[scribus] LSI 240% ink limit.

[John Culleton]

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
> > >
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> >
> > 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
>
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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. 

-- 
John Culleton
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