Patent Application
20250008138
This disclosure describes a set of advanced video/streaming coding/decoding technologies. More specifically, the disclosed technology involves improvement on block level adaptive weighted prediction (BAWP) to compensate local illumination variation.
Uncompressed digital video can include a series of pictures, and may specific bitrate requirements for storage, data processing, and for transmission bandwidth in streaming applications. One purpose of video coding and decoding can be the reduction of redundancy in the uncompressed input video signal, through various compression techniques.
The present disclosure describes various embodiments of methods, apparatus, and computer-readable storage medium for improving block level adaptive weighted prediction (BAWP) to model local illumination compensation (LIC).
According to one aspect, an embodiment of the present disclosure provides a method for decoding a current block of a current frame in a coded video bitstream. The method includes receiving, by a decoding device, a coded video bitstream comprising the current block of the current frame and a syntax element indicating a prediction mode for the current block. The device includes a memory storing instructions and a processor in communication with the memory, the memory also stores a plurality of scaling factor look-up tables. The method also includes determining, by the decoding device based on the coded video bitstream, the prediction mode based on a value of the syntax element, the prediction mode being used for predicting the current block based on a reference block of a reference frame; selecting, by the decoding device, a scaling factor look-up table from the plurality of scaling factor look-up tables based on at least one of the following: an inter prediction mode of the current block or a picture order count (POC) distance between the reference frame and the current frame, wherein a size of each of the plurality of scaling factor look-up tables is less than a predetermined threshold size; determining, by the decoding device, a scaling factor from the selected scaling factor look-up table; and reconstructing, by the decoding device, the current block based on the reference block and the determined scaling factor.
According to one aspect, an embodiment of the present disclosure provides a method for decoding a current block of a current frame in a coded video bitstream. The method includes receiving, by a device, a coded video bitstream. The device includes a memory storing instructions and a processor in communication with the memory. The method also includes determining, by the device based on the coded video bitstream, a prediction mode for predicting the current block based on a reference block of a reference frame; determining, by the device based on the coded video bitstream, a scaling factor for luma or chroma components of the current block; and reconstructing, by the device, the current block based on the reference block and the determined scaling factor according to a linear equation.
According to another aspect, an embodiment of the present disclosure provides an apparatus for processing a current block of a current frame in a coded video bitstream. The apparatus includes a memory storing instructions; and a processor in communication with the memory. When the processor executes the instructions, the processor is configured to cause the apparatus to perform the above methods for video decoding and/or encoding.
In another aspect, an embodiment of the present disclosure provides non-transitory computer-readable mediums storing instructions which when executed by a computer for video decoding and/or encoding cause the computer to perform the above methods for video decoding and/or encoding.
The above and other aspects and their implementations are described in greater detail in the drawings, the descriptions, and the claims.
Further features, the nature, and various advantages of the disclosed subject matter will be more apparent from the following detailed description and the accompanying drawings in which:
The invention will now be described in detail hereinafter with reference to the accompanied drawings, which form a part of the present invention, and which show, by way of illustration, specific examples of embodiments. Please note that the invention may, however, be embodied in a variety of different forms and, therefore, the covered or claimed subject matter is intended to be construed as not being limited to any of the embodiments to be set forth below. Please also note that the invention may be embodied as methods, devices, components, or systems. Accordingly, embodiments of the invention may, for example, take the form of hardware, software, firmware or any combination thereof.
Throughout the specification and claims, terms may have nuanced meanings suggested or implied in context beyond an explicitly stated meaning. The phrase “in one embodiment” or “in some embodiments” as used herein does not necessarily refer to the same embodiment and the phrase “in another embodiment” or “in other embodiments” as used herein does not necessarily refer to a different embodiment. Likewise, the phrase “in one implementation” or “in some implementations” as used herein does not necessarily refer to the same implementation and the phrase “in another implementation” or “in other implementations” as used herein does not necessarily refer to a different implementation. It is intended, for example, that claimed subject matter includes combinations of exemplary embodiments/implementations in whole or in part.
In general, terminology may be understood at least in part from usage in context. For example, terms, such as “and”, “or”, or “and/or,” as used herein may include a variety of meanings that may depend at least in part upon the context in which such terms are used. Typically, “or” if used to associate a list, such as A, B or C, is intended to mean A, B, and C, here used in the inclusive sense, as well as A, B or C, here used in the exclusive sense. In addition, the term “one or more” or “at least one” as used herein, depending at least in part upon context, may be used to describe any feature, structure, or characteristic in a singular sense or may be used to describe combinations of features, structures or characteristics in a plural sense. Similarly, terms, such as “a”, “an”, or “the”, again, may be understood to convey a singular usage or to convey a plural usage, depending at least in part upon context. In addition, the term “based on” or “determined by” may be understood as not necessarily intended to convey an exclusive set of factors and may, instead, allow for existence of additional factors not necessarily expressly described, again, depending at least in part on context.
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As shown, in FIG., 3, the receiver (331) may receive one or more coded video sequences from a channel (301). To combat network jitter and/or handle playback timing, a buffer memory (315) may be disposed in between the receiver (331) and an entropy decoder/parser (320) (“parser (320)” henceforth). The parser (320) may reconstruct symbols (321) from the coded video sequence. Categories of those symbols include information used to manage operation of the video decoder (310), and potentially information to control a rendering device such as display (312) (e.g., a display screen). The parser (320) may parse/entropy-decode the coded video sequence. The parser (320) 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. The 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 (320) may also extract from the coded video sequence information such as transform coefficients (e.g., Fourier transform coefficients), quantizer parameter values, motion vectors, and so forth. Reconstruction of the symbols (321) can involve multiple different processing or functional units. The units that are involved and how they are involved may be controlled by the subgroup control information that was parsed from the coded video sequence by the parser (320).
A first unit may include the scaler/inverse transform unit (351). The scaler/inverse transform unit (351) may receive a quantized transform coefficient as well as control information, including information indicating which type of inverse transform to use, block size, quantization factor/parameters, quantization scaling matrices, and the lie as symbol(s) (321) from the parser (320). The scaler/inverse transform unit (351) can output blocks comprising sample values that can be input into aggregator (355).
In some cases, the output samples of the scaler/inverse transform (351) can pertain to an intra coded block, i.e., a block that does not use 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 (352). In some cases, the intra picture prediction unit (352) may generate a block of the same size and shape of the block under reconstruction using surrounding block information that is already reconstructed and stored in the current picture buffer (358). The current picture buffer (358) buffers, for example, partly reconstructed current picture and/or fully reconstructed current picture. The aggregator (355), in some implementations, may add, on a per sample basis, the prediction information the intra prediction unit (352) has generated to the output sample information as provided by the scaler/inverse transform unit (351).
In other cases, the output samples of the scaler/inverse transform unit (351) can pertain to an inter coded, and potentially motion compensated block. In such a case, a motion compensation prediction unit (353) can access reference picture memory (357) based on motion vector to fetch samples used for inter-picture prediction. After motion compensating the fetched reference samples in accordance with the symbols (321) pertaining to the block, these samples can be added by the aggregator (355) to the output of the scaler/inverse transform unit (351) (output of unit 351 may be referred to as the residual samples or residual signal) so as to generate output sample information.
The output samples of the aggregator (355) can be subject to various loop filtering techniques in the loop filter unit (356) including several types of loop filters. The output of the loop filter unit (356) can be a sample stream that can be output to the rendering device (312) as well as stored in the reference picture memory (357) for use in future inter-picture prediction.
