A Novel Algorithm for Zero Block Detection in High Efficiency Video Coding

In HEVC, the effect of the RDO on compression efficiency increases while its computational complexity accounts for an important part of the computation burden. For H.264/AVC, zero block (ZB) detection has been used as an efficient scheme to reduce the complexity of RDO operations. For HEVC, ZB detection is different from the scheme for H.264/AVC because HEVC requires large transform sizes, 16 × 16 and 32 × 32. The increased transform size increases the complexity of ZB detection. It also decreases the accuracy of ZB detection because the variance among the quantized DCT coefficients increases and consequently the possibility of a block to be a ZB also increases even when not all of the quantized coefficients are equal to zero. For effective ZB detection of 16 × 16 and 32 × 32 blocks, this paper proposes a new ZB detection algorithm in which the DC components of the Hadamard coefficients are transformed again by Hadamard basis functions for 16 × 16 and 32 × 32 blocks and the results are compared with a predefined threshold. To reduce the computational complexity, the upper-bound of the SAD (or SATD) is defined and the Hadamard threshold is then tested only for the blocks with the SAD (or SATD) smaller than the upper-bound. Experimental results show that the proposed ZB detection reduces the computational complexity of RDO by about 40% with a negligible degradation of the RD performance.