Transform coefficient zero-out
Aspects of the disclosure provide methods and apparatuses for video encoding and/or decoding. In some examples, an apparatus for video decoding includes processing circuitry that can decode coded information of a transform block (TB) from a coded video bitstream. The coded information indicates a region of the TB on which a secondary transform is applied. The region includes a first sub-region having transform coefficients calculated by the secondary transform and a second sub-region that is a zero-out region. In response to a determination that a neighboring transform coefficient is in the second sub-region and a current transform coefficient in the TB is not in the second sub-region, the processing circuitry determines the current transform coefficient according to a default value for the neighboring transform coefficient. The processing circuitry reconstructs a sample in the TB based on the transform coefficient for the sample.
1. A method for video decoding in a decoder, the method comprising:
decoding coded information of a transform block (TB) from a coded video bitstream;
when the coded information indicates that a first region of the TB includes a first sub-region and a second sub-region with transform coefficients calculated by a secondary transform, determining whether the secondary transform is performed on the first region, wherein the transform coefficients of the second sub-region are set to 0; and
when the secondary transform is determined to be performed on the first region that includes the second sub-region with the transform coefficients set to 0, determining that transform coefficients of a second region in the TB are 0, wherein the second region is outside the first region.
2. The method of claim 1 , wherein
a size and a position of a coefficient unit in the TB is determined based on the first region, wherein
the coefficient unit includes a plurality of the transform coefficients in the TB, and
remaining transform coefficients in the TB outside the coefficient unit are zero.
3. The method of claim 2 , wherein
the first region is a top left 8×8 region in the TB,
the coefficient unit is the first region, and
the second region is adjacent to a top left 8×8 region.
4. The method of claim 2 , wherein
the first sub-region is a top left 4×4 region in the TB,
the coefficient unit is the first sub-region of the first region, and
the remaining transform coefficients in the TB are in a combined region that includes the second region and the second sub-region.
5. The method of claim 2 , wherein
the first region is a top left 4×4 region in the TB,
the coefficient unit is the first region, and
the second region is adjacent to the top left 4×4 region.
6. A method for video encoding in an encoder, the method comprising:
when a first region of a transform block (TB) includes a first sub-region and a second sub-region with transform coefficients calculated by a secondary transform, determining whether the secondary transform is performed on the first region, wherein the transform coefficients of the second sub-region are set to zero;
when the secondary transform is determined to be performed on the first region that includes the second sub-region with the transform coefficients set to 0, determining that transformation coefficients of a second region in the TB are zero, wherein the second region is outside the first region; and
encoding information of the TB into a video bitstream.
7. The method of claim 6 , wherein
a size and a position of a coefficient unit in the TB is determined based on the first region, wherein
the coefficient unit includes a plurality of the transform coefficients in the TB, and
remaining transform coefficients in the TB outside the coefficient unit are zero.
8. The method of claim 7 , wherein
the first region is a top left 8×8 region in the TB,
the coefficient unit is the first region, and
the second region is adjacent to a top left 8×8 region.
9. The method of claim 7 , wherein
the first sub-region is a top left 4×4 region in the TB,
the coefficient unit is the first sub-region of the first region, and
the remaining transform coefficients in the TB are in a combined region that includes the second region and the second sub-region.
10. The method of claim 7 , wherein
the first region is a top left 4×4 region in the TB,
the coefficient unit is the first region, and
the second region is adjacent to the top left 4×4 region.
11. A method of processing visual media data, the method comprising:
processing a bitstream that includes the visual media data according to a format rule, wherein
the bitstream includes coded information of a transform block (TB); and
the format rule specifies that:
when the coded information indicates that a first region of the TB includes a first sub-region and a second sub-region with transform coefficients calculated by a secondary transform, whether the secondary transform is performed on the first region is determined, the transform coefficients of the second sub-region being set to 0; and
when the secondary transform is determined to be performed on the first region that includes the second sub-region with the transform coefficients set to 0, transform coefficients of a second region in the TB are determined as 0, wherein the second region is outside the first region.
12. The method of claim 11 , wherein
a size and a position of a coefficient unit in the TB is determined based on the first region,
the coefficient unit includes a plurality of the transform coefficients in the TB, and
remaining transform coefficients in the TB outside the coefficient unit are zero.
13. The method of claim 12 , wherein
the first region is a top left 8×8 region in the TB,
the coefficient unit is the first region, and
the second region is adjacent to a top left 8×8 region.
14. The method of claim 12 , wherein
the first sub-region is a top left 4×4 region in the TB,
the coefficient unit is the first sub-region of the first region, and
the remaining transform coefficients in the TB are in a combined region that includes the second region and the second sub-region.
15. The method of claim 12 , wherein
the first region is a top left 4×4 region in the TB,
the coefficient unit is the first region, and
the second region is adjacent to the top left 4×4 region.