CS-321Dr. Mark L. Hornick

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Color Perception

CS-321Dr. Mark L. Hornick

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Color Perception

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Color Spectrum

Red Violet

750 THz430 THz

400 nm700 nm

CS-321Dr. Mark L. Hornick

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Additive colors

CS-321Dr. Mark L. Hornick

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CS-321Dr. Mark L. Hornick

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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-321Dr. Mark L. Hornick

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The Fovea

CS-321Dr. Mark L. Hornick

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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 nm700 nm

CS-321Dr. Mark L. Hornick

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RGB Color matching functions

CS-321Dr. Mark L. Hornick

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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-321Dr. Mark L. Hornick

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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-321Dr. Mark L. Hornick

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CIE

Commission Internationale de l’Éclairage International Commission on Illumination 1931

Color primaries Imaginary colors

Chromaticity diagram

CS-321Dr. Mark L. Hornick

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CIE Color Primaries

Color-matching functionsMix x,y,z primariesMatch any visible color

CS-321Dr. Mark L. Hornick

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CIE Chromaticity Diagram

CS-321Dr. Mark L. Hornick

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CIE Diagram Details

SIGGRAPH 1995 Educator’s Slides

Spectral colors around curve

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“Line of purples”White reference (C)

CS-321Dr. Mark L. Hornick

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Color Gamut

Line between color points indicates mixing results.Polygon (triangle) connecting primaries delimits gamut.

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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-321Dr. Mark L. Hornick

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Subtractive colors

CS-321Dr. Mark L. Hornick

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Color Models (2)

HSV: hue, saturation, value Hue: “color” Saturation: purity of color Value: black to white

HLS: hue, lightness, saturation