E-book formats: everything you need to know about e-books – part 3

If you’re pub­lish­ing a book in digital form, one of your main pri­or­it­ies will be to reach as many readers as possible. But whether or not a user can actually read the book easily on their device usually comes down to the file format you choose. This is an important issue, because the market for e-book readers is full of many different formats from a variety of man­u­fac­tur­ers. And there’s no standard format for digital books that will be supported by all readers.

We’ve already looked at two important aspects of e-books in our series, beginning with how to create an e-book, before dis­cuss­ing the various e-book templates available for authors and pub­lish­ers. Now, in the third part of our e-books series, we’ll take a look at the best and most popular e-book formats available on the market today, to help you decide which one is right for your needs.

Modern e-book readers usually support a number of formats when it comes to dis­play­ing digital documents. While all of them prefer spe­cific­ally designed standards for e-books that enable an optimised reading ex­per­i­ence on portable devices, many also support current data formats that you’ll be familiar with from saving classic office documents. Choosing the right e-book format really comes down to two factors: the features required and the expected target platform. Here are a selection of the most popular and well-known e-book formats.

ePUB is a widely-used format when it comes to the pub­lic­a­tion of digital books. It was developed by the In­ter­na­tion­al Digital Pub­lish­ing Forum (IDPF) and is supported by almost all e-book readers outside of the Amazon universe. This popular e-book format is based on standards like XHTML, XML, and CSS, and also supports HTML5, MathML, scalable vector graphics (SVG), and JavaS­cript embedding in version 3.

In addition to a stylish text format­ting, this file format features in­teg­ra­tion of mul­ti­me­dia elements like images, audio files, and videos, as well as in­ter­act­ive elements. Digital books in ePUB format (.epub) are designed to fit dy­nam­ic­ally to whatever display screen size the mobile device in question has. Al­tern­at­ively, it’s possible to assign a fixed layout to content. For copyright pro­tec­tion, ePUB users have the option of an extension to Digital Rights Man­age­ment (DRM), a system designed to handle copyright. Com­mer­cial ePUB e-books are protected by the Adobe software ADEPT DRM.

While numerous e-book reader man­u­fac­tur­ers remain flexible by making use of open standards, Amazon customers only have in-house formats available to use. Amazon e-book products are a closed system, con­sist­ing of the Kindle Shop, Kindle e-book readers, and the cor­res­pond­ing reader apps for computer, tablet, and smart­phone. Amazon relies on its own file formats: Mo­bi­pock­et, AWZ, and KF8, along with its own DRM system. This DRM system means that e-books purchased on Amazon can only be opened on Kindle devices or through Kindle apps.

• Mo­bi­pock­et: Mo­bi­pock­et is an older e-book format from an Amazon sub­si­di­ary of the same name. Documents in Mo­bi­pock­et format (.mobi) are supported by Kindle series reader devices and can be opened on older Windows versions (2000, XP, Vista) and mobile devices with the operating systems Palm OS, Symbian OS, or Windows Mobile via the Mo­bi­pock­et e-book reader software. The e-book format is also supported by the free e-book viewer pro­grammes Okular and FBReader. Mo­bi­pock­et is based on the same open e-book standard that serves as a template for ePUB, and likewise uses XHTML. But un­for­tu­nately, unlike other e-book formats, the Mo­bi­pock­et format has rather re­stric­ted flex­ib­il­ity when it comes to layout. In the Amazon universe, Mo­bi­pock­et format­ting has been replaced by the continued de­vel­op­ment of AZW.

• AZW: Tech­no­logy-wise, the AZW format (.azw) is based on Mo­bi­pock­et, but unlike its pre­de­cessor, AZW is ex­clus­ively supported by Amazon’s Kindle product range. E-books that are purchased in this format via the Kindle Shop can only be opened using Kindle devices or Amazon reader apps. Like Mo­bi­pock­et, AZW has only limited layout options available. Amazon has since developed a new format with a much wider spectrum of functions and greater flex­ib­il­ity for the release of its Kindle Fire reading device series. Kindle Format 8 (KF8) is also com­pat­ible with other Kindle series devices.

Kindle Format 8 (KF8): The e-book format KF8 (.azw3) offers a marked increase in functions than the previous Amazon formats Mo­bi­pock­et and AZW, largely thanks to the support of current web standards like HTML5 and CSS3. Documents in Kindle Format 8 adapt dy­nam­ic­ally to the device’s screen size and enable complex graphic displays for design and layout dependent pub­lic­a­tions like children’s books and comics. Like ePUB, Kindle Format 8 supports the in­teg­ra­tion of audio and video as well as scalable vector graphics (SVG), fixed layouts, and in­ter­act­ive elements. But it’s not possible to use MathML or JavaS­cript with KF8. But users are able to integrate ePUB3 files into KF8 using an interface. The long-term plan is for this new e-book format to fully replace the tra­di­tion­al Mo­bi­pock­et and AZW formats.

