Patent Application
20240107037
The present disclosure relates to image and video coding and decoding.
Digital video accounts for the largest bandwidth use on the internet and other digital communication networks. As the number of connected user devices capable of receiving and displaying video increases, it is expected that the bandwidth demand for digital video usage will continue to grow.
The present disclosure discloses techniques that can be used by video encoders and decoders for video processing using a palette mode in which a palette of representative sample values is used for representation of video.
In one example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video and a bitstream of the video using a palette mode in which samples of the video block are represented using a palette of representative color values. A size of the palette of the video block is determined based on whether a local dual tree is applied to the video block.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video and a bitstream of the video using a palette mode in which samples of the video block are represented using a palette of a representative color values. A size of a palette predictor of the video block is based on whether a local dual tree is applied to the video block.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video and a bitstream of the video using a palette mode in which samples of the video block are represented using a palette of representative color values. The bitstream conforms to a rule specifying that values of escape samples are coded in the bitstream using a quantization parameter constrained by at least a maximum allowed value or a minimum allowed value.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a block of a video and a bitstream of the video according to a format rule specifying that whether parameters associated with a chroma coding tool are present in an adaptation parameter set of the bitstream is based on a control flag in the adaptation parameter set.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a block of a video and a bitstream of the video. The bitstream conforms to a format rule specifying that a syntax element associated with a quantization parameter is omitted in a picture header of the bitstream in case the video is monochromatic or color components of the video are processed separately.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video and a bitstream of the video according to a rule specifying that, for the conversion, a palette mode in which samples of the video block are represented using a palette of representative color values and an adaptive color transform mode in which a color space conversion is carried out in a residual domain are mutually exclusively enabled.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video and a bitstream of the video. An adaptive color transform mode in which a color space conversion is carried out in a residual domain is applied to a residual block of the video block regardless of a color space of the residual block.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video and a bitstream of the video. The video block is coded using a transform skip residual coding tool in which residual coefficients of a transform skipped coding of the video block are coded using context coding process or a bypass coding process. During the conversion, an operation is applied at a beginning or an end of the bypass coding process to a variable that specifies a number of remaining context coded bins allowed in the video block.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video and a bitstream of the video using a transform skip residual coding process. During the conversion, an operation is applied to a variable indicating whether a syntax element belongs to a particular scan pass.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video and a bitstream of the video. During the conversion, whether a syntax element indicating a sign of a coefficient level is coded using a bypass coding process or a context coding process is based on an index of a scan pass in which same syntax elements of one or more coefficients in a region of the video block are coded in an order.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video and a bitstream of the video using a transform skip residual coding process. During the conversion, whether a syntax element indicating a sign of a coefficient level is coded using a bypass coding process or a context coding process is based on whether the syntax element is signalled in a same scan pass as another syntax element.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video and a coded representation of the video, wherein a palette mode is used for the coded representation of the video block in which samples of the video block are represented using a palette of a representative color values; and wherein samples outside of the palette are coded using an escape symbol and a value that is quantized using a quantization parameter that is in a range between a minimum allowed value and a maximum allowed value that are determined by a rule.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video and a coded representation of the video, wherein a palette mode is used for the coded representation of the video block in which samples of the video block are represented using a palette of a representative color values; and wherein a size of the palette is depended on a rule about whether local dual tree is used for the conversion between the video block and the coded representation.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video and a coded representation of the video, wherein a palette mode is used for the coded representation of the video block in which samples of the video block are represented using a palette of a representative color values; and wherein a size of the palette predictor is depended on a rule about whether local dual tree is used for the conversion between the video block and the coded representation.
In another example aspect, a video processing method is disclosed. The method includes determining, for a conversion between a video block of a video region of a video and a coded representation of the video, based on a coding condition, whether a syntax element identifying a deblocking offset for a chroma component of the video is included in the coded representation at the video region level; and performing the conversion based on the determining; wherein the deblocking offset is used to selectively enable a deblocking operation on the video block.
In another example aspect, a video processing method is disclosed. The method includes determining, for a conversion between a video block of a video region of a video and a coded representation of the video, based on a coding condition, whether a syntax element identifying use of a chroma coding tool is included in the coded representation at the video region level; and performing the conversion based on the determining; wherein the deblocking offset is used to selectively enable a deblocking operation on the video block.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video region of a video and a coded representation of the video, wherein the coded representation conforms to a format; wherein the format specifies that whether a first flag indicating a deblocking offset for a chroma component of the video is included in the coded representation is based on whether a second flag indicating a quantization parameter offset of the chroma component is included in the coded representation.
In another example aspect, a video processing method is disclosed. The method includes performing a conversion between a video block of a video region of a video and a coded representation of the video, wherein the coded representation conforms to a format rule; wherein the format rule specifies that a syntax element in the coded representation controls whether one or more parameters indicating applicability of one or more chroma coding tools are includes in the coded representation at the video region or the video block level.
In yet another example aspect, a video encoder apparatus is disclosed. The video encoder comprises a processor configured to implement above-described methods.
In yet another example aspect, a video decoder apparatus is disclosed. The video decoder comprises a processor configured to implement above-described methods.
In yet another example aspect, a computer readable medium having code stored thereon is disclosed. The code embodies one of the methods described herein in the form of processor-executable code.
These, and other, features are described throughout the present disclosure.
Section headings are used in the present disclosure for ease of understanding and do not limit the applicability of techniques and embodiments disclosed in each section only to that section. Furthermore, H.266 terminology is used in some description only for ease of understanding and not for limiting scope of the disclosed techniques. As such, the techniques described herein are applicable to other video codec protocols and designs also.
1. Overview
The present disclosure is related to video coding technologies. Specifically, it is related to index and escape symbols coding in palette coding, chroma format signalling, and residual coding. It may be applied to the existing video coding standard like High Efficiency Video Coding (HEVC), or the standard (e.g., Versatile Video Coding (VVC)) to be finalized. It may be also applicable to future video coding standards or video codec.
2. Video Coding Standards
Video coding standards have evolved primarily through the development of the well-known International Telecommunication Union (ITU) Telecommunication Standardization Sector (ITU-T) and International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC) standards. The ITU-T produced H.261 and H.263, ISO/IEC produced Moving Picture Experts Group (MPEG)-1 and MPEG-4 Visual, and the two organizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4 Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, the video coding standards are based on the hybrid video coding structure wherein temporal prediction plus transform coding are utilized. To explore the future video coding technologies beyond HEVC, Joint Video Exploration Team (JVET) was founded by Video Coding Experts Group (VCEG) and MPEG jointly in 2015. Since then, many new methods have been adopted by JVET and put into the reference software named Joint Exploration Model (JEM). In April 2018, the Joint Video Expert Team (JVET) between VCEG (Q6/16) and ISO/IEC JTC1 SC29/WG11 (MPEG) was created to work on the VVC standard targeting at 50% bitrate reduction compared to HEVC.
2.1 Palette Mode in HEVC Screen Content Coding Extensions (HEVC-SCC)
2.1.1 Concept of Palette Mode
The basic idea behind a palette mode is that the pixels in the coding unit (CU) are represented by a small set of representative colour values. This set is referred to as the palette. And it is also possible to indicate a sample that is outside the palette by signalling an escape symbol followed by (possibly quantized) component values. This kind of pixel is called escape pixel. The palette mode is illustrated in
2.1.2 Coding of the Palette Entries
For coding of the palette entries, a palette predictor is maintained. The maximum size of the palette as well as the palette predictor is signalled in the sequence parameter set (SPS). In HEVC-SCC, a palette_predictor_initializer_present_flag is introduced in the picture parameter set (PPS). When this flag is 1, entries for initializing the palette predictor are signalled in the bitstream. The palette predictor is initialized at the beginning of each coding tree unit (CTU) row, each slice and each tile. Depending on the value of the palette_predictor_initializer_present_flag, the palette predictor is reset to 0 or initialized using the palette predictor initializer entries signalled in the PPS. In HEVC-SCC, a palette predictor initializer of size 0 was enabled to allow explicit disabling of the palette predictor initialization at the PPS level.
