Introduction to Color Vision colour blindness by benbenzhou

VIEWS: 6 PAGES: 8

More Info
									                                                                 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   2




Plan                                                             Physical spectrum
• Physical spectrum                                              • 1666, Newton
• Trichromatic vision                                            • Pittoni, Allegory, 1925
      – Cones
      – Metamerism
      – Chromatic adaptation
      – Color blindness
• Color Opponents



Introduction to Color Vision                                 3   Introduction to Color Vision   4




Physical spectrum                                                Light source spectrum




Introduction to Color Vision                                 5   Introduction to Color Vision   6




                                                                                                    1
Reflectance Spectrum                                        Reflected spectrum
• Objects do not                                            • Depends
  have a “color”                                              on light
• They have a                                                 source
  reflectance                                                 and
  spectrum                                                    reflectance
                                                            • Multiply                     *   =




Introduction to Color Vision                            7   Introduction to Color Vision            8




Plan                                                        Trichromatic vision
• Physical spectrum                                         • Maxwell, Young, Helmholtz
• Trichromatic vision                                       • Cones
      – Cones
      – Metamerism
      – Chromatic adaptation
      – Color blindness
• Color Opponents



Introduction to Color Vision                            9   Introduction to Color Vision           10




Cone spectral sensitivity                                   Cones distribution
• Short, Medium and Long wavelength                         • LMS 40:20:1
                                                            • No S (blue)
                                     S     ML
                                                              in retina center
                   1.00

                   0.75

                   0.50

                   0.25

                   0.00
                               400       500 600 700
                                         wavelength
Introduction to Color Vision                           11   Introduction to Color Vision           12




                                                                                                        2
Cones do not “see” colors                                        Cones do not “see” colors
                                                                 • Different wavelength, different intensity
                                                                 • Same response
                                            M                                                               M
                   1.00                                                             1.00

                   0.75                                                             0.75

                   0.50                                                             0.50

                   0.25                                                             0.25

                   0.00                                                             0.00
                               400       500 600      700                                       400       500 600 700
                                         wavelength                                                       wavelength
Introduction to Color Vision                                13   Introduction to Color Vision                           14




Response comparison                                              Complex spectrum
• Different wavelength, different intensity
• But different response for different cones
                                     S      ML                                                        S     ML
                   1.00                                                             1.00

                   0.75                                                             0.75

                   0.50                                                             0.50

                   0.25                                                             0.25

                   0.00                                                             0.00
                               400       500 600      700                                       400       500 600 700
                                         wavelength                                                       wavelength
Introduction to Color Vision                                15   Introduction to Color Vision                           16




Summary                                                          Plan
                                                                 • Physical spectrum
                                                                 • Trichromatic vision
                                                                       – Cones
                                                                       – Metamerism
                                                                       – Chromatic adaptation
                                                                       – Color blindness
                                                                 • Color Opponents



Introduction to Color Vision                                17   Introduction to Color Vision                           18




                                                                                                                             3
Metamerism                                                  Color matching
• Different spectrum
• Same response




Introduction to Color Vision                           19   Introduction to Color Vision   20




Color synthesis                                             Future discussion
           Additive                 Subtractive             • Limited gamut
           red, green, blue    cyan, magenta, yellow




Introduction to Color Vision                           21   Introduction to Color Vision   22




Metamerism & light source                                   Metamerism & light source
• Metamers under a given light source
• May not be metamer under a different lamp
• Because different spectrum




Introduction to Color Vision                           23   Introduction to Color Vision   24




                                                                                                4
Metamerism & light source                                                     Plan
• Metamers under a given light source                                         • Physical spectrum
• May not be metamer under a different lamp                                   • Trichromatic vision
• Because different spectrum                                                        – Cones
                                                                                    – Metamerism
• Problem when buying cloths under neon lighting                                    – Chromatic adaptation
                                                                                    – Color blindness
                                                                              • Color Opponents



Introduction to Color Vision                                             25   Introduction to Color Vision   26




