CN115136603A

CN115136603A - Lossless codec mode for video codec

Info

Publication number: CN115136603A
Application number: CN202180013520.4A
Authority: CN
Inventors: 马宗全; 修晓宇; 王祥林; 陈漪纹; 朱弘正; 于冰
Original assignee: Beijing Dajia Internet Information Technology Co Ltd
Current assignee: Beijing Dajia Internet Information Technology Co Ltd
Priority date: 2020-02-07
Filing date: 2021-02-08
Publication date: 2022-09-30
Also published as: WO2021159081A1

Abstract

An electronic device performs methods of encoding and decoding video data. The method comprises the following steps: receiving a first syntax element of a current picture from a video bitstream; in accordance with a determination that the first syntax element indicates that residual coding for transform skipping is not disabled for the current picture, receiving a second syntax element of the current picture from the video bitstream; in accordance with a determination that the first syntax element indicates that residual coding for transform skipping is disabled for the current picture, setting a second syntax element to a default value that disables dependent quantization for the current picture; and performing residual decoding and inverse quantization on the current picture according to the first syntax element and the second syntax element.

Description

Lossless codec mode for video coding

RELATED APPLICATIONS

The present application claims priority from united states provisional patent application No. 62/971,841 entitled "LOSSLESS codec FOR VIDEO CODING" filed on month 07, 2020, which is incorporated herein by reference in its entirety.

Technical Field

The present application relates generally to video data coding and compression, and more particularly to methods and systems for improved and simplified lossless coding of video coding.

Background

Various electronic devices, such as digital televisions, laptop or desktop computers, tablet computers, digital cameras, digital recording devices, digital media players, video game consoles, smart phones, video teleconferencing devices, video streaming devices, and the like, support digital video. Electronic devices transmit, receive, encode, decode, and/or store digital video data by implementing video compression/decompression standards as defined by the MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Codec (AVC), High Efficiency Video Codec (HEVC), and general video codec (VVC) standards. Video compression typically includes performing spatial (intra) prediction and/or temporal (inter) prediction to reduce or remove redundancy inherent in the video data. For block-based video coding, a video frame is partitioned into one or more slices, each slice having a plurality of video blocks, which may also be referred to as Coding Tree Units (CTUs). Each CTU may contain one Coding Unit (CU) or be recursively split into smaller CUs until a predefined minimum CU size is reached. Each CU (also referred to as a leaf CU) contains one or more Transform Units (TUs) and each CU also contains one or more Prediction Units (PUs). Each CU may be coded in intra, inter, or IBC mode. Video blocks in an intra-coded (I) slice of a video frame are encoded using spatial prediction with respect to reference samples in neighboring blocks within the same video frame. Video blocks in an inter-coded (P or B) slice of a video frame may use spatial prediction with respect to reference samples in neighboring blocks within the same video frame or temporal prediction with respect to reference samples in other previous and/or future reference video frames.

A prediction block for a current video block to be coded is derived based on spatial prediction or temporal prediction of a reference block (e.g., a neighboring block) that has been previously coded. The process of finding the reference block may be accomplished by a block matching algorithm. Residual data representing pixel differences between the current block to be coded and the prediction block is called a residual block or prediction error. The inter-coded block is encoded according to the residual block and a motion vector pointing to a reference block forming a prediction block in a reference frame. The process of determining motion vectors is commonly referred to as motion estimation. And encoding the intra-coded block according to the intra-prediction mode and the residual block. For further compression, the residual block is transformed from the pixel domain to a transform domain (e.g., frequency domain), resulting in residual transform coefficients, which may then be quantized. The quantized transform coefficients, initially arranged in a two-dimensional array, may be scanned to generate one-dimensional vectors of transform coefficients, and then entropy encoded into a video bitstream to achieve even greater compression.

The encoded video bitstream is then saved in a computer readable storage medium (e.g., flash memory) for access by another electronic device having digital video capabilities or for direct transmission to the electronic device, either wired or wirelessly. The electronic device then performs video decompression (which is the inverse of the video compression described above), e.g., by parsing the encoded video bitstream to obtain syntax elements from the bitstream and reconstructing the digital video data from the encoded video bitstream to its original format based at least in part on the syntax elements obtained from the bitstream, and the electronic device presents the reconstructed digital video data on a display of the electronic device.

As the digital video quality changes from high definition to 4K × 2K or even 8K × 4K, the amount of video data to be encoded/decoded grows exponentially. It is a long-standing challenge how to encode/decode video data more efficiently while maintaining the image quality of the decoded video data.

Disclosure of Invention

The present application describes embodiments relating to video data encoding and decoding, and more particularly, embodiments relating to improved and simplified methods and systems for lossless codec of video codecs.

According to a first aspect of the present application, a method of decoding video data comprises: receiving a first syntax element of a current picture from a video bitstream; in accordance with a determination that the first syntax element indicates that residual coding for transform skipping is not disabled for the current picture, receiving a second syntax element of the current picture from the video bitstream; in accordance with a determination that the first syntax element indicates that residual coding for transform skipping is disabled for the current picture, setting a second syntax element to a default value that disables dependent quantization for the current picture; and performing residual decoding and inverse quantization on the current picture according to the first syntax element and the second syntax element.

According to a second aspect of the present application, an electronic device includes one or more processing units, a memory, and a plurality of programs stored in the memory. The program, when executed by one or more processing units, causes the electronic device to perform a method of decoding video data as described above.

According to a third aspect of the present application, a non-transitory computer-readable storage medium stores a plurality of programs for execution by an electronic device having one or more processing units. The program, when executed by one or more processing units, causes the electronic device to perform a method of decoding video data as described above.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification, illustrate embodiments described and together with the description serve to explain the principles. Like reference numerals designate corresponding parts.

Fig. 1 is a block diagram illustrating an exemplary video encoding and decoding system according to some embodiments of the present disclosure.

Fig. 2 is a block diagram illustrating an exemplary video encoder according to some embodiments of the present disclosure.

Fig. 3 is a block diagram illustrating an exemplary video decoder according to some embodiments of the present disclosure.

Fig. 4A-4E are block diagrams illustrating how a frame is recursively partitioned into multiple video blocks of different sizes and shapes according to some embodiments of the disclosure.

Fig. 5A-5B are block diagrams illustrating examples of transform coefficient codecs using context codec and bypass codec according to some embodiments of the present disclosure.

Fig. 6 is a block diagram illustrating an exemplary process of relying on scalar quantization, according to some embodiments of the present disclosure.

Fig. 7 is a block diagram illustrating an example state machine for switching between two different scalar quantizers, according to some embodiments of the present disclosure.

Fig. 8 is a flow diagram illustrating an exemplary process for a video decoder to decode a current picture of a video bitstream, according to some embodiments of the present disclosure.

Fig. 9 is a block diagram illustrating an example Context Adaptive Binary Arithmetic Coding (CABAC) engine, according to some embodiments of the present disclosure.

Detailed Description

Reference will now be made in detail to the present embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous non-limiting specific details are set forth in order to provide an understanding of the subject matter presented herein. It will be apparent, however, to one skilled in the art that various alternatives may be used and the subject matter may be practiced without these specific details without departing from the scope of the claims. For example, it will be apparent to one of ordinary skill in the art that the subject matter presented herein may be implemented on many types of electronic devices having digital video capabilities.

Fig. 1 is a block diagram illustrating an example system 10 for encoding and decoding video blocks in parallel according to some embodiments of the present disclosure. As shown in fig. 1, system 10 includes a source device 12, source device 12 generating and encoding video data to be later decoded by a target device 14. Source device 12 and target device 14 may comprise any of a wide variety of electronic devices, including desktop or laptop computers, tablet computers, smart phones, set-top boxes, digital televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, and so on. In some embodiments, source device 12 and target device 14 are equipped with wireless communication capabilities.

In some embodiments, target device 14 may receive encoded video data to be decoded via link 16. Link 16 may include any type of communication medium or device capable of moving encoded video data from source device 12 to destination device 14. In one example, link 16 may include a communication medium that enables source device 12 to transmit encoded video data directly to target device 14 in real-time. The encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to the target device 14. The communication medium may include any wireless or wired communication medium such as a Radio Frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network (e.g., a local area network, a wide area network, or a global network such as the internet). The communication medium may include routers, switches, base stations, or any other device that may facilitate communication from source device 12 to target device 14.