The video encoder (403) may receive video samples from a video source (401). According to some example embodiments, the video encoder (403) may code and compress the pictures of the source video sequence into a coded video sequence (443) in real time or under any other time constraints as required by the application. Enforcing appropriate coding speed constitutes one function of a controller (450). In some embodiments, the controller (450) may be functionally coupled to and control other functional units as described below. Parameters set by the controller (450) 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 the like.
In some example embodiments, the video encoder (403) may be configured to operate in a coding loop. The coding loop can include a source coder (430), and a (local) decoder (433) embedded in the video encoder (403). The decoder (433) reconstructs the symbols to create the sample data in a similar manner as a (remote) decoder would create even though the embedded decoder 433 process coded video steam by the source coder 430 without entropy coding (as any compression between symbols and coded video bitstream in entropy coding may be lossless in the video compression technologies considered in the disclosed subject matter). An observation that can be made at this point is that any decoder technology except the parsing/entropy decoding that may only be present in a decoder also may necessarily need to be present, in substantially identical functional form, in a corresponding encoder. For this reason, the disclosed subject matter may at times focus on decoder operation, which allies to the decoding portion of the encoder. The description of encoder technologies can thus be abbreviated as they are the inverse of the comprehensively described decoder technologies. Only in certain areas or aspects a more detail description of the encoder is provided below.
During operation in some example implementations, the source coder (430) may perform motion compensated predictive coding, which codes an input picture predictively with reference to one or more previously coded picture from the video sequence that were designated as “reference pictures.”
The local video decoder (433) may decode coded video data of pictures that may be designated as reference pictures. The local video decoder (433) replicates decoding processes that may be performed by the video decoder on reference pictures and may cause reconstructed reference pictures to be stored in a reference picture cache (434). In this manner, the video encoder (403) 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 (remote) video decoder (absent transmission errors).
The predictor (435) may perform prediction searches for the coding engine (432). That is, for a new picture to be coded, the predictor (435) may search the reference picture memory (434) 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 controller (450) may manage coding operations of the source coder (430), including, for example, setting of parameters and subgroup parameters used for encoding the video data.
Output of all aforementioned functional units may be subjected to entropy coding in the entropy coder (445). The transmitter (440) may buffer the coded video sequence(s) as created by the entropy coder (445) to prepare for transmission via a communication channel (460), which may be a hardware/software link to a storage device which would store the encoded video data. The transmitter (440) may merge coded video data from the video coder (403) with other data to be transmitted, for example, coded audio data and/or ancillary data streams (sources not shown).
The controller (450) may manage operation of the video encoder (403). During coding, the controller (450) 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: an Intra Picture (I picture), a predictive picture (P picture), a bi-directionally predictive picture (B Picture), a multiple-predictive picture. Source pictures commonly may be subdivided spatially into a plurality of sample coding blocks as described in further detail below.
For example, the video encoder (503) receives a matrix of sample values for a processing block. The video encoder (503) then determines whether the processing block is best coded using intra mode, inter mode, or bi-prediction mode using, for example, rate-distortion optimization (RDO).
In the example of
The inter encoder (530) is configured to receive the samples of the current block (e.g., a processing block), compare the block to one or more reference blocks in reference pictures (e.g., blocks in previous pictures and later pictures in display order), generate inter prediction information (e.g., description of redundant information according to inter encoding technique, motion vectors, merge mode information), and calculate inter prediction results (e.g., predicted block) based on the inter prediction information using any suitable technique.
The intra encoder (522) is configured to receive the samples of the current block (e.g., a processing block), compare the block to blocks already coded in the same picture, and generate quantized coefficients after transform, and in some cases also to generate intra prediction information (e.g., an intra prediction direction information according to one or more intra encoding techniques).
The general controller (521) may be configured to determine general control data and control other components of the video encoder (503) based on the general control data to, for example, determine the prediction mode of the block and provides a control signal to the switch (526) based on the prediction mode.
The residue calculator (523) may be configured to calculate a difference (residue data) between the received block and prediction results for the block selected from the intra encoder (522) or the inter encoder (530). The residue encoder (524) may be configured to encode the residue data to generate transform coefficients. The transform coefficients are then subject to quantization processing to obtain quantized transform coefficients. In various example embodiments, the video encoder (503) also includes a residual decoder (528). The residual decoder (528) is configured to perform inverse-transform, and generate the decoded residue data. The entropy encoder (525) may be configured to format the bitstream to include the encoded block and perform entropy coding.
In the example of
The entropy decoder (671) can be configured to reconstruct, from the coded picture, certain symbols that represent the syntax elements of which the coded picture is made up. The inter decoder (680) may be configured to receive the inter prediction information, and generate inter prediction results based on the inter prediction information. The intra decoder (672) may be configured to receive the intra prediction information, and generate prediction results based on the intra prediction information. The residual decoder (673) may be 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 reconstruction module (674) may be configured to combine, in the spatial domain, the residual as output by the residual decoder (673) and the prediction results (as output by the inter or intra prediction modules as the case may be) to form a reconstructed block forming part of the reconstructed picture as part of the reconstructed video.
It is noted that the video encoders (203), (403), and (503), and the video decoders (210), (310), and (610) can be implemented using any suitable technique. In some example embodiments, the video encoders (203), (403), and (503), and the video decoders (210), (310), and (610) can be implemented using one or more integrated circuits. In another embodiment, the video encoders (203), (403), and (503), and the video decoders (210), (310), and (610) can be implemented using one or more processors that execute software instructions.
Turning to block partitioning for coding and decoding, general partitioning may start from a base block and may follow a predefined ruleset, particular patterns, partition trees, or any partition structure or scheme. The partitioning may be hierarchical and recursive. After dividing or partitioning a base block following any of the example partitioning procedures or other procedures described below, or the combination thereof, a final set of partitions or coding blocks may be obtained. Each of these partitions may be at one of various partitioning levels in the partitioning hierarchy, and may be of various shapes. Each of the partitions may be referred to as a coding block (CB). For the various example partitioning implementations described further below, each resulting CB may be of any of the allowed sizes and partitioning levels. Such partitions are referred to as coding blocks because they may form units for which some basic coding/decoding decisions may be made and coding/decoding parameters may be optimized, determined, and signaled in an encoded video bitstream. The highest or deepest level in the final partitions represents the depth of the coding block partitioning structure of tree. A coding block may be a luma coding block or a chroma coding block. The CB tree structure of each color may be referred to as coding block tree (CBT). The coding blocks of all color channels may collectively be referred to as a coding unit (CU). The hierarchical structure of for all color channels may be collectively referred to as coding tree unit (CTU). The partitioning patterns or structures for the various color channels in in a CTU may or may not be the same.
In some implementations, partition tree schemes or structures used for the luma and chroma channels may not need to be the same. In other words, luma and chroma channels may have separate coding tree structures or patterns. Further, whether the luma and chroma channels use the same or different coding partition tree structures and the actual coding partition tree structures to be used may depend on whether the slice being coded is a P, B, or I slice. For example, For an I slice, the chroma channels and luma channel may have separate coding partition tree structures or coding partition tree structure modes, whereas for a P or B slice, the luma and chroma channels may share a same coding partition tree scheme. When separate coding partition tree structures or modes are applied, a luma channel may be partitioned into CBs by one coding partition tree structure, and a chroma channel may be partitioned into chroma CBs by another coding partition tree structure.
