The Joint Collaborative Team on Video Coding (jct-vc) of itu-t wp3/16 and iso/iec jtc 1/ sc 29/ wg 11 held its tenth meeting during 11-20 July 2012 at the City Conference Centre (ccc), a k. a

JCTVC-J0418 AHG6: Cross-check of JCTVC-J0090 Transform Dependent Deblocking Strength [Shuo Lu (Sony)] [late]
JCTVC-J0096 Suppression of blocking artifacts at 32x32 transform boundaries [D.-K. Kwon, M. Budagavi (TI)]

This contribution reports that blocking artifacts at 32x32 transform boundaries remain even after deblocking for some video sequences outside of common conditions test sequences. It is reported that these blocking artifacts at 32x32 transform boundaries can be suppressed by increasing beta_offset_div2 and tc_offset_div2 signaled in PPS or slice header, but at the cost of BD-rate degradation. When compared to HM-7.0 anchor (i.e. beta_offset_div2 = tc_offset_div2 = 0), setting beta_offset_div2 and tc_offset_div2 to 13 is reported to result in average BD-rate degradation in the range of 12.7% to 18.8% for Main and HE10 common conditions. (AI-Main: 12.7%, RA-Main: 13.3%, LB-Main: 17.7%, LP-Main: 15.3%, AI-HE10: 12.9%, RA-HE10: 13.8%, LB-HE10: 18.8%, and LP-HE10: 17.7%).

In this contribution, it is proposed to signal in PPS or slice header new syntax elements tu32_beta_offset_div2 and tu32_tc_offset_div2 that control beta and tc offsets for 32x32 transform boundaries. It is asserted that the proposed signaling of tu32_beta_offset_div2 and tu32_tc_offset_div2 smoothes 32x32 transform boundaries while reducing BD-rate degradation. When compared to HM-7.0 anchor, setting tu32_beta_offset_div2 and tu32_tc_offset_div2 to 13 results in BD-rate degradation in the range of 1.2% to 2.0% for Main and HE10 common conditions (AI-Main: 1.3%, RA-Main: 1.2%, LB-Main: 1.8%, LP-Main: 1.3%, AI-HE10: 1.5%, RA-HE10: 1.4%, LB-HE10: 2.0%, and LP-HE10: 1.7%).

An alternative approach, which is same as a previous proposal JCTVC-I0244, is also proposed. This method increases bS value for 32x32 transform boundaries so that strong loop filter could be applied more frequently. When compared to HM-7.0 anchor, this method results in BD-rate degradation in the range of 0.1% to 1.0% for Main and HE10 common conditions (AI-Main: 1.0%, RA-Main: 0.4%, LB-Main: 0.1%, LP-Main: 0.1%, AI-HE10: 1.0%, RA-HE10: 0.4%, LB-HE10: 0.1%, and LP-HE10: 0.1%).

The claim is made that by applying strong smoothing only for 32x32 TU boundaries the BD rate loss is less than applying it for all sizes.