DECODER SIDE QUANTIZATION SHIFTING OFFSET PREDICTION

An apparatus includes processing circuitry configured to receive a bitstream that comprises coded information of a current block, and determine a plurality of hypotheses for a decoder side quantization shifting offset prediction, a hypothesis in the plurality of hypotheses corresponds to a potential quantization shifting offset setting in a transform domain of the current block. The processing circuitry calculates cost values respectively associated with the plurality of hypotheses, select a specific hypothesis from the plurality of hypotheses according to the cost values, determine one or more quantization shifting offsets for transform coefficients in the transform domain based on the specific hypothesis, reconstruct the transform coefficients based on the one or more quantization shifting offsets, calculate residuals in a spatial domain of the current block based on the transform coefficients in the transform domain, and reconstruct the current block according to the residuals in the spatial domain.

TECHNICAL FIELD

The present disclosure describes aspects generally related to video coding.

BACKGROUND

Image/video compression can help transmit image/video data across different devices, storage and networks with minimal quality degradation. In some examples, video codec technology can compress video based on spatial and temporal redundancy. In an example, a video codec can use techniques referred to as intra prediction that can compress an image based on spatial redundancy. For example, the intra prediction can use reference data from the current picture under reconstruction for sample prediction. In another example, a video codec can use techniques referred to as inter prediction that can compress an image based on temporal redundancy. For example, the inter prediction can predict samples in a current picture from a previously reconstructed picture with motion compensation. The motion compensation can be indicated by a motion vector (MV).

SUMMARY

Aspects of the disclosure include bitstreams, methods, and apparatuses for video encoding/decoding. In some examples, an apparatus for video encoding/decoding includes processing circuitry.

Some aspects of the disclosure provide a method of processing visual media data. The method includes performing a conversion between a visual media file and a bitstream of visual media data according to a format rule. The bitstream includes coded information of one or more pictures. The format rule specifies that a plurality of hypotheses for a decoder side quantization shifting offset prediction is determined, a hypothesis in the plurality of hypotheses corresponds to a potential quantization shifting offset setting in a transform domain of a current block. The format rule further specifies that cost values respectively associated with the plurality of hypotheses are calculated, a cost value associated with a hypothesis in the plurality of hypotheses is calculated according to reconstructed pixels in the current block according to the hypothesis and one or more neighboring reconstructed blocks. The format rule further specifies that a specific hypothesis with a lowest cost value is selected when the lowest cost value is smaller than a threshold, one or more quantization shifting offsets for transform coefficients in the transform domain of the current block are determined based on the specific hypothesis, the transform coefficients are reconstructed based on the one or more quantization shifting offsets, residuals in a spatial domain of the current block are calculated based on the transform coefficients in the transform domain, and the current block is reconstructed according to the residuals in the spatial domain.

Some aspects of the disclosure provide an apparatus for video decoding. The apparatus includes processing circuitry configured to receive a bitstream that includes coded information of a current block, and determine a plurality of hypotheses for a decoder side quantization shifting offset prediction. A hypothesis in the plurality of hypotheses corresponds to a potential quantization shifting offset setting in a transform domain of the current block. The processing circuitry is configured to calculate cost values respectively associated with the plurality of hypotheses, select a specific hypothesis from the plurality of hypotheses according to the cost values, determine one or more quantization shifting offsets for transform coefficients in the transform domain based on the specific hypothesis, reconstruct the transform coefficients based on the one or more quantization shifting offsets, calculate residuals in a spatial domain of the current block based on the transform coefficients in the transform domain, and reconstruct the current block according to the residuals in the spatial domain.

According to an aspect of the disclosure, the plurality of hypotheses includes a hypothesis that sets a sign to at least a quantization shifting offset for a nonzero transform coefficient. In some examples, the plurality of hypotheses includes a first hypothesis that sets a positive sign to quantization shifting offsets for nonzero transform coefficients in a transform block, and a second hypothesis that sets a negative sign to the quantization shifting offsets for the nonzero transform coefficients in the transform block. In some examples, the plurality of hypotheses includes a first hypothesis that sets a positive sign to a first quantization shifting offset for a DC coefficient in a transform block, and a second hypothesis that sets a negative sign to the first quantization shifting offset for the DC coefficient in the transform block. In some examples, the plurality of hypotheses includes potential sign combinations of quantization shifting offsets for a subset of nonzero transform coefficients in a transform block.

According to an aspect of the disclosure, the plurality of hypotheses includes a hypothesis that sets a value to at least a quantization shifting offset for a nonzero transform coefficient. In some examples, the plurality of hypotheses includes a first hypothesis that sets a first value to quantization shifting offsets for nonzero transform coefficients in a transform block, and a second hypothesis that sets a second value to the quantization shifting offsets for the nonzero transform coefficients in the transform block.

In some examples, the processing circuitry is configured to select the specific hypothesis that has a lowest cost value.

