Color transform for video coding

An apparatus of video decoding, comprising circuitry configured to:

• receive an adaptive color transform (ACT) flag from a bitstream of a coded video indicating that ACT for which residual blocks of a current coding unit (CU) are processed with a color space conversion is enabled, the residual blocks of the current CU including a luma residual block, a first chroma residual block, and a second chroma residual block;
• and
• in response to ACT flag indicating that the ACT for which the residual blocks of the current CU are processed with the color space conversion is enabled,
• apply an inverse color space conversion color space conversion based on color space conversion equations to the residual blocks of the current CU to generate modified versions of the residual blocks of the current CU, the color space conversion equations including
• tmp=rY[x][y]—(rCb[x][y]>>1),
• rY[x][y]=tmp+rCb[x][y],
• rCb[x][y]=tmp−(rCr[x][y]>>1), and
• rCr[x][y]=rCb[x][y]+rCr[x][y],
• wherein
• inputs of the color space conversion equations include:
• an array of luma residual samples of the luma residual block with elements rY[x][y],
• an array of chroma residual samples of the first chroma residual block with elements rCb[x][y], and
• an array of chroma residual samples of the second chroma residual block with elements rCr[x][y];
• and
• outputs of the color space conversion equations include:
• a modified array of the luma residual samples of the luma residual block with elements rY[x][y],
• a modified array of the chroma residual samples of the first chroma residual block with elements rCb[x][y], and
• a modified array of the chroma residual samples of the second chroma residual block with elements rCr[x][y].

A non-transitory computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform a method of video decoding, the method comprising:

• receiving an adaptive color transform (ACT) flag from a bitstream of a coded video indicating that ACT for which residual blocks of a current coding unit (CU) are processed with a color space conversion is enabled, the residual blocks of the current CU including a luma residual block, a first chroma residual block, and a second chroma residual block;
• and
• in response to the ACT flag indicating that the ACT for which the residual blocks of the current CU are processed with the color space conversion and is enabled,
• applying an inverse color space conversion color space conversion based on color space conversion equations to the residual blocks of the current CU to generate modified versions of the residual blocks of the current CU, the color space conversion equations including
• tmp=rY[x][y]—(rCb[x][y]>>1),
• rY[x][y]=tmp+rCb[x][y],
• rCb[x][y]=tmp−(rCr[x][y]>>1), and
• rCr[x][y]=rCb[x][y]+rCr[x][y],
• wherein
• inputs of the color space conversion equations include:
• an array of luma residual samples of the luma residual block with elements rY[x][y],
• an array of chroma residual samples of the first chroma residual block with elements rCb[x][y], and
• an array of chroma residual samples of the second chroma residual block with elements rCr[x][y];
• and
• outputs of the color space conversion equations include:
• a modified array of the luma residual samples of the luma residual block with elements rY[x][y],
• a modified array of the chroma residual samples of the first chroma residual block with elements rCb[x][y], and
• a modified array of the chroma residual samples of the second chroma residual block with elements rCr[x][y].