In general, an image forming apparatus for transferring an image formed on an image carrier onto a recording sheet can attain higher-accuracy control by density control based on the patch density detected on a recording sheet after fixing than the patch density formed on the image carrier. In this case,...http://www.google.ca/patents/US6243542?utm_source=gb-gplus-sharePatent US6243542 - System for controlling the density of toner images in an image forming apparatus
