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lecture13-2

Y is brightness i orange cyan q green magenta are

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Unformatted text preview: hat is equivalent to a given RGB on monitor 1 monitor YIQ Color Space YIQ is the color model used for color TV in America. Y is brightness, I (orange-cyan) & Q (green-magenta) are color are • Note: Y is the same as CIE’s Y Note: • Result: Use the Y alone and backwards compatibility with Result: B/W TV! B/W • These days when you convert RGB image to B/W image, the These green and blue components are thrown away and red is used to control shades of grey (usually) to Converting Color Spaces Converting between color models can also be Converting expressed as such a matrix transform: expressed Y 0.30 I = 0.60 Q 0.21 0.59 − 0.28 − 0.52 0.11 R − 0.32G 0.31 B Note the relative unimportance of blue in Note computing the Y computing Perceptually Uniform Color Space Color space in which Euclidean distance between Color two colors in space is proportional to the perceived distance perceived • CIE, RGB, not perceptually uniform – Example with RGB – LUV was created to be LUV perceptually uniform perceptually The CMY Color Model Cyan, magenta, and yellow are the complements Cyan, of red, green, and blue of • We can use them as filters to subtract from white • The space is the same as RGB except the origin is white The instead of black instead This is useful for hardcopy This devices like laser printers devices C 1 R M = 1 − G Y 1 B • If you put cyan ink on the page, no red light is reflected • Add black as option (CMYK) to match equal parts CMY Halftoning A technique used in newspaper printing Only two intensities are possible, blob of ink and no Only blob of ink blob But, the size of the blob can be varied Also, the dither patterns of small dots can be used Halftoning Halftoning – dot size Halftoning – Moire Patterns Repeated use of same dot Repeated pattern for particular shade results in repeated pattern repeated • Perceived as a moire pattern • Instead, randomize halftone Instead, pattern pattern Dithering Halftoning for color images...
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