Weighting Quantization Matrices for HEVC/H.265-Coded RGB Videos

In the HEVC/H.265 video coding standard, weighting quantization matrices (WQMs) are supported to take advantage of the characteristics of the human visual system (HVS). However, the default WQMs utilized in HEVC are developed for YCbCr videos instead of RGB videos. In this paper, a set of new WQMs is proposed for video coding in RGB color space. First, we utilize the spatial contrast sensitivity function (CSF) to model the bandpass property of HVS. To derive the parameters of the spatial CSF, a series of subjective experiments is conducted to obtain the just-noticeable distortion (JND) thresholds of several selected DCT subbands. In addition, the sensitivities of different DCT subbands in one color channel, as well as among R, G, and B channels, are considered to design the WQMs of intra-coded 8 × 8 blocks. Moreover, to reduce the data size of WQMs, the WQMs for other block sizes are derived from intra 8 × 8 WQMs. The proposed WQMs are then applied into HEVC to directly code RGB videos. The experimental results demonstrate that when the PSNRs of G, B, and R channels are combined with a ratio of 4:1:1, the proposed WQMs can achieve an average BD-rate saving of 12.64% and 20.51%, respectively, in all-intra (AI) and low-delay (LD) profiles compared to HEVC without WQMs. The proposed scheme also enjoys a better video quality metric (VQM) performance.