The magazine of the Melbourne PC User Group
PDFs - Simplifying the Publishing Process
Stephen Davey

In the world of printing and publishing, constant change is the "normal" climate, particularly in the pre-press area.

The process of transferring computer graphics files from your computer to the printing press has been a somewhat complicated stream of processes, each fraught with difficulties and potential problems.

While improvements in technology have helped reduce the number of intermediate steps, many difficulties can still arise with missing fonts, incompatible file formats, and image resolution problems.

For many years the industry has been screaming out for a graphics arts file format that solves all the issues

  • platform independent (le. PC, MAC, UNIX)
  • device independent (le. will print at the best quality possible on a particular device)
  • embedded fonts (le. no requirement for the output device to have the font)
  • single file format (le. all components included. No separate or external parts such as fonts or images required)
  • high quality output supporting various colour models (ie CMYK, PMS, RGB)
Adobe Acrobat

Almost by accident a few years ago, Adobe went a long way towards solving the problem when it introduced the "Acrobat" tools and the "Portable Document Format" - PDF. Originally Adobe introduced Acrobat as a tool to create PDFs so that typical office documents created in an application on the PC could be easily be viewed on a MAC (and vice-versa).

In a cunning marketing ploy (since used by Microsoft and Netscape with their browsers), Adobe gave away the Acrobat Reader program free so that anyone could read/view and print PDF documents. If you wanted to create PDFs, the other "half" of the program (Acrobat Distiller) had to be purchased.

The original PDF format was a magnificent format, in that it was truly cross-platform and the viewer did not need to have the same fonts as the creator of the document. The PDF could be created so that all the fonts required were either actually embedded, or otherwise very good font substitution was employed to ensure the document looked the same on all platforms.

In its default setup, the first version of Distiller created PDFs that were very small because any included graphics were downsampled to 72 dpi. While many users were unaware that high resolution PDFs could be created, few users every imagined of what use a high resolution PDF could be.

High Quality Publishing

Today, the majority of professional graphic designers and publishers use either PageMaker, InDesign or Quark Express to create documents for high quality publishing. The designer must provide the film or plate bureau not only the particular application file, but also all the fonts and individual graphic files (photographs, logos etc). This can amount to many, many files, adding up to sometimes hundreds of megabytes. Adobe's PDFs presented a way of firstly reducing the number of files to one, and reduce the megabytes.

Limitations

While the first versions of PDFs very successfully provided solutions for transferring office documents, some limitations with the format meant that it was not suitable for high end publishing.

Firstly, the CMYK colour space and colour separations were not easily supported and secondly most imagesetting RIPS could only handle "Postscript" files. As PDF files were created by "distilling" a postscript file, there seemed little point in creating a postscript file, converting it to PDF, then converting it back to postscript.

Then Along Came 4!

Not long after the original release Adobe realised that PDFs could have a very useful future as a publishing media and set out to "re-invent" PDF for the publishing industry. With the recent release of Acrobat 4 (PDF version 1.3) most of the format's early limitations have been removed/resolved.

Postscript level 3 imagesetter RIPS can now process PDF files directly, and in-rip separations handle colour separation of PDFs very well. Adobe has also done a good job in convincing other software and hardware vendors of the future of PDF. As a result, there are many inexpensive third party applications, plug-ins or specially designed PDF workflow systems that have meant widespread acceptance of PDFs in the publishing industry.

PDF files are becoming (more and more) a standard in the publishing industry. In fact moves are already well in place for PDF to become the standard file format for press and magazines in Australia by as early as 2001 (see http://www.3dap.com.au).

Acrobat Now

Acrobat consists of two main parts, firstly Acrobat Reader (available free from http://www.adobe.com), and secondly Acrobat 4, made up of a more advanced version of the free reader and Distiller which is the part that allows you to create PDF (version 1.3) files from either postscript or EPS files.

Using different "Job Option" files it is possible to create a number of different types of PDF files for specific purposes.
  • Low resolution (say 72 dpi) PDFs with RGB (smaller than CMYK) images. These PDFs are very small compared with the raw application file or postscript files and very useful for e-mailing proofs of jobs to clients, or putting documents on the web.
  • Medium resolution (say 120 dpi) PDFs with RGB for producing reasonable quality colour laser prints.
  • High resolution (200-300 dpi) PDFs with CMYK images for publishing purposes.
Creating High Quality PDFs

There are several ways to convert your application file (PageMaker, Quark, CorelDraw, Illustrator etc) to PDF files.

The first two involve printing from your application to either of the two printer drivers (PDF Writer, Acrobat Distiller Driver) installed when Acrobat is installed.

The PDF Writer is not a suitable driver to use if you need to create high quality PDFs. The PDF Writer automatically downsamples images to 72 dpi (far too low) and uses only the screen header of any EPS files included.

Some applications allow you to "Export" the job as a PDF. Generally these export facilities also do not give you complete control over all the settings.

By far the best way to create a PDF is to create a postscript print file from the application and then distil that file into a PDF using the appropriate job option.

Creating Postscript Print Files

The start of a good PDF file is a good Postscript file and the best start is to install the Adobe Postscript Printer Driver (available free from http://www.adobe.com.

If the application you are printing from uses PPD files, select the Acrobat Distiller PPD. In most cases the bureau or publication will require trim marks and registration marks, so make sure these are selected. Ensure that the "paper" size chosen is large enough to include your complete job plus the trim/registration marks (eg. print an A4 page to A4 Extra).

Don't select colour separations or any items such as negative or mirror image etc. All these options are best done on the imagesetting end. Also ensure that the images print at their full resolution (le. don't let the application optimise or downsample, Acrobat will do a better job).

