A grey scale may be used by service technicians to detect display ageing or other display performance issues.
Eight grey strips are recommended, spaced between the minimum and the maximum luminance for each of the five mandatory colour tables.
The bit levels or signal levels producing the grey levels are evenly spaced from the level producing white to the level producing black. In order to select the appropriate grey level from a large set of available grey levels, use one of the following models:
Bit Levels in Software: Given n levels of grey that can be displayed on a screen, with 0 for black and w = n - 1 for white. We want to select a subset of m levels that are as evenly spaced as possible. The interval between the n levels to create m levels is ΔV = w/(m-1), which may not be an integer. So, the levels to select are the (integer) values of Vi= int[(i-1) ΔV] for i = 1, 2, ..., m, or Vi= 0, int(ΔV), int(2ΔV), int(3ΔV), ..., int[(m-1) ΔV], with int[(m-1) ΔV] = w for white. For example, if there are n = 256 = 28 levels from which we select m = 8 levels, white is w = 255; the interval is ΔV = 36.4286, and the chosen levels are: 0, 36, 73,109, 146, 182, 219, 255.
Analog Signal Levels: For analog signals, if Vw is the white level and Vb is the black level, then for m levels the signal step size is ΔV = (Vw - Vb)/m and Vj= Vb + jΔV.
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