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Color

Color. Contents. Light and color The visible light spectrum Primary and secondary colors Color spaces RGB, CMY, YIQ, HLS, CIE CIE XYZ, CIE xyY and CIE diagram properties. What do we see?. Visible electromagnetic radiation

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Color

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  1. Color

  2. Contents • Light and color • The visible light spectrum • Primary and secondary colors • Color spaces • RGB, CMY, YIQ, HLS, CIE • CIE XYZ, CIE xyY and CIE diagram properties

  3. What do we see? • Visible electromagnetic radiation • The type of electromagnetic wave that is visible to the human eye. • Electromagnetic radiation that has a wavelength in the range from about 4,000 (violet) to about 7,700 (red) angstroms and may be perceived by the normal unaided human eye. http://www.answers.com/color

  4. Electromagnetic radiation • Electromagnetic radiation is a kind of energy radiated in the form of a wave • The frequency define the energy • E = h  • And the hue:  = c  

  5. Electromagnetic spectrum and the visible light spectrum

  6. What is color? • It is a sensation • “Color is actually light waves that hit our eyes, translated into nerve impulses, and interpreted by our brains as all the various colors around us.” • Three components: RGB • Cones • Reds (low frequency) • Greens (medium frequency) • Blues (high frequency) http://www.stlukeseye.com/images/illustrations/anatomy_globe.jpg

  7. Mixing colors

  8. Primary and secondary colors Additive Colors Subtractive Colors

  9. Color spaces • Systems to define colors numerically • Device oriented • RGB • CMY • YIQ • Human oriented • HSV • CIE

  10. RGB • Additive model • Intensity of the three components (0, 1, 1) Cyan (0, 0, 1) Blue (1, 1, 1) White (1, 0, 1) Magenta (0, 0, 0) Black (0, 1, 0) Green (1, 1, 0) Yellow (1, 0, 0) Red

  11. RGB • Features • It is used by hardware devices • True color: 2563 = 16.777.216 • It is a standard on computing • bgcolor="#FFFFFF” • Problems • Their variations are not lineal • It isn’t intuitive

  12. CMY • Subtractive model (0, 1, 1) Red (0, 0, 1) Yellow (1, 1, 1) Black (1, 0, 1) Green (0, 0, 0) White (0, 1, 0) Magenta (1, 1, 0) Blue (1, 0, 0) Cyan

  13. CMY • Complementary of RGB [CMY] = [1,1,1] - [RGB] • Used in printing • Use of CMYK • Black (K) is added

  14. V 120 Green 60 Yellow 180 Cyan 0 Red H 1.0 White S 300 Magenta 240 Blue 0.0 Black HSV • Projection of RGB diagram about the biggest diagonal • Polar coordinates • Hue • Saturation • Value or brightness • Transformation to RGB (no lineal)

  15. HLS L 1.0 White • Two cones joined, with white on the upper vertex • Variation of HSV • L: lightness 120 Green 60 Yellow 180 Cyan 0 Red H S 300 Magenta 240 Blue 0.0 Black

  16. YIQ • Lineal transformation of RGB • Used by the NTSC (National Television Standards Committee) • Y is brightness (used in black-and-white television monitors)

  17. CIE Diagram http://www.lumitroncorp.com/rsrcs/CIE.gif

  18. CIE • 1931: measurement of color by the CIE (Commission International de L'Eclairage) • Based on Tristimulus Vision Theory • Represents any color detected by the human being

  19. Definition of CIE diagram • Experimentally • Red (700 nm) • Green (546,1 nm) • Blue (435,8 nm) • There is negative values (added the primary to the sample) • They can’t be used • It is made adding the primary to the sample http://www.imel1.kuis.kyoto-u.ac.jp/education/dip-arch/pre/images/graph10.gif

  20. The three standard primaries of CIE • They are not real colors • The functions are defined in tabular form (at 1 nm interval) • They are standards to define colors http://www.imel1.kuis.kyoto-u.ac.jp/education/dip-arch/pre/images/xyz.gif

  21. CIE XYZ Y • One color is defined by the X, Y, Z components. • The projection on the XY plane produces the CIE Chromatic Diagram. X Z

  22. CIE xyY • Normalizing the values: x + y + z = 1 • Y is the luminance information • function y() was chosen in this way http://hypertextbook.com/physics/waves/color/chromaticity.jpg

  23. Properties of CIE diagram • Gamut of different devices • The periphery is the spectrum colors • The purple line are non-spectral colors • The spectral component of a color is calculated with the line to the center http://www.tu-harburg.de/rzt/tuinfo/periph/drucker/Color_Reproduktion/cie_spectrum.gif

  24. Color spaces http://www.gg.caltech.edu/~dhl/images.html

  25. Cube RGB

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