According to an aspect of the disclosure, the processing circuitry is configured to calculate a cost value associated with a hypothesis according to reconstructed pixels in the current block due to the hypothesis and one or more neighboring reconstructed blocks. In some examples, the processing circuitry is configured to calculate the cost value that measures a discontinuity between the reconstructed pixels in the current block due to the hypothesis and the one or more neighboring reconstructed blocks. In some examples, the processing circuitry is configured to calculate the cost value that measures a derivative discontinuity between the reconstructed pixels in the current block due to the hypothesis and the one or more neighboring reconstructed blocks.

According to an aspect of the disclosure, the processing circuitry is configured to decode a flag from the bitstream, the flag indicates whether to perform the decoder side quantization shifting offset prediction. The flag can be signaled at any suitable level, such as a sequence level, a picture level, a slice level, a tile level, and a block level. In some examples, the processing circuitry is configured to determine to use a fixed quantization shifting offset when the flag indicates a no use of the decoder side quantization shifting offset prediction.

Some aspects of the disclosure also provide a method for video encoding. The method includes determining to use a decoder side quantization shifting offset prediction for a current block, and determining a plurality of hypotheses for the decoder side quantization shifting offset prediction. A hypothesis in the plurality of hypotheses corresponds to a potential quantization shifting offset setting in a transform domain of the current block. The method also includes calculating cost values respectively associated with the plurality of hypotheses, selecting a specific hypothesis with a lowest cost value from the plurality of hypotheses when the lowest cost value is smaller than a threshold, determining one or more quantization shifting offsets for transform coefficients in the transform domain based on the specific hypothesis, reconstructing the transform coefficients based on the one or more quantization shifting offsets, calculating residuals in a spatial domain of the current block based on the transform coefficients in the transform domain, and reconstructing the current block according to the residuals in the spatial domain.

In some examples, the method includes signaling a flag in a bitstream to indicate not to use the decoder side quantization shifting offset prediction when the lowest cost value is higher than the threshold. In some examples, the plurality of hypotheses includes a hypothesis that sets a sign to at least a quantization shifting offset for a nonzero transform coefficient. In some examples, the plurality of hypotheses includes a hypothesis that sets a value to at least a quantization shifting offset for a nonzero transform coefficient.

In some examples, the method includes calculating a cost value associated with a hypothesis according to reconstructed pixels in the current block due to the hypothesis and one or more neighboring reconstructed blocks.

Aspects of the disclosure also provide an apparatus for video encoding. The apparatus for video encoding including processing circuitry configured to implement any of the described methods for video encoding.

Aspects of the disclosure also provide a method for video decoding. The method including any of the methods implemented by the apparatus for video decoding.

Aspects of the disclosure also provide a non-transitory computer-readable medium storing instructions which, when executed by a computer, cause the computer to perform any of the described methods for video decoding/encoding.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of a video processing system (100) in some examples. The video processing system (100) is an example of an application for the disclosed subject matter, a video encoder and a video decoder in a streaming environment. The disclosed subject matter can be equally applicable to other video enabled applications, including, for example, video conferencing, digital TV, streaming services, storing of compressed video on digital media including CD, DVD, memory stick and the like, and so on.

The video processing system (100) includes a capture subsystem (113), that can include a video source (101), for example a digital camera, creating for example a stream of video pictures (102) that are uncompressed. In an example, the stream of video pictures (102) includes samples that are taken by the digital camera. The stream of video pictures (102), depicted as a bold line to emphasize a high data volume when compared to encoded video data (104) (or coded video bitstreams), can be processed by an electronic device (120) that includes a video encoder (103) coupled to the video source (101). The video encoder (103) 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 (104) (or encoded video bitstream), depicted as a thin line to emphasize the lower data volume when compared to the stream of video pictures (102), can be stored on a streaming server (105) for future use. One or more streaming client subsystems, such as client subsystems (106) and (108) in FIG. 1 can access the streaming server (105) to retrieve copies (107) and (109) of the encoded video data (104). A client subsystem (106) can include a video decoder (110), for example, in an electronic device (130). The video decoder (110) decodes the incoming copy (107) of the encoded video data and creates an outgoing stream of video pictures (111) that can be rendered on a display (112) (e.g., display screen) or other rendering device (not depicted). In some streaming systems, the encoded video data (104), (107), and (109) (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 (120) and (130) can include other components (not shown). For example, the electronic device (120) can include a video decoder (not shown) and the electronic device (130) can include a video encoder (not shown) as well.

FIG. 2 shows an example of a block diagram of a video decoder (210). The video decoder (210) can be included in an electronic device (230). The electronic device (230) can include a receiver (231) (e.g., receiving circuitry). The video decoder (210) can be used in the place of the video decoder (110) in the FIG. 1 example.

