Re: Colorimeter vs. Spectro
Re: Colorimeter vs. Spectro
- Subject: Re: Colorimeter vs. Spectro
- From: Roger Breton <email@hidden>
- Date: Sun, 02 Jan 2005 19:25:46 -0500
Marc,
> Consider this: In some cases, displays will exhibit
> spikes in their spectral behavior.
All commercially available red phosphors have these very sharp, narrow
spikes, as far as I can gather. So, modern LCDs and CRTs have them. It has
to do with the strontium rare earth used to make the red material.
> In the case where a spike falls between
> the narrow bands of a spectro - the instrument will fail to capture accurate
> visual data which may potentially compromise the accuracy of any subsequent
> profile.
Yes, this is so true. That is why to accurately make spectral radiance
measurements of a monitor, the instrument has to have the highest resolving
power, otherwise it will miss the sharp peaks of the strontium, like you
said. 10nm is never enough, even 5nm won't cut it. Only a PR-650 or Minolta
CS-1000 grade of instruments have that spectral resolving power to do this
job accurately (1nm resolution for the CS-1000).
> On the other hand, a colorimeter uses 3 or 4 wide band filters. Because the
> spectral behavior of each of these filters is known precisely, the
> instrument can "blanket" the spectral range of any sample and deliver a very
> precise colorimetric value.
Depends on the quality of the filters. The closer the filters to the
Standard Observer the better the measurement. But, that is not always
possible/feasible economically, is it? So, we have to rely on calibration to
fill the gap. Incidently, what kind of source is used at X-Rite, ColorVision
and GretagMacbeth to calibrate the likes of DTP-94s, Spyders and i1Displays?
> Incidentally, it is my impression that Colorimeter filters are engineered to
> match the human eye response and not the spectral character of the device
> which they are measuring.
This is the "broad" principle, Marc. But how closely do the filters used in
any wide band colorimeter match the Standard Observer is another story. I
have yet to see manufacturers named above publish this data -- which you can
see on instruments of the grade of UDT systems.
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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