Video encoding and decoding using adaptive color transform

1 . A method for decoding video data, the method comprising:

obtaining transform coefficients for a current block from a bitstream and reconstructing first residual data by transforming the transform coefficients from a frequency domain to a spatial domain;

determining whether to apply color space transform to the first residual data based on a high-level color transform control flag and a block-level color transform control flag;

in response to a determination that the color space transform is applied to the first residual data, generating second residual data by performing reverse color transform on the first residual data;

generating a prediction block for the current block;

generating a reconstructed block for the current block based on the prediction block and the second residual data,

wherein the high-level color transform control flag is signaled in the bitstream depending on a maximum transform size allowed in a sequence of pictures including the current block, and the block-level color transform control flag is signaled in the bitstream depending on the high-level color transform control flag, and

wherein, when the high-level color transform control flag and the block-level color transform control flag are not signaled, the high-level color transform control flag and the block-level color transform control flag are inferred to be false;

decoding a syntax element indicating the maximum transform size allowed for the sequence of the pictures from the bitstream; and

decoding the high-level color transform control flag from the bitstream when the syntax element indicates that the maximum transform size is smaller than a predetermined value.

2 . The method of claim 1 , further comprising:

when the high-level color transform control flag indicates that the application of the color space transform is allowed for blocks within the sequence, decoding the block-level color transform control flag for the current block from the bitstream.

3 . The method of claim 1 , further comprising:

when a luma component and chroma components of the current block are encoded based on a dual partitioning tree, determining that the color space transform is not applied to the current block without decoding the block-level color transform control flag.

4 . The method of claim 1 , further comprising:

when a chroma sampling format for the video data is a chroma sampling format other than 4:4:4, determining that the application of the color space transform is not allowed for the blocks in the sequence without decoding the high-level color transform control flag.

5 . The method of claim 1 , wherein generating the prediction block for the current block further includes: when the block-level color transform control flag indicates that the color space transform is applied to the current block, determining that a cross-component linear model (CCLM) is not applied to chroma components of the current block.

6 . The method of claim 1 , wherein generating the prediction block for the current block further includes predicting at least one of color components of the current block from other color component.

7 . The method of claim 1 , wherein the first residual data includes residual data for each of color components of the current block.

8 . A method for encoding video data, the method comprising:

encoding a syntax element indicating a maximum transform size allowed for a sequence of pictures of the video data into a bitstream;

when the syntax element indicates that the maximum transform size is smaller than a predetermined value, encoding a first control flag indicating whether application of color space transform is allowed for blocks within the sequence into the bitstream;

when the first control flag indicates that the application of the color space transform is allowed for the blocks within the sequence, encoding a second control flag indicating whether the color space transform is applied to a current block in the sequence into the bitstream;

generating a prediction block for the current block;

generating first residual data for the current block based on the prediction block;

when the second control flag indicates that the color space transform is applied to the current block, performing color transform on the first residual data to generate second residual data for the current block, and encoding the second residual data for the current block into the bitstream by transforming the second residual data to transform coefficients of a frequency domain; and

when the second control flag indicates that the color space transform is not applied to the current block, encoding the first residual data for the current block into the bitstream by transforming the first residual data to transform coefficients of the frequency domain.

9 . A method for providing a video decoding device with video data, the method comprising:

encoding the video data into a bitstream; and

transmitting the bitstream to the video decoding device,

wherein encoding the video data includes:

encoding a syntax element indicating a maximum transform size allowed for a sequence of pictures of the video data into the bitstream;

when the syntax element indicates that the maximum transform size is smaller than a predetermined value, encoding a first control flag indicating whether application of color space transform is allowed for blocks within the sequence into the bitstream;

when the first control flag indicates that the application of the color space transform is allowed for the blocks within the sequence, encoding a second control flag indicating whether the color space transform is applied to a current block in the sequence into the bitstream;

generating a prediction block for the current block;

generating first residual data for the current block based on the prediction block;

when the second control flag indicates that the color space transform is applied to the current block, performing color transform on the first residual data to generate second residual data for the current block, and encoding the second residual data for the current block into the bitstream by transforming the second residual data to transform coefficients of a frequency domain; and

when the second control flag indicates that the color space transform is not applied to the current block, encoding the first residual data for the current block into the bitstream by transforming the first residual data to transform coefficients of the frequency domain.