The receiver (231) may receive one or more coded video sequences, included in a bitstream for example, to be decoded by the video decoder (210). In an aspect, one coded video sequence is received at a time, where the decoding of each coded video sequence is independent from the decoding of other coded video sequences. The coded video sequence may be received from a channel (201), which may be a hardware/software link to a storage device which stores the encoded video data. The receiver (231) 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 (231) may separate the coded video sequence from the other data. To combat network jitter, a buffer memory (215) may be coupled in between the receiver (231) and an entropy decoder/parser (220) (“parser (220)” henceforth). In certain applications, the buffer memory (215) is part of the video decoder (210). In others, it can be outside of the video decoder (210) (not depicted). In still others, there can be a buffer memory (not depicted) outside of the video decoder (210), for example to combat network jitter, and in addition another buffer memory (215) inside the video decoder (210), for example to handle playout timing. When the receiver (231) is receiving data from a store/forward device of sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (215) may not be needed, or can be small. For use on best effort packet networks such as the Internet, the buffer memory (215) 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 (210).

The video decoder (210) may include the parser (220) to reconstruct symbols (221) from the coded video sequence. Categories of those symbols include information used to manage operation of the video decoder (210), and potentially information to control a rendering device such as a render device (212) (e.g., a display screen) that is not an integral part of the electronic device (230) but can be coupled to the electronic device (230), as shown in FIG. 2. 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 (220) 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 (220) 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 (220) may also extract from the coded video sequence information such as transform coefficients, quantizer parameter values, motion vectors, and so forth.

The parser (220) may perform an entropy decoding/parsing operation on the video sequence received from the buffer memory (215), so as to create symbols (221).

Reconstruction of the symbols (221) can involve multiple different units depending on the type of the coded video picture or parts thereof (such as: inter and intra picture, inter and intra block), and other factors. Which units are involved, and how, can be controlled by subgroup control information parsed from the coded video sequence by the parser (220). The flow of such subgroup control information between the parser (220) and the multiple units below is not depicted for clarity.

A first unit is the scaler/inverse transform unit (251). The scaler/inverse transform unit (251) 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) (221) from the parser (220). The scaler/inverse transform unit (251) can output blocks comprising sample values, that can be input into aggregator (255).

In some cases, the output samples of the scaler/inverse transform unit (251) can pertain to an intra coded block. The intra coded block 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 (252). In some cases, the intra picture prediction unit (252) 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 (258). The current picture buffer (258) buffers, for example, partly reconstructed current picture and/or fully reconstructed current picture. The aggregator (255), in some cases, adds, on a per sample basis, the prediction information the intra prediction unit (252) has generated to the output sample information as provided by the scaler/inverse transform unit (251).

In other cases, the output samples of the scaler/inverse transform unit (251) can pertain to an inter coded, and potentially motion compensated, block. In such a case, a motion compensation prediction unit (253) can access reference picture memory (257) to fetch samples used for prediction. After motion compensating the fetched samples in accordance with the symbols (221) pertaining to the block, these samples can be added by the aggregator (255) to the output of the scaler/inverse transform unit (251) (in this case called the residual samples or residual signal) so as to generate output sample information. The addresses within the reference picture memory (257) from where the motion compensation prediction unit (253) fetches prediction samples can be controlled by motion vectors, available to the motion compensation prediction unit (253) in the form of symbols (221) 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 (257) when sub-sample exact motion vectors are in use, motion vector prediction mechanisms, and so forth.

The output of the loop filter unit (256) can be a sample stream that can be output to the render device (212) as well as stored in the reference picture memory (257) 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 (220)), the current picture buffer (258) can become a part of the reference picture memory (257), and a fresh current picture buffer can be reallocated before commencing the reconstruction of the following coded picture.

FIG. 3 shows an example of a block diagram of a video encoder (303). The video encoder (303) is included in an electronic device (320). The electronic device (320) includes a transmitter (340) (e.g., transmitting circuitry). The video encoder (303) can be used in the place of the video encoder (103) in the FIG. 1 example.

The video encoder (303) may receive video samples from a video source (301) (that is not part of the electronic device (320) in the FIG. 3 example) that may capture video image(s) to be coded by the video encoder (303). In another example, the video source (301) is a part of the electronic device (320).

According to an aspect, the video encoder (303) may code and compress the pictures of the source video sequence into a coded video sequence (343) in real time or under any other time constraints as required. Enforcing appropriate coding speed is one function of a controller (350). In some aspects, the controller (350) 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 (350) 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 (350) can be configured to have other suitable functions that pertain to the video encoder (303) optimized for a certain system design.

In some aspects, the video encoder (303) is configured to operate in a coding loop. As an oversimplified description, in an example, the coding loop can include a source coder (330) (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 (333) embedded in the video encoder (303). The decoder (333) reconstructs the symbols to create the sample data in a similar manner as a (remote) decoder also would create. The reconstructed sample stream (sample data) is input to the reference picture memory (334). 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 (334) 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 (333) can be the same as a “remote” decoder, such as the video decoder (210), which has already been described in detail above in conjunction with FIG. 2. Briefly referring also to FIG. 2, however, as symbols are available and encoding/decoding of symbols to a coded video sequence by an entropy coder (345) and the parser (220) can be lossless, the entropy decoding parts of the video decoder (210), including the buffer memory (215), and parser (220) may not be fully implemented in the local decoder (333).

