With this Action, you get rid of the white in your drawings. It extracts your black outlines and leaves them surrounded by pure transparent nothingness!!
CAUTION: This Action works only with FLATTENED images. RGB and Grayscale will do.
Recomendation: before playing the action on your lineart, clean it up with curves or levels, and erase any unwanted spots.
The downloadable file contains now a "README" file!! OMG! that means I'm actually providing you with instructions on how to instal and run this action on Photoshop! Yai!!
BTW I used it here: [link]