Amalgamation of the wright and guild color-mixture data

The mixture data for the CIE 1931 standard observer were created by amalgamating two separate sets of mixture data provided by Wright and Guild. Both sets of data were expressed in terms of the NPL system and amalgamated. It is possible to express all three sets of data in terms of Wright's system and show in terms of that system that the CIE data represent an acceptable amalgamation of the Wright and Guild data. This avoids the use of a third system for amalgamating the two sets of data. The properties of the new set of data can be defined by giving the trichromatic coefficients (chromaticity coordinates) of the spectral colors and the luminosity coefficients of the three primaries. This new amalgamated set of data can be used in connection with the V(λ) curve to derive the standard 1931 XYZ diagram and the set of x?, ?, and z? values for use in photometry and colorimetry.     

Perceived lightness of chromatic object colors including highly saturated colors

A model was formulated for predicting the Helmholtz-Kohlrausch effect or the Y tristimulus values for chromatic object colors with the same perceived lightness (L/Y ratios). the model was extended from the previous one in Color Res. Appl. 16 , 16-25 (1991), making it possible to estimate the Helmholtz-Kohlrausch effect on chromatic object colors with any Munsell Value. By analyzing the two experiments by Wyszecki and by Sanders and Wyszecki using the extended model, the model parameters were estimated for each experiment. By using each of the two estimated equations, L/Y ratios for Y = 20.0 were predicted in the whole chromaticity gamut corresponding to the two kinds of experimental results. the derived contour lines for equal L/Y ratios correlated well with those estimated directly from each experimental data. In addition, extrapolated L/Y ratios for spectral colors with Y = 20.0 showed very good agreement with the luminance ratios for equally bright spectral stimuli, so-called brightness/luminance (B/L) ratios, derived from the luminous efficiency functions V_b,2(Λ) by CIE TC 1-02 and V_judd(Λ) proposed by D. B. Judd.     

Color vision model of macLeod and Boynton

MacLeod and Boynton started off with the assumption that the fundamental blue falls on the x' axis of Judd's 1951 chromaticity diagram. This leads to a constant luminance diagram in which the lines that converge at the fundamental blue in Judd's diagram are parallel. MacLeod and Boynton tried to solve this problem by a slight change in one of the constants in the transformation equations. It turns out that what this does is to shift the position of the alychne on Judd's diagram so that it does not coincide with the x' axis. The blue fundamental no longer lies on the alychne. This makes it possible to derive a constant luminance chromaticity diagram in which the fundamental blue falls at one of the corners. After having created this new diagram, they used it to formulate a theory of color vision in which the blue cones contribute nothing to luminance. This procedure needs to be understood because it can be used to convert any theory of color vision in which all three cones contribute to luminance to one in which only two contribute to luminance. This has nothing to do with having the blue fundamental fall on the x' axis. A more serious problem is that Judd has made an error in his assessment of the luminosity coefficients and the concepts of MacLeod and Boynton need to be reformulated in terms of the CIE 1931 chromaticity diagram.     

Mathematical determination of the numerical data corresponding to the color‐matching functions of three real observers using the RGB CIE‐1931 primary system and a new system of unreal primaries X′Y′Z′

In this work, we determine the numerical data of the experimental color‐matching functions (cmf's) of three real observers (JAM, MM, and CF) for two small fields (2°). In previous works, these cmf's have been shown generically and expressed only in a new system of unreal X′Y′Z′ primaries. Here, we show results found with these cmf's for the visible spectrum in intervals of 10 nm, from 400 to 700 nm. The data refer to both the RGB CIE‐1931 system and a new system of unreal primaries X′Y′Z′, established by a procedure similar to that of the XYZ CIE‐1931 system. This transformation was needed, because negative values appeared in various cmf's when they were referred to the XYZ CIE‐1931 system. Recently, we have called this new system G94 (Granada ‘94). Here, we also describe the method and calculation of the matrix that enables this transformation; in testing six real observers with new cmf’s, we found positive results. We have used these new and experimental cmf's in several preceding works, as have other authors as well, to whom J. A. Martínez privately communicated the corresponding numerical data. The use of these cmf's by all the authors has led to noteworthy results. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 89–95, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10127     

