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<title>Photometric Technique For Deriving A "Best Gamma" For Displays</title>

1979; SPIE; Volume: 0199; Linguagem: Inglês

10.1117/12.958051

1996-756X

S. J. Briggs,

Color Science and Applications

Each picture element (pixel) of a digitally-controlled display can be commanded to a finite number (typically 256) of luminance levels. The relation between the digital command levels and the resulting luminances is called a "gamma" function, using a loose adaptation of photographic terminology. The purpose of the technique described here is to obtain a gamma function which results in the contrast between each of the steps being equally visually discriminable. The procedure starts with a set of 51 photometric measures of a specific set of digitally-controlled targets designed to determine the interaction between the display's target and surround luminances, and the display's useful luminance range. These data are used in the Rogers-Carel Formula for predicting visual threshold of within-target modulation contrast, m as a function of average target luminance, t, average surround luminance, s, visual size of the target area, a, and the visual spatial frequency of detail within the target, f, (i.e., m = f(t, s, a, f)). Through curve fitting, optimization of viewing distances and other operations, the equation is reduced to m = f(ℓ) where ℓ is the luminance when all the display pixels are commanded to the same level. This equation is used to determine the number of just noticeable differences (JND's) in target contrast within the useful display luminance range and then to determine the luminance value for each command level so that each succeeding step represents the same number of JND's.