Method and apparatus for encoding/decoding image in intra prediction and recording medium for storing bitstream
Disclosed herein is an image encoding/decoding method. A method of decoding an image includes determining an intra prediction mode of a current block, and generating a prediction block of the current block, by performing prediction based on the intra prediction mode. When the intra prediction mode of the current block is a matrix-based intra prediction (MIP) mode, a length of a reference sample used for intra prediction is derived based on a length of the current block.
1. A method of decoding an image, the method comprising:
determining an intra prediction mode of a current block; and
generating a prediction block of the current block, by performing prediction based on the intra prediction mode,
wherein when the current block is a chroma block and the intra prediction mode of the current block is a cross-component prediction mode, the generating the prediction block of the current block includes:
generating neighboring samples of a luma block corresponding to the current block;
performing down-sampling with respect to the neighboring samples of the luma block by applying at least one filter to neighboring samples at specific locations among the neighboring samples of the luma block;
deriving a cross-component parameter based on the down-sampled neighboring samples; and
generating the prediction block of the current block based on the cross-component parameter,
wherein the neighboring samples of the luma block includes at least one of top neighboring samples or left neighboring samples,
wherein a number of samples used in a filter used for down-sampling of the top neighboring samples varies depending on whether a top boundary of the current block is a coding tree unit (CTU) boundary or not, and
wherein an interval between the specific locations is determined based on a type of the cross-component prediction mode and the number of available neighboring samples of the current block.
2. The method of claim 1 , wherein when the intra prediction mode of the current block is a matrix-based intra (MIP) mode, a length of top reference samples is derived as a width of the current block+1, and a length of left reference samples is derived as a height of the current block+1.
3. The method of claim 1 , wherein when the intra prediction mode of the current block is a matrix-based intra (MIP) mode, a length of top reference samples is derived as twice a width of the current block and a length of left reference samples is derived as twice a height of the current block.
4. The method of claim 1 ,
wherein, when the neighboring samples of the luma block are not available, the unavailable neighboring block is replaced with inner samples of the luma block.
5. The method of claim 4 ,
wherein, when the unavailable neighboring samples are the top neighboring samples, the inner samples of the luma block are inner samples adjacent to a top boundary of the luma block, and
wherein, when the unavailable neighboring samples the left neighboring samples, the inner samples of the luma block are inner samples adjacent to a left boundary of the luma block.
6. The method of claim 5 ,
wherein the unavailable top neighboring samples and the inner samples adjacent to the top boundary of the luma block have the same x coordinate, and
wherein the unavailable left neighboring samples and the inner samples adjacent to the left boundary of the luma block have the same y coordinate.
7. The method of claim 4 ,
wherein the generating the prediction block of the current block further includes performing down-sampling with respect to the inner samples of the luma block, and
wherein the filter used for down-sampling of the inner samples of the luma block is differently determined further based on whether the neighboring samples are available.
8. The method of claim 1 , wherein a number of the neighboring samples of the luma block and weights to be applied to the neighboring samples of the luma block with respect to the filter become different based on whether the positions of the chroma signal and the luma signal corresponding thereto are same.
9. A method of encoding an image, the method comprising:
determining an intra prediction mode of a current block; and
generating a prediction block of the current block, by performing prediction based on the intra prediction mode,
wherein when the current block is a chroma block and the intra prediction mode of the current block is a cross-component prediction mode, the generating the prediction block of the current block includes:
generating neighboring samples of a luma block corresponding to the current block;
performing down-sampling with respect to the neighboring samples of the luma block by applying at least one filter to neighboring samples at specific locations among the neighboring samples of the luma block;
deriving a cross-component parameter based on the down-sampled neighboring samples; and
generating the prediction block of the current block based on the cross-component parameter,
wherein the neighboring samples of the luma block includes at least one of top neighboring samples or left neighboring samples,
wherein a number of samples used in a filter used for down-sampling of the top neighboring samples varies depending on whether a top boundary of the current block is a coding tree unit (CTU) boundary or not, and
wherein an interval between the specific locations is determined based on a type of the cross-component prediction mode and the number of available neighboring samples of the current block.
10. The method of claim 9 , wherein when the intra prediction mode of the current block is a matrix-based intra (MIP) mode, a length of top reference samples is derived as a width of the current block+1, and a length of left reference samples is derived as a height of the current block+1.
11. The method of claim 9 , wherein when the intra prediction mode of the current block is a matrix-based intra (MIP) mode, a length of top reference samples is derived as twice a width of the current block and a length of left reference samples is derived as twice a height of the current block.
12. The method of claim 9 ,
wherein, when the neighboring samples of the luma block are not available, the unavailable neighboring block is replaced with inner samples of the luma block.
13. The method of claim 12 ,
wherein, when the unavailable neighboring samples are the top neighboring samples, the inner samples of the luma block are inner samples adjacent to a top boundary of the luma block, and
wherein, when the unavailable neighboring samples the left neighboring samples, the inner samples of the luma block are inner samples adjacent to a left boundary of the luma block.
14. The method of claim 12 ,
wherein the generating the prediction block of the current block further includes performing down-sampling with respect to the inner samples of the luma block, and
wherein the filter used for down-sampling of the inner samples of the luma block is differently determined further based on whether the neighboring samples are available.
15. The method of claim 9 , wherein a number of the neighboring samples of the luma block and weights to be applied to the neighboring samples of the luma block with respect to the filter become different based on whether the positions of the chroma signal and the luma signal corresponding thereto are same.
16. A non-transitory computer-readable recording medium for storing a bitstream generated by an image encoding method, the image encoding method comprises:
determining an intra prediction mode of a current block; and
generating a prediction block of the current block, by performing prediction based on the intra prediction mode,
wherein when the current block is a chroma block and the intra prediction mode of the current block is a cross-component prediction mode, the generating the prediction block of the current block includes:
generating neighboring samples of a luma block corresponding to the current block;
performing down-sampling with respect to the neighboring samples of the luma block by applying at least one filter to neighboring samples at specific locations among the neighboring samples of the luma block;
deriving a cross-component parameter based on the down-sampled neighboring samples; and
generating the prediction block of the current block based on the cross-component parameter,
wherein the neighboring samples of the luma block includes at least one of top neighboring samples or left neighboring samples,
wherein a number of samples used in a filter used for down-sampling of the top neighboring samples varies depending on whether a top boundary of the current block is a coding tree unit (CTU) boundary or not, and
wherein an interval between the specific locations is determined based on a type of the cross-component prediction mode and the number of available neighboring samples of the current block.