The influence of space and time varying distortions on objective intelligibility estimators for region-of-interest video

Objective estimators for video are expected to estimate accurately subjective ratings provided by humans. This work presents a subjective experiment designed to acquire intelligibility ratings for a collection of compressed ASL videos. The distortions present in the experimental database are analyzed in terms of their impact on the performance of objective estimators. Distortions that do not significantly vary across space or time cannot adequately challenge traditional objective estimators, such as PSNR and RMS distortion contrast, and an objective intelligibility measure designed specifically for ASL video provides negligible improvements in prediction accuracy. Distortions that vary across space and time, affecting only localized regions in the video, are considered spatially and temporally diverse. When the distortions present in the experimental database are sufficiently diverse, the objective intelligibility measure estimates subjective ratings more accurately than PSNR and RMS distortion contrast.