Color-Based Coding Unit Level Adaptive Quantization for HEVC
This is an incremental improvement for video compression systems, specifically enhancing HEVC efficiency by incorporating chroma data into quantization decisions.
The paper tackles the problem of improving coding efficiency in HEVC by proposing C-BAQ, a method that adjusts quantization parameters based on spatial activity in both luma and chroma components, resulting in a maximum BD-Rate reduction of up to 16.1% and decoding time reduction of 11.0%.
HEVC HM 16 includes a Coding Unit (CU) level perceptual quantization technique named AdaptiveQP. AdaptiveQP adjusts the Quantization Parameter (QP) at the CU level based on the spatial activity of samples in the four constituent NxN sub-blocks of the luma Coding Block (CB), which is contained within a 2Nx2N CU. In this paper, we propose C-BAQ, which, in contrast to AdaptiveQP, adjusts the CU level QP according to the spatial activity of samples in the four constituent NxN sub-blocks of both the luma and chroma CBs. By computing the sum of luma, chroma Cb and chroma Cr spatial activity in a CU, a richer reflection of spatial activity in the CU is attained. Therefore, a more appropriate CU level QP can be selected, thus leading to important improvements in terms of coding efficiency. We evaluate the proposed technique in HEVC HM 16.7 using 4:4:4, 4:2:2 and 4:2:0 YCbCr sequences. Both subjective and objective evaluations are undertaken during which we compare C-BAQ with AdaptiveQP. The objective evaluation reveals that C-BAQ attains a maximum BD-Rate reduction of 15.9% (Y), 13.1% (Cr) and 16.1% (Cb) in addition to a maximum decoding time reduction of 11.0%.