Add an "input args" parameter when defining derivative actions. In the UI, this field is only exposed for image derivatives, where it allows passing "input options" to imagemagick convert (houdini).
$form['inputargs']['#description'] = $this->t('Additional input options for ImageMagick convert (e.g. -density 144).<br>Check the <atarget="_blank"href="https://manpages.ubuntu.com/manpages/trusty/man1/convert.im6.1.html">man page</a> to see which options are input options.');
$form['inputargs']['#description'] = $this->t('Additional input options for ImageMagick convert (e.g. -density 144).<br>Check the <atarget="_blank"href="https://manpages.ubuntu.com/manpages/trusty/man1/convert.im6.1.html">man page</a> to see which options are input options.');