In an aspect, a decoder technology except the parsing/entropy decoding that is present in a decoder is present, in an identical or a substantially identical functional form, in a corresponding encoder. Accordingly, the disclosed subject matter focuses on decoder operation. The description of encoder technologies can be abbreviated as they are the inverse of the comprehensively described decoder technologies. In certain areas a more detail description is provided below.

During operation, in some examples, the source coder (330) 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.” In this manner, the coding engine (332) codes differences between pixel blocks of an input picture and pixel blocks of reference picture(s) that may be selected as prediction reference(s) to the input picture.

The local video decoder (333) may decode coded video data of pictures that may be designated as reference pictures, based on symbols created by the source coder (330). Operations of the coding engine (332) may advantageously be lossy processes. When the coded video data may be decoded at a video decoder (not shown in FIG. 3), the reconstructed video sequence typically may be a replica of the source video sequence with some errors. The local video decoder (333) 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 memory (334). In this manner, the video encoder (303) 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 (335) may perform prediction searches for the coding engine (332). That is, for a new picture to be coded, the predictor (335) may search the reference picture memory (334) 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 (335) 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 (335), an input picture may have prediction references drawn from multiple reference pictures stored in the reference picture memory (334).

The controller (350) may manage coding operations of the source coder (330), 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 (345). The entropy coder (345) translates the symbols as generated by the various functional units into a coded video sequence, by applying lossless compression to the symbols according to technologies such as Huffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (340) may buffer the coded video sequence(s) as created by the entropy coder (345) to prepare for transmission via a communication channel (360), which may be a hardware/software link to a storage device which would store the encoded video data. The transmitter (340) may merge coded video data from the video encoder (303) with other data to be transmitted, for example, coded audio data and/or ancillary data streams (sources not shown).

The controller (350) may manage operation of the video encoder (303). During coding, the controller (350) 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) may be coded and decoded without using any other picture in the sequence as a source of prediction. Some video codecs allow for different types of intra pictures, including, for example Independent Decoder Refresh (“IDR”) Pictures.

A predictive picture (P picture) may be coded and decoded using intra prediction or inter prediction using a motion vector and reference index to predict the sample values of each block.

A bi-directionally predictive picture (B Picture) may be coded and decoded using intra prediction or inter prediction using two motion vectors and reference indices to predict the sample values of each block. Similarly, multiple-predictive pictures can use more than two reference pictures and associated metadata for the reconstruction of a single block.

It is noted that the video encoders (103) and (303), and the video decoders (110) and (210) can be implemented using any suitable technique. In an aspect, the video encoders (103) and (303) and the video decoders (110) and (210) can be implemented using one or more integrated circuits. In another aspect, the video encoders (103) and (303), and the video decoders (110) and (210) can be implemented using one or more processors that execute software instructions.

Aspects of the disclosure provide techniques for decoder side quantization shifting offset prediction. The techniques are used for predicting the quantization shifting offset at the decoder side for image and video coding in some examples, and can achieve image quality improvement.

In video codec, techniques, such as transform, quantization, and the like are used to reduce redundancy in video signals. For example, transform techniques can reduce redundancy in the video signal by decorrelation, and quantization techniques can decrease the data of the transform coefficient representation by reducing precision, ideally by removing only imperceptible details, and thus reducing irrelevance in the data.

In some examples, transformation decorrelates a signal by transforming the signal from the spatial domain to a transform domain (typically a frequency domain), using a suitable transform basis. For example, a transform is applied to the prediction residual (regardless of whether it comes from inter- or intra-picture prediction), that is, the difference between the prediction and the original input video signal. In the transform domain, the essential information typically concentrates into a small number of coefficients. At the decoder, the inverse transform needs to be applied to reconstruct the residual samples.

Generally, quantization is used to reduce the precision of an input value or a set of input values in order to decrease the amount of data needed to represent the values. In some examples, the quantization is typically applied to individual transformed residual samples (e.g., transform coefficients), resulting in integer coefficient levels. The transform process is applied at the encoder. At the decoder, the corresponding process is known as inverse quantization or simply as scaling, which restores the original value range without regaining the precision.

