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Color Theory

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

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Color Theory

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

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

  3. Color Spectra Pure colors - single wavelength

  4. Color Spectra Sample lights: How do we perceive them?

  5. Human Visual System Rods - black & white receptors - peripheral vision - sensitive Cones - 3 type tuned to different frequencies - 3 cones have different sensitivities - central vision - less sensitive

  6. Tristimulus Theory of Color Important principle: Any color spectra is perceived by sensors with 3 different response frequencies! Tristimulus theory of color: Color is inherently a three-dimensional space Metamers: If two colors produce the same tristimulus values, then they are visually indistinguishable

  7. Spectral Response of Human Visual System

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

  9. Color Spectra Important principle: Any color spectra is perceived as: - a single dominant wavelength - its hue - mixed with a certain amount of white light (saturation) - of a certain intensity or brightness

  10. Stating the numbers Dominant wavelength (hue) Luminance (total power) Saturation (purity) Dominant Wavelength

  11. Luminance (L) = (D-A)B + AW Saturation = (D-A)B/L * 100% White light: D = A, i.e., Sat. = 0 Luminance and Saturation

  12. Use three primary color (r,g,b) C(λ) = r(λ)R + g(λ)G + b(λ)B negative!! RGB color description r(λ) g(λ) b(λ)

  13. RGB Primary Colors

  14. RGB Color Space

  15. 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? Sometimes CMYK - K: Black CMY Color Model

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

  17. (X,Y,Z) - Not real colors The combination coefficients are positive Perceptual space CIE Primary “Colors” C(λ) = x(λ)X + y(λ)Y + z(λ)Z

  18. CIE Primary Colors

  19. CIE Chromaticity Chart Project to xy plane

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

  21. CIE model is a good color reference Not necessarily the most natural one Many other color spaces are used RGB HLS CMY HSV YIQ ... Color Spaces

  22. HLS Color Space

  23. HLS Color Space (2)

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