For each entry in the palette predictor, a reuse flag is signalled to indicate whether it is part of the current palette. This is illustrated in
2.1.3 Coding of Palette Indices
The palette indices are coded using horizontal and vertical traverse scans as shown in
The palette indices are coded using two palette sample modes: ‘COPY_LEFT’ and ‘COPY_ABOVE’. In the ‘COPY_LEFT’ mode, the palette index is assigned to a decoded index. In the ‘COPY_ABOVE’ mode, the palette index of the sample in the row above is copied. For both “COPY_LEFT’ and ‘COPY_ABOVE’ modes, a run value is signalled which specifies the number of subsequent samples that are also coded using the same mode.
In the palette mode, the value of an index for the escape symbol is the number of palette entries. And, when escape symbol is part of the run in ‘COPY_LEFT’ or ‘COPY_ABOVE’ mode, the escape component values are signalled for each escape symbol. The coding of palette indices is illustrated in
This syntax order is accomplished as follows. First the number of index values for the CU is signalled. This is followed by signalling of the actual index values for the entire CU using truncated binary coding. Both the number of indices as well as the index values are coded in bypass mode. This groups the index-related bypass bins together. Then the palette sample mode (if necessary) and run are signalled in an interleaved manner. Finally, the component escape values corresponding to the escape symbols for the entire CU are grouped together and coded in bypass mode. The binarization of escape symbols is EG coding with 3rd order, i.e., EG-3.
An additional syntax element, last_run_type_flag, is signalled after signalling the index values. This syntax element, in conjunction with the number of indices, eliminates the need to signal the run value corresponding to the last run in the block.
In HEVC-SCC, the palette mode is also enabled for 4:2:2, 4:2:0, and monochrome chroma formats. The signalling of the palette entries and palette indices is almost identical for all the chroma formats. In case of non-monochrome formats, each palette entry consists of 3 components. For the monochrome format, each palette entry consists of a single component. For subsampled chroma directions, the chroma samples are associated with luma sample indices that are divisible by 2. After reconstructing the palette indices for the CU, if a sample has only a single component associated with it, only the first component of the palette entry is used. The only difference in signalling is for the escape component values. For each escape symbol, the number of escape component values signalled may be different depending on the number of components associated with that symbol.
In addition, there is an index adjustment process in the palette index coding. When signalling a palette index, the left neighboring index or the above neighboring index should be different from the current index. Therefore, the range of the current palette index could be reduced by 1 by removing one possibility. After that, the index is signalled with truncated binary (TB) binarization.
The texts related to this part is shown as follows, where the CurrPaletteIndex is the current palette index and the adjustedRefPaletteIndex is the prediction index.
The variable PaletteIndexMap[xC][yC] specifies a palette index, which is an index to the array represented by CurrentPaletteEntries. The array indices xC, yC specify the location (xC, yC) of the sample relative to the top-left luma sample of the picture. The value of PaletteIndexMap[xC][yC] shall be in the range of 0 to MaxPaletteIndex, inclusive.
The variable adjustedRefPaletteIndex is derived as follows:
When CopyAboveIndicesFlag[xC][yC] is equal to 0, the variable CurrPaletteIndex is derived as follows:
if(CurrPaletteIndex>=adjustedRefPaletteIndex)CurrPaletteIndex++
In addtion, the run length elements in the palette mode are context coded. The related context derivation process descirbed in JVET-02011-vE is shown as follows.
Inputs to this process are the bin index binIdx and the syntax elements copy_above_palette_indices_flag and palette_idx_idc.
Output of this process is the variable ctxInc.
The variable ctxInc is derived as follows:
ctxInc=(palette_idx_idc<1)?0:((palette_idx_idc<3)?1:2) (9-69)
2.2 Palette Mode in VVC
2.2.1 Palette in Dual Tree
In VVC, the dual tree coding structure is used on coding the intra slices, so the luma component and two chroma components may have different palette and palette indices. In addition, the two chroma component shares same palette and palette indices.
2.2.2 Palette as a Separate Mode
In some embodiments, the prediction modes for a coding unit can be MODE_INTRA, MODE_INTER, MODE_IBC and MODE_PLT. The binarization of prediction modes is changed accordingly.
When intra block copy (IBC) is turned off, on I tiles, the first one bin is employed to indicate whether the current prediction mode is MODE_PLT or not. While on P/B tiles, the first bin is employed to indicate whether the current prediction mode is MODE_INTRA or not. If not, one additional bin is employed to indicate the current prediction mode is MODE_PLT or MODE_INTER.
When IBC is turned on, on I tiles, the first bin is employed to indicate whether the current prediction mode is MODE_IBC or not. If not, the second bin is employed to indicate whether the current prediction mode is MODE_PLT or MODE_INTRA. While on P/B tiles, the first bin is employed to indicate whether the current prediction mode is MODE_INTRA or not. If it's an intra mode, the second bin is employed to indicate the current prediction mode is MODE_PLT or MODE_INTRA. If not, the second bin is employed to indicate the current prediction mode is MODE_IBC or MODE_INTER.
Example texts are shown as follows.
2.2.3 Palette Mode Syntax
2.2.4 Palette Mode Semantics
In the following semantics, the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture. The array indices xC, yC specify the location (xC, yC) of the sample relative to the top-left luma sample of the picture. The array index startComp specifies the first colour component of the current palette table. startComp equal to 0 indicates the Y component; startComp equal to 1 indicates the Cb component; startComp equal to 2 indicates the Cr component. numComps specifies the number of colour components in the current palette table.
The predictor palette consists of palette entries from previous coding units that are used to predict the entries in the current palette.
The variable PredictorPaletteSize[startComp] specifies the size of the predictor palette for the first colour component of the current palette table startComp. PredictorPaletteSize is derived as specified in clause 8.4.5.3.
The variable PalettePredictorEntryReuseFlags[i] equal to 1 specifies that the i-th entry in the predictor palette is reused in the current palette. PalettePredictorEntryReuseFlags[i] equal to 0 specifies that the i-th entry in the predictor palette is not an entry in the current palette. All elements of the array PalettePredictorEntryReuseFlags[i] are initialized to 0.
palette_predictor_run is used to determine the number of zeros that precede a non-zero entry in the array PalettePredictorEntryReuseFlags.
It is a requirement of bitstream conformance that the value of palette_predictor_run shall be in the range of 0 to (PredictorPaletteSize—predictorEntryIdx), inclusive, where predictorEntryIdx corresponds to the current position in the array PalettePredictorEntryReuseFlags. The variable NumPredictedPaletteEntries specifies the number of entries in the current palette that are reused from the predictor palette. The value of NumPredictedPaletteEntries shall be in the range of 0 to palette_max_size, inclusive.
num_signalled_palette_entries specifies the number of entries in the current palette that are explicitly signalled for the first colour component of the current palette table startComp.
When num_signalled_palette_entries is not present, it is inferred to be equal to 0.
The variable CurrentPaletteSize[startComp] specifies the size of the current palette for the first colour component of the current palette table startComp and is derived as follows:
CurrentPaletteSize[startComp]=NumPredictedPaletteEntries+num_signalled_palette_entries (7-155)
The value of CurrentPaletteSize[startComp] shall be in the range of 0 to palette_max_size, inclusive.
new_palette_entries[cIdx][i] specifies the value for the i-th signalled palette entry for the colour component cIdx.
The variable PredictorPaletteEntries[cIdx][i] specifies the i-th element in the predictor palette for the colour component cIdx.
The variable CurrentPaletteEntries[cIdx][i] specifies the i-th element in the current palette for the colour component cIdx and is derived as follows:
palette_escape_val_present_flag equal to 1 specifies that the current coding unit contains at least one escape coded sample. escape_val_present_flag equal to 0 specifies that there are no escape coded samples in the current coding unit. When not present, the value of palette_escape_val_present_flag is inferred to be equal to 1.
The variable MaxPaletteIndex specifies the maximum possible value for a palette index for the current coding unit. The value of MaxPaletteIndex is set equal to CurrentPaletteSize[startComp]−1+palette_escape_val_present_flag.
num_palette_indices_minus1 plus 1 is the number of palette indices explicitly signalled or inferred for the current block.
When num_palette_indices_minus 1 is not present, it is inferred to be equal to 0.
palette_idx_idc is an indication of an index to the palette table, CurrentPaletteEntries. The value of palette_idx_idc shall be in the range of 0 to MaxPaletteIndex, inclusive, for the first index in the block and in the range of 0 to (MaxPaletteIndex−1), inclusive, for the remaining indices in the block.
When palette_idx_idc is not present, it is inferred to be equal to 0.
