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PDF: The Future of Professional Print

Tom Arah looks at the benefits and pitfalls of the PDF-based publishing workflow.

A recurring theme of these articles is the gulf between the simplicity of producing local, composite, RGB-based print on a GDI-based inkjet or laser and the complexity of producing commercial, separated, CMYK-based print on a PostScript-based offset press. In a perfect world though this split need never have happened. The underlying Adobe PostScript page description language that drives the imagesetter was always intended to drive all other output devices and even, through Display PostScript, the computer display system. This closed PostScript solution was intended to provide the ideal publishing system – a single, reliable workflow that was platform, application and device-independent.

It didn’t happen because the demands of the CMYK separated press and the RGB composite monitor were just too different – can you imagine the frame-rate of a PostScript-driven Quake? With the exception of the seminal but ill-fated NeXT initiative, Display PostScript never made it to the OS level and the idea of the closed publishing workflow seemed to die. Instead the designer wanting to bridge the gap between computer and press was left in limbo choosing between two workarounds.

The first option is to move to PostScript early. Once you’re happy with your design you simply select a PostScript-based device – you don’t even have to have one installed, just its driver – and then print your colour separations to file. The result is a single, PostScript-based description of the page including all the colour, image and font information necessary to ensure the desired output. The problem is that once the file is created there’s no opportunity for editing or changing parameters. This means that the designer is responsible for ensuring correct separation settings such as line screening and trapping. Worse there’s no easy way of proofing so you often only find out that your hairlines are invisible, that a RGB image is coming through on the black plate, that your screening is too crude, or that you’ve inadvertently set up duplicate spot colours, when the plates have been made. It’s hard enough becoming a prepress expert without having to work blind.

A PostScript print-to-disk file can be used to output the same page on any PostScript device.

The second option is to leave the move to PostScript until the last moment by providing your bureau with your application files. This means that the separation settings can be fine-tuned to the individual press and paper conditions by an expert. Even better, those inevitable last minute changes can be accommodated without going back to square one. Unfortunately the disadvantages are just as obvious. To begin with you have to find a bureau that accepts work from your platform and particular application – try finding a bureau to take Ventura 6 or Canvas 4 files and you’ll understand the difficulty. Once you’ve found a bureau, the real problems begin. Successful final output requires the bringing together of document, graphics and fonts and with the application-specific’s multiple file approach this will always be a minefield. Unless your images and fonts are all provided exactly as expected, for example, it’s easy to end up with screen placeholders, or slightly shifted pagination, or your entire publication printed in Courier!

Clearly there has to be a better way. And there is – Adobe’s Acrobat PDF (portable document format). The PDF is effectively a pre-interpreted PostScript file, simplified and rewritten to conform to Adobe’s object-based Document Structuring Convention. The benefits are overwhelming. For the designer the PDF provides platform and application-independence, combines all fonts, images and colour information in a single composite file ideal for electronic delivery and easily viewable and proofable using the freely available Reader program. For the bureau the advantages are even more compelling. They need only support the one file format, can offer last minute touch-up capabilities via the full Acrobat program and, most important of all, are far more likely to produce the desired output.

Adobe’s Acrobat PDF provides the universality of PostScript and the flexibility of application-specific files.

The result is a format that combines the universal nature of the PostScript-file approach and the flexibility of the application-files approach and then adds strengths of its own. The minute you see the PDF format you know that this has to be the future of publishing - a point I made back in my very first RW article over four years ago. Unfortunately there’s a big difference between future potential and current practice.

To begin with the PDF format needed to be completely overhauled and repositioned as Adobe wasn’t actually thinking about prepress at all when it devised Acrobat. Instead the format was envisaged as an office-based universal electronic exchange standard. As such the first version of PDF actually converted any CMYK colours back to RGB! The only intended output was to composite print, preferably as short print runs on a new breed of dedicated digital printers based on Adobe’s scalable Extreme technology.

This situation changed radically back in 1996 with the launch of Acrobat 3 and its new PDF 1.2 format. This continued to develop the PDF’s multi-purpose role, but also began the push toward prepress. Support for the CMYK colour space and for spot colours was added along with output control over essential parameters such as halftone and overprint settings. With 1999’s launch of Acrobat 4 and its new PDF 1.3 format the remaining prepress features fell into place with handling of larger page sizes, OPI 2 and ICC-based colour management. Most important of all was the full support for all PostScript Level 3 operators including SmoothShading for improved blends and gradients and DeviceN for multi-channel handling of duotones and hexachrome within the composite file.

