Comparison of Gradation Characteristics between Three Typical Medical Imaging Display Devices Using Psychophysical Analysis

Although there are remarkable differences in maximum luminance in cathode ray tube(CRT)and liquid crystal display(LCD)monitors and film/viewer systems, these differences cannot be recognized in our perception of them. To clarify the reason for this conflict, we analyzed the psychophysical gradient(δ), which is based on the minimum perceptible luminance difference(ΔL_)and can express contrast visually recognized by observers. In this study, we first confirmed the compatibility of the psychophysical analysis to the CRT and the LCD monitors by using their threshold contrasts(C_ts). Second, we calculated and compared the δ's of the above output devices. The C_ts values of each device were in good agreement. Moreover, the Moon & Spencer model, which expressed the perceptibility of luminance change, was well suited to the measured C_ts over the whole luminance range. The psychophysical analysis is therefore available not only for the film/viewer system, but also for the CRT and LCD systems. The difference of physical gradient G of the luminance characteristics curve among the output devices was larger than 20 times, whereas that of δ was within 3 times. The display devices listed in the order of decreasing δ were film/viewer>LCD>CRT. These results corresponded to the visual contrast sensation and our clinical experience, which cannot recognize remarkable differences in perception. By using the psychophysical analysis, we clarified the reason for the conflict between the results of physical evaluation and the contrast visually recognized by observers.