Image scanner#Drum

A drum scanner is a building type of a scanner that was used between 1958 and about 2000 in prepress. A color scanner scans color documents from optical- electronic and converts color values ​​into electricity. With the help of correction systems, these values ​​can be deliberately changed, converted into light and recorded on photographic material. One of the most famous drum scanner was the Chromagraph DC 300, which was developed by Rudolf Hell in Kiel and in 1971 came on the market.

Technology

The electronic components for image acquisition are photomultiplier, it is light sensors that generate an electric current when incident light. They are color blind, that is, it is only the intensity of the color, but does not capture the color itself. With a photomultiplier, the signal is amplified. Therefore, the drum scanner has a larger density range than the flatbed scanner and can be especially in dark and very bright areas still reflect color and brightness gradations. Depending on the design, the drum can be horizontal, vertical or inclined.

The templates can be reflective originals or slides that are mounted on a uniformly rotating acrylic glass tube, the scanning roller with tape. For slides is done by means of a liquid, such as anti-Newton - oil or gel. The templates are point-like working or rayed and rotate under a moving parallel to the rotation axis scanning optics. This directs the light through color filters to the photomultipliers on. The analog signals are then digitized electronically. Frequently, this is a plug-in card for the computer, which also provides the SCSI connection.

On a second roller connected with the scanning roller, a photosensitive film is fixed, which receives the write signal. The write signal of the color computer is routed via the scale calculator for halftone recording head. A special device allows the rasterization of the color separations. The grid points are written with the help of a contact screen or by modulated laser beams at the film to be exposed. The exposed film is then developed and dried in a developing machine.

Current situation

Drum scanners are now barely made ​​because flatbed and film scanners are becoming cheaper and more powerful at the same time. One of the last great drum scanner manufacturer was the German company Linotype -Hell, which was acquired in 1996 by Heidelberger Druckmaschinen AG. A particularly interesting model and the last series was the Linotype -Hell Tango / Heidelberg Primescan, in which the scanning roller, was contrary to the usual horizontal arrangement of the scanner drum, used vertically. These devices are supported now under actual operating systems only by SilverFast. Existing devices are still used for the simultaneous reading of several bills and in the professional high -end range, that is, when very high resolution or density detection is required because of the drum scanner for high quality scans with great detail rendition still is unsurpassed.

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