The variable PaletteIndexIdc[i] stores the i-th palette_idx_idc explicitly signalled or inferred. All elements of the array PaletteIndexIdc[i] are initialized to 0.
copy_above_indices_for_final_run_flag equal to 1 specifies that the palette indices of the last positions in the coding unit are copied from the palette indices in the row above if horizontal traverse scan is used or the palette indices in the left column if vertical traverse scan is used. copy_above_indices_for_final_run_flag equal to 0 specifies that the palette indices of the last positions in the coding unit are copied from PaletteIndexIdc[num_palette_indices_minus1].
When copy_above_indices_for_final_run_flag is not present, it is inferred to be equal to 0.
palette_transpose_flag equal to 1 specifies that vertical traverse scan is applied for scanning the indices for samples in the current coding unit. palette_transpose_flag equal to 0 specifies that horizontal traverse scan is applied for scanning the indices for samples in the current coding unit. When not present, the value of palette_transpose_flag is inferred to be equal to 0. The array TraverseScanOrder specifies the scan order array for palette coding. TraverseScanOrder is assigned the horizontal scan order HorTravScanOrder if palette_transpose_flag is equal to 0 and
TraverseScanOrder is assigned the vertical scan order VerTravScanOrder if palette_transpose_flag is equal to 1.
copy_above_palette_indices_flag equal to 1 specifies that the palette index is equal to the palette index at the same location in the row above if horizontal traverse scan is used or the same location in the left column if vertical traverse scan is used. copy_above_palette_indices_flag equal to 0 specifies that an indication of the palette index of the sample is coded in the bitstream or inferred. The variable CopyAboveIndicesFlag[xC][yC] equal to 1 specifies that the palette index is copied from the palette index in the row above (horizontal scan) or left column (vertical scan). CopyAboveIndicesFlag[xC][yC] equal to 0 specifies that the palette index is explicitly coded in the bitstream or inferred. The array indices xC, yC specify the location (xC, yC) of the sample relative to the top-left luma sample of the picture. The value of PaletteIndexMap[xC][yC] shall be in the range of 0 to (MaxPaletteIndex−1), inclusive.
The variable PaletteIndexMap[xC][yC] specifies a palette index, which is an index to the array represented by CurrentPaletteEntries. The array indices xC, yC specify the location (xC, yC) of the sample relative to the top-left luma sample of the picture. The value of PaletteIndexMap[xC][yC] shall be in the range of 0 to MaxPaletteIndex, inclusive.
The variable adjustedRefPaletteIndex is derived as follows:
When CopyAboveIndicesFlag[xC][yC] is equal to 0, the variable CurrPaletteIndex is derived as follows:
if(CurrPaletteIndex>=adjustedRefPaletteIndex)CurrPaletteIndex++ (7-158)
palette_run_prefix, when present, specifies the prefix part in the binarization of PaletteRunMinus1.
palette_run_suffix is used in the derivation of the variable PaletteRunMinus 1. When not present, the value of palette_run_suffix is inferred to be equal to 0.
When RunToEnd is equal to 0, the variable PaletteRunMinus1 is derived as follows:
PaletteRunMinus1=palette_run_prefix (7-159)
PrefixOffset=1<<(palette_run_prefix−1)PaletteRunMinus1=PrefixOffset+palette_run_suffix (7-160)
The variable PaletteRunMinus1 is used as follows:
2.2.5 Line Based Coefficient Group (CG) Palette Mode
Line based CG palette mode was adopted to VVC. In this method, each CU of palette mode is divided into multiple segments of m samples (m=16 in this test) based on the traverse scan mode. The encoding order for palette run coding in each segment is as follows: For each pixel, 1 context coded bin is signalled indicating if the pixel is of the same mode as the previous pixel, i.e., if the previous scanned pixel and the current pixel are both of run type COPY_ABOVE or if the previous scanned pixel and the current pixel are both of run type INDEX and the same index value. Otherwise,
is signalled. If the pixel and the previous pixel are of different mode, one context coded bin
is signalled indicating the run type, i.e., INDEX or COPY_ABOVE, of the pixel. Same as the palette mode in VVC test model (VTM) 6.0, decoder doesn't have to parse run type if the sample is in the first row (horizontal traverse scan) or in the first column (vertical traverse scan) since the INDEX mode is used by default. Also, decoder doesn't have to parse run type if the previously parsed run type is COPY_ABOVE. After palette run coding of pixels in one segment, the index values (for INDEX mode) and quantized escape colors are bypass coded and grouped apart from encoding/parsing of context coded bins to improve throughput within each line CG. Since the index value is now coded/parsed after run coding, instead of processed before palette run coding as in VTM, encoder doesn't have to signal the number of index values
and the last run type
The texts of line-based CG palette mode in some embodiments is shown as follows.
In the following semantics, the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture. The array indices xC, yC specify the location (xC, yC) of the sample relative to the top-left luma sample of the picture. The array index startComp specifies the first colour component of the current palette table. startComp equal to 0 indicates the Y component; startComp equal to 1 indicates the Cb component; startComp equal to 2 indicates the Cr component. numComps specifies the number of colour components in the current palette table.
The predictor palette consists of palette entries from previous coding units that are used to predict the entries in the current palette.
The variable PredictorPaletteSize[startComp] specifies the size of the predictor palette for the first colour component of the current palette table startComp. PredictorPaletteSize is derived as specified in clause 8.4.5.3.
The variable PalettePredictorEntryReuseFlags[i] equal to 1 specifies that the i-th entry in the predictor palette is reused in the current palette. PalettePredictorEntryReuseFlags[i] equal to 0 specifies that the i-th entry in the predictor palette is not an entry in the current palette. All elements of the array PalettePredictorEntryReuseFlags[i] are initialized to 0.
palette_predictor_run is used to determine the number of zeros that precede a non-zero entry in the array PalettePredictorEntryReuseFlags.
It is a requirement of bitstream conformance that the value of palette_predictor_run shall be in the range of 0 to (PredictorPaletteSize−predictorEntryIdx), inclusive, where predictorEntryIdx corresponds to the current position in the array PalettePredictorEntryReuseFlags. The variable NumPredictedPaletteEntries specifies the number of entries in the current palette that are reused from the predictor palette. The value of NumPredictedPaletteEntries shall be in the range of 0 to palette_max_size, inclusive.
num_signalled_palette_entries specifies the number of entries in the current palette that are explicitly signalled for the first colour component of the current palette table startComp.
When num_signalled_palette_entries is not present, it is inferred to be equal to 0.
The variable CurrentPaletteSize[startComp] specifies the size of the current palette for the first colour component of the current palette table startComp and is derived as follows:
CurrentPaletteSize[startComp]=NumPredictedPaletteEntries+num_signalled_palette_entries (7-155)
The value of CurrentPaletteSize[startComp] shall be in the range of 0 to palette_max_size, inclusive.
new_palette_entries[cIdx][i] specifies the value for the i-th signalled palette entry for the colour component cIdx.
The variable PredictorPaletteEntries[cIdx][i] specifies the i-th element in the predictor palette for the colour component cIdx.
The variable CurrentPaletteEntries[cIdx][i] specifies the i-th element in the current palette for the colour component cIdx and is derived as follows:
numPredictedPaletteEntries=0
palette_escape_val_present_flag equal to 1 specifies that the current coding unit contains at least one escape coded sample. escape_val_present_flag equal to 0 specifies that there are no escape coded samples in the current coding unit. When not present, the value of palette_escape_val_present_flag is inferred to be equal to 1.
The variable MaxPaletteIndex specifies the maximum possible value for a palette index for the current coding unit. The value of MaxPaletteIndex is set equal to CurrentPaletteSize[startComp]−1+palette_escape_val_present_flag.
palette_idx_idc is an indication of an index to the palette table, CurrentPaletteEntries. The value of palette_idx_idc shall be in the range of 0 to MaxPaletteIndex, inclusive, for the first index in the block and in the range of 0 to (MaxPaletteIndex−1), inclusive, for the remaining indices in the block.
When palette_idx_idc is not present, it is inferred to be equal to 0.
palette_transpose_flag equal to 1 specifies that vertical traverse scan is applied for scanning the indices for samples in the current coding unit. palette_transpose_flag equal to 0 specifies that horizontal traverse scan is applied for scanning the indices for samples in the current coding unit.
