[argyllcms] Re: Display calibration

  • From: Frédéric Mantegazza <frederic.mantegazza@xxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 1 Dec 2007 13:34:22 +0100

On samedi 01 décembre 2007, Graeme Gill wrote:

> Which version of Argyll are you using ?

0.70 (BETA6)

> The profile white point certainly look strange.
> I suspect that iccexamin isn't computing the white point
> temperature the same way as Argyll though, or the extreme white point
> is showing up the difference between Visual Daylight Temperature
> (which is where Argyll uses a modern measure of closest to
> the daylight locus - CIEDE2000), vs. the traditional CIE 1960 UCS
> space color difference formula used for Correlated Daylight Temperature,
> or Correlated Color Temperature (black body locus).

Ok. Note that both iccexamin and lprof show the same value.

> > Second, it seems that red color is over-saturated...
> Neither the calibration nor channel response curves look unusual.

Could it be a problem with lcms-based apps? All of them show the images 
with the same red color saturation. Is there a tool in argyll suite to 
convert a picture in the monitor color space? Then, if I display it 
without any color engine, it should look the same. Am I wrong?

> This is strange. You specified -m, yet dispcal hasn't skipped
> the monitor adjustment step.

I sould have made a mistake when I cut/paste the log...

> > Adjust R,G & B gain to desired white point. Press space when done.
> >   Initial B 110.80, x 0.1985, y 0.3899, VDT 6762K DE 30.2
> > / Current B 110.72, x 0.1984, y 0.3907  VDT 6753K DE 30.2  R+  G-- B+
> Note the white point is correlated to 6753K with a delta E of 30 ! This
> means that the white point is far from actually being at 6753K, merely
> that 6753K is the closest daylight temperature to the actual white
> point.
> If you want to actually have a white point lying on the daylight
> temperature locus, you need to adjust the RGB gain controls so as to
> reduce the delta E to near zero. Notice that the interface is suggesting
> you reduce green to move the white point in the right direction, or
> possibly increase Red and Blue.

Ok, I understand.

> > Initial native brightness target = 80.845374 cd/m^2
> > Had to scale brightness from 80.845374 to 80.818901 to fit within
> > gamut Target white value is XYZ 40.724326 80.818901 84.670188
> Notice the strange X value - this is because you've let dispcal
> calibrate to the native white point, and you've set your native white
> point to be extremely green.

This is true that I really see a green color cast on my monitor. But as 
soon as I load the LUT, with dispwin, then, no more green! And even if 
there is a red saturation, grey remains grey.

I'll make more tests.



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