[argyllcms] Re: Using Argyll with an old densitometer (non-XYZ)
- From: "Wolf Faust" <mailinglist@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Sun, 09 Apr 2006 10:30:53 +0200
On 21 Mar 2006 at 9:26, Thomas Kumlehn wrote:
> Did any of you already use an X-Rite 810 colour densitometer, just capable
> of reading Neg densities in RGB ?
Yes. The X-Rite densitometers are often used by recorders for
calibrating the machines...
> Or can anyone point me to a book or web source how to convert the X-810
> RGB-densities to CIE-XYZ space as needed for CMS. I need the matrix
> coefficients or the primaries vectors for the color filters and light
> source used in the X-810.
If you can't get such data in a good accuracy, I would recommend you
measure the used negative film using a spectrometer in order to get
the XYZ data. Than use this data for calculating a density->XYZ
conversion for use with the X-Rite 810, but this conversion would be
material specific. So you would need to do this for all
dyes/materials measured. For slide films and photo paper you might
use the XYZ and density data published in reference files of IT8
targets to calculate a density<->XYZ conversion.
> The good thing about it - used X-810's are availlable and much cheaper than
> color spectrometers.
When measuring the calibration strips of my recorders the X-Rite
device already showed visible faults in the gray axis wich is why I
replaced the X-Rite devices here with a more stable spectrometer for
linearizing the recorder LUTs. Don't missunderstand me, the X-Rite
devices are reliable and have always worked here within the specified
tolerances. The problem was, that while you measure the recorders
calibration strip, the measurement of the X-Rite devices often
changes slightly. Even if a change of 0.01 in density doesn't sound
much, such a change can become visible in the gray axis. At least the
Kodak LVT/Durst Rhino software doesn't "smooth" the X-Rite readings
well enough to avoid sudden visible jumps in the gray axis.
So, if you use the 810, I would recommend a strong smoothing setup of
the approximation used in argyll in order to compensate the
measurement shifts of the device. This might avoid a visible shift or
jump in the profile. Once you have setup the density->XYZ conversion
I see no reason why the 810 should not work. But it must me a
nightmare to read several hundred or even thousand patches using the
device...
--
Wolf Faust Tel: +49-69-5486556
mailto:wfaust@xxxxxxxxx Fax: +49-69-95409598
http://www.coloraid.de Mobile: +49-179-6924769
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