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Browse Prior Art Database

Calibration of Photographic Scanning System

IP.com Disclosure Number: IPCOM000096202D
Original Publication Date: 1963-Jan-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Trampel, KM: AUTHOR [+2]

Abstract

In converting analog information on a photographic transparency to a digital output, the light transmission of each point on the transparency is compared with a variable reference. Photomultiplier tubes PMT are employed to transduce the analog information to electrical signals. Since drift between photomultiplier tubes occurs with time, provision is made in the scanning system for periodic drift compensation.

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Calibration of Photographic Scanning System

In converting analog information on a photographic transparency to a digital output, the light transmission of each point on the transparency is compared with a variable reference. Photomultiplier tubes PMT are employed to transduce the analog information to electrical signals. Since drift between photomultiplier tubes occurs with time, provision is made in the scanning system for periodic drift compensation.

The scanning system-employs a cathode ray tube as a flying spot scanner for a reference channel and an information channel. The reference channel includes PMT1, amplifier 1 and a decoder. The decoder gain is controlled by six binary lines to provide an output gain of 1/32 to 2 in 64 steps. The decoder output is supplied as one input to a differential amplifier.

The information channel includes the transparency containing the analog information, PMT2 and amplifier 2. The output of amplifier 2 is supplied as the other input to the differential amplifier. The differential amplifier detects the information signals greater than the decoder signals and applies this data to the computer.

For periodic drift compensation, a feedback circuit including an integrator and chopper circuit, servo amplifier, and servo motor and potentiometer, is connected through a switching circuit to the output of the differential amplifier and to PMT2 of the information channel. The switching circuit periodically responds to the output of the c...