Building a scanner profile

In a colour management workflow, the image or colour item follows a route through the various applications that use it. The colours inside this item —which can be a photo, a painting, a 3D object, or a drawing— will ideally be 'tagged' with a colour profile. That profile should remain attached to the item throughout its 'life cycle'.

When you enter an image into your system by scanning it, it is important that the scanner be calibrated and profiled prior to using the device for production purposes. If you have a scanner that came with SilverFast —almost all of them do these days, with the exception of Imacon— you're lucky in that you can buy a version with IT8.7 calibration capabilities.

If you want to read more on SilverFast and scanner calibration, I've written a complete series of articles on SilverFast and colour management on IT-Enquirer.

Other users who don't have SilverFast, or those users who want to use specialist profiling targets like the Hutcheson target, will first need to buy their scanner target (*). Scanner targets come in two versions: reflective and transparent. Use the reflective target for scanning reflective media such as silver halide prints or paper media. The transparent target should be used if you plan to use your scanner to scan slides.

There are no targets for creating negative film profiles. It wouldn't make sense to create a profile for an orange or brownish "bearer" layer that needs to be converted to positive colours before you can actually see what's on the film.

When you have the target you would like to use, place it on the scanner, following the instructions for regular scanning. Usually, you will have to position your media in a corner on a flatbed scanner. You should see to it that the entire target is scanned, without any detail left out as a result of bad positioning. Also, make sure you have the sides lined up with the scanner's rulers or sides neatly, so that we don't have to straighten the image as this will result in measuring errors. Of course, SilverFast users can skip these requirements completely. Their setup is semi-automatic.

You should scan the target at 240 dpi or ppi with Quality Factor set to 1 (if your scanner software provides you with a Quality Factor setting). The target should be scanned using the scanner's raw capabilities. Most scanners will have a setting called HDR. This is an acronym for High Dynamic Range and in scanner dialect it means: everything the scanner can 'see'. Profiling a scanner is much a process of trial and error, as most HDR images will be much too dark to discern any details in the scanned image. The target should therefore be scanned until the Tonal response Curve for the scanner is right. This TRC or gamma-setting should be somewhere around 2 or 3 for most scanners.

You set the TRC or gamma in the scanner software. With SilverFast this is an Options setting. With other scanner software, you should really consult your manual, as this may differ from manufacturer to manufacturer. Your scanner should also offer you the capability to fix its exposure setting. If it doesn't, your profiling a moving target. While you might create a profile for each exposure setting and then average the resulting set of profiles, this is not the ideal situation.

Next: Building a colour profile for a digital camera

(*): Some people will want to use a GretagMacbeth Digital ColorChecker as a scanner target. While in theory you can use such a target, I strongly recommend against it. The ColorChecker targets are specifically aimed atprofiling digital cameras, not scanners. The best result for your scanner will be with the IT8.7 target mentioned above.