When not present, the value of palette_transpose_flag is inferred to be equal to 0.
The array TraverseScanOrder specifies the scan order array for palette coding. TraverseScanOrder is assigned the horizontal scan order HorTravScanOrder if palette_transpose_flag is equal to 0 and TraverseScanOrder is assigned the vertical scan order VerTravScanOrder if if palette_transpose_flag is equal to 1.
run_copy_flag equal to 1 specifies that the palette run type is the same the run type at the previously scanned position and palette run index is the same as the index at the previous position if copy_above_palette_indices_flag is equal to 0. Ohterwise, run_copy_flag equal to 0
copy_above_palette_indices_flag equal to 1 specifies that the palette index is equal to the palette index at the same location in the row above if horizontal traverse scan is used or the same location in the left column if vertical traverse scan is used. copy_above_palette_indices_flag equal to 0 specifies that an indication of the palette index of the sample is coded in the bitstream or inferred. The variable CopyAboveIndicesFlag[xC][yC] equal to 1 specifies that the palette index is copied from the palette index in the row above (horizontal scan) or left column (vertical scan). CopyAboveIndicesFlag[xC][yC] equal to 0 specifies that the palette index is explicitly coded in the bitstream or inferred. The array indices xC, yC specify the location (xC, yC) of the sample relative to the top-left luma sample of the picture.
The variable PaletteIndexMap[xC][yC] specifies a palette index, which is an index to the array represented by CurrentPaletteEntries. The array indices xC, yC specify the location (xC, yC) of the sample relative to the top-left luma sample of the picture. The value of PaletteIndexMap[xC][yC] shall be in the range of 0 to MaxPaletteIndex, inclusive.
The variable adjustedRefPaletteIndex is derived as follows:
When CopyAboveIndicesFlag[xC][yC] is equal to 0, the variable CurrPaletteIndex is derived as follows:
if(CurrPaletteIndex>=adjustedRefPaletteIndex)CurrPaletteIndex++ (7-158)
palette_escape_val specifies the quantized escape coded sample value for a component.
The variable PaletteEscapeVal[cIdx][xC][yC] specifies the escape value of a sample for which PaletteIndexMap[xC][yC] is equal to MaxPaletteIndex and palette_escape_val_present_flag is equal to 1. The array index cIdx specifies the colour component. The array indices xC, yC specify the location (xC, yC) of the sample relative to the top-left luma sample of the picture.
It is a requirement of bitstream conformance that PaletteEscapeVal[cIdx][xC][yC] shall be in the range of 0 to (1<<<(BitDepthY+1))−1, inclusive, for cIdx equal to 0, and in the range of 0 to (1<<<(BitDepthC+1))−1, inclusive, for cIdx not equal to 0.
2.3 Local Dual Tree in VVC
In typical hardware video encoders and decoders, processing throughput drops when a picture has more small intra blocks because of sample processing data dependency between neighbouring intra blocks. The predictor generation of an intra block requires top and left boundary reconstructed samples from neighbouring blocks. Therefore, intra prediction has to be sequentially processed block by block.
In HEVC, the smallest intra CU is 8×8 luma samples. The luma component of the smallest intra CU can be further split into four 4×4 luma intra prediction units (PUs), but the chroma components of the smallest intra CU cannot be further split. Therefore, the worst-case hardware processing throughput occurs when 4×4 chroma intra blocks or 4×4 luma intra blocks are processed.
In VTM5.0, in single coding tree, since chroma partitions always follows luma and the smallest intra CU is 4×4 luma samples, the smallest chroma intra coding block (CB) is 2×2. Therefore, in VTM5.0, the smallest chroma intra CBs in single coding tree is 2×2. The worst-case hardware processing throughput for VVC decoding is only ¼ of that for HEVC decoding. Moreover, the reconstruction process of a chroma intra CB becomes much more complex than that in HEVC after adopting tools including cross-component linear model (CCLM), 4-tap interpolation filters, position-dependent intra prediction combination (PDPC), and combined inter intra prediction (CIIP). It is challenging to achieve high processing throughput in hardware decoders. In this section, a method that improve the worst case hardware processing throughput is proposed.
The goal of this method is to disallow chroma intra CBs smaller than 16 chroma samples by constraining the partitioning of chroma intra CBs.
In single coding tree, a SCIPU is defined as a coding tree node whose chroma block size is larger than or equal to TH chroma samples and has at least one child luma block smaller than 4TH luma samples, where TH is set to 16 in this contribution. It is required that in each SCIPU, all CBs are inter, or all CBs are non-inter, i.e., either intra or IBC. In case of a non-inter SCIPU, it is further required that chroma of the non-inter SCIPU shall not be further split and luma of the SCIPU is allowed to be further split. In this way, the smallest chroma intra CB size is 16 chroma samples, and 2×2, 2×4, and 4×2 chroma CBs are removed. In addition, chroma scaling is not applied in case of a non-inter SCIPU. In addition, when luma blocks are further split and chroma blocks are not split, a local dual tree coding structure is constructed.
Two SCIPU examples are shown in
In the proposed method, the type of a SCIPU is inferred to be non-inter if the current slice is an I-slice or the current SCIPU has a 4×4 luma partition in it after further split one time (because no inter 4×4 is allowed in VVC); otherwise, the type of the SCIPU (inter or non-inter) is indicated by one signalled flag before parsing the CUs in the SCIPU.
By applying the above method, the worst case hardware processing throughput occurs when 4×4, 2×8, or 8×2 chroma blocks, instead of a 2×2 chroma blocks, are processed. The worst case hardware processing throughput is the same as that in HEVC and is 4× of that in VTM5.0.
2.4 Transform Skip (TS)
As in HEVC, the residual of a block can be coded with transform skip mode. To avoid the redundancy of syntax coding, the transform skip flag is not signalled when the CU level MTS_CU_flag is not equal to zero. The block size limitation for transform skip is the same to that for MTS in JEM4, which indicate that transform skip is applicable for a CU when both block width and height are equal to or less than 32. Note that implicit multi transform selection (MTS) transform is set to discrete cosine transform (DCT) 2 when low-frequency non-separable transform (LFNST) or matrix-based intra prediction (MIP) is activated for the current CU. Also, the implicit MTS can be still enabled when MTS is enabled for inter coded blocks.
In addition, for transform skip block, minimum allowed Quantization Parameter (QP) is defined as 6*(internalBitDepth−inputBitDepth)+4.
2.5 Alternative Luma Half-Pel Interpolation Filters
In some embodiments, alternative half-pel interpolation filters are proposed.
The switching of the half-pel luma interpolation filter is done depending on the motion vector accuracy. In addition to the existing quarter-pel, full-pel, and 4-pel adaptive motion vector range (AMVR) modes, a new half-pel accuracy AMVR mode is introduced. Only in case of half-pel motion vector accuracy, an alternative half-pel luma interpolation filter can be selected.
For a non-affine non-merge inter-coded CU which uses half-pel motion vector accuracy (i.e., the half-pel AMVR mode), a switching between the HEVC/VVC half-pel luma interpolation filter and one or more alternative half-pel interpolation is made based on the value of a new syntax element hpelIfIdx. The syntax element hpelIfIdx is only signalled in case of half-pel AMVR mode. In case of skip/merge mode using a spatial merging candidate, the value of the syntax element hpelIfIdx is inherited from the neighbouring block.
2.6 Adaptive Color Transform (ACT)
In the VVC, unless the maximum transform size is smaller than the width or height of one coding unit (CU), one CU leaf node is also used as the unit of transform processing. Therefore, in the proposed implementation, the ACT flag is signalled for one CU to select the color space for coding its residuals. Additionally, following the HEVC ACT design, for inter and IBC CUs, the ACT is only enabled when there is at least one non-zero coefficient in the CU. For intra CUs, the ACT is only enabled when chroma components select the same intra prediction mode of luma component, i.e., direct mode (DM) mode.
The core transforms used for the color space conversions are kept the same as that used for the HEVC. Specifically, the following forward and inverse YCgCo color transform matrices, as described as follows. as applied.
Additionally, to compensate the dynamic range change of residuals signals before and after color transform, the QP adjustments of (−5, −5, −3) are applied to the transform residuals.
On the other hand, the forward and inverse color transforms need to access the residuals of all three components. Correspondingly, in the proposed implementation, the ACT is disabled in the following two scenarios where not all residuals of three components are available.
