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Colour Management - How It Works - Input (Scanner) Profiles

Before using a high-end scanner in a Colour Managed environment you will need to have ICC Input Profiles created for it. It is highly unlikely that any supplied (with the software or "found" on the Web) "canned" profiles will be of sufficient quality, or will match your particular scanner's optical, chromatic or gradation characteristics. Your scanner will need to be carefully calibrated before profiling can commence. This is especially important if you are presently scanning in CMYK, as you will now need to scan in RGB.  A high-end drum scanner such as a Crosfield or Fujifilm Celsis will need special "setup files" or "C.V.'s" (Customer Values). Your old CMYK setups cannot be used as they relate to specific (CMYK) printing processes.  Of course with RGB scanning you can forget about printing! This comes later at the output stage.  ("Device Independent Colour"). These setups will be used to scan both the IT8 Chart used to make the profile and the production images.  Do not get "Setups" and "Profiles" confused. Setup files tell the scanner how to make a scan and are proprietary to that particular scanner manufacturer, while ICC Profiles describe the colour data in an image created on a particular device (scanner, camera, etc.) and are made to precise formulae laid down by the ICC (International Colour Consortium). ICC Profiles can be used in "ICC-savvy" applications such as Adobe Photoshop or Fuji ColourKit Editor to convert images from one colour space to another.  i.e from the scanner's own RGB colour space to a printing press's CMYK colour space, or indeed a "standard" RGB colour space such as "Adobe (1998) RGB".

An IT8 colour chart is a colour transparency or reflection copy original containing carefully defined colour and grey patches. They are available for many (but by no means all) photographic emulsion types.

              

This chart will have a corresponding data file which describes the precise actual colour of each patch (as measured with a spectrophotometer by the chart's manufacturer). The RGB image of the chart will be taken into a special profiling application (such as Fujifilm ColourKit Profiler Suite or Gretag MacBeth ProfileMaker)) which will compare the scanned image's RGB values recorded on each patch with the relevant (CIE Lab or CIE XYZ) numbers in the data file. An ICC profile will then be generated.

The resulting profile will tell the scanner or Image editing software (Fujifilm ColourKit, etc.) or Photoshop how to convert a scanned image's RGB values (from 0 to 255) into the "Profile Connection Space" (PCS) which is usually CIE Lab (Lab for short). These Lab values will be the actual colours on the original transparency or reflection photo!  You may then decide to convert the image to a "standard RGB colour space" such as Adobe (1998) RGB, or to convert the image directly into your output (printer) colour space, usually CMYK.  

Digital cameras can be profiled in a similar manner. This involves incorporating a "Color Checker" chart into an image, or in portrait photography having a subject hold it!  This may entail creating a profile for every shoot. For some this works well, and yet others prefer to use their camera's supplied profile, or a generic RGB colour space.

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