All Effects of Psychophysical Variables on Color Attributes: A Classification System

This paper reports the research and structuring of a classification system for the effects of psychophysical variables on the color attributes. A basic role of color science is to psychophysically specify color appearance. An early stage is to specify the effects of the psychophysical variables (as singles, pairs, etc) on the color attributes (as singles, pairs, etc), for example to model color appearance. Current data on effects are often scarce or conflicting. Few effects are well understood, and the practice of naming effects after their discoverer(s) is inadequate and can be confusing. The number and types of possible effects have never been systematically analyzed and categorized. We propose a simple and rigorous system of classification including nomenclature. The total range of effects is computed from the possible combinations of three psychophysical variables (luminance, dominant wavelength, purity) and six color attributes (lightness, brightness, hue, chroma, colorfulness, saturation) in all modes of appearance. Omitting those effects that are normally impossible to perceive at any one time (such as four- or five-dimensional colors), the total number perceivable is 161 types of effects for all modes of appearance. The type of effect is named after the psychophysical stimulus (or stimuli) and the relevant color attribute(s), e.g., Luminance-on-hue effect (traditionally known as Bezold-Brucke effect). Each type of effect may include slightly different effects with infinite variations depending on experimental parameters.M. Melgosa was supported by the Ministry of Economy and Competitiveness of the Government of Spain, research project FIS2013-40661-P, with the European Research Development Fund

Ideal primary colours : theory and relations with other functions

4 page(s

Discrete and general roles of complementary colours in colour vision

Complementary colours have been researched for 340 years but little is known of their role in colour vision. Complementary colours are defined as a pair of colour stimuli which admix a given white (i.e. cancel all hue). This chapter aims to describe recent research of the roles of complementary colours in colour vision. Presently, only one role for complementary colours is accepted in the scientific literature: a colorimetric role in colour mixture. A second role, in chromatic induction, was generally accepted until (erroneously) usurped 50 years ago by the opponent colours theory of chromatic induction. The visual system develops many functions from complementary colours (whose physiological basis is color-opponent cells in retina and cortex.) For a start, two of the cones (S and L, peaks about 445 and 568 nm) are complementary. The third cone (M, peak about 530 nm) complements the nonspectral hues. This chapter shows complementarism structures ten visual functions. First, complementary colours are shown to form hue cycle structure. Second, a relative wavelength scale is derived from dominant and complementary wavelengths, extended into nonspectral hues to form an overarching wavelength-based metric over the ;whole hue cycle. Third, complementary wavelengths are shown to structure a colour constancy mechanism where constant hues and complementary constant hues form, remarkably, parallel straight lines (related by invariant wavelength ratios) in the plane of wavelength and reciprocal ilIuminant colour temperature. The relative wavelength scale is used to extend this grid-like mechanism into the nonspectrals. A key paper establishes a further seven roles, six by formulating math models for wavelength discrimination, u.mform hue, spectral sensitivity, saturation, chromatic adaptation, chromatic induction, from tbe ratio of either complementary wavelength intervals or complementary radiant powers. Complementary colours' II varied roles (including the colorimetric role) extend over the visual process from cones to cortex. These discrete roles have an overall structural role, in shaping functions to a trimodal framework (ROB peaks, complementary CMY troughs) which facilitates adapting functions to the illuminant. Thus the general role is evidently chromatic adaptation, for the purpose of colour constancy and improved image recognition in different iIIuminants. Given the role of complementary colours in colour constancy and hue discrimination, they may prove to be central to the visual process.44 pages(s

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

Part I of this article found, inter alia, that chroma resembles log inverted luminance. This article develops three math models of Munsell chroma and associated colorfulness from (1) inverted luminous reflectance Y, (2) inverted chromatic luminance, and (3) inverted chromatic luminance combined (over the mid-spectrum 480–580 nm) with the unimodal curve for spectral absorptance of M cones. The first two models are simple but of limited accuracy and demonstrate that inverted luminance (of any form) cannot fully account for varying relative chroma around the hue cycle, particularly the minor minimum and maximum about 490 and 520 nm (which also feature in B:L functions). The third model is rather complex but very accurate, apparently the only accurate model of Munsell chroma or other experimentally based scales of relative chromaticness in the literature. It adjusts to any level of luminance or purity, as demonstrated for several levels. Three models of brightness (B:L ratio) for 2⁰ field aperture colors are given, based on either Munsell chroma or log inverted chromatic luminance. The former provides two accurate and simple models of the CIE B:L function: (1) log chroma = B:L ratio ±0.1, and (2) (chroma/k)x = B:L ratio ±0.1. The latter also predicts B:L for nonspectral colors and those of lower purities, e.g., object colors. The results finally solve the relationship between brightness and chroma and demonstrate that B:L ratio (a contrast in constant luminance) arises directly from chroma (also a form of contrast in constant luminance), or the reverse.13 page(s

Chromatic induction : opponent color or complementary color process?

