Calculation of self-luminous neutral scale: how many neutral steps can you see on that display?

Abstract

One of the dimensions of visual perception usable for information display is neutral scale, the achromatic aspect of colour. An existing neutral scale calculation, CIE L*, relates reflected luminance to lightness magnitude and discrimination. But there is no similar international standard calculation for self‐luminous displays. In this article, we introduce a candidate self‐luminous neutral‐scale calculation, to complement CIE L*. We particularly examine its low‐contrast gain, the degree of crispening. This low‐contrast gain is a function of the background luminance, from which the target contrast is an increment or decrement. We demonstrate the use of the calculation to predict matches of neutral scale across different background luminances, and to model the successive thresholds of the Digital Imaging and Communications in Medicine Gray Scale Display Function. Finally, the proposed self‐luminous neutral scale is calculated to show the maximum number of discriminable differences, and the associated optimum background luminance, in representative ranges of display luminance.