[argyllcms] Re: dispwin vs xcalib loading LUT

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 02 Jan 2007 21:03:51 +1100

Stefan Döhla wrote:
Hm, I'm tempted to say "yes" - but: there are a bunch of other loaders
that count as well - Logo Calibration Loader, Monaco thing, Spyder
ProfileChooser, WindowsXP Color Control Panel, xcalib, dispwin, ...

I can't agree with you. It's not a matter of a vote, it's a matter of
what's technically correct. I can't imagine Apple changing what they
do because others have mis-implemented a private tag of theirs, no
matter how widespread such a mis-implementation is.

 >>   ramp[j] = 65536.0 *
 >>           pow (j * (rMax - rMin) / nEntries, rGamma * SYSTEM_GAMMA)
 >>           + rMin);

That doesn't differ much from my formula above

The handling of min/max is rather different - you've got it inside
the power, whereas the correct formula has it outside the power. In
practice I wouldn't imagine it will often matter, since there seem
to be few profiles that use the formula, and even fewer with values
for min/max other than 0.0 and 1.0 respectively.

Hm, maybe it's safe for both dispwin and xcalib to add a parameter for
a gamma-nominator/mulitplier or something like this. But still I'm
interested how all the other loaders work and will do some tests.

In practice it probably doesn't matter much - who's going to go to
the trouble of calibrating their system, and then use a single
number to represent it ? Anything serious is going to use a table.

        Graeme Gill.

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