Toward a more accurate and extensible colorimetry. Part VI. Improved weighting functions. Preliminary results

This Part VI is a progress report, with two motivations. (1) To publish the new method of extraction of weighting functions, and to show the demonstrated large reduction of tristimulus error in an array of ten disparate visually-matching pairs of white lights, and (2) to attempt to interest others in joining the work. The direct extraction of improved weighting functions (WFs) from an array of visually matching pairs of white lights is the subject of Part VI. This new approach is made necessary by our finding (Part I) that color-matching functions by either the Maxwell method or by the maximum saturation method lead to large errors (discrepancies) in computed chromaticities of pairs of visually-matching lights. Using spectral power distributions (SPDs) of 5 types from Part IV, eight observers make 5 strongly metameric visual matches to the same broadband reference white light, with 1.3° visual field and 70 cd/m² luminance of the reference white. Each of the resulting 5 SPDs is averaged over the 8 observers, and the 5 averaged SPDs are formed into 10 pairs (the five averaged visually-matching lights taken two at a time). Tristimulus values X, Y, and Z are computed for each member of each pair by the CIE 1931 weighting functions (color-matching functions) x , y , and z . Absolute ΔX, the tristimulus error (the difference between computed X1 and X2 of the visually-matching lights), is computed for each pair and summed over the 10 pairs, as are ΔY and ΔZ. The often-large 10-pair total tristimulus error TTE is computed for X, Y, or Z. For example TTE_X is the sum of the ten absolute ΔX's of the 10 pairs. Then x is progressively altered in spectral shape by an algorithm that on each iteration reduces TTE_X. Weighting functions y and z are altered in turn. Reduction to 1–3%, of the TTE initially associated with the CIE weighting function, is achieved in this preliminary work. The changes in shape of the resulting functions are discussed. The simpler term “weighting function” is used rather than “color-matching function” for these, and it is recognized that, when finally correct, these functions should represent the three spectral sensitivities of the normal human visual system. © 1998 John Wiley & Sons, Inc. Col Res Appl, 23, 226–233, 1998     

An optimisation study of colour measurements on digitised slides of painted works of art

This paper deals with the problem of the colorimetric fidelity of digitised colour slides of painted works of art. A six-matrix conversion model was derived that permitted the transformation of any RGB device-dependent measurement on digitised colour slides to XYZ CIE 1931 device-independent values. The model was calibrated against a reference colour chart. Eighty-one uniformly-painted colour samples were photographed together with a painting on a 4 × 5 inch colour slide that was digitised using a high resolution scanner. A 3 × 3 transformation matrix, of the corrected R, G and B values and the respective X, Y and Z tristimulus values provided by spectrophotometry, was calculated. The calculated matrix was then applied to a 13th century Byzantine fresco, captured on the same digitised slide, to transform the RGB measurements to XYZ CIE 1931 device-independent values which were then converted into the L* a* b* CIE 1976 colorimetric system.     

A relationship between zero‐grayness luminance by Evans and perceived brightness of spectrum colors

An important finding in the present study is that “zero‐grayness luminance” proposed by Evans gives approximately the same perceived brightness for spectrum colors irrespective of hues. The luminance values with the same perceived brightness for spectrum colors are directly derived on the basis of VCC method proposed by the senior author. It corresponds to the spectral luminosity function V_b2(λ;VCC). In the study process, we had some doubts on the luminosity function CIE V_b2(λ) on the heterochromatic brightness match. In other words, CIE V_b2(λ) may not be used for scientific study. The problem is discussed in Appendix briefly. © 2007 Wiley Periodicals, Inc. Col Res Appl, 33, 19–26, 2008     

Optimal yarn colour combination for full‐colour fabric design and mixed‐colour chromaticity coordinates based on CIE chromaticity diagram analysis

