Few digital libraries offer high quality scans that allow paper structure and ink layer thickness analysis.   But, is it worth to use them create a few GB PDF/DjVu if books are mainly intended for reading and not for scintific reserch on printing technology?   We should not reject any usable resolution.   Ankry   W dniu 2017-05-22 21:03:37 użytkownik Yann Forget yannfo@gmail.com napisał: As others say, 2 Mpixels should be the minimum resolution, although it is a bit small to do any work (i.e. restoration). That's the minimum requirement for quality and featured images on Commons.   For doing restoration, it is quite comfortable around 12 Mpixels (4000 x 3000). That's what most cameras offer today.