Method and apparatus for intra prediction for non-square blocks in video compression
A method for video decoding includes determining, for a current block that is a non-square block, whether an angular intra prediction mode for the current block is a wide angle mode that is in a direction outside of a range of directions that spans a bottom left diagonal direction and top right diagonal direction of the current block. The method further includes, in response to determining that the angular intra prediction mode is the wide angle mode, determining whether a condition to apply an intra smoothing filter to blocks neighboring the current block is satisfied. The method further includes, in response to determining that the condition is satisfied, applying the intra smoothing filter to the blocks neighboring the current block. The method also includes performing intra prediction based on the filtered blocks to obtain a characteristic value for the current block.
1. A method for video decoding, comprising:
determining, for a current block that is a non-square block, whether an angular intra prediction mode for the current block is a wide angle mode that is in a direction outside of a range of directions that spans a bottom left diagonal direction and top right diagonal direction of the current block;
in response to determining that the angular intra prediction mode is the wide angle mode, determining whether a block size of the non-square block is less than a block size threshold;
in response to determining that the block size of the non-square block is less than the block size threshold, enabling an intra smooth filter and applying the enabled intra smoothing filter to blocks neighboring the current block to generate filtered blocks; and
performing intra prediction based on a coding tool that utilizes the angular intra prediction mode and the filtered blocks to decode the current block, the performing the intra prediction further including:
(i) determining whether the coding tool that utilizes the filtered blocks for performing the intra prediction supports the wide angle mode,
(ii) in response to the determination that the coding tool does not support the wide angle mode, (a) changing the angular intra prediction mode from the wide angle mode to another intra prediction mode included in the range of directions that is nearest to the wide angle mode, and (b) retrieving a sample according to the another intra prediction mode that is used by the coding tool for decoding the current block, and
(iii) in response to the determination that the coding tool does support the wide angle mode, retrieving a sample according to the wide angle mode that is used by the coding tool for decoding the current block.
2. The method according to claim 1 , wherein the block size is determined in accordance with a height, width, or an arithmetic mean of the height and width of the current block.
3. The method of claim 2 , wherein the block size is determined in accordance with the arithmetic mean of the height and width of the current block.
4. The method according to claim 1 , wherein the coding tool is Position Dependent Prediction Combination (PDPC).
5. A video decoder for video decoding, comprising:
processing circuitry configured to:
determine, for a current block that is a non-square block, whether an angular intra prediction mode for the current block is a wide angle mode that is in a direction outside of a range of directions that spans a bottom left diagonal direction and top right diagonal direction of the current block,
in response to the determination that the angular intra prediction mode is the wide angle mode, determine whether a block size of the non-square block is less than a block size threshold,
in response to the determination that the block size of the non-square block is less than a block size threshold, enable an intra smoothing filter and apply the intra smoothing filter to blocks neighboring the current block to generate filtered blocks, and
perform intra prediction based on a coding tool that utilizes the angular intra prediction mode and the filtered blocks to decode the current block, the performance of the intra prediction further including:
(i) determine whether the coding tool that utilizes the filtered blocks for performing the intra prediction supports the wide angle mode,
(ii) in response to the determination that the coding tool does not support the wide angle mode, (a) change the angular intra prediction mode from the wide angle mode to another intra prediction mode included in the range of directions that is nearest to the wide angle mode, and (b) retrieve a sample according to the another intra prediction mode that is used by the coding tool for decoding the current block, and
(iii) in response to the determination that the coding tool does support the wide angle mode, retrieve a sample according to the wide angle mode that is used by the coding tool for decoding the current block.
6. The video decoder according to claim 5 , wherein the block size is determined in accordance with a height, width, or an arithmetic mean of the height and width of the current block.
7. The video decoder according to claim 5 , wherein the coding tool is Dependent Prediction Combination (PDPC).
8. A non-transitory computer readable medium including instructions stored therein, which when executed by a processor in a video decoding apparatus, causes the processor to execute a method comprising:
determining, for a current block that is a non-square block, whether an angular intra prediction mode for the current block is a wide angle mode that is in a direction outside of a range of directions that spans a bottom left diagonal direction and top right diagonal direction of the current block;
in response to determining that the angular intra prediction mode is the wide angle mode, determining whether a block size of the non-square block is less than a block size threshold;
in response to determining that the block size of the non-square block is less than the block size threshold, enabling an intra smooth filter and applying the enabled intra smoothing filter to blocks neighboring the current block; and
performing intra prediction based on a coding tool that utilizes the angular intra prediction mode and the filtered blocks to decode the current block, the performing the intra prediction further including:
(i) determining whether the coding tool that utilizes the filtered blocks for performing the intra prediction supports the wide angle mode,
(ii) in response to the determination that the coding tool does not support the wide angle mode, (a) changing the angular intra prediction mode from the wide angle mode to another intra prediction mode included in the range of directions that is nearest to the wide angle mode, and (b) retrieving a sample according to the another intra prediction mode that is used by the coding tool for decoding the current block, and
(iii) in response to the determination that the coding tool does support the wide angle mode, retrieving a sample according to the wide angle mode that is used by the coding tool for decoding the current block.
9. The non-transitory computer readable medium according to claim 8 , wherein the block size is determined in accordance with a height, width, or an arithmetic mean of the height and width of the current block.
10. The non-transitory computer readable medium according to claim 8 , wherein the coding tool is selected from a group of coding tools that includes Position Dependent Prediction Combination (PDPC).