2.7 Escape Value Binarization Using EG(k)
When using EG(k) for escape value binarization, when base Qp is large enough (or symbols to be coded are small enough), the bit length of EG(k) cannot be reduced any more. For example, when base Qp>=23, for EG(5), the bit length reaches 6, which is the minimal bit length for EG5. Similarly, when base Qp>=35, the bit length reaches the minimal for EG3. When base Qp>=29, the bit length reaches the minimal for EG4. In such a case, further increasing Qp cannot reduce bit rate but increase distortion. It is a waste of bits.
2.8 Coefficients Coding in Transform Skip Mode
In the current VVC draft, several modifications are proposed on the coefficients coding in transform skip (TS) mode compared to the non-TS coefficient coding in order to adapt the residual coding to the statistics and signal characteristics of the transform skip levels.
In current VVC, three scan passes are used in the transform skip residual coding process to code the coefficients. The first scan pass is used to code the syntax element indicating whether the transform coefficient level is greater than 0 and other related syntax elements (e.g., sig_coeff_flag, coeff_sign_flag, and par_level_flag). The second/greater than X scan pass is used to code the syntax element indicating whether the transform coefficient level is greater than X (e.g., X=1, 2, 3, 4, 5). The third/remainder scan pass is used to code the remainder syntax elements (e.g., abs_remainder and coeff_sign_flag).
In current VVC, as shown in Table 131, whether a syntax element indicating the sign of a transform coefficient level (e.g., coeff_sign_flag) is coded with bypass mode or context-coding mode depends on a syntax element indicating whether a transform is applied to the associated transform block or not (e.g., transform_skip_flag), the number of remaining allowed context coded bins (e.g., RemCcbs), a syntax element indicating whether the residual_coding( ) syntax structure is used to parse the residual samples of a transform skip block for the current slice (e.g., sh_ts_residual_coding_disabled_flag).
7.3.10.11 Residual Coding Syntax
2.8.1 Context Modeling and Context Index Offset Derivation of Sign Flag Coeff_Sign_Flag
9.3.4.2.10 Derivation Process of ctxInc for the Syntax Element Coeff_Sign_Flag for Transform Skip Mode
Inputs to this process are the colour component index cIdx, the luma location (x0, y0) specifying the top-left sample of the current transform block relative to the top-left sample of the current picture, the current coefficient scan location (xC, yC)
Output of this process is the variable ctxInc.
The variables leftSign and aboveSign are derived as follows:
leftSign=(xC==0)?0:CoeffSignLevel[xC−1][yC] (1594)
aboveSign=(yC==0)?0:CoeffSignLevel[xC][yC−1] (1595)
The variable ctxInc is derived as follows:
ctxInc=(BdpcmFlag[x0][y0][cIdx]==0?0:3) (1596)
ctxInc=(BdpcmFlag[x0][y0][cIdx]?1:4) (1597)
ctxInc=(BdpcmFlag[x0][y0][cIdx]?2:5) (1598)
3 Example Technical Problems Solved by Technical Solutions Described Herein
(1) EG(k) as a binarization method for escape values may waste bits when Qp is larger than a threshold.
(2) Palette size may be too large for local dual tree.
(3) Chroma parameters do not need to be signalled when chroma tools are not applied.
(4) Although the coefficient coding in JVET-R2001-vA can achieve coding benefits on screen content coding, the coefficients coding and TS mode may still have some drawbacks:
a. Whether to use bypass coding or context coding for the sign flags is unclear for the case:
4 Example Embodiments and Techniques
The listing of items below should be considered as examples to explain general concepts. These items should not be interpreted in a narrow way. Furthermore, these items can be combined in any manner.
The following examples may be applied on palette scheme in VVC and all other palette related schemes.
In the embodiments below, the added portions are marked as bold, underlined, and italicized texts. The deleted portions are marked within [[ ]].
CurrentPaletteEntries[cIdx][PaletteIndexMap[xCbL+xL][yCbL+yL]] (443)
qP=(Max(QpPrimeTsMin,Qp′Y)
(444)
qP=(Max(QpPrimeTsMin,Qp′Cb)
(445)
qP=(Max(QpPrimeTsMin,Qp′Cr)
(446)
tmpVal=(PaletteEscapeVal[cIdx][xCbL+xL][yCbL+yL]*levelScale[qP%6])<<(qP/6)+32)>>6 (447)
recSamples[x][y]=Clip3(0,(1<<BitDepth)−1,tmpVal) (448)
ph_cr_beta_offset_div2
ph_cr_tc_offset_div2
u(1)
. . . . . .
pps_chroma_tool[[offsets]]_present_flag equal to 1 specifies that chroma tool [[offsets]] related syntax elements are present in the PPS RBSP syntax structure. pps_chroma_tool_
[[offsets]]_present_flag equal to 0 specifies that chroma tool [[offsets]] related syntax elements are not present in the PPS RBSP syntax structure. When ChromaArrayType is equal to 0, the value of pps_chroma_tool_
[[offsets]]_present_flag shall be equal to 0.
. . . . . .
. . . . . .
. . . . . .
u(1)
. . . . . . to 1 specifies that chroma deblocking related syntax elements are present in the PPS RB SP syntax structure. pps_chroma_deblocking_params_present_flag equal to 0 specifies that chroma deblocking related syntax elements are not present in the PPS RBSP syntax structure. When ChromaArrayType is equal to 0, the value of pps_chroma_deblocking_params_present_flag shall be equal to 0.
. . . . . .
Alternatively, the following may be applied:
. . .
cu_act_enabled_flag equal to 1 specifies that the residuals of the current coding unit [[are coded in YCgCo colour space]]. cu_act_enabled_flag equal to 0 specifies that
the residuals of the current coding unit [[are coded in original colour space]]. When cu_act_enabled_flag is not present, it is inferred to be equal to 0.
9.3.4.2 Derivation Process for ctxTable, ctxIdx and bypassFlag
Where A is not equal to B. Such as A=0, B=1.
9.3.4.2 Derivation Process for ctxTable, ctxIdx and bypassFlag
remScanPass == B
remScanPass == A
coeff_sign_flag[n] specifies the sign of a transform coefficient level for the scanning position n as follows:
coeff
_sign_ctx_coding_
FL
cMax = 1
flag[ ]
9.3.4.2 Derivation Process for Ctx Table, ctxIdx and bypassFlag
transform
_skip_flag
[ x0 ][ y0 ][ cIdx ] = = 1
&& RemCcbs >= 0
&& !sh
_ts_residual_
coding
_disabled_flag
9.3.4.2.10 Derivation Process of ctxInc for the Syntax Element Coeff_Sign_Flag for Transform Skip Mode
Inputs to this process are the colour component index cIdx, the luma location (x0, y0) specifying the top-left sample of the current transform block relative to the top-left sample of the current picture, the current coefficient scan location (xC, yC)
Output of this process is the variable ctxInc.
The variables leftSign and aboveSign are derived as follows:
leftSign=(xC==0)?0:CoeffSignLevel[xC−1][yC] (1594)
aboveSign=(yC==0)?0:CoeffSignLevel[xC][yC−1] (1595)
The variable ctxInc is derived as follows:
ctxInc=(BdpcmFlag[x0][y0][cIdx]==0?0:3) (1596)
ctxInc=(BdpcmFlag[x0][y0][cIdx]?1:4) (1597)
ctxInc=(BdpcmFlag[x0][y0][cIdx]?2:5) (1598)
9.3.4.2.10 Derivation Process of ctxInc for the Syntax Element Coeff_Sign_Flag for Transform Skip Mode
Inputs to this process are the colour component index cIdx, the luma location (x0, y0) specifying the top-left sample of the current transform block relative to the top-left sample of the current picture, the current coefficient scan location (xC, yC)
Output of this process is the variable ctxInc.
