I have some scans of crayon drawings, but the colours are washed out (well, the colours are pretty light on paper too):
First, some due dilligence. Google for solutions. (Actually, first fire up GIMP and try a few ideas. But let's pretend I hit the books before hitting the lab).
- google'd: post processing scanned crayon drawings - no help, but kids drawing reenacted was entertaining.
- google'd: scanning crayon drawings - better, results in a yahoo answers entry... which suggests GIMP. Also a couple of references warning about crayon wax sticking to scanners (I didn't have this problem).
- searched flickr for examples in the hope of finding a discussion in comments. Photos tagged with crayon art was the best of the flickr searches. Several people, including Steve brandon, used a camera, rather than a scanner.
Ok, that's enough searching. Let's play with some balances. Here's screenshots of the settings (from GIMP's colour menu) and the changed versions of the image.
I bumped up blue similarly.
Applied these settings after inverting the image.
I expanded this settings box out to make fine control easier.
In the end I went with the first take, as the least abstract of the bunch.