Abstract
The coefficients of the spectral reflectances β1, β2, and β3 (at 430, 560, and 660 mμ, respectively) in the formula W = aβ1 + bβ2 + cβ3 were determined by least squares to fit visual judgments of the whitenesses of two groups of white cement samples. Somewhat different results were obtained for the two groups, for one of which β2 > β3, for the other set β2 < β3. The results were combined in the formula W = 1.68β1 − 0.34(β2 + β3) − q(β2 − β3), where q = 2.28 when β2 > β3, or q = −0.02 when β2 < β3. This formula was tested by application to the original two sets and to two other sets of white cements which differed even more widely in dominant wavelength. The correlations between the results and the subjective judgments of whiteness were in all cases higher than for any of 15 other whiteness formulas tried.
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