@article{kuehni_2016, title={How Many Object Colors Can We Distinguish?}, volume={41}, ISSN={["1520-6378"]}, DOI={10.1002/col.21980}, abstractNote={AbstractThe question of how many different colors humans can perceive has been of interest to philosophers, psychologists and color scientists for centuries. In recent years the question of the number of distinguishable object color stimuli has been addressed by color scientists by defining a distinguishable color as a given stimulus surrounded by the contour of stimuli just noticeably different from the central stimulus. For a particular set of conditions the number of distinguishable object color stimuli assessed in this manner has recently been found to be slightly larger than 2 million. In this article an argument is made that the related rules are arbitrary and unnecessarily limiting. Based on logical arguments and experimental just noticeable difference data it is shown that, for the conditions involved, a more realistic if conservative number of distinguishable object color stimuli is ∼40 million. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 439–444, 2016}, number={5}, journal={COLOR RESEARCH AND APPLICATION}, author={Kuehni, Rolf G.}, year={2016}, month={Oct}, pages={439–444} }
 @article{shamey_sawatwarakul_kuehni_2015, title={Cognitive Comparison of Unique and Intermediate Hues}, volume={40}, ISSN={["1520-6378"]}, DOI={10.1002/col.21875}, abstractNote={AbstractEight panels were prepared using the most highly chromatic Natural Colour System (NCS) samples for each hue. Each panel consisted of a test hue and two reference hues, the samples representing either mean unique hues (uH) R, Y, B, or G as determined in earlier experiments or intermediate hues half way between them, (iHs) Or, Pp, YG, and BG. Subjects were asked to determine whether they considered it possible to match the test hue with the reference hues. A total of 45 color‐normal subjects participated in the study in three separate trials with at least 24 h gap between consecutive trials. The results, with very few exceptions, showed that a match was considered possible for the four iHs based on a mixture of adjacent pairs of uHs, while the majority did not believe uHs could be matched based on amounts of adjacent iHs. Statistical analysis of the test results indicates that responses for the two sets of panels were significantly different (P ∼ 0, df = 539). The results provide support for Hering's uHs concept. However, a number of subjects believed that a mixture of adjacent iHs can result in a match of the reference uHs. Potential causes may include the use of experimental mean unique and intermediate hues and learned facts of colorant mixture. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 264–269, 2015}, number={3}, journal={COLOR RESEARCH AND APPLICATION}, author={Shamey, Renzo and Sawatwarakul, Weethima and Kuehni, Rolf G.}, year={2015}, month={Jun}, pages={264–269} }
 @article{cao_castle_sawatwarakul_fairchild_kuehni_shamey_2014, title={Scaling perceived saturation}, volume={31}, ISSN={["1520-8532"]}, DOI={10.1364/josaa.31.001773}, abstractNote={Two psychophysical experiments were conducted at North Carolina State University (NCSU) and Rochester Institute of Technology (RIT) to obtain replicated perceived saturation data from color normal observers on the order of one unit of saturation. The same 37 Munsell sample sheets, including up to four references that had similar perceived saturation but different hue, were used in both experiments. Different assessment methods included presenting either four references simultaneously or only one reference at a time to observers and obtaining judged saturation magnitudes for the given Munsell samples. Four saturation models comprising Sab*, Suv*, CIECAM02, as well as Richter/Lübbe, were tested. CIECAM02 gave the best prediction of saturation for data obtained at NCSU while Sab* outperformed other models for the RIT data. For the combined dataset, Sab*, the Richter/Lübbe, and CIECAM02-based saturation models exhibited comparable performances. The Standardized Residual Sum of Squares index was used to measure the inter- and intra-observer variability and goodness of fit. Inter- and intra-observer variability of assessments was smaller than or comparable to those reported for the typical color difference evaluation experiments.}, number={8}, journal={JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION}, author={Cao, R. and Castle, M. and Sawatwarakul, W. and Fairchild, M. and Kuehni, R. and Shamey, R.}, year={2014}, month={Aug}, pages={1773–1781} }
