Xrite DTP-92 and ColorVision Optical - VERY weird behaviour
Xrite DTP-92 and ColorVision Optical - VERY weird behaviour
- Subject: Xrite DTP-92 and ColorVision Optical - VERY weird behaviour
- From: Thomas Holm / Pixl <email@hidden>
- Date: Fri, 28 Jun 2002 14:54:24 +0200
Here's a weird on, I'd love to hear an explanation on...
I was called into a client having a problem with his monitor calibration.
His Mitsubishi 2045u (Mac OS 9.2.2 G4) calibrating with Optical 3.5.1 with a
DTP-92 couldn't achieve the default 0.3 black level.
First I Ran Precal set to 6500 K, No problem.
When doing the Optical calibration initially everything went fine, Did a
black calibration as prompted, set the black level to 0.2 Cdm2 (which I
prefer over 0.3) Brightness adjusted to 90CDm2.
Brightness on monitor ended up being 83% and Contrast about 90%.
Checked the curves, everything looks fine. Client was baffled and said he
just couldn't get the brightness high enough.
Then I ran Optical again, did another black calibration and had a black
reading of 0.00 CDm2. Quit Optical, ran it again, new black cal. Brightness
showed at 0.00 (where my previous calibration with same brightness setting
showed 0.20.
Quit Optical, try one of my DTP-92's and got a black of 0.16...
Quit Optical, try the same DTP-92 and got a black of 0.00...
The I figured something must be wrong with the black calibration, so
produced a double sheet of black velvet for the black calibration, pressed
the DTP down in the velvet, and packet the velvet around (absolutely no
chance of light hitting the sensor) and still had varying results on the
black reading without changing the brightness setting (this was consistently
weird on all 3 DTP's).
Puzzled, I opened the colorimeter window, punched in 0,0,0 on the reading,
initialised (black calibrated the device) and had a luminosity reading (Lab
and Luv) of 0.00 (which I know is bogus because at the time we had a lot of
incandescent light hitting the screen). Then I put a piece of black velvet
over and around the device and something really weird happened, the
Luminance INCREASED to L7,8.
So by insuring that even less light would reach the instrument, the
luminosity reading increased!?!
Retrying this procedure a few times (with the velvet over the sensor both
for black calibration and wrapped around the sensor for measuring) gave
varying values ranging from 0.00 to 7.8. The I attached a Spyder (one of the
new ones) and had a L reading of 14,6...
I guess the conundrum is two-fold, but both could be tied into the black
calibration of the DTP done by Optical:
1: Why do I see differing black readings without adjusting the monitor
settings (Black calibration done on table or velvet)?
2: If I have a black reading of 0.00, and put velvet over the instrument
when attached to the monitor, how can I possibly get a higher L reading when
less light hits the sensor?
Is it hardware (on 3 DTP-92 devices), software (black calibration of the
DTP-92 on Optical 3.5.1), is it that particular monitor, or is it the
computer config or a combination of the above???
I've been running optical myself for a 3-4 years and have seen nothing like
the above behaviour (I've had lots of other problems but unrelated to this
one).
Meanwhile my client can calibrate his monitor satisfactorily, but only when
the black level reads out as 0.2 Cdm2 (which is rarely), so it's a bit hit
or miss for him...
Any takers?
Best regards
Thomas Holm / Pixl ApS
---
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Home Page:
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