Chromatic adaptation                                                          Plan
• Von Kries adaptation                                                        • Physical spectrum
• Different gain control on L, M, S                                           • Trichromatic vision
                                                                                    – Cones
                                    0.75, 1, 1
                                                            0.75, 1, 1              – Metamerism
                                                                                    – Chromatic adaptation
                                                                                    – Color blindness
                    Gain control:
                    *1.33, *1, *1                                             • Color Opponents

                  0.2, 1, 0.2                                 0.2, 1, 0.2
                                             0.15, 1, 0.2

Introduction to Color Vision                                             27   Introduction to Color Vision   28




Color blindness                                                               We are all color blind
•   Dalton                                                                    • Center of retina
•   8% male, 0.6% female                                                      • No S (blue)
•   Genetic                                                                   • We compensate
•   Dichromate (2% male)                                                        via gaze
      – One type of cone missing                                                movement
      – L (protanope), M (deuteranope),                                       • Not well
        S (tritanope)                                                           understood
• Anomalous trichromat
      – Shifted sensitivity

Introduction to Color Vision                                             29   Introduction to Color Vision   30




                                                                                                                  5
Color blindness test                                              Color blindness test
                                                                  • Maze in subtle intensity contrast
                                                                  • Visible only to color blinds
                                                                  • Color contrast overrides intensity otherwise




Introduction to Color Vision                                 31   Introduction to Color Vision                            32




Color blind impressions                                           Color blindness & Painting
• A normal scene                                                  • Restricted to blue-yellow
• B
  protanope L
• C
  deuteranope M
• D
  tritanope S



                                                                                             Goethe after a color-blind
Introduction to Color Vision                                 33   Introduction to Color Vision                            34




Color blindness & Painting                                        Color blindness & Painting
• Restricted to blue-yellow                                       • Restricted to blue-yellow




                               Meryon, Le Vaisseau Fantôme                                          J. J.
Introduction to Color Vision                                 35   Introduction to Color Vision                            36




                                                                                                                               6
Color blindness & Painting                                      Plan
• Image reproduction (after Gauguin)                            • Physical spectrum
• Different strategies                                          • Trichromatic vision
                                                                      – Cones
                                                                      – Metamerism
                                                                      – Chromatic adaptation
                                                                      – Color blindness
                                                                • Color Opponents
 Normal color vision           Color blind   Color blind
                               (perceived)   (confusion)



Introduction to Color Vision                               37   Introduction to Color Vision                38




Color Opponents                                                 Color opponents wiring
• Hering                                                        • Sums for brightness
• A color can be “blue-green”, “yellow-red”,                    • Differences for
  “yellow-green”, etc                                             color opponents
• But never “yellow-blue” or “red-green”
• Suspected two opponents:
      – Blue-yellow axis                                                                            - +
      – Red-Green axis                                                                         ++ + + + -
                                                                                               +


Introduction to Color Vision                               39   Introduction to Color Vision                40




Double center surround opponents                                Color reparameterization
• Center-surround                                               • The input is LMS
• Color opponents                                               • The output has a different
                                                                  parameterization:
                                                                      – Light-dark
                                                                      – Blue-yellow
                                                                      – Red-green




Introduction to Color Vision                               41   Introduction to Color Vision                42




                                                                                                                 7
Color reparameterization                   Opponents and image compression
• The input is LMS                         • JPG, MPG
• The output has a different               • Color
  parameterization:                          opponents
      – Light-dark                           instead of
      – Blue-yellow                          RGB
      – Red-green                          • Compress
• A later stage may reparameterize:          color more
      – Brightness                           than
      – Hue                                  luminance
      – Saturation
Introduction to Color Vision          43   Introduction to Color Vision      44




Blue-yellow opponent and painting          Red-green opponent and painting
• Often used to depict                     • Jawlensky
  night
• (S cones share
  properties with rods…)
• Van Gogh
  Café at Night




Introduction to Color Vision          45   Introduction to Color Vision      46




Opponent and painting
• Degas




Introduction to Color Vision          47




                                                                                  8

								
To top