The variables leftSign and aboveSign are derived as follows:
leftSign=(xC==0)?0:CoeffSignLevel[xC−1][yC] (1594)
aboveSign=(yC==0)?0:CoeffSignLevel[xC][yC−1] (1595)
The variable ctxInc is derived as follows:
ctxInc=(BdpcmFlag[x0][y0][cIdx]==0?0:3) (1596)
ctxInc=(BdpcmFlag[x0][y0][cIdx]?1:4) (1597)
ctxInc=(BdpcmFlag[x0][y0][cIdx]?2:5) (1598)
The system 1900 may include a coding component 1904 that may implement the various coding or encoding methods described in the present disclosure. The coding component 1904 may reduce the average bitrate of video from the input 1902 to the output of the coding component 1904 to produce a coded representation of the video. The coding techniques are therefore sometimes called video compression or video transcoding techniques. The output of the coding component 1904 may be either stored, or transmitted via a communication connected, as represented by the component 1906. The stored or communicated bitstream (or coded) representation of the video received at the input 1902 may be used by the component 1908 for generating pixel values or displayable video that is sent to a display interface 1910. The process of generating user-viewable video from the bitstream representation is sometimes called video decompression. Furthermore, while certain video processing operations are referred to as “coding” operations or tools, it will be appreciated that the coding tools or operations are used at an encoder and corresponding decoding tools or operations that reverse the results of the coding will be performed by a decoder.
Examples of a peripheral bus interface or a display interface may include universal serial bus (USB) or high definition multimedia interface (HDMI) or DisplayPort, and so on. Examples of storage interfaces include serial advanced technology attachment (SATA), peripheral component interface (PCI), integrated drive electronics (IDE) interface, and the like. The techniques described in the present disclosure may be embodied in various electronic devices such as mobile phones, laptops, smartphones or other devices that are capable of performing digital data processing and/or video display.
As shown in
Source device 110 may include a video source 112, a video encoder 114, and an input/output (I/O) interface 116.
Video source 112 may include a source such as a video capture device, an interface to receive video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of such sources. The video data may comprise one or more pictures. Video encoder 114 encodes the video data from video source 112 to generate a bitstream. The bitstream may include a sequence of bits that form a coded representation of the video data. The bitstream may include coded pictures and associated data. The coded picture is a coded representation of a picture. The associated data may include sequence parameter sets, picture parameter sets, and other syntax structures. I/O interface 116 may include a modulator/demodulator (modem) and/or a transmitter. The encoded video data may be transmitted directly to destination device 120 via I/O interface 116 through network 130a. The encoded video data may also be stored onto a storage medium/server 130b for access by destination device 120.
Destination device 120 may include an I/O interface 126, a video decoder 124, and a display device 122.
I/O interface 126 may include a receiver and/or a modem. I/O interface 126 may acquire encoded video data from the source device 110 or the storage medium/server 130b. Video decoder 124 may decode the encoded video data. Display device 122 may display the decoded video data to a user. Display device 122 may be integrated with the destination device 120, or may be external to destination device 120 which be configured to interface with an external display device.
Video encoder 114 and video decoder 124 may operate according to a video compression standard, such as the High Efficiency Video Coding (HEVC) standard, Versatile Video Coding (VVC) standard and other current and/or further standards.
Video encoder 200 may be configured to perform any or all of the techniques of this disclosure. In the example of
The functional components of video encoder 200 may include a partition unit 201; a prediction unit 202, which may include a mode select unit 203, a motion estimation unit 204, a motion compensation unit 205, and an intra prediction unit 206; a residual generation unit 207; a transform unit 208; a quantization unit 209; an inverse quantization unit 210; an inverse transform unit 211; a reconstruction unit 212; a buffer 213; and an entropy encoding unit 214.
In other examples, video encoder 200 may include more, fewer, or different functional components. In an example, prediction unit 202 may include an intra block copy (IBC) unit. The IBC unit may perform prediction in an IBC mode in which at least one reference picture is a picture where the current video block is located.
Furthermore, some components, such as motion estimation unit 204 and motion compensation unit 205 may be highly integrated, but are represented in the example of
Partition unit 201 may partition a picture into one or more video blocks. Video encoder 200 and video decoder 300 may support various video block sizes.
Mode select unit 203 may select one of the coding modes, intra or inter, e.g., based on error results, and provide the resulting intra- or inter-coded block to a residual generation unit 207 to generate residual block data and to a reconstruction unit 212 to reconstruct the encoded block for use as a reference picture. In some example, mode select unit 203 may select a combination of intra and inter prediction (CIIP) mode in which the prediction is based on an inter prediction signal and an intra prediction signal. Mode select unit 203 may also select a resolution for a motion vector (e.g., a sub-pixel or integer pixel precision) for the block in the case of inter-prediction.
To perform inter prediction on a current video block, motion estimation unit 204 may generate motion information for the current video block by comparing one or more reference frames from buffer 213 to the current video block. Motion compensation unit 205 may determine a predicted video block for the current video block based on the motion information and decoded samples of pictures from buffer 213 other than the picture associated with the current video block.
Motion estimation unit 204 and motion compensation unit 205 may perform different operations for a current video block, for example, depending on whether the current video block is in an I slice, a P slice, or a B slice.
In some examples, motion estimation unit 204 may perform uni-directional prediction for the current video block, and motion estimation unit 204 may search reference pictures of list 0 or list 1 for a reference video block for the current video block. Motion estimation unit 204 may then generate a reference index that indicates the reference picture in list 0 or list 1 that contains the reference video block and a motion vector that indicates a spatial displacement between the current video block and the reference video block. Motion estimation unit 204 may output the reference index, a prediction direction indicator, and the motion vector as the motion information of the current video block. Motion compensation unit 205 may generate the predicted video block of the current block based on the reference video block indicated by the motion information of the current video block.
In other examples, motion estimation unit 204 may perform bi-directional prediction for the current video block, motion estimation unit 204 may search the reference pictures in list 0 for a reference video block for the current video block and may also search the reference pictures in list 1 for another reference video block for the current video block. Motion estimation unit 204 may then generate reference indexes that indicate the reference pictures in list 0 and list 1 containing the reference video blocks and motion vectors that indicate spatial displacements between the reference video blocks and the current video block. Motion estimation unit 204 may output the reference indexes and the motion vectors of the current video block as the motion information of the current video block. Motion compensation unit 205 may generate the predicted video block of the current video block based on the reference video blocks indicated by the motion information of the current video block.
In some examples, motion estimation unit 204 may output a full set of motion information for decoding processing of a decoder.
In some examples, motion estimation unit 204 may not output a full set of motion information for the current video. Rather, motion estimation unit 204 may signal the motion information of the current video block with reference to the motion information of another video block. For example, motion estimation unit 204 may determine that the motion information of the current video block is sufficiently similar to the motion information of a neighboring video block.
In one example, motion estimation unit 204 may indicate, in a syntax structure associated with the current video block, a value that indicates to the video decoder 300 that the current video block has the same motion information as the another video block.
In another example, motion estimation unit 204 may identify, in a syntax structure associated with the current video block, another video block and a motion vector difference (MVD). The motion vector difference indicates a difference between the motion vector of the current video block and the motion vector of the indicated video block. The video decoder 300 may use the motion vector of the indicated video block and the motion vector difference to determine the motion vector of the current video block.
As discussed above, video encoder 200 may predictively signal the motion vector. Two examples of predictive signalling techniques that may be implemented by video encoder 200 include advanced motion vector prediction (AMVP) and merge mode signalling.
Intra prediction unit 206 may perform intra prediction on the current video block. When intra prediction unit 206 performs intra prediction on the current video block, intra prediction unit 206 may generate prediction data for the current video block based on decoded samples of other video blocks in the same picture. The prediction data for the current video block may include a predicted video block and various syntax elements.
Residual generation unit 207 may generate residual data for the current video block by subtracting (e.g., indicated by the minus sign) the predicted video block(s) of the current video block from the current video block. The residual data of the current video block may include residual video blocks that correspond to different sample components of the samples in the current video block.
In other examples, there may be no residual data for the current video block for the current video block, for example in a skip mode, and residual generation unit 207 may not perform the subtracting operation.
Transform processing unit 208 may generate one or more transform coefficient video blocks for the current video block by applying one or more transforms to a residual video block associated with the current video block.
After transform processing unit 208 generates a transform coefficient video block associated with the current video block, quantization unit 209 may quantize the transform coefficient video block associated with the current video block based on one or more quantization parameter (QP) values associated with the current video block.
Inverse quantization unit 210 and inverse transform unit 211 may apply inverse quantization and inverse transforms to the transform coefficient video block, respectively, to reconstruct a residual video block from the transform coefficient video block. Reconstruction unit 212 may add the reconstructed residual video block to corresponding samples from one or more predicted video blocks generated by the prediction unit 202 to produce a reconstructed video block associated with the current block for storage in the buffer 213.
