Effective wedgelet partition coding using spatial prediction
In accordance with a first aspect, the intra prediction direction of a neighboring, intra-predicted block is used in order to predict the extension direction of the wedgelet separation line of a current block, thereby reducing the side information rate necessitated in order to convey the partitioning information. In accordance with a second aspect, the idea is that previously reconstructed samples, i.e. reconstructed values of blocks preceding the current block in accordance with the coding/decoding order allow for at least a prediction of a correct placement of a starting point of the wedgelet separation line, namely by placing the starting point of the wedgelet separation line at a position of a maximum change between consecutive ones of a sequence of reconstructed values of samples of a line of samples extending adjacent to the current block along a circumference thereof. Both aspects may be used individually or in combination.
1. A decoder for reconstructing a sample array from a data stream, the decoder comprising a processor configured for:
predicting a first block of the sample array using intra prediction based on an intra-prediction direction related to the first block;
deriving a position of a wedgelet separation line within a second block of the sample array neighboring the first block based on an extension direction of the wedgelet separation line within the second block, wherein the extension direction is based on the intra-prediction direction used to predict the first block, and the wedgelet separation line divides the second block into first and second wedgelet portions; and
decoding the second block based on a first value related to samples within the first wedgelet portion and a second value related to samples within the second wedgelet portion.
2. The decoder according to claim 1 , wherein the processor is configured for, in deriving the position of the wedgelet separation line within the second block, placing a starting point of the wedgelet separation line at a position of a maximum change between consecutive ones of a sequence of reconstructed values of samples of a line of samples extending adjacent to the second block along a portion of a circumference of the second block.
3. The decoder according to claim 1 , wherein the processor is configured for:
retrieving a coding option identifier from the data stream,
if the coding option identifier comprises a predetermined value, checking as to whether any of a set of candidate blocks neighboring the second block comprises a wedgelet separation line continuing into the second block, and
if so, deriving a position of a wedgelet separation line within the second block of the sample array depending on the wedgelet separation line of the respective block such that the wedgelet separation line at the derived position within the second block forms an extension of the wedgelet separation line of the neighboring block into the second block, and
if not, performing the derivation of the position of the wedgelet separation line and the prediction of the second block.
4. The decoder according to claim 1 , wherein the processor is configured for, in decoding the second block,
predicting the second block by assigning a first constant value to samples of the sample array positioned within the first wedgelet portion and a second constant value to samples of the sample array positioned within the second wedgelet portion, the assignment depending on information from the data stream.
5. The decoder according to claim 4 , wherein the processor is configured for refining the prediction of the second block by applying a first refinement value onto a mean value of values of neighboring samples associated with the first wedgelet portion, and/or applying a second refinement value onto a mean value of values of neighboring samples associated with the second wedgelet portion.
6. The decoder according to claim 5 , wherein the processor is configured for, in applying the first and/or second refinement value, linearly combining the first and/or second refinement value with the mean value of values of the neighboring samples associated with the first wedgelet portion, and/or the mean value of values of the neighboring samples associated with the second wedgelet portion, respectively.
7. The decoder according to claim 5 , wherein the sample array is a depth map, and the processor is configured for scaling the first and/or second refinement value using a quantization step size depending on a reference quantization step size at which a predetermined spatially sampled component associated with the sample array is transmitted, and using the reference quantization step size in order to reconstruct a texture sample array from the data stream, with which the depth map is associated.
8. The decoder according to claim 1 , wherein the sample array is a depth map associated with a picture, wherein the processor is configured for:
retrieving a coding option identifier from the data stream,
if the coding option identifier comprises a first predetermined value, performing the derivation of the position of the wedgelet separation line and the prediction of the second block, and
if the coding option identifier comprises a second predetermined value,
segmenting a reference block of the picture, co-located to the second block, by thresholding the picture within the reference block to acquire a bi-segmentation of the reference block into first and second wedgelet portions,
spatially transferring the bi-segmentation of the reference block of the picture onto the second block of the depth map so as to acquire first and second wedgelet portions of the second block, and
predicting the second block by assigning a first constant value to samples of the depth map positioned within the first wedgelet portion of the second block and a second constant value to samples of the depth map positioned within the second wedgelet portion of the second block, the assignment depending on the data stream.
