JCTVC-J0494 Crosscheck of JCTVC-J0286: AHG6: Reduction of block artifacts in HEVC for large blocks [D.-K. Kwon, M. Budagavi (TI)] [late]
JCTVC-J0556 AHG6: Cross Check of JCTVC-J0286 Algorithm 2 [G. Van der Auwera (Qualcomm)] [late]
JCTVC-J0091 AHG6: Chroma QP Offset and Deblocking [G. Van der Auwera, M. Karczewicz (Qualcomm)]
The cb_qp_offset and cr_qp_offset syntax elements are signalled in the PPS and specify the offsets that are added to the luma QP before deriving the corresponding chroma QP values. The HM7 chroma deblocking filter determines the chroma filtering strength without considering the cb_qp_offset and cr_qp_offset values, which can significantly modify the chroma QP values for coding and, therefore, the filtering strength of chroma blocking artifact edges may be too weak or too strong. To resolve this issue, it is proposed to include the cb_qp_offset and cr_qp_offset values into the chroma deblocking filter process. The HM7.0 anchor is reproduced under common test conditions. The chroma deblocking strength correction is illustrated.
The solution is slightly more complex, as the tc table lookup becomes necessary for each of the chroma components separately.
It would also imply that the chroma qp offset values need to be stored for the purpose of deblocking.
The decoder would become more complex, an advantage might be that an encoder using QP offset for rate control would not need to consider the effect on the deblocking. However, rate control algorithms might be designed which take this into account.
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