[argyllcms] Re: Custom Illuminant

  • From: <robert@xxxxxxxxxxxxxxxxxx>
  • To: <argyllcms@xxxxxxxxxxxxx>
  • Date: Mon, 7 Jul 2014 11:38:53 +0100

Quote:
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> - I'm not sure if I mentioned this, but Soft-Proofing with Simulate Paper
in
> Photoshop does the equivalent of: Convert to Profile with selected intent;
> Convert back to working space with Absolute Colorimetric.

Right, but exactly how does it convert from the printing device to display ?
You say "with Absolute Colorimetric", but for the printer to PCS _and_ PCS
to display, or
just the first part ?

Note that the ICC seem to think that people expect/want the "half absolute"
conversion,
where it becomes a relative colorimetric interpretation of the absolute
appearance
of the print (hence the forced use of the chromatic adaptation tag in V4).
This is not
 strict soft proof. A strict soft proof is absolute for both, so that the
XYZ values on
the screen are the same as the XYZ of the (expected) print.
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Reply:

I don't know how to test this properly. What I've done is to use three
copies of a ColorChecker image.
Copy1 is soft-proofed with RelCol, Simulate Paper On
Copy2 is converted to paper using RelCol, converted to working space using
AbsCol, converted to monitor using RelCol
Copy3 is converted to paper using RelCol, converted to monitor using AbsCol 

The D50 Lab values measured using an i1Pro (same spot, measurements taken
seconds from each other) are close to each other.
  
Delta E from Copy1 to Copy2 is 1.4 on yellow
Delta E from Copy1 to Copy3 is 0.5 on yellow

Delta E from Copy1 to Copy2 is 0.9 on blue
Delta E from Copy1 to Copy3 is 0.8 on blue

So, hardly conclusive, but slightly favouring the AbsCol to monitor (not
AbsCol followed by RelCol).

If you know how I can test this correctly I'll be happy to give it a go.

Robert



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