Try pdfimages if you're on a unix system. It can extract images in their native format, speaking of.. As far as I'm aware the images are jpgs, i.e. already compressed, you gain nothing by converting them to png.
Two things: First, if the images are already in JPG format, why compress them any further by extracting them as JPGs? Second, If you are in the process of converting the PDFs to CBRs, I would be one of at least a few people who would definitely be interested in a upload. I guess I forgot to mention the program I found for extracting images from PDF files is offline, meaning I don't have to deal with uploading the PDFs to a server somewhere for random Joe Schmoes to see while converting.
That's the nice thing with pdfimages. It can extracted the images as-is, it doesn't convert the images any further, what you get is the files that were put in the pdf to begin with.
The images themselves should be the same. I did strip all metadata from them though. That and there could be some bytes saved by the rar compression I suppose. Worst case, some images were dropped. The entire conversion was automated in the end and I haven't gone through every single page so I can't be sure.
for that there's pornhub, xhamster, xvideos, etc and svscomics has plenty of porncomics.