 @misc{kuehni_2014, title={Unique Hues and Their Stimuli-State of the Art}, volume={39}, ISSN={["1520-6378"]}, DOI={10.1002/col.21793}, abstractNote={AbstractThe relationship between the information the visual system gathers at its interface with the outside world and the perceptual reality of four primary hues and the resulting hue circle has been and remains of interest since the second half of the 19th century. Considerable effort has been expended over many decades in determining statistical mean choices of color stimuli that for individuals represent unique hues in given conditions of viewing. In this article, historical and recent data are used to show the present state of knowledge. To have a means of comparison, in this article spectral and display unit stimuli are converted to Munsell hues on basis of dominant or complementary wavelengths of highest chroma data. Relatively good agreement was found between spectral and color sample data, with display data being significantly different in case of unique green. The issue of significant interobserver variability found in all data and its implications are highlighted. Problems with generating simple psychophysical models, particularly related to unique red, are discussed and a brief survey of the current knowledge on neural processing that may lead to unique hue perception is presented. Data still required for a meaningful definition of mean unique hue stimulus data are listed. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 279–287, 2014; Published Online 20 March 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/col.21793}, number={3}, journal={COLOR RESEARCH AND APPLICATION}, author={Kuehni, Rolf G.}, year={2014}, month={Jun}, pages={279–287} }
 @article{shamey_shepherd_abed_chargualaf_garner_dippel_weisner_kuehni_2011, title={How well are color components of samples of the Natural Color System estimated?}, volume={28}, ISSN={["1520-8532"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-80053594693&partnerID=MN8TOARS}, DOI={10.1364/josaa.28.001962}, abstractNote={The aim of this study was to determine how accurately color-normal subjects that have received basic information about, but do not have practical experience with, the Natural Color System (NCS) can estimate the Heringian components of a representative selection of samples. Twenty-five color-normal subjects, taking part in two trials with at least a 24 h gap between assessments, selected four samples representing individual unique hues (uHs) from a set of 40 highly chromatic NCS samples on a rotatable tray. The samples selected for assessment of components were displayed to the subjects who estimated the hue components of 16 high-chroma samples, hue and white/black components of 16 tonal color samples, and three achromatic samples with different blackness values. Variability in selection of samples representing uHs as well as the relationship between the subjects' estimates of unique hue components and the defined values of the system was obtained. It was found that hues alone are easier to correctly estimate than hues together with white and black and that the components of colors of higher chroma are easier to estimate accurately than those of lower chroma. It was also found that, for R and G, the mean uH choices of subjects differed very little from the NCS's R and G, whereas selections for yellow and blue deviated, the former by 1.22 hue steps (slightly greener than G90Y), and the latter by 1.36 hue steps (represented approximately by R85B). This may impact the accuracy of color models that employ NCS unique hues.}, number={10}, journal={JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION}, author={Shamey, Renzo and Shepherd, Sarah and Abed, Mira and Chargualaf, Michael and Garner, Nicholas and Dippel, Nicholas and Weisner, Nathan and Kuehni, Rolf G.}, year={2011}, month={Oct}, pages={1962–1969} }
 @article{shamey_sedito_kuehni_2010, title={Comparison of Unique Hue Stimuli Determined by Two Different Methods Using Munsell Color Chips}, volume={35}, ISSN={["1520-6378"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78349293404&partnerID=MN8TOARS}, DOI={10.1002/col.20560}, abstractNote={AbstractUnique hue stimuli were determined by male and female observers using two different visual experimental procedures involving Munsell color chips of varying hue but identical chroma and value. The hypothesis was that unique hues can be more reliably established by explicit selection from a series of ordered stimuli than implicitly by hue scaling a series of stimuli in terms of neighboring UHs and this was statistically confirmed. The implicit selections based on long term memory of UHs appears to have been more challenging to observers since variability was increased by nearly 50% compared to when UHs were explicitly selected. The ranges of unique hues selected in the two methods were, however, comparable and no statistically significant difference was found between the results of females and males. The intra‐observer variability in picking a stimulus to represent a unique hue, for all observers and averaged for all hues, was approximately 12% of the mean spread of unique hues, confirming that the large inter‐observer variability is driven by differences in color vision and perhaps cognitive processes. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010}, number={6}, journal={COLOR RESEARCH AND APPLICATION}, author={Shamey, Renzo and Sedito, Michael G. and Kuehni, Rolf G.}, year={2010}, month={Dec}, pages={419–424} }