Like Amazon, Apple insists on its own e-book format: iBooks. But this man­age­ment software for Mac, iPad, and iPhone also supports external file formats like ePUB or PDF. Digital documents can be created in iBook format through the iBooks Author software, which can be down­loaded in the Mac App Store free of charge. You can also create documents in PDF or ePUB format on iBooks Author. The iBook format is based on the ePUB design, but dis­tin­guishes itself through dif­fer­ences in CSS char­ac­ter­ist­ics.

Broadband eBook (BBeB) is a group of pro­pri­et­ary file formats that were developed by Sony and Canon spe­cific­ally for the pub­lic­a­tion of elec­tron­ic books. BBeB variants like LRF and LRX were used on early Sony devices, which were wide­spread across the US. But since 2009, Sony has com­pletely re­vo­lu­tion­ized its e-books store, replacing all BBeB formats with ePUB instead. As a result, BBeB has no real use among today’s modern e-book formats.

The e-book format Fic­tion­Book (.fb2) is par­tic­u­larly popular in Russia. This open standard is based on XML and is supported by free e-book reader pro­grammes like FBReader, Okular, CoolRead­er, and STDU Viewer. Since meta data like author details, title, and ISBN are saved directly in the e-book file, FB2 makes it easy to manage digital documents. But DRM functions are not supported by Fic­tion­Book.

PDB is an e-book format that was ori­gin­ally developed for the Palm handheld or­gan­izers (Personal Digital As­sist­ants, PDAs). They were used in e-book format­ting by the US pub­lish­ing company Barnes & Noble. In addition to the in-house software eReader, there are other viewer pro­grammes for a variety of platforms. But today, Barnes & Noble sells all its e-books in ePUB format; PDB is no longer used com­mer­cially.

In addition to specific formats for dis­play­ing elec­tron­ic books, most e-readers also support popular file formats like DOC, TXT, HTML, or RTF, which are used on PCs for word pro­cessing. These formats usually play a lesser role in the com­mer­cial pre­par­a­tion of e-books, however. Another option is the flexible, industry-standard Portable Document Format (PDF), which enables easy fixed sharing of documents on different devices. The non-text file format Comic Book Archive has also es­tab­lished itself for dis­play­ing digital picture books and comics.

• PDF: the Portable Document Format (.pdf) developed by Adobe Systems is a cross-platform file format that enables digital documents to be shared re­gard­less of the software or hardware ori­gin­ally used for reference. A PDF document can be viewed on devices exactly as it was created by the author. All that’s needed is PDF software, which is normally available on your e-book reader. But as a file format for elec­tron­ic books, PDF is quite limited. Ad­mit­tedly, it gives the format a great reach and supports DRM functions, but the rigid format, optimised for print versions, isn’t ideal for use on portable devices, even with the built-in zoom function.

• Comic Book Archive: this non-text format is designed for dis­play­ing image sequences, par­tic­u­larly those used in comic books. Comic Book Archive files normally consist of a series of images in PNG or JPEG format that are saved in a shared ZIP file (.cbz). Archiving through RAR (.cbr), 7z (.cb7), TAR (.cbt), ACE (.cba), TrueCrypt (.cbtc), and Mac OS X Bundle (.cvbdl) is possible. If your reader doesn’t support Comic Book Archive format, you can unzip the archive files and open them with any regular image viewing software.

Despite the diverse technical options available to help you publish your digital book, the e-book market is really dominated by three formats. While Amazon is going its own way with KF8, all the other big players in the e-book industry have opted for ePUB. This creates a problem for authors and pub­lish­ers: if you publish books in the Amazon format, you can only reach users of the Kindle series and the cor­res­pond­ing Kindle reader apps. The reach is greater for e-books published in ePUB format. But by using ePUB, you’re com­mit­ting to ignore the market leader and the biggest online retailer in the US, because ePUB-formatted e-books can’t be opened on Kindle devices or apps. 

There is an al­tern­at­ive: PDF. The Portable Document Format is supported by all modern e-book readers and so can be viewed – in theory at least – on PCs, laptops, tablets, and smart­phones. But there’s a catch to the lack of platform op­tim­isa­tion: PDFs have a very rigid layout and don’t always im­me­di­ately fit to every display screen size. This causes the most issues on mobile devices like smart­phones, where there are a number of slightly dif­fer­ently sized small-screen displays. So if you want to focus on e-book readers spe­cific­ally, it’s worth con­sid­er­ing pub­lish­ing your elec­tron­ic book in one or both of the spe­cial­ized formats, KF8 and ePUB. But if your content is designed to be read on a PC first and foremost, perhaps even to be printed out, then the flexible PDF format is a very good option.

The question of the dis­tri­bu­tion channel is also relevant. If you want to take advantage of the Amazon network and its huge customer base, then you’ll need to use their KF8 format. The same is true of Apple iBooks as well as other e-book shops – even ones that don’t use their own pro­pri­et­ary format.