can be enabled through the use of cache memory, that can be closely associated with one or more CPU (1841), GPU (1842), mass storage (1847), ROM (1845), RAM (1846), and the like.

JEM: joint exploration model

VVC: versatile video coding

BMS: benchmark set

MV: Motion Vector

HEVC: High Efficiency Video Coding

SEI: Supplementary Enhancement Information

VUI: Video Usability Information

GOPs: Groups of Pictures

PUs: Prediction Units

CTUs: Coding Tree Units

CTBs: Coding Tree Blocks

HRD: Hypothetical Reference Decoder

SNR: Signal Noise Ratio

CPUs: Central Processing Units

GPUs: Graphics Processing Units

CRT: Cathode Ray Tube

CD: Compact Disc

DVD: Digital Video Disc

RAM: Random Access Memory

PLD: Programmable Logic Device

LAN: Local Area Network

GSM: Global System for Mobile communications

CANBus: Controller Area Network Bus

USB: Universal Serial Bus

PCI: Peripheral Component Interconnect

FPGA: Field Programmable Gate Areas

IC: Integrated Circuit

CU: Coding Unit