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

[Thomas Kumlehn <thomaskumlehn@xxxxxxxx>]

Your reply was as helpful as could be.
Thanks a lot - also for the very interesting PDF links. 
Unfortunately, the shop download didn't work for my account this time.

--- Graeme Gill <graeme@xxxxxxxxxxxxx> wrote:

> Thomas Kumlehn wrote:
> 
> > Did any of you already use an X-Rite 810 colour densitometer, just
> capable
> > of reading Neg densities in RGB ?
> 
> What you're asking for can be done, but it needs a fair bit of work,
> if you have to do it all yourself.
> 
> Basically you have to create a mapping between the negative densities,
> and CIE values of whatever it is you think you want to control.
> At one extreme this might be the colors that the end viewer sees,
> after the image on the negative has gone through the complete
> production chain, or you may pick some intermediate point,
> and attempt to control it instead.
> 
> The bottom line though, is that you are going to have to measure
> some test patches with both you X-810, and a colorimeter/spectrometer,
> in order to create the mapping.
> 
> I think some of the folks involved with the ICC Motion Picture Working
> group have attempted this type of thing (see
> <http://www.color.org/groups.html#digital2>).
> [I know at least one of the people characterizing film built an automatic
> film patch reader using a Gretag i1 out of LEGO, so that they could read
> their whole
> 33^3 grid of motion picture film test patches automatically.]
> 
> There are probably some articles out there that could help you.
> See <http://www.imaging.org/store/epub.cfm?abstrid=22202>,
> <http://www.imaging.org/store/epub.cfm?abstrid=22204>,
> <http://www.imaging.org/store/epub.cfm?abstrid=22205>,
> <http://www.imaging.org/store/epub.cfm?abstrid=6893>
> for instance.
> 
> > 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.
> 
> This isn't going to take you in a useful direction. The filters and light
> source in the X-810 are irrelevant, since they are optimized for
> process control, not reading CIE values. The mapping between density and
> CIE
> values could possibly be modelled mathematically (after taking
> a lot of measurements to create the models from), but in practice you
> might be better off created a general (LUT based) transform based
> on a large set of measurement pairs. This is analogous to creating
> a device profile, except that instead of device values, you
> use density values. After creating the "profile", you can then
> map three densities to a CIE value. Such a transformation will
> be specific to certain film stock and production chain of course.
> 
> > If successful and of interest for this community, I'd be happy to
> provide
> > the sources for my filmread solution. But regarding the reduced
> > functionality of the X-810 compared to the newer devices, I doubt it'll
> fit
> > to the general device interface used by argyll.
> > The good thing about it - used X-810's are availlable and much cheaper
> than
> > color spectrometers.
> 
> But cannot substitute for a colorimeter or spectrometer.
> 
> Graeme Gill.
> 
> 



        

        
                
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• References:
  • [argyllcms] Re: Using Argyll with an old densitometer (non-XYZ)
    • From: Graeme Gill

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