PDF/X – Global Graphics Software blog

August 25, 2022November 24, 2022

Processing PDF without in-RIP color management

Twenty years ago it was common to find people RIPping jobs for production print with no color management. Indeed, many print service providers (PSPs), magazine publishers etc actively avoided it as being “too complicated” and “unpredictable”. You might read that as an indictment of their vendors for a lack of investment either in developing good product or in educating their users. Alternatively it might simply show that the printing companies were quite understandably risk-averse because it could be expensive if the client didn’t like the resulting color, especially in an environment like display advertising in a major magazine, or packaging for a major brand.

A decade after that more and more people (on both the buying and the printing sides) grasped the value of color management in print and were using it, but there was still a significant minority that had not managed to make the time to understand it. This is borne out by the uproar when Adobe ‘forced’ people to use color management by changing from using CMYK for the alternate color space for Pantone spots in Creative Cloud to using Lab¹, and by the continuing demand for support for PDF/X‑1a, where everything has already been converted to press colorants before the PDF is made.

Now we’re in 2022, and the need for color management is accepted almost universally in print sectors that use an ink set based on CMYK. I phrased it that way because some of the industrial print space (textiles, ceramics, laminate flooring etc) have historically used many inks, but usually job-specific rather than CMYK. Some of those markets will continue to use job-specific ink sets as they transition to digital, while others would find a switch to digital extremely challenging without a concurrent switch to a color managed workflow².

So, why am I writing this now?

It’s because I still talk to people who tell me that they don’t need to do any color management inside the RIP when processing PDF; they RIP it first and then apply color management.

I’m sorry, that just won’t work reliably and with maximum quality.

There was a time, back in the days when PDF 1.3 was the latest and greatest (which pretty much means last millennium) when a PSP could get away with this approach, because their customers were happy to define all their colors in CMYK and spots. As soon as they used anything else, including Lab or colors tagged with ICC profiles, they’d have to have some fallback to generate CMYK values from that data. It doesn’t need a full color management module (CMM), but they’d need something.

And then along came PDF 1.4, adding transparency. And transparency requires that you can convert colors between color spaces, potentially multiple times. That’s because PDF transparency includes the concept of transparency groups. Each group is one or more graphics that are blended with any graphics that are behind them in the design.

The blending depends on a number of parameters, the most obvious of which are the blend mode (Overlay, Multiply, Hard Light etc), and the blend color space. The result of rendering all graphics that are underneath the transparency group will be transformed from whatever space the RIP holds it in (often the CMYK for the output device) into the blending color space. The result of rendering all the graphics inside the transparency group itself is also transformed into the blending color space. Then the blend mode is applied, to do the actual transparency calculation, and the result is transformed back into whatever color space the RIP needs it to be in for further processing (again, often the CMYK of the output device). The blending color space is quite often sRGB, because that’s the default in a number of popular design applications.

So correct rendering of the transparency will often require color transforms between the color space in which graphics are specified (such as, maybe, an image tagged with an ECI RGB ICC profile), the blend color space (most commonly sRGB) and the output device color space (usually a specific CMYK). That’s just not possible without applying a pretty complete color management process during RIPping. And if you try to take short-cuts you’ll usually get a visually different result, sometimes very different.

Color transformation with transparency requires a full color management capability.

Even so, back in the early 2000s a PSP could avoid the need to upgrade software, process control and operator training by insisting that their customers supplied files in a format such as PDF/X-1a, which prohibited device-independent colors and transparency. But making a PDF/X-1a file from a rich design in a creative application requires a number of compromises affecting graphical elements that were originally specified in device independent colors, or which use transparency. Both risk degrading the quality of the final piece.

These days insisting on PDF/X-1a to avoid the need for color management in the RIP is no longer widely acceptable to customers³. And therefore neither is color managing after the RIPping is complete.

Your check-list is therefore:

Don’t use PDF/X-1a. In fact don’t use PDF/X-3 either. Both are two decades old. PDF/X-3 may allow device-independent colors, but both of them force the creation tool to flatten transparency, discard layers and a bunch of other potentially damaging procedures. It’s over ten years since PDF/X-4 was published, and that’s currently the best balance between capability and getting too far ahead of common usage in print workflows.

