Re: Re(2): Dumb question for european prepress specialists: Which profile?
Re: Re(2): Dumb question for european prepress specialists: Which profile?
- Subject: Re: Re(2): Dumb question for european prepress specialists: Which profile?
- From: ELIE KHOURY <email@hidden>
- Date: Sun, 27 Nov 2005 13:34:19 +0100
I agree with Olaf, this is a good description of how profiles and TAC
should be managed in a print oriented workflow.
FYI, another software that allows automated preflighting and/or
correction of PDF color space and TAC is Alwan CMYK Optimizer.
Kind Regards,
Elie KHOURY
ALWAN COLOR EXPERTISE
www.alwancolor.com
On 27 nov. 2005, at 12:34, Olaf Drümmer wrote:
email@hidden wrote Sat, 26 Nov 2005 14:39:17 +0100:
.... We sat by his computer and
he opened a file that I had made and that contained a profile. He
discarded
the profile at opening and took his measuring tool. He measured a
patch that
was supposed to be 50% Magenta. Of course it wasn't 50% Magenta any
more, for
without profile, the values were misinterpreted.
Paul
Sad, but true:
Most printers that I have talked to have their Computer To Plate
machine set
to ignore embedded profiles.
and that actually works well more often than it does not. We have to
keep in mind that not only printers have to better understand the ins
and outs of color managed files, but also those creating and
submitting
files.
As a first step towards better handling of color managed or not color
managed files, I'd expect from a printer:
- to check incoming files whether they have color spaces other than
plain CMYK and spot colors.
- if only plain CMYK plus maybe spot is used, either rely on the
business contract (i.e. if it is the submitting party's responsibility
to get the file right, and if that party can be trusted, just go
ahead)
or double check whether the file makes sense, e.g. by making a proof,
checking ink coverage (in newspaper printing you'll want to do that
anyway, to avoid too high ink coverage); if in doubt ether touch base
with the submitting party or make adjustments to your liking
- if CMYK source profiles are used this most often happens
inadvertently
(e.g . when exproting PDF from Indesign, or after flattening
transparency in Acrobat, or after using color conversion in Acrobat
inadequately by attaching the destination profile for the color
conversion as a source profile in the PDF, as opposed to attaching
it as
an OutputIntent); check whether that source profiles (or those source
profiles, as there could be more than one) are the same as or
equivalent
to the right destination profile for the printing process at hand; if
so, stripping it out is the best way to go; on the other hand, if
there
is a mismatch (e.g.Euroscale source, actual printing condition is
newsprint) there are essentially two options (besides requesting a
new/
better file from the party submitting the file): just re-separate from
that CMYK source to the right CMYK destination, biggest risk:
unnecessarily impure colors, and black possibly ending up on all four
plates; or use adequate device link profile based process conversion
(minimizes risks involved when re-separating)
- if other profiles or device independent color is in the PDF file
(i.e.
ICC based gray and RGB, Lab, CalRGB and CalGray) there definittey
has to
be a separation from ICC based RGB, CalRGB and Lab. With regard to ICC
based gray and CalGray (and actually also RGB and Lab stuff that is
'gray' or 'black') make sure that conversion results in K only (decent
color conversion tools, like our own pdfColorConvert or Heidelbergs
ColorEditor will help you ensure this, Acrobat 7 Pro's conversion
actually has a weakness here)
- of course there could be a combination of ICC based RGB/Gray/Lab and
ICC based CMYK in the same PDF file, each has to be dealt with in its
own right
- finally, I very honestly believe that the RIP itself is not a good
place to do any color conversion (the only adjustments that really
belong in the RIP are transfer curves to adjust plates for the
respective plate/press/paper/ink combo to achieve the needed TVI on
press). Especially with PDF files it is much much better to do any
color
conversion _before_ the PDF reaches the RIP. Given that today's
tools to
get such color conversions done have become relatively inexpensive
(e.g.
pdfColorConvert is just 299 Euro, though an automated version will
set
you back by a few thousand Euros, Heidelberg's ColorEditor I
believe is
sold at 1700 Euro). BTW - especially when dealing with color I'd
say use
a specific tool for a specific task. General purpose all encompassing
solutions (like the typical PDF output workflow systems) can be quite
good, but do not expect them to be excellent in each regard.
- to make the learning curve less steep for both sides (senders and
recipients of PDFs), I strongly believe adhering to applicable
standards
makes a lot of sense. In this context there are two standards (or
groups
of standards):
-- file preparation and exchange: PDF/X (choose your preferred flavor
between PDF/A-1a with only plain CMYK and spot colors allowed in
it, or
PDF/X-3 which also allows device independent color, i.e. ICC based
color
spaces, Lab, or CalGray/CalRGB); PDF/X addresses al essential aspects,
including color (it does not address certain aspects that vary too
much
between vertical segments/printing conditions, like for example
minimum
image resolution or maximum number of spot colors allowed)
-- printing standards: ISO 12647 and related standards (e.g. ISO 2846
for inks), in conjunction with well established characterization data
sets (available at the ICC website www.color.org) and suggested ICC
profiles (available at ECI's website www.eci.org, for newsprint see
Ifra's website www.ifra.com). Unless you know what you are doing stick
with the suggested profiles. (If you do know what you are doing you do
not need my hints anyway.) Organize creation and submission of PDFs as
much as possible around the established printing conditions. As a
printer set up your printing process as much as possible according to
ISO 12647. Do any proofing on the background of PDF/X and ISO 12647
based characterization data/profiles.
Gee - this post has gotten way longer than originally intended... To
make a long story short:
- a printer should check color aspects when receiving files
- if the file is in principle acceptable do any necessary color
conversions and color adjustments after receiving the file but
***before*** sending it to the RIP (only feed CMYK with spot to the
RIP
as such)
- stick to applicable standards (PDF/X and ISO 12647)
BTW - those who have achieved this level never want to go back!
Olaf Druemmer
callas software
(maker of pdfColorConvert, I hope this post wasn't too much of a
shameless plug for it)
Rolf
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