Drum scanner
A drum scanner is a type of scanner that was used in prepress between 1958 and around 2000 . A color scanner scans colored documents optically and electronically and converts color values into electrical current. With the help of correction systems, these values can be changed in a targeted manner, converted into light and recorded on photographic material.
technology
The electronic components for image capture are photomultipliers , which are light sensors that generate an electrical current when light falls. They are color-blind, which means that only the intensity of the color is recorded, but not the color itself. With a photomultiplier, the signal is amplified. The drum scanner therefore has a greater density range than the flatbed scanner and can still reproduce color and brightness gradations, especially in dark and very light areas. Depending on the design, the drum can be arranged horizontally, vertically or inclined.
The originals can be reflective originals or slides, which are attached to an evenly rotating drum (made of acrylic glass or metal), the so-called scanning drum, with adhesive tape. With slides this is done using a non-volatile liquid such as oil or gel. The originals are spotlighted or transilluminated and rotate under scanning optics that move parallel to the axis of rotation. This forwards the light via color filters to the photomultipliers. The analog signals are then digitized electronically. Often it is a plug-in card for the computer that also provides the SCSI connection.
A photosensitive film which receives the write signal is attached to a second roller connected to the scanning roller. The writing signal of the color computer is directed to the halftone or raster recording head via the scale computer. A special device enables the color separations to be rasterized. The raster points are written on the film to be exposed with the aid of a contact raster or modulated laser beams . The exposed film is then developed in a developing machine and dried.
Todays situation
Drum scanners are now rarely manufactured, as flatbed and film scanners are becoming cheaper and more powerful at the same time. One of the last major drum scanner manufacturers was the German company Linotype- Hell , which was taken over 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, in contrast to the usual horizontal arrangement of the scanner drum, was used vertically. Nowadays, these devices are only supported by SilverFast under current operating systems . Existing devices are still used for the simultaneous reading of several templates and in the professional high-end area, i. H. when very high resolution or density detection is required, as the drum scanner is still unsurpassed for high quality scans with great detail reproduction.