It is challenging for textile designers to achieve full‐colour effects in woven fabric using a limited set of coloured yarns. The common problems encountered during full‐colour fabric design include an insufficient number of colours and a failure to match the fabric colour with the desired colour. Using the theories of primary colours and optical colour mixing, we examine the mixed‐colour distribution of primary colour yarns on the basis of the CIE 1976 chromaticity diagram (CIE u′v′). In our experiment, dope‐dyed polyester filament yarns were selected as raw materials. Eight kinds of gradually varied weave structures and four types of primary colour combination were adopted in order to make different types of full‐colour fabric colour chart. Spectrophotometer and DigiEye colour measurement systems were selected to measure the reflectance and colour value of the fabric samples. By comparing the colour distribution of mixed fabrics in the CIE u′v′ diagram, the relationship between the primary colour combinations and the colour distribution of mixed fabrics is discussed. Of RGB, CMY, NCS, and RGBCMY combinations, only RGBCMY resulted in a relatively complete and large colour gamut. Moreover, the colour positions of mixed fabrics in the CIE u′v′ diagram were almost all distributed on or near the connecting line of the primary colour coordinates. The specific colour position of mixed fabrics in the CIE u′v′ diagram were mainly determined by the proportion of primary colours on the fabric surface. In this way, a new method for computing colour position in the CIE u′v′ diagram is introduced.     

Statistical confirmation of Thornton's zero-crossing conjecture for metameric blacks

In an effort to use statistics to arbitrate the recent debate about the clustering of zero crossings of metameric blacks, the statistically-most-significant metameric black was determined as a linear combination of the mean daylight and the first three daylight phases. This spectrum, S₄(Λ), is orthogonal to all the 1931 CIE color matching functions, and has zero crossings near 450, 540, and 610 nm. W. Thornton observed that these wavelengths tend to be crossover points for real reflectances that are metameric under some daylight. For the present work, a metameric black is defined as a difference between two matching spectral power distributions rather than between two matching spectral reflectances. The zero crossings of S₄(Λ) amply confirm the zero-crossing conjecture for metameric blacks.     

CIE1931色度图非线性均匀化

本文采用了一种全新的非线性均匀化方法,引入收缩参数,使用Matlab优化程序对C(?)E1931色谱图进行了优化变换,得到的新色谱图与C(?)E1960UCS色谱图相比,均匀性有了一定的改善。     

A system of photometry and colorimetry based on cone excitations

A system of photometry and colorimetry is proposed that is based upon cone action spectra. Instead of X, Y, Z tristimulus values, the new system divides the visual stimulus into L, M, and S components, which are related to the relative excitation levels of the three classes of human cone photoreceptors (long-wavelength-sensitive L, middle-wavelength-sensitive M, and short-wavelength-sensitive S). On the assumption that luminance is proportional to L + M, with S cones making no contribution to it, a chromaticity diagram results in which the relation between chromaticity coordinates and cone excitations is transparent, rather than inadvertently obscured as in the CIE system.     

Colour matching using LEDs as primaries

In our metameric experiment, the colour of a filtered incandescent lamp was matched with the additive mixture of three LEDs in a Lummer–Brodhun‐type visual photometer. Two sets of primaries were used, one had their dominant wavelengths at 467, 533, and 600 nm; the other set had dominant wavelengths at 478, 552, and 635 nm. These values correspond approximately to the characteristic wavelengths of the Prime and Non‐Prime Colour spectral regions defined by W. A. Thornton. 1 Both the light of the incandescent lamp and that of the LED clusters were seen monocularly in a centrally divided bipartite field at a visual angle of 2°. The luminance of the matching fields was in the order of 20 cd/m² to provide sufficient gamut for the LED mixture. Ten young observers with normal colour vision participated in the experiment. The emission spectra of the viewing fields were measured with an array‐type spectroradiometer, and two sets of colour‐matching functions were used to calculate the chromaticity of the matching stimuli: the CIE 1931 standard colorimetric observer and the Judd–Vos modification of the colour‐matching functions. We found that the Judd–Vos modification of the CIE 1931 standard observer represents more accurately the real observers in the evaluation of our results. No systematic differences between the use of the two sets of LEDs were detected in contradiction to Thornton's findings. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 360–364, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20044     

