[Ghostscript](https://ghostscript.com) is required. When installing Ghostscript, make sure there is an executable called `gs` in your path. This should happen automatically with Linux, but Windows users will have to add the path to Ghostscript to the `PATH` environment variable manually, eg:
`C:\Program Files\gs\gs9.21\bin`
Then the Ghostscript executable `gswin64.exe` should be copied to a new executable called `gs.exe`.