[argyllcms] Re: Using Argyll with an old densitometer (non-XYZ)

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...

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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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