Investigations to Define Acceptability Tolerance Ranges in Various Regions of Color Space

Current acceptance of goods for color by the Army depends on visual comparison against a standard and eight limit samples. The Army wished to have a numerical method of setting color tolerances to be used with instrumental measurement. The limit samples, on examination, were seen to be somewhat erratic as guides for instrumental tolerances. Instead, we selected pairs of samples from a large number of previous submissions by industry. These pairs showed four graduate lightness steps, four graduated chroma steps, and four graduated hue steps. Six observers looked at each pair 10 times, randomly interspersed with other pairs, and issued a pass or fail judgement each time. From these data we established lightness, chroma, and hue tolerance limits. For an olive green and a tan shade, these tolerances were roughly in the ratio 321 for a dark blue, the ratios were roughly 221. We wrote simple equations that can be used with instrumental measurement in order to determine quickly whether a sample passes or fails. We recommended similar treatment of all samples for which the Army desires acceptability limits.