21_color_ii

21_color_ii - Color Vision 1 Color Color Vision 2 Review of...

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Unformatted text preview: Color Vision 1 Color Color Vision 2 Review of last week Color Vision 3 Review of color • Spectrum • Cone sensitivity function • Metamers – same color, different spectrum • Opponent – black-white, blue-yellow, red-green • Color spaces – Linear algebra – Problem with negative values – Standard: CIE XYZ • Perceptually uniform color space – CIE Lab (non-linear wrt XYZ) Color Vision 4 CIE-Lab (a.k.a. CIE L*a*b*) Image adapted from Wyszecki, G., and W. S. Stiles, Color science: Concepts and methods, quantitative data and formulae. Wiley-Interscience; 2nd Edition. July 2000. ISBN: 0471399183 Color Vision 5 Perceptually Uniform Space: MacAdam In color space CIE-XYZ, the perceived distance between colors is not equal everywhere In perceptually uniform color space, Euclidean distances reflect perceived differences between colors MacAdam ellipses (areas of unperceivable differences) become circles 560 550 540 530 520 510 490 480 470 460 450 .05 x y .10 .15 .20 .45 .50 .55 .60 .65 .25 .25 .20 .15 .10 .05 .35 .40 .45 Spectrum locus .50 .55 .60 .65 .70 .30 400 nm 700 nm 650 620 610 600 590 580 570 P u r p l e l i n e Wyszecki, G. and W. S. Stiles. Color science: Concepts and Methods, Quantitative Data and Formulae. Wiley-Interscience, 2nd ed. July 2000. ISBN: 0471399183. Image adapted from: Color Vision 6 ue Saturation Value • Value: from black to white • Hue: dominant color (red, orange, etc) • Saturation: from gray to vivid color • HSV double cone value saturation saturation hue Color Vision 7 ue Saturation Value • One interpretation in spectrum space • Not the only one because of metamerism • Dominant wavelength (hue) • Intensity • Purity (saturation) Color Vision 8 CIE color space • Match color at some point A • A is mix of white C , spectral B ! • What is dominant wavelength of A ? • What is excitation purity (%) of A ? – Move along AC/BC C 0.1 0.1 0.2 400 480 490 500 510 520 540 560 B A D E C F G 580 600 700 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.6 0.7 x y 0.7 0.8 Hunt, R. W. G. The Reproduction of Colour. John Wiley & Sons Incorporated. September 2004. ISBN: 0-470-02425-9. Image adapted from: Color Vision 9 Plan • Color Vision • Color spaces • Color effects – Definitions – Spatial sensitivity – Color illusion and color appearance • Producing color Color Vision 10 Color terms (Fairchild 1998 • Color • Hue • Brightness vs. lightness • Colorfulness and Chroma • Saturation • Unrelated and related colors Color Vision 11 Color – chromatic and achromatic content. This attribute can be described by chromatic color names such as yellow, orange, brown, red, pink, green, blue, purple, etc., or by achromatic color names such as white, gray, black, etc., and qualified by bright, dim, light, dark, etc., or by combinations of such names....
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21_color_ii - Color Vision 1 Color Color Vision 2 Review of...

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