color Image processing.ppt - Color Image Processing 1 For a long time I limited myself to one color – as a form of discipline Pablo Picasso It is only

color Image processing.ppt - Color Image Processing 1 For a...

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Color Image Processing 10/22/19 1
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For a long time I limited myself to one color as a form of discipline. Pablo Picasso It is only after years of preparation that the young artist should touch color not color used descriptively , that is, but as a means of personal expression . Henri Matisse
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Preview Why use color in image processing? Color is a powerful descriptor Object identification and extraction eg. Face detection using skin colors Humans can discern thousands of color shades and intensities c.f. Human discern only two dozen shades of grays
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Preview (cont.) Two category of color image processing Full color processing Images are acquired from full-color sensor or equipments Pseudo-color processing In the past decade, color sensors and processing hardware are not available Colors are assigned to a range of monochrome intensities
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Color fundamentals Physical phenomenon Physical nature of color is known Psysio-psychological phenomenon How human brain perceive and interpret color?
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Color fundamentals (cont.) 1666, Isaac Newton
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Visible light Chromatic light span the electromagnetic spectrum (EM) from 400 to 700 nm
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Color fundamentals (cont.) The color that human perceive in an object = the light reflected from the object Illumination source scene reflection eye
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describe a chromatic light source Radiance : total amount of energy that flow from the light source, measured in watts (W) Luminance : amount of energy an observer perceives from a light source, measured in lumens (lm) Far infrared light: high radiance, but 0 luminance Brightness : subjective descriptor that is hard to measure, similar to the achromatic notion of intensity
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How human eyes sense light? 6~7M Cones are the sensors in the eye 3 principal sensing categories in eyes Red light 65%, green light 33%, and blue light 2%
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Primary and secondary colors In 1931, CIE (International Commission on Illumination) defines specific wavelength values to the primary colors B = 435.8 nm, G = 546.1 nm, R = 700 nm However, we know that no single color may be called red, green, or blue Secondary colors : G+B= C yan, R+G= Y ellow, R+B= M agenta
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Primary colors of light v.s. primary colors of pigments Primary color of pigments Color that subtracts or absorbs a primary color of light and reflects or transmits the other two Color of light: R G B Color of pigments: absorb R absorb G absorb B C yan M agenta Y ellow
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Application of additive nature of light colors Color TV
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CIE XYZ (Tristimulus) model RGB -> CIE XYZ model Normalized tristimulus values Z Y X X x Z Y X Y y Z Y X Z z B G R Z Y X 939 . 0 130 . 0 020 . 0
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