Flying-Spot Scanner


flying-spot scanner

[¦flī·iŋ ‚spät ′skan·ər] (electronics) A scanner used for television film and slide transmission, electronic writing, and character recognition, in which a moving spot of light, controlled mechanically or electrically, scans the image field, and the light reflected from or transmitted by the image field is picked up by a phototube to generate electric signals. Also known as optical scanner.

Flying-Spot Scanner

 

a television device in which the image transmitted is scanned by a light spot traveling along the screen of a projection kinescope.

The flying-spot scanner is most widely used in color-television broadcasting to transmit motion picture films and transparencies. Its principle of operation is explained in Figure 1. A television raster with unmodulated luminance (constant intensity) is formed on the kinescope screen by line-scanning and frame-scanning generators. This raster is projected onto a film frame or transparency by an objective lens. During the scanning a light spot consecutively transilluminates the entire film frame or transparency line by line, affecting the brightness of the light flux according to the optical density (transparency) of the image. The modulated light flux is then picked up by a condensing lens and directed to a device that splits the light flux into its spectral components. After color separation for light fluxes pass through photomultipliers for linear conversion to videosignals of red, green, and blue. The amplitudes are determined by the luminance and chrominance of the area of the image being transmitted at the moment. In motion-picture transmission the movement of the film is coordinated with the interlaced scanning of the image by a device in the motion picture projector.

Figure 1. Diagram of flying-spot scanner: (1) pulse amplifier for blanking retrace of kinescope electron beam; (2) focusing system; (3) deflecting system; (4) line-scanning and frame-scanning generators; (5) projection kinescope; (6) high-voltage source; (7) objective lens; (8) film transport device; (9) frame window; (10) condensing lens; (11) and (12) semitransparent dichroic mirrors; (13), (14), and (15) light filters; (16), (17), and (18) photomultipliers; (ER video signals corresponding to red, (EG ) green, and (EB blue

The flying-spot scanner is also used as an episcope for transmitting opaque images (cards, photographs, maps) and, occasionally, action scenes from a television studio; in these cases the light flux from the kinescope is projected onto an opaque image. The studio must be darkened when using the scanner. The object is illuminated by light pulses during the vertical retrace.

REFERENCE

Teoriia i praktika tsvetnogo televideniia. Edited by P. V. Shmakov. Mos-cow, 1962.

N. G. DERIUGIN