Model of saturation and brightness: Relations with luminance

Abstract

The model is simple: Forflicker luminance stimuli and m aimum purity, the hue cycle's relative luminance (computed from ClE data) is reciprocal to relative saturation. Brightnesslluminance ratio BIL is proportional to relative saturation S, i.e., BIL = 1.5 Sii4. S times BIL ratio gives relative saturation for brightness stimuli; just as relative luminance times BIL ratio gives brightness. Predictions for any purity agree with data on saturation discrimination, color appearance in CIE space, BIL, and CIE brightness V,,. Predictions support Hunt's concept of "colorfulness" and indicate its causal role in proportionality of S and BIL. 4 and 5 . The following paragraphs review early data and ideas on saturation and luminance. Saturation Discrimination DataRelations between saturation and purity are nonlinear and a function of wavelength.1-'*5.9.1'-2' S aturation discrimination experiments employ the formula:

Chroma, chromatic luminance, and luminous reflectance. Part I: Basic research and illustration of relations

“…[10][11][12][13] The data generally agreed that the luminance amount of monochromatic light required to detect just-noticeable-differences in hue is more for yellow light about 570 nm and least for shortwavelength light (blue-violet). The function's inverse was deduced to indicate the chromaticness of spectral colors, as Helmholtz had predicted and as Sinden 15 and later Pridmore 16 confirmed with experimental and colorimetric data. The broadly inverse relationship of chromaticness to luminance is generally implied in color appearance models, [16][17][18] but the models use varying empirical factors and the basic relation is not self evident.…”

“…The function's inverse was deduced to indicate the chromaticness of spectral colors, as Helmholtz had predicted and as Sinden 15 and later Pridmore 16 confirmed with experimental and colorimetric data. The broadly inverse relationship of chromaticness to luminance is generally implied in color appearance models, [16][17][18] but the models use varying empirical factors and the basic relation is not self evident. Hence this study.…”

Chroma, chromatic luminance, and luminous reflectance. Part II: Related models of chroma, colorfulness, and brightness

“…[4][5][6][7] The studies generally agreed that the luminance amount of monochromatic light required to detect just-noticeable-differences of hue is greatest for yellow light about 570 nm and least for short-wavelength light (blue-violet). The function's inverse was deduced to indicate the chromaticness of spectral colors, as Helmholtz had predicted and as Sinden 8 and later Pridmore 9 confirmed with experimental and colorimetric data. The broadly inverse relationship of chromaticness to luminance is inferred in color appearance models, 10,11 but the exact relationship is not clear.…”

Chromatic luminance, colorimetric purity, and optimal aperture‐color stimuli

“…The B, R peaks of CIE RGB and XYZ color matching functions (CMFs) are 446, 602 nm and 446, 599 nm, 4 but due to the CMFs' curvatures the optimum components of nonspectrals are rather shorter and longer (442 and 613 nm, see below).The RGB CMFs' relevance to color appearance, rather than only colorimetry, is indicated by their peak wavelengths' similarity to those of visual sensitivity, 9 wavelength discrimination, 10 and relative saturation. 1,11 5. In Munsell and NCS color order systems, nonspectrals comprise spectral components about 445 and 615 nm.…”

“…(1) below]. This article proposes a new and more useful method of calculating colorimetric purity for nonspectral hues, which has long been problematic.…”