Re: monitor calibrators
Re: monitor calibrators
- Subject: Re: monitor calibrators
- From: Chris Murphy <email@hidden>
- Date: Mon, 23 Apr 2001 11:28:20 -0600
C. David Tobie writes:
>
On to part two: what about other devices? We've heard a lot lately about the
>
advantages of using real spectrophotometers to calibrate monitors, from
>
companies that have supported the SpectroCam, and now from Gretag Macbeth
>
with thier EyeOne moniotor calibrator. "True 64 band spectral data, capable
>
of reading the quirks and spikes of LCD screens!"... but lets consider the
>
balance of this capability carefully. If three sensors is unsufficient to
>
determine the color of monitor phosphors, and only capable of accurately
>
deermining luminance, what about the other extreme? What value can we place
>
on 64 bands of spectral data, versus the three in a Chroma4, or the 8 or 9
>
in
>
a Monitor Spyder or a DTP92? Considering that these monitor profiles need to
>
be applied using current technology, there is such a thing as overkill.
It's not about extra data because you get the same AMOUNT of data
regardless of the measurement device since ultimately we must use XYZ or
Lab in our monitor profiles.
The difference in quality comes from more accurate readings. Colorimeters
don't see spectra, they have to assume spectral behavior in order to
measure color. These assumptions are good so long as what is being
measured has the assumed spectral behavior. In the case of emissive
colorimeters, this is for a CRT.
The spectra are different between a CRT and LCD, therefore the assumption
of the colorimeter is basically wrong when it comes to LCD's. It will
report a colorimetric value that does not jive with what our eyeballs are
telling us.
An emissive spectrophotometer makes no assumptions (or more honestly, it
makes far fewer assumptions). It sees the full spectrum and mathmatically
determines how a human would "see" a given spectral emission.
Now one might be able to argue that the assumption used for CRTs aren't
global for all CRTs, as different tubes are made with slightly different
materials. Usually this isn't a big deal, as the assumption a colorimeter
makes is still valid. Theoretically an emissive spectrophotometer would
do a slightly better job. Is it noticable? I think the potential
variation is getting down to the mathematics of the software at this
point - it's possible to get slightly more accurate readings from the
hardware device, but for the software to cause some discrepency (keep in
mind it has to play nicely with other profiles, CMM's, engines - etc.)
>
Until we are doing something significant with
>
true 3d look up tables for monitors, then the 8 or 9 sensor level is an
>
optimal balance for monitor profiling. 64 bands it a bit analogous to
>
carving
>
it with a scalpel, then applying it with a sledgehammer... but until
>
ColorVision releases an LCD optimized version of the Monitor Spyder, we
>
won't
>
know what the practical comparison really is.
In the case of using a colorimeter, there are some challenges targeting
the sensors to a stimulus response that works for both CRTs and for LCDs.
Additionally it would be necessary for either the device or software
(possibly both) to be instructed on what spectral assumption to make.
Assume an LCD spectrum, or CRT spectrum. And not only that but which LCD
spectrum as there clearly are more than one possible spectra for LCD -
perhaps more than CRT. (Note how a Monitor Optimizer does a respectable
job calibrating and profiling an Apple Cinema Display, yet produces dog
doo on laptop LCDs.)
Chris Murphy
Color Remedies (tm)
Boulder, CO
303-415-9932