Deblocking tC table extension and adaptation to 10-bit video
In VVC, Maximum QP was changed from 51 to 63, and it is desired to reflect corresponding change to deblocking table, which derive values of deblocking parameters tC based on the block QP. The table was also adapted to 10-bit video instead of 8-bit video as was the case for HEVC. The following is updated tC table to accommodate the extension of the QP range and 10-bit video.
tC = [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3,4,4,4,4,5,5,5,5,7,7,8,9,10,10,11,13,14,15,17,19,21,24,25,29,33,36,41,45,51,57,64,71,80,89,100,112,125,141,157,177,198,222,250,280,314,352,395]
4x4 deblocking grid for luma
HEVC uses an 8x8 deblocking grid for both luma and chroma. In VVC, deblocking on a 4x4 grid for luma boundaries was introduced to handle blocking artifacts from rectangular transform shapes. Parallel friendly luma deblocking on a 4x4 grid is achieved by restricting the number of samples to be deblocked to 1 sample on each side of a vertical luma boundary where one side has a width of 4 or less or to 1 sample on each side of a horizontal luma boundary where one side has a height of 4 or less.
Stronger deblocking filter for luma
A bilinear filter (stronger deblocking filter) is used when samples at either one side of a boundary belong to a large block. A sample belonging to a large block is defined as when the width is larger than or equal to 32 for a vertical edge, and when height is larger than or equal to 32 for a horizontal edge. Block boundary samples pi for i = 0 to Sp − 1 and qi for j = 0 to Sq − 1 are then replaced by linear interpolation as follows:
(3-0)
(3-0)
where and term is a position dependent clipping and , , , and are given below:
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