 @article{kuehni_shamey_mathews_keene_2010, title={Perceptual prominence of Hering's chromatic primaries}, volume={27}, ISSN={["1520-8532"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-76749144264&partnerID=MN8TOARS}, DOI={10.1364/josaa.27.000159}, abstractNote={Reported are results of an experiment involving perceptual assessment of very large color differences using samples representing approximate mean Hering opponent generic unique hues (guHs) based on subject selections, intermediate hues (iHs) using Munsell samples intermediate between guHs, and pairings of both guHs and iHs with a neutral gray. Sample pairs were assessed by 28 color normal subjects twice, with a gap of at least 24 hours between assessments. Results were calculated for individual subjects and the entire group. The hypothesis was that perceived chromatic differences of Hering's guHs are larger than those of iHs, and this was found to be statistically valid at the 99% confidence level based on a t-test. In addition, gray as a percept was found to have prominence comparable to that of generic unique hues.}, number={2}, journal={JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION}, author={Kuehni, Rolf G. and Shamey, Renzo and Mathews, Mara and Keene, Brandi}, year={2010}, month={Feb}, pages={159–165} }
 @article{kuehni_hardin_2010, title={Churchland's Metamers}, volume={61}, ISSN={["1464-3537"]}, DOI={10.1093/bjps/axp021}, abstractNote={Paul Churchland proposed a conceptual framework for translating reflectance profiles into a space he takes to be the color qualia space. It allows him to determine color metamers of spectral surface reflectances without reference to the characteristics of visual systems, claiming that the reflectance classes that it specifies correspond to visually determined metamers. We advance several objections to his method, show that a significant number of reflectance profiles are not placed into the space in agreement with the qualia solid, and produce two sets of counterexamples to his claim for metamers. 1. Introduction2. Preliminary Explanations and Objections 2.1. Color spaces and solids2.2. Visual metamers2.3. Matching and appearance2.4. Effect of light on appearance of objects3. Churchland's ‘Canonical Approximation’ Hypothesis4. Does the CA Cylinder House SSRs in Agreement with the Perceptual Color Solid?5. Two Sets of Metameric Counterexamples 5.1. Three metameric grays5.2. Three metameric yellows6. Birds, Bees, and Anthropocentrism Redux Introduction Preliminary Explanations and Objections 2.1. Color spaces and solids2.2. Visual metamers2.3. Matching and appearance2.4. Effect of light on appearance of objects Color spaces and solids Visual metamers Matching and appearance Effect of light on appearance of objects Churchland's ‘Canonical Approximation’ Hypothesis Does the CA Cylinder House SSRs in Agreement with the Perceptual Color Solid? Two Sets of Metameric Counterexamples 5.1. Three metameric grays5.2. Three metameric yellows Three metameric grays Three metameric yellows Birds, Bees, and Anthropocentrism Redux}, number={1}, journal={BRITISH JOURNAL FOR THE PHILOSOPHY OF SCIENCE}, author={Kuehni, Rolf G. and Hardin, C. L.}, year={2010}, month={Mar}, pages={81–92} }
 @article{kuehni_2008, title={Color difference formulas: An unsatisfactory state of affairs}, volume={33}, ISSN={["0361-2317"]}, DOI={10.1002/col.20419}, abstractNote={AbstractColor difference formulas are of considerable importance in production control of colored materials, as they offer a kind of quantitative numerical method to predict perceived differences. Current formulas are based on various sets of empirical difference perception data established with different kinds of materials, under different evaluation conditions, and with different observer panels. The best current formulas predict the average of these perceptual data only with an accuracy of about 65%, a PF/3 value of about 35 (zero being optimal). This article argues that this is an unsatisfactory state of affairs and proposes the development of new uniformly established perceptual data and a new formula/system that predicts the visual results, statistically verified to represent the world‐average observer, with an accuracy of 95%, a PF/3 value (or appropriate improved measure) of 5 or lower. Such a multiyear effort requires a solid experimental plan and a consortium supported by Government and industry to achieve its goal. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 324–329, 2008.}, number={4}, journal={COLOR RESEARCH AND APPLICATION}, author={Kuehni, Rolf G.}, year={2008}, month={Aug}, pages={324–326} }
 @book{kuehni_schwarz_2008, title={Color ordered a survey of color order systems from antiquity to the present}, publisher={Oxford ;|aNew York: Oxford University Press}, author={Kuehni, Rolf G. and Schwarz, Andreas}, year={2008} }
