Perceptual Evaluation of Psychovisual Rate-Distortion Enhancement in Video Coding

Abstract

Psychovisual rate-distortion optimization (Psy-RD) has been used in the industrial video coding practice as a tool to improve perceptual video quality. It has earned significant popularity through the wide spread of the open source x264 video encoders, where the Psy-RD option is employed by default. Nevertheless, little work has been dedicated to validate the impact of Psy-RD optimization on perceptual quality, so as to provide meaningful guidance on the practical usage and future development of the idea. In this work, we build a database that contains Psy-RD encoded video sequences at different strength and bitrates. A subjective user study is then conducted to evaluate and compare the quality of the Psy-RD encoded videos. We observe that there is considerable agreement between subjects' opinions on the test video sequences. Unfortunately, the impact of Psy-RD optimization on video quality does not appear to be encouraging. Somewhat surprisingly, the perceptual quality gain of Psy-RD ON versus Psy-RD OFF cases is negative on average. Our results suggest that Psy-RD optimization should be used with caution. Further investigations show that most state-of-the-art full-reference objective quality models correlate well with the subjective experiment results overall. But in terms of the paired comparison between Psy-RD ON and OFF cases, the false alarm rates are moderately high.