In some other implementations, the encoded video data may be sent from the output interface 22 to the storage device 32. Subsequently, the encoded video data in storage device 32 may be accessed by target device 14 via input interface 28. Storage device 32 may include any of a variety of distributed or locally accessed data storage media such as a hard drive, blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data. In another example, storage device 32 may correspond to a file server or another intermediate storage device that may hold encoded video data generated by source device 12. The target device 14 may access the stored video data from the storage device 32 via streaming or download. The file server may be any type of computer capable of storing encoded video data and transmitting the encoded video data to the target device 14. Exemplary file servers include web servers (e.g., for a website), FTP servers, Network Attached Storage (NAS) devices, or local disk drives. The target device 14 may access the encoded video data over any standard data connection suitable for accessing encoded video data stored on a file server, including a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both wireless and wired connections. The transmission of the encoded video data from the storage device 32 may be a streaming transmission, a download transmission, or a combination of both a streaming and a download transmission.

As shown in fig. 1, source device 12 includes a video source 18, a video encoder 20, and an output interface 22. Video source 18 may include sources such as the following or a combination of such sources: a video capture device (e.g., a video camera), a video archive containing previously captured video, a video feed interface for receiving video from a video content provider, and/or a computer graphics system for generating computer graphics data as source video. As one example, if video source 18 is a video camera of a security monitoring system, source device 12 and destination device 14 may form a camera phone or video phone. However, embodiments described herein are generally applicable to video codecs, and may be applied to wireless and/or wired applications.

Captured, pre-captured, or computer-generated video may be encoded by video encoder 20. The encoded video data may be sent directly to the target device 14 via the output interface 22 of the source device 12. The encoded video data may also (or alternatively) be stored on storage device 32 for later access by target device 14 or other devices for decoding and/or playback. The output interface 22 may further include a modem and/or a transmitter.

The target device 14 includes an input interface 28, a video decoder 30, and a display device 34. Input interface 28 may include a receiver and/or a modem and receives encoded video data over link 16. Encoded video data communicated over link 16 or provided on storage device 32 may include various syntax elements generated by video encoder 20 for use by video decoder 30 in decoding the video data. Such syntax elements may be included within encoded video data sent over a communication medium, stored on a storage medium, or stored on a file server.

In some embodiments, the target device 14 may include a display device 34, and the display device 34 may be an integrated display device and an external display device configured to communicate with the target device 14. Display device 34 displays the decoded video data to a user and may include any of a variety of display devices, such as a Liquid Crystal Display (LCD), a plasma display, an Organic Light Emitting Diode (OLED) display, or another type of display device.

Video encoder 20 and video decoder 30 may operate according to a proprietary or industry standard (e.g., VVC, HEVC, MPEG-4, Part 10, Advanced Video Codec (AVC)) or an extension of such a standard. It should be understood that the present application is not limited to a particular video encoding/decoding standard and may be applicable to other video encoding/decoding standards. It is generally recognized that video encoder 20 of source device 12 may be configured to encode video data according to any of these current or future standards. Similarly, it is also generally recognized that video decoder 30 of target device 14 may be configured to decode video data in accordance with any of these current or future standards.

Video encoder 20 and video decoder 30 may each be implemented as any of a variety of suitable encoder circuits, such as one or more microprocessors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), discrete logic, software, hardware, firmware or any combinations thereof. When implemented in part in software, the electronic device may store instructions for the software in a suitable non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the video encoding/decoding operations disclosed in this disclosure. Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in the respective device.

Fig. 2 is a block diagram illustrating an exemplary video encoder 20 according to some embodiments described in the present application. Video encoder 20 may perform intra-prediction coding and inter-prediction coding of video blocks within video frames. Intra-prediction coding relies on spatial prediction to reduce or remove spatial redundancy in video data within a given video frame or picture. Inter-prediction coding relies on temporal prediction to reduce or remove temporal redundancy in video data within adjacent video frames or pictures of a video sequence.

As shown in fig. 2, video encoder 20 includes a video data memory 40, a prediction processing unit 41, a Decoded Picture Buffer (DPB)64, an adder 50, a transform processing unit 52, a quantization unit 54, and an entropy encoding unit 56. Prediction processing unit 41 further includes a motion estimation unit 42, a motion compensation unit 44, a partition unit 45, an intra prediction processing unit 46, and an intra Block Copy (BC) unit 48. In some embodiments, video encoder 20 also includes an inverse quantization unit 58, an inverse transform processing unit 60, and an adder 62 for video block reconstruction. A deblocking filter (not shown) may be located between adder 62 and DPB 64 to filter block boundaries to remove blockiness from the reconstructed video. In addition to a deblocking filter, an in-loop filter (not shown) may be used to filter the output of adder 62. Video encoder 20 may take the form of, or be dispersed among, one or more of the fixed or programmable hardware units illustrated.

Video data memory 40 may store video data to be encoded by components of video encoder 20. The video data in video data storage 40 may be obtained, for example, from video source 18. DPB 64 is a buffer that stores reference video data for use by video encoder 20 in encoding video data (e.g., in intra or inter prediction coding modes). Video data memory 40 and DPB 64 may be formed from any of a variety of memory devices. In various examples, video data memory 40 may be on-chip with other components of video encoder 20, or off-chip with respect to those components.

As shown in fig. 2, upon receiving the video data, a partition unit 45 within prediction processing unit 41 partitions the video data into video blocks. This partitioning may also include partitioning the video frame into slices, partitions (tiles), or other larger Coding Units (CUs) according to a predefined splitting structure, such as a quadtree structure, associated with the video data. A video frame may be divided into a plurality of video blocks (or a set of video blocks referred to as partitions). Prediction processing unit 41 may select one of a plurality of feasible prediction coding modes, such as one of one or more inter-prediction encoding modes of a plurality of intra-prediction coding modes, for the current video block based on the error results (e.g., coding rate and distortion level). Prediction processing unit 41 may provide the resulting intra-predicted or inter-predicted encoded blocks to adder 50 to generate a residual block, and to adder 62 to reconstruct the encoded block for subsequent use as part of a reference frame. Prediction processing unit 41 also provides syntax elements, such as motion vectors, intra-mode indicators, partition information, and other such syntax information, to entropy encoding unit 56.

To select a suitable intra-prediction coding mode for the current video block, intra-prediction processing unit 46 within prediction processing unit 41 may perform intra-prediction coding of the current video block in relation to one or more neighboring blocks in the same frame as the current block to be encoded to provide spatial prediction. Motion estimation unit 42 and motion compensation unit 44 within prediction processing unit 41 perform inter-prediction coding of the current video block in relation to one or more prediction blocks in one or more reference frames to provide temporal prediction. Video encoder 20 may perform multiple encoding passes, for example, to select an appropriate codec mode for each block of video data.

In some implementations, motion estimation unit 42 determines the inter-prediction mode for the current video frame by generating motion vectors according to predetermined patterns within the sequence of video frames, the motion vectors indicating the displacement of Prediction Units (PUs) of video blocks within the current video frame relative to prediction blocks within the reference video frame. Motion estimation performed by motion estimation unit 42 is the process of generating motion vectors that estimate motion for video blocks. For example, a motion vector may indicate a displacement of a PU of a video block within a current video frame or picture relative to a prediction block (or other coding unit) within a reference frame that is related to a current block (or other coding unit) being coded within the current frame. The predetermined pattern may designate video frames in the sequence as P-frames or B-frames. Intra BC unit 48 may determine vectors (e.g., block vectors) for intra BC coding in a similar manner as the motion vectors determined by motion estimation unit 42 for inter prediction, or may determine block vectors using motion estimation unit 42.

In terms of pixel differences, which may be determined by Sum of Absolute Differences (SAD), Sum of Squared Differences (SSD), or other difference metrics, a prediction block is a block of the reference frame that is considered to closely match a PU of the video block to be encoded. In some implementations, video encoder 20 may calculate values for sub-integer pixel positions of reference frames stored in DPB 64. For example, video encoder 20 may interpolate values for a quarter-pixel position, an eighth-pixel position, or other fractional-pixel positions of the reference frame. Thus, motion estimation unit 42 may perform a motion search with respect to the full pixel position and the fractional pixel position and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates motion vectors for PUs of video blocks in the inter-prediction coded frame by: the location of the PU is compared to locations of prediction blocks of reference frames selected from a first reference frame list (list 0) or a second reference frame list (list 1), each of which identifies one or more reference frames stored in the DPB 64. The motion estimation unit 42 sends the calculated motion vector to the motion compensation unit 44 and then to the entropy coding unit 56.

