Proceedings of 2nd International Symposium for Color Science and Art 2020

The Art of Color Science: Individual Differences
Mark D. Fairchild
Rochester Institute of Technology, Program of Color Science / Munsell Color Science Laboratory,
One Lomb Memorial Drive, Rochester, NY 14623 USA
nor interest in, carefully defining individual color matching
functions and the variance of the population.
One approach to efficiently defining individual color
matching functions has been Monte Carlo simulation of thevarious physiological parameters that make up color
matching functions (lens, macula, pigments) in order tosynthesize individual functions.[5] Such techniques have
proven quite accurate and effective. In addition, the CIE,
in 2006, defined more accurate mean functions forvariable age and field size [6] and Asano et al. refined theMonte Carlo techniques to the point that individualobservers
could
beaccuratelymodeledandcharacterized.[7]Ultimately, these advances have allowed systems ofindividual colorimetry to be practically implemented andthe first practical system to predict both mean color
matches and confidence volumes about such matches
representing the spread of the observer population as firstsuggested by Nimeroff et al. in 1961[8] and as pursued by
the author for approximately three decades.

ABSTRACTThe fundamental data of color science are color
matching functions, which represent the spectral
absorption properties of cone photoreceptors. All
colorimetry follows from these functions, which, instandard form, are intended to represent the averagesensitivities of the population of human observers withnormal color vision. Individuals are, however, individualand have their own color matching functions and othervisual responses that naturally vary from the mean. This
paper provides a review of the nature and magnitude ofindividual differences in color matching functions andother mechanisms of color perception along withsuggestions for practical systems to account for individual
differences in colorimetric practice.
1. The Big Questions
The two big questions discussed in this paper are (1)What do you see? And (2) Do you see what I see? Suchquestions often cross into the domain of the psychology
and philosophy of perception [1] or into the insoluble
questions of qualia [2] (e.g., is what you perceive whenseeing a stimulus described as red the same is what I
perceive when seeing a stimulus described as red).
However, these questions can be addressed to adegree from a more fundamental level. This isaccomplished by examining individual differences in theabsorption of light by the three cone classes in various
observers (individual differences in color matchingfunctions) and the anatomy and physiology underlying
them. The phenomena of individual differences in color
matching functions is often described under the rubric ofobserver metamerism (two stimuli that match in color toone observer might mismatch to another). In addition, thispaper examines individual differences in the higher-ordermechanisms of chromatic adaptation.

3. Chromatic Adaptation
Once cone signals are established through absorptionof light according to the cone responsivities (i.e. color
matching functions), they are subject to the mechanismsof chromatic adaptation to produce signals that ultimately
correlate with color appearance. While it is wellestablished that there are individual differences in color
matching functions, the question of whether there areadditional individual differences in chromatic adaptation
mechanisms (not due to the CMFs themselves) remains
open. One reason this has not been previously explored in
the context of color appearance is that correspondingcolors data, required to quantify chromatic adaptation
mechanisms, are often very imprecise and any potential
individual differences are masked by uncertainty in theresults. Once averaged across observers, correspondingcolors data are well described using the von Kries
hypothesis, and modern implementations of what is now
called the von Kries model, that dates back more than acentury.[9]More recently, research has been completed to obtainsignificantly more precise corresponding colors data.[10]These results indicate that there are very significant
individual differences in chromatic adaptation and that it
might be necessary to have individual models of chromaticadaptation, in addition to individual CMFs, in order toproperly predict appearance.

2. Color Matching Functions
The CIE standard colorimetric observer was first
defined in 1931 (with a second version established in 1964
for larger fields of view) as well understood and utilized inpractical colorimetry.[3] These functions were intended torepresent the color sensitivities of a mean, or average,observer and they have performed admirably in that rolefor nearly a century. It has also long been known that
individual observers exhibit significant variation about
those means in their color matching function data.[4]However, until recently, there were neither resources for,29

Proceedings of 2nd International Symposium for Color Science and Art 2020
promise for an improved future system of colorimetry isstrong.