PDF 1.3 is certainly capable of acting as a high-end publishing exchange medium, but it’s not straightforward. To begin with you first have to work out how. Acrobat 4’s multi-purpose background is confusing here with multiple ways of producing your PDF. The default method is to use the PDFWriter which is installed as a printer driver accessible to all applications. For prepress work avoid this like the plague as it produces output based on Windows GDI which just wasn’t designed with CMYK in mind. For more recent high-end publishing applications meanwhile, such as Corel Draw 9 and InDesign 1.5, the preferred route seems to be to save to PDF directly. This is certainly the most likely creation method for the future but should be viewed with some caution until firmly established as its reliability depends on how well the developer has integrated Adobe’s PDF Library and SDK.

Currently then the safest route is to use the separate Distiller 4.05 application that comes with the latest Acrobat. To use this you first print to a PostScript file but this time as a composite rather than pre-separated file (Adobe recommends using its ADIST4.PPD in those apps that let you specify). Next you choose your output settings from the drop-down list in the main Distiller dialog. Adobe provides three of these - Screen, Print and PressOptimized - depending on whether you are targeting web distribution, composite print or commercial print. In this case PressOptimized is clearly the right option and all that’s left is to open the PS print file for it to be automatically converted to PDF ready for inspection in Reader or Acrobat.

Distiller offers considerable customisation control through its job settings.

In normal circumstances this is all you need to do, but Distiller’s role is so fundamental that it’s worth understanding exactly what it’s doing through exploring its Job Settings dialog. The General tab lets you choose PDF format and also enter your imagesetter resolution to determine the final stepping of blends. The Compression tab controls how images are dealt with. There’s no point having excess information so if your images are over one and a half times the resolution you set here – normally 300dpi for colour/grayscale and 1200dpi for b&w – they will be downsampled. You can also choose a desired compression method with JPEG producing far smaller files than the lossless ZIP system. The Font tab is crucial as it lets you embed all fonts complete with control over whether the entire font is included or just the subset of characters used. The Colour tab becomes important if you are moving to an ICC colour-managed workflow or need to preserve halftone settings. Finally there’s the Advanced tab which is really the preserve of the bureau with options for automatically sending setup files to the imagesetter, managing error warnings and so on.

OK - we now know the right tool to use and how to use it. Presumably with the right Distiller settings we’re now guaranteed successful PDF output and final commercial print? Again it’s not that simple. Acrobat can’t solve problems that were there in the source file. Hairlines will still be near invisible at high-resolution, RGB images can still end up on the black plate, it’s still easy to duplicate spot colours and, if your final images aren’t in the right location, you’re still going to end up with coarse screen-quality images.

Font handling is even more problematic. Acrobat 4 now embeds the Base 14 fonts (Courier, Helvetica, Times, Symbol and ZapfDingbats) and automatically renames fonts so that you won’t get any unexpected substitution at the imagesetter – but instead you can get substitution in the file itself. Distiller 4 now plays safe regarding TrueType licensing so unless your font explicitly allows itself to be embedded it won’t be. Worse, it’s difficult to spot substitution as by default Acrobat uses all installed fonts so the file will look fine on your own system. You can get around this by disabling View > Use Local Fonts, but even here Acrobat’s use of MultipleMaster fonts to simulate missing fonts can hide the problem until it’s too late. Even worse, if you try to edit text that’s not locally installed, Acrobat 4 now insists on substituting the entire font!

In other words even with Acrobat we’ve still got the same image, colour and font problems that we’ve always had to contend with. Sadly that’s only the beginning as Acrobat adds some limitations all of its own. The first regards the printers’ marks and bleeds that are essential for managing commercial print. In fact PDF 1.3 added support for dedicated trim, art and bleed boxes, but few applications take advantage of them. The result is that the PDF either removes the bleed necessary for safe up-to-the-edge printing or its page size is larger than the intended print size which interferes with impositioning. As it’s rare for single pages to be sent to print this is a serious limitation. It pales into insignificance however, when compared to Acrobat’s biggest failing. Look in Acrobat’s Print dialog and you’ll see that it just doesn’t provide colour separation!

This is ridiculous. The entire PDF-based workflow is geared towards final separation of the composite PDF, but when you get there the capability just hasn’t been built in. Fortunately this doesn’t mean that producing separated work is impossible. To avoid the problem entirely many users choose to pre-separate their work with each CMYK or spot colour represented by its own black page in the PDF. If you remember to preserve halftone settings in the PDF and to override the output device’s, this system is certainly feasible and even has the advantage of preserving features such as duotones, DCS images, colourized TIFFs and XPress trapping settings. Composite proofing and editing capabilities are lost however, and by pushing prepress settings back to the designer, the principle of output flexibility is lost too. Effectively this is just using PDF as a new delivery system for those PostScript print-to-disk files.

Separation workarounds include creating pre-separated PDFs or exporting to EPS.