The motion compensation performed by motion compensation unit 44 may involve extracting or generating a prediction block based on the motion vector determined by motion estimation unit 42. Upon receiving the motion vector for the PU of the current video block, motion compensation unit 44 may locate the prediction block to which the motion vector points in one of the reference frame lists, retrieve the prediction block from DPB 64, and forward the prediction block to adder 50. Adder 50 then forms a residual video block of pixel difference values by subtracting the pixel values of the prediction block provided by motion compensation unit 44 from the pixel values of the current video block being coded. The pixel difference values forming the residual video block may comprise a luminance difference component or a chrominance difference component or both. Motion compensation unit 44 may also generate syntax elements associated with video blocks of the video frame for use by video decoder 30 in decoding the video blocks of the video frame. The syntax elements may include, for example, syntax elements that define motion vectors used to identify the prediction blocks, any flags indicating prediction modes, or any other syntax information described herein. It should be noted that motion estimation unit 42 and motion compensation unit 44 may be highly integrated, but are illustrated separately for conceptual purposes.

In some embodiments, intra BC unit 48 may generate vectors and extract prediction blocks in a manner similar to that described above in connection with motion estimation unit 42 and motion compensation unit 44, but in the same frame as the current block being encoded, and these vectors are referred to as block vectors rather than motion vectors. In particular, intra BC unit 48 may determine the intra prediction mode to be used for encoding the current block. In some examples, intra BC unit 48 may encode current blocks using various intra prediction modes, e.g., during separate encoding passes, and test their performance through rate-distortion analysis. Next, intra BC unit 48 may select an appropriate intra prediction mode among the various tested intra prediction modes to use and generate an intra mode indicator accordingly. For example, intra BC unit 48 may calculate rate-distortion values for various tested intra-prediction modes using rate-distortion analysis, and select the intra-prediction mode having the best rate-distortion characteristics among the tested modes to use as the appropriate intra-prediction mode. Rate-distortion analysis generally determines the amount of distortion (or error) between an encoded block and the original, unencoded block that was encoded to generate the encoded block, as well as the bit rate (i.e., number of bits) used to generate the encoded block. Intra BC unit 48 may calculate ratios from the distortion and rate for various encoded blocks to determine which intra prediction mode exhibits the best rate-distortion value for the block.

In other examples, intra BC unit 48 may use, in whole or in part, motion estimation unit 42 and motion compensation unit 44 to perform such functions for intra BC prediction according to embodiments described herein. In either case, for intra block copying, the prediction block may be a block that is considered to closely match the block to be coded in terms of pixel differences, which may be determined by Sum of Absolute Differences (SAD), Sum of Squared Differences (SSD), or other difference metrics, and the identification of the prediction block may include calculating values for sub-integer pixel locations.

Whether the prediction block is from the same frame according to intra-prediction or from a different frame according to inter-prediction, video encoder 20 may form a residual video block by subtracting pixel values of the prediction block from pixel values of the current video block being coded, forming pixel difference values. The pixel difference values forming the residual video block may include both luminance component differences and chrominance component differences.

As an alternative to inter prediction performed by motion estimation unit 42 and motion compensation unit 44 or intra block copy prediction performed by intra BC unit 48 as described above, intra prediction processing unit 46 may intra predict the current video block. In particular, intra-prediction processing unit 46 may determine an intra-prediction mode for encoding the current block. To this end, the intra prediction processing unit 46 may encode the current block using various intra prediction modes, for example, during separate encoding passes, and the intra prediction processing unit 46 (or, in some examples, a mode selection unit) may select an appropriate intra prediction mode from the tested intra prediction modes for use. Intra-prediction processing unit 46 may provide information to entropy encoding unit 56 indicating the intra-prediction mode selected for the block. Entropy encoding unit 56 may encode information indicating the selected intra-prediction mode into a bitstream.

After prediction processing unit 41 determines a prediction block for the current video block via inter prediction or intra prediction, adder 50 forms a residual video block by subtracting the prediction block from the current video block. The residual video data in the residual block may be included in one or more Transform Units (TUs) and provided to transform processing unit 52. The transform processing unit 52 transforms the residual video data into residual transform coefficients using a transform such as a Discrete Cosine Transform (DCT) or a conceptually similar transform.

Transform processing unit 52 may send the resulting transform coefficients to quantization unit 54. The quantization unit 54 quantizes the transform coefficients to further reduce the bit rate. The quantization process may also reduce the bit depth associated with some or all of the coefficients. The quantization level may be modified by adjusting a quantization parameter. In some examples, quantization unit 54 may then perform a scan of a matrix including quantized transform coefficients. Alternatively, entropy encoding unit 56 may perform scanning.

After quantization, entropy encoding unit 56 entropy encodes the quantized transform coefficients into a video bitstream using, for example, a context-adaptive variable length codec (CAVLC), a context-adaptive binary arithmetic codec (CABAC), a syntax-based context-adaptive binary arithmetic codec (SBAC), a Probability Interval Partition Entropy (PIPE) codec, or another entropy codec method or technique. The encoded bitstream may then be transmitted to video decoder 30, or archived in storage device 32 for later transmission to video decoder 30 or retrieval by video decoder 30. Entropy encoding unit 56 may also entropy encode the motion vectors and other syntax elements for the current video frame being encoded.

Inverse quantization unit 58 and inverse transform processing unit 60 apply inverse quantization and inverse transform, respectively, to reconstruct the residual video block in the pixel domain for use in generating reference blocks for predicting other video blocks. As noted above, motion compensation unit 44 may generate a motion compensated prediction block from one or more reference blocks of a frame stored in DPB 64. Motion compensation unit 44 may also apply one or more interpolation filters to the prediction blocks to calculate sub-integer pixel values for use in motion estimation.

The adder 62 adds the reconstructed residual block to the motion compensated prediction block generated by the motion compensation unit 44 to generate a reference block for storage in the DPB 64. The reference block may then be used by intra BC unit 48, motion estimation unit 42, and motion compensation unit 44 as a prediction block to inter-predict another video block in a subsequent video frame.

Fig. 3 is a block diagram illustrating an exemplary video decoder 30 according to some embodiments of the present application. The video decoder 30 includes a video data memory 79, an entropy decoding unit 80, a prediction processing unit 81, an inverse quantization unit 86, an inverse transform processing unit 88, an adder 90, and a DPB 92. Prediction processing unit 81 further includes a motion compensation unit 82, an intra prediction processing unit 84, and an intra BC unit 85. Video decoder 30 may perform a decoding process that is substantially reciprocal to the encoding process described above with respect to video encoder 20 in connection with fig. 2. For example, motion compensation unit 82 may generate prediction data based on motion vectors received from entropy decoding unit 80, while intra-prediction unit 84 may generate prediction data based on intra-prediction mode indicators received from entropy decoding unit 80.

In some examples, the units of video decoder 30 may be tasked to perform embodiments of the present application. Furthermore, in some examples, embodiments of the present disclosure may be dispersed in one or more of the plurality of units of video decoder 30. For example, intra BC unit 85 may perform embodiments of the present application alone or in combination with other units of video decoder 30, such as motion compensation unit 82, intra prediction processing unit 84, and entropy decoding unit 80. In some examples, video decoder 30 may not include intra BC unit 85, and the functions of intra BC unit 85 may be performed by other components of prediction processing unit 81 (such as motion compensation unit 82).

Video data memory 79 may store video data to be decoded by other components of video decoder 30, such as an encoded video bitstream. The video data stored in video data storage 79 may be obtained, for example, from storage device 32, from a local video source (such as a camera), via wired or wireless network communication of the video data, or by accessing a physical data storage medium (e.g., a flash drive or hard disk). Video data memory 79 may include a Coded Picture Buffer (CPB) that stores encoded video data from an encoded video bitstream. Decoded Picture Buffer (DPB)92 of video decoder 30 stores reference video data for use by video decoder 30 in decoding the video data (e.g., in intra or inter prediction coding mode). Video data memory 79 and DPB 92 may be formed from any of a variety of memory devices, such as Dynamic Random Access Memory (DRAM) (including synchronous DRAM (sdram)), magnetoresistive ram (mram), resistive ram (rram), or other types of memory devices. For illustrative purposes, video data memory 79 and DPB 92 are depicted in fig. 3 as two different components of video decoder 30. It will be apparent to those skilled in the art that video data memory 79 and DPB 92 may be provided by the same memory device or separate memory devices. In some examples, video data memory 79 may be on-chip with other components of video decoder 30, or off-chip with respect to those components.

