[argyllcms] Re: Black generation and black ink limiting

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 06 Apr 2010 09:23:23 +1000

Fabrizio Levati wrote:
I was just trying to understand how CMY limiting is achieved.
If I boost the K level to meet deeper blacks but without decreasing CMY I am 
not exceeding
the total ink limit selected for the profile, what else comes into play?

It's just a property of Argyll meeting the constraints. The constraints are:

 * Staying under the ink limits (C+M+Y+K and K)
 * Hitting the target color, or clipping to the closest possible to it.

That's it.

Since K substitutes for C+M+Y but uses 1/3 the amount of ink, if you
specify a low K, then this can be achieved only up to a certain point.
After that K is substituted for CMY.

[There are basically 3 zones as you approach the black point. Not
 all will be evident. In the normal zone the target color is achievable
 with a wide range of K values, so the black generation curve can
 be met. In the second zone, the minimum level of CMY increases,
 as it is needed to hit the correct density. In the third zone, the ink
 limit is reached, and CMY has to be reduced and K increased.]

Graeme Gill.

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