Chroma block prediction method and device
The present disclosure provides a chroma block prediction method and a device. The method includes: parsing a bitstream to obtain first indication information; downsampling a first luma block by a first filter when a value of the first indication information is a first value or by using a second filter when a value of the first indication information is a second value, to obtain a second luma block; obtaining a plurality of chroma samples and a plurality of luma samples; obtaining linear model coefficients based on the plurality of chroma samples and the plurality of luma samples; and obtaining a prediction value of the current chroma block based on the second luma block and the linear model coefficients.
1 . A method, comprising:
parsing a bitstream to obtain first indication information, wherein the first indication information is included in a sequence parameter set (SPS) of the bitstream;
performing a downsampling operation on a first luma block, to obtain a second luma block, wherein the downsampling operation on the first luma block is performed using a first filter when a value of the first indication information is a first value, or the downsampling operation on the first luma block is performed using a second filter when a value of the first indication information is a second value, wherein the second filter is different from the first filter, the first filter corresponds to a first sample position type, the second filter corresponds to a second sample position type, and the first luma block is a luma block corresponding to a current chroma block;
obtaining linear model coefficients based on a plurality of chroma samples and a plurality of luma samples; and
obtaining a prediction value of the current chroma block based on the second luma block and the linear model coefficients.
2 . The method according to claim 1 , wherein for the first sample position type, a sample position (xb, yb) of a current chroma block corresponds to a sample position (2*xb, 2*yb+0.5) of the first luma block.
3 . The method according to claim 1 , wherein for the second sample position type, a sample position (xb, yb) of the current chroma block corresponds to a sample position (2*xb, 2*yb) of the first luma block.
4 . The method according to claim 1 , wherein an image which comprises the first luma block and the current chroma block is in a 4:2:0 or 4:2:2 format.
5 . The method according to claim 1 , wherein the method further comprises:
obtaining the plurality of chroma samples and the plurality of luma samples, wherein the plurality of chroma samples comprise a plurality of neighboring chroma samples of the current chroma block, and the plurality of luma samples are obtained by performing a downsampling operation on a plurality of neighboring luma samples of the first luma block.
6 . The method according to claim 5 , wherein obtaining the plurality of luma samples comprises:
performing the downsampling operation on the plurality of neighboring luma samples of the first luma block to obtain the plurality of luma samples, wherein the downsampling operation on the plurality of neighboring luma samples of the first luma block is performed by using the first filter when the value of the first indication information is the first value or by using the second filter when the value of the first indication information is the second value.
7 . The method according to claim 5 , wherein before obtaining the plurality of chroma samples and the plurality of luma samples, the method further comprises:
parsing the bitstream to obtain second indication information, wherein the second indication information indicates that an intra prediction mode used for current decoding is a linear model (LM) mode.
8 . The method according to claim 1 , wherein the first indication information is indicated by a SPS parameter, and when the value of the SPS parameter is 0, the first filter is used for performing the downsampling operation.
9 . The method according to claim 1 , wherein the first indication information is indicated by a SPS parameter, and when the value of the SPS parameter is 1, the second filter is used for performing the downsampling operation.
10 . A decoding device, comprising:
a non-transitory computer-readable storage medium storing instructions; and
one or more processors in communication with the non-transitory computer-readable storage medium, wherein the instructions, when executed by the one or more processors, cause the decoding device to:
parse a bitstream to obtain first indication information, wherein the first indication information is included in a sequence parameter set (SPS) of the bitstream;
perform a downsampling operation on a first luma block to obtain a second luma block, wherein the downsampling operation on the first luma block is performed using a first filter when a value of the first indication information is a first value, or the downsampling operation on the first luma block is performed using a second filter when a value of the first indication information is a second value, wherein the second filter is different from the first filter, the first filter corresponds to a first sample position type, the second filter corresponds to a second sample position type, and the first luma block corresponds to a current chroma block;
obtain linear model coefficients based on a plurality of chroma samples and a plurality of luma samples; and
obtain a prediction value of the current chroma block based on the second luma block and the linear model coefficients.
11 . The decoding device according to claim 10 , wherein for the first sample position type, a sample position (xb, yb) of a current chroma block corresponds to a sample position (2*xb, 2*yb+0.5) of the first luma block.
12 . The decoding device according to claim 10 , wherein for the second sample position type, a sample position (xb, yb) of the current chroma block corresponds to a sample position (2*xb, 2*yb) of the first luma block.
13 . The decoding device according to claim 10 , wherein an image which comprises the first luma block and the current chroma block is in a 4:2:0 or 4:2:2 format.
14 . The decoding device of claim 10 , wherein the instructions, when executed by the one or more processors, cause the decoding device to:
parse the bitstream to obtain second indication information, wherein the second indication information indicates that an intra prediction mode used for current decoding is a linear model (LM) mode.
15 . The decoding device of claim 10 , wherein the first indication information is indicated by a SPS parameter, and when the value of the SPS parameter is 0, the first filter is used for performing the downsampling operation.
16 . The decoding device of claim 10 , wherein the first indication information is indicated by a SPS parameter, and when the value of the SPS parameter is 1, the second filter is used for performing the downsampling operation.
17 . The decoding device of claim 10 , wherein an image which comprises the first luma block and the current chroma block is in a 4:2:0 or 4:2:2 format.
18 . A non-transitory storage medium storing an encoded bitstream for video signals, wherein the encoded bitstream, when decoded by a coding device, is used by the coding device to generate a video, and the encoded bitstream comprises a plurality of syntax elements, and wherein the plurality of syntax elements comprises:
first indication information, wherein a downsampling operation on a first luma block is performed to obtain a second luma block, wherein the downsampling operation on the first luma block is performed using a first filter when a value of the first indication information is a first value or, the downsampling operation on the first luma block is performed using a second filter when a value of the first indication information is a second value, wherein the second filter is different from the first filter, the first filter corresponds to a first sample position type, the second filter corresponds to a second sample position type, and the first luma block is a luma block corresponding to a current chroma block, and wherein the first indication information is included in a sequence parameter set (SPS) of the encoded bitstream;
wherein linear model coefficients based on plurality of chroma samples and plurality of luma samples are obtained; and
wherein a prediction value of the current chroma block based on the second luma block and the linear model coefficients are obtained.