[argyllcms] Re: How do I create a linear luminance LUT?

  • From: Geoff Ghose <geoff@xxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 6 Jul 2011 19:18:34 -0500

Thanks for you quick response.

Yes, I've been doing both a profile and calibration. The luminance I'm
interested in XYZ. And when I do a calibration with a target gamma of 1.0,
and then do report on calibrated monitor (using DisplayCalGUI) I get the
native gamma, not 1.0.

Moreover, quick spotreads verify that the gamma isn't close to 1.0.

On Tue, Jul 5, 2011 at 7:33 PM, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote:

> Geoff Ghose wrote:
>> I apologize if this is a very basic question, but I'm really quite lost. I
>> want an icc monitor
>> profile that approximates linear input to luminance. (Yes, I realize that
>> it can only be an
>> approximation, and will suffer especially at low values).
> Please read 
> <http://www.argyllcms.com/doc/**calvschar.html<http://www.argyllcms.com/doc/calvschar.html>
> >.
> Now do you mean a profile or calibration ?
> A monitor profile doesn't give you any particular luminance, it
> characterizes
> the device (i.e. tells you what XYZ/D50 L*a*b* value you get for any
> RGB input).
>  So an RGB value of 128,128,128 is half the luminance of 255,255,255. (This
>> are for visual
>> psychophysics experiments).
> Luminance defined in what space ? L*a*b* space ? Jab space ? XYZ space ?
> They will all be different.
>  I have tried setting target gamma to 1.0, but that really doesn't seem to
>> do much of anything:
>> when I run a report on the uncalibrated and calibrated monitors I get
>> essentially the same
>> gamma. My impression is that all the calibration is doing is trying to
>> ensure that the color
>> temperature is pretty consistent across input levels, but not remapping
>> the input output
>> relationship so as to significantly change gamma.
> Sounds like you are talking about calibration. You can setup a calibration
> that maps
> RGB to L* using the dispcal -gl, but note that if you are interested in
> precisely
> what's going on, the non-zero nature of black on a real device will mess
> this
> up - see 
> <http://www.argyllcms.com/doc/**dispcal.html#g<http://www.argyllcms.com/doc/dispcal.html#g>
> >
> Graeme Gill.

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