In some related video and image codecs, a quantization shifting offset ρ* that is predefined can be applied on the transform coefficient values. In some examples, the quantization shifting offset ρ* is used to control a quantization dead zone. For example, at the decoder side, a reconstructed transform coefficient value yi is shifted with the predefined quantization shifting offset ρ*, such as according to Eq. (1):

According to some aspects of the disclosure, the quantization shifting offset ρ* for each non-zero coefficient or some subset of all non-zero coefficients can be determined (predicted) at the decoder side using techniques described in the present disclosure. In some examples, the sign and/or value of one or more quantization shifting offsets for one or more nonzero transform coefficients can be determined at the decoder side. For example, encoder/decoder can determine a plurality of hypotheses for a decoder side quantization shifting offset prediction, a hypothesis in the plurality of hypotheses corresponds to a potential quantization shifting offset setting in a transform domain of the current block. The encoder/decoder can calculate cost values respectively associated with the plurality of hypotheses, select a specific hypothesis from the plurality of hypotheses according to the cost values, determine one or more quantization shifting offsets for transform coefficients in the transform domain based on the specific hypothesis and reconstruct the transform coefficients based on the one or more quantization shifting offsets.

In some examples, a two-step process is applied to obtain the quantization shifting offset. For example, in the first step, several hypotheses of quantization shifting offset settings are used for reconstruction respectively. In the second step, the final quantization shifting offset is determined by selecting one of the hypotheses from the first step based on the already decoded information available at the decoder side.

The present disclosure describes various techniques that can be used in the first step and the second step of the two-step process.

In some examples, in the first step of the two-step process, a sign of the quantization shifting offset(s) is determined for the whole block (e.g., transform block, transform subblock and the like) or each nonzero transform coefficient in the block or a subset of the nonzero transform coefficients in the block.

In an example, the sign of quantization shifting offset(s) is determined for the whole block. FIG. 4 shows diagrams for hypotheses in some examples. FIG. 4 shows a 4×4 block (410) of positive signs as “Hypothesis 1”, and a 4×4 block (420) of negative signs as “Hypothesis 2”. In FIG. 4, when “Hypothesis 1” is used, the positive signs are used for the quantization shifting offsets of transform coefficients for reconstruction; otherwise, when the “Hypothesis 2” is used, negative signs are used for the quantization shifting offsets of transform coefficients for reconstruction at the decoder side. It is noted that the absolute values of the quantization shifting offsets can be the same or can be different.

In another example, the sign of quantization shifting offset is determined only for the DC coefficient in the block. Other transform coefficients in the block can utilize the fixed quantization shifting offset or do not apply quantization shifting.

FIG. 5 shows diagrams for hypotheses in some examples. FIG. 5 shows a 4×4 block (510) having a positive sign at the DC coefficient as “Hypothesis 1”, and a 4×4 block (520) having a negative sign at the DC coefficient as “Hypothesis 2”. When “Hypothesis 1” is used, the positive sign is used for a quantization shifting offset that is used for reconstruction of the DC coefficient; otherwise, when “Hypothesis 2” is used, negative sign is applied for the quantization shifting offset to reconstruct the DC coefficient at the decoder side.

In another example, the signs of quantization shifting offsets are determined for a subset, such as n transform coefficients in the block. Other transform coefficients in the block can utilize the fixed quantization shifting offset or do not apply quantization shifting. The number of hypotheses can be up to 2n.

FIG. 6 shows diagrams for hypotheses in some examples. In the FIG. 6 example, hypotheses are formed for signs of transform coefficients in the upper-left 2×2 subblock of a 4×4 block. FIG. 6 shows a 4×4 block (601) (with signs “++++” in the 2×2 subblock) as “Hypothesis 1”, a 4×4 block (602) (with signs “+++−” in the 2×2 subblock) as “Hypothesis 2”, a 4×4 block (603) (with signs “++−+” in the 2×2 subblock) as “Hypothesis 3”, and a 4×4 block (616) (with signs “−−−−” in the 2×2 subblock) as “Hypothesis 16”. It is noted that other hypotheses, such as “Hypothesis 4” with signs “+−++” in the 2×2 subblock, “Hypothesis 5” with signs “−+++” in the 2×2 subblock, “Hypothesis 6” with signs “−−++” in the 2×2 subblock, “Hypothesis 7” with signs “−+−+” in the 2×2 subblock, “Hypothesis 8” with signs “−++−” in the 2×2 subblock, “Hypothesis 9” with signs “+−−+” in the 2×2 subblock, “Hypothesis 10” with signs “++−−” in the 2×2 subblock, “Hypothesis 11” with signs “+−+−” in the 2×2 subblock, “Hypothesis 12” with signs “−−−+” in the 2×2 subblock, “Hypothesis 13” with signs “−−+−” in the 2×2 subblock, “Hypothesis 14” with signs “−+−−” in the 2×2 subblock, “Hypothesis 15” with signs “+−−−” in the 2×2 subblock are not shown in FIG. 6. It is noted that when n=4, the number of hypotheses can be up to 24=16.

In some examples, a value of the quantization shifting offset is determined for the whole block or each nonzero transform coefficient in the block or a subset of the nonzero coefficients in the block.

In an example, the quantization shifting offset value is determined for the whole block.

