Visual study of perceptually optimized displays

Perceptually linear displays have been proposed as a standard for medical imaging. Current displays (display driver/monitor) have intrinsic display characteristics that differ from this proposal. Visual comparisons of the proposed perceptually linear displays and current technology have not been made to date. The subjective assessment presented in this paper is the first such comparison. Clinical images were printed on a 12-bit laser printer to simulate the display characteristics of perceptually linear and currently available 8-bit medium-resolution gray-scale displays. Images were compared subjectively and by means of a 4-alternative forced choice (4-AFC) protocol. In addition, predictions of visible differences were made with Daly's Visible Differences Predictor model. We find that currently available displays can produce clinical images that are visually indistinguishable from those that would be displayed on a perceptually linear display when viewed at currently available monitor luminance levels (200 nits). Therefore, intrinsic display functions may be sufficiently close to perceptually optimized performance that the expense associated with the design and fabrication of special perceptually linear display cards and/or monitors would not be justified. In any case, substantial deviation from perceptual linearity may be tolerable before visible differences will be discerned as long as the image is correctly mapped to the appropriate display function. Further study of the diagnostic benefits claimed for perceptually linear displays would be prudent before human visual models are adopted as the basis for display standardization.