Please read for an updated status on RailsCasts:
Learn more or hide this
GitHub User: jschroeder9000
I'm probably too late to help, but for anyone else wondering... ghostscript is your friend here. Quality can certainly be an issue like you mention in a later post. So what I do is create an intermediary image rasterized at 288 dpi (with -r 288) - I like to use png for this. Then convert that to a thumbnail or whatever in any format with imagemagick. I like to use png because if you say have something with white letters you can then use imagemagick to convert the transparency to black or something so the white letters will be visible - I've encountered this with some eps images.
Imagemagick delegates rasterizing to ghostscript, but I find it's better to just cut out the middle man and create a high dpi image that can be more easily manipulated with imagemagick directly. Postscript is a pain, but if you have to use it then ghostscript is the right tool for the job - at least the first part of it.
Obviously I share Ryan's love/hate relationship with imagemagick.
P.S. magick bindings suck - I always use a wrapper or system calls.
Just thought I'd mention that !! works in bash, but it doesn't auto-expand like that. I wasn't aware of it... hopefully I don't forget before I have occasion to use it.