Colour Management Information from

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Colour Management - How It Works - Output Profiles

Output profiles are a description of the characteristics of either your own 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 an inkjet 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 chart. This must be printed exactly as a production job.
This is also a variety of IT8 or 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 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 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 Lab.  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).

Hints and Tips for Inkjet Calibrating and Profiling.

Inkjet printers, whether used as "large format" (display) printers or as proofers, can give extremely good colour rendition when properly profiled. The profile quality, and therefore the print quality, is heavily dependent on the initial calibration however. This calibration, which may be a part of the printer driver, or a part of the RIP software, needs to be done very carefully prior to profiling. This is also known as "linearizeation".

The calibration will optimise the quantity of ink to the particular paper or substrate which you are using. By doing this, you will achieve the best quality possible for a particular paper type. This is particularly important if you are not using the standard stock for your printer. The calibration involves setting the Total Ink and/or Ink Limits and Restrictions and Ink Linearizations. It also ensures reasonable Grey Balance, before profiling. The calibration routines may be visual, or preferably, use a spectrophotometer. This ensures that just enough ink to produce good solid colours and black is printed, and no more! Too much ink results in poor drying, "puddling" and degraded or dirty colours.  Some modern RIPs require as many as four test charts to be printed, and critically, allowed to dry. This all adds to the time and cost involved in profiling an inkjet, but the resulting print quality is well worth the extra effort. If you are using a cheaper, low weight paper, you will only get the best quality achievable from that paper and ink, but no more.

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