[argyllcms] Re: Profiling backlit film with Monitor

  • From: Edgar Loser <loser@xxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 23 Nov 2017 09:34:05 +0100

Well to be honest I would not recommend...

Ok the whitepoint of your monitor would be well defined (D65) but the spectral distribution of this "light source" would be quite poor: it only contains very narrow areas (peaks) for red, green, and blue region. This will lead to very strong metamerism effects (poor CRI/TLCI). Another problem will be the homogeneity of the screen...

For your purpose (I guess your intention is to use the printer profile not for "absolute colorimetric" output, but for "relative colorimetric" or "perceptual") you can (primarily) forget the color temperature of your illumination (i.e. the color of your illu, i.e. the color of your white) because it will be adapted.

I would wait for direct sunlight, stick a sheet of (homogeneous) paper on your window, stick your backlit chart on top of it and measure there. If you cannot wait for sunlight and you want to use another light source take care that the distribution of the light is very homogeneous. And you should choose a light source with high CRI/ high TLCI.

Perhaps the best solution would be to measure you backlit material with white backing using the i1 in reflectance mode and do some numerical adjustment of your spectral measurement. I don't know argyll in any detail, perhaps it's already implemented so I explain what to do. For each patch and for each spectral value you have to:
Take the spectral value of the color patch (Rc) and the spectral value of the unprinted patch (Rp) and calculate the result (Rf). Rf= sqrt(Rc/Rp)*Rp
The idea behind this numerical adaption: In reflectance mode the light coming out of i1 is passing the colored layer of your backlit material once, afterwards it will be scattered back by the back of the backlit material or the white backing and it will pass a second time the colored layer. So the "color" will be measured twice by the i1 and the only thing for the correction is we have to do the sqrt()...

Am 23.11.2017 um 07:15 schrieb Tony Mah:

Wondering if this is possible?

I have an NEC monitor with a 3d LUT set at D65, could I:
1. print a sheet of backlit film with color patches
2. display white on the monitor
3. put the film on my calibrated monitor
4. use my i1pro and measure each patch like a piece of paper
5. generate an rgb profile that will work on my printer?

In theory if the backlit display of the sign holder is 5000k, I should be able to calibrate my NEC to 5000K and profile patches on the printed file.

What do you guys think?

lakeBits Inh. Edgar Loser
Haydnstr. 25
78464 Konstanz
Tel 0049 7531 5844154 0
Fax 0049 7531 5844154 9

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