Block-based parallel deblocking filter in video coding
Deblocking filtering is provided in which an 8×8 filtering block covering eight sample vertical and horizontal boundary segments is divided into filtering sub-blocks that can be independently processed. To process the vertical boundary segment, the filtering block is divided into top and bottom 8×4 filtering sub-blocks, each covering a respective top and bottom half of the vertical boundary segment. To process the horizontal boundary segment, the filtering block is divided into left and right 4×8 filtering sub-blocks, each covering a respective left and right half of the horizontal boundary segment. The computation of the deviation d for a boundary segment in a filtering sub-block is performed using only samples from rows or columns in the filtering sub-block. Consequently, the filter on/off decisions and the weak/strong filtering decisions of the deblocking filtering are performed using samples contained within individual filtering blocks, thus allowing full parallel processing of the filtering blocks.
1. A method for deblocking filtering a reconstructed picture in a video encoder or a video decoder, the method comprising:
computing a first measure of deviation at a first four sample boundary segment covered by a first filtering sub-block of an 8×8 filtering block, wherein the first measure of deviation is computed using only samples of the reconstructed picture in the first filtering sub-block;
using the first measure of deviation in deblocking filter decisions for the first four sample boundary segment;
computing a second measure of deviation at a second four sample boundary segment covered by a second filtering sub-block of the 8×8 filtering block, wherein the second measure of deviation is computed using only samples of the reconstructed picture in the second filtering sub-block; and
using the second measure of deviation in deblocking filter decisions for the second four sample boundary segment,
wherein the first filtering sub-block is a top 8×4 filtering sub-block, the second filtering sub-block is a bottom 8×4 filtering sub-block, and the first and second four sample boundary segments are vertical boundary segments, or the first filtering sub-block is a left 4×8 filtering sub-block, the second filtering sub-block is a right 4×8 filtering sub-block, and the first and second four sample boundary segments are horizontal boundary segments, and wherein computing the first measure of deviation comprises computing the first measure of deviation using samples from a first row of the first filtering sub-block and a second row of the first filtering sub-block when the first filtering sub-block is the top 8×4 filtering sub-block; and computing the first measure of deviation using samples from a first column of the first filtering sub-block and a second column of the first filtering sub-block when the first filtering sub-block is the left 4×8 filtering sub-block.
2. The method of claim 1 , wherein using the first measure of deviation in deblocking filter decisions comprises:
making a filter on/off decision jointly for all rows of the first filtering sub-block using the first measure of deviation when the first filtering sub-block is the top 8×4 filtering sub-block; and
making a filter on/off decision jointly for all columns of the first filtering sub-block based on the first measure of deviation when the first filtering sub-block is the left 4×8 filtering sub-block.
3. The method of claim 1 , wherein using the first measure of deviation in deblocking filter decisions comprises:
making a strong/weak filter decision jointly for all rows of the first filtering sub-block using the first measure of deviation when the first filtering sub-block is the top 8×4 filtering sub-block; and
making a strong/weak filter decision jointly for all columns of the first filtering sub-block using the first measure of deviation when the first filtering sub-block is the left 4×8 filtering sub-block.
4. The method of claim 1 , further comprising:
computing a first boundary strength for the first four sample boundary segment; and
computing a second boundary strength for the second four sample boundary segment.
5. The method of claim 1 , further comprising:
determining values for first deblocking filter thresholds β and tc for the first filtering sub-block;
using the first deblocking filter thresholds β and tc in deblocking filter decisions for the first boundary segment;
determining values for second deblocking filter thresholds β and tc for the second filtering sub-block; and
using the second deblocking filter thresholds β and tc in deblocking filter decisions for the second boundary segment.
6. A non-transitory computer readable medium comprising instructions that, when executed in a digital system, cause the digital system to:
compute a first measure of deviation at a first four sample boundary segment covered by a first filtering sub-block of an 8×8 filtering block, wherein the first measure of deviation is computed using only samples of a reconstructed picture in the first filtering sub-block;
use the first measure of deviation in deblocking filter decisions for the four sample first boundary segment;
compute a second measure of deviation at a second four sample boundary segment covered by a second filtering sub-block of the 8×8 filtering block, wherein the second measure of deviation is computed using only samples of the reconstructed picture in the second filtering sub-block; and
use the second measure of deviation in deblocking filter decisions for the second four sample boundary segment,
wherein the first filtering sub-block is a top 8×4 filtering sub-block, the second filtering sub-block is a bottom 8×4 filtering sub-block, and the first and second four sample boundary segments are vertical boundary segments, or the first filtering sub-block is a left 4×8 filtering sub-block, the second filtering sub-block is a right 4×8 filtering sub-block, and the first and second four sample boundary segments are horizontal boundary segments, and wherein computing the first measure of deviation comprises computing the first measure of deviation using samples from a first row of the first filtering sub-block and a second row of the first filtering sub-block when the first filtering sub-block is the top 8×4 filtering sub-block; and computing the first measure of deviation using samples from a first column of the first filtering sub-block and a second column of the first filtering sub-block when the first filtering sub-block is the left 4×8 filtering sub-block.
7. The non-transitory computer readable medium of claim 6 , wherein the instructions that cause the digital system to use the first measure of deviation in deblocking filter decisions include instructions that cause the digital system to:
make a filter on/off decision jointly for all rows of the first filtering sub-block using the first measure of deviation when the first filtering sub-block is the top 8×4 filtering sub-block; and
make a filter on/off decision jointly for all columns of the first filtering sub-block based on the first measure of deviation when the first filtering sub-block is the left 4×8 filtering sub-block.
8. The non-transitory computer readable medium of claim 6 , wherein the instructions that cause the digital system to use the first measure of deviation in deblocking filter decisions include instructions that cause the digital system to:
make a strong/weak filter decision jointly for all rows of the first filtering sub-block using the first measure of deviation when the first filtering sub-block is the top 8×4 filtering sub-block; and
make a strong/weak filter decision jointly for all columns of the first filtering sub-block using the first measure of deviation when the first filtering sub-block is the left 4×8 filtering sub-block.
9. The non-transitory computer readable medium of claim 6 , wherein the instructions further cause the digital system to:
compute a first boundary strength for the first four sample boundary segment; and
compute a second boundary strength for the second four sample boundary segment.
10. The non-transitory computer readable medium of claim 6 , wherein the instructions further cause the digital system to:
determine values for first deblocking filter thresholds β and tc for the first filtering sub-block;
use the first deblocking filter thresholds β and tc in deblocking filter decisions for the first boundary segment;
determine values for second deblocking filter thresholds β and tc for the second filtering sub-block; and
use the second deblocking filter thresholds β and tc in deblocking filter decisions for the second boundary segment.