Infrared cleaning

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Infrared cleaning is a technique used by some film scanners to reduce or remove the effect of dust and scratches upon the finished scan. It works by collecting an infrared channel from the scan at the same time as the visible colour channels (red, green, and blue). This is accomplished by using a light source that also produces infrared radiation, and having a fourth row of sensors on the linear CCD sensor. Most modern color photographic film emulsions are effectively transparent to infrared radiation (no matter what the visible image contains) but dust and scratches aren't, so they show up in the IR channel. This information can then be used to automatically remove the appearance of dust and scratches in the visible channels and replace them with information interpolated from the surrounding area in the film.

Not all types of film can be used with infrared cleaning. Traditional black and white film, as well as (in many cases) Kodak Kodachrome color slide film, may scatter or appear opaque to infrared radiation. This is due in large part to the presence of image-forming residual metallic silver in the emulsions after processing. When properly processed, most modern color negative and positive process films (C-41, E-6, and similar) will contain essentially no residual silver. Because chromogenic black and white films (which use the C-41 process) contain an image formed of dye clouds instead of metallic silver after processing, they are typically compatible with infrared cleaning.

Scanner manufacturers usually have their own name attached to this technique. Kodak developed Digital ICE at their Austin development centre, and is licensed by Epson, Nikon, Microtek and others. Canon developed its own FARE (Film Automatic Retouching and Enhancement) system.