If you’re a print service provider, converter, industrial printing manufacturer or digital press vendor, don’t cut corners; use a workflow that applies the color management in or before the RIP⁴. It shouldn’t be hard; all the leading RIP vendors (and therefore leading press vendors, because they license technology from the RIP vendors) supply suitable systems.

About the author

Martin Bailey, consultant and former 0CTO, Global Graphics Software

Martin Bailey, consultant at Global Graphics Software, is a former CTO of the company and currently the primary UK expert to the ISO committees maintaining and developing PDF and PDF/VT. He is the author of Full Speed Ahead: how to make variable data PDF files that won’t slow your digital press, a guide offering advice to anyone with a stake in variable data printing including graphic designers, print buyers, composition developers and users.

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Notes
¹ – If a spot color will be emulated using process inks on press, then using a CMYK alternate gives predictable color numbers in those inks, but is less good at producing a predictable color appearance. Using Lab for the alternate color space often leads to unpredictable color numbers on each separation, but a more predictable color appearance on the print. There is a benefit to both models, but when it comes to paying for printing the color appearance usually wins!

² – if run-lengths on digital are long enough to justify warehousing a variety of inks, and changings inks on inkjet presses, it can be reasonable to stay with job-specific ink sets, especially if it’s difficult or expensive to make usable inks for all of CMY and K. As an example, the best Magenta ink for inkjet printing on ceramics is made with gold. Any move to using digital presses for short-run printing more or less requires a fixed ink set to allow for quick job changes without excessive waste, and that typically means CMYK+.

³ – and I say that as the chair of the committees that developed PDF/X for many years, first in CGATS and then in ISO.

⁴ – There are situations where applying color management in a color server before the RIP can be useful, especially when multiple presses will be used in parallel. This approach brings its own challenges around handling spot colors in the job that will be emulated on press, but can produce excellent results when used with care.

February 10, 2021February 3, 2021

Second edition now available: Full Speed Ahead: How to make variable data PDF files that won’t slow your digital press

At the beginning of 2020, in what we thought was the run-up to drupa, Global Graphics published a new guide called “Full Speed Ahead: How to make variable data PDF files that won’t slow your digital press”. It was designed to complement the recommendations available for how to maximize sales from direct mail campaigns, with technical recommendations as to how you can make sure that you don’t make a PDF file for a variable data job that will bring a digital press to its knees. It also carried those lessons into additional print sectors that are rapidly adopting variable data, such as labels, packaging, product decoration and industrial print, with hints around using variable data in unusual ways for premium jobs at premium margins.

Well, as they say, a lot has happened since then.

And some of that has been positive. At the end of 2020 several new International Standards were published, including a “dated revision” (a 2^nd edition) of the PDF 2.0 standard, a new standard for submission of PDF files for production printing: PDF/X-6, and a new standard for submission of variable data PDF files for printing: PDF/VT-3.

We’ve therefore updated Full Speed Ahead to cover the new standards. And at the same time we’ve taken the opportunity to extend and clarify some of the rest of the text in response to feedback on the first edition.

So now you can keep up to date, just by downloading the new edition!

DOWNLOAD THE GUIDE

What’s the difference between PDF/X-1a and PDF/X-4?

Which PDF/X should I use?

Somebody asked me recently what the difference is between PDF/X-1a (first published in 2001) and PDF/X-4 (published in 2010). I thought this might also be interesting to a wider audience.

Both are ISO standards that deliberately restrict some aspects of what you can put into a PDF file in order to make them more reliable for delivery of jobs for professional print. But the two standards address different needs/desires:

PDF/X-1a content must all have been transformed into CMYK (optionally plus spots) already, so it puts all of the responsibility for correct separation and transparency handling onto the creation side. When it hits Harlequin, all the RIP can do is to lock in the correct overprint settings and (optionally) pre-flight the intended print output condition, as encapsulated in the output intent.

