Exposure preferences for digital still imaging: a psychophysical study

The automatic exposure control (AEC) for a camera phone is typically a simple function of the brightness of the image. This brightness, or intensity, value generated from a frame is compared to a predefined target. If the intensity value is less than a specified target, the exposure is increased. If the value is greater, exposure will be decreased. Is using an intensity target statistic a good model for AEC? In order to answer this question, we conducted psychophysical experiments to understand subjective preferences. We used a high-end DSLR to take 64 different outdoor and indoor scenes. Each scene was captured using five different exposure values (EV), from EV-1 to EV+1 with half EV increments. Subjects were shown the five exposures for each scene and asked to rank them based on their preferences. The collected data were analyzed along different dimensions: preferences as a function of the subjects, EV levels, image quality scores, and the images themselves. Our data analysis concludes that a dynamic intensity target is needed to match the exposure preferences collected from our subjects.