Color Management System 1

Copyright 2006 Printing Industry Center at RIT– May not be reproduced without permission.

V_2005a

Color Management System

R. Chung, Professor Color management is about managing the extended print media process involving more than putting dots on plate and ink on paper.

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Topics

!  Color imaging reality

!  Color management solutions

!  Color management components

!  Color management in action

!  Color imaging challenges

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Color Management System 2

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Color Imaging Reality

!  A color imaging system typically consists of a number of diverse components.

Input� Process� Output�

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Color Imaging Reality

!  Poor device-to-device color agreement exists. –  Input devices

-  Scanners / Digital cameras / stock photos –  Display devices

-  Monitors used by art directors, prepress houses –  Output devices

-  Presses / Digital printers / Proofers

!  This lecture focuses on color management issues, i.e., achieving color agreement.

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Color Management System 3

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Color Imaging Reality

!  Large number of color-related mistakes –  High level of failure, wastes, and frustration

?

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Color Management Solutions

!  Huge number of possible conversions from any input to any output –  (n x m) combinations

(n x m) conversions

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Color Management System 4

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Color Management Solutions

!  Solution by ICC color management –  A hub is used to go from one device to the other. –  (n + m) combinations

(n + m) conversions

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Color Management Solutions

!  International Color Consortium –  Founded in 1993 –  Purpose

-  To create and promote the standardization of an open, vendor-neutral color management system

–  http://www.color.org

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Color Management System 5

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CMS Components

!  PCS !  Profiles !  CMM

•  Rendering intents •  API

A B A

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PCS

!  Profile Connection Space –  Denoted as �B� space –  Allows us to give a color an unambiguous numerical value in

CIEXYZ or CIELAB that doesn�t depend on the various devices

!  Is the parameter to measure and define colors

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Color Management System 6

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Profiles

!  A profile describes the relationship between a device�s (RGB or CMYK) signals and the actual color that those signals produce –  A profile is device specific.

!  A profile is a look-up table (LUT). –  Denoted as �A� space

!  Profile doesn�t alter a device behavior. –  It only describes the behavior.

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Profiles

!  The CMM takes two profiles, i.e., a source profile and a destination profile, to convert colors pixel by pixel. –  The source profile tells the CMS where the color comes from. –  The destination profile tells the CMS where the color is going.

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Color Management System 7

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CMM

!  Color Management Module

!  Software engine that converts RGB or CMYK values of an image using the LUTs in the profiles.

ICCProfile

ICCProfilePCS

CMM

DataFile

DataFile

API

(Source) (Destination)

A AB

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CMM

!  It converts values from the source color space to the PCS (A2B).

!  It, then, converts values from the PCS to a destination space (B2A).

ICCProfile

ICCProfilePCS

CMM

DataFile

DataFile

API

(Source) (Destination)

A AB

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Color Management System 8

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CMM

!  Available CMMs can be located at Library/ColorSync/CMM in OS X –  Apple –  Ace (Adobe Color Engine)

!  Adobe CMM was released in 2006 for use in non-Adobe applications. –  http://labs.adobe.com/downloads/cmm.html

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Rendering Intents

!  Three look-up tables (LUTs) –  ‘0’ for perceptual –  ‘1’ for colorimetric –  ‘2’ for saturation

!  Four rendering intents –  Perceptual –  Relative colorimetric –  Absolute colorimetric –  Saturation

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Color Management System 9

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Perceptual Rendering

!  Denoted as ‘B2A0’

!  Preserves the overall color appearance and the overall color relationships while the entire gamut is compressed –  Suitable for rendering pictorial color images that contain many

out-of-gamut colors.

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Relative Colorimetric Rendering

!  Denoted as ‘B2A1’

!  Recognizes the white point from the destination profile

!  Matches reproducible colors –  Does not affect colors already within the destination gamut

!  Clips out-of-gamut colors

!  Used for proofing on actual substrate

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Color Management System 10

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Absolute Colorimetric Rendering

!  Map the white point of the source to its destination.

!  Matches reproducible colors –  Least delta_E –  Clips out-of-gamut colors to the closest reproducible hue.

!  Used for proofing to simulate the final substrate

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Saturation Rendering

!  Denoted as ‘B2A2’

!  Keep saturated colors in the source to the destination to produce vivid colors. –  Suitable for pie charts and other business graphics

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Color Management System 11

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API

!  Application Programming Interface –  A feature in operating system software

-  Provides color matching to application software using standard architecture and profile format

ICCProfile

ICCProfilePCS

CMM

DataFile

DataFile

API

(Source) (Destination)

A AB

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CMS in Action

!  Photoshop as API –  Assigning profiles –  Embedding profiles –  Converting with profiles

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Color Management System 12

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Assigning Profiles

!  Use menu command to assign or not assign a profile to an image.

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Assigning Profiles

!  Give the RGB or CMYK numbers specific definition. –  It will change the colors, not the numbers.

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Color Management System 13

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Assigning Profiles

!  The same digital values, e.g., 200R, 100G, 50B will appear differently in different RGB working spaces.

1) Build a RGB image.2) Make a duplicate, and3) Assign different RGB working space to the duplicate.4) Compare with the initial RGB image.

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Embedding Profiles

!  Embed or not embed a profile when saving the file.

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Color Management System 14

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Embedding Profiles

!  Provide color portability –  Scan to print –  Digital illustration to display

!  Increase the file size –  The size of the profile

!  Not suited for test targets and terminal files

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Converting with Profiles

!  It needs two profiles, i.e., a source profile and a destination profile. –  The source profile figures out what actual colors the numbers

represent. –  The destination profile figures out the new set of RGB or CMYK

numbers needed to represent those same actual colors on the output device.

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Color Management System 15

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Converting with Profiles

!  It changes the RGB or CMYK numbers in the file. –  Denoted as ‘A2B2A’

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Color Imaging Challenges

!  Desktop prepress technology has revolutionized imaging and publishing industries. –  ICC-based color management pushes its boundary.

!  The success of CMS depends on –  Process stability –  Device profiling –  Process control

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Color Management System 16

Color Imaging Challenges

!  Color management is about managing the extended print media process. –  Involving more than putting dots on plate and ink on paper

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Summary

!  ICC color management system simplifies the color conversion. –  It reduces (n x m) number of conversions to (m + n) number of

conversions from the source color space to the destination color space.

!  Color management has two tasks. –  CMS has to figure out what perceived colors our RGB and

CMYK numbers represent by ‘assigning’ a profile to an image. –  CMS has to keep those colors consistent as we go from device

to device by ‘converting’ an image from one device color space to the other.

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