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CRT Beam Servo Not Requiring a Constant Level of Grey

IP.com Disclosure Number: IPCOM000094735D
Original Publication Date: 1965-May-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Hilton, HT: AUTHOR

Abstract

In several photodigital stores, double frequency recording is employed. A 1 is represented by a transparent area followed by an opaque area. A 0 is represented by an opaque area followed by a transparent area. If the data is scanned by a photocell, a grey level output results since there is an equal number of opaque and transparent areas. Data is normally stored on opposite sides of an opaque line. The two rows of data separated by an opaque line are in turn separated by a transparent area from adjacent data-opaque line combinations. While scanning, the spot from the CRT is captured. The output of the scanning photocell is compared with the grey level to control the tracking of the spot.

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CRT Beam Servo Not Requiring a Constant Level of Grey

In several photodigital stores, double frequency recording is employed. A 1 is represented by a transparent area followed by an opaque area. A 0 is represented by an opaque area followed by a transparent area. If the data is scanned by a photocell, a grey level output results since there is an equal number of opaque and transparent areas. Data is normally stored on opposite sides of an opaque line. The two rows of data separated by an opaque line are in turn separated by a transparent area from adjacent data-opaque line combinations. While scanning, the spot from the CRT is captured. The output of the scanning photocell is compared with the grey level to control the tracking of the spot. If the scanning spot moves in toward the opaque area, less light is seen as compared to the idealized grey level and the deflection of the spot is changed to compensate for this drift.

Single frequency recording, however, is desirable since the space required to store one bit is effectively cut in half. A 1 can be represented by an opaque area while a 0 can be represented by a transparent area. With single frequency recording, no reference grey level exists for servo control since a line of data may be composed entirely of 1's or 0's or various combinations of them.

This system provides servo tracking control and uses single frequency recording. Data is recorded between transparent and opaque stripes on a film which is swept by a CRT. Two photomultiplier tubes are utilized. The first photomultiplier is a...