[scribus] LSI 240% ink limit.

Sun Aug 9 01:56:20 CEST 2009

On Saturday 08 August 2009 07:23:49 pm Hal V. Engel wrote:
> On Saturday 08 August 2009 03:52:25 pm John Culleton wrote:
> > On Saturday 08 August 2009 04:54:09 pm Hal V. Engel wrote:
> > > On Saturday 08 August 2009 12:07:59 pm John Culleton wrote:
> > > > On Saturday 08 August 2009 11:58:40 am Gregory Pittman 
wrote:
> > > > > On 08/08/2009 11:57 AM, John Culleton wrote:
> > > > > > On Friday 07 August 2009 07:19:29 pm John Culleton 
wrote:
> > > > > >> LSI is enforcing a rule that total ink coverage of any
> > > > > >> CMYK color cannot exceed 240% The usual example is
> > > > > >> rich black.
> > > > > >>
> > > > > >> 1. Can this be a problem in Scribus?
> > > > > >> 2. If so, how does one detect/fix such overcolored
> > > > > >> areas?
> > > > > >>
> > > > > >> I presume that none of the standard colors exceed this
> > > > > >> limit. But I worry about graphics from e.g., Gimp
> > > > > >> which are RGB converted to CMYK when Scribus writes
> > > > > >> the file.
> > > > > >
> > > > > > To further illuminate the question, these are the
> > > > > > recommended values whan using Photoshop:
> > > > > > ------------------------
> > > > > > Engine: Adobe (ACE)
> > > > > > Intent: Relative Colorimetric
> > > > > > Use Black Point Compensation: Yes
> > > > > > Use Dither: Yes
> > > > > > -------------------------------
> > > > > > and
> > > > > > -----------------------------------
> > > > > >      Ink Colors: SWOP (Newsprint)
> > > > > >      Dot Gain: 25%
> > > > > >      Separation Type: GCR
> > > > > >      Black Generation: Medium
> > > > > >      Black Ink Limit: 100%
> > > > > >      Total Ink Limit: 240%
> > > > > >      UCA Amount: 0%
> > > > > > -------------------------------
> > > > > > for the custom CMYK settings.
> > > > > >
> > > > > > Perhaps there is an ICC profile that can take care of
> > > > > > all this.
> > > > >
> > > > > I don't know that there are any color sets that come with
> > > > > Scribus that will exceed this. Of course, we get some
> > > > > list questions from some who think that they want all the
> > > > > CMYK saturated, but obviously don't understand the
> > > > > printing issue.
> > > > >
> > > > > What it does suggest, though, is that one of the things
> > > > > the Preflight Verifier could do would be to check for ink
> > > > > limits. Maybe you could file an RFE.
> > > > >
> > > > > Not sure how they might imagine someone specifying > 100%
> > > > > Black...seems that would be kicked out by the printing
> > > > > equipment.
> > > > >
> > > > > Greg
> > > > >
> > > > > _______________________________________________
> > > > > scribus mailing list
> > > > > scribus at lists.scribus.net
> > > > > http://lists.scribus.net/mailman/listinfo/scribus
> > > >
> > > > Consider the image from Gimp that has black on it. That is
> > > > RGB 0 0 0. What would Scribus change it to in CMYK?
> > >
> > > There seems to be some misconceptions here.  CMYK is a
> > > subtractive color space so higher values mean more ink (if
> > > you are talking about a printer).  The K ink in a CMYK system
> > > is used as a substitute for higher levels of process gray (C
> > > = M = Y) to create darker tones and reduce ink load for the
> > > same darkness. Many printer/ink/paper combinations can handle
> > > total ink levels much higher than the 240% talked about above
> > > but some can not and some can not handle even 240%.
> > >
> > > The darkest blacks on most printers are a combination of K
> > > plus C and M (sometimes called rich black).  In addition on
> > > many modern ink jet printers the "black" ink has a yellow
> > > tint that is intended to allow these very dark blacks without
> > > causing a hue shift because of the added C and M ink (IE. to
> > > keep the resultant black neutral). The normal operation for
> > > these printers is to always mix some C and M ink with the K
> > > ink to shift the hue toward neutral even for lighter grays
> > > although for the very lightest grays this may not be needed
> > > because the white point will be shifted toward blue (IE. away
> > > from yellow) because of the "whiteners" used in many papers.
> > >
> > > All of this is very device specific, meaning specific to a
> > > printer/paper/ink/work flow, and the only way to insure that
> > > you are doing the right CMYK separation for your device is to
> > > use the correct ICC profile for the device in question. 
> > > These profiles will have an optimized GCR setup and also have
> > > proper ink limits so that there is no over inking and there
> > > are proper transitions to the K ink as well as proper use of
> > > C and M inks to keep grays and blacks neutral.
> > >
> > > Hal
> > >
> > > _______________________________________________
> > > scribus mailing list
> > > scribus at lists.scribus.net
> > > http://lists.scribus.net/mailman/listinfo/scribus
> >
> > LSI wants the SWOP profile but also enforces the 240% rule for
> > cover files.  They have an ink and paper combo that requires
> > this limit. The usual way to make sure that their specs are met
> > is through Photoshop.  I am looking for a Scribus way.
>
> If LSI is so picky about this perhaps they can give you a profile
> that insures that you produce separations to their
> specifications.  But if that is not the case then create a
> profile that uses the SWOP characterization data set but that has
> a 240% ink limit instead of the default for SWOP (320% for the
> newer profiles and 300% for the older ones).  This can be done
> using ArgyllCMS. There are threads on the ArgyllCMS email list
> about how to get and use the SWOP characterization data.  
> Setting a custom ink limit is easy to do when you get to that
> part of the profile creation process.
>
> Hal
>
I'll follow up on that.  The issue may revolve around rich black. 

-- 
John Culleton
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