On the other hand, PDF/X-4 supports quite a few things that PDF/X-1a does not, including:

Device-independent color spaces
Live PDF transparency
Optional content (layers)

That moves a lot more of the responsibility downstream into the RIP, because it can carry unseparated colors and transparency.

Back when the earlier PDF/X standards were designed transparency handling was a bit inconsistent between RIPs, and color management was an inaccessible black art to many print service providers, which is why PDF/X-1a was popular with many printers. That’s not been the case for a decade now, so PDF/X-4 will work just fine.

In other words, the choice is more down to where the participants in the exchange want the responsibility to sit than to anything technical any more.

In addition, PDF/X-4 is much more easily transitioned between different presses, and even between completely different print technologies, such as moving a job from offset or flexo to a digital press. And it can also be used much more easily for digital delivery alongside using it for print. For many people that’s enough to push the balance firmly in favour of PDF/X-4.

For further reading about PDF documents and standards:

About the author

Martin Bailey, CTO, Global Graphics Software

Martin Bailey is Global Graphics’ Chief Technology Officer. He’s currently the primary UK expert to the ISO committees maintaining and developing PDF and PDF/VT and is the author of Full Speed Ahead: how to make variable data PDF files that won’t slow your digital press, a new guide offering advice to anyone with a stake in variable data printing including graphic designers, print buyers, composition developers and users.

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November 30, 2016November 21, 2019

Getting to know PDF 2.0 – update from Down Under

I’ve been in the ISO PDF committee meeting in Sydney, Australia for a couple of days this week to review the comments submitted to the most recent ballot on PDF 2.0. Over 100 comments were received, including some complex issues around digital signatures, structure tagging (especially lists), optional content, document parts and soft masks. In all cases the committee was able to reach a consensus on what should be done for PDF 2.0.

The plan is now for one more ballot, the responses to which will be reviewed in Q2 next year, with an expectation that final text for PDF 2.0 will be delivered to ISO for publication shortly thereafter.

So we’re still on track for publication next year.

All of which means that it’s past time that a couple of PDF’s unsung heroes were acknowledged. The project leaders for PDF 2.0 have invested very substantial amounts of time and mental energy updating text in response to comments and ballots over the last several years. When somebody like me requests a change it’s the project leaders who help to double-check that every last implication of that change is explored to ensure that we don’t have any inconsistency.

So a big thank you to Duff Johnson of the PDF Association and Peter Wyatt of CISRA (Canon)!

It’s also worth noting that one of the significant improvements in PDF 2.0 that probably won’t get highlighted elsewhere is that the text now is much more consistent. When you’re writing a detailed technical document 1000 pages long it’s inevitable that some disconnections between different sections will creep in. PDF 2.0 illustrates the value of a broad group of people from many countries and many industries reviewing text in the ISO process: we’ve managed to stamp on many of those cases in this new version.

