Color Management Systems

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.or
  g.
• 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 PCSs CIELAB and CIEXYZ
• Both specified with D50 white point
• Devicelt--gtPCS must account for viewing
  conditions, gamut mapping and tone (e.g. gamma)
  mapping.

4
Gamut mapping, tone control, etc
Viewing-conditionindependent space
Input imageand device
Chromatic adaptation and color appearance models
input devicecolorimetriccharacterization
DVI color space(PCS)
DVI color cpace
DVI color space (e.g. XYZ)
Chromatic adaptation and color appearance models
output devicecolorimetriccharacterization
Chromatic adaptation and color appearance models
Output image and device
Viewing-conditionindependent space
Gamut mapping, tone control, etc
5
ICC Profiles

• Device profiles
• Colorspace profiles
• data conversion
• Device Link profile
• concatenated D1-gtPCS-gtD2
• 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
Pantone Color Combo of the Month January 1999
That's all for today