In some other example implementations for coding block partitioning, a quadtree structure may be used. Such quadtree splitting may be applied hierarchically and recursively to any square shaped partitions. Whether a base block or an intermediate block or partition is further quadtree split may be adapted to various local characteristics of the base block or intermediate block/partition.
In yet some other examples, a ternary partitioning scheme may be used for partitioning a base block or any intermediate block, as shown in
The above partitioning schemes may be combined in any manner at different partitioning levels. As one example, the quadtree and the binary partitioning schemes described above may be combined to partition a base block into a quadtree-binary-tree (QTBT) structure. In such a scheme, a base block or an intermediate block/partition may be either quadtree split or binary split, subject to a set of predefined conditions, if specified. A particular example is illustrated in
In some example implementations of the QTBT, the quadtree and binary splitting ruleset may be represented by the following predefined parameters and the corresponding functions associated therewith:
In some example implementations of the QTBT partitioning structure, the CTU size may be set as 128×128 luma samples with two corresponding 64×64 blocks of chroma samples (when an example chroma sub-sampling is considered and used), the MinQTSize may be set as 16×16, the MaxBTSize may be set as 64×64, the MinBTSize (for both width and height) may be set as 4×4, and the MaxBTDepth may be set as 4. The quadtree partitioning may be applied to the CTU first to generate quadtree leaf nodes. The quadtree leaf nodes may have a size from its minimum allowed size of 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If a node is 128×128, it will not be first split by the binary tree since the size exceeds the MaxBTSize (i.e., 64×64). Otherwise, nodes which do not exceed MaxBTSize could be partitioned by the binary tree. In the example of
In some example implementations, the QTBT scheme above may be configured to support a flexibility for the luma and chroma to have the same QTBT structure or separate QTBT structures. For example, for P and B slices, the luma and chroma CTBs in one CTU may share the same QTBT structure. However, for I slices, the luma CTBs maybe partitioned into CBs by a QTBT structure, and the chroma CTBs may be partitioned into chroma CBs by another QTBT structure. This means that a CU may be used to refer to different color channels in an I slice, e.g., the I slice may consist of a coding block of the luma component or coding blocks of two chroma components, and a CU in a P or B slice may consist of coding blocks of all three colour components.
The various CB partitioning schemes above and the further partitioning of CBs into PBs may be combined in any manner. The following particular implementations are provided as non-limiting examples.
Inter-prediction may be implemented, for example, in a single-reference mode or a compound-reference mode. In some implementations, a skip flag may be first included in the bitstream for a current block (or at a higher level) to indicate whether the current block is inter-coded and is not to be skipped. If the current block is inter-coded, then another flag may be further included in the bitstream as a signal to indicate whether the single-reference mode or compound-reference mode is used for the prediction of the current block. For the single-reference mode, one reference block may be used to generate the prediction block for the current block. For the compound-reference mode, two or more reference blocks may be used to generate the prediction block by, for example, weighted average. The reference block or reference blocks may be identified using reference frame index or indices and additionally using corresponding motion vector or motion vectors which indicate shift(s) between the reference block(s) and the current blocks in location relative to a frame, e.g., in horizontal and vertical pixels. For example, the inter-prediction block for the current block may be generated from a single-reference block identified by one motion vector in a reference frame as the prediction block in the single-reference mode, whereas for the compound-reference mode, the prediction block may be generated by a weighted average of two reference blocks in two reference frames indicated by two reference frame indices and two corresponding motion vectors. The motion vector(s) may be coded and included in the bitstream in various manners.
In some example implementations, one or more reference picture lists containing identification of short-term and long-term reference frames for inter-prediction may be formed based on the information in the Reference Picture Set (RPS). For example, a single picture reference list may be formed for uni-directional inter-prediction, denoted as L0 reference (or reference list 0) whereas two picture referenced lists may be formed for bi-direction inter-prediction, denoted as L0 (or reference list 0) and L1 (or reference list 1) for each of the two prediction directions. The reference frames included in the L0 and L1 lists may be ordered in various predetermined manners. The lengths of the L0 and L1 lists may be signaled in the video bitstream. Uni-directional inter-prediction may be either in the single-reference mode, or in the compound-reference mode when the multiple references for the generation of prediction block by weighted average in the compound prediction mode are on a same side of the frame where the block to be predicted is located. Bi-directional inter-prediction may only be compound mode in that bi-directional inter-prediction involves at least two reference blocks.
In some implementations, a merge mode (MM) for inter-prediction may be implemented. Generally, for the merge mode, the motion vector in single-reference prediction or one or more of the motion vectors in compound-reference prediction for the current PB may be derived from other motion vector(s) rather than being computed and signaled independently. For example, in an encoding system, the current motion vector(s) for the current PB may be represented by difference(s) between the current motion vector(s) and other one or more already encoded motion vectors (referred to as reference motion vectors). Such difference(s) in motion vector(s) rather than the entirety of the current motion vector(s) may be encoded and included in the bit stream and may be linked to the reference motion vector(s). Correspondingly in a decoding system, the motion vector(s) corresponding to the current PB may be derived based on the decoded motion vector difference(s) and decoded reference motion vector(s) linked therewith. As a specific form of the general merge mode (MM) inter-prediction, such inter-prediction based on motion vector difference(s) may be referred to as Merge Mode with Motion Vector Difference (MMVD). MM in general or MMVD in particular may thus be implemented to leverage correlations between motion vectors associated with different PB s to improve coding efficiency. For example, neighboring PB s may have similar motion vectors and thus the MVD may be small and can be efficiently coded. For another example, motion vectors may correlate temporally (between frames) for similarly located/positioned blocks in space.
In some example implementations of MMVD, a list of reference motion vector (RMV) or MV predictor candidates for motion vector prediction may be formed for a block being predicted. The list of RMV candidates may contain a predetermined number (e.g., 2) of MV predictor candidate blocks whose motion vectors may be used for predicting the current motion vector. The RMV candidate blocks may include blocks selected from neighboring blocks in the same frame and/or temporal blocks (e.g., identically located blocks in proceeding or subsequent frame of the current frame). These options represent blocks at spatial or temporal locations relative to the current block that are likely to have similar or identical motion vectors to the current block. The size of the list of MV predictor candidates may be predetermined. For example, the list may contain two or more candidates. To be on the list of RMV candidates, a candidate block, for example, may be required to have the same reference frame (or frames) as the current block, must exist (e.g., when the current block is near the edge of the frame, a boundary check needs to be performed), and must be already encoded during an encoding process, and/or already decoded during a decoding process. In some implementations, the list of merge candidates may be first populated with spatially neighboring blocks (scanned in particular predefined order) if available and meeting the conditions above, and then the temporal blocks if space is still available in the list. The neighboring RMV candidate blocks, for example, may be selected from left and top blocks of the current bock. The list of RMV predictor candidates may be dynamically formed at various levels (sequence, picture, frame, slice, superblock, etc.) as a Dynamic Reference List (DRL). DRL may be signaled in the bitstream.
In some implementations, an actual MV predictor candidate being used as a reference motion vector for predicting a motion vector of the current block may be signaled. In the case that the RMV candidate list contains two candidates, a one-bit flag, referred to as merge candidate flag may be used to indicate the selection of the reference merge candidate. For a current block being predicted in compound mode, each of the multiple motion vectors predicted using an MV predictor may be associated with reference motion vector from the merge candidate list. The encoder may determine which of the RMV candidate more closely predicts the MV of a current coding block and signal the selection as an index into the DRL.
