kobofix.py is a Python script designed to process and adjust TTF fonts for Kobo e-readers for a better reading experience with the default kepub renderer.

It generates a renamed font, fixes PANOSE information based on the filename, adjusts the baseline with the font-line utility, and adds a legacy kern table which allows the kepub engine for improved rendering of kerned pairs.

You can use this to modify or fix your own, legally acquired fonts (assuming you are permitted to do so).

License

Licensed under the MIT License.

Requirements

Python 3, FontTools, font-line.

You can install them like so:

pip3 install fonttools
pip3 install font-line

If you want to use the --hint additive or --hint overwrite options, you also need ttfautohint:

brew install ttfautohint  # macOS

On macOS, if you're using the built-in version of Python (via Xcode), you may need to first add a folder to your PATH to make font-line available, like:

echo 'export PATH="$HOME/Library/Python/3.9/bin:$PATH"' >> ~/.zshrc
source ~/.zshrc

Usage

Open a terminal and navigate to the directory containing your font files. Make sure your font files are named correctly. The script will process files that contain the string:

Regular
Italic
Bold
BoldItalic

This is the naming convention used on Kobo devices for proper compatibility with both the epub and kepub renderer.

You can then run:

python3 kobofix.py --preset kf ./src/*.ttf

If no preset or flags are provided, the script will prompt you to choose a preset. See the Presets section below for details.

With the Kobo Fix (KF) preset, the script will:

Validate all filenames. If there are any invalid filenames, you will be prompted and can continue with all valid filenames, but it is recommended that you fix the invalid files.
Remove any WWS name metadata from the font. This is done because the font is renamed afterwards.
Modify the internal name of the font. The KF prefix is applied (replacing the NV prefix if present). A custom name can also be specified with --name.
PANOSE metadata is checked and fixed. Sometimes, the PANOSE information does not match the font style. This is often an oversight but it causes issues on Kobo devices, so this fixes that.
Font weight metadata is updated. There's other metadata that is part of the font that reflects the weight of the font. In case this information needs to be modified, it is adjusted.
Kern pairs from the GPOS table are copied to the legacy kern table. This only applies to fonts that have a GPOS table, which is used for kerning in modern fonts.

Other presets and flags can change this behavior. For example, the NV preset applies 20% line spacing and skips kerning, and the --hint flag can be used to control hinting.

See Customization and Presets for details.

The modified fonts are saved in the directory where the original fonts are located.

Customization

You can customize what the script does. For more information, consult:

./kobofix.py -h

Given the right arguments, you can:

Control kerning behavior (--kern): add a legacy kern table, remove GPOS after extraction, or skip entirely (default)
Control hinting (--hint): strip hints, apply ttfautohint to unhinted fonts, apply ttfautohint to all fonts, or skip (default)
Use a custom name for a font
Use a custom name for the prefix
Adjust the percentage of the font-line setting
Skip running font-line altogether

For debugging purposes, you can run the script with the --verbose flag.

Presets

The script includes presets for common workflows. If no preset or flags are provided, you will be prompted to choose one.

NV preset

Prepares fonts for the ebook-fonts repository. Applies the NV prefix and 20% line spacing. Does not modify kerning or hinting.

./kobofix.py --preset nv *.ttf

You can override individual settings, for example to use relaxed spacing:

./kobofix.py --preset nv --line-percent 50 *.ttf

KF preset

Prepares KF fonts from NV fonts for use on Kobo devices. Applies the KF prefix, replaces the NV prefix, and adds a legacy kern table. No line spacing changes are made (since NV fonts already have those applied).

./kobofix.py --preset kf *.ttf

Custom processing

You can also specify all flags manually:

./kobofix.py --prefix KF --name="Fonty" --line-percent 20 --kern add-legacy-kern *.ttf