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In the OSA-UCS (Optical Society of America–Uniform Color Scales), except for colors on the boundary of the three-dimensional solid (L, j, g), each color is surrounded by the 12 nearest neighboring colors that are supposed to be perceptually equally different (local uniformity). In the Swedish NCS (Natural Color System), colors are arranged so as to gradually vary in each of the three perceptual attributes: hue, ϕ; blackness, s; and chromaticness, c. The gradual change in an attribute may correspond to change of color difference from one to the next with a constant step (local uniformity). In each of these color-order systems, the uniformity was tested by a color-difference formula d based on color-component differences. When a coordinate is fixed (e.g., j in OSA-UCS, or c in NCS), d for neighboring pairs turned out fairly constant. However, systematic differences were found between d in one coordinate and d in another coordinate. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 277–283, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10162

Today chromatic adaptation transforms (CATs) are reconsidered, since their mathematical inconsistency has been shown in Color Res. Appl.38, 188 (2013) and by the CIE technical committee TC 8-11: CIECAM02 Mathematics. In 2004-2005 the author proposed an adaptation transform based on the uniform color scale system of the Optical Society of America (OSA-UCS) [J. Opt. Soc. Am. A21, 677 (2004); Color Res. Appl. 30, 31 (2005)] that transforms the cone-activation stimuli into adapted stimuli. The present work considers all the 37 available corresponding color (CC) datasets selected by CIE and (1) shows that the adapted stimuli obtained from CC data are defined up to an unknown transformation, and an unambiguous definition of the adapted stimuli requires additional hypotheses or suitable experimental data (as it is in the OSA-UCS system); (2) produces a CAT, represented by a linear transformation between CCs, associated with any CC dataset, whose high quality measured in ΔE units discards the possibility of nonlinear transformations; (3) analyzes these color-conversion matrices in a heuristic way with a reference adaptation that is approximately that of the OSA-UCS adapted colors for the D65 illuminant and particularly shows accordance with the Hunt effect and the Bezold-Brucke hue shift; (4) proposes the measurements of CC stimuli with a reference adaptation equal to that of the visual situation of the OSA-UCS system for defining adapted colors for any considered illumination adaptation and therefore for defining a general CAT formula.

Classical color-matching error data have been compared in L, M, S cone response space to small and large color-difference data to reveal their agreements and divergences. The color-matching error data analyzed (with exception of the Brown data) and, implicitly, the Boynton–Kambe data were found to be similar, with a large ratio of S increment to L increment. Another group is formed by the Richter threshold data, small color-difference data and the CIE94 formula fitted to the latter. This group has an S/L increment ratio of approximately one third that of the first. The Optical Society of America Uniform Color Scales and the Munsell set are on average comparable and intermediate in S/L increment ratio. Color-matching error data, threshold and small color-difference data as well as the formula fitted to it reveal a characteristic V shape of the cone response increment functions. It is explained as the overlay of a crispening effect onto the basic global increment function revealed in Munsell or OSA-UCS data. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 384–393, 2001

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

The Optical Society of America's Uniform Color Scales (OSA-UCS) is one of the color spaces that most closely approximate a "true" uniform color space. Different techniques have been used to convert OSA-UCS-based color specification parameters, L, j, and g, to the CIE tristimulus values, X, Y, and Z. However, none of these methods provides a direct method of inverting OSA-UCS to CIEXYZ values. Thus, numerical algorithms, such as the Newton-Raphson method, have been employed to obtain the transformations. The relative low accuracy and long computation time of this method makes it undesirable for practical applications. An artificial neural network (ANN) was employed to convert OSA-UCS to CIEXYZ. Its performance was compared with that of numerical methods. After optimization, ANN gave a better performance with a mean error (ΔEXYZ) of 1.0×10(-4) and a conversion time of less than 1 s for 1891 samples.

In a previous work, the authors reported on the results of a color naming experiment performed on native Italian speakers regarding the location of focal colors and centroids in the Uniform Color Scales of the Optical Society of America color system. That work was aiming at comparing such data with those previously obtained by Boynton and Olson (B&O) accounting for the differences in the paradigm and the language. The number of consistency and consensus colors in the different lightness plans was also reported but no information was provided on their placement. Though, such information is very important for any subsequent modeling stage. The objective of this article is to fill such a gap and share such data with the scientific community to provide a reference database for future investigation. Three different datasets were considered: the extended OSA (E-OSA), the reduced OSA (R-OSA), and the B&O's (B&O) sets of reference colors. Results show a good overlap among the locations of the consensus colors in the {L, j, g} color model between B&O and the subset of E-OSA colors overlapping with the B&O 424 colors (R-OSA), as well as a strong agreement on consistency. Furthermore, a close proximity among the centroids of homologue regions for the majority of the classes was found. © 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 437–447, 2013

A Chromatic Adaptation based on the OSA-UCS system makes a Color Conversion between different illuminations and defines adapted coordinates with uniform perceived scales, whose digitalization has a color independent color degradation.