FIG. 7 shows diagrams for hypotheses in some examples. FIG. 7 shows a 4×4 block (710) with quantization shifting offset equal α for the whole block as “Hypothesis 1”, and a 4×4 block (720) with quantization shifting offset equal b for the whole block as “Hypothesis 2”. In the FIG. 7 example, when “Hypothesis 1” is used, the quantization shifting offset ρ* equals a; otherwise, when the “Hypothesis 2” is used, the quantization shifting offset ρ* equals b.

According to an aspect of the disclosure, a cost J is calculated from the pixels inside the current and neighboring reconstructed block for each hypothesis, such as based on a discontinuity measure. The hypothesis that provides the lowest cost J is used as the final quantization shifting offset setting.

FIG. 8 shows a diagram of a current block (810) in some examples. The current block (810) can be a current reconstructed block according to a hypothesis. FIG. 8 also shows neighboring reconstructed pixels associated with the current block (810) in grey color. It is noted that the neighboring reconstructed pixels are reconstructed according to coding information of neighboring blocks. In FIG. 8, p(x, y) represents a reconstructed pixel value at position (x, y). When x or y is negative, p(x, y) indicates the pixel values of the neighboring reconstructed blocks.

In an example, the cost of hypothesis i is calculated as a discontinuity measure according to Eq. (2):

where M and N indicates the number of pixels in a column and row of a block.

In another example, the cost of hypothesis i is calculated as a discontinuity measure according to Eq. (3):

In another example, the cost of hypothesis i is calculated as a derivative discontinuity measure according to Eq. (4):

According to some aspects of the disclosure, a flag can be signaled in the bitstream at sequence/picture/slice/tile/block etc. level to control whether the decoder quantization shifting offset prediction is used.

In some examples, the same block-level quantization shifting offset prediction method is applied at the encoder side, and the flag is signaled in the bitstream to control the usage of the quantization shifting offset prediction method at the decoder side.

In an example, when the cost of all hypotheses is larger than a threshold T, the flag indicating not using decoder side quantization offset prediction is signaled in the bitstream.

In some examples, when a sequence/picture/slice/tile/block does not use quantization shifting offset prediction, a fixed offset value is used for reconstruction or quantization shifting is not applied.

Using FIG. 7 in an example, two hypotheses are considered at the encoder side. “Hypothesis 1” indicates the quantization shifting offset ρ* equals a for the whole block and “Hypothesis 2” indicates the quantization shifting offset ρ* equals b for the whole block. The costs of two hypotheses J1 and J2 are calculated using Eq. (2). If both J1 and J2 are larger than a threshold T, the control flag having “false” value is signaled in the bitstream at block level. Otherwise, the control flag having “true” values is signaled in the bitstream at block level. At the decoder side, when the control flag has “true” value, quantization shifting offset prediction method is applied. Otherwise, when the control flag has “false” value, a fixed offset value is used for reconstruction or quantization shifting is not applied.

FIG. 9 shows a flow chart outlining a process (900) according to an aspect of the disclosure. The process (900) can be used in a video decoder. In various aspects, the process (900) is executed by processing circuitry, such as the processing circuitry that performs functions of the video decoder (110), the processing circuitry that performs functions of the video decoder (210), and the like. In some aspects, the process (900) is implemented in software instructions, thus when the processing circuitry executes the software instructions, the processing circuitry performs the process (900). The process starts at (S901) and proceeds to (S910).

At (S910), a bitstream that comprises coded information of a current block is received.

At (S920), a plurality of hypotheses for a decoder side quantization shifting offset prediction are determined. A hypothesis in the plurality of hypotheses corresponds to a potential quantization shifting offset setting in a transform domain of the current block.

At (S930), cost values respectively associated with the plurality of hypotheses are calculated.

At (S940), a specific hypothesis is selected from the plurality of hypotheses according to the cost values.

At (S950), one or more quantization shifting offsets for transform coefficients in the transform domain are determined based on the specific hypothesis.

At (S960), the transform coefficients are reconstructed based on the one or more quantization shifting offsets. For example, quantized coefficients are decoded from the bitstream, dequantization can be performed to obtain dequantized coefficients, and the dequantized coefficients are combined with the quantization shifting offsets to obtain the transform coefficients.

At (S970), residuals in a spatial domain of the current block are calculated based on the transform coefficients in the transform domain. For example, inverse transform can be performed according to the transform coefficients to obtain the residuals in the spatial domain.

At (S980), the current block is reconstructed according to the residuals in the spatial domain. For example, a predictor of the current block can be combined with the residuals to obtain the reconstructed current block.

According to an aspect of the disclosure, the plurality of hypotheses includes a hypothesis that sets a sign to at least a quantization shifting offset for a nonzero transform coefficient. In some examples, the plurality of hypotheses includes a first hypothesis that sets a positive sign to quantization shifting offsets for nonzero transform coefficients in a transform block, and includes a second hypothesis that sets a negative sign to the quantization shifting offsets for the nonzero transform coefficients in the transform block. In an example, the plurality of hypotheses includes a first hypothesis that sets a positive sign to a first quantization shifting offset for a DC coefficient in a transform block, and includes a second hypothesis that sets a negative sign to the first quantization shifting offset for the DC coefficient in the transform block.

