Pages Pre-Rendered by images
This technique is heavily used inside the highly interactive magazines published using the Adobe Digital Solutions environment: well known examples are the Condé Nast magazines (Wired is one of the most famous examples).
The way these magazines are implemented starts with the well known suite of Adobe Digital Publishing tools, In Design in primis. These tools are used by many publishers around the world and the latest versions offer the pos sibility to export the project, other than in the ubiquitous pdf format, in a package suited for distribution through iPad. The output of these files can be tested using the free app Adobe Content Viewer downloadable from the App Store, but of course the final branded app, together with the server infrastructure required to serve the contents, requires a higher tier license.
What characterizes this kind of magazines is that at the moment of project creation all pages are pre-rendered as jpeg or png images and then special effects are overlaid.
This means that the core section of the magazine reader is essentially an image viewer. Sure these images will span an area slightly larger than the iPad screen, so they will be embedded inside a scroll view, but they are still images. All in all technically the choice is not bad: the iPad is quite better in rendering images than PDF files, as the required calculations needed to transform the pdf data in bitmaps is completely skipped here, while the CPU will just need to decompress the image and send it to the graphics hardware. Exactly as we did in the PDF case, we can apply the overlay technique to over impose somecontent that requires user interaction on top of the bottom rendering layer.
While this technique is highly efficient from the point of view of rendering time, and is simple to implement as all the page layout complexities have been taken into account and solved by the desktop publishing tools, it offers a few limitations that need to be considered:
• every single page takes quite more space on disk and download time of this kind of magazines is increased correspondingly; in comparison with a pdf page, the space taken is much more as every pixel of text must be provided in the file and we cannot force high compression ratios if we don’t want to introduce blurring in the text. The pdf page, especially those pages made of text only, is much lighter as the text is not pre-
• zooming or font resizing is not feasible: both pdf and core text redraw the text using vectorial algorithms or per-size font representations, this is not possible to achieve on a static image. This means that the magazine needs to be drawn with specific fonts types and sizes, fonts which are well suited for jpeg compression (no blur) and the screen resolution (132 dpi, not so high; things will be better with the next retina display iPad!)
• text search, highlight and selection is impossible, unless the digital publishing tool exports together with the pre-rendered pages a full map of text coordinates, something I haven’t seen yet!
Adobe is not alone in publishing this kind of magazines:
there are several custom apps in the market that follow exactly the same approach. It’s not bad but is not leveraging the great publishing frameworks that Apple is offering to its developers. And it has too many limitations if compared with other techniques. For sure a publisher that is mastering the digital publishing tools I mentioned before can take advantage of this approach, as the final quality is undoubtable and the time to market is the shorter, and at the same time allows to provide a content suited for the iPad, and not just a pdf fit on screen.
But I would recommend to all developers that are making custom products and are not using specialized page composition tools to stay away from such methodology.