In some example implementations of MMVD, after an RMV candidate is selected and used as base motion vector predictor for a motion vector to be predicted, a motion vector difference (MVD or a delta MV, representing the difference between the motion vector to be predicted and the reference candidate motion vector) may be calculated in the encoding system. Such MVD may include information representing a magnitude of MV difference and a direction of the MV difference, both of which may be signaled in the bitstream in various manners.
In some example implementations of the MMVD, a distance index may be used to specify magnitude information of the motion vector difference and to indicate one of a set of pre-defined offsets representing predefined motion vector difference from the starting point (the reference motion vector). An MV offset according to the signaled index may then be added to either horizontal or vertical component of the starting (reference) motion vector. An example predefined relation between distance index and predefined offsets is specified in Table 1.
In some example implementations of the MMVD, a direction index may be further signaled and used to represent a direction of the MVD relative to the reference motion vector. In some implementations, the direction may be restricted to either one of the horizontal and vertical directions. An example 2-bit direction index is shown in Table 2. In the example of Table 2, the interpretation of the MVD could be variant according to the information of the starting/reference MVs. For example, when the starting/reference MV corresponds to a uni-prediction block or corresponds to a bi-prediction block with both reference frame lists point to the same side of the current picture (i.e. POCs of the two reference pictures are both larger than the POC of the current picture, or are both smaller than the POC of the current picture), the sign in Table 2 may specify the sign (direction) of MV offset added to the starting/reference MV. When the starting/reference MV corresponds to a bi-prediction block with the two reference pictures at different sides of the current picture (i.e. the POC of one reference picture is larger than the POC of the current picture, and the POC of the other reference picture is smaller than the POC of the current picture), and a difference between the reference POC in picture reference list 0 and the current frame is greater than that between the reference POC in picture reference list 1 and the current frame, the sign in Table 2 may specify the sign of MV offset added to the reference MV corresponding to the reference picture in picture reference list 0, and the sign for the offset of the MV corresponding to the reference picture in picture reference list 1 may have an opposite value (opposite sign for the offset). Otherwise, if the difference between the reference POC in picture reference list 1 and the current frame is greater than that between the reference POC in picture reference list 0 and the current frame, the sign in Table 2 may then specify the sign of MV offset added to the reference MV associated with the picture reference list 1 and the sign for the offset to the reference MV associated with the picture reference list 0 has opposite value.
In some example implementations, the MVD may be scaled according to the difference of POCs in each direction. If the differences of POCs in both lists are the same, no scaling is needed. Otherwise, if the difference of POC in reference list 0 is larger than the one of reference list 1, the MVD for reference list 1 is scaled. If the POC difference of reference list 1 is greater than list 0, the MVD for list 0 may be scaled in the same way. If the starting MV is uni-predicted, the MVD is added to the available or reference MV.
In some example implementations of MVD coding and signaling for bi-directional compound prediction, in addition or alternative to separately coding and signaling the two MVDs, a symmetric MVD coding may be implemented such that only one MVD needs signaling and the other MVD may be derived from the signaled MVD. In such implementations, motion information including reference picture indices of list-0 and list-1 are not both signaled. Specifically, at a slice level, a flag may be included in the bitstream, referred to as “mvd_11_zero_flag,” for indicating whether the reference list-1 is not signaled in the bitstream. If this flag is 1, indicating that reference list-1 is equal to zero (and thus not signaled), then a bi-directional-prediction flag, referred to as “BiDirPredFlag” may be set to 0, meaning that there is no bi-directional-prediction. Otherwise, if mvd_11_zero_flag is zero, if the nearest reference picture in list-0 and the nearest reference picture in list-1 form a forward and backward pair of reference pictures or a backward and forward pair of reference pictures, BiDirPredFlag may be set to 1, and both list-0 and list-1 reference pictures are short-term reference pictures. Otherwise BiDirPredFlag is set to 0. BiDirPredFlag of 1 may indicate that a symmetrical mode flag is additionally signalled in the bitstream. The decoder may extract the symmetrical mode flag from the bitstream when BiDirPredFlag is 1. The symmetrical mode flag, for example, may be signaled (if needed) at the CU level and it may indicate whether the symmetrical MVD coding mode is being used for the corresponding CU. When the symmetrical mode flag is 1, it indicates the use of the symmetrical MVD coding mode, and that only reference picture indices of both list-0 and list-1 (referred to as “mvp_10_flag” and “mvp_11_flag”) are signaled with MVD associated with the list-0 (referred to as “MVD0”), and that the other motion vector difference, “MVD1”, is to be derived rather than signaled. For example, MVD1 may be derived as-MVD0. As such, only one MVD is signaled in the example symmetrical MVD mode.
In some other example implementations for MV prediction, a harmonized scheme may be used to implement a general merge mode, MMVD, and some other types of MV prediction, for both single-reference mode and compound-reference mode MV prediction. Various syntax elements may be used to signal the manner in which the MV for a current block is predicted. For example, for single-reference mode, the following MV prediction modes may be signaled: NEARMV—use one of the motion vector predictors (MVP) in the list indicated by a DRL (Dynamic Reference List) index directly without any MVD; NEWMV—use one of the motion vector predictors (MVP) in the list signaled by a DRL index as reference and apply a delta to the MVP (e.g., using MVD); and GLOBALMV—use a motion vector based on frame-level global motion parameters.
Likewise, for the compound-reference inter-prediction mode using two reference frames corresponding to two MVs to be predicted, the following MV prediction modes may be signaled: NEAR_NEARMV—use one of the motion vector predictors (MVP) in the list signaled by a DRL index without MVD for each of the two of MVs to be predicted. NEAR_NEWMV—for predicting the first of the two motion vectors, use one of the motion vector predictors (MVP) in the list signaled by a DRL index as reference MV without MVD; for predicting the second of the two motion vectors, use one of the motion vector predictors (MVP) in the list signaled by a DRL index as reference MV in conjunction with an additionally signaled delta MV (an MVD). NEW_NEARMV—for predicting the second of the two motion vectors, use one of the motion vector predictors (MVP) in the list signaled by a DRL index as reference MV without MVD; for predicting the first of the two motion vectors, use one of the motion vector predictors (MVP) in the list signaled by a DRL index as reference MV in conjunction with an additionally signaled delta MV (an MVD). NEW_NEWMV—use one of the motion vector predictors (MVP) in the list signaled by a DRL index as reference MV and use it in conjunction with an additionally signaled delta MV to predict for each of the two MVs. GLOBAL_GLOBALMV—use MVs from each reference based on their frame-level global motion parameters.
The term “NEAR” above thus refers to MV prediction using a reference MV without any MVD as a general merge mode, whereas the term “NEW” refers to MV prediction involving using a reference MV and offsetting it with a signaled or derived MVD as in an MMVD mode. For the compound inter-prediction, both the reference base motion vectors and the motion vector deltas above, may be generally different or independent between the two references or the two MVDs, even though the two MVDs, for example, may be correlated and such correlation may be leveraged to reduce the amount of information needed for signaling the two motion vector deltas. To leverage such correlation, a joint signaling of the two MVDs may be implemented and indicated in the bitstream, as described in further detail below.
