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the transmission of publication ads, where the same ad may be placed in many magazines, and every magazine
obviously includes ads from many sources. A need for detailed, individual discussions around every placement
would be a significant barrier to increasing efficiency on both sides of the submission.
There are, however, situations where it’s necessary for the sender and receiver of a file (or file set) to have
more discussion about how data should be prepared and exchanged, and in many of these cases there can be a
requirement that the content of a single job is contained within multiple content files, possibly residing at
different sites.
The combination of these two divisions led to a decision to create several PDF/X standards:
•
PDF/X-1a for CMYK-only blind exchange.
•
PDF/X-3 for color-managed blind exchange
•
PDF/X-2 for open exchange
Each of these is a superset of the preceding one, removing restrictions in a staged manner.
No standard for CMYK-only open exchange was needed because the two parties are in technical discussion
anyway, and may therefore add their own further restrictions as to the construction of the files.
Note that this section is a summary of the rational behind the split into three standards. Unfortunately the
groups involved were not in a position to set out that rationale in advance of PDF/X standards development
work, and achieving worldwide consensus was not, initially, an easy task. This is also one reason why the
numerical sequence of the standards does not appear to be as logical as it might be.
10. PDF/X-1a
The PDF/X-1a standard addresses blind exchanges where all files should be delivered in CMYK (and/or spot
colors), with no RGB or device independent (color-managed) data.
This is a common requirement in many areas around the world and in many print sectors. It’s often tied to an
environment where the file supplier wants to retain maximum control of the print job; it’s very hard to transmit
data as RGB or Lab and still to include your own trap definitions, for instance.
Alternatively, it’s requested by many print service providers and publishers who have had bad experiences with
color managed data in the past, leading to inconsistent and unacceptable print quality. With the tools in current
widespread use it tends to be easier to produce consistently reasonable color reproduction when files are
supplied in CMYK.
Pre-conversion to CMYK works best where there is a clearly defined CMYK color space to convert into.
Remember that a set of CMYK values do not specify a particular color until you also define what device it’s
being printed on; the same CMYK values printed on gravure, flexo, or offset litho presses, or on a laser or ink
jet printer are likely to look quite different. For an excellent discussion of this see
http://na.i1color.com/html/toast.htm
.
In the US publication market most printers are attempting to standardize on the SWOP specifications, and
much of the European newsprint market is converging on IFRA26. Thus an ad prepared for SWOP or IFRA26
is likely to produce the expected colors in most magazines or newspapers in those areas. Specifications like
SWOP or IFRA26 are described as “characterized printing conditions”.
Other sectors of the print market are more difficult to characterize; many commercial printers, for instance,
claim to squeeze a larger gamut or better print contrast out of their presses than their local competitors. A wide
range of paper stocks, in different colors, textures and coatings, obviously adds to the kind of color variation
you’d see from the same CMYK values.
Several groups such as GRACoL, CGATS SC3, FOGRA, ECI and Printing Across Borders are working on
characterizations and associated ICC profiles for commercial print but these are not yet in universal use,
especially outside of continental Europe. In the meantime it’s a little difficult to provide a file in CMYK to
many commercial printers and have your proof exactly match the final printed piece off their press without
significant discussion or on-press adjustments. In the absence of such discussion it’s becoming commonplace
for designers to separate to a form of “generic CMYK”, often either SWOP or the default settings in Adobe
PhotoShop. They must then simply hope that it will fall near enough to the press behavior to be acceptable, or
that the print service provider will supply them with a proof that will match the press (see “Which
characterized printing condition should I label files as using?”).
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The rise of non-impact digital presses, based on either ink jet or laser technology, also makes it difficult to send
CMYK data without knowing exactly what press it will be run on, because presses from the different
manufacturers may print the same CMYK values as very different colors. CGATS is investigating the
possibility of standardized characterizations in this area too (CGATS SC6 TF2). Attacking the same problem
from the other end, many digital press front ends can color manage incoming CMYK data, producing output
that is a reasonable emulation of a SWOP press, for instance.
The first PDF/X-1a standard, better referred to as PDF/X-1a:2001 was published as ISO standard
15930-1:2001. See below for details of how to obtain a copy (“Where can I get more information?”), and for
new revisions (“2003 revisions” and “Should I start using the 2003 revisions?”).
11. PDF/X-3
While some market sectors require exchanges with all color data already converted to CMYK, others are better
served by transferring data in other spaces, such as CIELab or RGB with a profile attached.
The PDF/X-3 standard is a superset of PDF/X-1a; a PDF/X-1a file meets all of the technical requirements of
PDF/X-3 except for the label that actually says “I’m a PDF/X-3 file”. The primary difference between the two
is that a PDF/X-3 file can also contain color managed data.
