A comparison between 8-bit and 10-bit luminance resolution when generating low-contrast sinusoidal test pattern on an LCD

Radiological images are today mostly displayed on monitors, but much is still unknown regarding the interaction between monitor and viewer. Issues like monitor luminance range, calibration, contrast resolution and luminance distribution need to be addressed further. To perform vision research of high validity to the radiologists, test images should be presented on medical displays. One of the problems has been how to display low contrast patterns in a strictly controlled way. This paper demonstrates how to generate test patterns close to the detection limit on a medical grade display using subpixel modulation. Patterns are generated with both 8-bit and 10-bit monitor input. With this technique, up to 7162 luminance levels can be displayed and the average separation is approximately 0.08 of a JND (Just Noticeable Difference) on a display with a luminance range between 1 and 400 cd/m2. These patterns were used in a 2AFC detection task and the detection threshold was found to be 0.75 ± 0.02 of a JND when the adaptation level was the same as the target luminance (20 cd/m2). This is a reasonable result considering that the magnitude of a JND is based on the method of adjustment rather than on a detection task. When test patterns with a different luminance than the adaptation level (20 cd/m2) were displayed, the detection thresholds were 1.11 and 1.06 of a JND for target luminance values 1.8 and 350 cd/m2, respectively.