[argyllcms] Re: dispwin vs xcalib loading LUT

  • From: Stefan Döhla <color@xxxxxxxxx>
  • To: Frédéric <argyllcms@xxxxxxxxxxxxx>
  • Date: Mon, 1 Jan 2007 13:22:11 +0100

Hi Frederic, Graeme,

>> Not being the author of xcalib, not without some effort. Can you clarify
>> a little how xcalib and dispwin behave on these two profiles (ie.
>> description of four cases).

I am, however I'm not the author of dispwin ;-)

When I started xcalib, I crosschecked with some other calibration
loaders to find out why gamma 1.0 in the vcgt tag makes the screen
darker when using these other loaders - 1.0 was supposed to mean
linear ...

Therefore I took the system gamma into account, which is 2.2 on Win32
and 2.222 on Unixes - voila: results were the same!

The ramp is then created from the gamma values rGamma, rMax and rMin like this:

for(j=0; j<nEntries;j++)
  ramp[j] = 65536.0 *
          pow (j * (rMax - rMin) / nEntries, rGamma * SYSTEM_GAMMA)
          + rMin);

I think xcalib's behaviour is correct - at least if the
result is compared to other calibration loaders like the WindowsXP
color panel, ...

Happy new year everyone


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