9. The decoder according to claim 1 , wherein the processor is configured for using the second block as a reference in a prediction loop of the decoder.
10. An encoder for encoding a sample array into a data stream, the encoder comprising a processor configured for:
predicting a first block of the sample array using intra prediction based on an intra-prediction direction related to the first block;
deriving a position of a wedgelet separation line within a second block of the sample array neighboring the first block based on an extension direction of the wedgelet separation line within the second block, wherein the extension direction is based on the intra-prediction direction used to predict the first block, and the wedgelet separation line divides the second block into first and second wedgelet portions; and
encoding the second block based on a first value related to samples within the first wedgelet portion and a second value related to samples within the second wedgelet portion.
11. The encoder according to claim 10 , wherein the processor is configured for, in deriving the position of the wedgelet separation line within the second block, placing a starting point of the wedgelet separation line at a position of a maximum change between consecutive ones of a sequence of reconstructed values of samples of a line of samples extending adjacent to the second block along a portion of a circumference of the second block.
12. The encoder according to claim 10 , wherein the processor is configured for encoding a coding option identifier into the data stream, wherein a predetermined value of the coding option identifier indicates whether any of a set of candidate blocks neighboring the second block comprises a wedgelet separation line that continuing into the second block.
13. The encoder according to claim 10 , wherein the processor is configured for, in encoding the second block,
predicting the second block by assigning a first constant value to samples of the sample array positioned within the first wedgelet portion and a second constant value to samples of the sample array positioned within the second wedgelet portion.
14. The encoder according to claim 13 , wherein the processor is configured for:
refining the prediction of the second block by applying a first refinement value onto a mean value of values of neighboring samples associated with the first wedgelet portion, and/or applying a second refinement value onto a mean value of values of neighboring samples associated with the second wedgelet portion; and
encoding the first and second refinement values into the data stream.
15. The encoder according to claim 14 , wherein the processor is configured for, in applying the first and/or second refinement value, linearly combining the first and/or second refinement value with the mean value of values of the neighboring samples associated with the first wedgelet portion, and/or the mean value of values of the neighboring samples associated with the second wedgelet portion, respectively.
16. The encoder according to claim 14 , wherein the sample array is a depth map, and the processor is configured for scaling the first and/or second refinement value using a quantization step size depending on a reference quantization step size at which a predetermined spatially sampled component associated with the sample array is transmitted.
17. A non-transitory computer readable medium including a computer program comprising a program code for performing, when running on a computer, operations for reconstructing a sample array from a data stream, the operations comprising:
predicting a first block of the sample array using intra prediction based on an intra-prediction direction related to the first block;
deriving a position of a wedgelet separation line within a second block of the sample array neighboring the first block based on an extension direction of the wedgelet separation line within the second block, wherein the extension direction is based on the intra-prediction direction used to predict the first block, and the wedgelet separation line divides the second block into first and second wedgelet portions; and
decoding the second block based on a first value related to samples within the first wedgelet portion and a second value related to samples within the second wedgelet portion.
18. The non-transitory computer readable medium according to claim 17 , wherein the operations comprise, in deriving the position of the wedgelet separation line within the second block, placing a starting point of the wedgelet separation line at a position of a maximum change between consecutive ones of a sequence of reconstructed values of samples of a line of samples extending adjacent to the second block along a portion of a circumference of the second block.
19. The non-transitory computer readable medium according to claim 17 , wherein the operations comprise:
retrieving a coding option identifier from the data stream,
if the coding option identifier comprises a predetermined value, checking as to whether any of a set of candidate blocks neighboring the second block comprises a wedgelet separation line continuing into the second block, and
if so, deriving a position of a wedgelet separation line within the second block of the sample array depending on the wedgelet separation line of the respective block such that the wedgelet separation line at the derived position within the second block forms an extension of the wedgelet separation line of the neighboring block into the second block, and
if not, performing the derivation of the position of the wedgelet separation line and the prediction of the second block.
20. The non-transitory computer readable medium according to claim 17 , wherein the operations comprise, in decoding the second block, predicting the second block by assigning a first constant value to samples of the sample array positioned within the first wedgelet portion and a second constant value to samples of the sample array positioned within the second wedgelet portion, the assignment depending on information from the data stream.