  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%.