In some example implementations of MVD, a predefined pixel resolution for the MVD may be allowed. For example, a ⅛-pixel motion vector precision (or accuracy) may be allowed. The MVD described above in the various MV prediction modes may be constructed and signaled in various manners. In some implementations, various syntax elements may be used to signal the motion vector difference(s) above in reference frame list 0 or list 1.
For example, a syntax element referred to as “mv_joint” may specify which components of the motion vector difference associated therewith are non-zero. m For example, mv_joint having a value of: 0 may indicate that there is no non-zero MVD along either the horizontal or the vertical direction; 1 may indicate that there is non-zero MVD only along the horizontal direction; 2 may indicate that there is non-zero MVD only along the vertical direction; and/or 3 may indicate that there is non-zero MVD along both the horizontal and the vertical directions.
When the “mv_joint” syntax element for an MVD signals that there is no non-zero MVD component, then no further MVD information may be signaled. However, if the “mv_joint” syntax signals that there is one or two non-zero components, then additional syntax elements may be further signaled for each of the non-zero MVD components as described below.
For example, a syntax element referred to as “mv_sign” may be used to additionally specify whether the corresponding motion vector difference component is positive or negative.
For another example, a syntax element referred to as “my class” may be used to specify a class of the motion vector difference among a predefined set of classes for the corresponding non-zero MVD component. The predefined classes for motion vector difference, for example, may be used to divide a contiguous magnitude space of the motion vector difference into non-overlapping ranges of classes. A signaled MVD class thus indicates the magnitude range of the corresponding MVD component. In the example implementation shown in Table 3 below, a higher class corresponds to motion vector differences having range of a larger magnitude. The symbol (n, m] is used for representing a range of motion vector difference that is greater than n pixels, and smaller than or equal to m pixels.
In some other examples, a syntax element referred to as “mv_bit” may be further used to specify an integer part of the offset between the non-zero motion vector difference component and starting magnitude of a correspondingly signaled MV class magnitude range. In some other examples, a syntax element referred to as “mv_fr” may be further used to specify first 2 fractional bits of the motion vector difference for a corresponding non-zero MVD component, whereas a syntax element referred to as “mv_hp” may be used to specify a third fractional bit of the motion vector difference (high resolution bit) for a corresponding non-zero MVD component. The two-bit “mv_fr” essentially provides ¼ pixel MVD resolution, whereas the “mv_hp” bit may further provide a ⅛-pixel resolution. In some other implementations, more than one “mv_hp” bit may be used to provide MVD pixel resolution finer than ⅛ pixel. In some example implementations, additional flags may be signaled at one or more of the various levels to indicate whether ⅛-pixel or higher MVD resolution is supported. If MVD resolution is not applied to a particular coding unit, then the syntax elements above for the corresponding non-supported MVD resolution may not be signaled.
However, in some other example implementations, resolution for motion vector difference in various MVD magnitude classes may be differentiated or adaptive. Specifically, high resolution MVD for large MVD magnitude of higher MVD classes may not provide statistically significant improvement in compression efficiency or coding gain. As such, the MVDs may be coded with decreasing or non-increasing resolution (integer pixel resolution or fractional pixel resolution) for larger MVD magnitude ranges, which correspond to higher MVD magnitude classes. The term “resolution” may be further referred to as “pixel resolution.” Adaptive MVD resolution may be implemented in various manners as described by the example implementations below for achieving an overall better compression efficiency. In particular, the reduction of number of signaling bits by aiming at less precise MVD may be greater than the additional bits needed for coding inter-prediction residual as a result of such less precise MVD, due to the statistical observation that treating MVD resolution for large-magnitude or high-class MVD at similar level as that for low-magnitude or low-class MVD in a non-adapted manner may not significantly increase inter-prediction residual coding efficiency for bocks with large-magnitude or high-class MVD. In other words, using higher MVD resolutions for large-magnitudes or high-class MVD may not produce much coding gain over using lower MVD resolutions.
In some implementations, for NEW_NEARMV and NEAR_NEWMV mode, the precision of the MVD depends on the associated class and the magnitude of MVD. Firstly, fractional MVD may be allowed only if MVD magnitude is equal to or less than one-pixel. Secondly, only one MVD value may be allowed when the value of the associated MV class is equal to or greater than MV_CLASS_1, and the MVD value in each MV class is derived as 4, 8, 16, 32, 64 for MV class 1 (MV_CLASS_1), 2 (MV_CLASS_2), 3 (MV_CLASS_3), 4 (MV_CLASS_4), or 5 (MV_CLASS_5). In some examples, the allowed single value may be the higher end values of the respective ranges for these MV classes in Table 3. The allowed MVD values in each MV class may be illustrated in Table 4.
In some example implementations, each MVD class may be associated with a single allowed resolution. In some other implementations, one or more MVD classes may each be associated with two or more optional MVD pixel resolutions. For example, the adaptively allowed MVD pixel resolution may include but not limited to 1/64-pel (pixel), 1/32-pel, 1/16-pel, ⅛-pel, 1-4-pel, ½-pel, 1-pel, 2-pel, 4-pel . . . (in descending order of resolution).
In some other example implementations, for MV classes equal to or higher than a threshold MV class, only a single MVD value may be allowed. For example, such threshold MV class may be MV_CLASS 2. Thus, MV_CLASS_2 and above may only be allowed to have a single MVD value and without fractional pixel resolution.
Turning to the various compound inter-prediction mode where each MV may be predicted by a reference motion vector and coded by an MVD, the two MVDs may be separately signaled or jointly signaled in the bit stream, as described above. As such, in some example implementations, besides the NEAR_NEARMV, NEAR_NEWMV, NEW_NEARMV, NEW_NEWMV, and GLOBAL_GLOBALMV modes described above, another inter-prediction mode, referred to as JOINT_NEWMV may be introduced for a mode in which the MVDs for joint signaling of reference list 0 and 1. Specifically, if the inter-prediction mode is indicated as NEW_NEWMV, then the MVDs for reference lists 0 and 1 are separately signaled, whereas when the inter-prediction mode is indicated as JOINT_NEWMV mode, the MVDs for reference lists 0 and 1 are jointly signaled. Particularly for the joint MVDs, only one MVD, referred to as joint_delta_mv, may need to be signaled and transmitted in the bitstream, and the MVDs for reference lists 0 and 1 may be derived from joint_delta_mv. The derived MVDs may then be combined with the reference motion vectors in the reference list 0 or 1 to generate the two motion vectors for locating the reference blocks for compound inter-prediction.
In some implementations of compound inter-prediction, the JOINT_NEWMV mode may be signaled together with NEAR_NEARMV, NEAR_NEWMV, NEW_NEARMV, NEW_NEWMV, and GLOBAL_GLOBALMV mode. In such implementations, a syntax may be included in the bitstream for an indication of any one of these alternative compound inter-prediction modes, at any one of various signaling levels (e.g., sequence level, picture level, frame level, slice level, tile level, superblock level, and the like). Alternatively, the JOINT_NEWMV mode may be implemented as a submode of the NEW_NEWMV mode. In other words, under the NEW_NEWMV mode, the two MVDs for the two reference blocks are either jointly signaled (hence the JOINT_NEWMV submode) or not (another submode of the NEW_NEWMV mode). In such an implementation, a first syntax element may be included in the bitstream for indication of any one the NEAR_NEARMV, NEAR_NEWMV, NEW_NEARMV, NEW_NEWMV, and GLOBAL_GLOBALMV modes, and when the first syntax element indicates that NEW_NEWMV mode is selected for the coding block, then a second syntax element may be further included in the bitstream and extractable by a decoder for indicating whether the MVDs for the coding block are separately signaled or jointly signaled.
