Range constrains for block vector in intra-block copy mode
A method of video processing is described. The method includes performing a conversion between a current video block of a video picture of a video and a coded representation of the video according to a buffer allocation rule, wherein the conversion uses an intra block copy (IBC) mode in which a prediction of the current video block is derived based on sample values from a same video slice with the current video block, and wherein the sample values are determined by block vectors, wherein the buffer allocation rule specifies that a virtual buffer allocated for the conversion using the IBC mode is greater than a minimum size of memory for storing a portion of the video picture searched for determining the block vectors.
1. A method of processing video data, comprising:
determining, for a conversion between a current video block of a video picture and a bitstream of the video picture, a prediction mode being applied to the current video block,
determining, a block vector of the current video block based on the prediction mode,
maintaining, a virtual buffer comprising reference samples derived from blocks of sample values of the video picture;
deriving, in the prediction mode, prediction samples of the current video block based on the block vector and the virtual buffer, and
performing the conversion based on the prediction samples,
wherein a range constrain is applied to the block vector, and
wherein the block vector is constrained in the range of [−2 m , 2 m −1], wherein m is equal to 17.
2. The method of claim 1 , wherein the virtual buffer is reset before processing a coding tree unit (CTU) row.
3. The method of claim 2 , wherein the reference samples in the virtual buffer are reset to be −1.
4. The method of claim 2 , wherein availability of one or more reference samples in the virtual buffer for deriving the prediction samples is determined based on a size of a virtual unit.
5. The method of claim 4 , wherein a subset of reference samples determined based on the size of the virtual unit in the virtual buffer are unavailable.
6. The method of claim 4 , wherein the size of the virtual unit is equal to Min(64, CtbSizeY), where CtbSizeY denotes a size of a coding tree block.
7. The method of claim 1 , wherein when a size of a coding tree block is 128, the size of the virtual buffer is equal to a size of two coding tree blocks.
8. The method of claim 1 , wherein the conversion comprises encoding the video picture into the bitstream.
9. The method of claim 1 , wherein the conversion comprises decoding the video picture from the bitstream.
10. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:
determine, for a conversion between a current video block of a video picture and a bitstream of the video picture, a prediction mode being applied to the current video block,
determine, a block vector of the current video block based on the prediction mode,
maintain, a virtual buffer comprising reference samples derived from blocks of sample values of the video picture;
derive, in the prediction mode, prediction samples of the current video block based on the block vector and the virtual buffer, and
perform the conversion based on the prediction samples,
wherein a range constrain is applied to the block vector, and
wherein the block vector is constrained in the range of [−2 m , 2 m −1], wherein m is equal to 17.
11. A non-transitory computer-readable storage medium storing instructions that cause a processor to:
determine, for a conversion between a current video block of a video picture and a bitstream of the video picture, a prediction mode being applied to the current video block,
determine, a block vector of the current video block based on the prediction mode,
maintain, a virtual buffer comprising reference samples derived from blocks of sample values of the video picture;
derive, in the prediction mode, prediction samples of the current video block based on the block vector and the virtual buffer, and
perform the conversion based on the prediction samples,
wherein a range constrain is applied to the block vector, and
wherein the block vector is constrained in the range of [−2 m , 2 m −1], wherein m is equal to 17.
12. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:
determining, for a current video block of a video picture, a prediction mode being applied to the current video block,
determining, a block vector of the current video block based on the prediction mode,
maintaining, a virtual buffer comprising reference samples derived from blocks of sample values of the video picture;
deriving, in the prediction mode, prediction samples of the current video block based on the block vector and the virtual buffer, and
generating the bitstream based on the determining,
wherein a range constrain is applied to the block vector, and
wherein the block vector is constrained in the range of [−2 m , 2 m −1], wherein m is equal to 17.
13. The apparatus of claim 10 , wherein the virtual buffer is reset before processing a coding tree unit (CTU) row.
14. The apparatus of claim 13 , wherein the reference samples in the virtual buffer are reset to be −1.
15. The apparatus of claim 14 , wherein availability of one or more reference samples in the virtual buffer for deriving the prediction samples is determined based on a size of a virtual unit.
16. The apparatus of claim 15 , wherein a subset of reference samples determined based on the size of the virtual unit in the virtual buffer are unavailable.
17. The apparatus of claim 15 , wherein the size of the virtual unit is equal to Min(64, CtbSizeY), where CtbSizeY denotes a size of a coding tree block.
18. The apparatus of claim 10 , wherein when a size of a coding tree block is 128, the size of the virtual buffer is equal to a size of two coding tree blocks.
19. The non-transitory computer-readable storage medium of claim 11 , wherein the virtual buffer is reset before processing a coding tree unit (CTU) row.
20. The non-transitory computer-readable storage medium of claim 19 , wherein the reference samples in the virtual buffer are reset to be −1.