The same PDF/X-3 file may contain data in color-managed color spaces (such as Lab, CalRGB or using an
embedded ICC profile), and other data in grayscale, CMYK and spot colors. The combination means that
images can be included in a defined RGB space (for instance), while solid black text can be guaranteed to print
in solid black without unexpected color fringing caused by color management spreading the black data to all
the process separations.
Different prepress software may handle embedded ICC color profiles, etc, in color-managed jobs, which means
that some care must be taken to ensure that a proof of device independent colors will accurately predict the
final presswork. This is not to say that consistent color cannot be achieved in non-CMYK workflows, only that
you must invest more effort to learn the behavior and capabilities of all equipment involved in your workflow.
Both of the PDF/X-3 and PDF/X-2 standards are clear as to how a compliant proofing or plate-setter device
should act on the colors in a file. In many situations, however, a print service provider may need to use a
mixture of PDF/X-compliant and non-compliant tools. This gets more complicated when a customer expects a
print company to match their proof; the print company needs to be aware that the customer’s proofing device
may not be PDF/X-compliant. They also need to watch that other steps in their workflow, such as stand-alone
imposition or OPI tools, don’t lose the PDF/X data or construct inconsistent files.
ISO has recommended that all tools designed to read PDF/X-3 should also be able to read PDF/X-1a files.
Indeed, in the 2003 revision of PDF/X-3 (see “2003 revisions”), a compliant PDF/X-3 reader must be able to
read PDF/X-1a files as well. A PDF/X-3 file may also be made explicitly for monochrome and RGB
characterized print conditions, although RGB is likely to be very rare in practice. A PDF/X-1a file may only be
made for CMYK characterizations.
The first PDF/X-3 standard, better referred to as PDF/X-3:2002 was published as ISO standard 15930-3:2002.
See below for details of how to obtain a copy (“Where can I get more information?”), and for new revisions
(“2003 revisions” and “Should I start using the 2003 revisions?”).
12. PDF/X-2
Both PDF/X-1a and PDF/X-3 define file formats for blind exchange. In some workflows that’s not required, or
asingle file per job is not appropriate, but some additional restrictions on file formatting rather than just saying
“PDF” would be desirable to increase reliability.
PDF/X-2 is designed to address exchanges where there is more discussion between the supplier and receiver of
the file. It enables an “OPI-like” workflow. The OPI specification is not actually used, instead the “reference
XObject” mechanism defined in PDF version 1.4 has been extended slightly to provide greater confidence that
the correct subsidiary files have been located. One of the consequences of this is that all of the external files
must also be in PDF/X.
There are a number of situations where it is envisaged that PDF/X-2 may prove useful. The only common
theme between these is the use of a single ‘master’ file referring to others that will be rendered in the final
output – the business reasons that provide the value in that separation vary from case to case. Maybe the
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receiver already holds high resolution images to replace proxy images (low resolution previews) in the supplied
file.
There are many occasions where an “OPI-like” workflow can provide value (e.g. to increase the response
speed of design workstations), but which do not automatically lead to a requirement for PDF/X-2. If an OPI
workflow is resolved entirely within a single company (or a division within a larger company) then PDF/X-2 is
not necessary.
PDF/X-2 adds value where a set of several files should be exchanged between companies or divisions. It can
also add value where the company running a purely internal OPI workflow has little control over the names of
files used in that workflow, and where the ability to resolve conclusively between files from different sources
but with the same name can help to avoid the use of the wrong image.
It is a superset of PDF/X-3, and will therefore allow device independent color spaces, like Lab and those base
on ICC profiles, to be used, just like PDF/X-3. The rather confusing hierarchy running from PDF/X-1a through
PDF/X-3 to PDF/X-2 is a historical accident caused by the development process in CGATS and ISO.
The first PDF/X-2 standard, better referred to as PDF/X-2:2003 was published as ISO standard 15930-2:2003.
See below for details of how to obtain a copy (“Where can I get more information?”).
13. Who’s accepting PDF/X-1a files?
The first known complete test-run of a PDF/X-1a ad was in early August 2001, and by the end of August an ad
delivered as PDF/X-1a had been printed in a national American magazine (both handled by LTC/Vertis). In
September 2001 the SWOP calibration test kit was issued in PDF/X-1a. In December 2001 the first known case
of PDF/X-1a being used for the whole of a magazine transmission from publisher to printer was recorded
(Wizards of the Coast – Dragon issue 292). The latest SWOP version recommends that all digital ads are
supplied in either TIFF/IT-P1 or PDF/X-1a.
PDF/X-1a is now a very common approach to solving problems of production file reliability and customer
education.
