Abstract

In previous papers a correlate for lightness (L) was found in terms of CIE-tristimulus values for colors of approximately constant luminous reflectance (Y). L could be expressed by a second degree equation with X, Y, Z as variables. In the present study about 100 samples were selected to cover the gamut of existing surface colors. The lightness-equivalent neutrals were estimated by three observers for these colors under the same conditions as described in a previous paper. The original type of equation could not be used to fit the observational data because of the large differences in luminous reflectance among the samples. However, the L/Y ratios could be expressed by a second degree equation with chromaticity coordinates x, y as variables. This type of equation appears to be valid for all reflecting surface colors.

© 1958 Optical Society of America

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References

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  1. C. L. Sanders and G. Wyszecki, J. Opt. Soc. Am. 47, 398 (1957).
    [Crossref]
  2. G. Wyszecki and C. L. Sanders, J. Opt. Soc. Am. 47, 840 (1957).
    [Crossref] [PubMed]
  3. R. B. Bedford and G. Wyszecki, J. Opt. Soc. Am. (to be published).

1957 (2)

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Figures (3)

Fig. 1 and 2
Fig. 1 and 2

CIE-chromaticity diagram showing contour lines obtained by observers GW and CLS in 1956 and 1957. The contour lines are ellipses around the centers shown by the open circles.

Fig. 3
Fig. 3

CIE-chromaticity diagram showing contour lines obtained by observer GS.

Fig. 4
Fig. 4

Difference between the observed L/Y ratio and calculated L/Y ratio plotted against Y, for the 1957 data.

Tables (2)

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Table I CIE specifications for the 106 samples, and observed and calculated L/Y ratios for three observers.

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Table II Coefficients of Eq. (1) for different sets of observational data.

Equations (1)

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L / Y = a 1 x 2 + a 2 y 2 + a 3 x y + a 4 x + a 5 y + a 6 .