[argyllcms] Re: Number of patches - well behaved printer?

  • From: Iliah Borg <ib@xxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 24 Feb 2011 07:30:01 -0500

Dear Rishi,

On Feb 24, 2011, at 1:44 AM, Rishi Sanyal wrote:

> "Profile is between measured values and scanned values, mapping
> scanned values to measured values. So it reproduces the chart."
> Reproduces 'the chart' or the 'the chart on the film'?

But of course, chart is on the film. Reproduction here is of a physical object, 
that is why we are operating measured values, not the desired values. So, in 
your words - "the chart on the film" is the subject of reproduction. This 
allows to approximate how the particular film responds to the light. 

For reproduction of the original scene, not the reproduction of the 
reproduction of the particular scene on a particular scene, one needs to shoot 
the target himself. In my view, the truth is in-between, and I often use two 
profiles on two layers and blend them.

> Sorry, again I'm confused. Let's leave out my own film & just talk
> about Wolf Faust's, say, Velvia 50 IT8 target. You confirmed that Wolf
> (or whomever) will, after recording the IT8 chart on the film, read
> the spectral values of the IT8 chart as recorded on the film (not the
> theoretical XYZ values of the IT8 chart itself, but the values of the
> chart as they appear on the exposed film, back-illuminated by a
> standard illuminant). Then the profile will map the scanned values to
> the XYZ (or whatever device independent tristimulus values) values
> measured by the spectrophotometer of the image of the chart on the
> very film you're scanning.
> This does not create a profile that reproduces the chart's theoretical
> color. It only reproduces the chart's colors on the film, correct?


> If, on the other hand, I took a reflective IT8 target, illuminated
> with a D50 lamp, and:
>     1. Measured all chart values using a spectrophotometer, saved
> these as XYZ measurements in a reference file
>     2. Shot the same chart with the same illumination on my own
> Velvia 50 film using a SLR
>     3. Developed then scanned said shot in my Minolta DSE 5400 w/ all
> auto corrections off
>     4. Built a profile from this raw scan using the measurement file
> created in 1.
> *Then* I would build a profile that reproduces the original chart
> (under that illumination). That would in a sense, I believe, remove
> the film from the equation & attempt to recreate what the
> spectrophotometer saw of that chart under that illumination.

Yes, except it is not D50 but the light the film is balanced for. 

Iliah Borg

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