Method and apparatus of encoding or decoding with mode dependent intra smoothing filter in intra prediction
A video processing method for a video encoder or decoder comprises receiving input data of a current block, determining an intra prediction mode and reference samples according to the intra prediction mode, determining an intra reference sample filter from a Gaussian interpolation filter and an alternative interpolation filter for the current block, applying the intra reference sample filter to the reference samples to generate an intra predictor for the current block, and encoding or decoding the current block based on the intra predictor. A determination between the Gaussian and alternative interpolation filters is depending on a comparison of a mode difference value calculated by the intra prediction mode with a size-dependent threshold. The size-dependent threshold is set to be equal to 24 for blocks with block size smaller than or equal to 32 samples according to an embodiment. The alternative interpolation filter may be a DCT-IF interpolation filter.
1. A method of encoding or decoding video data in a video coding system, comprising:
receiving input data associated with a current block coded or to be coded by intra prediction in a video picture;
determining an intra prediction mode for the current block;
determining reference samples of the current block according to the intra prediction mode of the current block;
determining an intra reference sample filter from a Gaussian interpolation filter and an alternative interpolation filter according to the intra prediction mode and a block size of the current block, wherein the determining between the Gaussian interpolation filter and the alternative interpolation filter is depending on a comparison of a mode difference value calculated by the intra prediction mode with a size-dependent threshold, wherein the size-dependent threshold is determined according to a variable nTbS, and the variable nTbS is defined as Log 2 of a width of the current block plus Log 2 of a height of the current block shifted by one (nTbS=Log 2(width)+Log 2(height)>>1), wherein the size-dependent threshold is set to be equal to 24 for blocks with block sizes smaller than or equal to 32 samples, wherein the mode difference value calculated by the intra prediction mode is a minimum of an absolute mode number difference between the intra prediction mode and a horizontal mode and an absolute mode number difference between the intra prediction mode and a vertical mode;
applying the intra reference sample filter to the reference samples of the current block to generate an intra predictor for the current block; and
encoding or decoding the current block in the video picture based on the intra predictor.
2. The method of claim 1 , wherein the Gaussian interpolation filter is determined to be applied when the mode difference value calculated by the intra prediction mode of the current block is larger than the size-dependent threshold, and the alternative interpolation filter is determined to be applied when the mode difference value calculated by the intra prediction mode of the current block is smaller than or equal to the size-dependent threshold.
3. The method of claim 1 , wherein the reference samples of the current block are determined from neighboring reconstructed samples of the current block.
4. The method of claim 1 , wherein the size-dependent threshold is equal to 24 when the variable nTbS is 2.
5. The method of claim 1 , wherein the size-dependent threshold is equal to 14 when the variable nTbS is 3, the size-dependent threshold is equal to 2 when the variable nTbS is 4, and the size-dependent threshold is equal to 0 when the variable nTbS is equal to or larger than 5.
6. The method of claim 1 , wherein the alternative interpolation filter is a Cubic or DCT-IF interpolation filter.
7. The method of claim 1 , wherein the intra prediction mode of the current block is a regular directional intra prediction mode or a wide-angle intra prediction mode.
8. The method of claim 1 , wherein the current block is a luma Coding Block (CB), and the block size counts a number of luma samples in the current block.
9. The method of claim 1 , further comprising: determining a [1 2 1] reference sample smoothing filter for the current block when the block size is larger than 32 samples and when the intra prediction mode of the current block is a predefined mode.
10. The method of claim 9 , wherein the predefined mode is one or a combination of Planar mode, modes −14, −12, −10, −6, 2, 34, 66, 72, 76, 78, and 80.
11. The method of claim 1 , wherein the determining step comprises excluding the Gaussian interpolation filter when the intra prediction mode of the current block is one of Planar mode, modes −14, −12, −10, −6, 2, 34, 66, 72, 76, 78, and 80.
12. The method of claim 1 , wherein the determining step comprises determining the alternative interpolation filter for the current block if the intra prediction mode is a vertical or horizontal mode, and the alternative interpolation filter is a DCT-IF filter with coefficients [0 64 0 0].
13. The method of claim 1 , wherein the determining step comprises excluding a [1 2 1] reference sample smoothing filter for the current block if the block size is 4×4, 4×8, or 8×4 and the intra prediction mode is mode 2, 34, or 66, or if the block size is 4×8 and the intra prediction mode is mode −6, or if the block size is 8×4 and the intra prediction mode is mode 72.
14. The method of claim 1 , wherein the determining step comprises determining from a [1 2 1] reference sample filter and the Gaussian interpolation filter for the current block if the block size is larger than 32 samples, wherein the alternative interpolation filter is a DCT-IF interpolation filter, and the determining step comprises determining the DCT-IF interpolation filter for the current block if the block size is smaller than or equal to 32 samples.
15. An apparatus for performing video coding, comprising: a computer processor configured for receiving video data; and programming executable on the computer processor for video coding by performing steps comprising:
receiving input data associated with a current block coded or to be coded by intra prediction in a video picture;
determining an intra prediction mode for the current block;
determining reference samples of the current block according to the intra prediction mode of the current block;
determining an intra reference sample filter from a Gaussian interpolation filter and an alternative interpolation filter according to the intra prediction mode and a block size of the current block, wherein the determining between the Gaussian interpolation filter and the alternative interpolation filter is depending on a comparison of a mode difference value calculated by the intra prediction mode with a size-dependent threshold, wherein the size-dependent threshold is determined according to a variable nTbS, and the variable nTbS is defined as Log 2 of a width of the current block plus Log 2 of a height of the current block shifted by one (nTbS=Log 2(width)+Log 2(height)>>1), wherein the size-dependent threshold is set to be equal to 24 for blocks with block sizes smaller than or equal to 32 samples, wherein the mode difference value calculated by the intra prediction mode is a minimum of an absolute mode number difference between the intra prediction mode and a horizontal mode and an absolute mode number difference between the intra prediction mode and a vertical mode;
applying the intra reference sample filter to the reference samples of the current block to generate an intra predictor for the current block; and
encoding or decoding the current block in the video picture based on the intra predictor.
16. A non-transitory computer readable medium storing program instruction causing a processing circuit of an apparatus to perform a video processing method for video data, and the method comprising:
receiving input data associated with a current block coded or to be coded by intra prediction in a video picture;
determining an intra prediction mode for the current block;
determining reference samples of the current block according to the intra prediction mode of the current block;
determining an intra reference sample filter from a Gaussian interpolation filter and an alternative interpolation filter according to the intra prediction mode and a block size of the current block, wherein the determining between the Gaussian interpolation filter and the alternative interpolation filter is depending on a comparison of a mode difference value calculated by the intra prediction mode with a size-dependent threshold, wherein the size-dependent threshold is determined according to a variable nTbS, and the variable nTbS is defined as Log 2 of a width of the current block plus Log 2 of a height of the current block shifted by one (nTbS=Log 2(width)+Log 2(height)>>1), wherein the size-dependent threshold is set to be equal to 24 for blocks with block sizes smaller than or equal to 32 samples, wherein the mode difference value calculated by the intra prediction mode is a minimum of an absolute mode number difference between the intra prediction mode and a horizontal mode and an absolute mode number difference between the intra prediction mode and a vertical mode;
applying the intra reference sample filter to the reference samples of the current block to generate an intra predictor for the current block; and
encoding or decoding the current block in the video picture based on the intra predictor.
17. The apparatus of claim 15 , wherein the programming is executable on the computer processor to further perform the step of applying the Gaussian interpolation filter when two conditions are met.