Method and apparatus for chrominance processing in video coding and decoding
A method of video coding in respect of a 4:2:2 chroma subsampling format includes dividing image data into transform units. In a case of a non-square transform unit, the method includes splitting the non-square transform unit into square blocks prior to applying a spatial frequency transform. The method further includes applying a spatial frequency transform to the square blocks to generate corresponding sets of spatial frequency coefficients.
1. A method of video coding, comprising:
dividing, by circuitry, image data into transform units;
when a transform unit is a non-square transform unit, splitting the non-square transform unit into square blocks and applying a spatial frequency transform to the square blocks to generate corresponding sets of spatial frequency coefficients; and
associating, by the circuitry, intra-prediction mode angles for square prediction units with different intra-prediction mode angles for non-square prediction units.
2. A method according to claim 1 , further comprising:
combining the sets of spatial frequency coefficients relating to the square blocks derived from a transform unit.
3. The method according to claim 1 , wherein the non-square transform unit is rectangular, and the splitting comprises selecting respective square blocks on either side of a center axis of the rectangular transform unit.
4. The method according to claim 1 , wherein the transform unit has twice as many samples in a vertical direction as in a horizontal direction.
5. The method according to claim 1 , wherein, in respect of transform units of an intra-prediction unit, the splitting is performed before generating predicted image data in respect of the intra-prediction unit.
6. The method according to claim 1 , for a 4:2:2 chroma subsampling format, further comprising:
interpolating a chroma intra-prediction unit having a height twice that of a corresponding 4:2:0 format prediction unit using a chroma filter employed for the corresponding 4:2:0 format prediction unit; and
using only alternate vertical values of the interpolated chroma prediction unit.
7. The method according to claim 1 , further comprising:
deriving a luma motion vector for a prediction unit; and
independently deriving a chroma motion vector for the prediction unit.
8. The method according to claim 1 , further comprising:
indicating that luma residual data is to be included in a bitstream losslessly; and
independently indicating that chroma residual data is to be included in the bitstream losslessly.
9. The method according to claim 1 , further comprising:
defining one or more quantization matrices as difference values with respect to quantization matrices defined for a different chroma subsampling format.
10. A method of video decoding, comprising:
applying a spatial frequency transform to blocks of spatial frequency coefficients to generate two or more corresponding square blocks of samples; and
combining by circuitry the two or more square blocks of samples into a non-square transform unit.
11. The method according to claim 10 , further comprising:
splitting a block of spatial frequency coefficients into two or more sub-blocks; and
applying the spatial frequency transform separately to each of the sub-blocks.
12. The method according to claim 10 , wherein the non-square transform unit is rectangular, and the combining comprises concatenating the respective square blocks on either side of a center axis of the rectangular transform unit.
13. The method according to claim 10 , wherein the transform unit has twice as many samples in a vertical direction as in a horizontal direction.
14. The method according to claim 10 , wherein the video coding is in respect of a 4:2:2 chroma subsampling format.
15. A non-transitory computer readable medium including computer program instructions, which when executed by a computer causes the computer to perform the method of claim 1 .
16. A video coding apparatus, comprising:
circuitry configured to divide image data into transform units;
a splitter configured to, when a transform unit is a non-square transform unit, split the non-square transform unit into square blocks; and
a spatial frequency transformer configured to apply a spatial frequency transform to the square blocks to generate corresponding sets of spatial frequency coefficients, wherein
the circuitry is further configured to associate intra-prediction mode angles for square prediction units with different intra-prediction mode angles for non-square prediction units.
17. The video coding apparatus of claim 16 , configured to encode video data in a 4:2:2 chroma sampling format.
18. A video decoding apparatus, comprising:
a spatial frequency transformer configured to apply a spatial frequency transform to blocks of spatial frequency coefficients to generate two or more corresponding square blocks of samples; and
circuitry configured to combine the two or more square blocks of samples into a non-square transform unit.
19. The video decoding apparatus of claim 18 , configured to decode video data in a 4:2:2 chroma sampling format.
20. A video capture, storage, display, transmission and/or reception apparatus comprising the coding apparatus according to claim 16 .
21. A video capture, storage, display, transmission and/or reception apparatus comprising the decoding apparatus according to claim 18 .