lecture13-2

Lecture13-2

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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) Can and 2 nm between blue and yellow and Metamers – different energy radiations look like the same color Metamers different 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 Cannot saturated light. saturated Sensitivity to changes in saturation for a fixed hue Sensitivity and brightness ranges from 16 to 23 depending on hue. on Talked about representing intensities last lecture Human Color Vision Humans have 3 light sensitive pigments in their cones, Humans called L, M, and S called Each has a different Each spectral response curve: spectral 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 Three to define 3D color space? to Idea: Idea: • Shine given wavelength (λ) on a screen • User must control three lasers producing three wavelengths (say User R=700nm, G=546nm, and B=436nm) R=700nm, • Adjust intensity of RGB until colors are identical Adjust • 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 Some “knobs” on RGB intensity output of CRT “knobs” • Equivalently (theoretically), Equivalently some red could have been removed from CRT output removed • Figure shows that red Figure phosphor must remove some cyan for perfect match cyan • CRT phosphors cannot CRT 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.

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