Lightness and Brightness and Other Confusions

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greater than the smallest colour differences that they can distinguish. Any observer whose variation from the standard was much greater than his ability to distinguish differences would be dissatisfied with the match. 2 It is possible to determine the extent of matching differences among normal observers and to gain some insight into the causes of the variation. 3 Using an instrument called the anomaloscope, a standard instrument for diagnosing colour deficiencies, colour-normal observers are asked to match an orange test hemifield with a mixture hemifield of red and green primaries in which the observer can set the red/green ratio. For men, the distribution of ratios is bimodal, falling into two distinct groups, with 60 percent of the observers in one group and 40 percent in the other. The distribution of ratios for women is unimodal, and broader than that for men. In the last decade it has been shown that these distributions are correlated with genetically based polymorphisms of longwave and middlewave cone photopigments. The match that an observer makes between the two hemifields of an anomaloscope is a metameric match. The two sides have different spectra, but when the match is made, they look identical. Although metameric matches are rare in nature, they are very common in the modern world; the images of colour photography and colour television are metameric or approximately metameric matches to the colour appearances of the objects that they represent, as are most colorant matches. Because of inevitable variations in viewing conditions and in observers, such matches are to one degree or another problematic and rely on the large reservoir of forgiveness that the human brain has for colour variation when the samples are not put side by side. Observers differ from each other in their colour-matching and metameric classes, so it should come as no surprise that their opponent responses are different. In fact, the differences are large enough to be shocking, as we shall now see. The stimulus locus for a perception of unique hue has been studied with a variety of techniques for many years. Every study with a reasonably large number of observers has found a wide distribution of unique hue loci among normal perceivers. Because the studies have used different experimental protocols and different perceiver groups, the mean results do not agree well across experiments, but substantial variability among observers within any given study is a constant. It is often supposed that more “naturalistic” experiments using surface colours will reduce the amount of variance from one observer to another, so here are the results of a recent hue experi- 2 Evans, R. M. (1948). An Introduction to Colour. John Wiley and Sons, New York, 196- 77 3 See Neitz, M. and Neitz, J. (1998) Molecular Genetics and the Biological Basis of Colour Vision, in W. G. K. Backhaus, R. Kliegl, and J. S. Werner (eds.), Colour Vision: Perspectives from Different Disciplines. Walter de Gruyter, Berlin , 101-119. 12
P Y ment with coloured Munsell papers. 4 A 40-step hue set of constant lightness and chroma was used. The Munsell chips are approximately perceptually equispaced, so each chip is 1/40 of the hue circle. Observers adapted to a standard illuminant and viewed the chips against a light grey background. The figure shows the range of mean unique hue choices. Each observer performed the experiment three times. This enabled a comparison of variability within and between observers. 90 10 P 95 2,5 RP 5 RP 7,5 RP RP 100 10 RP 2,5 R 5 5 R R 7,5 R 10 10 R 2,5 YR YR 15 5 YR 7,5 YR 10 YR 20 2,5 Y 7,5 P 85 25 5 P 5 Y 80 10 PB 2,5 P 7,5 PB N 7,5 Y 2,5 GY 10 Y 30 PB GY 5 PB 75 5 GY 35 2,5 PB 7,5 GY 10 B 70 7,5 B 5 B 65 B 2,5 B 10 BG 60 7,5 BG BG 5 BG 55 2,5 BG G 10 G 50 7,5 G 5 G 45 2,5 G 10 GY 40 Figure 1. Conceptual hue circle diagram of the Munsell system with the ranges of samples (marked with arrows) selected to represent the four unique hues of the Hinks et al. experiment. Only about 15% of the variability is intra-observer. The sum of the ranges in the diagram showing individual unique hue sample choices is 57.5% of the total. Observers can vary significantly in their individual “signatures” of unique hue choices. This suggests that there may not be a simple mechanism guiding unique hue stimulus choices. Perhaps past visual experiences are 4 Hinks, D., L. Cardenas, R. Shamey, R. G. Kuehni. (2007) Unique Hue Stimulus Selection Using Munsell Color Chips. Journal of the Optical Society of America A 26, 3371- 3378. 13
Page 5: Contents Foreword .................
Page 8 and 9: faculties. It is therefore most fit
Page 10 and 11: We are left with the paint chip. He
Page 12 and 13: The domain of colour psychophysics
Page 16 and 17: involved. It is worth mentioning th
Page 18 and 19: Ulf Klarén Natural Experiences and
Page 20 and 21: that without “benefit of logic”
Page 22 and 23: er of mental categories perceptions
Page 24 and 25: ence derives its origin from multip
Page 26 and 27: oth for perception of lightness (Gi
Page 28 and 29: knowledge constitutes logical knowl
Page 30 and 31: INDIRECT EXPERIENCE culturally tran
Page 32 and 33: tinctions and colour similarities.
Page 34 and 35: References Baumgarten, Gottlieb (19
Page 36 and 37: Harald Arnkil Seeing and Perceiving
Page 38 and 39: ception is entirely integrated with
Page 40 and 41: parallel lines although they almost
Page 42 and 43: What Gregory is saying is that at t
Page 44 and 45: Zeki goes on to say to say that Mon
Page 46 and 47: References Billger, Monica (1999).
Page 48 and 49: Light and colour as experienced thr
Page 50 and 51: conventional concepts, which can be
Page 52 and 53: could be called the constancy colou
Page 54 and 55: colours yellow, red, blue and green
Page 56 and 57: etween about 380 and 780 nm, which
Page 58 and 59: Cadmium Red 1.0 0.8 0.6 0.4 0.2 0 4
Page 60 and 61: meaning of the word to be more corr
Page 62 and 63: Examples of photometric concepts an
Page 64 and 65:
Examples of colorimetric concepts a
Page 66 and 67:
Figure 15. Visual measuring of nomi
Page 68 and 69:
References Billger, M. (1999). Colo
Page 70 and 71:
Especially problematic is the situa
Page 72 and 73:
continually confused with each othe
Page 74 and 75:
W 05 10 20 30 40 50 C 60 90 70 80 7
Page 76 and 77:
elation to the light source or obse
Page 78 and 79:
ecause the lower reflectance of p i
Page 80 and 81:
and religious symbolism. It is also
Page 82 and 83:
Munsell’s principal hues and Heri
Page 84 and 85:
As the inks developed the three-pri
Page 86 and 87:
David Hubel has proposed that the f
Page 88 and 89:
any hue is one of constant value. I
Page 90 and 91:
saturation, taken together, and is
Page 92 and 93:
Discussion From all of this one may
Page 94 and 95:
The real colours of objects To see
Page 96 and 97:
measured either trichromatically wi
Page 98 and 99:
Inherent, identity and nominal colo
Page 100 and 101:
uniformly coloured. Colour variatio
Page 102 and 103:
flexibility is a natural part of th
Page 104 and 105:
About the Authors Harald Arnkil is
Page 106 and 107:
Hardin wrote the book for philosoph
Page 108 and 109:
- system 9-10, 13, 22, 29, 49, 51-
Page 110 and 111:
- colour 8, 24-25, 30, 42, 49-50, 5
Page 112:
110
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Lightness and Brightness and Other Confusions

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