Practical Color Management: Eddie Tapp on Digital Photography

CHAPTER 2: Understanding Key Color Management Concepts

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Device Profiles

Once you calibrate a device, you’ll then want to create a

pro le that describes the device’s range of color and tone in

its calibrated state. These device pro les can communicate

with other device pro les in a color-managed work ow to

increase the consistency of results.

Output Pro les

An output pro le is a characterization of

the range of colors that a speci c printing

device and paper type reproduces.

To create an output pro le, a variety

of color patches must be printed and

measured with a device known as a

spectrophotometer. The next step is to

enter the data from the patches into a

software-pro ling application to create

an ICC pro le. The software compares the

known color values of the patches sent

to the printer to the actual colors that

were read with the spectrophotometer

and, using the data from that

comparison, creates an ICC pro le.

Monitor Pro les

A monitor pro le is created during the

calibration process with a device known

as a colorimeter, which compares the

values and colors that it reads to a

known set of values and colors. The

monitor pro le (also known as the system

pro le) will serve as a viewing  lter,

allowing you to see your image data

more accurately. The dynamic range, or

contrast levels, of the monitor is limited

by the maximum brightness that it has.

Newer LCD monitors are usually brighter

than older CRT monitors, and are thus

capable of a wider dynamic range.

Colorimeters

The Xrite Pulse Elite, a color spectrophotometer

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Input Pro les

Because scanners and digital cameras

don’t have a  xed gamut (see the next

section, “Color Space”), input pro les

for these devices are a little bit di erent

than output and monitor pro les.

Input pro les do, however, have a  xed

dynamic range. So an input pro le can

characterize a device, but it is limited

to the target that you use to create the

pro le. With scanners, this limitation is

usually not a problem because you can

make a target with a dynamic range and

gamut of colors as good as any image

that you would scan. A digital camera,

on the other hand, captures colors in the

real world much better than any target

that could be made. The camera-pro ling

software has to extrapolate the colors that

are outside the target’s gamut. For this

reason, pro ling digital cameras is limited.

Matrix and LUT Pro les

Pro les themselves can be matrix-based

or LUT (lookup table)-based, both of

which include the white point of the

device. But matrix-based pro les are

very small, while LUT pro les are much

larger and more complex. A matrix

pro le is a mathematical model made

up of the three primary colorants of the

device and some simple tonal curves,

referred to as a 3 x 3 matrix. A LUT-based

pro le contains much more information,

consisting of a table of numbers that

allows you to  nd an input value and

its corresponding output value. Matrix-

based pro les are used for simpler

devices, such as scanners and monitors,

while LUT-based pro les are used for

more complex devices, such as printers.

GretagMacbeth Color Checker SG

An IT-8 chart

Device Profiles

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