Quantitative estimates of saturation.

Abstract

Scales relating saturation to colorimetric purity have been derived from magnitude estimations for red (W29) and green (W65) test stimuli of 4° and 1.5° subtense. Scales based on homochromatic comparisons at several luminance levels follow a power-law form, with exponents ranging from 1.80 to 2.30. There is evidence that saturation scales for red and green light differ in slope, with the red scale being of consistently higher slope than the green. This difference is demonstrated clearly by heterochromatic saturation matches for a large number of colorimetric purities, but is not substantiated by magnitude estimations utilizing heterochromatic comparisons. It is suggested that observers are not able to apply a ratio definition of saturation in making quantitative comparisons of heterochromatic stimuli by the method of magnitude estimation, and that real differences between saturation scales for differing hues may be masked by the adoption of median magnitude estimations as a quantitative index of perceived saturations.