During the decoding process, video decoder 30 receives an encoded video bitstream representing video blocks and associated syntax elements of an encoded video frame. Video decoder 30 may receive syntax elements at the video frame level and/or the video block level. Entropy decoding unit 80 of video decoder 30 entropy decodes the bitstream to generate quantized coefficients, motion vectors or intra prediction mode indicators, and other syntax elements. The entropy decoding unit 80 then forwards the motion vector and other syntax elements to the prediction processing unit 81.

When a video frame is encoded as an intra-prediction encoded (I) frame or as an intra-coded prediction block for use in other types of frames, intra-prediction processing unit 84 of prediction processing unit 81 may generate prediction data for a video block of the current video frame based on the signaled intra-prediction mode and reference data from previously decoded blocks of the current frame.

When a video frame is encoded as an inter-prediction encoded (i.e., B or P) frame, motion compensation unit 82 of prediction processing unit 81 generates one or more prediction blocks for the video block of the current video frame based on the motion vectors and other syntax elements received from entropy decoding unit 80. Each of the prediction blocks may be generated from a reference frame within one of the reference frame lists. Video decoder 30 may use a default construction technique to construct reference frame lists, list 0 and list 1, based on the reference frames stored in DPB 92.

In some examples, when encoding and decoding a video block according to the intra BC mode described herein, intra BC unit 85 of prediction processing unit 81 generates a prediction block for the current video block based on the block vectors and other syntax elements received from entropy decoding unit 80. The prediction block may be within a reconstruction region of the same picture as the current video block defined by video encoder 20.

Motion compensation unit 82 and/or intra BC unit 85 determine prediction information for the video block of the current video frame by parsing the motion vectors and other syntax elements and then use the prediction information to generate a prediction block for the current video block being decoded. For example, motion compensation unit 82 uses some of the received syntax elements to determine a prediction mode (e.g., intra-prediction or inter-prediction) for coding a video block of a video frame, an inter-prediction frame type (e.g., B or P), construction information for one or more of a list of reference frames for the frame, a motion vector for each inter-prediction encoded video block of the frame, an inter-prediction state for each inter-prediction coded video block of the frame, and other information for decoding a video block in the current video frame.

Similarly, some of the received syntax elements, such as flags, may be used by intra BC unit 85 to determine that the current video block is predicted using an intra BC mode, build information for which video blocks of the frame are within the reconstruction region and should be stored in DPB 92, a block vector for each intra BC predicted video block of the frame, intra BC prediction status for each intra BC predicted video block of the frame, and other information for decoding the video blocks in the current video frame.

Motion compensation unit 82 may also perform interpolation using interpolation filters as used by video encoder 20 during encoding of video blocks to calculate interpolated values for sub-integer pixels of a reference block. In this case, motion compensation unit 82 may determine the interpolation filters used by video encoder 20 from the received syntax elements and use these interpolation filters to generate the prediction blocks.

Inverse quantization unit 86 inverse quantizes the quantized transform coefficients provided in the bitstream and entropy decoded by entropy decoding unit 80 using the same quantization parameter calculated by video encoder 20 for each video block in the video frame to determine the degree of quantization. Inverse transform processing unit 88 applies an inverse transform (e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process) to the transform coefficients in order to reconstruct the residual block in the pixel domain.

After motion compensation unit 82 or intra BC unit 85 generates a prediction block for the current video block based on the vector and other syntax elements, adder 90 reconstructs the decoded video block for the current video block by adding the residual block from inverse transform processing unit 88 to the corresponding prediction block generated by motion compensation unit 82 and intra BC unit 85. An in-loop filter (not shown) may be located between adder 90 and DPB 92 to further process the decoded video block. The decoded video blocks in a given frame are then stored in DPB 92, and DPB 92 stores reference frames for subsequent motion compensation of subsequent video blocks. DPB 92, or a memory device separate from DPB 92, may also store decoded video for later presentation on a display device (e.g., display device 34 of fig. 1).

In a typical video codec, a video sequence typically includes an ordered set of frames or pictures. Each frame may include three arrays of samples, denoted SL, SCb, and SCr. SL is a two-dimensional array of brightness samples. SCb is a two-dimensional array of Cb chroma samples. SCr is a two-dimensional array of Cr chroma samples. In other cases, the frame may be monochromatic, and thus include only one two-dimensional array of luminance samples.

As shown in fig. 4A, video encoder 20 (or, more specifically, segmentation unit 45) generates an encoded representation of a frame by first segmenting the frame into a set of Coding Tree Units (CTUs). A video frame may include an integer number of CTUs ordered sequentially from left to right and top to bottom in raster scan order. Each CTU is the largest logical coding unit, and the width and height of the CTUs are signaled by video encoder 20 in a sequence parameter set such that all CTUs in a video sequence have the same size of one of 128 × 128, 64 × 64, 32 × 32, and 16 × 16. It should be noted, however, that the present application is not necessarily limited to a particular size. As shown in fig. 4B, each CTU may include one Coding Tree Block (CTB) of luma samples, two corresponding coding tree blocks of chroma samples, and syntax elements for coding samples of the coding tree blocks. The syntax elements describe the properties of the different types of units that encode the pixel blocks and how the video sequence may be reconstructed at video decoder 30, including inter or intra prediction, intra prediction modes, motion vectors, and other parameters. In a monochrome picture or a picture with three separate color planes, a CTU may comprise a single coding tree block and syntax elements for coding samples of the coding tree block. The coding tree block may be a block of N × N samples.

To achieve better performance, video encoder 20 may recursively perform tree partitioning, e.g., binary tree partitioning, ternary tree partitioning, quaternary tree partitioning, or a combination of both, on the coding tree blocks of the CTUs and partition the CTUs into smaller Coding Units (CUs). As depicted in fig. 4C, the 64 × 64CTU 400 is first divided into four smaller CUs, each having a block size of 32 × 32. Of the four smaller CUs, CU 410 and CU 420 are divided into four CUs with block sizes of 16 × 16, respectively. Two 16 × 16

CUs

430 and 440 are further divided into four CUs having a block size of 8 × 8, respectively. Fig. 4D depicts a quadtree data structure showing the final result of the segmentation process of the CTU 400 as depicted in fig. 4C, each leaf node of the quadtree corresponding to one CU of various sizes ranging from 32 x 32 to 8 x 8. Similar to the CTU depicted in fig. 4B, each CU may include a Coded Block (CB) of luma samples and two corresponding coded blocks of chroma samples of the same size frame, and syntax elements for coding the samples of the coded blocks. In a monochrome picture or a picture with three separate color planes, a CU may comprise a single coding block and syntax structures for coding samples of the coding block. It should be noted that the quadtree partitioning depicted in fig. 4C and 4D is for illustrative purposes only, and one CTU may be split into CUs to adapt to varying local characteristics based on the quadtree/ternary tree/binary tree partitioning. In a multi-type tree structure, one CTU is partitioned by a quadtree structure, and each quadtree-leaf CU can be further partitioned by binary and ternary tree structures. As shown in fig. 4E, there are five segmentation types, i.e., a quad segmentation, a horizontal binary segmentation, a vertical binary segmentation, a horizontal ternary segmentation, and a vertical ternary segmentation.

In some implementations, video encoder 20 may further partition the coding block of the CU into one or more mxn Prediction Blocks (PBs). A prediction block is a block of rectangular (square or non-square) samples to which the same prediction (inter or intra) is applied. A Prediction Unit (PU) of a CU may include a prediction block of luma samples, two corresponding prediction blocks of chroma samples, and syntax elements for predicting the prediction block. In a monochrome picture or a picture with three separate color planes, a PU may include a single prediction block and syntax structures used to predict the prediction block. Video encoder 20 may generate predicted luma, predicted Cb, and predicted Cr blocks for the luma, Cb, and Cr predicted blocks for each PU of the CU.

Video encoder 20 may generate the prediction block for the PU using intra prediction or inter prediction. If video encoder 20 uses intra-prediction to generate the prediction block for the PU, video encoder 20 may generate the prediction block for the PU based on the decoding samples of the frame associated with the PU. If video encoder 20 uses inter-prediction to generate the prediction block for the PU, video encoder 20 may generate the prediction block for the PU based on decoding samples of one or more frames other than the frame associated with the PU.

