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Color Theory

Color Theory. What is color? How do we describe and match colors? Color spaces. What is color?. Interaction of light and eye-brain system Light: electromagnetic phenomenon Discerned by different wavelength. Color Spectra. Pure colors. Color Spectra. Sample lights: How to describe

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Color Theory

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  1. Color Theory • What is color? • How do we describe and match colors? • Color spaces

  2. What is color? • Interaction of light and eye-brain system • Light: electromagnetic phenomenon • Discerned by different wavelength

  3. Color Spectra Pure colors

  4. Color Spectra Sample lights: How to describe them numerically?

  5. Human Perception System Trichromacy – 3 primary colors

  6. negative!! Describe color • Use three primary color (r,g,b) • C(l) = r(l)R’ + g(l)G’ + b(l)B’ r(l) g(l) b(l)

  7. CIE Primary “Colors” • (X’,Y’,Z’) - Not real colors • The combination coefficients are positive C(l) = x(l)X’ + y(l)Y’ + z(l)Z’

  8. CIE Primary Colors

  9. CIE Chromaticity Chart Project to xy plane

  10. Dominant Wavelength

  11. CIE Gamuts - The range of colors that can be produced on a device Green CRT Gamut Red Blue

  12. Gamut of Various Devices

  13. Color Spaces • CIE model is not necessarily the most natural one • Many other color spaces are used • RGB • HLS • CMY • HSV • ….

  14. RGB Color Space

  15. HLS Color Space

  16. HLS Color Space (2)

  17. CMY Color Model • C: Cyan; M: Magenta; Y: Yellow • Subtractive primaries - Cyan, Magenta, and Yellow are the compliment of Red, Green Blue • Specified by what is being removed from white • Example: Cyan color = (1,0,0) means red is removed; CMY: (1,1,0) -> red and green is removed => what color?

  18. CMY <-> RGB C 1 R M = 1 - G Y 1 B

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