Re: HP Dreamcolor Display: So far, so good.
Re: HP Dreamcolor Display: So far, so good.
- Subject: Re: HP Dreamcolor Display: So far, so good.
- From: Graeme Gill <email@hidden>
- Date: Mon, 29 Sep 2008 19:41:45 +1000
email@hidden wrote:
Simply put, if you know what you are measuring, you can tune either a
spectral device or a colorimeter device to well-reproduce what you are likely to
measure. Its similar in concept to the discussion we had recently about camera
profiling. Think of the monitor calibrator as a simple camera. The colorimeter
has only several bands while the spectral device has many. But since no device
perfectly satsifies the Luther condition, the device has to be calibrated (kind
of profile) for the likely scene (monitors) to get the best performance.
No, I don't think so. Spectrometers aren't "tuned" for any particular
device, they are calibrated to measure the spectrum as accurately as possible,
and the XYZ values flow from the spectral values. (There is
no "LCD" or "CRT" mode for a spectrometer for instance).
Display colorimeters on the other hand are calibrated with a 3x3 matrix,
and typically have physical filters that don't quite match the XYZ observer
curves, so it is quite natural to compensate for the resulting errors
by tuning the matrix to suite particular classes of peaky emissive sources
(typically CRT and LCD). For a general purpose colorimeter (not
dedicated to emissive displays), you couldn't really do that.
Since the spectral device has more bands, this argues for going spectral for the
better accuracy, in principle. Unfortunately, as with many things in life, it
comes down to signal/noise. Since the bands of a spectrophotometer are much
narrower than that of a colorimeter, the signal reaching the detector is much
less. So at a similar price, all else equal, the spectral device will have better
This seems faulty logic to me. Yes spectrometers have smaller bands,
so for a given amount of light each band has a lower S/N, but there
as precisely as many more bands as they are narrow, canceling out the
overall effect. The more likely explanation for colorimeters (generally)
having a higher S/N ration for a given integration time is that it's
easy/cheap to have much larger sensors that pick up more light. Typically
a spectrometer has to be able to read a small reflective area (3-6mm dia)
and then squeeze it through a slit that sets the bands width. This restricts
the amount of light collected, hence the S/N.
Graeme Gill.
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