After video encoder 20 generates the predicted luma, predicted Cb, and predicted Cr blocks for one or more PUs of the CU, video encoder 20 may generate a luma residual block for the CU by subtracting the predicted luma block of the CU from the original luma coding block of the CU, such that each sample in the luma residual block of the CU indicates a difference between a luma sample in one of the predicted luma blocks of the CU and a corresponding sample in the original luma coding block of the CU. Similarly, video encoder 20 may generate the Cb residual block and the Cr residual block for the CU, respectively, such that each sample in the Cb residual block of the CU indicates a difference between a Cb sample in one of the predicted Cb blocks of the CU and a corresponding sample in the original Cb coding block of the CU, and each sample in the Cr residual block of the CU may indicate a difference between a Cr sample in one of the predicted Cr blocks of the CU and a corresponding sample in the original Cr coding block of the CU.

Furthermore, as shown in fig. 4C, video encoder 20 may decompose the luma, Cb, and Cr residual blocks of the CU into one or more luma, Cb, and Cr transform blocks using quadtree partitioning. A transform block is a block of rectangular (square or non-square) samples to which the same transform is applied. A Transform Unit (TU) of a CU may include a transform block of luma samples, two corresponding transform blocks of chroma samples, and syntax elements for transforming the transform block samples. Thus, each TU of a CU may be associated with a luma transform block, a Cb transform block, and a Cr transform block. In some examples, the luma transform block associated with a TU may be a sub-block of a luma residual block of a CU. The Cb transform block may be a sub-block of a Cb residual block of the CU. The Cr transform block may be a sub-block of the Cr residual block of the CU. In a monochrome picture or a picture with three separate color planes, a TU may comprise a single transform block and syntax structures for transforming the samples of the transform block.

Video encoder 20 may apply one or more transforms to a luma transform block of a TU to generate a luma coefficient block for the TU. The coefficient block may be a two-dimensional array of transform coefficients. The transform coefficients may be scalars. Video encoder 20 may apply one or more transforms to a Cb transform block of a TU to generate a Cb coefficient block for the TU. Video encoder 20 may apply one or more transforms to a Cr transform block of a TU to generate a Cr coefficient block for the TU.

After generating the coefficient block (e.g., a luminance coefficient block, a Cb coefficient block, or a Cr coefficient block), video encoder 20 may quantize the coefficient block. Quantization generally refers to the process by which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, thereby providing further compression. After video encoder 20 quantizes the coefficient block, video encoder 20 may entropy encode syntax elements that indicate the quantized transform coefficients. For example, video encoder 20 may perform Context Adaptive Binary Arithmetic Coding (CABAC) on syntax elements indicating quantized transform coefficients. Finally, video encoder 20 may output a bitstream that includes the bit sequence that forms a representation of the encoded frames and associated data, which is stored in storage device 32 or transmitted to target device 14.

Upon receiving the bitstream generated by video encoder 20, video decoder 30 may parse the bitstream to obtain syntax elements from the bitstream. Video decoder 30 may reconstruct the frames of video data based at least in part on syntax elements obtained from the bitstream. The process of reconstructing the video data is generally reciprocal to the encoding process performed by video encoder 20. For example, video decoder 30 may perform inverse transforms on coefficient blocks associated with TUs of the current CU to reconstruct residual blocks associated with the TUs of the current CU. Video decoder 30 also reconstructs the encoded block of the current CU by adding samples of the prediction block for the PUs of the current CU to corresponding samples of the transform blocks of the TUs of the current CU. After reconstructing the encoded blocks for each CU of a frame, video decoder 30 may reconstruct the frame.

As described above, video coding mainly uses two modes, i.e., intra-frame prediction (or intra-frame prediction) and inter-frame prediction (or inter-frame prediction), to achieve video compression. Palette-based coding is another coding scheme that has been adopted by many video coding standards. In palette-based codecs, which may be particularly suitable for screen-generated content codecs, a video codec (e.g., video encoder 20 or video decoder 30) forms a palette table that represents the colors of video data for a given block. The palette table includes the most dominant (e.g., frequently used) pixel values in a given block. Pixel values that are not frequently represented in the video data of a given block are not included in the palette table or are included in the palette table as escape colors.

Each entry in the palette table includes an index for a corresponding pixel value in the palette table. The palette index for a sample in a block may be encoded to indicate which entry from the palette table is to be used to predict or reconstruct which sample. This palette mode begins with a process of generating a palette predictor for a first block of a picture, slice, tile, or other such grouping of video blocks. As will be explained below, the palette predictor for a subsequent video block is typically generated by updating a previously used palette predictor. For the purpose of illustration, it is assumed that the palette predictor is defined at the picture level. In other words, a picture may include multiple coding blocks, each with its own palette table, but there is one palette predictor for the entire picture.

To reduce the bits required to signal palette entries in a video bitstream, a video decoder may utilize a palette predictor to determine new palette entries in a palette table used to reconstruct a video block. For example, the palette predictor may include palette entries from a previously used palette table, or even be initialized with a recently used palette table by including all entries of the recently used palette table. In some implementations, the palette predictor may include fewer than all entries from the most recently used palette table, then incorporate some entries from other previously used palette tables. The palette predictor may have the same size as the palette table used to encode the different block, or may be larger or smaller than the palette table used to encode the different block. In one example, the palette predictor is implemented as a first-in-first-out (FIFO) table comprising 64 palette entries.

To generate a palette table for a block of video data from the palette predictor, a video decoder may receive a one-bit flag for each entry of the palette predictor from an encoded video bitstream. The one-bit flag may have a first value (e.g., a binary one) indicating that the associated entry of the palette predictor is to be included in the palette table or a second value (e.g., a binary zero) indicating that the associated entry of the palette predictor is not to be included in the palette table. If the size of the palette predictor is larger than the palette table for the block of video data, the video decoder may stop receiving more flags once the maximum size for the palette table is reached.

In some embodiments, some entries in the palette table may be signaled directly in the encoded video bitstream without palette predictor determination. For such entries, the video decoder may receive three separate m-bit values from the encoded video bitstream that indicate pixel values for the luma component and the two chroma components associated with the entry, where m represents a bit depth of the video data. Those palette entries derived from the palette predictor require only one-bit flags compared to the multiple m-bit values required for the directly signaled palette entries. Thus, signaling some or all of the palette entries using the palette predictor may significantly reduce the number of bits required to signal the entries of the new palette table, thereby improving the overall codec efficiency of palette mode codec.

In many cases, the palette predictor for a block is determined based on a palette table used to encode one or more previously encoded blocks. But when the first coding tree unit in a picture, slice, or tile is coded, the palette table for the previously coded block may not be available. Thus, the entries of the previously used palette table cannot be used to generate palette predictors. In this case, the sequence of palette predictor initialization values, which are values used to generate the palette predictor when a previously used palette table is not available, may be signaled in a Sequence Parameter Set (SPS) and/or a Picture Parameter Set (PPS). SPS generally refers to a syntax structure of syntax elements applied to a series of consecutive coded video pictures, called a Coded Video Sequence (CVS), determined by the content of syntax elements found in PPS referenced by syntax elements found in the header of each slice segment. PPS generally refers to a syntax structure applied to syntax elements of one or more individual pictures within a CVS determined by the syntax elements found in each slice segment header. Thus, SPS is generally considered to be a higher level syntax structure than PPS, meaning that syntax elements included in SPS typically change less frequently and apply to a larger portion of video data than syntax elements included in PPS.

The transform coefficient codecs in VVC are similar to those in HEVC in that they all use non-overlapping coefficient groups (also referred to as CGs or sub-blocks). However, there are also some differences between the two schemes. In HEVC, each CG of a coefficient has a fixed size of 4 × 4. In VVC draft 6, CG size becomes dependent on TB size. Therefore, various CG sizes (1 × 16, 2 × 8, 8 × 2, 2 × 4, 4 × 2, and 16 × 1) are available in the VVC. The CGs within the coded blocks and the transform coefficients within the CGs are coded according to a predefined scan order.

To limit the maximum number of context-coded bins (CCBs) per pixel, the area of the TB and the type of video component (i.e., luma component and chroma component) are used to derive the maximum number of context-coded bins (CCBs) for the TB. In some embodiments, the maximum number of context coded bins is equal to TB _ zosize × 1.75. Here, TB _ zosize represents the number of samples within TB after the coefficient is zeroed. Note that coded _ sub _ block _ flag, which is a flag indicating whether CG contains a non-zero coefficient, is not considered for CCB counting.

