On the Role of the Observer and a Distortion Measure in Image Transmission

This paper considers the characteristics of the human visual system as they are related to sensitivity to encoding errors in still achromatic images. The starting point is a discussion in Section I of the role of a numerical measure of distortion in the determination of optimum encoding. Section II then discusses several ways of determining properties of the human observer and discusses the methodology of psychophysical experiments. Section III then discusses the results of a number of pertinent experiments and presents a model based on these experiments for detecting perturbations of an image. Section IV concludes by discussing how this model can be incorporated into a distortion measure and how this distortion measure might be used. Since the model of the human observer is quite complicated, the mathematical model is not tractable analytically, and results in this last section are as yet fragmentary.