Amongst the foremost PDF/X-1a evangelists are Time, Inc, who provide a comprehensive guide to creation of
good files at direct2.time.com
.
Many of the member organizations of the Ghent PDF Working Group (see “What’s PDF/X Plus?”) also
indirectly recommend that jobs be submitted as PDF/X, because the 2004 and earlier Ghent specifications are
all based on PDF/X-1a.
Many PDF/X-1a compliant tools are now available – mainly initially addressed at converting PDF files into
PDF/X, and in pre-flighting such files. The DDAP constructed a list of available PDF/X applications at
www.pdf-x.com
,although applications are now so common that it is no longer being maintained.
14. Who’s taking PDF/X-3?
There is a general, but very slow, move towards accepting device-independent color data in files for print. To
date this is most advanced in northern Europe, although many large magazine publishers across North America
are actively investigating how to move in that direction for submitted advertising. Work intended for output on
digital presses can also benefit from the color-managed workflows implied by submission of device-
independent color. Obviously PDF/X-3 is the PDF/X standard of choice for all of these cases.
There is, however, an unfortunate tendency for some companies to require that jobs be submitted as PDF/X-3,
while simultaneously demanding that all data in them be supplied in CMYK. This approach is driven by
politics rather than by technical issues. In terms of the standards, very nearly the only reason that a PDF/X-1a
file is not PDF/X-3 compliant is that it is labeled as PDF/X-1a rather than as PDF/X-3. The PDF/X-3:2003
standard makes that very clear, and requires that a PDF/X-3-compliant application that reads files must also be
able to read and process PDF/X-1a files. It is to be hoped that CMYK-only PDF/X-3 file requirements will be
dropped in the future, and that the companies involved will accept PDF/X-1a as well, or instead.
Afree PDF/X-3 verifier is available from www.pdfx.info
.
Several tools for creation and verification of PDF/X-3 files are also available – see the list at the same web site.
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Copyright © Global Graphics Software Limited, 1999-2005. All Rights Reserved.
15. And who’s taking PDF/X-2?
At the time of writing there are no known products that can construct or validate files against the PDF/X-2
standard. Some products will act on reference XObjects in PDF files, and can therefore consume PDF/X-2 file
sets, but the additional robustness that the standard was written to enable will not be achieved using these tools.
16. What’s PDF/X Plus?
The PDF/X standards are each designed to be applicable to broad ranges of the print industry world wide,
across many geographical regions, print technologies and sectors. That means it’s not possible for them to
define all the appropriate limitations for any particular usage of PDF, such as minimum image resolution,
minimum type size, bleeds, etc. The values appropriate for high quality magazine production would be
completely wrong for newsprint, for instance.
It’s therefore entirely appropriate that additional specifications be built by industry associations on top of the
PDF/X standards, each constructed for a particular niche. Because these specifications use PDF/X as a
foundation they are often called “PDF/X Plus”.
One interesting observation made after the PDF/X standards were published was that the issues left to be
addressed in PDF/X Plus specifications are the kind of things that people working in the graphic arts are
already familiar with: image resolution, type size, bleed size and selection of a print characterization (usually
guided by tone value increase (dot gain)). The standards themselves cover all the “propeller head” technical
issues that deal more with the details of the PDF file format, and that most professionals in print could not be
expected to know in great detail.
PDF/X
Embedded fonts, no encryption,
TrimBox required, no HalftoneName,
no threshhold screens,
no annotations within the page
etc
PDF/X Plus
Min & max image resolutions, min type size
Required bleed, which print characterization
etc.
Trim size, live area,
etc.
Individual title or
print job
Print sector
Whole print
industry
At the time of writing much of the development of PDF/X Plus specifications appears to be converging on the
Ghent PDF Work Group (GWG, www.gwg.org
). This association now comprises many industry associations
from across northern Europe, plus others from North America, including the IPA and FTA. In addition, a
number of vendors provide support and assistance. They have published several specifications intended for use
in advertising delivery to magazines and newspapers and for commercial print.
In the UK the Periodical Publishers Association (PPA, www.ppa.co.uk
)have also published the Pass4Press and
Proof4Press specifications, which address some of the same issues as the GWG specifications, but with more
concentration on the behavior of prepress equipment. This work is converging with the GWG (PPA is a GWG
member).
17. Which PDF/X should I use?
That’s obviously quite a few different PDF/X standards, but it’s expected that any particular market will settle
on one, or two at the most, of these.
If you’re a print buyer or advertiser, or anyone else who is generating files to send to a print service provider,
ask your service providers what they can work with reliably. If they don’t suggest PDF/X but you think it
would be advantageous to both of you then raise the idea. There’s no point in supplying files that you know
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