This article provides Munsell (aim and actual), NCS (aim and actual), DIN (aim and actual), Coloroid (aim), Colorcurve (aim and actual), and OSA-UCS (aim and actual) notations for the 237 colour samples that comprise BS5252. These notations were obtained from recent spectrophotometric measurement of the standard, using a new version of the colour notation conversion program initially developed at the University of Teesside. © 1995 John Wiley & Sons. Inc.

In digital image capture, the camera signals produced by the D65 illuminant, once translated into tristimulus values of the CIE 1931 standard colorimetric observer (assuming the Maxwell-Ives-Luther criterion is satisfied), are considered good to produce accurate color rendering. An image obtained under any illuminant other than D65 does not appear realistic and the tristimulus values of the camera must be transformed into the corresponding ones produced by the D65 illuminant. This transformation must satisfy color constancy. In this work, the transformation is obtained by a color-vision model based on the Optical Society of America-Uniform Color Scales system [Color Res Appl 2005; 30: 31–41] and is represented by a matrix dependent on the adaptation illuminant. This matrix is obtained by minimizing the distance between the pairs of the uniform scale chromatic responses related to the tristimulus values of the 99 different color samples of the SG Gretag-Macbeth ColorChecker measured under a pair of different illuminants, one of which is the D65. Then any picture captured under a given light source can be translated into the picture of the same scene under the D65 illuminant. Metameric reason allows only approximate solutions. The transformations from Daylight and Planckian illuminants to the D65 illuminant have a very regular dependence on the color temperature, that appears to be the typical parameter for the color conversion. © 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 412–422, 2013

An earlier article has compared the perceptual scaling of the Munsell, NCS, DIN, Coloroid, and OSA-UCS colour order systems. This article expands on the earlier article by presenting a comparison of the Colorcurve and SCA-2541 [Swiss Colour Atlas] colour order systems, again using the OSA- UCS system as a reference model. To enable direct comparison with the earlier article, the same varied but systematic sets of OSA- UCS cleavage planes were used in this new comparison. To enable comparison between these systems, and the Munsell, NCS, DIN, and Coloroid systems, thejndings are graphically presented in a format similar to that used in the earlier article. © 1994 John Wiley & Sons, Inc.

Colorcurve (D65/1964) and Coloroid (C/1931) notations of the 558 OSA-UCS atlas samples are presented in two tables. One table provides the Colorcurve and Coloroid notations for the 424 regular samples; the other for the 134 near-neutral (half-step) samples. Colorcurve notations are derived from the OSA-UCS aim points, and Coloroid notations are derived from colorimetric data of the OSA-UCS samples contained in MacAdam's copy of the OSA-UCS colour atlas.

This article presents an evaluation of the deviation of the Colorcurve atlas samples from their designated aim points. Sample deviations are evaluated in terms of hue, chroma, and lightness. In addition, the deviation of the Colorcurve samples from their respective aim points are graphically represented for eighteen lightness levels, Comparison is provided with NCS, DIN, and OSA-UCS atlas sample deviation.

NCS (C/1931) and DIN (C/1931 and D65/1964) notations of the 558 OSA-UCS atlas samples are presented in two tables. One table provides the NCS and DIN notations for the 424 regular samples; the other for the 134 near-neutral (half-step) samples.

In 1985 a research program was instigated to determine the feasibility and desirability of developing a computer based colour notation conversion program. Results indicated that the development of such a program covering the Munsel, NCS, DIN, OSA-UCS, Coloroid, CIELAB and CIELUV colour specification systems for use as a research tool was both feasible and desirable. The program was completed early in 1989 and this is the first of a number of articles that uses this program as a research tool. The colour notation conversion program has been used to evaluate the accuracy of the samples which comprise the NCS, DIN and OSA-UCS colour atlases.

An investigation of the color metrics and the complexity of the CIEDE2000 formula shows that CIELAB space is inadequate to represent small-medium color differences. The OSA-UCS (Uniform Color Space) Committee has shown that no space with uniform scale for large color differences exists. Therefore the practical way for color-difference specification is a color-difference formula in a nonuniform space. First, the BFD (Bradford University) ellipses are considered in the OSA-UCS space, and their very high regularity suggests a new and very simple color-difference formula at constant luminance. Then the COM (combined) data set used for the development of the CIEDE2000 formula is considered in the OSA-UCS space, and the color-difference formula is extended to sample pairs with a different luminance factor. The value of the performance factor PF/3 for the proposed OSA-UCS-based formula shows that the formula performs like the more complex CIEDE2000 formula for small-medium color differences.

Two different transformations between the (X 10 , Y 10 , Z 10 ) coordinates and the (L OSA , g, j) ones of the Uniform Color System of the Optical Society of America (OSA- UCS) are given related to two possible different geometrical structures. Both transformations are logarithmic functions obtained by integration of Weber fractions of ratios of suitable color stimuli. The first structure is related to the color opponency proper of the (g, j) coordinates of the OSA-UCS) system and the second one to a mixing of the (g, j) coordinates. The second transformation has a simpler and highly symmetrical structure, and the regularity of the OSA- UCS lattice is higher.

