Imaging Technology Group Forum

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Imaging Technology Group Forum

• Color Management Essentials
• Matching Colors Between
• Monitors and Printers

Ben Grosser April 6, 2003
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The Color Problem
you see
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The Color Problem
your camera sees
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The Color Problem
in Photoshop you see
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The Color Problem
your colleague down the hall sees
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The Color Problem
printed out you see
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Why do we have this problem?

• Input and output devices see and/or reproduce
  colors differently
• technology
• age
• materials (paper, ink)
• color reproduction is variable and
  device-independent

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Why do we have this problem?
RGB 63,165,0
RGB 63,165,0
RGB 63,165,0
RGB 63,165,0
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The Solution A Color Management System
CMS
RGB 63,165,0
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The Components of a Color Management System

• calibrated display
• device profiles for each device
• methods for dealing with out-of-gamut colors
• document working space (embedded profile)
• color management aware application(s)
• color management engine
• cooperative device drivers

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Display Calibration

• optimize dynamic range, set to recognized
  standard
• display, not monitor
• parameters
• luminance (brightness)
• color of white, in Kelvins
• tone response curve (gamma)
• colorimeter or spectrophotometer for measurement
• what about software calibrators?

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Device Profiles

• a profile describes the color production/reproduct
  ion behavior characteristics of an individual
  device
• a lookup table for input/output vs. perceived
  color

Color Management System
RGB 63,165,0
RGB 62,167,0
display profile
printer profile
RGB 63,165,0 LAB 58, -76, 65
LAB 58, -76, 65 RGB 62,167,0
profile connection space
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Gamut

• a collection of colors that a device can produce

monitor 1
monitor 2
printer
camera
CIE 1931 chromaticity diagram
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working space

• an intermediate color space for editing

• Common Spaces
• Adobe RGB (1998)
• sRGB

• Others
• Apple RGB
• Colormatch RGB
• etc.

• Destination Recommendations
• Adobe RGB for printing
• sRGB for displays

CIE 1931 chromaticity diagram
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out-of-gamut

• gamut areas which do not overlap between devices

additive (RGB)
subtractive (CMYK)

• rendering intents (perceptual, saturated, rel/abs
  colorimetric)

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Calibration and Profiling Demonstrations

• display calibration
• printer profiling
• soft proofing in Photoshop CS
• out-of-gamut examples

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Other Applications?

• Adobe
• Acrobat uses profiles, but assumes a rendering
  intent (appears to be relative colorimetric)
• Acrobat does not support soft proofs
• Illustrator supports soft proofs and profiles,
  but again, no rendering intent
• Microsoft
• All MS apps are not color-managed apps!
• method 1 convert to PDF, and use Acrobat for
  printing
• method 2 use ICM OS-level color management
  (windows)
• method 3 use Colorsync OS-level color management
  (Mac)
• Word 2003 has CM bug! (XP ok)

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Beckman-Specific Considerations

• All VMIL workstation displays are calibrated and
  profiled
• We have printer profiles for
• HP DeskJet 5000 Poster Printer
• Tektronix Phaser 560 color laser
• Epson 2200 Inkjet
• HP Business Inkjet 3000 (matte and glossy)
• HP Laserjet 5500
• We have a scanner profile for the VMILs Epson
  1680
• profiles (done) and instructions (in progress)
  available from
• http//www.itg.uiuc.edu/help/printing/
• EyeOne available for checkout to ITG users

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Some Caveats

• Viewing conditions (ambient light) and display
  technology make a huge difference
• Any color management setup is not 100 accurate!
• cant model every color
• gets close enough
• calibration goes a long way on its own (w/
  generic profiles)
• Not all applications support color management
• dual-monitor support non-existent
• CRT vs. LCDs ?
• digital camera profiles impractical

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Bibliography

• Books
• Real World Color Management by Bruce Fraser et
  al
• Understanding Color Management by Abhay Sharma
• Mastering Digital Printing by Harald Johnson
• Websites
• http//www.robgalbraith.com (color mgmt. forum)
• http//www.computer-darkroom.com (tutorials)
• http//www.digitaldog.net (tutorials)

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Acknowledgements
Anni Hsia
Marc Taylor
Daniel Weber