In some example implementations, when JOINT_NEWMV mode is signaled, and the POC distances between two reference frames and current frame are different, the MVD may scaled for reference list 0 or reference list 1 based on the POC distances. To be specific, the distance between reference frame list 0 and current frame may be denoted as td0 and the distance between reference frame list 1 and current frame may be denoted as td1. If td0 is equal to or larger than td1, joint_mvd may be directly used for reference list 0 and the MVD for reference list 1 may be derived from joint_mvd based on the equation (1).
Otherwise, if td1 equal to or larger than td0, joint_mvd is directly used for reference list 1 and the MVD for reference list 0 is derived from joint_mvd based on the equation (2).
In some example implementations, another inter coded mode, named as AMVDMV, may be added to single reference case. When AMVDMV mode is selected, it indicates that AMVD (Adaptive Motion Vector Difference) is applied to signal MVD. One flag, e.g., named as amvd_flag, may be added under the JOINT_NEWMV mode to indicate whether AMVD is applied to joint MVD coding mode or not. When adaptive MVD resolution is applied to joint MVD coding mode, also named as joint AMVD coding mode, MVD for two reference frames are jointly signaled and the precision of MVD is implicitly determined by MVD magnitudes. Otherwise, MVD for two (or more than two) reference frames are jointly signaled, and conventional MVD coding is applied. Alternatively, one new inter prediction mode, named as JOINT_AMVDNEWMV is added to indicate that AMVD is applied to joint MVD coding mode.
Turning to compound inter modes, as shown in
Alternatively, as shown in
In some implementations, adaptive motion vector resolutions (AMVR) may be supported. In a specific example implementation, a total of 7 MV precisions (8, 4, 2, 1, ½, ¼, ⅛) may be supported. For each prediction block, an AMVR encoder may search all the supported precision values and signals the best precision to the decoder.
To reduce the encoder run-time, two MV precision sets are supported. Each precision set may contain, for example, 4 predefined precisions. The precision set may be adaptively selected at the frame level based on the value of maximum precision of the frame. The maximum precision may be signaled in the frame header. Table 5 summarizes example supported precision values based on the example frame level maximum precision.
In some example implementations of AMVR, there may be a frame level flag to indicate if the MVs of the frame contains sub-pel precisions or not. The AMVR may be enabled only if the value of cur_frame_force_integer_mv flag is 0. In the AMVR, if precision of the block is lower than the maximum precision, motion model and interpolation filters may not be signaled. If the precision of a block is lower than the maximum precision, motion mode is inferred to translation motion and interpolation filter is inferred to REGULAR interpolation filter. Similarly, if the precision of the block is either 4-pel or 8-pel, inter-intra mode may not be signaled and may be inferred to be 0.
In some implementations, when one block is coded as joint MVD coding mode, JOINT_NEWMV or JOINT_AMVDNEWMV, a new syntax, named as mvd_scaling_factor_idx, may be signaled into the bitstream to explicitly indicate the scaling factor for MVD between reference frame 0 and reference frame 1. As shown in Table 6 and Table 7, two pre-defined look-up tables may be used to store the supported/allowed scaling factors for JOINT_NEWMV or JOINT_AMVDNEWMV, separately. The associated entry index for the selected scaling factor in the look-up table may be signaled in the bitstream. For JOINT_AMVDNEWMV mode, same scaling factors are applied to both vertical and horizontal components of the MVD for reference frame list 0 and/or 1. For JOINT_NEWMV mode, the scaling factor for one component (either vertical component or horizontal component) of MVD may be restricted to be 1, and the scaling factor for the other component of MVD may be other values, for example 2 or ½. In one example, the MVD for reference frame list 0 or 1 (mvd_ref0 or mvd_ref1) is calculated in the following equation.
In some example implementations, in a bi-prediction with CU-level weight (BCW), a bi-prediction signal may be generated by averaging two prediction signals obtained from two different reference pictures and/or using two different motion vectors. In some other implementations, the bi-prediction mode may be extended beyond simple averaging to allow weighted averaging of the two prediction signals. For example, Pbi-pred=((8−w)*P0+w*P1+4)»3. Five weights may be allowed in the weighted averaging bi-prediction, w∈{−2, 3, 4, 5,10}. When w is equal to 4, equal weighting factor is used to do the weighted average of two prediction samples. For each bi-predicted CU, the weight w may be determined in one of two ways: 1) for a non-merge CU, the weight index is signalled after the motion vector difference; and/or 2) for a merge CU, the weight index is inferred from neighbouring blocks based on the merge candidate index. BCW may be only applied to CUs with 256 or more luma samples (i.e., CU width times CU height is greater than or equal to 256). For low-delay pictures, all 5 weights are used. For non-low-delay pictures, only 3 weights (w∈{3,4,5}) are used.
In another implementations, the COMPOUND_AVERAGE mode may be extended to enable weighted averaging of the prediction signals. This extended mode is named as compound weighted prediction (CWP). Specifically, when the two reference frames are from different directions, five weighting factors w∈{8, 10, 6, 12, 4} are supported, while when they are from the same direction, five different weighting factors w∈{8, 12, 4, 20, −4} are supported. As a result, the above equation may be modified as, P(x, y)=(W×P0(x, y)+(16−W)×P1(x, y)+8)»4.
In some implementations, the index of the selected weighting factor may be signaled when all of the following conditions are satisfied: (i) Compound type is COMPOUND_AVERAGE; (ii) Inter prediction mode is NEAR_NEARMV, JOINT_NEWMV, or JOINT_AMVDNEWMV; and (iii) MVD scaling factors (1, 1) are used in joint MVD mode. In some implementations, the index of the selected weighting factor may be signaled when only a portion of the above conditions may be satisfied. In some implementations, for skip mode, the index of the selected weighting factor is inferred from the neighboring blocks based on the DRL index of motion vector predictor.
In some implementations, a block adaptive weighted prediction (BAWP) may comprise a block-level weighted prediction to model local illumination variation between current block and its prediction block as a function of that between current block template (or the causal samples of current block) and reference block template. The template (or referred as current template, 1212) of the current block (1210) and the template (or referred as reference template, 1222) of the reference block (1220) are illustrated in
In some implementations, when one block is coded as BAWP mode, one flag may be signaled to indicate whether explicit or implicit signaling for BAWP scaling factors is used. When implicit signaling of BAWP scaling factors is employed, the BAWP scaling factor and offset value may be derived from the linear equation based on the template of current block and the template of the reference block pointed by the motion vector of current block. When explicit signaling of BAWP scaling factors is employed, another flag is signaled to indicate which scaling factor is used for current block and the offset is derived as zero. The supported scaling factors may be stored in one or multiple pre-defined look-up tables, and the index of the scaling factors in the look-up table is signaled into the bitstream and parsed at the decoder side.
