Colour Management - How It Works - Output (Printer) Profiles
Output profiles are a description of the characteristics of either your own inkjet printer or printing press, or more likely, a particular printing standard's (ie ISO) "ink on paper." In the case of an offset litho press they will be in a CMYK colour space, and this is usually also the case with a high-end inkjet or other digital printer. They automatically factor in Dot Gain and the all-important Total Ink Coverage.
Printer
Profiles
are
created by
printing an image of a
special characterization
chart. This must be printed exactly
as a
production job.
This chart is also a variety of an IT8 chart or
increasingly an ECI2002 chart. In
this case it is in CMYK
format. It will have hundreds of patches made of precisely
defined CMYK tints. This chart
will be measured by a spectrophotometer,
which is connected to the computer running the special profiling
software. A spectro
measures the spectral
response at many
points on the
spectrum, unlike a densitometer
which measures the density
of just three colours and black.
The
measurements
obtained for each patch will be in either CIE Lab or CIE
XYZ
values.
These represent
the exact
colour achieved on
each patch on the printed IT8 chart.Usually the software will ask various questions about Total Ink Coverage, GCR & Black Printer, Rendering Intent, etc.
An output profile will then be generated. This will be more complex than an input or monitor profile. The biggest part of the profile will have tables which convert the Lab values to the CMYK percentages required for our printing process.
So our input profile takes our image from our scanner's or camera's RGB colour space to CIELab. Lab is our Profile Connection Space (PCS). Next our output profile takes it from Lab to our press's CMYK.
We can therefore go from any input device to any output device. We can also scan a single RGB image and output it to several totally different printing conditions, even after the original has been returned to the client. This is true "device independent colour", otherwise known as SOOM (Scan Once Output Many).Our Press Profile can also be used for proofing purposes, either soft (using a computer display) or hard (typically as a Reference Profile for an inkjet system).
Inkjet printers are profiled using the same technology, but only after a lengthy calibration (linearization) process has been completed. Inkjet and Proofing page.
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