Video encoding using a directional mode and a non-separable transform
A method for video encoding includes generating coding information of a block to be encoded, the coding information indicating intra prediction information for the block. In response to the block being coded with a directional mode, the method includes determining the directional mode based on a nominal mode and an angular offset, and determining a non-separable transform for the block based on the nominal mode. The method also includes encoding the block based on the determined directional mode and the determined non-separable transform. The non-separable secondary transform is only applied to a first N transform coefficients that are consecutively arranged along a scanning order used for entropy coding transform coefficients of the block.
1. A method for video encoding, comprising:
generating, by processing circuitry of an encoder, coding information of a block to be encoded and included in a coded video bitstream, the coding information indicating intra prediction information for the block; and
in response to the block being coded with a directional mode,
determining the directional mode based on a nominal mode and an angular offset, the generated coding information indicating the nominal mode and the angular offset,
determining a non-separable transform for the block based on the nominal mode, wherein the non-separable transform is a non-separable secondary transform, and
encoding the block based on the determined directional mode and the determined non-separable transform, wherein the encoding includes applying the non-separable secondary transform only to a first N transform coefficients that are consecutively arranged along a scanning order used for entropy coding transform coefficients of the block, wherein N is a positive integer, and not applying the non-separable secondary transform to remaining transform coefficients of the block.
2. The method of claim 1 , wherein the determining the non-separable transform further comprises determining a transform set mode that is associated with the nominal mode, the determined transform set mode indicating a set of one or more non-separable transforms that includes the non-separable transform.
3. The method of claim 2 , wherein
the generated coding information further indicates a non-separable transform index; and
the non-separable transform index indicates the non-separable transform in the set of one or more non-separable transforms.
4. The method of claim 3 , wherein the encoding the block further includes not applying the non-separable secondary transform to the block in response to a determination that the block is to be encoded with a transform skip mode.
5. The method of claim 4 , wherein, in response to the determination that the block is to be encoded with the transform skip mode, the non-separable transform index is not signaled in the generated coding information.
6. The method of claim 1 , wherein the non-separable secondary transform does not apply to a PAETH mode.
7. The method of claim 1 , wherein the non-separable secondary transform does not apply to a recursive filtering mode.
8. The method of claim 1 , wherein a horizontal transform and a vertical transform in a primary transform for the block are included in a subset of a set of line graph transforms.
9. The method of claim 1 , wherein
the block includes the first N transform coefficients obtained with the non-separable secondary transform and second transform coefficients obtained without the non-separable secondary transform; and
the encoding the block further includes entropy encoding the first N transform coefficients and the second transform coefficients separately.
10. The method of claim 1 , wherein
non-directional modes include a DC mode, a PAETH mode, a SMOOTH mode, a SMOOTH_V mode, a SMOOTH_H mode, recursive filtering modes, and a chroma from luma (CfL) mode, the DC mode, the PAETH mode, the SMOOTH mode, the SMOOTH_V mode, and the SMOOTH_H mode being based on averaging of neighboring samples of the block, and
in response to the block being coded with one of the non-directional modes,
determining a set of one or more non-separable transforms associated with the one of the non-directional modes, one of (a) at least another one of the non-directional modes or (b) a non-directional nominal mode being associated with the set of one or more non-separable transforms,
determining a particular non-separable transform in the set of one or more non-separable transforms, and
encoding the block based on the one of the non-directional modes and the particular non-separable transform.
11. The method of claim 10 , wherein the one of the non-directional modes and the one of the at least another one of the non-directional modes or the non-directional nominal mode includes one of (a) the recursive filtering modes and one of the DC mode or the SMOOTH mode, (b) the SMOOTH mode, the SMOOTH_H mode, and the SMOOTH_V mode, (c) the SMOOTH mode, the SMOOTH_H mode, the SMOOTH_V mode, and the PAETH mode, (d) the recursive filtering modes, the SMOOTH mode, and the PAETH mode, (e) a vertical mode for the nominal mode and the SMOOTH_V mode, (f) a horizontal mode for the nominal mode and the SMOOTH_H mode, and (g) the CfL mode and one of the DC mode, the SMOOTH mode, or the PAETH mode.
12. An apparatus for video encoding, comprising:
processing circuitry configured to
generate coding information of a block to be encoded and included in a coded video bitstream, the coding information indicating intra prediction information for the block; and
in response to the block being coded with a directional mode,
determine the directional mode based on a nominal mode and an angular offset, the generated coding information indicating the nominal mode and the angular offset,
determine a non-separable transform for the block based on the nominal mode, wherein the non-separable transform is a non-separable secondary transform, and
encode the block based on the determined directional mode and the non-separable transform,
wherein the processing circuitry is further configured to apply the non-separable secondary transform only to a first N transform coefficients that are consecutively arranged along a scanning order used for entropy coding transform coefficients of the block, wherein N is a positive integer, and not apply the non-separable secondary transform to remaining transform coefficients of the block.
13. The apparatus of claim 12 , wherein the processing circuitry is further configured to determine a transform set mode that is associated with the nominal mode, the determined transform set mode indicating a set of one or more non-separable transforms that includes the non-separable transform.
14. The apparatus of claim 13 , wherein
the generated coding information further indicates a non-separable transform index; and
the non-separable transform index indicates the non-separable transform in the set of one or more non-separable transforms.
15. The apparatus of claim 14 , wherein the processing circuitry is further configured not to apply the non-separable secondary transform to the block in response to a determination that the block is to be encoded with a transform skip mode.
16. The apparatus of claim 15 , wherein, in response to the determination that the block is to be encoded with the transform skip mode, the non-separable transform index is not signaled in the generated coding information.
17. The apparatus of claim 12 , wherein the non-separable secondary transform does not apply to a PAETH mode and to a recursive filtering mode.
18. The apparatus of claim 12 , wherein a horizontal transform and a vertical transform in a primary transform for the block are included in a subset of a set of line graph transforms.
19. The apparatus of claim 12 , wherein
the block includes the first N transform coefficients obtained with the non-separable secondary transform and second transform coefficients obtained without the non-separable secondary transform; and
the processing circuitry is configured to entropy encode the first N transform coefficients and the second transform coefficients separately.
20. A method for video encoding, comprising:
generating, by processing circuitry of an encoder, coding information of a block to be encoded and included in a coded video bitstream, the coding information indicating intra prediction information for the block; and
in response to the block being coded with a directional mode,
determining the directional mode based on a nominal mode and an angular offset, the generated coding information indicating the nominal mode and the angular offset,
determining a non-separable transform for the block based on the nominal mode, wherein the non-separable transform is a non-separable secondary transform, and
encoding the block based on the determined directional mode and the determined non-separable transform, wherein the encoding includes applying the non-separable secondary transform only to first transform coefficients in the block, each of the first transform coefficients having a coordinate (x, y) where a sum of x and y coordinates for each of the first transform coefficients is less than a threshold value, and not applying the non-separable secondary transform to remaining transform coefficients of the block.