In the present disclosure, look-up tables may also be referred as lists, and scaling factor look-up tables may be referred as lists of scaling factor candidates. In the present disclosure, a NEARMV mode may be referred as a coding mode that inherits neighboring block motion vectors; and/or a NEWMV mode may be referred as a coding mode that signals motion vector difference relative to a motion vector predictor selected from a spatially or temporally neighboring block; and/or an AMVDNEWMV mode may be referred as a coding mode that signals motion vector difference relative to a motion vector predictor selected from a spatially or temporally neighboring block and the precision of the motion vector is implicitly determined based on the magnitude of the motion vector.
In some implementations, there are some issues or problems associated with BAWP method, particularly the look-up tables storing scaling factors, which may be addressed or improved to increase coding/decoding efficiency. For a non-limiting example, the distribution of supported scaling factors may vary depending on coded information, so there may be room for further improvement on the signaling of scaling factors to enhance the coding/decoding efficiency. The present disclosure describes various embodiments for enhancing BAWP, addressing at least one of the issues or problems discussed above, improving coding/decoding efficiency, and advancing the video codec technology.
Various embodiments and/or implementations described in the present disclosure may be performed 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). The one or more processors execute a program that is stored in a non-transitory computer-readable medium. In the present disclosure, the term block may be interpreted as a prediction block, a coding block, or a coding unit (CU).
Another exemplary method may include a portion or all of the following steps: receiving a coded video bitstream; determining, based on the coded video bitstream, a prediction mode for predicting the current block based on a reference block of a reference frame; selecting a scaling factor look-up table from a plurality of scaling factor look-up tables based on at least one of the following: an inter prediction mode of the current block or a picture order count (POC) distance between the reference frame and the current frame; determining, based on the coded video bitstream, a scaling factor from the selected scaling factor look-up table; and/or reconstructing the current block based on the reference block and the determined scaling factor according to a linear equation.
In any portion or combination of the implementations above, the plurality of scaling factor look-up tables comprises a same number of scaling factors. For example, the number of scaling factors in the look-up table may be 2, 3, 4, 5, or 6.
In any portion or combination of the implementations above, the selecting the scaling factor look-up table from the plurality of scaling factor look-up tables comprises: in response to the inter prediction mode of the current block being a NEARMV mode, selecting a first look-up table of the plurality of scaling factor look-up tables as the scaling factor look-up table; and/or in response to the inter prediction mode of the current block being an AMVDNEWMV mode, selecting a second look-up table of the plurality of scaling factor look-up tables as the scaling factor look-up table; and/or in response to the inter prediction mode of the current block being a NEWMV mode, selecting a third look-up table of the plurality of scaling factor look-up tables as the scaling factor look-up table.
In any portion or combination of the implementations above, scaling factors in the first look-up table have smaller absolute value than a threshold; scaling factors in the second look-up table have larger absolute value than the threshold; and/or scaling factors in the third look-up table have larger absolute value than the threshold, wherein the threshold is a pre-defined threshold or a derived threshold.
In any portion or combination of the implementations above, the selecting the scaling factor look-up table from the plurality of scaling factor look-up tables comprises: in response to the POC distance being smaller than a threshold, selecting a first look-up table of the plurality of scaling factor look-up tables as the scaling factor look-up table; and/or in response to the POC distance being larger than the threshold, selecting a second look-up table of the plurality of scaling factor look-up tables as the scaling factor look-up table.
In any portion or combination of the implementations above, the selecting the scaling factor look-up table from the plurality of scaling factor look-up tables comprises: in response to the inter prediction mode of the current block being a NEARMV mode and the POC distance being smaller than a threshold, selecting a first look-up table of the plurality of scaling factor look-up tables as the scaling factor look-up table; and/or in response to the inter prediction mode of the current block being an AMVDNEWMV mode and the POC distance being smaller than the threshold, selecting a second look-up table of the plurality of scaling factor look-up tables as the scaling factor look-up table; and/or in response to the inter prediction mode of the current block being a NEWMV mode and the POC distance being smaller than the threshold, selecting a third look-up table of the plurality of scaling factor look-up tables as the scaling factor look-up table; and/or in response to the inter prediction mode of the current block being the NEARMV mode and the POC distance being larger than a threshold, selecting a fourth look-up table of the plurality of scaling factor look-up tables as the scaling factor look-up table; and/or in response to the inter prediction mode of the current block being the AMVDNEWMV mode and the POC distance being larger than the threshold, selecting a fifth look-up table of the plurality of scaling factor look-up tables as the scaling factor look-up table; and/or in response to the inter prediction mode of the current block being the NEWMV mode and the POC distance being larger than the threshold, selecting a sixth look-up table of the plurality of scaling factor look-up tables as the scaling factor look-up table.
In any portion or combination of the implementations above, the plurality of scaling factor look-up tables comprises a same number of scaling factors.
In any portion or combination of the implementations above, the determining, based on the coded video bitstream, the prediction mode for predicting the current block based on the reference block of the reference frame comprises: in response to the inter prediction mode of the current block being a NEARMV mode or a NEWMV mode, extracting a flag from the coded video bitstream, wherein the flag indicates the prediction mode for predicting the current block based on the reference block of the reference frame.
In any portion or combination of the implementations above, in response to the inter prediction mode of the current block being an AMVDNEWMV mode, the flag is disabled.
In any portion or combination of the implementations above, the method further includes in response to the POC distance being larger than or equal to a threshold, adding an offset to the scaling factor or multiplying a factor to the scaling factor.
In any portion or combination of the implementations above, the method further includes determining, by the device, the reference block of the reference frame based on a motion vector.
In any portion or combination of the implementations above, the reconstructing the current block based on the reference block and the determined scaling factor according to the linear equation comprises: computing pixel values of the current block as a*p+b, wherein a is the determined scaling factor, b is a determined offset, and p is a reference pixel value at a reference point determined by a motion vector.
The present disclosure describes another exemplary method for decoding a current block of a current frame in a coded video bitstream. The method includes a portion or all of the following steps: receiving, by a device comprising a memory storing instructions and a processor in communication with the memory, the coded video bitstream; determining, by the device based on the coded video bitstream, a prediction mode for predicting the current block based on a reference block of a reference frame; determining, by the device based on the coded video bitstream, a scaling factor for luma or chroma components of the current block; and reconstructing, by the device, the current block based on the reference block and the determined scaling factor according to a linear equation.
In any portion or combination of the implementations above, signaling of the scaling factor for the chroma component is based on signaling of the scaling factor for the luma component. In any portion or combination of the implementations above, in response to a luma flag being signaled for the luma component, a chroma flag for the chroma component is signaled; and/or in response to a luma flag not being signaled for the luma component, a chroma flag for the chroma component is not signaled.
In any portion or combination of the implementations above, in response to a luma flag being signaled for the luma component and a chroma flag for the chroma component being signaled, the scaling factor for the luma component is used as the scaling factor for the chroma component.
In any portion or combination of the implementations above, the determining, based on the coded video bitstream, the prediction mode for predicting the current block based on the reference block of the reference frame comprises: extracting a flag from the coded video bitstream, wherein the flag indicates the prediction mode for predicting the current block based on the reference block of the reference frame.
In any portion or combination of the implementations above, the method may further include deriving a derived scaling factor based on a current template of the current block and a reference template of the reference block.
In any portion or combination of the implementations above, the method may further include determining the reference block of the reference frame based on a motion vector.
In any portion or combination of the implementations above, the reconstructing the current block based on the reference block and the determined scaling factor according to the linear equation comprises: computing pixel values of the current block as a*p+b, wherein a is the determined scaling factor, b is a determined offset, and p is a reference pixel value at a reference point determined by a motion vector.
