CS-321 Dr. Mark L. Hornick 1 Color Perception

CS-321 Dr. Mark L. Hornick 2 Color Perception

3 Color Spectrum RedViolet 750 THz430 THz 400 nm700 nm

CS-321 Dr. Mark L. Hornick 4 Additive colors

CS-321 Dr. Mark L. Hornick 5

6 The Human Eye The photosensitive part of the eye is called the retina. The retina is largely composed of two types of cells, called rods and cones. Only the cones are responsible for color perception.

CS-321 Dr. Mark L. Hornick 7 The Fovea

CS-321 Dr. Mark L. Hornick 8 There are three types of cones, referred to as S, M, and L. They are roughly equivalent to blue, green, and red sensors, respectively. Their peak sensitivities are located at approximately 430nm, 560nm, and 610nm for the "average" observer. Colorblindness results from a deficiency of one cone type. 400 nm 700 nm

CS-321 Dr. Mark L. Hornick 9 RGB Color matching functions

CS-321 Dr. Mark L. Hornick 10 Color Perception Different spectra can result in a perceptually identical color sensations called metamers Color perception results from the simultaneous stimulation of 3 cone types (trichromat) Our perception of color is also affected by surround effects and adaptation Different spectral distributions that “look” the same Infinitely many metamers produce the same perceived color

CS-321 Dr. Mark L. Hornick 11 Primary Colors Set of colors E.g., phosphor colors Combined to produce colors Within a specified gamut Can’t produce all visible colors Good enough approximation for most cases

CS-321 Dr. Mark L. Hornick 12 CIE Commission Internationale de l’Éclairage International Commission on Illumination 1931 Color primaries Imaginary colors Chromaticity diagram

CS-321 Dr. Mark L. Hornick 13 CIE Color Primaries Color-matching functions Mix x,y,z primaries Match any visible color

CS-321 Dr. Mark L. Hornick 14 CIE Chromaticity Diagram

CS-321 Dr. Mark L. Hornick 15 CIE Diagram Details SIGGRAPH 1995 Educator’s Slides Spectral colors around curve “Line of purples” White reference (C)

CS-321 Dr. Mark L. Hornick 16 Color Gamut Line between color points indicates mixing results. Polygon (triangle) connecting primaries delimits gamut

CS-321 Dr. Mark L. Hornick 17 Color Models (1) RGB: red,green,blue YIQ: luminance, chrominance Y: luminance, 4 MHz I: orange-cyan, 1.5 MHz Q: green-magenta, 0.6 MHz CMY: cyan, magenta, yellow Subtractive primaries (CMYK?)

CS-321 Dr. Mark L. Hornick 18 Subtractive colors

CS-321 Dr. Mark L. Hornick 19 Color Models (2) HSV: hue, saturation, value Hue: “color” Saturation: purity of color Value: black to white HLS: hue, lightness, saturation