Zeroing of coefficients is an operation performed on a transform block such that coefficients located in a specific area of the transform block are set to zero. For example, in the current VVC, 64 × 64TB has an associated zeroing operation. Thus, transform coefficients that lie outside the upper left 32 × 32 region of the 64 × 64TB are all forced to zero. Indeed, in the current VVC, for any transform block whose size along a particular dimension exceeds 32, a coefficient zeroing operation is performed along that dimension to zero coefficients that lie outside the upper-left 32 × 32 region.

In the transform coefficient codec in VVC, the variable rembinpass 1 is first set to the maximum number of bits allowed for context codec (MCCB). During the codec process, this variable is decremented by one each time a context coded binary bit is signaled. When rembinpass 1 is greater than or equal to 4, the coefficients are signaled with syntax elements including sig _ coeff _ flag, abs _ level _ 1_ flag, par _ level _ flag, and abs _ level _ 3_ flag, all using context coded bins in the first channel. The remainder of the level information for the coefficients is coded in the second pass using the golomb rice codec and the bypass-coded binary bits, using the syntax element abs _ remaining. When remBinsPass1 becomes less than 4 when codec in the first pass, the current coefficient is not coded in the first pass, but rather the bin that was coded in the second pass using golomb rice coding and bypass coding is coded directly with syntax element dec _ abs _ level. After all the above-described hierarchical codecs, symbols (sign _ flag) for all scan positions where sig _ coeff _ flag is equal to 1 are finally codec into bypass binary bits. Such a process is depicted in fig. 5A. Rembinpass 1 is reset for each TB. The transition from using the context coded bits for sig _ coeff _ flag, abs _ level _ gt1_ flag, par _ level _ flag, and abs _ level _ gt3_ flag to using the bypass coded bits for the remaining coefficients occurs at most once per TB. For a coefficient sub-block, if remBinsPass1 is less than 4 before coding its first coefficient, the entire coefficient sub-block is coded using the bypass coded binary bits.

Unlike HEVC, where a single residual coding scheme is designed for coding both transform coefficients and transform skip coefficients, in VVC, two separate residual coding schemes are used for the transform coefficients and transform skip coefficients (i.e., residuals), respectively.

For example, it is observed that the statistical properties of the residual in the transform skip mode are different from those of the transform coefficients, and there is no energy compression around the low frequency components. The residual codec is modified to take into account different signal characteristics of the (spatial) transform skipped residual, which includes:

(1) not signaling the last x/y position;

(2) coding the coded _ sub _ block _ flag for each subblock except the DC subblock when all previous flags are equal to 0;

(3) sig _ coeff _ flag context modeling with two adjacent coefficients;

(4) par level flag using only one context model;

(5) additional more than 5, 7, 9 flags;

(6) modified rice parameter derivation for residual binarization;

(7) determining context modeling for the symbol flag based on left and upper neighboring coefficient values, and parsing the symbol flag after sig _ coeff _ flag to leave all context coded binary bits together;

as shown in fig. 5B, syntax elements sig _ coeff _ flag, coeff _ sign _ flag, abs _ level _ gt1_ flag, par _ level _ flag are coded in an interleaved manner on a residual sample-by-residual sample basis in the first channel, followed by coding of abs _ level _ gtX _ flag bitplanes in the second channel and coding of abs _ remaining in the third channel.

Channel 1: sig _ coeff _ flag, coeff _ sign _ flag, abs _ level _ 1_ flag, par _ level _ flag

And (3) a channel 2: abs _ level _ 3_ flag, abs _ level _ 5_ flag, abs _ level _ 7_ flag, abs _ level _ 9_ flag

And (3) passage: abs _ remainder

Fig. 6 is a block diagram illustrating an example process of relying on scalar quantization, in accordance with some embodiments of the present disclosure.

In the current VVC, the maximum QP value extends from 51 to 63, and the signaling of the initial QP is changed accordingly. When non-zero values of slice _ qp _ delta are coded, the initial value of SliceQpY may be modified at the slice layer. For transform skip blocks, the minimum allowed QP is defined as 4 because the quantization step size becomes 1 when QP equals 1.

In addition, the scalar quantization used in HEVC adapts to a new concept called "dependent scalar quantization". Dependent scalar quantization refers to a method of: the set of allowable reconstruction values for a transform coefficient depends on the values of the transform coefficient level preceding the current transform coefficient level in reconstruction order. When compared to conventional independent scalar quantization used in HEVC, the reconstructed vectors may be allowed to be packed more densely in the N-dimensional vector space (N represents the number of transform coefficients in the transform block). That is, for a given average of allowable reconstruction vectors per N-dimensional unit volume, the average distortion between the input vector and the closest reconstruction vector is reduced. The method of dependent scalar quantization is implemented by: (a) defining two scalar quantizers having different levels of reconstruction, and (b) defining a process for switching between the two scalar quantizers.

The two scalar quantizers used, denoted by Q0 and Q1, are shown in fig. 6. The position of the available reconstruction levels is uniquely specified by the quantization step size delta. The scalar quantizer used (Q0 or Q1) is not explicitly signaled in the bitstream. Instead, the quantizer for the current transform coefficient is determined by the parity of the transform coefficient level preceding the current transform coefficient in the codec order or reconstruction order.

As shown in fig. 7, switching between two scalar quantizers (Q0 and Q1) is accomplished via a state machine having four quantizer states (QState). QState can take four different values: 0. 1, 2 and 3. Which is uniquely determined by the parity of the transform coefficient level preceding the current transform coefficient in codec order/reconstruction order. At the start of the inverse quantization for the transform block, the state is set equal to 0. The transform coefficients are reconstructed in scan order (i.e., in the same order in which they were entropy decoded). After reconstruction of the current transform coefficient, the state is updated as shown in fig. 7, where k represents the value of the transform coefficient level.

Signaling of default scaling matrices and user-defined scaling matrices is also supported. The default mode scaling matrix is flat, with elements equal to 16 for all TB sizes. IBC and intra codec modes currently share the same scaling matrix. Therefore, for the case of a matrix of USER-DEFINED (USER _ DEFINED), the number of MatrixType and MatrixType _ DC is updated as follows:

MatrixType: 30 ═ 2 (2 for intraframe and IBC/interframe) × 3(Y/Cb/Cr component) × 5 (square TB size: from 4 × 4 to 64 × 64 for luminance, from 2 × 2 to 32 × 32 for chrominance)

MatrixType _ DC: 14 ═ 2 (2 × 1 for Y component for intra and IBC/inter) × 3(TB size: 16 × 16, 32 × 32, 64 × 64) +4 (2 × 2 for Cb/Cr component for intra and IBC/inter) × 2(TB size: 16 × 16, 32 × 32)

The DC values are coded for the following scaling matrices, respectively: 16 × 16, 32 × 32, and 64 × 64. For TBs smaller than 8 x 8 in size, all elements in one scaling matrix are signaled. If the size of the TB is greater than or equal to 8 × 8, only 64 elements in one 8 × 8 scaling matrix are signaled as the basic scaling matrix. To obtain square matrices of size greater than 8 × 8, an 8 × 8 basic scaling matrix is upsampled (by replication of elements) to the corresponding square size (i.e. 16 × 16, 32 × 32, 64 × 64). When zeroing of the high frequency coefficients for the 64-point transform is applied, the corresponding high frequencies of the scaling matrix are also zeroed out. That is, if the width or height of the TB is greater than or equal to 32, only the left half or top half of the coefficients are retained and the remaining coefficients are assigned to zero. Furthermore, the number of elements signaled for the 64 × 64 scaling matrix is also reduced from 8 × 8 to three 4 × 4 sub-matrices, since the bottom right 4 × 4 elements are never used.

The choice of the probability model for the syntax elements related to the absolute value for the transform coefficient level depends on the value of the absolute level or the partially reconstructed absolute level in the local neighborhood.

The selected probability model depends on the sum of the absolute levels (or partially reconstructed absolute levels) in the local neighborhood and the number of absolute levels greater than 0 in the local neighborhood (given by the number of sig _ coeff _ flag equal to 1). Context modeling and binarization depend on the following measures of the local neighborhood:

numSig: the number of non-zero levels in the local neighborhood;

sumAbs 1: the sum of the absolute levels (absLevel1) partially reconstructed after the first channel in the local neighborhood;

SumAbs: summation of absolute levels of reconstruction in local neighborhood

Diagonal position (d): sum of horizontal and vertical coordinates of current scan position within transform block

Based on the values of numSig, sumAbs1, and d, probability models for coding and decoding sig _ coeff _ flag, abs _ level _ gt1_ flag, par _ level _ flag, and abs _ level _ gt3_ flag are selected. The rice parameter used to binarize abs _ remaining and dec _ abs _ level is selected based on the values of the sumAbs and numSig.

