12 Facsimile (Fax) systems

These systems, originally developed to transmit photographic and documentary information over standard telephone cables, are now used over radio and satellite links (Docfax) as well. The wide variety of services available range from the transmission of simple letters, to weather and geological mappings and the transmission of complete pages of a newspaper for remote printing (Pagefax).

The information in a document to be transmitted usually lies in dark markings on a light background. This can be analysed by segmenting the document into elemental areas small enough to resolve the finest detail needed. To achieve this, the document is scanned sequentially by a light beam, in a series of very narrow strips. The magnitude ...

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