Infrared cleaning is a technique used by some film scanner

Film scanner

A film scanner is a device made for scanning photographic film directly into a computer without the use of any intermediate printmaking. It provides several benefits over using a flatbed scanner to scan in a print of any size: the photographer has direct control over cropping and aspect ratio from...

s and flatbed scanners to reduce or remove the effect of dust and scratches upon the finished scan. It works by collecting an additional infrared

Infrared

Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 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

Inpainting

Inpainting is the process of reconstructing lost or deteriorated parts of images and videos. For instance, in the case of a valuable painting, this task would be carried out by a skilled image restoration artist...

.

Approaches

Scanners use three different techniques for doing this:

• Nikon film scanners use four colored light-emitting diodes which are pulsed on and off, one at a time. These LEDs are pulsed on and off at each scan position, the light is gathered by a linear array and then the CCD is moved to the next scan line.

• Minolta film scanners use a constant visible light source with a pulsed infrared light source. At each scan position, the scanner uses an RGB linear array to scan the film in RGB and RGB+Infrared. This is as fast as the Nikon approach, since only one physical pass over the film needs to be done.

• Flatbed scanners and some film scanners have two different light sources, an RGB light source and an infrared light source. These scanners make two passes over the film - once for RGB and once for infrared. This is slower than the Nikon or Minolta approach, since two passes need to be made over the film. It also produces lower quality since software methods need to be used to align the two passes. In addition, the two light sources usually have a different focus position and produce images that are stretched in the CCD direction, which results in another source of lower quality.

Applicability

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

Nikon

, also known as just Nikon, is a multinational corporation headquartered in Tokyo, Japan, specializing in optics and imaging. Its products include cameras, binoculars, microscopes, measurement instruments, and the steppers used in the photolithography steps of semiconductor fabrication, of which...

 Coolscan LS 9000 with ICE professional), VueScan's and SilverFast

SilverFast

SilverFast is software for scanning and image processing, including photos, documents and slides, developed by LaserSoft Imaging.- History :...

's, claim to use infrared cleaning to find dust spots even when scanning Kodachrome.

Infrared cleaning doesn't work at all with silver halide

Silver halide

A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide , chloride , iodide , and three forms of silver fluorides. As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX...

 black-and-white film, but does work with chromogenic

Chromogenic

Chromogenic refers to color photographic processes in which a traditional silver image is first formed, and then later replaced with a colored dye image.- Description :...

 black-and-white films This is because silver particles respond equally in visible light and infrared light.

History

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

Digital ICE

Digital Image Correction and Enhancement is a set of technologies related to producing an altered image in a variety of frequency spectra. The objective of these technologies is to render an image more usable by Fourier or other filtering techniques...

 name, so instead calls it Film Automatic Retouching and Enhancement (FARE). Other companies, like Hamrick Software and LaserSoft Imaging

LaserSoft Imaging

LaserSoft Imaging AG is a software developer designing software such as SilverFast for scanners and digital cameras. The company's headquarters are located in Kiel, Germany, north of Hamburg, and another office in Sarasota, Florida, United States....

, 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.