A SCALABLE WAVELET-BASED VIDEO DISTORTION METRIC AND APPLICATIONS 1 A Scalable Wavelet-Based Video Distortion Metric and Applications

Abstract — Video distortion metrics based on models of the hu-man visual system have traditionally used comparisons between the distorted signal and a reference signal to calculate distortions objectively. In video coding applications, this is not prohibitive. In quality monitoring applications, however, access to the reference signal is often limited. This paper presents a computationally effi-cient video distortion metric that can operate in full- or reduced-reference mode as required. The metric is based on a model of the human visual system implemented using the wavelet transform and separable filters. The visual model is parameterized using a set of video frames and the associated quality scores. The visual model’s hierarchical structure, as well as the limited impact of fine scale distortions on quality judgments of severely impaired video, are exploited to build a framework for scaling the bitrate required to represent the reference signal. Two applications of the metric are also presented. In the first, the metric is used as the distor-tion measure in a rate-distortion optimized rate control algorithm for MPEG-2 video compression. The resulting compressed video sequences demonstrate significant improvements in visual qual-ity over compressed sequences with allocations determined by the TM5 rate control algorithm operating with MPEG-2 at the same rate. In the second, the metric is used to estimate time series of objective quality scores for distorted video sequences using refer-ence bitrates as low as 10 kbps. The resulting quality scores more accurately model subjective quality recordings than do those esti-mated using the Mean Squared Error as a distortion metric while requiring a fraction of the bitrate used to represent the reference signal. The reduced-reference metric’s performance is compara-ble to that of the full-reference metrics tested in the first Video Quality Experts Group evaluation. I