[scribus] LSI 240% ink limit.

[Hal V. Engel]

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