Image decoding method for chroma component and apparatus therefor
An image decoding method performed by a decoding apparatus, according to the present document, comprises the steps of: acquiring image information including chroma quantization parameter data of at least one chroma QP mapping table for chroma components, and prediction information and residual information regarding the chroma components; deriving the chroma QP mapping table on the basis of the chroma quantization parameter data; deriving a chroma quantization parameter for the chroma components on the basis of the chroma QP mapping table; deriving prediction samples for the chroma components on the basis of the prediction information; deriving residual samples on the basis of the residual information and the chroma quantization parameter; and generating a reconstructed picture on the basis of the prediction samples and the residual samples.
1. An image decoding method, performed by a decoding apparatus, the method comprising:
obtaining image information including prediction information and residual information for chroma components and chroma quantization parameter data of at least one chroma Quantization Parameter (QP) mapping table for the chroma components;
deriving the chroma QP mapping table based on the chroma quantization parameter data;
deriving a chroma quantization parameter for the chroma components based on the chroma QP mapping table;
deriving prediction samples for the chroma components by performing inter prediction or intra prediction based on the prediction information;
deriving transform coefficients for the chroma components based on the residual information;
deriving residual samples by dequantizing the transform coefficients based on the chroma quantization parameter; and
generating a reconstructed picture based on the prediction samples and the residual samples,
wherein the chroma quantization parameter data includes a syntax element for the number of points in the chroma QP mapping table, a syntax element for a delta value used to derive an input coordinate of a target point of the chroma QP mapping table, and a syntax element for a delta value used to derive an output coordinate of the target point of the chroma QP mapping table,
wherein the chroma quantization parameter data is signaled through a sequence parameter set (SPS),
wherein the chroma QP mapping table for the chroma components is derived based on (i) a flag related to whether one chroma QP mapping table is signaled and applied for a Cb component, a Cr component, and a joint CbCr component and (ii) a joint CbCr enable flag,
wherein, based on a value of the flag being equal to 1, the one chroma QP mapping table is signaled and applied for the Cb component, the Cr component, and the joint CbCr component, and
wherein, based on the value of the flag being equal to 0 and a value of the joint CbCr enable flag being equal to 1, a plurality of chroma QP mapping tables including each chroma QP mapping table for each of the Cb component, the Cr component, and the joint CbCr component are signaled.
2. An image encoding method performed by an encoding apparatus, the method comprising:
deriving prediction samples for chroma components based on inter prediction or intra prediction;
deriving residual samples for the chroma components based on the prediction samples;
generating chroma quantization parameter data of at least one chroma Quantization Parameter (QP) mapping table for the chroma components; and
encoding prediction information for the chroma components, residual information for the chroma components, and the chroma quantization parameter data,
wherein the chroma quantization parameter data includes a syntax element for the number of points in the chroma QP mapping table, a syntax element for a delta value used to derive an input coordinate of a target point of the chroma QP mapping table, and a syntax element for a delta value used to derive an output coordinate of the target point of the chroma QP mapping table,
wherein the chroma quantization parameter data is signaled through a sequence parameter set (SPS),
wherein the chroma QP mapping table for the chroma components is derived based on (i) a flag related to whether one chroma QP mapping table is signaled and applied for a Cb component, a Cr component, and a joint CbCr component and (ii) a joint CbCr enable flag,
wherein, based on a value of the flag being equal to 1, the one chroma QP mapping table is signaled and applied for the Cb component, the Cr component, and the joint CbCr component, and
wherein, based on the value of the flag being equal to 0 and a value of the joint CbCr enable flag being equal to 1, a plurality of chroma QP mapping tables including each chroma QP mapping table for each of the Cb component, the Cr component and the joint CbCr component are signaled.
3. A non-transitory computer-readable storage medium storing a bitstream generated by a method, the method comprising:
deriving prediction samples for chroma components based on inter prediction or intra prediction;
deriving residual samples for the chroma components based on the prediction samples;
generating chroma quantization parameter data of at least one chroma Quantization Parameter (QP) mapping table for the chroma components;
encoding prediction information for the chroma components, residual information for the chroma components, and the chroma quantization parameter data; and
generating the bitstream including image information comprising the prediction information, the residual information, and the chroma quantization parameter data,
wherein the chroma quantization parameter data includes a syntax element for the number of points in the chroma QP mapping table, a syntax element for a delta value used to derive an input coordinate of a target point of the chroma QP mapping table, and a syntax element for a delta value used to derive an output coordinate of the target point of the chroma QP mapping table,
wherein the chroma quantization parameter data is signaled through a sequence parameter set (SPS),
wherein the chroma QP mapping table for the chroma components is derived based on (i) a flag related to whether one chroma QP mapping table is signaled and applied for a Cb component, a Cr component, and a joint CbCr component and (ii) a joint CbCr enable flag,
wherein, based on a value of the flag being equal to 1, the one chroma QP mapping table is signaled and applied for the Cb component, the Cr component, and the joint CbCr component, and
wherein, based on the value of the flag being equal to 0 and a value of the joint CbCr enable flag being equal to 1, a plurality of chroma QP mapping tables including each chroma QP mapping table for each of the Cb component, the Cr component, and the joint CbCr component are signaled.
4. A transmission method of data for image, the method comprising:
obtaining a bitstream of image information including prediction information for chroma components, residual information for the chroma components, and chroma quantization parameter data of at least one chroma quantization parameter (QP) mapping table for the chroma components; and
transmitting the data including the bitstream of the image information including the prediction information, the residual information, and the chroma quantization parameter data,
wherein the chroma quantization parameter data includes a syntax element for the number of points in the chroma QP mapping table, a syntax element for a delta value used to derive an input coordinate of a target point of the chroma QP mapping table, and a syntax element for a delta value used to derive an output coordinate of the target point of the chroma QP mapping table,
wherein the chroma quantization parameter data is signaled through a sequence parameter set (SPS),
wherein the chroma QP mapping table for the chroma components is derived based on (i) a flag related to whether one chroma QP mapping table is signaled and applied for a Cb component, a Cr component, and a joint CbCr component and (ii) a joint CbCr enable flag,
wherein, based on a value of the flag being equal to 1, the one chroma QP mapping table is signaled and applied for the Cb component, the Cr component, and the joint CbCr component, and
wherein, based on the value of the flag being equal to 0 and a value of the joint CbCr enable flag being equal to 1, a plurality of chroma QP mapping tables including each chroma QP mapping table for each of the Cb component, the Cr component, and the joint CbCr component are signaled.