Photocopying processes

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Processes that use light to generate copies directly from original paper documents. Light is employed to examine an original document and to detect the presence or absence of an image. In most cases, light reflected from the original subject directly exposes the medium used to produce an image on a copy. However, in an increasing number of cases, the light is converted into an electrical signal, which is later converted back to light to expose the copying medium.

Xerography, the most popular of the photocopying processes, relies on photoconductors and toner powders to create copies. The toner is fused to copy paper by heat or pressure. Microfilming employs silver halide films which must normally be developed and fixed by using wet chemicals. Electrofax, diazo, thermography, and nonmicrofilm forms of silver halide photocopying, although not used as widely as in the past, also have continuing applications. See also Photographic materials.

The emergence of dual-imaging systems that accept both optical and digital input is making it increasingly difficult to characterize a given piece of equipment as a photocopier (optical input) or electronic printer (digital input). A number of electronic printers equipped with scanner attachments can function as either, and some employ both photocopying and digital imaging processes in generating an individual copy. See also Printing.