Electronic detection and concealment of film dirt

Film as an image source for television has four obvious impairments; film grain, dirt, unsteadiness and motion aliasing. The first three of these impairments can, at least in theory, be minimized electronically. A new method is described that can detect and conceal the image of dirt particles and printed dirt on both monochrome and color film. The methods of detection and concealment are described together with details of a preferred realization of the equipment. A description of the unsuccessful techniques examined during the course of this investigation is also included, for completeness. The prototype equipment has a single adjustable parameter which governs the maximum detectable size of dirt for a given visibility of motion impairment. The small dirt only mode may be safely used without previewing, when it will conceal the majority of dirt in typical 16 mm film with negligible motion impairment. The remaining large dirt can be concealed by adjusting the motion protection compromise manually, but source material should then be previewed, to check for motion of the type likely to cause noticeable motion impairment.