Uniform color space modeled with cone responses

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Forty observers determined their unique hues from arrays of Munsell chips in a standard surround under artificial daylight. There was some discrepancy in the results of males and females. Essentially no variability due to age of observer was found. The standard deviation around the total mean was less than 1 Munsell 40 hue step. Simple linear opponent-color a and b values were calculated. The ranges were found to straddle in all but the red color the system axes for the CIE 2°observer, but not for the 10°ob-server. NCS unique hues determined at similar chroma and lightness values fell in all cases within the ranges. The shifts in cross-over wavelengths of the color-matching functions necessary to match the extreme range values were determined to be between 6 -11 nm. The results provide support for an opponent-color system based on subtractions of color-matching functions. They also point to significant variation in color normal observers.

Section: Resultsmentioning

confidence: 99%

Determination of unique hues using Munsell color chips

Kuehni¹

2000

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“…Even though derivable from cone response data, the opponent-color space is structured significantly differently. As shown in an earlier article, 7 the Y dimension of the X, Y, Z tristimulus color space (for the 2°observer) is composed of Y ϭ 0.667M ϩ 0.333L. The X dimension is composed approximately of X ϭ 2L Ϫ 1.2M ϩ 0.2S, and Z ϭ S. Redness-greenness is expressed by changes in X (therefore, a complex change in all three cones), and yellowness-blueness by changes in Z. Subtraction of X or Z from Y has the purpose of centering the origin of the a, b diagram on the neutral gray of the corresponding luminous reflectance level.…”

Section: Color Differences In the Opponent-color Spacementioning

confidence: 96%

“…Using L, M, and S functions linearly related to CIE 2°c olor-matching functions, described in a previous publication, 7 the MacAdam ellipses have been expressed in terms of L, M, and S values. The l , m , s functions used have a value of 100 for the sum under the curves.…”

Section: Infra-threshold and Threshold Color Differencesmentioning

confidence: 99%

Threshold color differences compared to supra-threshold color differences

Kuehni¹

2000

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Threshold color difference ellipses, as represented by the MacAdam ellipses have been compared to unit contours implicit in the CIE94 color difference formula, found to represent small supra‐threshold color differences well, both in the CIE chromaticity diagram as well as the a*, b* diagram. The results indicate that the two types of contours are significantly different. While threshold differences are well described by incremental changes in cone sensitivity supra‐threshold differences are well‐described by increments in the opponent color parameters a* and b*. A comparison of the hue angles in the a*, b* diagram of the MacAdam ellipses and the CIE94 contours for the same 25 colors indicates no correlation (correlation coefficient −0.1). The conclusion is that threshold and supra‐threshold color difference perception operates at different levels in the color vision system.

“…The model used for this comparison is an opponent-color model in which the input is three magnitudes designated X, Y, and Z (the CIE tristimulus values) from three putative cone responses L, M, and S as discussed in a previous article. 3 Two of the three tristimulus values have direct neurophysiological correlates in the retina. The correlate for X has not yet been located.…”

Section: Sensitivity Regulation In the Visual Systemmentioning

confidence: 99%

“…The linear a, b values have for this purpose been recalculated as optimized a ∧ , b ∧ values by applying the powers and multipliers described in Ref. 3. Figure 10 illustrates the hue angle differences in this diagram between adjacent Munsell hues around the 40 hue circle (beginning with 7.5RP and going counterclockwise), at three value levels.…”

Section: Huementioning

confidence: 99%

A structural comparison of the Munsell renotation and the OSA-UCS uniform color systems

Kuehni¹

2000

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A structural comparison has been made of the lightness, chroma, and hue scales of the Munsell system, as expressed in the Munsell Renotations, and of the OSA‐UCS system. While the lightness scales are similar (except for the adjustment for the Helmholtz–Kohlrausch effect and the inclusion of a “crispening” effect in OSA–UCS), there are significant differences in the chroma scales along the major chromatic axes. Unlike in CIELAB, the increments in X and Z along these axes for equal chroma steps in both systems do not fall on a continuous function. In the two systems, as well as in CIELAB lines connecting colors of equal chroma differences at different Y values point to nonreal origins. These differ among the three systems. A major difference between Munsell and OSA–UCS is the size of the first chroma step away from gray. An experiment has been performed with the result that the OSA–UCS system is in much better agreement with the average observer in this respect than the Munsell system. OSA–UCS exhibits considerably more internal uniformity in terms of X and Z increments between steps than the Munsell system. © 2000 John Wiley & Sons, Inc. Col Res Appl, 25, 186–192, 2000