In present convention, chromatic induction (simultaneous and successive contrast) is usually held to be an opponent color process. Fifty years ago, it was an accepted complementary color process. The latter was never disputed yet apparently overlooked, and is here shown to be the more accurate account by inspecting afterimages and published data on simultaneous and successive hue induction.11 page(s

Color constancy from invariant wavelength ratios. II : The nonspectral and global mechanisms

Given the spectral mechanism of color constancy (Part I of this series), the remaining nonspectral mechanism is formulated here in Part II by the constraint of correlation with known spectral illuminant–invariant functions, i.e., invariant wavelength ratios between constant hues, which plot straight parallel lines in the plane of wavelength and reciprocal illuminant color temperature (MK 21). The same is assumed to apply to nonspectral constant hues in the same plane and dominant wavelength scale extended to cover the nonspectrals (see accompanying article ‘‘Relative wavelength metric for the complete hue cycle .. .’’). To simplify analysis, stimuli are optimal aperture colors; their monochromatic stimuli lie between 442 and 613 nm, common boundaries with optimal compound stimuli (nonspectrals). It is shown that the wavelengths and invariant ratios of spectral constant hues can be formulated exactly (60.5%) from the ratios of an harmonic period, which shifts wavelength with MK21. The formula implies this color-constant hue cycle is isomorphic across illuminants and allows prediction of nonspectral constant hues. To identify these colorimetrically, their spectral complementary wavelengths are specified for various illuminants. This completes the global color constancy mechanism for the illuminant color temperature range 2800 to 25,000 K.11 page(s

Theory of primary colors and invariant hues

Additive primaries or peaks of color-matching functions are defined as peaks of complementary efficiency and of saturation per watt. These are near 447, 532, and 607 nm for all CIE illuminants. (CIE 1931 r, g, b functions peak at 447, 543, and 604 nm.) Subtractive or colorant primaries are defined as saturation minima and peaks of brightness or lightness per watt. Additive and subtractive primaries (e.g., red and cyan) are complementaries and opposites in saturation and lightness. In equal radiance color-space the six lines of constant mean saturation are invariant hues (473, 508, 574 nm and 558 c) and their complementaries.8 page(s

Model of saturation and brightness : relations with luminance

The model is simple: For flicker luminance stimuli and maximum purity, the hue cycle's relative luminance (computed from CIE data) is reciprocal to relative saturation. Brightness/luminance ratio B/L is proportional to relative saturation S, i.e., B/L = 1.5 S¹/⁴. S times B/L ratio gives relative saturation for brightness stimuli; just as relative luminance times B/L ratio gives brightness. Predictions for any purity agree with data on saturation discrimination, color appearance in CIE space, B/L, and CIE brightness Vb. Predictions support Hunt's concept of “colorfulness” and indicate its causal role in proporitionality of S and B/L.14 page(s

Unique and binary hues as functions of luminance and illuminant color temperature, and relations with invariant hues

For aperture color 3 s stimuli, the four unique hues, and at times the four (equally-balanced) binary hues, were measured for: (1) adapting white color temperatures 2850, 3400, 5500, 6500 K; and (2) luminance (L) for 5 and 6 log L ranges (about 0.01–3200 cd:m²) in 3.2:1 L steps (viewed singly) for 1 subject per white, 3 log L in 10:1 steps for 6 subjects for white 6500 K, and 1 log L for 2–11 subjects per white. The full hue cycle is graphed to the extended wavelength scale. With higher L, unique hues *b and *y shift longer, *g and *r shorter, and spectral binaries and 460 nm are invariant wavelengths, for Ls viewed singly. But for Ls viewed in successive contrast (Bezold–Brucke effect), unique hues are practically invariants. As interstimuli interval increases from 0–40 s (from successive L contrast to no-contrast), invariants shift away from uniques (which become hue-shift maxima) and coincide with spectral binaries (but not r/b, 565 c) at 495, 546, 600 nm. Successive L contrast switches spectral uniques’ hue-shift off (as invariants), and spectral binaries on (as hue-shift maxima); and no-contrast switches the reverse. With higher illuminant color temperature 2850–6500 K, wavelength of 10 constant hues shortens 5–10 nm for *b, *y, g:y, y:r, but others are constant ±2 nm.17 page(s

Bezold–Brucke effect exists in related and unrelated colors and resembles the Abney effect

I wish to correct a sometimes-held misconception that Bezold–Brucke hue-shift applies only to aperture colors and not to real object colors. I also demonstrate the broad similarity between this and Abney hue-shift, despite a contrary report.6 page(s