 @article{kuehni_hinks_shamey_2008, title={Experimental Object Color Unique Hue Data for the Mean Observer for Color Appearance Modeling}, volume={33}, ISSN={["0361-2317"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-63349089809&partnerID=MN8TOARS}, DOI={10.1002/col.20449}, abstractNote={AbstractColor appearance models, among other things, predict the hue of a stimulus when compared with defined stimuli that represent the four unique hues. Recent studies have indicated that the stimuli representing with high reliability unique hue (UH) percepts vary widely for different color‐normal observers. The average yellow and blue UH stimuli for 102 observers, as determined in a recent experiment at medium chroma, differ considerably from the CIECAM02 defined unique hues, based on the Swedish NCS. Wide inter‐observer variability precludes color appearance models from accurately predicting, for individual observers, all four unique hue stimuli. However, models should predict accurately those of a well‐defined average observer. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 505–506, 2008}, number={6}, journal={COLOR RESEARCH AND APPLICATION}, author={Kuehni, Rolf and Hinks, David and Shamey, Renzo}, year={2008}, month={Dec}, pages={505–506} }
 @article{hinks_cardenas_kuehni_shamey_2007, title={Unique-hue stimulus selection using Munsell color chips}, volume={24}, ISSN={["1084-7529"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-36949037955&partnerID=MN8TOARS}, DOI={10.1364/JOSAA.24.003371}, abstractNote={Presented are intra- and inter-observer variability data comparing the unique-hue (UH) selections of sets of males and females, using two different visual experimental procedures incorporating Munsell color chips of varying hue but identical chroma and value. Although 34 of the 40 Munsell hue chips were selected by at least one observer as a UH, selections were generally repeatable. In addition, intra-observer variability represented approximately 15% of inter-observer variability. Also, when only three consecutive Munsell chips were viewed at a time, females showed significantly larger intra-observer variability than males, especially when making unique green selections. However, variability in UH selections was statistically insignificant between males and females when all Munsell chips were viewed simultaneously. No correlation was found between UH selections or intra-observer variability and hue ordering ability.}, number={10}, journal={JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION}, author={Hinks, David and Cardenas, Lina M. and Kuehni, Rolf G. and Shamey, Renzo}, year={2007}, month={Oct}, pages={3371–3378} }
 @article{kuehni_2007, title={Ludwig Pilgrim, a pioneer of colorimetry}, volume={32}, ISSN={["0361-2317"]}, DOI={10.1002/col.20288}, abstractNote={AbstractColorimetry derives from the early efforts of Newton, Young, Maxwell, and Helmholtz. In 1901 Pilgrim published a paper in which he quantitatively described a colorimetric system both in trichromatic as well as opponent color format. He appears to be the first to have offered a depiction of the cone‐shaped surface of spectral vectors in the space of color fundamentals. © 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 5–10, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20288}, number={1}, journal={COLOR RESEARCH AND APPLICATION}, author={Kuehni, Rolf G.}, year={2007}, month={Feb}, pages={5–10} }
 @article{brown_kuehni_hinks_2006, title={The Villalobos Colour Atlas: An analysis}, volume={31}, ISSN={["1520-6378"]}, DOI={10.1002/col.20188}, abstractNote={AbstractThe Villalobos Colour Atlas with its 7273 samples, published in 1947 in Argentina, represents one of the most ambitious attempts at a systematic object color sample collection. Its authors saw it as a practical visual color measuring and specification instrument at a time when spectrophotometers were a rarity in research institutes. In part, its organization is similar to that of the Munsell system but differs in regard to saturation. After a brief description of the structure of the Atlas data, what may be the first extensive measurement data of samples of the Atlas is presented in the CIELAB system. The results, unsurprisingly, show that the Atlas (as represented by the over‐60‐year‐old copy) meets some of its stated goals only to a limited extent. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 109–116, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20188}, number={2}, journal={COLOR RESEARCH AND APPLICATION}, author={Brown, M and Kuehni, RG and Hinks, D}, year={2006}, month={Apr}, pages={109–116} }
 @book{kuehni._2005, title={Color an introduction to practice and principles}, publisher={Hoboken: J Wiley & Sons}, author={Kuehni., Rolf G.}, year={2005} }
