Implementation aspects in intra block copy in video coding
A method of visual media processing includes determining, for a conversion between a current video block of visual media data and a bitstream representation of the current video block, a buffer that stores reference samples for prediction in an intra block copy mode; for a sample spatially located at location of the current video block relative to an upper-left position of a coding tree unit including the current video block and having a block vector, computing a corresponding reference in the buffer at a reference location, wherein the reference location is determined using the block vector and the location; and upon determining that the reference location lies outside the buffer, re-computing the reference location based at least in part on a location of the current video block relative to the coding tree unit including the current video block.
1. A method of visual media processing, comprising:
determining, for a conversion of a current video block of a video and a bitstream of the video, that a first coding mode is applied on the current video block;
deriving a first block vector (BVx, BVy) for the current video block;
generating prediction samples for the current video block based on the first block vector and a luma buffer, wherein reconstructed samples of previous video blocks without being applied a filtering operation are stored in the luma buffer, and wherein in the first coding mode, the prediction samples are derived from a same video region in a same picture including the current video block; and
performing the conversion based on the prediction samples,
wherein for any pixel (x0, y0) in the current video block, y0+BVy and x0+BVx are restricted to a certain range, and
wherein elements of the luma buffer are reset with a fixed value.
2. The method of claim 1 , wherein a size of the luma buffer is indicated by M=mW and N=H, wherein M is a width of the luma buffer, N is a height of the luma buffer, W is a width of a coding tree block including the current video block, and H is a height of the coding tree block; and
wherein m is a positive integer and is derived based on W or H, and W, H, M and N are all positive integers.
3. The method of claim 1 , wherein xVb should be in a range of [0, . . . , M−1], and yVb should be in a range of [0, . . . , N−1], wherein (xVb, yVb) specifies a location determined based on the first block vector in the luma buffer.
4. The method of claim 1 , wherein the luma buffer is reset before coding a CTU row.
5. The method of claim 1 , wherein a reference area includes nearest available m−1 coding tree blocks in a coding tree block row.
6. The method of claim 1 , wherein after reconstructing a position (x, y) relative to an upper-left corner of a picture, a value at position (x mod M, y mod N) in the luma buffer is updated with a reconstructed value of the position (x, y).
7. The method of claim 1 , wherein the prediction samples are extracted from the luma buffer after a bit-depth alignment operation.
8. The method of claim 1 , wherein the conversion includes encoding the current video block into the bitstream.
9. The method of claim 1 , wherein the conversion includes decoding the current video block 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 of a current video block of a video and a bitstream of the video, that a first coding mode is applied on the current video block;
derive a first block vector (BVx, BVy) for the current video block;
generate prediction samples for the current video block based on the first block vector and a luma buffer, wherein reconstructed samples of previous video blocks without being applied a filtering operation are stored in the luma buffer, and wherein in the first coding mode, the prediction samples are derived from a same video region in a same picture including the current video block; and
perform the conversion based on the prediction samples,
wherein for any pixel (x0, y0) in the current video block, y0+BVy and x0+BVx are restricted to a certain range, and
wherein elements of the luma buffer are reset with a fixed value.
11. The apparatus of claim 10 , wherein a size of the luma buffer is indicated by M=mW and N=H, wherein M is a width of the luma buffer, N is a height of the luma buffer, W is a width of a coding tree block including the current video block, and H is a height of the coding tree block; and
wherein m is a positive integer and is derived based on W or H, and W, H, M and N are all positive integers.
12. The apparatus of claim 10 , wherein xVb should be in a range of [0, . . . , M−1], and yVb should be in a range of [0, . . . , N−1], wherein (xVb, yVb) specifies a location determined based on the first block vector in the luma buffer.
13. The apparatus of claim 10 , wherein the luma buffer is reset before coding a CTU row.
14. The apparatus of claim 10 , wherein a reference area includes nearest available m−1 coding tree blocks in a coding tree block row.
15. The apparatus of claim 10 , wherein after reconstructing a position (x, y) relative to an upper-left corner of a picture, a value at position (x mod M, y mod N) in the luma buffer is updated with a reconstructed value of the position (x, y).
16. The apparatus of claim 10 , wherein the prediction samples are extracted from the luma buffer after a bit-depth alignment operation.
17. A non-transitory computer-readable storage medium storing instructions that cause a processor to:
determine, for a conversion of a current video block of a video and a bitstream of the video, that a first coding mode is applied on the current video block;
derive a first block vector (BVx, BVy) for the current video block;
generate prediction samples for the current video block based on the first block vector and a luma buffer, wherein reconstructed samples of previous video blocks without being applied a filtering operation are stored in the luma buffer, and wherein in the first coding mode, the prediction samples are derived from a same video region in a same picture including the current video block; and
perform the conversion based on the prediction samples,
wherein for any pixel (x0, y0) in the current video block, y0+BVy and x0+BVx are restricted to a certain range, and
wherein elements of the luma buffer are reset with a fixed value.
18. 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 that a first coding mode is applied on a current video block of the video;
deriving a first block vector (BVx, BVy) for the current video block;
generating prediction samples for the current video block based on the first block vector and a luma buffer, wherein reconstructed samples of previous video blocks without being applied a filtering operation are stored in the luma buffer, and wherein in the first coding mode, the prediction samples are derived from a same video region in a same picture including the current video block; and
generating the bitstream based on the prediction samples,
wherein for any pixel (x0, y0) in the current video block, y0+BVy and x0+BVx are restricted to a certain range,
wherein elements of the luma buffer are reset with a fixed value.
19. The non-transitory computer-readable storage medium of claim 17 , wherein the luma buffer is reset before coding a CTU row.
20. The non-transitory computer-readable recording medium of claim 18 , wherein the luma buffer is reset before coding a CTU row.