Introduction to Colour
Management
This is
intended as a basic introduction with a few hints & tips.
Modern Colour
Management revolves around the use of ICC
Profiles. These
describe
how a particular device "sees" colour. In the case of a scanner or
camera; or outputs colour, such as a printing press, or even a colour
monitor. This
is
usually
in conjunction with a particular type of material; such as a colour
transparency
or reflection print on a scanner; or a particular paper stock and
ink on a
press.
What is the ICC?
ICC is short for
"International
Colour Consortium", a body comprising of
many manufacturers of equipment and software used in colour
reproduction. They
oversee the internal format of profiles, but not the
resultant pictorial
quality.
How
many Profiles do I need for scanning?
When
converting an
RGB image, from a scanner or digital camera, to a
CMYK image for use on a printing press, there are
three profiles involved:
1) Input or Scanner Profile. This
is in an RGB colour space and
describes how the input device captures
colour. In the case of a scanner it should be specific to
your own machine (and be created on your
machine). So it may be
named something like "CompanyName Celsis 6250
Tranny.icc" Click
for
information on scanner profiling.
In the case of a
digital camera it may be
specific to that camera model, or be a
generic RGB colour space such as "Adobe (1998) RGB" or "sRGB." These
later are not strictly profiles, but are used as profiles. If there are
no quality profiles available for your particular camera, select the
RGB colour space which gives the best results. Your camera will likely
have been tuned for that RGB space.
2) Output or Printer Profile. In
the case of a printing press this is in CMYK. It
describes how the press prints colour using a particular paper stock
and ink set. It also defines the "Total
Area
Coverage"
(maximum ink weight), black printer and GCR (Grey Component
Replacement) parameters. It will most likely be to a commom
standard (rather than a particular press) such as "ISO",
"Euroscale" (now obsolete), or "SWOP" (a U.S. web offset
standard).
For
information on printer profiling.
Please note that the ISO (International Standards Organisation) do not
actually issue or endorse profiles. Profiles labelled "ISO" have been
generated for use on presses printing to ISO 12647-2 standard.
3) Monitor Profile. This is an RGB profile describing how your
monitor displays colour. So if calibrated, it may be
something like
"Bobs MacPro Monitor 20_03_08.icc". If your monitor is uncalibrated,
your Mac will use a "generic" profile (such as "MacPro"). For
information on monitor calibrating and profiling.
How
many Profiles do I need for proofing?
When proofing using
an inkjet proofer, there are two profiles required:
1) A Reference Profile which is
in a CMYK colour space.
This describes the
final printing conditions which you are simulating. It might
be
describing a real company's press and paper such as "CompanyName
PressName
Glossy.icc"; or it could be generic
such as "Euroscale...icc", "ISO...coated.icc" or "SWOP_coated.icc".
2) A Paper Profile which is usually CMYK. This describes the
inkjet printer, which you are using
as a proofer, and it's ink and
paper. It might be named
something like "Epson xxxx Coated.icc". The extension ".icc" denotes
"International Colour Consortium". Profiles supplied with the
printer or proofing software will only be relevant if using the
appropriate manufacturer's paper and ink, and Linearization, etc. Even then you are usually
better off having custom profiles created. You should also investigate
using quality proofing papers which conform to ISO 12647 standard, and having
this paper profiled.
How it all comes together
Input Profiles convert a device
such as a
scanner's or digital camera's RGB values into a Profile
Connection Space (PCS)
which is
usually CIE Lab.
Output Profiles convert Lab values to a printing press's or
inkjet printer's CMYK, or occasionally (some inkjets, dye-subs, etc.)
RGB, values. Read
our
next page, Scanner
Profiling.
