What is an
ICC color workflow? First lets remove ICC from the question. The
purpose of a managed color workflow or color management system is
to provide color consistency and predictability throughout the entire
workflow. Ideally we would like to maintain color accuracy
from start to finish, regardless of the hardware and software we
use and we would like the process to be standardized and repeatable.
is simply an abbreviation for International Color Consortium,
a fancy name for a color standards organization that included big
names like Kodak, Agfa and Fuji among others back in 1993. This
group developed new standards and rules for color profiles, the
data file that characterizes a devices color. This standardization
made it possible for different software and hardware devices to
communicate color in the same consistent and repeatable way. It
paved the way for a workable color managed system or workflow utilizing
any device or software, something once only possible with a closed
A closed loop
system is just that, a color managed system that utilizes one input
device, a single computer for data editing and one output device.
Additional devices or software cannot be added to the mix. Photographers
and lab managers have managed closed loop systems for years by painstakingly
calibrating and monitoring their systems and by utilizing well established
and proven process control procedures. For example Eastman Kodak
developed strict process control procedures for color processes
like E-6 ,C-41 and Kodachrome to help lab owners and photographers
manage and control these processes. Professional photo processing
labs, even today are highly revered for their process control. Their
customer's livelihood (photographers) is dependent on the accuracy
and repeatability of their equipment, processes and workflow.
With the advent
of digital, however, the traditional closed loop controlled process
gave way to an open and difficult to control process or workflow.
The variables in the process increased dramatically. Traditional
silver based processes were well known and understood, digital files
and the digital process was not. With the advent of ICC standardization,
however, digital files could now be quantified and labeled. Critical
color information could be attached to digital files via a standard
that other devices could translate and interpret.
Photography Analogy... Minilab process control:
a traditional photographic minilab, a chemical based closed loop
workflow system, is the same in concept as the electronic one shown
in the diagram below.
The key to
a color managed workflow is the color conversion process, how do
we convert and maintain color consistency from one device to another.
First we should take a look at color limitations and color
gamut. Color gamut is the range of color reproducible by
a particular device, for example computer monitors generally have
a larger color gamut than inkjet printers, and can therefore reproduce
and display a greater range of color than an inkjet printer. This
is a very important concept to understand. Photographers and generally
anyone that works with digital imagery tend to analyze and make
corrections to their images on a computer monitor. Photographic
images will never be an exact match in print to the screen because
a conversion and re mapping of color values occurs during the printing
process. Optimally the printed image will closely match the original
on screen, but it will never match it exactly because each has a
different color gamut.
These two images
clearly demonstrate color gamut differences and limitations between
devices. The original image on the left is a screen capture from
Photoshop as displayed in Adobe 98 color space on a monitor. The
image on the right is another screen capture from the monitor but
print emulation (soft proofing) has been activated and out of gamut
colors are displayed as black. What you see in this second image
is an approximation (utilizing ICC standards, profiles and a color
conversion engine) of what this image would look like when printed
to an ink jet printer. Even though we have optimized and controlled
our process the ink jet printer has color limitations, it cannot
reproduce all of the vivid red colors displayed on the monitor as
noted by the muted colors and "black" out of gamut warning.
Many of you
are probably familiar with the word calibration but maybe not as
familiar with characterization. These two words and their definitions
are often confused when we discuss color management.
is the act of tuning or bringing a device to a known standard. If
for example we have an adjustable thermometer (some of you may remember
these from the darkroom days) you can place that thermometer into
a bucket of water along with a more expensive, highly accurate and
certified mercury thermometer. You can adjust the adjustable thermometer
so that it matches the temperature read on the mercury thermometer,
in effect calibrating it. In the digital color world, monitors,
printers, scanners, etc. are all devices that can be adjusted or
calibrated to a known standard.
is the act of characterizing or describing how a device
performs; its capabilities, limitations, etc. We can for example
characterize an automobiles performance? Does the vehicle perform
well under adverse weather conditions, does it have front wheel,
rear wheel or four wheel drive? How does it handle sharp turns and
bumps in the road? Is it a luxury sedan (smooth ride) or an off
road truck (rough ride)?
scanners, printers, color management hardware, etc. can all be described
in mathematical terms that computers can understand and utilize.
Software enables us to characterize these devices.
This characterization describes how the device interprets or creates
color, what are its tendencies limitations or faults. A particular
device may have a color bias or lack sensitivity to a certain color.
Software lets us create files that describe
our devices, this descriptive file, called a PROFILE
can then be interpreted by hardware and software within an ICC color
workflow. It enables us to convert colors from one device to another
and manage color in a predictable and repeatable fashion.
to a known standard, characterize to
describe. It is important to remember these definitions and what
role they play in managing color.
The Fuji 3500
printer on the left has a built in calibrator and calibration routine.
