[sane-devel] gamma correction procedure

[abel deuring]

Christopher,

> I see what you (and Gerard) are saying now.
> 
> Assuming I used an IT8 target to calibrate my scanner, could I then use the procedure I outlined
> to calibrate my printer?  Or I am still not getting everything you are saying?

In general, yes. The professional way would be to use a colour 
densitometer, but these devices are really expensive. A cheaper solution 
would be (1) to create an ICC profile for the scanner, (2) to print an 
IT8 target image on your printer, and (3) to create an ICC profile for 
your printer. But I have never tried this before, so it's pure theory...

The main problem will probably be a "complete ICC integration": In order 
to use the ICC profile for the printer, you need a printer driver or 
another program which knows how to handle ICC profiles for the printer. 
I know just one larger Linux program  that supports ICC profiles: 
Scribus. But if you are mainly interested in good prints of photos, the 
TIFF/JPEG processing tools coming with lcms might be sufficient.

> 
> I take it there are at least three gamma distortions I need to worry about: my monitor, my
> scanner, and my printer.
> 
> Using an IT8 target would allow me to separate the scanner's gamma distortion from the other two. 
> The procedure I proposed could then let me calculate the gamma distortion for my printer.

Right; only that ICC profiles provide a far better color correction than 
pure gamma manipulation ;)

> 
> Correcting my monitor would be the hardest of all.  The simplest thing to do would be to display
> an image of the IT8 target on my screen, hold a physical IT8 target in my hand next to the
> monitor, and make adjustements to the monitor's gamma settings until my eye felt the two agreed
> largely.

At http://www.littlecms.com you'll also find a profiler program for 
monitors.

Abel