An important part in our study of color imaging science is the subject of image perception. Before we embark on that topic, we need to review some general results from visual psychophysics. In many cases, understanding how we perceive a reproduced image is not sufficient, because we also need to understand how we perceive the original (three-dimensional) scene so that we can make a reasoning about and judgment of the imaging and reproduction processes.

In this chapter, we will discuss the nature of psychophysical measurements and the various psychophysical phenomena in visual perception. Psychophysics is the science of studying the (human) psychological responses to physical stimuli. Since our psychological responses are subject to the influence of many variables, the major problem in psychophysics is to define the physical stimulus carefully so that only the relevant response is measured. The formulation of most psychophysical problems is obviously very difficult and the majority of psychophysical experiments have not succeeded well in this respect. Therefore, most experimental results in psychophysics are not easy to interpret. The dilemma is that, if the stimulating configurations are very specific, we wonder if the results are useful for other configurations. If they are not well controlled, we wonder which factors in the configurations are affecting the responses. Discussions on these concerns and other theoretical issues would take us too far from our main objective here. Our emphasis will be more on experimental observations, rather than theoretical models. If visual perception were better understood, we would be able to present our knowledge in a better organized manner.