After reconstruction unit 212 reconstructs the video block, loop filtering operation may be performed reduce video blocking artifacts in the video block.
Entropy encoding unit 214 may receive data from other functional components of the video encoder 200. When entropy encoding unit 214 receives the data, entropy encoding unit 214 may perform one or more entropy encoding operations to generate entropy encoded data and output a bitstream that includes the entropy encoded data.
The video decoder 300 may be configured to perform any or all of the techniques of this disclosure. In the example of
In the example of
Entropy decoding unit 301 may retrieve an encoded bitstream. The encoded bitstream may include entropy coded video data (e.g., encoded blocks of video data). Entropy decoding unit 301 may decode the entropy coded video data, and from the entropy decoded video data, motion compensation unit 302 may determine motion information including motion vectors, motion vector precision, reference picture list indexes, and other motion information. Motion compensation unit 302 may, for example, determine such information by performing the AMVP and merge mode.
Motion compensation unit 302 may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used with sub-pixel precision may be included in the syntax elements.
Motion compensation unit 302 may use interpolation filters as used by video encoder 200 during encoding of the video block to calculate interpolated values for sub-integer pixels of a reference block. Motion compensation unit 302 may determine the interpolation filters used by video encoder 200 according to received syntax information and use the interpolation filters to produce predictive blocks.
Motion compensation unit 302 may uses some of the syntax information to determine sizes of blocks used to encode frame(s) and/or slice(s) of the encoded video sequence, partition information that describes how each macroblock of a picture of the encoded video sequence is partitioned, modes indicating how each partition is encoded, one or more reference frames (and reference frame lists) for each inter-encoded block, and other information to decode the encoded video sequence.
Intra prediction unit 303 may use intra prediction modes for example received in the bitstream to form a prediction block from spatially adjacent blocks. Inverse quantization unit 304 inverse quantizes, i.e., de-quantizes, the quantized video block coefficients provided in the bitstream and decoded by entropy decoding unit 301. Inverse transform unit 305 applies an inverse transform.
Reconstruction unit 306 may sum the residual blocks with the corresponding prediction blocks generated by motion compensation unit 202 or intra-prediction unit 303 to form decoded blocks. If desired, a deblocking filter may also be applied to filter the decoded blocks in order to remove blockiness artifacts. The decoded video blocks are then stored in buffer 307, which provides reference blocks for subsequent motion compensation/intra prediction and also produces decoded video for presentation on a display device.
A listing of solutions preferred by some embodiments is provided next.
The following solutions show example embodiments of techniques discussed in the previous section (e.g., item 1).
1. A method of video processing (e.g., method 900 depicted in
2. The method of solution 1, wherein the maximum allowed value depends on a binarization method used for the coded representation of the video block.
3. The method of solution 1, wherein the maximum allowed value is represented as T+B, where B is a number based on a bit dept of representation of the samples of the video block and T is a pre-defined number.
The following solutions show example embodiments of techniques discussed in the previous section (e.g., item 2).
4. A method of video processing, comprising: performing a conversion between a video block of a video and a coded representation of the video, wherein a palette mode is used for the coded representation of the video block in which samples of the video block are represented using a palette of a representative color values; and wherein a size of the palette is depended on a rule about whether local dual tree is used for the conversion between the video block and the coded representation.
5. The method of solution 4, wherein the size of the palette depends on a color component of the video due to use of the local dual tree.
6. The method of solution 5, the rule specifies to use a smaller palette size in case the video block is a chroma block than a case in which the video block is a luma block.
The following solutions show example embodiments of techniques discussed in the previous section (e.g., item 3).
7. A method of video processing, comprising: performing a conversion between a video block of a video and a coded representation of the video, wherein a palette mode is used for the coded representation of the video block in which samples of the video block are represented using a palette of a representative color values; and wherein a size of the palette predictor is depended on a rule about whether local dual tree is used for the conversion between the video block and the coded representation.
8. The method of solution 7, wherein the size of the palette predictor depends on a color component of the video block due to use of the local dual tree.
9. The method of solution 8, the rule specifies to use a smaller palette size in case the video block is a chroma block than a case in which the video block is a luma block.
The following solutions show example embodiments of techniques discussed in the previous section (e.g., item 4).
10. A method of video processing, comprising: determining, for a conversion between a video block of a video region of a video and a coded representation of the video, based on a coding condition, whether a syntax element identifying a deblocking offset for a chroma component of the video is included in the coded representation at the video region level; and performing the conversion based on the determining; wherein the deblocking offset is used to selectively enable a deblocking operation on the video block.
11. The method of solution 10, wherein the video region is a video slice or a video picture.
12. The method of any of solutions 10-11, wherein the coding condition comprises a color format of the video.
13. The method of any of solutions 10-12, wherein the coding condition is based on whether separate plane coding is enabled for the conversion.
14. The method of any of solutions 10-13, wherein the coding condition is based on whether a chroma array type is includes in the coded representation.
The following solutions show example embodiments of techniques discussed in the previous section (e.g., item 5).
15. A method of video processing, comprising: determining, for a conversion between a video block of a video region of a video and a coded representation of the video, based on a coding condition, whether a syntax element identifying use of a chroma coding tool is included in the coded representation at the video region level; and performing the conversion based on the determining; wherein the deblocking offset is used to selectively enable a deblocking operation on the video block.
16. The method of solution 15, wherein the video region is a video slice or a video picture.
17. The method of any of solutions 15-16, wherein the coding condition corresponds to inclusion of a syntax element in an adaptation parameter set.
The following solutions show example embodiments of techniques discussed in the previous section (e.g., items 6, 7).
18. A method of video processing, comprising: performing a conversion between a video block of a video region of a video and a coded representation of the video, wherein the coded representation conforms to a format; wherein the format specifies that whether a first flag indicating a deblocking offset for a chroma component of the video is included in the coded representation is based on whether a second flag indicating a quantization parameter offset of the chroma component is included in the coded representation.
19. The method of solution 1, wherein the format rule specifies that the coded representation includes a third flag indicative of whether the first flag and the second flag are includes in the coded representation.
20. The method of any of solutions 1-2, wherein the third flag is included in the coded representation in a picture parameter set.
The following solutions show example embodiments of techniques discussed in the previous section (e.g., items 8-12).
21. A method of video processing, comprising: performing a conversion between a video block of a video region of a video and a coded representation of the video, wherein the coded representation conforms to a format rule; wherein the format rule specifies that a syntax element in the coded representation controls whether one or more parameters indicating applicability of one or more chroma coding tools are includes in the coded representation at the video region or the video block level.
22. The method of solution 1, wherein the syntax element is included in an adaptation parameter set.
23. The method of any of solutions 1-2, wherein the format rule specifies that a first value of the syntax element indicates that the one or more parameters are excluded from the coded representation, and skipped during parsing of the coded representation.
24. The method of any of above solutions, wherein the conversion uses the method due to the video meeting a condition.
25. The method of solution 24, wherein the condition comprises a type of video content or a profile or a tier or a level used by the coded representation.
26. The method of any of above solutions, wherein the condition includes a block dimension of the video block and/or a neighboring video block or a color format of the video or a coding tree structure used for the conversion of the video block or a type of the video region.
27. The method of any of solutions 1 to 26, wherein the conversion comprises encoding the video into the coded representation.
28. The method of any of solutions 1 to 26, wherein the conversion comprises decoding the coded representation to generate pixel values of the video.
29. A video decoding apparatus comprising a processor configured to implement a method recited in one or more of solutions 1 to 28.
30. A video encoding apparatus comprising a processor configured to implement a method recited in one or more of solutions 1 to 28.
31. A computer program product having computer code stored thereon, the code, when executed by a processor, causes the processor to implement a method recited in any of solutions 1 to 28.
32. A method, apparatus or system described in the present disclosure.
In some embodiments, in case a local dual tree is applied to a coding unit, a partition operation is applied only on a luma block of the coding unit based on partition parameters of the coding unit, and the partition operation not applicable to at least one chroma block of the coding unit according to a mode type of the coding unit. In some embodiments, the size of the palette is reduced in case the local dual tree is applied for the video block. In some embodiments, in case the local dual tree is applied for the video block, the size of the palette is reduced as compared to a size of the palette in case the local dual tree is not applied for the video block. In some embodiments, in case the local dual tree is applied for the video block, the size of the palette is reduced as compared to a size of the palette in case a regular single tree is applied for the video block. In some embodiments, the size of the palette is reduced by half.
