Color Management with Mac OS X Tiger




Introduction

Color has the ability to communicate, to please, to excite, and to engage. Color makes
a difference—often a dramatic difference—in your photographs, your graphics, and
your layouts. Getting color right early in the workflow, and keeping it right to the end,
is increasingly critical in the fast-paced, deadline-driven digital world. Yet photographers
and designers are frequently dismayed when they print an image and the color is wildly
different from expectations. These disruptive surprises can cost time and money and
cause delivery delays and disappointed clients.
Color is an elusive phenomenon. Say “red,” and you’re describing a sensation that your
eyes and brain associate with a certain wavelength of light. But exactly how “red” is
the red? Computers use numbers to more precisely define color; for example, Red 255,
Green 0, Blue 0 is a ratio of numbers that describes the maximum “red” in a digital file.
But what does this red really look like? And how do you ensure its consistency at every
step of the workflow—from capture to computer screen to ink on paper—when each
camera, scanner, and printer records or outputs colors a bit differently?
Mac OS X version 10.4 Tiger provides a robust, standards-based solution for color management.
ColorSync, Apple’s universal color translator, delivers consistent and accurate
color across devices and at all stages of production. With ColorSync integrated into
Mac OS X, you can implement a complete color-managed workflow.



The ColorSync Foundation

Creative workflows make use of a wide variety of imaging devices, such as digital
cameras, scanners, printers, and computer displays. But for each device, the same combination
of numerical values yields a different color. For example, a single pixel where
red equals 100, green equals 100, and blue equals 100 should produce a completely
neutral gray tone, but on some devices the gray will look warm, or reddish, and on
others the gray will look cool, or bluish. The inherent disparities between the devices
can cause the colors within an image to render differently from one device to another.
In fact, every device—from scanners to displays to printers—has unique color capabilities.
Successful color management involves translating color accurately from one
device to another across your workflow.
The International Color Consortium (ICC) was established to address this issue.
Founded in 1993 by Apple and seven other vendors, the ICC now has a member base
of more than 70 industry-leading manufacturers and software developers, including
Sony, Hewlett-Packard, Creo, Adobe, and Quark. The charter of the ICC is to create and
promote an open color management architecture and vendor-neutral file formats. At
the core of its development efforts are ways of characterizing device color and transforming
colors between devices.


Color Management Module

To reproduce consistent color from camera to display to printer, a translation—known
as a color space conversion—has to occur between devices. The color management
module, or CMM, is the mathematical engine that ColorSync uses to perform the color
transformation based on an ICC device profile to produce the expected color. The more
accurate the ICC profiles are for each device, the greater the consistency that ColorSync
will have in translating color from device to device.
When an image created with a digital camera is displayed, the CMM translates the color
space of the camera (its input profile) to the color space of the display (the destination
profile). Another such translation occurs when the image is printed, using the ICC profile
to define the printer. For each translation, the CMM must consider the gamut of colors
for each device and what must be done to accommodate the differences. This is where
rendering intents come in.


Rendering Intent

Because color spaces can vary greatly, the rendering intent determines how the CMM
will translate colors from one device’s color space to that of another. Each ICC profile is
tagged with a default rendering intent (usually perceptual), but the user might prefer
to select a rendering intent from within a color-savvy application. The following four
rendering intents are used to reflect different imaging requirements.