[argyllcms] Re: Calibrating a projector with a X-Rite DTP92
- From: Frédéric <frederic.mantegazza@xxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Sun, 4 Feb 2007 15:58:34 +0100
On Sunday 04 February 2007 13:37, Graeme Gill wrote:
> > Looking at the profil using iccexamin first shows that the LUT is
> > strangely corrected. The red and blue channels do not start from zero,
> > but from 0.15 and 0.07 repectively :o/ It can easily be seen on a
> > black desktop background, which becomes dark-red once the lut is
> > loaded by dispwin.
>
> The profile doesn't currently correct very well for offsets in the
> channels. The calibration does a much better job of this. Did you
> calibrate or just profile ?
We did both.
> > Do you have any ideas/experiences of the problem? Do you think the
> > DTP92 can't be used for such calibration? Is it very different from
> > the DTP94, which gives good resultat on projectors? Maybe there is a
> > piece of hardware missing on the 92, like a IR filter or so?
>
> I did have a play with calibrating and profiling a projector at one
> stage, but had a limited amount of time, and had a bug that was
> upsetting the result. I haven't tried that type of thing out again.
>
> I would imagine there could be spectral differences between the
> projector and a typical CRT, which is what the DTP92 is set for. A
> projector with dichroic filters and LCD, or a filter wheel and DLP +
> typical projector lamp probably won't have a CRT spectrum.
Hmmm, so the DTP92 can't be used? What about the DTP94? Is there anybody
here using it for projector calibration? Could someone make a test?
> The other aspect is the geometry and stray light aspect. You need to
> fill the aperture of the instrument with the screen somehow, either
> getting it close (without self shadowing of course), or use some sort
> of telescopic adapter. Stray light may be an issue too, since it will
> make the low end appear to be unresponsive.
The DTP was close to th screen (about 50cm), with an angle of 30° (to avoid
its own shadow).
> I built a telescopic adapter to try this stuff out, although I
> haven't characterized it's performance to any great degree.
> The lens I got hold of is acrylic, and needs a fair amount of
> correction at the blue end, to counteract the UV stabilizers in
> the plastic. The idea is to collect more light at a distance, while
> narrowing the instrument acceptance angle. I would have thought
> that the DTP92 was well filtered in terms of keeping stray wavelengths
> out.
Well, we could try such optical adapter...
--
Frédéric
http://www.gbiloba.org
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