Page 128 - Graphic Design and Print Production Fundamentals

4.10 The Components and Purpose of a Colour Management System

Alan Martin

Our primary goal in colour management is to provide a consistent perceptual experience. As we move
from device to device, within the limits of the individual device’s colour gamut, our interpretation of the
colour event should be the same.

As we’ve discussed, but it’s worth repeating, we achieve that goal in two fundamental steps:

1. We give colour its meaning through device independent colour values correlated to a specific
device’s RGB or CMYK numbers.

2. We transform our destination device’s specific values to match the perceived colour
definitions of our source.

The Components

We have spoken at great length about colour profiles, but there are three additional pieces required to
enact a colour-managed workflow: the profile connection space (PCS), a colour management module
(CMM), and rendering intents.

The PCS provides the device independent colour definitions to which device values can be matched. The
ICC specification allows the XYZ or Lab colour spaces for the PCS.

Profiles provide the look up table for the conversion of device values to PCS and vice versa. Any
conversion requires two profiles (or a device link into which two profiles have been merged).

The CMM is the software engine that actually does the conversion. It lives in a product like Adobe
Photoshop or Kodak Prinergy, where file processing takes place. The CMM provides two major
benefits: it reduces profile size by doing the interpolation in colour calculations and compensates for
shortcomings in the Lab colour space. The CMM does the heavy lifting by providing the computation of
the conversion. For consistency, it is best to keep to a common CMM as much as possible. The Adobe
Color Engine or ACE is the CMM seen referenced in the Color Setup dialog window of the Adobe
Creative products.

Rendering intents are the instructions for dealing with out-of-gamut colours (see Figure 4.10). They are
user-selectable controls to define colour rendition when you move colour from one device to another.
There are four types of rendering intents: perceptual, saturation, relative colorimetric, and absolute
colorimetric. Each intent represents a different colour conversion compromise, resulting in a different
gamut mapping style.

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