[argyllcms] Re: Characterizing a scanner using Argyll

  • From: Nikolay Pokhilchenko <nikolay_po@xxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sun, 01 Feb 2009 10:14:47 +0300

-----Original Message-----
From: "Asman, Andrew J" <Andrew.Asman@xxxxxxx>
To: "argyllcms@xxxxxxxxxxxxx" <argyllcms@xxxxxxxxxxxxx>
Date: Fri, 30 Jan 2009 15:45:41 -0500

> ...I usually modify the color values on the patches to include significantly 
> more pure colors because I am predominantly measuring a printers ability to 
> uniformly print pure colors (CMYK) on a page.

But nevertheless, use You enough in-gamut patches to profile a scanner? May be 
Your profiles are exact only on a gamut boundary of a particular printer?

> ...For example, if I create a profile using pages from a printer and then use 
> the ICC profile to measure pages that were printed on the same printer, the 
> average delta E value when compared to the Gretag Spectrolino is consistently 
> under 2.
This is very good result. What scanner do You use? Generally it's quite hard to 
achieve dE76 less than 5.8.

> However, if I measure pages using a printer that has a larger gamut than the 
> one used to create the profile, then the out-of-gamut colors tend to produce 
> extremely large max delta E value ranging anywhere up to 100 depending on the 
> printers used.

What about in-gamut colors? Under 2dE? :)))

> Is there any way to increase the accuracy of the profile when faced with 
> out-of-gamut colors?

IMHO the way is the matrix+gamma scanner profile, because the LUT and even the 
shaper profiles can't predict out-of-gamut colors anyway. But the gamma can. 
The in-gamut and gamut boundary dE may get significant worse, but out-of-gamut 
colors must get significant better.
> When I create the profile from a ti3 file I generally use the following 
> command:
> colprof -v -qh -u -al <base_name>

colprof -v -qu -u -ag <base_name>
I suppose.

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