Additionally, the results indicated that it might bepossible that chromatic adaptation is not reversible.[11] Inother words, when given a reference color under lightsource A and asked to select a corresponding color underlight source B, the answer might differ from the reverse
task when the reference is under source B and the matchis selected under source A. Chromatic adaptation might
not follow a transitive property across changes inillumination. This result is surprising and requires
additional data to be confirmed. Such research is now
underway.
Putting this all together allows improvements in avariety of applications such as the potential for
individualized color reproduction for high-quality
applications and quantifying the individual variability inassessment and specification of the color rendering
properties of illumination.[13]6. REFERENCES[1] D. Katz, “The World of Colour,” Kegan Paul, London(1935).
[2] D. Dennett,“Quining Qualia,” in Mind and Cognition,
W. Lycan (ed.), Oxford: Blackwell, 519–548 (1990).
[3] CIE, “Colorimetry, 4th Ed.,” CIE 015:2018 (2018).
[4] G. Wyszecki and W.S. Stiles, “Color Science, 2nd Ed.”
Wiley, New York (1982).
[5] M.D. Fairchild and R.L. Heckaman, “Metamericobservers: A Monte Carlo approach,” pp.185-190,
IS&T 21st Color & Imaging Conference,Albuquerque (2013).
[6] CIE, “Fundamental Chromaticity Diagram with
Physiological Axes - Part 1,” CIE 170:2006 (2006).
[7] Y. Asano, M.D. Fairchild, and L. Blondé, “Individualcolorimetric observer model,” e0145671 , PLOS
ONE, Vol. 11 (2016).
[8] I. Nimeroff, J.R. Rosenblatt and M.C. Dannemiller,“Variability of spectral tristimulus values,” pp.475483, J. Research NBS A, Vol. 65A, No. 6 (1961).
[9] J. von Kries, “Chromatic adaptation,” Festschrift derAlbrecht-Ludwig-Universität, (Fribourg) (1902)[Translation: D.L. MacAdam, Sources of Color
Science, MIT Press, Cambridge, (1970)].
[10] S. Cai and M.D. Fairchild, “Individual correspondingcolors data and chromatic adaptation transform,” pp.
248-253, IS&T 24th Color & Imaging Conference,
San Diego (2016).
[11] S. Cai and M.D. Fairchild, “Bidirectional individualcorresponding colors data,” pp.643-654, Color
Research and Application , Vol. 43 (2018).
[12] M.D. Fairchild, “What sets the state of chromaticadaptation?,” in press, OSA Fall Vision Meeting,Washington, D.C. (2019).
[13] M.J. Murdoch and M.D. Fairchild, “Modeling theeffects of inter-observer variation on color rendition,”
pp.1-18, Lighting Research and Technology, Vol. 49(2017).
[14] H.L. DeVries, “The fundamental response curves ofnormal and abnormal dichromatic and trichromaticeyes,” Physica, pp.367-380, Vol. 14 (1948).
[15] G. Jordan and J.D. Mollon, “A study of womenheterozygous for color deficiencies,” Vision Res.,
pp.1495-1508, Vol. 33, No. 11 (1993).
[16] G. Jordan, S.S. Deep, J.M. Bosten, and J.D. Mollon,“The dimensionality of color vision in carriers ofanomalous trichromacy,” J. Vision, 12, Vol. 10, No. 8(2010).

4. A Note On Tetrachromacy
One topic of individual differences that has recently
sparked more interest than warranted is the potential for
tetrachromacy in female carriers of anomaloustrichromacy. The potential for female trichromacy wasdiscussed as early as 1948[14] and speculated upon
decades earlier.[15] Because these females, especially ifthey have one son with normal color vision and anotherwith anomalous trichromacy, have the genetic coding for
four distinct classes of cones, it is likely that they have fourclasses of cones in their retina. However, what seems
likely, and perhaps ubiquitous, is that these women still
have trichromatic color appearance such that the fourcone classes are fed into three color responses at somepoint in the visual system. No female observer has yet
been identified with strong tetrachromacy (a fourdimensional color space) although Jordan et al.[16] did
manage to find one female carrier out of 24 evaluated thatshowed some signs of additional discrimination ability.
However, the extra dimension was not fully established inthat work and there are no indications of observers who
cannot function with trichromatic color reproduction (i.e.
would require a fourth primary in imaging systems) so it ispossible there are not functional, or strong, tetrachromats
despite the potential being there.
6. Conclusions
Colorimetry has been successful for nearly a decade
based on the psychophysical measurement and modelingof average, or mean, observers in terms of color matching
functions and chromatic adaptation models. More recent
data suggest that individual differences in both can havesignificant impact on the correlation between predicted
matches and appearance and individual visualassessments. Fortunately advances are underway toallow colorimetry to be personalized for individual
differences in both aspects of color perception and the30