MacAdam color space

Color Difference Evaluation. Shade evaluation is comparable in importance to relative strength evaluation for dyes. This is of interest to both dye manufacturer and dye user for purposes of quaUty control. Objective evaluation of color differences is desirable because of the well-known variabihty of observers. A considerable number of color difference formulas that intend to transform the visually nonuniform International Commission on Illumination (CIE) tristimulus color space into a visually uniform space have been proposed over the years. Although many of them have proven to be of considerable practical value (Hunter Lab formula, Friele-MacAdam-Chickering (FMC) formula, Adams-Nickerson formula, etc), none has been found to be satisfactorily accurate for small color difference evaluation. Correlation coefficients for the correlation between average visually determined color difference values and those based on measurement and calculation with a formula are typically of a magnitude of approximately 0.7 or below. In the interest of uniformity of international usage, the CIE has proposed two color difference formulas (CIELAB and CIELUV) one of which (CIELAB) is particularly suitable for appHcation on textiles (see Color). 

Hitherto we have discussed measurement of the distance separating two colors plotted in a visually uniform color space. Instead of transforming the C.I.E. space into a uniform color space, its known distortions can be compensated by MacAdam ellipsoids (MacAdam, 1942). Davidson (1951)... 

Fio. 5. MacAdam ellipsoids. Any point in the color plane may be surrounded by an ellipse, and in the color solid by an ellipsoidal volume, the boundary of which represents a finite number of perceptual color differences. For any fixed number of differences, the size of the ellipsoid depends upon its position in the color space. By courtesy Dr. D, L. MacAdam by permission of the Optical Society. 

B. Color Matching and MacAdam Space Recommended Reading... 

Figure 15 shows the so-called MacAdam discrimination ellipses plotted in the CIE chromaticity diagram. These were produced more than 40 years ago by an experimental subject who repeatedly attempted to make perfect color matches to samples located at 25 points in chromaticity space. The apparatus provided projected rather than sur-... 

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