November 17, 2016November 21, 2019

Getting to know PDF 2.0: rendering PDF transparency

In the middle of 2017 ISO 32000-2 will be published, defining PDF 2.0. It’s eight years since there’s been a revision to the standard. In the second of a series of blog posts Martin Bailey, the primary UK expert to the ISO committee developing PDF 2.0, looks at the changes to rendering PDF transparency for print.
These changes are all driven by what we’ve learned in the last few years about where the previous PDF standards could trip people up in real-world jobs.
Inheritance of transparency color spaces
Under certain circumstances a RIP will now automatically apply a color-managed (CIEBased) color space when a device color space (such as DeviceCMYK) is used in a transparent object. It will do that by inheriting it from a containing Form XObject or the current page.
That sounds very technical, but the bottom line is that it will now be much easier to get the correct color when imposing multiple PDF files from different sources together. That’s especially the case when you’re imposing PDF/X files that use different profiles in their output intents, even though they may all be intended for the same target printing condition. The obvious examples of this kind of use case is placing display advertising for publications, or gang-printing.
We’ve tried hard to minimize impact on existing workflows in making these improvements, but there will inevitably be some cases where a PDF 2.0 workflow will produce different results from at least some existing solutions, and this is one case where that could happen. But we believe that the kinds of construct where PDF 2.0 will produce different output are very uncommon in PDF files apart from in the cases where it will provide a benefit by allowing a much closer color match to the designer/advertiser’s goal than could be achieved easily before.
Clarifications on when object colors must be transformed to the blend color space
The ISO PDF 1.7 standard, and all previous PDF specifications were somewhat vague about exactly when the color space of a graphical object involved with PDF transparency needed to be transformed into the blending color space. The uncertainty meant that implementations from different vendors could (and sometimes did) produce very different results.
Those statements have been greatly clarified in PDF 2.0.
This is another area where an upgrade to a PDF 2.0 workflow may mean that your jobs render slightly differently … but the up-side is that if you run pre-press systems or digital presses from multiple vendors they should now all be more similar to each other.
As a note to Harlequin RIP users, the new rules are in line with the way that Harlequin has always behaved; in other words, you won’t see any changes in this area when you upgrade.
ColorDodge & Burn
It tends to be taken for granted that the older PDF specifications must match what Adobe® Acrobat® does, but that’s not always correct. As an example, the formulae for the ColorDodge and ColorBurn transparency blending modes in the PDF specification have never matched the implementation in Acrobat. In pursuit of compatibility Harlequin was changed to match Acrobat rather than the specification many years ago. In PDF 2.0 the standard is finally catching up with reality and now both Acrobat and Harlequin will be formally ‘correct’!
The background
The last few years have been pretty stable for PDF; PDF 1.7 was published in 2006, and the first ISO PDF standard (ISO 32000-1), published in 2008, was very similar to PDF 1.7. In the same way, PDF/X 4 and PDF/X 5, the most recent PDF/X standards, were both published in 2010, six years ago.
In the middle of 2017 ISO 32000-2 will be published, defining PDF 2.0. Much of the new work in this version is related to tagging for content re-use and accessibility, but there are also several areas that affect print production. Among them are some changes to the rendering of PDF transparency, ways to include additional data about spot colors and about how color management should be applied.

November 1, 2016November 21, 2019

Getting to know PDF 2.0

Just when you’ve all cozied down with PDF 1.7 what happens? Yes, that’s right. A new standard rears its head.

Around the middle of 2017 the ISO committee will publish PDF 2.0 (ISO 32000-2). So by the end of 2017 you’ll probably need to be considering how to ensure that your workflow can handle PDF 2.0 files correctly.

As the primary UK expert to this committee I thought I’d give you a heads up now on what to expect. And over the coming months via this blog and our newsletter I’ll endeavor to keep you posted on what to look out for as far as print is concerned. Because, of course, there are many aspects to the standard that do not concern print at all. For instance there are lots of changes in areas such as structure tagging for accessibility and digital signatures that might be important for business and consumer applications.

As you probably already know, in 2008 Adobe handed over ownership and development of the PDF standard to the International Standards Organization. Since that time I’ve been working alongside other experts to ensure that standards have real-world applicability.

And here’s one example relating to color.

The printing condition for which a job was created can be encapsulated in professional print production jobs by specifying an “output intent” in the PDF file. The output intent structure was invented for the PDF/X standards, at first in support of pre-flight, and later to enable color management at the print site to match that used in proofing at the design stage.

But the PDF/X standards only allow a single output intent to be specified for all pages in a job.

PDF 2.0 allows separate output intents to be included for every page individually. The goal is to support jobs where different media are used for various pages, e.g. for the first sheet for each recipient of a transactional print job, or for the cover of a saddle-stitched book. The output intents in PDF 2.0 are an extension of those described in PDF/X, and the support for multiple output intents will probably be adopted back into PDF/X-6 and into the next PDF/VT standard.

But of course, like many improvements, this one does demand a little bit of care. A PDF 1.7 or existing PDF/X reader will ignore the new page level output intents and could therefore produce the wrong colors for a job that contains them.
In my next post I’ll be covering changes around live transparency in PDF 2.0. Bet you can’t wait!
You can sign up to the Global Graphics newsletter here.

The background
The last few years have been pretty stable for PDF; PDF 1.7 was published in 2006, and the first ISO PDF standard (ISO 32000-1), published in 2010, was very similar to PDF 1.7. In the same way, PDF/X 4 and PDF/X 5, the most recent PDF/X standards, were both published in 2010, six years ago.

