New and recently published data, comprising a total of approximately 30 000 judgments (ratio and paired comparisons) made by several observers on 176 pairs of colors, are used to check the 1964 CIE color-difference formula. The results indicate that the formula predicts observed color difference, ranging from about 4 to about 60 CIE units, with reasonable accuracy. Approximately 90% of the observed differences are predicted correctly to within ±25%. The precision of the observed differences is estimated to be also about ±25%. It has been noticed that several pairs (about 20 out of 100) have predicted color differences deviating significantly from the observed differences. Observations are affected by the luminous reflectance of the achromatic surround, but the deviations between color differences observed with a white surround and color differences observed with a black surround are masked somewhat by the limited precision of the observations, and thus, in the average, the CIE formula predicts both cases equally well.
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