[CavemanJoe]

Originally Posted by DNSB

Have you looked at the Kindle Comic Converter? It will convert images to epub and has quite a few options. See Kindle Comic Converter - Convert comics/manga to MOBI/EPUB

Thanks for the rec but I'm already very happy with how Calibre processes comics, I just want to use that same auto-resize-greyscale-etc functionality on images inside regular .epub files for things like massive chapter heading images, maps, ads for the publisher's other books, author mugshots, that kind of thing.