Complexity reduction in parameter derivation intra prediction
A method for video processing is provided. The method includes determining, for a conversion between a current video block of a video that is a chroma block and a coded representation of the video, parameters of a cross-component linear model using a parameter table whose entries are retrieved according to two chroma sample values and two luma sample values; and performing the conversion based on the determining.
1. A video coding method, comprising:
determining, for a conversion between a current video block of a video that is a chroma block and a bitstream of the video, parameters of a cross-component linear model using a look-up table, wherein indices of the look-up table are retrieved according to two luma values which are derived based on reconstructed luma samples; and
performing the conversion based on the determining,
wherein the two luma values are denoted as L0 and L1 and the indices of the look-up table are derived based on a difference between L1 and L0.
2. The method of claim 1 , wherein the L0 and L1 are derived further based on the positions of neighboring chroma samples of the current video block.
3. The method of claim 1 , wherein the look-up table has a size of V that is less than 2 P , P being an integer.
4. The method of claim 3 , wherein P is equal to 5.
5. The method of claim 1 , wherein the look-up table has entries, each entry storing an F-bit integer number and F being 3.
6. The method of claim 1 , wherein predicted samples of the current video block are derived based on reconstructed samples of a luma block corresponding to the current video block and the parameters of the cross-component linear model.
7. The method of claim 1 wherein in a case that L1 is equal to L0, predicted samples of the current video block are based on a specific chroma value C0, and wherein the C0 is derived based on the neighboring chroma samples of the current video block.
8. The method of claim 7 , wherein the predicted samples of the current video block are set to the C0.
9. The method of claim 1 , wherein the performing of the conversion includes decoding the current video block from the bitstream.
10. The method of claim 1 , wherein the performing of the conversion includes encoding the current video block into the bitstream.
11. A video coding apparatus comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:
determine, for a conversion between a current video block of a video that is a chroma block and a bitstream of the video, parameters of a cross-component linear model using a look-up table, wherein indices of the look-up table are retrieved according to two luma values which are derived based on reconstructed luma samples; and
perform the conversion based on the determination,
wherein the two luma values are denoted as L0 and L1 and the indices of the look-up table are derived based on a difference between L1 and L0.
12. The apparatus of claim 11 , wherein the L0 and L1 are derived further based on the positions of neighboring chroma samples of the current video block.
13. The apparatus of claim 11 , wherein the look-up table has a size of V that is less than 2 P , P being an integer.
14. The apparatus of claim 13 , wherein P is equal to 5.
15. The apparatus of claim 11 , wherein the look-up table has entries, each entry storing an F-bit integer number and F being 3.
16. The apparatus of claim 11 , wherein predicted samples of the current video block are derived based on reconstructed samples of a luma block corresponding to the current video block and the parameters of the cross-component linear model.
17. The apparatus of claim 11 , wherein in a case that L1 is equal to L0, predicted samples of the current video block are based on a specific chroma value C0, and wherein the C0 is derived based on the neighboring chroma samples of the current video block.
18. A non-transitory computer-readable storage medium storing instruction that cause a processor to:
determine, for a conversion between a current video block of a video that is a chroma block and a bitstream of the video, parameters of a cross-component linear model using a look-up table, wherein indices of the look-up table are retrieved according to two luma values which are derived based on reconstructed luma samples; and
perform the conversion based on the determination,
wherein the two luma values are denoted as L0 and L1 and the indices of the look-up table are derived based on a difference between L1 and L0.
19. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:
determining, for a conversion between a current video block of the video that is a chroma block and the bitstream, parameters of a cross-component linear model using a look-up table, wherein indices of the look-up table are retrieved according to two luma values which are derived from based on reconstructed luma samples; and
generating the bitstream based on the determining,
wherein the two luma values are denoted as L0 and L1, the indices of the look-up table are derived based on a difference between L1 and L0.