In some embodiments, in case the local dual tree is applied, the size of a palette of a video block of a chroma component is different than the size of a palette of a video block of a luma component. In some embodiments, the size of a palette of a video block of a chroma component is smaller than the size of a palette of a video block of a luma component. In some embodiments, the size of a palette of a video block of a chroma component is a half of the size of a palette of a video block of a luma component.
In some embodiments, the size of the palette predictor is reduced in case the local dual tree is applied for the conversion. In some embodiments, in case the local dual tree is applied, the size of a palette predictor of a video block of a chroma component is different than the size of a palette predictor of a video block of a luma component. In some embodiments, the size of a palette predictor of a video block of a chroma component is smaller than the size of a palette of a video block of a luma component. In some embodiments, the size of a palette predictor of a video block of a chroma component is reduced by half as compared to the size of a palette of a video block of a luma component.
In some embodiments, the escape samples include a subset of the samples that is not categorized to the representative color values of the palette, and the quantization parameter is constrained to be no greater than the maximum allowed value or no smaller than the minimum allowed value. In some embodiments, the maximum allowed value is determined based on a binarization method used for the conversion. In some embodiments, the maximum allowed value is represented as (T+B), wherein B represents a bit depth. In some embodiments, T is indicated in a video region in the bitstream. In some embodiments, T is signalled in a video parameter set, a sequence parameter set, a picture parameter set, a picture header, or a slice header. In some embodiments, B is equal to a bit depth offset associated with the quantization parameter. In some embodiments, the maximum allowed value is equal to the bit depth offset associated with the quantization parameter plus T. In some embodiments, T is a constant. In some embodiments, T is equal to 23, 35 or 39. In some embodiments, T is a constant that is smaller than 23, smaller than 35, or smaller than 29. In some embodiments, the values of the escape samples are coded using a bit length of EG5, EG3, or EG4.
In some embodiments, in case the control flag is equal to 0, the parameters are omitted in the adaptation parameter set. In some embodiments, the parameters include at least a signal flag for a chroma component of an adaptive loop filter, a signal flag for Cb component of an adaptive loop filter, a signal flag for Cr component of an adaptive loop filter, or a signal flag indicating whether a scaling list for a chroma component is present.
In some embodiments, the adaptive color transform mode is disabled in case the palette mode is applied for the conversion. In some embodiments, signalling of information of the adaptive color transform mode is omitted for the conversion. In some embodiments, usage of the adaptive color transform mode is inferred to be disabled. In some embodiments, the palette mode is disabled in case the adaptive color transform mode is applied for the conversion. In some embodiments, signalling of information of the palette mode is omitted for the conversion. In some embodiments, usage of the palette mode is inferred to be disabled.
In some embodiments, the operation comprises storing the number of remaining context coded bins allowed in the video block in a temporary variable; and setting the variable based on the temporary variable. In some embodiments, the operation comprises setting the variable to a value N, wherein N is an integter. In some embodiments, N is smaller than M, and M is equal to 3. In some embodiments, N is based on another variable or another syntax element. In some embodiments, whether a syntax element indicating a sign of a coefficient level is coded using the bypass coding process or a context coding process is based on the number of remaining context coded bins allowed in the video block.
In some embodiments, the sign of the coefficient level is coded using the bypass coding process in case the number of remaining context coded bins allowed in the video block is equal to N, N being an integer equal to or greater than 0. In some embodiments, the sign of the coefficient level is coded using the context coding process in case the number of remaining context coded bins allowed in the video block is greater than or equal to M, N being an integer.
In some embodiments, the operation comprises assigning a value to the variable indicating that a current scan pass is a third or a remainder scan pass. In some embodiments, the operation comprises assigning a value to the variable indicating that a current scan pass is a first scan pass. In some embodiments, the operation comprises assigning a value to the variable indicating that a current scan pass is a second pass or a greater-than-X scan pass. In some embodiments, the operation comprises assigning a first value to the variable at a beginning of a first scan pass and assigning a second value to the variable at a beginning of a third or a remainder scan pass, wherein the first value is not equal to the second value.
In some embodiments, whether a syntax element indicating a sign of a coefficient level is coded using the bypass coding process or a context coding process is based on the variable. In some embodiments, the sign of the coefficient level is coded using the bypass coding process in case the variable indicates that the particular scan pass is a third or a remainder scan pass. In some embodiments, the sign of the coefficient level is coded using the context coding process in case the variable indicates that the particular scan pass is a first scan pass.
In some embodiments, the syntax element is signalled as sig_coeff_flag or par_level_flag. In some embodiments, the syntax element is coded using the bypass coding process in case the syntax element is signalled in the same scan pass as abs_remainder.
In some embodiments, applicability of one or more of the above methods is based on a characteristic of the video. In some embodiments, the characteristic comprises a content of the video. In some embodiments, the characteristic comprises a message signalled in a Decoder Parameter Set, a Sequence Parameter Set, a Video Parameter Set, a Picture Parameter Set, a Adaptation Parameter Set, a picture header, a slice header, a tile group header, a Largest coding unit (LCU), a Coding unit (CU), a LCU row, a group of LCUs, a Transform Unit (TU), a Picture Unit (PU) block, or a video coding unit. In some embodiments, the characteristic comprises a position of a coding unit, a picture unit, a transform unit, or a block. In some embodiments, the characteristic comprises a dimension or a shape of the video block and/or a neighboring block of the video block. In some embodiments, the characteristic comprises a quantization parameter of the video block. In some embodiments, the characteristic comprises a color format of the video. In some embodiments, the characteristic comprises a coding tree structure of the video. In some embodiments, the characteristic comprises a type of a slice, a tile group, or a picture. In some embodiments, the characteristic comprises a color component of the video block. In some embodiments, the characteristic comprises a temporal layer identifier. In some embodiments, the characteristic comprises a profile, a level, or a tier of a video standard. In some embodiments, the characteristic comprises whether the video block includes an escape sample. In some embodiments, the method is only applicable in case the video block includes at least one escape sample. In some embodiments, the characteristic comprises whether the video block is coded using a lossless mode. In some embodiments, the method is only applicable in case the video block is not coded using the lossless mode.
In some embodiments, the conversion comprises encoding the video into the bitstream. In some embodiments, the conversion comprises decoding the video from the bitstream.
In the present disclosure, the term “video processing” may refer to video encoding, video decoding, video compression or video decompression. For example, video compression algorithms may be applied during conversion from pixel representation of a video to a corresponding bitstream representation or vice versa. The bitstream representation of a current video block may, for example, correspond to bits that are either co-located or spread in different places within the bitstream, as is defined by the syntax. For example, a macroblock may be encoded in terms of transformed and coded error residual values and also using bits in headers and other fields in the bitstream.
The disclosed and other solutions, examples, embodiments, modules and the functional operations described in this disclosure can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this disclosure and their structural equivalents, or in combinations of one or more of them. The disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them. The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus.
A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.
The processes and logic flows described in this disclosure can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC).
Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random-access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., erasable programmable read-only memory (EPROM), electronically erasable programmable read-only memory (EEPROM), and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and compact disc, read-only memory (CD-ROM) disks and digital versatile disc, read-only memory (DVD-ROM) disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.
While the present disclosure contains many specifics, these should not be construed as limitations on the scope of any subject matter or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular techniques. Certain features that are described in the present disclosure in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in the present disclosure should not be understood as requiring such separation in all embodiments.
Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/CN2020/074316 | Feb 2020 | WO | international |
| PCT/CN2020/091661 | May 2020 | WO | international |
This application is a continuation of U.S. application Ser. No. 17/882,359, filed on Aug. 5, 2022, which is a continuation of International Patent Application No. PCT/CN2021/075408, filed on Feb. 5, 2021, which claims the priority to and benefits of International Patent Application No. PCT/CN2020/074316, filed on Feb. 5, 2020, and International Patent Application No. PCT/CN2020/091661, filed on May 21, 2020. All the aforementioned patent applications are hereby incorporated by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17882359 | Aug 2022 | US |
| Child | 18513020 | US | |
| Parent | PCT/CN2021/075408 | Feb 2021 | US |
| Child | 17882359 | US |
