| JCTVC-B062 [M. Zhou (TI)] Sub-picture based raster scanning coding order for HEVC UHD video coding
One of the application areas of HEVC is ultra high definition (UHD) video coding, in which the picture size can go up to 8K x 4K (7680 x 4320). The large search range required for the UHD video coding poses a great challenge for chip design in terms of on-chip memory size and memory bandwidth. In this contribution, it was proposed to enable sub-picture based raster scanning order in the HEVC to facilitate the cost-effective UHD video designs.
Discusses vertical motion versus horizontal motion referencing – suggesting a preferred limitation of vertical search range relative to horizontal search range.
It was proposed to use rectangular picture area scanning for wide pictures, with some limitation of both horizontal and vertical search range. The concept is similar to use of slice group map type 2, but not necessarily requiring multiple slices.
It was remarked that providing excessive freedom to an encoder in such usage could result in making it more difficult to decode rather than less.
For UHD (8Kx4K and beyond) it is necessary to constrain memory accesses (picture size increases faster than memory bandwidth). One solution could be restriction of vertical search range (not limiting horizontal). Another solution is growing window. Sub-picture raster scanning order (simlar to FMO type 2) would also restrict horizontal search range (and cause overlap and therefore increased memory accesses). With search range of +/- 256x256 applied to an 8Kx4K picture size, the need for on-chip memory is reduced to approx. 25% with 6 sub-partition columns compared to no usage of sub-partitions.
A participant remarked that the number of columns should not become high to avoid too much necessary variability on the decoder implementation.
Reduction of on-chip memory seems to converge approximately beyond K=4 columns.
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