@ neptunehs use the parameter to do extraction, otherwise you are up-scaling them:
pdfimages -j [PDF file] [Output Path]
(-j for forcing it stripped original .jpg out of .PPM container, but you need to be sure it's .jpg, not .png, otherwise leave it)
that's for picture part.
For novel part, I don't suggest xpdf, using any pdf reader with snapshot function which will render much better than the simple commandline. Convert snapshoted files to 4bit indexed .png.
After that, use those extracted pictures to replace what is rendered and snapshoted.
@Lord of Evil Sorry but I'm poor in English...I can't fully understand what the forum said You mean 150dpi is enough for pictures?Xpdf default dpi is 150 and 300 for text? or if I don't add -r trigger,it will change dpi itself? I can't find a free somepdf copy,so I can only use xpdf
=============================================== I try to snapshoted in acrobat,but the result of novels are too bad.Why?