[sane-devel] gamma correction procedure

[Karl Heinz Kremer]

On Feb 9, 2004, at 2:56 PM, abel deuring wrote:

> 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 IT8 target is not very useful when you want to create printer 
profiles. You need much more color patches, and you need colors that 
actually allow the profiler to calculate a profile from. The patches on 
the IT8 target are not evenly spaced enough for a printer target.

One way to avoid the spectrophotometer is to (ab)use a scanner as a 
spectrometer/colorimeter. The mechanism is such that you first 
calibrate the scanner, then scan a printer target and read the color 
values from the scanner, color correct them and use these values as 
basis for a profiler.

At the end you will have three ICC profiles: One for the scanner, one 
for the monitor and one for the printer. Your ICC-aware software would 
then calculate the correct color transforms for image->screen and 
image->printer (the image would contain your scanner profile).

>
> 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.

My color tool (hack) for the Gimp can be used to apply ICC profiles 
within Gimp: http://www.khk.net/color/color_manager.html
This is almost four years old, and I have no idea how it works with 
current versions of Gimp and LCMS. You've been warned ... :-)

Karl Heinz