RE: differences between colorimeter & spectrophotometer
RE: differences between colorimeter & spectrophotometer
- Subject: RE: differences between colorimeter & spectrophotometer
- From: "Raymond Cheydleur" <email@hidden>
- Date: Mon, 8 Oct 2001 11:28:18 -0400
- Thread-topic: differences between colorimeter & spectrophotometer
You take a day off and see what develops! Warning in advance this post
will be a bit long.
While I don't want to start pointing fingers, given that Don (who I
respect) points some in the direction of X-Rite, and then some
additional responses/questions were thrown in by Phil Green, CDTobie and
Roger Breton I will chime in with my two cents worth. I'm also going to
limit my response to a CRT discussion only, because I think there are a
whole host of issues other than instrument type when talking about LCD
calibration and profiling.
First from Don:
--------------
The myth that colorimeters out-perform spectrophotometers on CRTs was
perpetrated several years ago by X-Rite in an attempt to defend their
DTP-92
colorimeter against the superior (but more expensive) GretagMacbeth
SpectroLino. It is of course bunkum. The claim that three or four
mass-produced "broad-band" RGB filters which vary from batch to batch
and
instrument to instrument can somehow simulate CIEXYZ more effectively
than a
properly-calibrated spectrophotometer is a classic example of
pseudo-science. Don't believe it.
<snip>
---------------
It isn't pseudo-science, and of course the comment of "three or four
mass-produced "broad-band" RGB filters which vary from batch to batch"
is misleading at the minimum, and probably much worse. These filters are
highly controlled and in fact one of the filters in this instrument
probably costs more than all of the filters in some of our competitors
instruments.
As Phil Green points out in his response:
-----------
It's simply that CRT phosphors have very spiky emissions (a large
proportion of energy concentrated into vary narrow wavebands),
especially in red. To accurately record the resulting spectral emission,
you would need to sample at very small wavelength intervals. Most
spectrophotometers in commercial use sample at between 5 and 20nm, but
even 5nm is too crude.
-----------
This is REAL SCIENCE which has been backed up time and again from our
OEM customers, who have compared the 92 to other colorimeters and
spectrophotometers. Of course spectrophotometers attempt to smooth these
curves mathematically, but if you are unaware of the spike, you can't
take care of it with math. Of course there are other REAL issues when we
look at monitor calibration: Spot size, low light sensitivity,
interinstrument agreement... We generally come out on top here as well.
None of this is meant to be a slam against the Spectrolino or the EyeOne
Pro, both have versatility that the DTP92 doesn't offer and isn't
intended to. I contend that with this versatility you pay a price
somewhere in the mix, and again, this is backed up with REAL SCIENCE,
not just what is "good enough" for the marketplace.
------------
Don goes on to say:
I teach real-world color management six times a year at GATF and part of
the
course involves profiling 14 monitors in various stages of decay. We use
four SpectroLinos and the rest are profiled with the DTP-92 Monitor
Optimizer. Guess what? When you stand at the back of the room and look
at
the same gray test target displayed on all 14 monitors, four look
virtually
identical (guess which ones) and the rest make up a rainbow of different
pastel colors.
<snip>
----------
All I can say is this DOES NOT match what we've seen when we've done
similar test, nor does it match what plenty of OEM testing data reveals.
----------
Finally Don adds:
There are enough real problems in color management without deliberate
misinformation.
----------
I'd agree here completely, but I believe there is a point where thinking
men can disagree without tarring the other's reputation. I've got enough
Real Science and Real Data to disagree with Don on the facts. Don has
lots of Real World experience and has come to different conclusions.
Lastly, Roger and CDTobie both posed questions/responses about
recertification of instruments and whether an emissive colorimeter
should need this as compared to a spectrophotometer. I would contend
that ALL instruments should be recertified regularly. These are the
tools that you are basing your work on, and they should be maintained
like any critical part of your workflow. Yes, an emissive colorimeter
should require less frequent maintenance than a Spectral instrument, but
filters, diffusers and components age and any instrument should have a
regular maintenance schedule.
I'm going back to digging out from a day off now. :-)
RayC
Raymond Cheydleur, Lead Application Support Specialist,
Imaging and Graphic Arts, Developer Support
X-Rite Incorporated
Application Support email@hidden
Customer Support 888-826-3059