[argyllcms] Re: Using Argyll with an old densitometer (non-XYZ)
- From: Thomas Kumlehn <thomaskumlehn@xxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Mon, 10 Apr 2006 09:44:18 +0200 (CEST)
Thanks for your advice and sharing your experiences.
I'll have a look for spectrophotometers - to better handle different film
stocks. And for sure it needs to work automatically from remote. The X-810
manual lens punch mechanism is indeed a nightmare.
y.s.
Thomas Kumlehn
PIXEL PARTNER (C) Digital Film Services
http://www.PixelPartner.de
mailto:ThomasKumlehn@xxxxxxxx
--- Wolf Faust <mailinglist@xxxxxxxxx> schrieb:
> 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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