Color scales in simulated daylight

The pigmentation plan used for production of the color cards made available by the Optical Society of America (OSA) for its Committee on Uniform Color Scales (UCS) was designed in such a manner that the color scales should, within the production tolerances, appear uniform in all phases of daylight. The production specifications were based on D₆₅ of the Commission International de L'Eclairage (CIE) and the CIE supplementary observer (1964) for 10° visual-field subtense. To test for the intended invariance of uniformity of the scales in daylight, for normal observers, the effects on color differences between all nearest neighbors of the OSA colors have been studied for CIE Illuminant C with the 1931 observer, and for a “daylight” fluorescent luminaire (color temperature 6500 K) with both the 1931 and 1964 CIE observers. Although the colorimetric specifications (Y, x, y) of each color card are different for those three illuminant + observer combinations, the color differences computed with the formula of the OSA-UCS committee are, within the production tolerances, unchanged. The purpose of this article is to show how well the aim and expectation is fulfilled—that the uniformity of color differences between nearest neighbors in the scales of the OSA-UCS colors be essentially unchanged for normal observers and for ordinary variations of the quality of natural and artificial daylight. This invariance is found, even for daylight-quality fluorescent-lamp light.     

Specification of individual variation in luminous efficiency for brightness

Principal component analysis was applied to spectral luminous efficiencies determined by the heterochromatic brightness matching by 51 and 70 observers for the field size. 2° and 10°, respectively, which were used to derive the CIE V_b,2(Λ) and V_b,10(Λ). Four principal components were found to explain the individual variation. the two deviation indices were introduced by slightly modifying the first and second principal scores and they were effectively used to specify individual variations and to predict the spectral luminous efficiency curve. Equations were derived to predict these two deviation indices as functions of luminous efficiencies at two wavelengths, 460 and 640 nm in the case of 2° field and 470 and 630 mm in 10° field. the luminous efficiency curves thus predicted by the two deviation indices fitted very nicely to the experimentally determined luminous efficiency curves of all the observers. A way to utilize the deviation indices in practice where observers play an important role is proposed to avoid some confusion that may take place because of individual variation.     

Preference index for Japanese complexion under illuminations

This article proposes a useful evaluation method based on preferred complexion as one of color‐rendering methods of light sources. A relational equation between subjective evaluation values of preferred Japanese complexion under various illuminations and the D65 corresponding colors by adopting CIE94 chromatic adaptation transform on the CIE 1976 u′v′ chromaticity diagram was derived by using multiple regression. Then, preference index of skin color or PS was developed in order to evaluate quantitatively the degrees of preferred complexion from the equation. Furthermore, a new index PS_(ac,bc) was derived by using CAM02 color appearance model instead of the CIE94. Each relationship of R_a, R₁₅, CQS, MCRI, FCI, CCRI, and HCR to PS was examined. Then, the PS was found as an independent index which was quite different from the other indices when the PS was more than or equal to 80. Therefore, it is useful to develop and evaluate light sources to realize more comfortable lighting environments by applying the concept of the PS. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 143–153, 2016     

Concerning the calculation of the color gamut in a digital camera

Several methods to determine the color gamut of any digital camera are shown. Since an input device is additive, its color triangle was obtained from their spectral sensitivities, and it was compared with the theoretical sensors of Ives‐Abney‐Yule and MacAdam. On the other hand, the RGB digital data of the optimal or MacAdam colors were simulated to transform them into XYZ data according to the colorimetric profile of the digital camera. From this, the MacAdam limits associated to the digital camera are compared with the corresponding ones of the CIE‐1931 XYZ standard observer, resulting that our color device has much smaller MacAdam loci than those of the colorimetric standard observer. Taking this into account, we have estimated the reduction of discernible colors by the digital camera applying a chromatic discrimination model and a packing algorithm to obtain color discrimination ellipses. Calculating the relative decrement of distinguishable colors by the digital camera in comparison with the colorimetric standard observer at different luminance factors of the optimal colors, we have found that the camera distinguishes considerably fewer very dark than very light ones, but relatively much more colors with middle lightness (Y between 40 and 70, or L* between 69.5 and 87.0). This behavior is due to the short dynamic range of the digital camera response. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 399–410, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20245     