In some examples, the plurality of hypotheses includes potential sign combinations of quantization shifting offsets for a subset of nonzero transform coefficients in a transform block. For example, in the FIG. 6 example, 16 hypotheses correspond to 16 sign combinations of quantization shifting offsets for the 2×2 nonzero transform coefficients at up-left corner of the transform block.

According to an aspect of the disclosure, the plurality of hypotheses includes a hypothesis that sets a value to at least a quantization shifting offset for a nonzero transform coefficient. In some examples, the plurality of hypotheses includes a first hypothesis that sets a first value to quantization shifting offsets for nonzero transform coefficients in a transform block, and includes a second hypothesis that sets a second value to the quantization shifting offsets for the nonzero transform coefficients in the transform block.

In some examples, the specific hypothesis that has a lowest cost value is selected.

According to an aspect of the disclosure, a cost value associated with a hypothesis is calculated according to reconstructed pixels in the current block due to the hypothesis and one or more neighboring reconstructed blocks. In some examples, the cost value that measures a discontinuity between the reconstructed pixels in the current block due to the hypothesis and the one or more neighboring reconstructed blocks is calculated, such as using Eq. (2) and Eq. (3). In some examples, the cost value that measures a derivative discontinuity between the reconstructed pixels in the current block due to the hypothesis and the one or more neighboring reconstructed blocks is calculated, such as using Eq. (4).

In some examples, a flag is decoded from the bitstream, the flag indicates whether to perform the decoder side quantization shifting offset prediction. The flag is signaled at a suitable level, such as a sequence level, a picture level, a slice level, a tile level, a block level, and the like. In some examples, to use a fixed quantization shifting offset is determined when the flag indicates a no use of the decoder side quantization shifting offset prediction.

Then, the process proceeds to (S999) and terminates.

The process (900) can be suitably adapted. Step(s) in the process (900) can be modified and/or omitted. Additional step(s) can be added. Any suitable order of implementation can be used.

FIG. 10 shows a flow chart outlining a process (1000) according to an aspect of the disclosure. The process (1000) can be used in a video encoder. In various aspects, the process (1000) is executed by processing circuitry, such as the processing circuitry that performs functions of the video encoder (103), the processing circuitry that performs functions of the video encoder (303), and the like. In some examples, the process (1000) is implemented in software instructions, thus when the processing circuitry executes the software instructions, the processing circuitry performs the process (1000). The process starts at (S1001) and proceeds to (S1010).

At (S1010), to use a decoder side quantization shifting offset prediction for a current block is determined. In an example, a predictor for the current block is determined and a residual block of the current block in the spatial domain is calculated. Then, transform is applied on the residual block to obtain transform coefficients. Further, quantization shifting offsets are determined, and quantization is applied to obtain quantized coefficients, and the quantized coefficients can be suitably encoded into a bitstream. In some examples, the quantization shifting offsets are determined according to the decoder side quantization shifting offset prediction.

At (S1020), a plurality of hypotheses for the decoder side quantization shifting offset prediction is determined. A hypothesis in the plurality of hypotheses corresponds to a potential quantization shifting offset setting in a transform domain of the current block.

At (S1030), cost values respectively associated with the plurality of hypotheses are calculated.

At (S1040), a specific hypothesis is selected from the plurality of hypotheses based on the cost values.

At (S1050), one or more quantization shifting offsets for transform coefficients in the transform domain are determined based on the specific hypothesis.

At (S1060), the transform coefficients are reconstructed based on the one or more quantization shifting offsets.

At (S1070), residuals in a spatial domain of the current block are calculated based on the transform coefficients in the transform domain.

At (S1080), the current block is reconstructed according to the residuals in the spatial domain. The current block is encoded accordingly.

According to an aspect of the disclosure, the plurality of hypotheses includes a hypothesis that sets a sign to at least a quantization shifting offset for a nonzero transform coefficient. In some examples, the plurality of hypotheses includes a first hypothesis that sets a positive sign to quantization shifting offsets for nonzero transform coefficients in a transform block, and includes a second hypothesis that sets a negative sign to the quantization shifting offsets for the nonzero transform coefficients in the transform block. In an example, the plurality of hypotheses includes a first hypothesis that sets a positive sign to a first quantization shifting offset for a DC coefficient in a transform block, and includes a second hypothesis that sets a negative sign to the first quantization shifting offset for the DC coefficient in the transform block.

In some examples, the plurality of hypotheses includes potential sign combinations of quantization shifting offsets for a subset of nonzero transform coefficients in a transform block. For example, in the FIG. 6 example, 16 hypotheses correspond to 16 sign combinations of quantization shifting offsets for the 2×2 nonzero transform coefficients at up-left corner of the transform block.

