Cross-component prediction using multiple components
Devices, systems and methods for digital video coding, which includes Prediction from Multiple Cross-components (PMC) methods, are described. An exemplary method for video processing includes making a first determination that a cross-component prediction (CCP) mode is disabled for a conversion between a video block of a video and a bitstream representation of the video and making a second determination, based on the first determination, regarding whether a first syntax element indicating usage of an enhanced Two-Step Cross-component Prediction Mode (TSCPM) coding tool or an enhanced cross-component linear model (CCLM) coding tool is included in the bitstream representation. The method also includes performing a conversion based on the second determination.
1 . A method of video processing, comprising:
determining, for a conversion between a chroma block of a video and a bitstream of the video, that a first intra prediction mode is applied to derive prediction samples of the chroma block, wherein in the first intra prediction mode, prediction samples of the chroma block are derived based on corresponding luma samples of the chroma block and a linear model,
determining, for the chroma block, a first parameter and a second parameter of the linear model,
performing the conversion based on the first parameter and the second parameter,
wherein the first parameter is set to a first default value and the second parameter is set to a second default value in response to left and/or above neighboring reference samples of the chroma block are not available.
2 . The method of claim 1 , wherein the first intra prediction mode is a Prediction from Multiple Cross-component (PMC) mode, or a PMC_LT mode, or a Two-Step Cross-component Prediction Mode (TSCPM), or a TSCPM_LT, or a TSCPM_L, or a TSCPM_T, and
wherein the first parameter is set to the first default value and the second parameter is set to the second default value in response to left and above neighboring reference samples of the chroma block are not available.
3 . The method of claim 1 , wherein the first intra prediction mode is a PMC_L mode, and
wherein the first parameter is set to the first default value and the second parameter is set to the second default value in response to left neighboring reference samples of the chroma block are not available.
4 . The method of claim 1 , wherein the first intra prediction mode is a PMC_T mode, and
wherein the first parameter is set to the first default value and the second parameter is set to the second default value in response to above neighboring reference samples of the chroma block are not available.
5 . The method of claim 1 , wherein the first default value and the second default value are different.
6 . The method of claim 1 , wherein the chroma block is a Cb chroma block, and the linear model comprises predChroma[x][y]=Clip1(((α Cb *I[x][y])>>iShift)+β Cb ),
wherein α Cb denotes the first parameter,
wherein β Cb denotes the second parameter,
wherein iShift is an integer,
wherein x is an integer no less than 0 and less than 2 W, and W is the width of the Cb chroma block,
wherein y is an integer no less than 0 and less than 2H, and His the height of the Cb chroma block,
wherein I[x][y] denotes a luma sample value in the location [x][y], and
wherein predChroma are used to derive prediction samples of the chroma block.
7 . The method of claim 6 , wherein the first default value is equal to 0.
8 . The method of claim 6 , wherein the second default value is equal to 1<< (BitDepth−1), where BitDepth denotes a bit depth of chroma samples.
9 . The method of claim 6 , wherein the first intra prediction mode is applied to a Cr chroma block corresponding to the Cb chroma block, and
wherein prediction samples of the Cr chroma block are derived based on ((((α Cb +α Cr )*I[x][y])>>iShift)+β Cb +β Cr ), where α Cr and β Cr denote two parameters.
10 . The method of claim 9 , wherein prediction samples of the Cr chroma block are derived as following:
predMatrixTemp[0 ][n ]=(predChroma[0][2 n ]+predChroma[0][2 n+ 1]+1)>>1,
predMatrixTemp[ m][n ]=(predChroma[2 m −1][2 n]+ 2*predChroma[2 m ][2 n ]+predChroma[2 m +1][2 n ]+predChroma[2 m −1][2 n+ 1]+2*predChroma[2 m ][2 n+ 1]+predChroma[2 m +1][2 n+ 1]+4)>>3, and
predMatrix[ k][n ]=predMatrixTemp[ k][n]−Cb[k][n],
wherein m is an integer greater than 0 and less than W, n is an integer no less than 0 and less than H, and k is an integer no less than 0 and less than W,
wherein predChroma[ ][ ] are derived based on ((((α Cb +α Cr )*I[x][y])>>iShift)+β Cb +β Cr ), and
wherein predMatrix[ ][ ] denotes a prediction sample of the Cr chroma block.
11 . The method of claim 9 , wherein α Cr is set to the first default value and β Cr is set to the second default value in response to left and/or above neighboring reference samples of the chroma block are not available.
12 . The method of claim 1 , wherein a first syntax element indicating whether the first intra prediction mode is enabled is included in the bitstream.
13 . The method of claim 1 , wherein a second syntax element indicating whether TSCPM is enabled is included in the bitstream, and Enhanced TSCPM is only enabled in response to the second syntax element indicating TSCPM being enabled.
14 . The method of claim 1 , wherein one or more flags indicating a type of TSCPM are included in the bitstream in case that Enhanced TSCPM is enabled.
15 . The method of claim 1 , wherein in case that a fourth syntax element indicates Intra Block Copy (IBC) mode is disabled for a video block of the video, Adaptive BV Resolution (ABVR) is inferred to be disabled for the video block.
16 . The method of claim 1 , wherein the conversion includes encoding the chroma block into the bitstream.
17 . The method of claim 1 , wherein the conversion includes decoding the chroma block from the bitstream.
18 . An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:
determine, for a conversion between a chroma block of a video and a bitstream of the video, that a first intra prediction mode is applied to derive prediction samples of the chroma block, wherein in the first intra prediction mode, prediction samples of the chroma block are derived based on corresponding luma samples of the chroma block and a linear model,
determine, for the chroma block, a first parameter and a second parameter of the linear model,
perform the conversion based on the first parameter and the second parameter,
wherein the first parameter is set to a first default value and the second parameter is set to a second default value in response to left and/or above neighboring reference samples of the chroma block are not available.
19 . A non-transitory computer-readable storage medium storing instructions that cause a processor to:
determine, for a conversion between a chroma block of a video and a bitstream of the video, that a first intra prediction mode is applied to derive prediction samples of the chroma block, wherein in the first intra prediction mode, prediction samples of the chroma block are derived based on corresponding luma samples of the chroma block and a linear model,
determine, for the chroma block, a first parameter and a second parameter of the linear model,
perform the conversion based on the first parameter and the second parameter,
wherein the first parameter is set to a first default value and the second parameter is set to a second default value in response to left and/or above neighboring reference samples of the chroma block are not available.
20 . A method for storing a bitstream of a video, comprising:
determining, for a chroma block of the video, that a first intra prediction mode is applied to derive prediction samples of the chroma block, wherein in the first intra prediction mode, prediction samples of the chroma block are derived based on corresponding luma samples of the chroma block and a linear model;
determining, for the chroma block, a first parameter and a second parameter of the linear model;
generating the bitstream based on the first parameter and the second parameter; and
storing the bitstream in a non-transitory computer-readable recording medium,
wherein the first parameter is set to a first default value and the second parameter is set to a second default value in response to left and/or above neighboring reference samples of the chroma block are not available.