Color and Contrast Perception in Monochrome Medical Imaging Flat-panel Displays

The interpretation of diagnostic grayscale images by human beings relies on luminance discrimination at photopic levels. The observer in his search for abnormality relies on luminance modulation. If this hypothesis is valid, then the color of a monochrome presentation should not affect diagnostic performance when the image luminance is equivalent to grayscale levels. Does observer preference for a particular tint influence his performance defining an ideally colored grayscale? In this paper, we studied the variations in supra-threshold contrast perception when using different colored scales to display psychophysics targets on uniform background. We used targets with six different colored scales based upon the hue and saturation levels, while maintaining a constant luminosity. The six colored scales and the ”white” grayscale constituted our set of seven colored scales used in a two-alternative forced choice scheme with random presentation and eighteen observers. All image targets contained the same degree of physical contrast and the same luminance values. We computed the degree of preference for all possible combinations of two colored scales. In spite of large inter-observer variability, we found that green and blue scales result in higher perceived contrast. Keyword List: contrast perception, achromatic contrast, flat-panel display, medical display.