In various embodiments, when a block adaptive weighted prediction is applied to one block, one flag (e.g., called bawp_type) may be signaled to indicate whether explicit or implicit signaling for BAWP scaling factors is used. When explicit signaling of weighted prediction scaling factors is employed for current block, the scaling factor or its corresponding index in look-up table(s) may be signaled into the bitstream and parsed at the decoder side. The offset values β may be derived from the linear equation between reference block and current block.
In some implementations, the context for signaling bawp_type may depend on the coded information of current block. In some implementations, the context for signaling bawp_type depends on the inter prediction mode of current block. For a non-limiting example, a first context is used when current block is NEARMV mode, and/or a second context is used when current block is AMVDNEWMV mode, and/or otherwise the third context is used.
In various embodiments, In one embodiment, multiple pre-defined look-up tables are supported, and the selection of the look-up table for each block is implicitly determined based on the encoded/decoded information of current block and/or the neighboring blocks, including but not limited to inter prediction mode information, reference frame, distance between reference frame and current frame, temporal level in the GOP structure, the index/value of the scaling factors and/or offset values of neighboring blocks, and so on. Note that the encoded/decoded information may include one or a combination of multiple of the above parameters. Supporting multiple pre-defined look-up tables can ensure that the size of each look-up table is small, which can improve the lookup time. Specifically, in one embodiment, a size of each of the plurality of scaling factor look-up tables is less than a predetermined threshold size. In some implementations, the BAWP is disabled (e.g., bwap_flag equals 0) for AMVDNEWMV mode, and/or is enabled (e.g., bwap_flag equals to 1) for NEARMV mode or NEWMV mode.
In some implementations, the selection of the look-up tables is implicitly determined based on the inter prediction mode and/or the picture order count distance between the reference frame and current frame. For a non-limiting example, the first look-up table is used for NEARMV mode, and the second look-up table is used for AMVDNEWMV mode, and the third look-up table is used for NEWMV mode.
In some implementations in various embodiments in the present disclosure, a “first” item may refer to an “earliest” (or the most top) item in a list, and does not merely refer to “an” item. For example, a “first” look-up table in a plurality of look-up tables may refer to the “most top” look-up table in the look-up table list (i.e., the plurality of look-up tables).
In one embodiment, when comparing to the look-up tables for AMVDNEWMV and NEWMV mode, the supported scaling factor for NEARMV mode is closer to one predefined (or derived) threshold. For non-limiting example, the threshold may be 1.
In some implementations, the size of the different look-up tables is the same. For non-limiting example, the size of the look-up table may be 2.
In some implementations, when the picture order count distance between current frame and reference frame is greater than or equal to one threshold, and a predefined offset (delta for scaling factor) is added (or multiplied) to the selected scaling factor for current block. In one non-limiting example, the threshold is set to 4.
In various embodiments, the signaling of weighted prediction scaling factor is only applied to a subset of multiple color components, e.g., luma component.
In various embodiments, the signaling of weighted prediction scaling factor may be signaled for luma and chroma components (or YUV channels) separately.
In some implementations, a luma flag for the luma component may be signed first. When the luma flag is off, a chroma flag for the chroma component may not be signed. When the luma flag is on the chroma flag may be further signaled. When the chroma flag is on, luma signaling factor for the luma component may be used as the chroma signaling factor for the chroma component.
In some implementations, the signaling of weighted prediction scaling factor for a first color component (for example, chroma components (or UV channels)) depends on whether explicit (or implicit) signaling of weighted prediction scaling factor is applied to a second color component (for example, luma component) or not.
In some implementations, when explicit signaling of weighted prediction scaling factor is applied to luma component and weighted prediction is also applied to chroma component, then only the explicit signaling of scaling factor is allowed for chroma component.
In some implementations, when implicit or explicit signaling of weighted prediction scaling factor is applied to luma component and weighted prediction is also applied to chroma component, then chroma may share the same weighted prediction scaling factor as luma component.
Various embodiments in the present disclosure may include methods for encoding a current block into a video bitstream, which are performed by an encoder, including inverse processes as any portion or all of the processes that are described for the decoder.
Operations above may be combined or arranged in any amount or order, as desired. Two or more of the steps and/or operations may be performed in parallel. Embodiments and implementations in the disclosure may be used separately or combined in any order. Further, each of the methods (or embodiments), an encoder, and a 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. Embodiments in the disclosure may be applied to a luma block or a chroma block. The term block may be interpreted as a prediction block, a coding block, or a coding unit, i.e. CU. The term block here may also be used to refer to the transform block. In the following items, when saying block size, it may refer to either the block width or height, or maximum value of width and height, or minimum of width and height, or area size (width*height), or aspect ratio (width: height, or height: width) of the block.
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,
The computer software can be coded using any suitable machine code or computer language, that may be subject to assembly, compilation, linking, or like mechanisms to create code comprising instructions that can be executed directly, or through interpretation, micro-code execution, and the like, by one or more computer central processing units (CPUs), Graphics Processing Units (GPUs), and the like. The instructions can be executed on various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smartphones, gaming devices, internet of things devices, and the like.
The components shown in
Computer system (1800) may include certain human interface input devices. 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) may also include certain human interface output devices. Such human interface output devices may be stimulating the senses of one or more human users through, for example, tactile output, sound, light, and smell/taste. Such human interface output devices may include tactile output devices (for example tactile feedback by the touch-screen (1810), data-glove (not shown), or joystick (1805), but there can also be tactile feedback devices that do not serve as input devices), audio output devices (such as: speakers (1809), headphones (not depicted)), visual output devices (such as screens (1810) to include CRT screens, LCD screens, plasma screens, OLED screens, each with or without touch-screen input capability, each with or without tactile feedback capability—some of which may be capable to output two dimensional visual output or more than three dimensional output through means such as stereographic output; virtual-reality glasses (not depicted), holographic displays and smoke tanks (not depicted)), and printers (not depicted).
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.
Those skilled in the art should also understand that term “computer readable media” as used in connection with the presently disclosed subject matter does not encompass transmission media, carrier waves, or other transitory signals.
Computer system (1800) can also include an interface (1854) to one or more communication networks (1855). Networks can for example be wireless, wireline, optical. Networks can further be local, wide-area, metropolitan, vehicular and industrial, real-time, delay-tolerant, and so on. Examples of networks include local area networks such as Ethernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TV wireline or wireless wide area digital networks to include cable TV, satellite TV, and terrestrial broadcast TV, vehicular and industrial to include CAN bus, and so forth.
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), graphics adapters (1850), 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). In an example, the screen (1810) can be connected to the graphics adapter (1850). Architectures for a peripheral bus include PCI, USB, and the like.
The computer readable media can have computer code thereon for performing various computer-implemented operations. The media and computer code can be those specially designed and constructed for the purposes of the present disclosure, or they can be of the kind well known and available to those having skill in the computer software arts.
While this disclosure has described several exemplary embodiments, there are alterations, permutations, and various substitute equivalents, which fall within the scope of the disclosure. It will thus be appreciated that those skilled in the art will be able to devise numerous systems and methods which, although not explicitly shown or described herein, embody the principles of the disclosure and are thus within the spirit and scope thereof.
This application is based on and claims the benefit of priority to U.S. Provisional Application No. 63/524,545, filed on Jun. 30, 2023, which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63524545 | Jun 2023 | US |
