Infrared cleaning is a technique used by some film scanners and flatbed scanners to reduce or remove the effect of dust and scratches upon the finished scan. It works by collecting an additional infrared channel from the scan at the same position and resolution as the three visible colour channels (red, green, and blue). This infrared channel can be used to automatically remove the appearance of dust and scratches in the visible channels and replace them by inpainting.
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Scanners use three different techniques for doing this:
The three color dyes in modern color film emulsions respond equally to infrared light, so the infrared image looks relatively opaque compared to the RGB image. Any dust spots or scratches appear as dark spots in infrared, making it easy to find and correct for these dust spots.
Kodachrome film dyes are more sensitive to infrared than Ektachrome film dyes, making it more difficult to find dust spots in Kodachrome. Some software algorithms, such as the latest ICE implementation (Nikon Coolscan LS 9000 with ICE professional[1]), VueScan's[2] and SilverFast's[3], claim to use infrared cleaning to find dust spots even when scanning Kodachrome.
Infrared cleaning doesn't work at all with silver halide black-and-white film, but does work with chromogenic black-and-white films This is because silver particles respond equally in visible light and infrared light.
IBM originally developed and patented infrared cleaning, and subsequently licensed this patent to Applied Science Fiction (ASF). Canon has a patent cross-licensing agreement with IBM and was able to use the IBM's infrared cleaning patent. Canon couldn't use the trademarked Digital ICE name, so instead calls it Film Automatic Retouching and Enhancement (FARE). Other companies, like Hamrick Software and LaserSoft Imaging, independently developed infrared cleaning algorithms which are completely different from IBM's patented algorithm.
ASF subsequently went out of business, having spent all their money trying to develop dry film development in a kiosk when film sales significantly dropped. Kodak purchased the assets of ASF, but hasn't done anything with any of ASF's technologies.