Rollfilm or roll film is any type of spool-wound photographic film protected from white light exposure by a paper backing, as opposed to film which is protected from exposure and wound forward in a cartridge. Confusingly, roll film was originally often referred to as "cartridge" film because of its resemblance to a shotgun cartridge. The opaque backing paper allows roll film to be loaded in daylight. It is typically printed with frame number markings which can be viewed through a small red window at the rear of the camera. A spool of roll film is usually loaded on one side of the camera and pulled across to an identical take up spool on the other side of the shutter as exposures are made. When the roll is fully exposed, the take up spool is removed for processing and the empty spool on which the film was originally wound is moved to the other side, becoming the take up spool for the next roll of film.