 @article{kuehni_ramanath_2006, title={Sensing spectral stimuli: Sensor functions and number}, volume={31}, ISSN={["1520-6378"]}, DOI={10.1002/col.20171}, abstractNote={AbstractUsing synthesized and real spectra this article addresses questions regarding the degree to which synthetic and real sensor systems with one, two, and three sensors can distinguish among stimuli and can reconstruct the original spectra. Based on 64 synthetic spectra, the trichromatic sensors L, M, S distinguish the spectra at the level of 85% of the optimal result but reconstruct them only at the level of 70%. For symmetrical and symmetrically placed sensors the corresponding values are 76 and 94%. The conclusion is drawn that distinguishability was a more important goal of evolution than reconstructability. © 2005 Wiley Periodicals, Inc. Col Res Appl, 31, 30–37, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20171}, number={1}, journal={COLOR RESEARCH AND APPLICATION}, author={Kuehni, Rolf G. and Ramanath, Rajeev}, year={2006}, month={Feb}, pages={30–37} }
 @article{kuehni_2005, title={The  CMC(l: c) color difference formula and the values for the weights l and c}, volume={5}, number={11}, journal={AATCC Review}, author={Kuehni, R. G.}, year={2005}, pages={25–26} }
 @article{kuehni_2005, title={Visual color difference evaluation, mind the conditions}, volume={5}, number={9}, journal={AATCC Review}, author={Kuehni, R. G.}, year={2005}, pages={27–28} }
 @article{kuehni_ramanath_2004, title={Comparing observers}, volume={29}, ISSN={["1520-6378"]}, DOI={10.1002/col.20004}, abstractNote={AbstractColor‐matchingfunctions may be considered dimension reduction functions that project a spectral reflectance function into the desired space of colors. Using a gray metameric pair with maximal spectral difference we compare the abilities of various human and other observers with regard to the transition wavelengths for that metameric pair. Transition wavelengths are shown to be a convenient tool for comparing and classifying observers regardless of the number of dimension reduction functions. Four human observers were identified as differing in a comparable manner from the CIE 2° standard observer. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 183–186, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20004}, number={3}, journal={COLOR RESEARCH AND APPLICATION}, author={Kuehni, RG and Ramanath, R}, year={2004}, month={Jun}, pages={183–186} }
 @book{kuehni_2003, title={Color space and its divisions: Color order from antiquity to the present}, ISBN={0471326704}, DOI={10.1063/1.1650231}, abstractNote={Color Space and Its Divisions: Color Order From Antiquity to the Present , Rolf G. Kuehni Wiley, Hoboken, N.J., 2003. $99.95 (408 pp.). ISBN 0-471-32670-4 Buy at Amazon}, publisher={Hoboken, NJ: J. Wiley}, author={Kuehni, R. G.}, year={2003} }
 @article{kuehni_2003, title={Colour difference formulas: accurate enough for objective colour quality control of textiles?}, volume={119}, DOI={10.1111/j.1478-4408.2003.tb00167.x}, abstractNote={The best formulas for predicting mean perceived small colour differences of industrially produced coloured goods have an average accuracy of about 65%. This should be considered unsatisfactory. Factors that influence accuracy are discussed in this paper and a proposal is made for determining if the accuracy can be significantly improved as a preliminary step toward developing more reliable data and a formula to predict it.}, number={3}, journal={Coloration Technology}, author={Kuehni, R. G.}, year={2003}, pages={164–169} }
 @article{ramanath_kuehni_snyder_hinks_2004, title={Spectral spaces and color spaces}, volume={29}, ISSN={["1520-6378"]}, DOI={10.1002/col.10211}, abstractNote={AbstractIt has long been known that color experiences under controlled conditions may be ordered into a color space based on three primary attributes. It is also known that the color of an object depends on its spectral reflectance function, among other factors. Using dimensionality reduction techniques applied to reflectance measurements (in our case a published set of 1 nm interval reflectance functions of Munsell color chips) it is possible to construct 3D spaces of various kinds. In this article we compare color spaces, perceptual or based on dimensionality reduction using color matching functions and additional operations (uniform color space), to spectral spaces derived with a variety of dimensionality reduction techniques. Most spectral spaces put object spectra into the ordinal order of a psychological color space, but so do many random continuous functions. In terms of interval scales there are large differences between color and spectral spaces. In spectral spaces psychophysical metamers are located in different places. © 2003 Wiley Periodicals, Inc. Col Res Appl, 29, 29–37, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10211}, number={1}, journal={COLOR RESEARCH AND APPLICATION}, author={Ramanath, R and Kuehni, RG and Snyder, WE and Hinks, D}, year={2004}, month={Feb}, pages={29–37} }
 @article{kuehni_2002, title={A brief history of calico printing}, volume={2}, number={7}, journal={AATCC Review}, author={Kuehni, R. G.}, year={2002}, pages={7–11} }