Image decoding method/device, image encoding method/device, and recording medium in which bitstream is stored
An image encoding/decoding method and device according to the present disclosure may configure a reference sample for a cross component prediction of a chroma component block, derive a cross component prediction parameter by using the reference sample, and make a cross component prediction of the chroma component block on the basis of the cross component prediction parameter and a luma component block corresponding to the chroma component block.
1. A method of decoding an image, comprising:
obtaining, from a bitstream, an intra prediction mode of a chroma component block in the image;
constructing reference samples for cross component prediction of the chroma component block;
down-sampling a luma component block corresponding to the chroma component block;
deriving a cross component prediction parameter using at least one of the reference samples; and
performing the cross component prediction of the chroma component block based on the down-sampled luma component block and the cross component prediction parameter,
wherein the down-sampling is performed using a corresponding sample of the luma component block and neighboring samples of the corresponding sample,
wherein, in response to a case in which a number of the neighboring samples is 5, the neighboring samples include a sample adjacent to at least one of a left, a right, a bottom, a bottom-left, or a bottom-right of the corresponding sample,
wherein the reference samples for the cross component prediction include at least one of left reference samples or top reference samples,
wherein the left reference samples for the cross component prediction include a first sample belonging to a left neighboring block of the luma component block and a second sample belonging to a bottom-left neighboring block of the luma component block,
wherein the top reference samples for the cross component prediction include a third sample belonging to a top neighboring block of the luma component block and a fourth sample belonging to a top-right neighboring block of the luma component block,
wherein the reference samples used for deriving the cross component prediction parameter are variably constructed according to coding information of the chroma component block,
wherein the coding information includes the intra prediction mode of the chroma component block,
wherein, in response to the intra prediction mode being equal to a first value, the cross component prediction parameter is derived using only the left reference samples belonging to the left neighboring block and the bottom-left neighboring block, and
wherein, in response to the intra prediction mode being equal to a second value, the cross component prediction parameter is derived using only the top reference samples belonging to the top neighboring block and the top-right neighboring block.
2. A method of encoding an image, comprising:
determining an intra prediction mode of a chroma component block in the image;
constructing reference samples for cross component prediction of the chroma component block;
down-sampling a luma component block corresponding to the chroma component block;
deriving a cross component prediction parameter using at least one of the reference samples; and
performing the cross component prediction of the chroma component block based on the down-sampled luma component block and the cross component prediction parameter,
wherein the intra prediction mode of the chroma component block is encoded into a bitstream,
wherein the down-sampling is performed using a corresponding sample of the luma component block and neighboring samples of the corresponding sample,
wherein, in response to a case in which a number of the neighboring samples is 5, the neighboring samples include a sample adjacent to at least one of a left, a right, a bottom, a bottom-left, or a bottom-right of the corresponding sample,
wherein the reference samples for the cross component prediction include at least one of left reference samples or top reference samples,
wherein the left reference samples for the cross component prediction include a first sample belonging to a left neighboring block of the luma component block and a second sample belonging to a bottom-left neighboring block of the luma component block,
wherein the top reference samples for the cross component prediction include a third sample belonging to a top neighboring block of the luma component block and a fourth sample belonging to a top-right neighboring block of the luma component block,
wherein the reference samples used for deriving the cross component prediction parameter are variably constructed according to coding information of the chroma component block,
wherein the coding information includes the intra prediction mode of the chroma component block,
wherein, in response to the intra prediction mode being equal to a first value, the cross component prediction parameter is derived using only the left reference samples belonging to the left neighboring block and the bottom-left neighboring block, and
wherein, in response to the intra prediction mode being equal to a second value, the cross component prediction parameter is derived using only the top reference samples belonging to the top neighboring block and the top-right neighboring block.
3. A non-transitory computer-readable medium for storing a bitstream generated by an image encoding method, the image encoding method comprising:
determining an intra prediction mode of a chroma component block;
constructing reference samples for cross component prediction of the chroma component block;
down-sampling a luma component block corresponding to the chroma component block;
deriving a cross component prediction parameter using at least one of the reference samples; and
performing the cross component prediction of the chroma component block based on the down-sampled luma component block and the cross component prediction parameter,
wherein the intra prediction mode of the chroma component block is encoded into the bitstream,
wherein the down-sampling is performed using a corresponding sample of the luma component block and neighboring samples of the corresponding sample,
wherein, in response to a case in which a number of the neighboring samples is 5, the neighboring samples include a sample adjacent to at least one of a left, a right, a bottom, a bottom-left, or a bottom-right of the corresponding sample,
wherein the reference samples for the cross component prediction include at least one of left reference samples or top reference samples,
wherein the left reference samples for the cross component prediction include a first sample belonging to a left neighboring block of the luma component block and a second sample belonging to a bottom-left neighboring block of the luma component block,
wherein the top reference samples for the cross component prediction include a third sample belonging to a top neighboring block of the luma component block and a fourth sample belonging to a top-right neighboring block of the luma component block,
wherein the reference samples used for deriving the cross component prediction parameter are variably constructed according to coding information of the chroma component block,
wherein the coding information includes the intra prediction mode of the chroma component block,
wherein, in response to the intra prediction mode being equal to a first value, the cross component prediction parameter is derived using only the left reference samples belonging to the left neighboring block and the bottom-left neighboring block, and
wherein, in response to the intra prediction mode being equal to a second value, the cross component prediction parameter is derived using only the top reference samples belonging to the top neighboring block and the top-right neighboring block.
4. The method of claim 1 , wherein the reference samples used for deriving the cross component prediction parameter are variably constructed based on comparison of a width and a height of the chroma component block.