In the middle of 2017 ISO 32000-2 will be published, defining PDF 2.0. Much of the new work in this version is related to tagging for content re-use and accessibility, but there are also several areas that affect print production. Among them are some changes to the rendering of PDF transparency, ways to include additional data about spot colors and about how color management should be applied.

March 9, 2016November 21, 2019

Why online print is set to change

Remember in olden times how you sent a file to print on a wing and a prayer? OK, it wasn’t that bad! But it was unreliable. Figures showed that print-ready file delivery had failure rates of between 30 – 70% and this was a real problem for print service providers with high throughput like magazine houses.

Then PDF/X came along and greatly improved the situation. It was strengthened by additional standardisation efforts from several other bodies including Ghent PDF Workgroup and Altona.

PDF/X worked because it ensured delivery of files ready to high-quality print. And because it dealt with the headache so well, print service providers recommended it.

Fast forward for a moment to today and to the tidal wave that is variable data printing. Most buyers deliver the brief and the dataset to the print service provider (PSP). A full service PSP will offer data mining, graphic design, composition and print. Offering a full service promises higher margins. If you only provide a print service you can expect lower margins, but your model connects better to web-to-print services that are burgeoning. But if you try to “just print” VDP jobs, those that fail will eliminate profit.

I’ve been invited to speak at the Online Print Symposium in Munich (17th – 18th March) about why PDF/VT and Industry 4.0 are set to change online print forever. The truth is that VDP has been hanging around street corners looking for a PDF/X. Well, now it’s found one because that’s what PDF/VT is. It’s been created to deal with every page being different and to give PSPs more control over the workflow.

I would go so far to suggest that print-ready file delivery of graphically rich variable data from outside the print company is unlikely to succeed without it! And on that bombshell…!

To receive a copy of my presentation email me. Meanwhile take a look at http://www.globalgraphics.com/doPDFVTright

February 3, 2016November 21, 2019

PDF/VT – bringing all the advantages of PDF workflow to the world of variable data printing

Standards for variable data printing (VDP) have come a long way since the first work by CGATS to develop a universal delivery format in the late 1990s. In 2010 the International Standards Organization published the PDF/VT standard, marking the first really effective specification for a reliable, vendor-neutral exchange of variable data jobs, both within and between companies.

A special type of the PDF file format, PDF/VT is specifically used for variable data and transactional printing in a variety of environments, from desktop printing to high volume digital production presses. Built on PDF/X, it therefore brings all the advantages of that standard in enforcing best practices for reproducible and predictable color and appearance to the variable data and transactional print worlds.

The industry is gradually realizing its value to improve quality, competitiveness and productivity, and I’ve been working with the PDF/VT Competence Center, especially with Christoph Oeters (Sofha), Paul Jones (Teclyn bv) and Tim Donahue (technical consultant) to produce a new set of Application Notes highlighting the benefits of using PDF/VT and the workflows that it enables.

The Application Notes explain how to make the highest quality and most efficient PDF/VT files to achieve the required visual appearance of a job, so if you develop software to read and write PDF/VT files, for example in composition tools, RIPs, digital front ends and imposition tools, or if you work on print workflow integration, you’ll find the notes really beneficial. They also show how document part metadata can be applied and leveraged for VDP specific production workflows.

Of course, there are wider benefits to using PDF/VT: The adoption of PDF/VT will allow the industry to finally move towards a reliable, vendor-neutral exchange of variable data jobs, simplifying the process of variable data printing significantly.

The application notes are free to download, pick up your copy here: http://www.pdfa.org/publication/pdfvt-application-notes/.

Let me know what you think of them – feedback is always welcome.

Additional reading:

Do PDF/VT right by Global Graphics Software

PDF/VT for personalized print by the PDF/A Competence Center

Read the press release from the PDF Association (http://www.pdfa.org/2016/01/pdf-association-publishes-pdfvt-application-notes-showcasing-the-benefits-for-variable-data-print-streams/)