Ebook technology from 50,000 feet

A little bit about the technology behind ebooks...

Ebooks and the technologies behind them are fundamentally changing not only the way we read books, but also the way we create them. And the interesting thing is, by design, ebooks have been built using already-existing technologies - so actually there is no real mystery here.

EPUB is the industry standard file format for ebooks - we'll talk about Kindle formats later, but for now let's just look at what an EPUB actually is, in layman's terms.

An EPUB file is simply a ZIP file that contains a simple website along with a list of the files and the reading order. The EPUB standard is maintained by the International Digital Publishers Forum (IDPF). It's completely open and anyone can read it, use it, or contribute to its development. The important thing about EPUB and what has made it successful is an attempt not to reinvent the wheel – whenever possible, the IDPF have used existing standards like XHTML and CSS, or well- known formats like ZIP. That meant that it was very easy for technology companies to pick up the standard and work with it - there was no big learning curve. That's the good news.

Also good news is that standard EPUB files can be read by many apps on tablet devices (iBooks, Google Play Books, Bluefire reader, Kobo, Nook, etc.), on specialist e-ink e-readers (Kobo, Nook, Sony Reader etc.) or on desktop software readers (ADE, iBooks desktop, Kobo, Nook etc.).

Although EPUB is a standard, reading software and devices limit what is supported by that standard. BISG has developed a web-based tool and support grid that lists which enhancements and features of EPUB3 render correctly on which devices, apps, and reading systems. That helps a lot.

Ok. So then what is Mobi/KF8?

The Mobi file format was developed for the MobiPocket reader for PalmPilot. It was extended by Amazon and uses a proprietary DRM (encryption) scheme. KF8 is Kindle's update to the original Mobi format optimised for the KindleFire tablet, and like EPUB it is also based on HTML5 and CSS3. If you download the Amazon Previewer tool, you can convert EPUB files to Mobi/KF8 files and view them on Kindle reading devices. Any file created by recent versions of the Amazon converter software contains the content formatted in Mobi for older readers and KF8 for newer readers. The reader will automatically pick the format it can handle best.

Right. So. What exactly is the difference between EPUB and Mobi/KF8?

Well, one thing to know is that EPUB is a collaborative effort between many publishers and technology organisations. It’s a standard format not controlled by any single organisation. Mobi/KF8 is the product of a single company. Functionally, the subsection of HTML and CSS that is supported by Mobi/KF8 is different from that of EPUB/EPUB3 so many publishers decide to release different files for EPUB and for Mobi/KF8. 

Let's hear it from both sides.

EPUB is the distribution and interchange format standard for digital publications and documents based on Web Standards. EPUB defines a means of representing, packaging and encoding structured and semantically enhanced Web content — including XHTML, CSS, SVG, images, and other resources — for distribution in a single-file format. EPUB allows publishers to produce and send a single digital publication file through distribution and offers consumers interoperability between software/hardware for unencrypted reflowable digital books and other publications.
(IDPF, “EPUB”, accessed 07/07/2013)

Kindle Format 8 is Amazon’s next generation file format offering a wide range of new features and enhancements – including HTML5 and CSS3 support that publishers can use to create all types of books. KF8 adds over 150 new formatting capabilities, including drop caps, numbered lists, fixed layouts, nested tables, callouts, sidebars and Scalable Vector Graphics - opening up more opportunities to create Kindle books that readers will love. Kindle Fire is the first Kindle device to support KF8 - in the coming months KF8 will be rolled out to our latest generation Kindle e-ink devices as well as our free Kindle reading apps.
(Amazon, “Kindle Format 8 Overview”, accessed 07/07/2013)

Umm, thanks.

You're welcome!

Moving on. EPUB3 v EPUB2?

With EPUB2.01, if you needed some features, you had to create an app. However, EPUB3 allows embedded audio, video and interactivity. If you’ve seen an iBooks enhanced ebook or a fixed layout ebook, then none of this will be a surprise: much of what is in the EPUB3 spec just adds already been used in enhanced ebooks into the spec. EPUB3 is a standard, and will hopefully solve some problems with files behaving differently on every device. EPUB3 is an extension of EPUB2 in almost every way.

EPUB3 is backwards compatible with very little effort, and an EPUB2 file can be converted to EPUB3 by changing a single line in the OPF file (although you won’t see any advantages).
There is very little reason for publishers to continue to create EPUB2 files anymore. EPUB3: 

  • Solves some problems with EPUB 2.01 
  • Standardises things that used to be reader-specific features 
  • Supports scripting (e.g. pop-up footnotes, interactive quizzes)
  • Is accessible
  • Is based on HTML5 with some modifications 
  • Uses CSS2.1 stylesheets with some support for CSS3 features 
  • Supports multi-column layout, audio, video, read-along, better font support, directional text, MathML support, SVG support, etc. 

But ... it's important to remember that reading systems will continue to override many of the formatting decisions we make (i.e., the CSS). Just because it is in the EPUB standard, doesn't mean that the reading systems will support it.

So there you go. 

Next time you are asked to explain EPUB in a nutshell, you'll have an answer!