In the current VVC, a reduced 32-point MTS (also referred to as RMTS32) is based on skipping high frequency coefficients and is used to reduce the computational complexity of the 32-point DST-7/DCT-8. And, it is accompanied by coefficient codec changes that include all types of zeroing (i.e., existing zeroing for high frequency components in RMTS32 and DCT 2). Specifically, binarization for the last non-zero coefficient position codec is coded based on the reduced TU size, and the context model selection for the last non-zero coefficient position codec is determined by the original TU size. In addition, sig _ coeff _ flag of the transform coefficient is coded using 60 context models. The selection of the context model index is based on the sum of the absolute grades of up to five previous partial reconstructions (called loc SumAbsPasss 1) and the quantization dependent state QState, as follows:

if cIdx is equal to 0, ctxInc is derived as follows:

ctxInc＝12×Max(0，QState-1)+Min((locSumAbspass1+1)>>1，3)+(d<28：(d<5？4：0))

otherwise (cIdx is greater than 0), ctxInc is derived as follows:

ctxInc＝36+8×Max(0，QState-1)+Min((locSumAbspass1+1)>>1，3)+(d<24：0)

in the current VVC, the slice-level syntax element "slice _ ts _ residual _ coding _ disabled _ flag" is employed to indicate whether residual coding for transform skip is disabled at the slice level, even if the current TU is in transform skip mode. For example, if slice _ ts _ residual _ coding _ disabled _ flag is equal to 1, residual coding for transform skip is disabled and residual coding for non-transform skip mode is invoked for the current TU. Furthermore, the transform coefficients in the residual codec for the non-transform skip mode depend on the quantizer state (QState). But since dependent scalar quantization is exclusively applied to the transform skip mode, dependent scalar quantization should be disabled if residual coding for non-transform skip mode is applied to the current TU with the transform skip mode.

In some embodiments, the picture header syntax element "ph _ ts _ residual _ coding _ disabled _ flag" is employed to indicate at the picture level whether to disable residual coding for the transform skip mode. If ph _ ts _ residual _ coding _ disabled _ flag is equal to 1, residual coding for transform skip is disabled for the current picture and all slices of the current picture associated with the picture header. Thus, since ph _ ts _ residual _ coding _ disabled _ flag is equal to 1, there is no need to signal the corresponding slice _ ts _ residual _ coding _ disabled _ flag (which is inferred to be 1) in the respective slice header associated with the picture header; if ph _ ts _ residual _ coding _ disabled _ flag is equal to 0, the syntax element slice _ ts _ residual _ coding _ disabled _ flag may still be signaled to indicate whether residual coding for transform skipping is enabled in the current slice.

In some embodiments, if residual coding for the transform skip mode is disabled, then dependent scalar quantization is disabled (including using dependent quantization states to derive context modeling and rice parameters for resolving residual samples, as described in the introductory portion). In other words, if ph _ ts _ residual _ coding _ disabled _ flag is equal to 1, ph _ dep _ quant _ enabled _ flag is set to 0. If ph _ dep _ quant _ enabled _ flag is equal to 1, ph _ ts _ residual _ coding _ disabled _ flag is set to 0. In another example, if ph _ dep _ quant _ enabled _ flag is equal to 1, slice _ ts _ residual _ coding _ disabled _ flag is set to 0. In yet another example, ph _ dep _ quant _ enabled _ flag and slice _ ts _ residual _ coding _ disabled _ flag may both be equal to 1; but for transform skipping the application of quantization dependent, state dependent context model and rice parameter derivation is omitted, e.g. checking if the current TU is in transform skip mode, i.e. |! transform _ skip _ flag [ x0] [ y0] [ cIdx ].

In some embodiments, syntax element ph _ ts _ residual _ coding _ disabled _ flag equal to 1 indicates that residual coding for transform skip is disabled and only residual coding for non-transform skip is invoked for the current picture, and syntax element ph _ ts _ residual _ coding _ disabled _ flag equal to 0 indicates that residual coding for transform skip is applied for the current picture. If the syntax element ph _ ts _ residual _ coding _ disabled _ flag is not present, it is inferred to be 0. Syntax element ph _ dep _ quant _ enabled _ flag equal to 0 indicates that dependent quantization is disabled for the current picture, and syntax element ph _ dep _ quant _ enabled _ flag equal to 1 indicates that dependent quantization is enabled for the current picture. When the syntax element ph _ dep _ quant _ enabled _ flag is not present, it is inferred to be 0. The following table shows one example syntax design in which the syntax element ph _ ts _ residual _ coding _ disabled _ flag is used to determine the presence of the syntax element ph _ dep _ quant _ enabled _ flag.

In some embodiments, the inverse quantization method (including both quantization dependent and state dependent context modeling and state dependent rice parameter derivation) is enabled for the transform skip mode. With this design, the following combinations are supported by changing the values of ph _ dep _ quant _ enabled _ flag and slice _ ts _ residual _ coding _ disabled _ flag:

apply dependent quantization to the transform skip mode when both flags are equal to 1. Furthermore, residual coding for non-transform-skip mode is applied to transform-skip TUs together with state-dependent context modeling and state-dependent rice parameter derivation

When slice _ ts _ residual _ coding _ disabled _ flag is equal to 1 and ph _ dep _ quant _ enabled _ flag is equal to 0. In this case, a conventional quantization method is applied to the transform skip TU. Meanwhile, the residual coding of the non-transform skip mode is applied to the transform skip mode, without applying the state-dependent context modeling and the state-dependent rice parameter derivation to the transform skip mode

When slice _ ts _ residual _ coding _ disabled _ flag is equal to 0 and ph _ dep _ quant _ enabled _ flag is equal to 1. In this case, dependent quantization is applied to the transform-skip mode and also residual coding of the transform-skip mode is applied to the transform-skip TU, i.e. state-dependent context modeling and rice parameter derivation etc. are not applied to the transform-skip TU.

Fig. 8 is a flow diagram illustrating an example process 800 for a video decoder to decode a current picture of a video bitstream, according to some embodiments of the present disclosure. As mentioned above, since dependent scalar quantization is exclusively applied to the transform skip mode, dependent scalar quantization should be disabled if residual coding for the non-transform skip mode is applied to the current picture with the transform skip mode.

In particular, a video decoder (e.g., video decoder 30) receives a first syntax element (e.g., ph _ ts _ residual _ coding _ disabled _ flag) for a current picture from a video bitstream (810). The video decoder then checks whether residual coding for transform skipping is disabled for the current picture (820). In accordance with a determination that the first syntax element indicates that residual coding for transform skipping is not disabled for the current picture (820-no), the video decoder then receives a second syntax element (e.g., ph _ dep _ quant _ enabled _ flag) for the current picture from the video bitstream (830); in accordance with a determination that the first syntax element indicates that residual coding for transform skipping is disabled for the current picture (820-yes), the video decoder sets a second syntax element to a default value that disables dependent quantization for the current picture (840). The video decoder then performs residual decoding and inverse quantization on the current picture according to the first syntax element and the second syntax element (850).

In some embodiments, when the first syntax element indicates that residual coding for transform skipping is disabled for the current picture, the video decoder performs residual coding for non-transform skipping on the current picture (860); when the first syntax element indicates that residual coding for transform skip is not disabled for the current picture or that the first syntax element is not present in the video bitstream for the current picture, the video decoder performs residual coding for transform skip on the current picture (870).

In some embodiments, when the second syntax element indicates that dependent quantization is disabled for the current picture or that the second syntax element is not present in the video bitstream for the current picture, the video decoder disables dependent quantization for the current picture (880); when the second syntax element indicates that dependent quantization is enabled for the current picture, the video decoder enables dependent quantization for the current picture (890).

In some embodiments, the video decoder receives a third syntax element (e.g., slice _ ts _ residual _ coding _ disabled _ flag) from the video bitstream when residual coding for transform skipping is not disabled for the current picture, wherein the third syntax element indicates whether residual coding for transform skipping is enabled for a current slice associated with the current picture. When disabling residual coding for transform skipping for the current picture, the video decoder sets the third syntax element to a default value that disables residual coding for transform skipping for all stripes associated with the current picture. In some embodiments, a video decoder derives context modeling and rice parameters for parsing residual samples of a current picture independent of a dependent quantization state of the residual samples of the current picture. In other words, there is no dependency between the context modeling and the derivation of the rice parameter and the use of dependent quantization states.

