lecture2_color_quant

lecture2_color_quant - Lecture 2 Color Representation and...

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Lecture 2 Color Representation nd Quantization and Quantization Yao Wang Polytechnic Institute of NYU, Brooklyn, NY 11201 With contributions from Zhu Liu, AT&T Labs Most figures from Gonzalez/Woods: Digital Image Processing
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Lecture Outline Color perception and representation Human perception of color Trichromatic color mixing theory Different color representations Color image display True color image dexed color images Indexed color images Pseudo color images uantization Fundamentals Quantization Fundamentals Uniform, non-uniform, dithering Color quantization Yao Wang, NYU-Poly EL5123: color and quantization 2
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Light is part of the EM wave Yao Wang, NYU-Poly EL5123: color and quantization 3
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Illuminating and Reflecting Light Illuminating sources (primary light): mit ht (e.g. the sun, light bulb, TV monitors) emit light (e.g. the sun, light bulb, TV monitors) perceived color depends on the emitted freq. follow additive rule R+G+B=White Reflecting sources (secondary light): reflect an incoming light (e.g. the color dye, matte surface, cloth) erceived color depends on reflected freq (=emitted perceived color depends on reflected freq (=emitted freq-absorbed freq.) follow subtractive rule Yao Wang, NYU-Poly EL5123: color and quantization 4 R+G+B=Black
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Eye vs. Camera amera components ye components Camera components Eye components Lens Lens, cornea Shutter Iris, pupil Yao Wang, NYU-Poly EL5123: color and quantization 5 Film Retina Cable to transfer images Optic nerve send the info to the brain
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Human Perception of Color Retina contains receptors ones – Cones Day vision, can perceive color tone Red, green, and blue cones – Rods Night vision, perceive brightness only olor sensation Color sensation Luminance (brightness) hrominance From Chrominance Hue (color tone) Saturation (color purity) http://www.macula.org/anatomy/ retinaframe.html Yao Wang, NYU-Poly EL5123: color and quantization 6
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Frequency Responses of Cones and the uminous Efficiency Function Luminous Efficiency Function Yao Wang, NYU-Poly EL5123: color and quantization 7 y b g r i d a C C i i , , , , ) ( ) (
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Tri-chromatic Color Mixing Tri-chromatic color mixing theory Any color can be obtained by mixing three primary colors with a ght proportion right proportion Primary colors for illuminating sources: Red, Green, Blue (RGB) Color monitor works by exciting red, green, blue phosphors using separate electronic guns follow additive rule: R+G+B=White Primary colors for reflecting sources (also known as secondary colors): Cyan, Magenta, Yellow (CMY) Color printer works by using cyan, magenta, yellow and black (CMYK) dyes follow subtractive rule: R+G+B=Black Yao Wang, NYU-Poly EL5123: color and quantization 8
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RGB vs CMY Magenta = Red + Blue yan = Blue + Green Magenta = White - Green yan = White - ed Yao Wang, NYU-Poly EL5123: color and quantization 9 Cyan Blue Green Yellow = Green + Red Cyan White Red Yellow = White - Blue
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Demo with Photoshop Show the mixing using RGB, CMY colors
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This note was uploaded on 01/22/2012 for the course EL 5123 taught by Professor Yaowang during the Fall '07 term at NYU Poly.

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lecture2_color_quant - Lecture 2 Color Representation and...

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