Current issues and new techniques in visual quality assessment

This paper deals with two current issues in visual quality assessment, namely, contextual effects in quality judgments and the evaluation of time-varying image quality. A scaling experiment is described showing that contextual effects due to stimulus spacing are negligible when a method based on difference judgments is used. It is also shown that subjects can record their impressions of time-varying image quality by means of moving a slider along a graphical scale. The research on contextual effects as well as on the continuous assessment of time-varying image quality illustrate the important role psychological factors play in image quality evaluation.