Motion vector dependent filter strength computation for high performance H.264 de-blocking loop filter

Block based video codec inevitably induce blocking artifacts due to discrete quantization approach. Blocking artifacts impairs subjective picture quality and coding efficiency. De-blocking loop filter reduces visually objectionable artifacts associated with the coding of macroblocks (MB) and their constituent sub-blocks. Filter operation is adaptive in nature and strength of filter (strong/weak) depends on quantum of introduced blocking artifact, measured through Boundary strength (BS). Out of 5 BS values (0,1,2,3,4), computation cost of motion vector (MV) and reference picture dependent BS=1 and BS=0 is in range of 21- 12 cycles for hardware based solutions. To meet 4k@60 fps performance LPF needs to finish each mb filter in 100 cycles and BS=1/0 computation will take minimum 12% of cycle budget. The paper proposes a novel approach to use hardware accelerator of entropy coding (ECD) to pre-calculate BS=1/0 value for LPF. The proposed scheme results in significant silicon area savings as well as reduction in processing cycles. The approach enables reaching performance goal of 4K@60 fps in TI´s video engine (IVAHD2).