The Epson printer on the right does not and thus cannot be calibrated.
Once a profile is created for the Fuji printer the calibration routine
will keep it in control (consistent color) even when paper is changed.
If however ink or paper are changed on the Epson printer the original
profile may not provide consistent or accurate color because it
cannot be calibrated (brought to a known standard). Which printer
would be easiest to manage, as far as color is concerned?
Color Conversion Process
OK, how do
we make this all work? We know that digitally captured images cannot
be reproduced on the printed page so as to completely match the
original scenes color. The color gamut of our original scene must
be compressed and altered, but how can we retain as much of the
color and color relationships of that scene as possible?
As shown in
the illustration above the colors from the original scene had to
be compressed throughput the process and the number of colors available
from the original to the printed image is dramatically reduced.
The color conversion process that takes place within an ICC workflow
manages this compression by re mapping colors to retain the look
of the original, even though the color gamut may often be compressed
or reduced. The method used to remap colors from one device to another
is critical to the success of a Color Management
System or CMS.
There are four
components that make up an ICC color management system, the PCS
(Profile connection space, normally CIELAB), the device Profile,
a CMM (color management module)
and Rendering Intent. Lets take a look at all four
of these components and the role they play in a color management
The profile connection space is the color space in which
the color conversion or remapping takes place. We already know that
CIELAB is an ideal color space for this conversion because it is
not Device Dependent, for this reason CIELAB is
usually the profile connection color space used.
A Profile is a file that describes the color characteristics
of a particular device or color space. For example monitors, scanners,
printers and cameras can all have profiles that describe their unique
color properties. An image is often described as tagged with a profile,
basically this is a very small file that is actually "tagged"
or associated with your image file. A profile can be removed or
changed, but doing so does not alter the original file.
A color management module is the engine that converts color
data from one profile or color space to another. For example Apple's
Colorsync engine can convert an images colors from a monitor color
space to a printer color space and vice versa.
When a color conversion is applied from one profile to
another four different rendering intents can be applied. A rendering
intent is simply the method for mapping or re mapping color values.
You can select the rendering intent that best suits your purpose
or image characteristics.
Is the default standard for digital imagery. Any colors
that fall outside of the devices color gamut are replaced within
the target gamut, hue and lightness are preserved. For most images
this intent best retains the overall color qualities of an image
as it is converted from one profile space to another.
When the color conversion or remapping takes place colors
may be shifted, but the relationships between colors is retained,
perceptually retaining the look of the original. If the Relative
Colorimetric intent does not produce satisfactory results, perceptual
mapping is generally the second choice for images.
Colorimetric: Colors that reside outside of the target
devices color gamut are simply clipped or removed. This is not an
ideal choice for images.
Tries to retain color saturation of original at the expense
of hue and lightness. Often used for graphics where saturation is
important, but again generally not a good choice for photographic
on the image below to see how different rendering intents effect
Conversion in Action...
OK, lets put
this all together. As an example, lets look at the workflow we might
use if we wanted to ICC color manage an image from scan to output
above illustrates a typical ICC color managed workflow from scan
to print. If the device can be calibrated then
by all means do so. Calibrating to a known standard gives us a standard
and consistent base on which to view and judge color.
As the digital
image or file passes from one device to the next a color conversion
takes place via these device profiles. Remember device profiles
characterize how a device renders color. A color management module
(CMM) like Apple computers ColorSync
translates color information from one device to another by utilizing
The CMM takes
in data and converts it according to the specification (Rendering
Intent) you select. A simple analogy would be baking cookies. You
start with a recipe, put it all together and bake it in an oven
(the conversion engine). If the recipe changes (profile/color lookup
table) or the oven is set to a different temperature (rendering
intent), the resulting cookies will be different. The
important point to remember here again is that the goal is to produce
predictable and consistent results. A properly adhered to cookie
recipe and color managed ICC workflow can both do that for us.
Concepts and terminology....
review of all of the material covered in this tutorial check
out this Review form
purpose of a managed color workflow or color management
system is to provide color consistency and predictability
throughout the entire workflow.
is the act of tuning or bringing a device to a known standard.
Characterization is the act of characterizing
or describing how a device performs.
ICC (International Color
Consortium) is a color standards organization.
gamut is the range of color reproducible by a particular
File that describes numerically the color characteristics
of a device or color space.
The profile connection
space is the color space in which the color conversion or
color re mapping takes place.
A color management
module is the engine that converts color data from one profile
or color space to another.
Intent: The method used for remapping color values.
There are 4 different rendering intents used in an ICC color
managed workflow, Perceptual, Relative Colorimetric, Absolute
Colorimetric and Saturation.
colorimetric is the best rendering intent choice for most
digital image files.
managed workflow goal is to produce consistent and predictable
on to the Color Tools page....