Introduction to color vision The Art and Science of Depiction
Introduction to Color Vision Fredo Durand MIT- Lab for Computer Science Introduction to Color Vision
Plan
Physical spectrum
• Physical spectrum • Trichromatic vision
• 1666, Newton • Pittoni, Allegory, 1925
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– Cones – Metamerism – Chromatic adaptation – Color blindness
• Color Opponents
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Physical spectrum
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Light source spectrum
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1
Reflectance Spectrum
Reflected spectrum
• Objects do not have a “color” • They have a reflectance spectrum
• Depends on light source and reflectance • Multiply
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Introduction to Color Vision
Plan
Trichromatic vision
• Physical spectrum • Trichromatic vision
• Maxwell, Young, Helmholtz • Cones
=
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– Cones – Metamerism – Chromatic adaptation – Color blindness
• Color Opponents
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Introduction to Color Vision
Cone spectral sensitivity
Cones distribution
• Short, Medium and Long wavelength
• LMS 40:20:1 • No S (blue) in retina center
S
1.00
ML
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0.75 0.50 0.25 0.00 400 Introduction to Color Vision
500 600 700 wavelength 11
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Cones do not “see” colors
Cones do not “see” colors • Different wavelength, different intensity • Same response
M
1.00
M
1.00
0.75
0.75
0.50
0.50
0.25
0.25
0.00
0.00 400
500 600 wavelength
700
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Response comparison
500 600 700 wavelength
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Complex spectrum
• Different wavelength, different intensity • But different response for different cones S
1.00
ML
0.75
0.75
0.50
0.50
0.25
0.25
0.00 400 Introduction to Color Vision
500 600 wavelength
S
1.00
ML
0.00
700
400 15
Summary
500 600 700 wavelength
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Plan • Physical spectrum • Trichromatic vision – Cones – Metamerism – Chromatic adaptation – Color blindness
• Color Opponents
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Metamerism
Color matching
• Different spectrum • Same response
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Color synthesis Additive red, green, blue
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Future discussion Subtractive cyan, magenta, yellow
Introduction to Color Vision
• Limited gamut
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Metamerism & light source
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Metamerism & light source
• Metamers under a given light source • May not be metamer under a different lamp • Because different spectrum
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Metamerism & light source
Plan
• Metamers under a given light source • May not be metamer under a different lamp • Because different spectrum
• Physical spectrum • Trichromatic vision – Cones – Metamerism – Chromatic adaptation – Color blindness
• Problem when buying cloths under neon lighting
• Color Opponents
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Introduction to Color Vision
Chromatic adaptation
Plan
• Von Kries adaptation • Different gain control on L, M, S
• Physical spectrum • Trichromatic vision
0.75, 1, 1
– Cones – Metamerism – Chromatic adaptation – Color blindness
0.75, 1, 1
Gain control: *1.33, *1, *1 0.2, 1, 0.2
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• Color Opponents 0.15, 1, 0.2
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Introduction to Color Vision
Color blindness
We are all color blind
• • • •
• Center of retina • No S (blue) • We compensate via gaze movement • Not well understood
Dalton 8% male, 0.6% female Genetic Dichromate (2% male) – One type of cone missing – L (protanope), M (deuteranope), S (tritanope)
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• Anomalous trichromat – Shifted sensitivity Introduction to Color Vision
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Color blindness test
Color blindness test • Maze in subtle intensity contrast • Visible only to color blinds • Color contrast overrides intensity otherwise
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Color blind impressions
Color blindness & Painting
• A normal scene • B protanope L • C deuteranope M • D tritanope S
• Restricted to blue-yellow
Goethe after a color-blind Introduction to Color Vision
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Color blindness & Painting
Color blindness & Painting
• Restricted to blue-yellow
• Restricted to blue-yellow
Meryon, Le Vaisseau Fantôme Introduction to Color Vision
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Introduction to Color Vision
J. J.
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Color blindness & Painting
Plan
• Image reproduction (after Gauguin) • Different strategies
• Physical spectrum • Trichromatic vision – Cones – Metamerism – Chromatic adaptation – Color blindness
• Color Opponents Normal color vision
Color blind (perceived)
Color blind (confusion)
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Color Opponents
Color opponents wiring
• Hering • A color can be “blue-green”, “yellow-red”, “yellow-green”, etc • But never “yellow-blue” or “red-green” • Suspected two opponents:
• Sums for brightness • Differences for color opponents
+++ + + ++ -
– Blue-yellow axis – Red-Green axis
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Introduction to Color Vision
Double center surround opponents
Color reparameterization
• Center-surround • Color opponents
• The input is LMS • The output has a different parameterization:
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– Light-dark – Blue-yellow – Red-green
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Color reparameterization
Opponents and image compression
• The input is LMS • The output has a different parameterization:
• JPG, MPG • Color opponents instead of RGB • Compress color more than luminance
– Light-dark – Blue-yellow – Red-green
• A later stage may reparameterize: – Brightness – Hue – Saturation Introduction to Color Vision
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Introduction to Color Vision
Blue-yellow opponent and painting
Red-green opponent and painting
• Often used to depict night • (S cones share properties with rods…) • Van Gogh Café at Night
• Jawlensky
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Opponent and painting • Degas
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