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Unformatted text preview: e Light How well do we see color?
What color do we see the best?
• Yellow-green at 550 nm
What color do we see the worst?
• Blue at 440 nm
Flashback: Colortables (colormaps) for color storage
• Which RGB value gets the most bits?
Can perceive color differences of 10 nm at extremes (violet and red)
and 2 nm between blue and yellow
Metamers – different energy radiations look like the same color
Color perception also affected by surrounding light and adaptation Just noticeable difference (JND)
128 fully saturated hues can be distinguished
Cannot perceive hue differences with less
Sensitivity to changes in saturation for a fixed hue
and brightness ranges from 16 to 23 depending
Talked about representing intensities last lecture Human Color Vision
Humans have 3 light sensitive pigments in their cones,
called L, M, and S
Each has a different
spectral response curve:
L = ∫ L(λ )E(λ )dλ M = ∫ M( λ) E( λ) dλ
S = ∫ S(λ )E(λ )dλ This leads to metamerism
“Tristimulus” color theory Color Spaces
Three types of cones suggests color is a 3D quantity. How
to define 3D color space?
• Shine given wavelength (λ) on a screen
• User must control three lasers producing three wavelengths (say
R=700nm, G=546nm, and B=436nm)
• Adjust intensity of RGB until colors are identical
• Note phosphors of TV are not perfect RGB
emitters as the results to right demonstrate A Problem Exists
Exact target match (λ ) with phosphors not possible
• Some red had to be added to target color to permit exact match using
“knobs” on RGB intensity output of CRT
• Equivalently (theoretically),
some red could have been
removed from CRT output
• Figure shows that red
phosphor must remove some
cyan for perfect match
• CRT phosphors cannot
remove cyan, s...
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This note was uploaded on 01/23/2012 for the course CS 445 taught by Professor Bloomfield,a during the Spring '08 term at UVA.
- Spring '08
- Computer Graphics