Fig. 9 is a block diagram illustrating an example Context Adaptive Binary Arithmetic Coding (CABAC) engine, according to some embodiments of the disclosure.

Context Adaptive Binary Arithmetic Coding (CABAC) is a form of entropy coding used in many video coding standards, such as h.264/MPEG-4AVC, High Efficiency Video Coding (HEVC), and VVC. CABAC is based on arithmetic coding with some innovations and changes to adapt it to the needs of video coding standards. For example, CABAC encodes binary symbols, which keeps complexity low and allows probabilistic modeling of more frequently used bits of any symbol. Since the codec modes are usually locally well correlated, the probability model is adaptively selected based on the local context, allowing better modeling of the probabilities. Finally, CABAC uses multiplication-free range division by using quantized probability ranges and probability states.

CABAC has multiple probability modes for different contexts. It first converts all non-binary symbols to binary. Then, for each bin (or bit), the codec chooses which probability model to use, and then uses information from nearby elements to optimize the probability estimates. And finally, compressing the data by applying arithmetic coding and decoding.

Context modeling provides an estimate of the conditional probability of a coded symbol. With a suitable context model, a given inter-symbol redundancy can be exploited for encoding by switching between different probability models depending on the coded symbols in the vicinity of the current symbol. Encoding and decoding the data symbols involves the following stages.

Binarization: CABAC uses binary arithmetic coding, which means that only binary decisions (1 or 0) are coded. Non-binary valued symbols (e.g., transform coefficients or motion vectors) are "binarized" or converted to binary codes prior to arithmetic coding. This process is similar to the process of converting data symbols into variable length codes, but the binary code is further encoded (by an arithmetic encoder) prior to transmission. These stages are repeated for each binary digit (or "bit") of the binarized symbol.

Selecting a context model: the "context model" is a probabilistic model for one or more binary bits of a binarized symbol. The model may be selected from a selection of available models based on statistics of recently coded data symbols. The context model stores the probability that each binary bit is either a "1" or a "0".

Arithmetic coding: the arithmetic coder codes each binary bit according to the selected probability model. Note that there are only two subranges for each binary bit (corresponding to "0" and "1").

And (3) probability updating: the selected context model is updated based on the value of the actual codec (e.g., if the binary bit value is "1", the frequency count "1" is incremented).

By decomposing each non-binary syntax element value into a sequence of bins, the further processing of each bin value in CABAC depends on the associated codec mode decision, which may be selected as normal mode or bypass mode. The latter is selected for the bins, which are assumed to be evenly distributed, so that the entire conventional binary arithmetic encoding (and decoding) process is simply bypassed for these bins. In a conventional codec mode, each bin value is encoded using a conventional binary arithmetic codec engine, where the associated probability model is determined by a fixed selection based on the type of syntax element and the bin position or bin index (binIdx) in the binarized representation of the syntax element, or the associated probability model is adaptively selected from two or more probability models according to relevant side information (e.g., spatial neighbors, components, depth or size of CU/PU/TU, or position within TU). The selection of a probabilistic model is referred to as context modeling. As an important design decision, the latter case is typically applied only to the most frequently observed bits, while other bits that are typically less frequently observed will be processed using a joint, typically zeroth order probability model. In this way, CABAC enables selective adaptive probabilistic modeling at the sub-symbol level, thus providing an efficient tool for exploiting inter-symbol redundancy, significantly reducing overall modeling or learning costs. Note that for the fixed case and the adaptive case, in principle, the switching from one probability model to another may occur between any two consecutive conventional codec bits. In general, the design of context models in CABAC reflects the following objectives: a good compromise is found between avoiding unnecessary modeling cost overhead and exploiting the conflicting goals of statistical correlation to a large extent.

The parameters of the probability model in CABAC are adaptive, which means that adaptation of the model probabilities to the statistical variation of the source of binary bits is performed in the encoder and decoder on a binary bit by binary bit basis in a backward adaptive and synchronous manner; this process is called probability estimation. To this end, each probability model in CABAC may take one of 126 different states with an associated model probability value p, ranging from [0: 01875; 98125] interval. Two parameters for each probabilistic model are stored in the context memory in the form of 7-bit entries: 6 bits are used for each of the 63 probability states of the model probability pLPS representing the Least Probable Symbol (LPS), and 1 bit is used for the nMPS, i.e. the value of the Most Probable Symbol (MPS).

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. The computer readable medium may include a computer readable storage medium, which corresponds to a tangible medium, such as a data storage medium, or a communication medium including any medium that facilitates transfer of a computer program from one place to another (e.g., according to a communication protocol). In this manner, the computer-readable medium may generally correspond to (1) a non-volatile tangible computer-readable storage medium, or (2) a communication medium, such as a signal or carrier wave. A data storage medium may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementing the implementations described herein. The computer program product may include a computer-readable medium.

The terminology used in the description of the embodiments herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the claims. As used in the description of the embodiments and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms "comprises" and/or "comprising …," when used in this specification, specify the presence of stated features, elements, and/or components, but do not preclude the presence or addition of one or more other features, elements, components, and/or groups thereof.

It will also be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first electrode may be referred to as a second electrode, and similarly, a second electrode may be referred to as a first electrode, without departing from the scope of embodiments. The first electrode and the second electrode are both electrodes, but they are not the same electrode.

The description of the present application has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications, variations and alternative embodiments will become apparent to those of ordinary skill in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments and with the various embodiments with various modifications as are suited to the particular use contemplated. Therefore, it is to be understood that the scope of the claims is not to be limited to the specific examples of the embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.

Claims

1. A method of decoding video data, comprising:

receiving a first syntax element of a current picture from a video bitstream;

in accordance with a determination that the first syntax element indicates that residual coding for transform skipping is not disabled for the current picture, receiving a second syntax element of the current picture from the video bitstream;

in accordance with a determination that the first syntax element indicates that residual coding for transform skipping is disabled for the current picture, setting the second syntax element to a default value that disables dependent quantization for the current picture; and is

Performing residual decoding and inverse quantization on the current picture according to the first syntax element and the second syntax element.

2. The method of claim 1, wherein the performing residual decoding on the current picture according to the first syntax element and the second syntax element further comprises:

performing residual coding for non-transform skipping on the current picture when the first syntax element indicates that residual coding for transform skipping is disabled for the current picture; and is

Performing transform-skipped residual coding on the current picture when the first syntax element indicates that residual coding for transform skipping is not disabled for the current picture or the first syntax element is not present in the video bitstream for the current picture.

3. The method of claim 1, wherein the performing inverse quantization of the current picture in accordance with the first syntax element and the second syntax element further comprises:

disabling dependent quantization for the current picture when the second syntax element indicates that dependent quantization is disabled for the current picture or that the second syntax element is not present in the video bitstream for the current picture; and is

When the second syntax element indicates that dependent quantization is enabled for the current picture, dependent quantization is enabled for the current picture.

4. The method of claim 1, further comprising:

receiving a third syntax element from the video bitstream when residual coding for transform skipping is not disabled for the current picture, wherein the third syntax element indicates whether residual coding for transform skipping is enabled for a current slice associated with the current picture.

5. The method of claim 4, further comprising:

setting the third syntax element to a default value that disables residual coding for transform skip for all stripes associated with the current picture when residual coding for transform skip is disabled for the current picture.

6. The method of claim 1, further comprising:

deriving context modeling and Rice parameters for parsing residual samples of the current picture independent of a dependent quantization state of the residual samples of the current picture when residual coding for transform skipping is disabled for the current picture.

7. The method of claim 1, wherein the second syntax element is 0 when the first syntax element is 1.

8. The method of claim 1, wherein the first syntax element is 0 when the second syntax element is 1.

9. An electronic device, comprising:

one or more processing units;

a memory coupled to the one or more processing units; and

a plurality of programs stored in the memory, which when executed by the one or more processing units, cause the electronic device to perform the method of claims 1-8.

10. A non-transitory computer readable storage medium storing a plurality of programs for execution by an electronic device having one or more processing units, wherein the plurality of programs, when executed by the one or more processing units, cause the electronic device to perform the method of claims 1-8.