A versatile radiochromic dosimeter for low‐medium gamma radiation and its application to food irradiation

This article presents a novel radiochromic film for selective detection of low‐medium (0–10 kGy) gamma radiation (⁶⁰Co) doses. This dosimeter is based on a printed fluorescent multilayer structure comprising a paper substrate having layers of copper phthalocyanine (DY220) (a green emitter material) on the bottom, and layers of poly[2‐methoxy‐5(2′‐ethylhexyloxy)‐p‐phenylenevinylene] (MEH‐PPV) (a green‐light absorber, red emitter, and radiation sensitive polymer) on the top. The effect of gamma radiation on the optical properties of DY220/MEH‐PPV was described: it was observed as a strong correlation between radiation dose and fluorescent, color coordinates for CIE (1931) chromatic diagram, and Pantone color reference of the dosimeter. The rate of these changes can be altered by manipulation of top–bottom layers to represent easily the radiation dose to be determined in a wide range. This versatile dosimeter has many uses in the field of food radiation for monitoring, quality assurance, and control of the gamma radiation process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45729.     

New deviate observer (JF‐DO) obtained from experimental color‐matching functions for small fields of real observers

The CIE established the Standard Deviate Observer (SDO) CIE 1989 for fields of 10°, enabling the evaluation of discrepancies caused by the variability among these observers. This observer could also be applied to smaller fields, depending on the physiological causes of this variability in color‐matching functions (cmf's) among observers. Here, we have obtained a new Deviate Observer (which we call JF‐DO) established from the cmf's for small fields (2°) corresponding to two groups of real observers: JAM, MM and CF; AY, JR, MR, JL, JA and FA. Both groups of cmf's were measured experimentally in our laboratories using one for each of the different experimental methods and devices. All the new cmf's of the 9 real observers were referred to a new, unique system of unreal primaries, which we call X′Y′Z′ (derived in a way similar to that of the CIE 1931 XYZ system of unreal primaries). To establish a new JF‐DO for small fields, we followed a procedure similar to the one used by the CIE to establish the CIE 1989 SDO. A comparative study was also made between the cmf's of the CIE 1989 SDO (established for fields of 10°), the SDO from Stiles‐Burch (which we call Poza‐SDO, developed for small fields), and our JF‐DO. For this comparison, the cmf's of all these deviate observers were referred to the new system of unreal primaries X′Y′Z′. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 209–215, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10146     

The quantification of small visual colour differences

The Shademaster system, developed at UMIST, was used to explore the use of on-screen colour in order to assess the reliability of the CMC(l:c) formula as a measurement of small colour differences. Differences limited to almost pure hue, chroma and lightness changes around nine colour centres were judged by a group of ten observers. Each colour difference pair was presented on-screen in the form of a divided tile. The colour difference between each pair was measured using a Bentham telespectroradiometer and by a method using reverse transformation of RGB to CIE coordinates. The resultant measurements were used to determine the visibility of a particular colour difference, how that visibility varied from colour to colour and how it varied in different directions (i.e. hue, chroma or lightness). The data obtained from the judgements were used to construct perceptibility boundaries around each colour centre.     

A better colorimetric standard observer for color-vision studies: The stiles and burch 2° color-matching functions

The validity of the 1931 CIE Standard Observer color-matching functions (c.m.f.) rests on the assumption that V_λ is a linear combination of actually measured c.m.f. It is shown here that no combination of c.m.f. can reproduce any photometric function. For research on basic questions of color vision it is suggested that the c.m.f. of the Stiles and Burch 2° preliminary study be used. These c.m.f. are reproduced here, after correction and renormalization for a calibration error in the original study. Since photometry appears to be intrinsically more complicated and less well understood than basic colorimetry, it is also suggested the two disciplines be considered as separate aspects of the visual process.