Flying-spot scanner

A flying-spot scanner (FSS) uses a scanning source of a spot of light, such as a high-resolution, high-light-output, low-persistence Cathode Ray Tube (CRT), to scan an image, usually from motion picture film or a slide. The output of the scanner is usually a television signal.

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Basic principle

In the case of the CRT-based scanner, as the electron beam is drawn across the face of the CRT, it creates a scan that has the correct number of lines and aspect ratio for the format of the signal. The image of this scan is focused with a lens onto the film frame. Its light passes through the image being scanned and is converted to a proportional electrical signal by Photomultiplier tube(s), one for each color (Red, Green, Blue) that detect the variations in intensity of the beam spot as it scans across the film, and are converted to proportional electrical signals, on for each of the color channels.

Telecines that use a monochrome CRT as the light source can be referred to as flying-spot scanners. The advantage of the FSS technique is that as colour analysis is done after scanning, simple dichroics may be used to split the light to each photomultiplier — and there are be no registration errors, as would have been introduced by early electronic cameras.

Early use

Historically, flying-spot scanners were also used as primitive live-action studio cameras at the dawn of electronic television, in the 1920s.^[1][2] A projector equipped with a spinning perforated disc created the spot that scanned the stage. Scanning a subject this way required a completely dark stage, and was impractical for production use, but gave early researchers a way to generate live images before practical imaging pickup tubes were perfected.

See also

• Frank Gray (researcher), inventor of (mechanical) flying-spot scanner

References

External links

• Science Newsletter, April 16, 1927 (reproduced at Science News Online) "How New Television Process Works" with Gray's flying-spot scanner innovation