Effective Wedgelet partition coding
Wedgelet separation lines of neighboring blocks are predicted from each other by aligning the wedgelet separation lines of such neighboring blocks to each other, thereby reducing the side information coding rate that may be used.
1. A decoder for reconstructing a sample array of a video from a data stream, the decoder configured to:
determine a set of wedgelet patterns to decode a block of the sample array of the video, wherein each wedgelet pattern of the set represents a line defined by a start position and an end position, the line dividing the corresponding wedgelet pattern into two wedgelet partitions and the start and end positions being on a boundary of the corresponding wedgelet pattern, and a number of wedgelet patterns in the set varies in accordance with a size of the block;
extract, from the data stream, an index value specifying one of the set of wedgelet patterns;
obtain the specified wedgelet pattern from the set of wedgelet patterns based on the index value; and
decode the block based at least on the two wedgelet partitions yielded by the line of the specified wedgelet pattern.
2. The decoder of claim 1 , wherein a size of each wedgelet pattern of the set is based on a size of the block.
3. The decoder of claim 1 , wherein the decoder is configured to determine a plurality of sets of wedgelet patterns, wherein each set of the plurality of sets corresponds to one of a plurality of sizes of blocks of the sample array of the video.
4. The decoder of claim 1 , wherein each wedgelet pattern of the set is a two-dimensional array including binary-valued elements.
5. The decoder of claim 1 , wherein the index value is represented in a fixed number of bits in the data stream, and the decoder is configured to decode the index value based on fixed-length coding.
6. The decoder of claim 1 , wherein the decoder is configured to: extract, from the data stream, a mode syntax element; and decode the mode syntax element to determine whether the index value is used to decode the block.
7. The decoder of claim 1 , wherein, to determine a first wedgelet pattern of the set of wedgelet patterns, wherein the first wedgelet pattern is an array having elements all with a first binary value, the decoder is configured to:
update first elements of the array from the first binary value to a second binary value, wherein the first elements form a line joining the start and end positions of the first wedgelet pattern;
determine whether an existing wedgelet pattern in the set of wedgelet patterns is identical to, or is an inverse of, the first wedgelet pattern based on a comparison of elements of the existing wedgelet pattern and the elements of the first wedgelet pattern; and
responsive to a determination that the existing wedgelet pattern is not identical to and is not an inverse of the first wedgelet pattern, add the first wedgelet pattern to the set of wedgelet patterns.
8. The decoder of claim 1 , wherein each wedgelet pattern of the set is associated with a resolution of the start and end positions of the corresponding wedgelet pattern, wherein the resolution is based on a size of the block.
9. The decoder of claim 1 , wherein the decoder is configured to, in decoding the block, predict the block by assigning a first constant partition value to samples of the sample array positioned within a first of the two wedgelet partitions and a second constant partition value to samples of the sample array positioned within a second of the two wedgelet partitions.
10. The decoder of claim 9 , wherein the sample array is a depth map, and the decoder is configured to use a reference quantization step size in order to reconstruct a texture sample array from the data stream, with which the depth map is associated.
11. The decoder of claim 1 , further configured to use the block as a reference in a prediction loop of the decoder.
12. An encoder for encoding a sample array of a video into a data stream, the encoder configured to:
determine a set of wedgelet patterns, wherein each wedgelet pattern of the set represents a line defined by a start position and an end position, the line dividing the corresponding wedgelet pattern into two wedgelet partitions and the start and end positions being on a boundary of the corresponding wedgelet pattern, and a number of wedgelet patterns in the set varies in accordance with a size of the block;
select, for a block of the sample array of the video, a wedgelet pattern from the set of wedgelet patterns;
insert, into the data stream, an index value identifying the selected wedgelet pattern in the set of wedgelet patterns; and
encode the block based at least on the two wedgelet partitions yielded by the line of the selected wedgelet pattern.
13. The encoder of claim 12 , wherein a size of each wedgelet pattern of the set is based on a size of the block.
14. The encoder of claim 12 , wherein the encoder is configured to determine a plurality of sets of wedgelet patterns, wherein each set of the plurality of sets corresponds to one of a plurality of sizes of blocks of the sample array of the video.
15. The encoder of claim 12 , wherein the index value is represented in a fixed number of bits in the data stream, and the encoder is configured to encode the index value based on fixed-length coding.
16. The encoder of claim 12 , wherein the encoder is configured to insert, into the data stream, a mode syntax element indicating the index value is used to encode the block.
17. The encoder of claim 12 , wherein, to determine a first wedgelet pattern of the set of wedgelet patterns, wherein the first wedgelet pattern is an array having elements all with a first binary value, the encoder is configured to:
update first elements of the array from the first binary value to a second binary value, wherein the first elements form a line joining the start and end positions of the first wedgelet pattern;
determine whether an existing wedgelet pattern in the set of wedgelet patterns is identical to, or is an inverse of, the first wedgelet pattern based on a comparison of elements of the existing wedgelet pattern and the elements of the first wedgelet pattern; and
responsive to a determination that the existing wedgelet pattern is not identical to and is not an inverse of the first wedgelet pattern, add the first wedgelet pattern to the set of wedgelet patterns.