[argyllcms] Re: Argyll in the classroom

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 21 Apr 2005 12:49:15 +1000

Roger Breton wrote:

> I wanted to say that I managed to use argyll in a college classroom setting
> today, with success. The students generated, printed and measured a 60
> patches target (I know it's not much but they had to measure one patch at a
> time). And they made a profile out of it.

Hi Roger,
        good to hear that you have had some success.

> I wonder how I can have them identify the limit of the gamut of this printer
> with argyll?

There are a couple of ways. One is to visualize the gamut using
a VRML viewer. Use iccgamut <http://www.argyllcms.com/doc/iccgamut.html>
to create a .wrl file, and then view it.

To create a view in L*a*b* of the absolute gamut of a CMYK file with an ink
limit of 260%, one might use:

     iccgamut -w -ff -ia -l260 profile.icm

and the resulting files will be profile.gam and profile.wrl.

You would need to locate a suitable standalone VRML viewer or
browser plugin to view the result. This
<http://vrmlworks.crispen.org/get_browser.html> might be a good place
to start looking.

You can use the viewgam utility <http://www.argyllcms.com/doc/viewgam.html>
to compare multiple gamut surfaces and view them.

If you want to explore the gamut in more technical detail, then the xicclu
utility <http://www.argyllcms.com/doc/xicclu.html> will let you do that.
Setup a reverse lookup, and an out of gamut target color will return the
annotation [clip], along with the nearest device values. For instance,
to explore the absolute gamut of a CMYK profile, 260% ink limit in L*a*b* space:

        xicclu -fif -ia -pl -l260 -a profile.icm

and feed in the Lab values line by line, separated by spaces. If you use the
-kv or -kl, then you can also feed black locus or target values in as a
fourth parameter.

[e.g. xicclu -fif -ia -pl -kl -l260 -a profile.icm
  and feed in 50 0 0 0 and 50 0 0 1 for the mid grey with
  minimum and maximum black respectively. 50 0 0 .5 would give
  you the halfway black point.]

Graeme Gill.

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