The Photoshop PDF format has big implications for desktop publishing. So why is no one using them?
Elisabetta Bruno’s article about the Photoshop file format and desktop publishing sparks an interesting discussion: in a desktop publishing world where there’s more than QuarkXPress, what is the best file format for placed images? Formats like DCS were designed to overcome shortcomings created by XPress and early DTP systems. With InDesign a lot of those shortcomings are gone, and many users are happily creating Photoshop files (.psd) to place in their InDesign layouts. But what of Photoshop PDF (technically .pdp, but usually generated with the usual .pdf suffix)? This file format has all the positives of .psd plus a few features of its own, but with Photoshop CS and CS2 it’s easy to save PDFs that will not work for the standard desktop publishing workflow. In this article we will look at the benefits of Photoshop PDFs, as well as what to do and not to do in order to use them properly.
A Photoshop file with all the features of PDF
This 2003 article by Nick Hodge, Channel Sales Manager and part-time Technology Evangelist for Adobe, is what got me hooked on Photoshop PDF. Photoshop PDF retains all the functionality of the Photoshop .psd file format, including:
- Alpha channels
- Clipping paths
- Spot channels
- Vector type
Photoshop PDFs, by their nature, also enjoy the added features that make it a PDF:
- Increased compatibility. Photoshop PDFs can be read by Acrobat and Adobe Reader. (This can be a downfall too, since double-clicking Photoshop PDFs will open the file in Acrobat or Adobe Reader, the default application for PDFs. According to Hodge, a .pdp suffix will make Photoshop the default app, but I can’t duplicate this in my tests. I’m on a Mac though, and PC users may find it useful.).
- Security features. Set passwords and restrict file usage with PDF’s built-in security tools.
- Compression. ZIP and JPEG compression are both available to Photoshop PDFs.
- Smaller file sizes. PDFs are naturally smaller than other graphics formats, including the Photoshop file format.
If you work with a lot of CMYK + spot color images, Photoshop PDF works really well. This other article by Nick Hodge will help clarify how it can be used in this situation.
Photoshop can be PDf’s best friend or worst enemy
Figure 1: The PDF Options dialog box, only with Photoshop 6 and 7.
The Photoshop PDF file format was introduced with Photoshop 6, and creating one was pretty easy. Figure 1 shows the PDF Options dialog box from versions 6 and 7 with settings for:
- Encoding. Save your file with ZIP or JPEG compression, and control image quality.
- Save Transparency for retaining transparent layers.
- Image Interpolation, which will allow interpolation (anti-aliasing) when printing low-resolution images.
- Downgrade Color Profile will save down the embedded color profile for less advanced systems.
- PDF Security, to set and change security settings.
- Include Vector Data to retain vector graphics, whether by embedding fonts or converting text to outlines.
Figure 2: The “new and improved” Save Adobe PDF dialog box.
The key is a little checkbox titled Preserve Photoshop Editing Capabilities. If this is left unchecked, all that great Photoshop data is going to be lost…
But with Photoshop CS and CS2, Adobe implemented a standardized Save Adobe PDF dialog box (see Figure 2) that can ruin an image if you’re not careful. The key is a little checkbox titled Preserve Photoshop Editing Capabilities. If this is left unchecked, all that great Photoshop data is going to be lost, including layers, spot channels and alpha channels. And the big pitfall is the standardized interface’s presets. It’s very easy to just choose the [PDF/X-1a] preset when saving a file; it’s the standard for CMYK files going to a press, which is what most of us are using them for. Unfortunately the X-1a spec does not allow Photoshop editing capabilities, so when you open the file again to make changes you will find it very flattened and devoid of anything other than CMYK data.
Another pitfall is that the Save Adobe PDF dialog box can and will override any image settings established in Photoshop, including any in the preceeding Save As dialog box. If you have an image with resolution of 300ppi, but inadvertently save it with the [Smallest File Size] preset you will convert that file to 100ppi resolution and there’s no going back. Photoshop even has a warning message (Fig. 3) for you the first time you try this. It used to be that the act of saving a Photoshop PDF did not affect the pixels in your image; not anymore. And care must be taken nowadays or you can do something terrible to your images.
Figure 3: Don’t try this at home, kiddos.
As long as you keep Preserve Photoshop Editing Capabilities checked, and don’t allow the Save Adobe PDF dialog box to mess with necessary resolution or color mode, the Photoshop PDF file format will serve you well. But it can take some practice.
Elisabetta has another article on the history and features of the PDF file format. This delves more into the specifications of various PDF formats, including PDF/X, PDF/X-1a and PDF/X-3 as well as the version numbers, which version of Acrobat they are native to and the technologies they support (like transparency, which was first supported by PDF 1.4). One PDF format I do not see listed is PDF/A, designed as a long-term archiving format. Here is a United States Library of Congress webpage that details the PDF/A format, including features and restrictions.
The TIFF format was widely used in desktop publishing, before InDesign made the Photoshop file format (and Photoshop PDF) viable alternatives. Here is Elisabetta’s article on the use of TIFFs in desktop publishing. It’s still widely used by QuarkXPress users, and I like to use it when working with line art since it can be colored on the fly in any page layout application.
PlanetPDF.com is maybe the top site on the web focusing on PDF technology.
Here is the Wikipedia entry for Portable Document Format (PDF).