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Color

Color. Understanding Color. What is a color? How is color perceived? How can color be represented?. Blackbody Radiators. A theoretical model of how objects emit radiation based on temperature Examples Incadescent light 2854K Direct sunlight 4874K. Importance of Color.

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Color

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  1. Color

  2. Understanding Color What is a color? How is color perceived? How can color be represented?

  3. Blackbody Radiators • A theoretical model of how objects emit radiation based on temperature • Examples • Incadescent light2854K • Direct sunlight4874K

  4. Importance of Color • Painters first used charcoal • Early artists used ochre to add red • Colors are not always the same from culture to culture

  5. Emotional Response to Color • Temperature is associated with colors • Blue is cold • Red is warm • Depends on overall scene illumination

  6. Thomas Young • English Physician • 1773-1829 • Every color can be matched by adding three primaries

  7. Hermann Helmholtz • German Scientist • 1821-1894 • Verified Young's theory by identifying three types of receptors in the eye in 1852-3 • Invented opthalmoscope

  8. Retinal Structure • Eye has photoreceptors for 3 colors

  9. Color Vision • Each cone type is sensitive to a different range • Research indicates we can see about 10 million colors • How can one color be distinguished from another? • How are colors specified?

  10. Color Vision • Depends on relative stimulation of photoreceptors • Depends on wavelength • Monomers • Same colors • Different spectra • Color depends on surrounding colors

  11. Color Deficiency About 10% have some deficiency 9% men 1% women Most missing red or green cones Red and green percieved as brown Monochromats have only rods Dichromats have 2 of the three cones Low light vision is not affected Care needs to be taken when creating visual materials for others Web pages Brochures Design in black and white, then add color

  12. Color Blindness • Protanopia • No red cones • Red, orange, and yellow are shifted toward green • Violet is shifted towards blue • severe cases • traffic lights are black • Purple flowers are blue • Problems in extreme lighting conditions

  13. Color Blindness Deutanopia No green cones Green, yellow, and orange are shifted toward red Poor discrimitation of blues

  14. Color Blindness Tritanopia No blue cones

  15. Color Blindness

  16. Ishihara Tests

  17. Quantifying Color • CIE • Commision Internationale d'Eclairage • began work in 1931 • First chart in 1947

  18. CIE Chart • Revised in 1976 • Spectral colors (pure tones) are around perimeter curve • Purple line is not • Neutral color point • Complementary colors • Primary hue

  19. CIE Chart

  20. Complementary colors • Opposites • Enhance one another because of optimal color contrast

  21. Color Gamut • Only a small subset of possible percievable colors can be reproduced • Fall into convex hull of primaries • Two primaries results in a line • Three primaries results in a triangle

  22. Munsell System • Created in 1905 by artist A. H. Munsell • Five hues spaced preceptually equal • Purple, Yellow, Green, Blue, Purple • Saturation • Value

  23. RGB System • RGB Color model uses three primaries • Red • Green • Blue • Colors are in the interior of cube

  24. RGB Color Space

  25. Macbeth Color Chart • Grayscale • Light to dark • Colors • Designed to match reflectance of natural objects

  26. Subtractive Color Mixing • Uses reflected light • Some is absorbed • Some is reflected • Three primaries • Red (Magenta) • Yellow • Blue (Cyan)

  27. Subtractive Color Mixing • Du Hauron • 1869 • Les Couleours en Photographie

  28. Additive Color Mixing • Uses emitted light or light transmitted through a filter • Three primaries • Red (Vermillion) • Green • Blue (Royal)

  29. Additive Color Mixing • 3 Flashlights

  30. Hue, Saturation, Value

  31. Hue, Lightness, Saturation • Similar to HSV and RGB models

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