Not all images are printed on smooth paper; some are printed on textured paper, or on cloth in the case of dakimakura, for artistic effect. The different shadows and textures appear as rough shadows when scanned. Unlike screening, which is in a somewhat regular pattern, paper texture is noise (random), and much harder to get rid of.

See this topic for more information on how to filter these types of scans:
http://moe.imouto.org/forum/show/2789

Updated by Aurelia over 15 years ago