The OSA-UCS is a color order system developed by the Optical Society of America's Committee on Uniform Color Scales. The color specification value (L,j,g) of the OSA-UCS is derived from the CIE 1964 tristimulus value (X10, Y10, Z10). However, no direct conversion algorithm from OSA-UCS to CIEXYZ has been reported. In this paper, analytic conversion algorithm from OSA-UCS to CIEXYZ has been developed, and its effectiveness is justified.

The OSA uniform color system is a 3-D collection of color samples according to the regular rhombohedral structure in which each color is surrounded by its 12 nearest neighbors, all perceptually equally different (local uniformity). The Swedish NCS system is a 3-D collection of color samples that vary gradually in each of the three perceptual attributes. It is not clear that this arrangement implies all neighboring pairs along the respective coordinates being perceptually equally different (local uniformity). Of pairs (j,k) of interest, predicted color differences djk were calculated that have the following property. Suppose an observer selects a pair of Munsell grays (Va, Vb) that matches in size with the color difference between (j,k), then djk=|Va-Vb| is predicted by djk, on the average, with error of 0.34 in Munsell V-unit. Variation of djk in this unit was in the order of 0.22V for nearest neighboring pairs (j,k) in various cleavage planes of OSA-UCS and in the order of 0.11V for neighboring pairs (j,k) along s-coordinate and c-coordinate in sheets with fixed hue of NCS. Both were well within the prediction error range, but some systematic trends in values of djk were found.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The most widely used color-difference formulas are based on color-difference data obtained under D65 illumination or similar and for a 10° visual field; i.e., these formulas hold true for the CIE 1964 observer adapted to D65 illuminant. This work considers the psychometric color-vision model based on the Optical Society of America–Uniform Color Scales (OSA-UCS) system previously published by the first author [J. Opt. Soc. Am. A21, 677 (2004)JOAOD60740-323210.1364/JOSAA.21.000677; Color Res. Appl.30, 31 (2005)CREADU0361-231710.1002/col.20072] with the additional hypothesis that complete illuminant adaptation with perfect color constancy exists in the visual evaluation of color differences. In this way a computational procedure is defined for color conversion between different illuminant adaptations, which is an alternative to the current chromatic adaptation transforms. This color conversion allows the passage between different observers, e.g., CIE 1964 and CIE 1931. An application of this color conversion is here made in the color-difference evaluation for any observer and in any illuminant adaptation: these transformations convert tristimulus values related to any observer and illuminant adaptation to those related to the observer and illuminant adaptation of the definition of the color-difference formulas, i.e., to the CIE 1964 observer adapted to the D65 illuminant, and then the known color-difference formulas can be applied. The adaptations to the illuminants A, C, F11, D50, Planckian and daylight at any color temperature and for CIE 1931 and CIE 1964 observers are considered as examples, and all the corresponding transformations are given for practical use.

Judgments of relative magnitudes of color differences exhibited by 128 selected nearest-neighbor pairs of 59 colored tiles were recorded by 49 to 76 observers, all of whom had normal color vision. Scale values that represent the perceived magnitudes of the color differences were obtained by statistical analysis of their reports. From colorimetric specifications of the tiles, formulas have been devised that define a three-dimensional euclidean space in which the distances between the points that represent the colors correlate reasonably well with the reported magnitudes of the perceived color differences. Lattice points of a regular rhombohedral crystal in that space have been used to specify about 500 colors that are being made for distribution by the Optical Society. Because of the manner of selection of those colors, each except the most saturated of the chosen colors will exhibit equal magnitudes of color difference from 12 others. About 2500 equally noticeable color differences can be exhibited by suitable arrangements of those colors. Each except the most saturated of the colors can be arranged in six different series. Each of those series exhibits from three to ten color differences, all of equal magnitude. Such a series of colors, which exhibits equal color differences is known as a uniform color scale. Provision of a set of colors with which the maximum possible number and variety of uniform color scales can be constructed was the goal of the Optical Society Committee on Uniform Color Scales, of which this is a report.

Colorimetric specifications and measured values of one of the sets of cards issued by the Optical Society of America for its Committee on Uniform Color Scales are reported. In addition to the CIE values for illuminant D65 and color-mixture data for 10° observing fields, the corresponding L,j,g notations of the committee are also given. The average discrepancy between the actual colors and their specifications is 14% of the intended difference between pairs of nearest neighbors of the full-step set of colors. The full-step set of 424 colors exhibits 2058 pairs of nearest neighbors. The root-mean-square deviation from the average difference, evaluated by use of the committee’s formula for color difference, is 12%. To bisect the color differences in the frequently used medium-lightness range of low-saturation colors, 134 additional colors are included in the set. Together with 13 embedded and 38 immediately adjacent colors of the full-step set, they provide 740 half-step pairs of colors. The rms deviation is 17% of their average.