Display fidelity: link between psychophysics and contrast discrimination models

In medical images, the data often represent information with a quantitative meaning, such as the radiation absorption by tissues. Therefore, it is crucial that this quantitative information is accurately transferred into brightness impressions from luminance patterns on the display. Perceptual linearization was proposed by Pizer (1981) as a way to guarantee the display fidelity in as much as equal steps in the grey value evoke equal steps in brightness sensation. In this study, the fidelity of achromatic displays prior to and after perceptual linearization was investigated. First, magnitude estimation of brightness differences between grey square patches embedded in a uniform background was used to make equal-interval brightness series. Then, the brightness contrast discrimination models of Whittle (1986, 1992), and Kingdom and Moulden (1991) for grey patches in a uniform background were extended to the suprathreshold data. A good fit was found. Finally, the look-up tables that provide perceptual linearization for the grey patches were applied to complex images. Brightness matching with a scale of reference grey patches was used to estimate grey levels at specified image locations. The experimental results indicate that the accuracy of this task is not necessarily affected by perceptual linearization.