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

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 06 Jul 2011 10:33:44 +1000

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>.

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>

Graeme Gill.

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