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Color Management Systems

Color Management Systems. Problems Solve gamut matching issues Attempt uniform appearance Solutions Image dependent manipulations (e.g. Stone) Device independent image editors (e.g. Photoshop) with embedded CMS ICC Profiles. ICC Color Profiles.

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Color Management Systems

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  1. Color Management Systems • Problems • Solve gamut matching issues • Attempt uniform appearance • Solutions • Image dependent manipulations (e.g. Stone) • Device independent image editors (e.g. Photoshop) with embedded CMS • ICC Profiles

  2. ICC Color Profiles • International Color Consortium http://www.color.org. • ICC Profile • device description text • characterization data • calibration data • invertible transforms to a fixed virtual color space, the Profile Connection Space (PCS)

  3. Profile Connection Space • Presently only two PCS’s: CIELAB and CIEXYZ • Both specified with D50 white point • Device<-->PCS must account for viewing conditions, gamut mapping and tone (e.g. gamma) mapping.

  4. Gamut mapping, tone control, etc Input imageand device Viewing-conditionindependent space input devicecolorimetriccharacterization Chromatic adaptation and color appearance models DVI color space(PCS) DVI color space (e.g. XYZ) DVI color cpace Chromatic adaptation and color appearance models Chromatic adaptation and color appearance models output devicecolorimetriccharacterization Viewing-conditionindependent space Output image and device Gamut mapping, tone control, etc

  5. ICC Profiles • Device profiles • Colorspace profiles • data conversion • Device Link profile • concatenated D1->PCS->D2 • Abstract profile • generic for private purposes, e.g. special effects

  6. ICC Profiles • Named color profile • Allows data described in Pantone system (and others?) to map to other devices, e.g. view. • Supported in Photoshop

  7. ICC Profile Data Tags • Profile header tags: • administrative and descriptive • Start of Header • Byte count of profile • Profile version number • Profile or device class (input, display, output, link, colorspace, abstract, named color profile) • PCS target (CIEXYZ or CIELab)

  8. ICC Profile Data Tags • Profile header tags: • ICC registered device manufacturer, model • Media attributes 64 attribute bits, 32 reserved (reflective/transparent; glossy/matte. ) • XYZ of illuminant • Rendering intent (Perceptual, relative colorimetry, saturation, absolute colorimetry)

  9. ICC Profile Rendering Intents • perceptual: “full gamut of the image is compressed or expanded to fill the gamut of the destination device. Gray balance is preserved but colorimetric accuracy might not be preserved.” (ICC Spec Clause 4.9) • saturation: “specifies the saturation of the pixels in the image is preserved perhaps at the expense of accuracy in hue and lightness.” (ICC Spec Clause 4.12) • absolute colorimetry: relative to illuminant only • relative colorimetry: relative to illuminant and media whitepoint

  10. ICC Profile Data Tags • Tone Reproduction Curve (TRC) tags: • grayTRC, redTRC, greenTRC, blueTRC • single number (gamma) if TRC is exponential • array of samples of the TRC appropriate to interpolation

  11. ICC Profile Data Tags • Mapping tags (“AtoB0Tag”, “BtoA0Tag”, etc.) • Map between device and PCS • Includes 3x3 matrix if mapping is linear map of CIEXYZ spaces, or lookup table on sample points if not.

  12. ICC Profile Special Goodies • Initimate with PostScript • Support for PostScript Color Rendering Dictionaries reduces processing in printer • Support for argument lists to PostScript level 2 color handling • Halftone screen geometry and frequency • Undercolor removal • Embedding profiles in pict, gif, tiff, jpeg,eps

  13. Canteen (Pantone 405 C) Violet Quartz (Pantone 689 C) Mecca Orange (Pantone 1675C) Pantone Color Combo of the Month January 1999 That's all for today

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