I've used the free omniformat software from the pdf995 folks (www.software995.com
) to extract image files from PDF's. I think when you convert pdf to image file you can only save in 300 dpi, if I remember correctly.
You place a copy of a PDF file in a specified "watch" folder, then the program converts all the pages to image files, so you'd have to delete the ones you don't need. I say "a copy" because Omniformat automatically deletes the file in the conversion process, so keep a copy of the file separate.
Hope this helps.