RGB

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RGB

• Models human visual system?
• Gives an absolute color description?
• Models color similarity?
• Linear model?
• Convenient for color displays?

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RGB

• Models human visual system
• Gives an absolute color description
• Models color similarity
• Linear model
• Convenient for color displays

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Spectra

• Light reaching the retina is characterized by
  spectral distribution, i.e. (relative) amount of
  power at each wavelength.
• Each kind of cone (S,M,L) responds differently.

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Sources of colored light used in modern fireworks.

• Yellow Sodium D-line 589 nm
• Orange CaCl 591- 599 nm 603-608 nm
  
• Red SrCl 617-623 nm
  627-635 nm 640-646 nm
• Green BaCl 511-515 nm 524-528
  nm 530-533 nm
• Blue CuCl 403-456 nm,

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Lens
Retina
Cornea
Fovea
Pupil
Optic nerve
Iris
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Optic nerve
Light
Ganglion
Amacrine
Bipolar
Horizontal
Cone
Rod
Epithelium
Retinal cross section
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Photoreceptors

• Cones -
• respond in high (photopic) light
• differing wavelength responses (3 types)
• single cones feed retinal ganglion cells so give
  high spatial resolution but low sensitivity
• highest sampling rate at fovea

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Photoreceptors

• Rods
• respond in low (scotopic) light
• none in fovea
• one type of spectral response
• several hundred feed each ganglion cell so give
  high sensitivity but low spatial resolution

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Optic nerve

• 130 million photoreceptors feed 1 million
  ganglion cells whose output is the optic nerve.
• Optic nerve feeds the Lateral Geniculate Nucleus
  approximately 1-1
• LGN feeds area V1 of visual cortex in complex
  ways.

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Rods and cones

• Rods saturate at 100 cd/m2 so only cones work at
  high (photopic) light levels
• All have same spectral sensitivity
• Low light condition is called scotopic
• Three cone types differ in spectral sensitivity
  and somewhat in spatial distribution.

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Cones

• L (long wave), M (medium), S (short)
• describes sensitivity curves.
• Red, Green, Blue is a misnomer. See
  spectral sensitivity.

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