KOReader: a free electronic-book reader for e-ink devices

Your editor has a certain tendency to accumulate books, to the point that they crowd everything else out of the house. There is a lot to be said for books: a physical book has a user interface that has been optimized over centuries, and one can have a reasonably high degree of certainty that any given book will still work a few decades from now. Neither of those can be said for electronic books, but they do have the advantages of taking less shelf space and being more portable. So electronic books are part of the reading menu, which naturally leads to the search for a free reader for those books; KOReader turns out to be an interesting alternative.

KOReader is distributed under version 3 of the GNU Affero General Public License. It is, seemingly, a highly portable application, being available for Linux, Android, Windows, and a number of dedicated reader devices. The Android version is available via F-Droid, which makes this version a good starting place for anybody wanting to try out KOReader without performing surgery on a more specialized reader device. In this setting, it is a worthy alternative to FBReader (which is also a reasonable application) and, unlike FBReader, it doesn't try to sell proprietary plugins.

Those of us who have been playing with Linux for a long time, though, remember the special adrenaline rush that comes with trying to install free software onto a device that wasn't intended to support modification by its owner. One does not really know a piece of software until one has given it the opportunity to turn a useful device into electronic waste. So naturally your editor went quickly from the Android application to installing KOReader on his Kobo device. The Kobo, as it turns out, is a relatively open device; the installation is just a matter of mounting it as USB storage and unzipping a couple of files into it. Then comes the long, sweaty-palms pause while the Kobo meditates on the new software while presenting a blank screen.

Turning the pages

Eventually that phase passes, the device comes back to life. KOReader, at least when this installation method is used, does not replace the existing Kobo interface; instead, it presents itself as if it were just another book waiting to be read. Entering the application (by telling the device to "read" the KOReader "book") yields a list of top-level directories on the device; there does not appear to be a way to just list all of the books on the device short of just dumping them all into the root directory. The top-level view, in other words, is essentially a file browser. One moves through the directory hierarchy in the usual way; tapping on a book will open it to the cover image.

KOReader, it seems, must go through a process of rendering the entire book before it can present the first page. Asking it to read a large text book led to a long delay (for a "several minutes" value of "long") before the cover was shown. If one changes a parameter like the font size, the entire process begins again, making tweaking such parameters a less than fully rewarding experience. Neither FBReader nor the native Kobo reader exhibit this behavior. Rendering time for more reasonably sized books is not terrible, though.

User interfaces for electronic-ink devices must be developed with that medium's constraints in mind. Flashy animations just do not translate well, for example; the application needs to put up its control interfaces with a minimum of screen rewriting. KOReader has clearly been written with this kind of screen in mind, and the interface works well on the Kobo reader. This interface will be familiar to users of other book-reading applications. Tapping on the right edge moves forward one page; the left edge moves back. Swiping up or down the left edge adjusts the screen brightness. Tapping at the top yields information about the book and a plethora of menu options. It is possible to jump in and start reading books without having to work through the manual first.

That said, a reading of the manual does have its rewards. One place where KOReader clearly stands out is in its extensive customization options, not all of which are obvious without a bit of supplementary description. Almost any electronic-book reader allows the tweaking of the font size and, perhaps, margins. KOReader lets one adjust just about anything that somebody might have thought of to play with. There are controls for font hinting and kerning, for example. Spacing within and between words can be tweaked, as can the line spacing. There is a set of menus to tweak the style sheets used for rendering or do things like suppress blank pages at the end of a chapter. Most of these tweaks (and more) can be assigned to any of a large set of gestures recognized by the software. If one wants to adjust the bottom margin with a two-finger diagonal (bottom right to upper left swipe), it is possible.

One truly useful feature is that the default value for most parameters can be set with a long tap. Every book seems to come with its own wacky font size; setting the default size eliminates the process of adjusting it at the beginning of every new book.

Beyond the usual EPUB, KOReader can handle PDF files (and a long list of other formats as well). The results are variable. PDF is a page-oriented format, and full pages tend not to render legibly on small reader screens, so some accommodations must be made. KOReader has a whole set of options to try to ease the process, starting with simply eliminating the margins on the page. There is a mode that will divide each page into squares and step through them in any of eight different sequences; the primary use case for this mode appears to be comic books. There's another mode that simply tries to identify comic panels (and step through them) automatically. KOReader can be asked to extract the text from the PDF and reflow it for the screen, an option that works reasonably well for some PDFs that contain recognizable text. For the truly hard cases, KOReader can use Tesseract to perform optical character recognition and then reflow the results.

There are a number of connectivity modes available with KOReader. One can, of course, just plug in the reader as a USB-storage device and dump books onto it. Or KOReader can start up its own SSH server and accept files copied in that way. There is a plugin to obtain books from a number of cloud-storage services. KOReader can also connect to a local Calibre server and be fed books that way — though, when your editor tried this, the result was a crash and an illegible traceback on the reader screen, which is not the reading material that had been hoped for.

Many of the other expected features are there. KOReader allows the highlighting of sections and attaching notes to books. It can look up words in a dictionary. Happily for the purposes of this article, KOReader can take screen shots (just simultaneously tap on two diagonally opposite corners). And so on; the basic point that KOReader is a program with a lot of features should be clear by now.

One thing that KOReader cannot do, of course, is read books that are protected by DRM; it doesn't even make them visible in the interface if they exist on the device. There are authors and publishers who make at least some of their books available without DRM; for the rest, it's a matter of falling back to the built-in reader or employing one of the ways of removing DRM that are alleged to exist. This is not ideal, but it is a reflection of the less-than-ideal world we live in rather than on KOReader itself.

Looking at the code

The KOReader source is available on GitHub. It turns out to be a little over 140,000 lines of mostly Lua code that can be built for any of the platforms that KOReader supports.

The project seems to produce a release on a roughly monthly schedule. Since the v2021.03 release (March, 2021), 873 non-merge commits have been made to the project trunk; that is a little over two per day. That work was contributed by 47 developers, with the top two developers ("NiLuJe" and "hius07") being responsible for just under half of the total. This project, in other words, appears to be alive and well, though doubtless more contributors would be appreciated.

Will KOReader take the place of the native Kobo reader application on this device? There are a few more science-fiction novels to be read in KOReader before the decision can be made, but at least the research is entertaining. KOReader will be a good reader application for users who are willing to spend a bit of time tweaking its knobs to get the ideal experience. KOReader will also be good for anybody who might (rightly) worry that their proprietary reader device might just be spying on them. Users who want a simpler interface or who have to work with DRM-encumbered books will probably want to look for something else. Either way, KOReader provides a free-software alternative that can be used across a wide range of hardware, and that seems like a good thing.

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