@jackr - AFAIK the drawing library that calibre and this plug in uses doesn't support translucent fonts. I have no idea what an inverted font is. Surely making the font transparent is giong to make it even harder to make the text stand out rather than easier?
As for the other idea of sizing based on the background image - that sounds fair enough. Though I'm kind of "over" this plugin at the moment having just made so many changes to it for this release so it will have to sit on the todo list for a future release for now.