A more advanced variation is to stick with the composite PDF but to then use Acrobat’s ability to export individual PDF pages to EPS files, as these can then be brought into any high-end publishing package and separated from there. A more promising long-term solution is to cut out the EPS middleman and open the PDF file directly. Adobe has promoted the benefits of this direct high-end support for PDF first with its single-page Illustrator and now with its multi-page InDesign. The prospect is certainly exciting, taking the last-minute editability of PDF to new levels, but for the moment the conversion of PDF objects to application-native objects just isn’t reliable enough, especially with the danger of font substitution.

These conversion-based solutions to the problem of separation all have their place, but by their nature they are a bottleneck and a potential trouble spot in the smooth running of the PDF workflow. True efficiency and reliability demand that the PDFs be handled and separated directly. Fortunately the prepress vacuum left by Adobe has been filled over the years by a proliferation of third-party solutions. Picking up potential problems are the preflighting options such as Markzware FlightCheck, Extensis Preflight Pro and Enfocus PitStop. Taking care of impositioning and RGB to CMYK conversion are options such as Quite Software’s Quite Imposing and Quite A Box of Tricks. Finally for the actual separation, choices include Lanterna Crackerjack and Callas pdfOutput Pro.

Sites like pdfzone.com provide access to hundreds of third-party PDF tools.

In one way the sheer number of these third-party solutions is an indication of the PDF workflow’s maturity, but in another it just adds more confusion to a system whose entire purpose was to make things simple. PDF was meant to provide a single simple solution, but between the different PDF formats, target uses, creation methods, job settings, potential pitfalls, output methods, and now third-party tools the whole system seems little better than the mess it was designed to replace. It’s clear that what’s needed is for some standards to be imposed.

Thankfully that is exactly what is happening. Various independent standards bodies are working on defining a focused subset of PDF designed specifically for prepress handling called PDF/X. The ideal is for users to be able to select a PDF/X checkbox in their export dialog and know that the resulting file can be exchanged easily and output as expected. At the same time Adobe has finally released its own dedicated prepress solution, InProduction. This is a set of five prepress plug-ins for Acrobat. Preflight picks up on issues such as font embedding and image resolution. Trim/Bleed enables the setting of art, trim and bleed boxes. Colour Converter manages ICC-based RGB to CMYK conversions. Trapping allows trapping parameters to be embedded via PDF’s companion Portable Job Ticket Format (PJTF). Best of all, Separator at last officially enables Acrobat to manage, preview and output spot and CMYK separations.

Don’t get too excited however. To begin with Distiller 4.05 can’t actually produce PDF/X conforming files and by the time a new version appears, it looks like the standard itself will have already split into PDF/X-1, PDF/X-1a and even PDF/X-2! Regarding InProduction, the situation is currently even more disappointing. The functionality is undoubtedly impressive, apart from the lack of any impositioning control, but incredibly the first release is Mac-only. Admittedly the platform independence of PDF means that Mac bureaux can still handle PC files, but all high-end PDF users will want to get their hands on this level of control so the lack of a Windows version is unforgivable.

By this stage it might seem that terminal disillusion has set in, but that’s not the case at all. To begin with, on the software front things are definitely moving in the right direction. Even more important though are the hardware developments. So far I’ve been talking about the production of in-Host separations needed for common Level 1 and early Level 2 PostScript output devices. Using PDF with these devices, we’ve seen how the necessary prepress control can be moved downstream to the last possible moment before the final PostScript-based separations are created. The real strength of PDF, however, comes with PostScript Level 3 devices which can handle native PDF files without ever converting to PostScript. In other words, with PostScript 3 devices the necessary separation process can be pushed downstream and off the computer entirely and onto the output device.

This in-RIP separation of the composite PDF on a dedicated device is far more efficient and the logical conclusion of what now becomes a PDF-only workflow from beginning to end. It also offers more power with recent PostScript 3 imagesetters, for example, offering improved quality through in-RIP trapping. The real long-term targets of the new PDF-only workflow though are the new monsters based on Adobe’s Extreme-based prepress technology. These take advantage of the instruction handling of PJTF and the page independence of PDF files to automatically preflight work, produce colour-managed composite proofs, create impositioned layouts on the fly, process multiple page in parallel on multiple job ticket processors and finally to archive completed jobs. In other words they take the scalability of the RGB-based Extreme digital printers and run with it to provide true industrial-style automation within an offset CMYK context.

It’s clear that the evolution of an all PDF-based workflow hasn’t been easy and that there’s still a long way to go before its full promise becomes everyday reality. However, by shifting its vision from PostScript to PDF, it looks as if Adobe will finally succeed in providing not just the universal integrated publishing solution it originally envisioned, but one with even more power throughout the production workflow from screen to paper and from designer to press.

Tom Arah

August 2000

For more information on PDF visit adobe.com and pdfzone.com.


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