According to an aspect of the disclosure, the plurality of hypotheses includes a hypothesis that sets a value to at least a quantization shifting offset for a nonzero transform coefficient. In some examples, the plurality of hypotheses includes a first hypothesis that sets a first value to quantization shifting offsets for nonzero transform coefficients in a transform block, and includes a second hypothesis that sets a second value to the quantization shifting offsets for the nonzero transform coefficients in the transform block.

According to an aspect of the disclosure, a cost value associated with a hypothesis is calculated according to reconstructed pixels in the current block due to the hypothesis and one or more neighboring reconstructed blocks. In some examples, the cost value that measures a discontinuity between the reconstructed pixels in the current block due to the hypothesis and the one or more neighboring reconstructed blocks is calculated, such as using Eq. (2) and Eq. (3). In some examples, the cost value that measures a derivative discontinuity between the reconstructed pixels in the current block due to the hypothesis and the one or more neighboring reconstructed blocks is calculated, such as using Eq. (4).

In some examples, the specific hypothesis is determined to be the one with a lowest cost value among the cost values. In some examples, when all the cost values are higher than a threshold, not to use the decoder side quantization shifting offset prediction is determined, and a flag is signaled in the bitstream to indicate not to use the decoder side quantization shifting offset prediction. In some examples, the flag can be signaled at a suitable level, such as a sequence level, a picture level, a slice level, a tile level, a block level, and the like. In some examples, a fixed quantization shifting offset is used when the decoder side quantization shifting offset prediction is not used.

Then, the process proceeds to (S1099) and terminates.

The process (1000) can be suitably adapted. Step(s) in the process (1000) can be modified and/or omitted. Additional step(s) can be added. Any suitable order of implementation can be used.

According to an aspect of the disclosure, a method of processing visual media data is provided. In the method, a conversion between a visual media file and a bitstream of visual media data is performed according to a format rule. For example, the bitstream may be a bitstream that is decoded/encoded in any of the decoding and/or encoding methods described herein. The format rule may specify one or more constraints of the bitstream and/or one or more processes to be performed by the decoder and/or encoder.

In an example, the bitstream includes coded information of one or more pictures. The format rule specifies that a plurality of hypotheses for a decoder side quantization shifting offset prediction is determined, a hypothesis in the plurality of hypotheses corresponds to a potential quantization shifting offset setting in a transform domain of a current block. The format rule also specifies that cost values respectively associated with the plurality of hypotheses are calculated, a cost value associated with a hypothesis is calculated according to reconstructed pixels in the current block according to the hypothesis and one or more neighboring reconstructed blocks. Further, the format rule specifies that a specific hypothesis with a lowest cost value is selected when the lowest cost value is smaller than a threshold, one or more quantization shifting offsets for transform coefficients in the transform domain of the current block are determined based on the specific hypothesis, the transform coefficients are reconstructed based on the one or more quantization shifting offsets, residuals in a spatial domain of the current block are calculated based on the transform coefficients in the transform domain, and the current block is reconstructed according to the residuals in the spatial domain.

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. 11 shows a computer system (1100) suitable for implementing certain aspects of the disclosed subject matter.

The components shown in FIG. 11 for computer system (1100) are examples and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing aspects of the present disclosure. Neither should the configuration of components be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the example aspect of computer system (1100).

Computer system (1100) may include certain human interface input devices.

Input human interface devices may include one or more of (only one of each depicted): keyboard (1101), mouse (1102), trackpad (1103), touch screen (1110), data-glove (not shown), joystick (1105), microphone (1106), scanner (1107), camera (1108).

Computer system (1100) can also include human accessible storage devices and their associated media such as optical media including CD/DVD ROM/RW (1120) with CD/DVD or the like media (1121), thumb-drive (1122), removable hard drive or solid state drive (1123), 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 (1140) of the computer system (1100).

The core (1140) can include one or more Central Processing Units (CPU) (1141), Graphics Processing Units (GPU) (1142), specialized programmable processing units in the form of Field Programmable Gate Areas (FPGA) (1143), hardware accelerators for certain tasks (1144), graphics adapters (1150), and so forth. These devices, along with Read-only memory (ROM) (1145), Random-access memory (1146), internal mass storage such as internal non-user accessible hard drives, SSDs, and the like (1147), may be connected through a system bus (1148). In some computer systems, the system bus (1148) 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 (1148), or through a peripheral bus (1149). In an example, the screen (1110) can be connected to the graphics adapter (1150). Architectures for a peripheral bus include PCI, USB, and the like.

CPUs (1141), GPUs (1142), FPGAs (1143), and accelerators (1144) can execute certain instructions that, in combination, can make up the aforementioned computer code. That computer code can be stored in ROM (1145) or RAM (1146). Transitional data can also be stored in RAM (1146), whereas permanent data can be stored for example, in the internal mass storage (1147). 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 (1141), GPU (1142), mass storage (1147), ROM (1145), RAM (1146), and the like.