Well it is very nonobvious, because IIRC the module only passes the same raw arguments you would use on the commandline on to ImageMagick. If you want to learn it, try to play around with ImageMagick on the commandline, using the regular docs. Those aren't excellent either, but better.
in reply to Image::Magick "geometry" argument?
I've given up on using Image::Magick a long time ago, because it was so buggy and really didn't offer anything extra - I just wound up using system calls instead. Maybe it has become better or at least more stable now, I don't know.
You have moved into a dark place.
It is pitch black. You are likely to be eaten by a grue.