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EPUB 3 – A small revolution

EPUB (acronym for "electronic publication") is an open standard for e-books. As opposed to PDF documents, the documents in EPUB format are usually not set and defined to match a fixed page size. The contents adapt to the size of the screen. If the screen is mall there are more pages, if the screen is larger there are fewer pages to leaf through.

EPUB format

ePub Logo

The EPUB format shows the ".epub" file extension. The format, however, represents a file structure that is grouped together as a ZIP file. When the file name is changed to ".zip" the contents can be unzipped with a standard program and the file structure is visible. The content of an EPUB document is in XHTML format. The definition of the structure and the table of contents are XML files (*.opf, *.ncx). Images, photos, icons and similar objects feature as independent files. EPUB supports DRM mechanisms (Digital Rights Management). In this context, all of the files are encoded within the ZIP file.

The EPUB specifications are determined by the International Digital Publishing Forum (abbreviated as IDPF). The respective material cites 143 members for the 3.0 format. It is interesting to note that this group includes 7 persons from Apple, 5 persons from Google as well as 5 members from Adobe. It would appear that this format is attracting strong interest.

To date, EPUB was known in connection with all types of books. The standard was extended in the Version 3.0 of the specifications that was issued in October 2011. These extensions represent a small revolution. HTML5 including audio and video element and media overlay documents are now possible. A number of CSS 3 features can be used, as well as JavaScript. OpenType and WOFFm fonts can be embedded. With the support of MathML, mathematical formulas are also possible. The example document by AZARDI demonstrates what is possible with EPUB 3. The manufacturer of an EPUB reader has compiled an example document entitled EPUB3 UNLEASHED.

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In the new 3.0 version EPUB is competing directly with Amazon Kindle Format 8 (KF8), which was unveiled in January this year. This format is also based on HTML5 and CSS3. The direction is discernible: contents are presented in HTML. Thanks to the diverse possibilities offered by HTML5 and CSS3 other tools are required, in order to generate designed and appealing pages.

iBooks fixed layout

Example of the presentation of fixed layout in EPUB 3

With iBooks Author, Apple has shown what such a tool can look like and how easy it should be to operate. Apple, however, has not solved the problem as to how layouts should be generated for different screen sizes. This is not something the company is forced to do, because even the fourth generation of the iPad and the iPad mini have the same aspect ratio as the first generation. In this way, only one document needs to be generated that is presented in different resolutions.

EPUB 3 reader

The problem is that there are virtually no EPUB 3 readers available to date. The solution to this problem should not be long off, however. At an open source reference implementation of IDPF is available. The first extension for the Google Chrome browser is also already available. Since March 2012, EUPUB3 books can also be uploaded to the Apple iTunes store as the article It’s Official: iBooks Now Supports Epub3 reports. Initial tests show, however, that the iBooks app only supports extensions for the representation (audios, videos, fixed layouts). Interactive elements are not possible as yet.

The Apple iBook Store features an attractive interactive example entitled "The Beatles Yellow Submarine". It is also an EPUB file. Similar to a PDF file, the book is structured as individual pages which are scaled to the respective screen size. Interactive elements, audio and video components are placed on the pages. The display size and resolution of the pages can be reduced or enlarged. In this way, the book can be read on an iPhone in same way as on an iPad. If this file is opened in another EPUB reader the results are disappointing. All of the designed and interactive elements are gone and only the contents remain to be viewed. A look into the file shows that Apple has extended the EPUB format. At present, these extensions can only be interpreted and displayed by Apple devices.

In January 2012 Apple issued the free "iBooks Author" application. With this application it is simple to create e-books for the Apple iBookstore. The screen size is fixed and defined to the Apple iPad. As in a layout program it is possible to position and design texts, images, photos and videos. The files are transmitted to the Apple iBook Store as *.ibooks" files. But what is behind this file format? The format is EPUB with extensions.

EPUB creation

How are EPUB files created? Adobe InDesign represents one possibility. EPUB 2 files can be created, as well as EPUB 3 files, since the introduction of CS-6. When EPUB 2 is used the result can only be a text with embedded images. This is why all of the boxes of the pages are added to the text sequentially. Contents of text boxes are converted to HTML, while contents of image boxes are inserted as images. In the case of an UPUB export two options are available: "EPUB 3.0" and "EPUB 3.0 with layout". The option "EPUB 3.0" additionally supports audio and video files. The option "EPUB 3.0 with layout" issues a warning message informing the user that this is still an experimentally developed format. Initial tests and video on YouTube show that the warning is justified. Output with fixed layouts is conspicuous by absence.

EPUB Creation with Adobe InDesign

Apple Pages offers another option. Here, EPUB 2 files can be created conveniently.

The censhare solution

censhare EPUB Asset Structure

Example of asset structure

EPUB is becoming more and more similar to a web page in the version 3. Therefore, this is an additional indication that media neutral contents are becoming increasingly important. In censhare, outputting EPUB is nothing more than an additional output channel, which is supported as from the censhare Version 4.5. Media neutral contents (XML) that are also used for other channels can be compiled and bundled together as chapters and EPUB editions. The display and presentation can be defined by way of CSS files. Author and publisher assets can be linked, while additional attributes can be defined. Creating an EPUB file is an activity that can either be manually or automatically launched. Examples for EPUB 2 and EPUB 3 formats are available.

censhare iBook EPUB3

Example in in Apple iBook App exported from censhare to EPUB 3 format

EPUB sources


EPUB 3 specifications

Kindle Format 8



  • Good example for the potential EPUB3 offers

  • Only looks good on the AZARDI-Reader - interactive elements are not available on the iPhone or the iPad

Google EPUB 3 examples

  • Many EPUB3 examples

The Beatles Yellow Submarine

Adobe Sample eBook Library



  • Free reader for Windows, Macintosh and Linux

  • Spartan user interface

  • EPUB 3 support

Adobe Digital Editions

  • EPUB 2 support


  • Add-on for Mozilla Firefox

  • EPUB 2 support


  • Open source reference implementation of an EPUB 3 reader

  • Extension for Google Chrome



  • EPUB 2 support

Checking programs


Apple demands the checking with this program on submitting EPUB files to the Apple iBookstore