10/10/2017
1
Color Vision
Color
• Secondary quality
• Colors help discriminate objects
• Colors have semantic associations
10/10/2017
2
Color
• Colors can elicit emotions (Elliot & Niesta, 2008)
Perceiving Color
• Correlation between wavelength and color
• 620 – 700 nm = red
• 590 – 620 nm = orange
• 575 – 590 nm = yellow
• 500 – 575 nm = green
• 450 – 490 nm = blue
• 400 – 450 nm = violet
• Light waves themselves are colorless
• Monochromatic light
• Polychromatic light
R
O
Y
G
B
I
V
Perceiving Color
• Perceptual dimensions of color
• Visible spectrum is continuous (400 nm – 700 nm)
• We can distinguish hundreds of colors
• But, we perceive colors categorically
10/10/2017
3
Perceiving Color
• Perceptual dimensions of color
• Hue
• Brightness
• Saturation
Perceiving Color
• Perceptual Color Categories
• Primary colors
• Secondary colors
• Tertiary colors
Perceiving Color
• Additive color mixing
• Results from a mixture of light beams onto a single location
10/10/2017
4
Perceiving Color
• Subtractive color mixing
• Results mixture of pigments
0
10
20
30
40
50
60
70
80
90
100
410
430
45
0
470
49
0
510
530
550
570
590
610
630
65
0
670
69
0
710
730
% R
efl
ect
ed
Wavelength
Yellow
Blue
Yellow + Blue
Perceiving Color
0
10
20
30
40
50
60
70
80
90
100
410
42
0
430
44
0
45
0
46
0
470
48
0
49
0
500
510
520
530
540
550
560
570
580
590
60
0
610
62
0
630
64
0
65
0
66
0
670
68
0
69
0
700
710
720
730
% R
efl
ect
ed
Wavelength
0
10
20
30
40
50
60
70
80
90
100
410
42
0
430
44
0
45
0
46
0
470
48
0
49
0
500
510
520
530
540
550
560
570
580
590
60
0
610
62
0
630
64
0
65
0
66
0
670
68
0
69
0
700
710
720
730
% R
efl
ect
ed
Wavelength
0
10
20
30
40
50
60
70
80
90
100
410
42
0
430
44
0
45
0
46
0
470
48
0
49
0
500
510
520
530
540
550
560
570
580
590
60
0
610
62
0
630
64
0
65
0
66
0
670
68
0
69
0
700
710
720
730
% R
efl
ect
ed
Wavelength
0
10
20
30
40
50
60
70
80
90
100
410
42
0
430
44
0
45
0
46
0
470
48
0
49
0
500
510
520
530
540
550
560
570
580
590
60
0
610
62
0
630
64
0
65
0
66
0
670
68
0
69
0
700
710
720
730
% R
efl
ect
ed
Wavelength
0
10
20
30
40
50
60
70
80
90
100
410
42
0
430
44
0
45
0
46
0
470
48
0
49
0
500
510
520
530
540
550
560
570
580
590
60
0
610
62
0
630
64
0
65
0
66
0
670
68
0
69
0
700
710
720
730
% R
efl
ect
ed
Wavelength
Trichromatic Theory
• Young-Helmholtz Theory
• Cones are involved with color perception
10/10/2017
5
Trichromatic Theory
• Problem of Univariance
• Any one cone cannot discriminate color
• Same output to different wavelengths
Trichromatic Theory
• There are three types of cones on the retina (S, M, L)
400420
440460
480500
520
540560 580
600620
64066
0680
700
Wavelength (nm)
Re
ce
pto
r R
es
po
ns
e
S Cones
M Cones
L Cones
Trichromatic Theory
• Color perception is based on the unique output across the three types of cones
• Problems with Young-Helmholtz?
10/10/2017
6
LGN Color Channels
• Luminance Channel
White-Black (L + M)
• Chromatic Channels
• Red-Green (L - M)
• Yellow-Blue [S - (L + M)]
S M L
Y- B+ R- G+ W+ B-Y+ B- R- G+ W- B+
Activation
Inhibition
Color-Opponent Process Theory
• “Opposing responses” from LGN channels
• Illegal color combinations
• Negative afterimages
• Simultaneous color contrast
Color-Opponent Process Theory
10/10/2017
7
Color-Opponent Process Theory
Color Vision Deficiencies
• Found in ~8% of males and ~0.5% of females
• Ishihara Colorblindness Plates
• Color Matching Experiments
Color Deficiencies• Cone dichromatism
• Deuteranopia
• Protanopia
• Tritanopia
• Unilateral dichromatism
• Monochromatism
• Cone monochromat
• Rod monochromat
10/10/2017
8
Perception of Color and Culture?
• Can culture influence perception?
• Davidoff, Fonteneau & Fagot (2008)
• Himba tribe
• Global-local choice task
Culture % Global Choices
Western 86.01 %
Himba 22.81 %
“Standard”
“Global Match”“Local Match”
Perception of Color and Culture?
• Eleanor Rosch (1972)
• Dani tribe (New Guinea) have two color words:
• mola = light
• mili = dark“Remember”
“Test”
‘mola’ ‘mola’
‘mola’ ‘mola’ ‘mola’‘mili’
Color Assimilation
10/10/2017
9
Shadows
• Which parallelogram appears darker?
Shadows
Shadows
10/10/2017
10
Shadows
• Which dotted square appears to be darker?
Shadows
• Visual system takes into account “shadows” caused by the cylinder
Shadows
10/10/2017
11
Cornsweet Illusion
Cornsweet Illusion
McCollough Effect
10/10/2017
12
Color Constancy • Why does a colored surface appear the same under
different Illuminants?
Should look very different
Color Constancy
• R = I x S
• R: “Wavelengths Hitting Retina”
• I: “Wavelengths in Illuminant”
• S: “Wavelengths from Surface”
• Visual system adapts to
(discounts) illuminant
• Emphasis placed on unique
wavelengths from the surface