TECHNICAL FIELD

The present disclosure describes embodiments generally related to video coding.

BACKGROUND

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

Video coding and decoding can be performed using inter-picture prediction with motion compensation. Uncompressed digital video can include a series of pictures, each picture having a spatial dimension of, for example, 1920×1080 luminance samples and associated chrominance samples. The series of pictures can have a fixed or variable picture rate (informally also known as frame rate), of, for example 60 pictures per second or 60 Hz. Uncompressed video has significant bitrate requirements. For example, 1080p60 4:2:0 video at 8 bit per sample (1920×1080 luminance sample resolution at 60 Hz frame rate) requires close to 1.5 Gbit/s bandwidth. An hour of such video requires more than 600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction of redundancy in the input video signal, through compression. Compression can help reduce the aforementioned bandwidth or storage space requirements, in some cases by two orders of magnitude or more. Both lossless and lossy compression, as well as a combination thereof can be employed. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal. When using lossy compression, the reconstructed signal may not be identical to the original signal, but the distortion between original and reconstructed signals is small enough to make the reconstructed signal useful for the intended application. In the case of video, lossy compression is widely employed. The amount of distortion tolerated depends on the application; for example, users of certain consumer streaming applications may tolerate higher distortion than users of television distribution applications. The compression ratio achievable can reflect that: higher allowable/tolerable distortion can yield higher compression ratios.

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

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

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

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

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

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

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

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec. H.265, “High Efficiency Video Coding”, December 2016).

Referring toFIG. 1, a current block (101) comprises samples that have been found by the encoder during the motion search process to be predictable from a previous block of the same size that has been spatially shifted. Instead of coding that MV directly, the MV can be derived from metadata associated with one or more reference pictures, for example from the most recent (in decoding order) reference picture, using the MV associated with either one of five surrounding samples, denoted A0, A1, and B0, B1, B2(102through106, respectively). In H.265, the MV prediction can use predictors from the same reference picture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for video coding at a decoder. In an embodiment, a method of video coding at a decoder is provided. In the method, a bit stream including coded bits of bins of syntax elements is received. The syntax elements correspond to residues of a region of a transform skipped block in a coded picture. Context modeling is performed to determine a context model for each of a number of the bins of syntax elements of the region. The number of the bins of syntax elements that are context coded does not exceed a maximum number of context coded bins set for the region. The coded bits of the number of the bins of syntax elements are decoded based on the determined context models.

In an embodiment, the number of the bins of syntax elements that are context coded is less than or equal to a total number of the bins of syntax elements for the region of the transform skipped block.

In an embodiment, the maximum number of context coded bins for the region of the transform skipped block is B×A, where B is a positive number and A is a number of quantized residues in the region.

In an embodiment, the coded bits of the remaining total number of the bins of syntax elements that are not context coded for the region of the transform skipped block are decoded based on an equal probability model.

In an embodiment, B is an integer.

In an embodiment, B is a fractional number.

In an embodiment, B is set according to A.

In an embodiment, the transform skipped block contains only the region and A is equal to W×H of the transform skipped block, where W is a width of the transform skipped block and H is a height of the transform skipped block.

In an embodiment, the transform skipped block is divided into a plurality of regions including the region, and the maximum number of context coded bins for each of the plurality of regions of the transform skipped block is B×A, where B is a positive number and A is a number of quantized residues in the each of the plurality of regions.

In an embodiment, a method of video coding at a decoder is provided. In the method, a coded video bit stream is received. An indicator is received. The indicator indicates whether at least one of a current block and a neighboring block of the coded video bit stream is coded with block differential pulse-code modulation (BDPCM). The current block is adjacent to the neighboring block. When the at least one of the current block and the neighboring block is indicated as being coded with BDPCM, a boundary strength is determined to be applied to a boundary between a current sub-block in the current block and a neighboring sub-block in the neighboring block, and deblocking is performed on the boundary between the current sub-block in the current block and the neighboring sub-block in the neighboring block using a deblocking filter according to the determined boundary strength.

In an embodiment, the neighboring sub-block is not coded with BDPCM.

In an embodiment, when the neighboring sub-block is coded with BDPCM, the boundary strength of the deblocking filter is determined to be 1 or 2.

In an embodiment, when the current and neighboring sub-blocks are coded with BDPCM, the deblocking is performed on the boundary between the current sub-block in the current block and the neighboring sub-block in the neighboring block based on a determination that a difference in quantization parameters between the current sub-block and the neighboring sub-block is greater than a threshold.

In an embodiment, when the current and neighboring sub-blocks are coded with BDPCM, the deblocking is performed on the boundary between the current sub-block in the current block and the neighboring sub-block in the neighboring block based on a determination that the current sub-block and the neighboring sub-block are coded with different BDPCM prediction modes.

In an embodiment, when the current and neighboring sub-blocks are coded with BDPCM, the deblocking is performed on the boundary between the current sub-block in the current block and the neighboring sub-block in the neighboring block based on a determination that at least one of the current sub-block and the neighboring sub-block has non-zero coefficients.

Aspects of the disclosure also provide non-transitory computer-readable storage mediums storing instructions which when executed by a computer cause the computer to perform any of the above methods.