The resulting postscript file (which may be considerably larger than the application file) can then be distilled into a PDF using Acrobat Distiller.

Setting Distiller's Job Option for High Quality PDFs

General Settings
  • Format
    Normally, unless you have difficulty in transferring files, do not select ASCII as this will result in a larger file.
  • Compatibility
    Unless you know that the bureau/publication can accept Acrobat 4 files, set the file compatibility to Acrobat 3.
  • Optimise
    Always "Optimise". While this slightly increases the time it takes to distil a file, the resulting PDF is very well organised and will usually be processed through a RIP very efficiently. Since much of the important font and other information is moved to the front of the file, in the unlikely event of a PDF failing to RIP, they normally fail very early in the ripping process - thus saving valuable time.
  • Thumbnails
    Choose whether you want "Thumbnails" to be generated. Thumbnails are tiny images of each page, which in a multi page document, make it easy to navigate to a particular page. Adding thumbnails will slightly increase the size of the final PDF.
  • Resolution
    Set the resolution to at least 2400 (or higher if you know the exact resolution of the image setting by which the file will be processed). This setting affects only vector EPS files, ie. to determine the number of steps for a blend or fade. It has no effect of any bitmaps included in the file (sec compression settings).
Compression

• Colour and Greyscale images

(While Acrobat has separate sections for Colour and Greyscale images, normally you should treat both types of bitmaps in the same way)

Part of the secret of PDFs is that bitmap images are processed so that no extra unnecessary information is included in the file. This results in a file that is the smallest possible for the given purpose. For this reason the Compression settings are some of the most important.

Choose "Bicubic" rather than "Average" downsampling. "Average" simply throws out (for example) every second pixel. "Bicubic", on the other hand, looks at a small group of pixels and keeps those that best represent what was there originally.

Many "experts" say that the dpi (dots per inch) should be twice that of the lpi (lines per inch) of the "Screen Ruling used for the publication. PC Update, for instance, is printed using 150 lpi, so the dpi would be 300. However, I believe this is overkill. After conducting many test and real examples over the years I know that setting the dpi to 1.5 times the lpi will give perfect results. In fact, in emergency situations where you are trying to dramatically reduce the file size, setting the dpi to the same as the lpi will still give you acceptable results. (If anyone ever tells you that you must scan or downsample at/to 300 dpi, ask them if they have actually conducted any tests at lower resolutions to determine the difference.)

With regard to compression, always use "ZIP-8 bit" as this is a loss-less process. "JPEG" on the other hand removes some information and may adversely image quality.

For monochrome images set the dpi to about 8 times the lpi, the compression as "CCITT Group 4" and make sure Text and Line art compression is on.

Fonts

Select "Embedded All Fonts" and "Subset All Embedded Fonts Below 100%"

In order that your PDF file will print out at the "other" end exactly as intended it is vital that all the fonts are not only embedded but also "subset". If, for example, the font "FuturaBold" is embedded in a PDF, and the file is printed out to a imagesetter that already has a "FuturaBold" installed, the font installed in the imagesetter will be used rather than the font embedded in the PDF. Whilst they might have the same names the two fonts could be and often are slightly different. "Subsetting" embeds the font but gives it a unique name, meaning that the imagesetter will never have the font installed and will use the font embedded in the PDF.

Colour

Under the "conversion" settings select only the "leave colour unchanged" option. All other "conversion" and "Assumed Profile" options should be left unchecked.

In the "Option" section, select all the options except "Preserve Halftone Information". This would be used only in unique circumstances where the halftone details set in the file are to override the halftone setup in the RIP (in most cases the bureau imagesetter operators are better able to determine the correct halftone screen ruling, angles and dot shape. Leave it to them.)

Normally the PDF file will want to preserve or keep the "Overprint", "Under Colour Removal", "Black Generation" and "Transfer Function" already existing in components within your job, so all these options should be selected.

"Overprinting" refers to what happens when one colour is laid over the top of another - does it "knockout" a hole in the background colour, or does it "Overprint" or cover the colour underneath? In most cases light colours need to knock a hole in darker colours so their colour value does not change. Very dark colours, in particular black, should overprint any lighter colour underneath so as to make the registration of the colours easier on the press.

"Under Colour Removal" and "Black Generation" really are the topic of another complete article, but for the moment, trust me - just preserve it!

Advanced

The settings in this area can be very specific to particular RIPS and they highlight one of the great things about Acrobat 4. The service bureau or film house can do all the hard work to find out exactly which settings suit their equipment and all you have to do is install and select the job-option file they supply.

However, there are two items here that may be useful to users who need to distil EPS files. As well as being able to distil postscript print files Acrobat Distiller can distil EPS files. This can be extremely useful when you have an EPS file that is causing problems in either an application or RIP, often, distilling the EPS file into a PDF and then exporting it back out as an EPS from Acrobat, can solve the problem.

If you want to distil an EPS, then the "Default Page Size" dictates the size of the final PDF. A postscript print file contains information about the page size of a job, however an EPS file does not, so Distiller needs to be "told" what size to make the PDF.

If you need to distil EPS files and need the PDF file to be made the exact size of the EPS, then select "Process DSC Comments" and "Resize Page and Centre Artwork for EPS files".

Some Important Issues

Trial and more trial is probably one of the most important techniques. Spending time making a few (small) trial PDFs in consultation with your bureau, will ensure that your PDFs work as intended.

Common mistakes are:

  • Using RGB instead of CMYK images.
  • Neglecting to add trim marks and registration bullets.
  • Making the printer pages size too small to include the actual page size plus trims.
  • Using True Type fonts instead of Postscript fonts.
Reprinted from the September 2000 issue of PC Update, the magazine of Melbourne PC User Group, Australia

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