Color Perception CS321 Dr Mark L Hornick 1

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

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

Color Spectrum Red Violet 430 THz 750 THz 700 nm 400 nm 3

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

CS-321 Dr. Mark L. Hornick 5

The Human Eye l l 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 6

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

700 nm l l 400 nm 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 430 nm, 560 nm, and 610 nm for the "average" observer. Colorblindness results from a deficiency of one cone type. CS-321 Dr. Mark L. Hornick 8

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

Color Perception l l l 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 10

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

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

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

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

CIE Diagram Details 520 510 500 490 Spectral colors around curve “Line of purples” White reference (C) 540 560 580 600 700 480 CS-321 SIGGRAPH 1995 Educator’s Slides Dr. Mark L. Hornick 15

Color Gamut 520 510 500 490 Line between color points indicates mixing results. 540 560 580 600 Polygon (triangle) connecting primaries delimits gamut. 700 480 CS-321 Dr. Mark L. Hornick 16

Color Models (1) l l RGB: red, green, blue YIQ: luminance, chrominance l l Y: luminance, 4 MHz I: orange-cyan, 1. 5 MHz Q: green-magenta, 0. 6 MHz CMY: cyan, magenta, yellow l Subtractive primaries (CMYK? ) CS-321 Dr. Mark L. Hornick 17

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

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