There is no definitive answer to how many colors exist because the concept of color depends on factors like the illumination, viewing conditions, and human perception. Computational models can predict color gamuts under different scenarios, but the largest gamut volume estimated is around 6.6 million colors using real measured light sources, which still may not capture all possible colors perceivable by humans. Determining all possible colors ultimately requires a color appearance model that more closely mimics the complexities of human vision.

1. Why we don’t know
how many colors there are
Ján Morovič, Vien Cheung* & Peter Morovič
Hewlett-Packard Company
*University of Leeds
Presented by Dr. Vien Cheung at CGIV ‘12, Amseterdam on 7th May 2012
CGIV 2012

2. How many colors are there?
28 × 28 × 28 = ~ 16.8 million
3 infinity

3. How many colors are there?
o interesting!
o usefulness in engineering decision processes
o but ... what is color? and what does ‘all possible
colors’ mean?

4. What does ‘all possible colors’
mean?
16 million | 2-10 million
CIE system | visual system
physical colors | perceptual colors

5. Color illusions
o the notion of color is essentially a property of an
object does not explain color illusions

6. Color ‘illusions’
[255 0 0]
physical colors > perceptual colors
physical colors < colors depend upon context

7. Related studies
2010 Maric-France & Foster
2008 Linhares et al.
2005 Heckaman et al.
o natural surface
2004 Inui et al.
o color spaces | gamut computations
2001 Morovič et al.
o viewing condition
1999 McCann
o illumination | adapted white
1980 Pointer
o natural scenes
o all possible surface colors
1920 Schrodinger

8. Our work
o counting all possible colors ‘by hand’
o computationally predicting all possible colors
o discuss the limitations of gamut computation and
appearance prediction

9. Counting colors ‘by hand’
o this exercise can tell us how many colors there are on a gray
background, when viewed under a certain light source, etc.!

10. Counting colors ‘by hand’

11. Computational prediction
o an ecosystem enabling varying color experiences
o CIECAM02
o color appearance attributes  effect on predicting
gamut
o explore the effect of various model parameters

12. Computational prediction

13. Computational prediction
Light source D50 F11
Surround average dim dark average
Background 20% 20% 20% 20%
Luminance of ~60 cd/m2 ~60 cd/m2 ~60 cd/m2 ~60 cd/m2
adapting field
Gamut volume 3.8 MJab 3.5 MJab 3.0 MJab 4.2 MJab
o D50 + F11 = 4.4 MJab
o D50 + F11 + A (3.5 MJab) = 4.5 MJab

14. Computational prediction
o expanding to standard iluminants to freely varying their SPD
o 242 synthetic light sources
0.9
0.8
0.7
0.6 11
log10 Jab gamut volume
0.5 10
CIE y
9
0.4
8
0.3
7
0.2
6
0.2
0.1
5 0.4
0.1 0.2 CIE x
0 0.3 0.4 0.6
0.5 0.6
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.7 0.8
CIE y
CIE x

15. Computational prediction
o CIECAM02 dramatically predicts color gamut with 1011 volumes
in Jab space
o i.e. 100,000 times of all possible surface colors under D50
o however, this increment does not agree with experience and is a
psychophysical data-based model
o the difficulty of viewing all possible visual ecosystems remains

16. Computational prediction
o a revised prediction uses 173 measured light sources
1
0.9
0.8
0.7
relative spectral power
0.6
0.5
0.4
0.3
0.2
0.1
0
400 450 500 550 600 650 700
wavelength (nm)

17. Computational prediction
0.5
11
0.4
10
log10 Jab gamut volume
CIE y
0.3 9
8
0.2
7
6
0.1 0.2
5 0.4
0.1 CIE x
0.2 0.3 0.4 0.6
0 0.5 0.6
CIE y 0.7 0.8
0.1 0.2 0.3 0.4 0.5 0.6 0.7
CIE x
o a total gamut volume of 6.6 MJab
o i.e. the surface, which under D50 (3.8 MJab), result in ~2× that
range of colors viewed under a variety of light sources

18. Computational prediction
200 200
150 150
100 100
50 50
CIE b*
CIE b*
0 0
−50 −50
−100 −100
−150 −150
−200 −200
−200 −150 −100 −50 0 50 100 150 200 −200 −150 −100 −50 0 50 100 150 200
CIE a* CIE a*
D50 | 173 measured light sources
120
120
100
100
80
80
CIE L*
60
CIE L*
60
40 40
20 20
0 0
200 200
150 150
100 100
50 50
200 200
0 150 0 150
CIE b* 100 CIE b* 100
−50 −50 50
50
−100 0 −100 0
−50 −50 CIE a*
−150 CIE a* −150 −100
−100
−150 −150
−200 −200 −200 −200

19. CAM
o Note that CIECAM02 does not include
many complexities of colour vision
such as contrast effects
o using CAM to indicate all possible
colors should consider the color
gamuts of colour appearance they are
derived from
o CIECAM02 (LUTCHI data) – 1.7 MJab

20. Conclusions
o based upon the available data to-date there are at
least ~1.7 million colors
o to go beyond this type of number would require:
o a color appearance model closely mimics the
human visual system
o extend psychophysical basis