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Photosensed Film Compensating Arrangement

IP.com Disclosure Number: IPCOM000092457D
Original Publication Date: 1966-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Weir, R: AUTHOR

Abstract

Film strips frequently are addressed by binary coding bits on an edge of each film frame. This binary coding is then projected upon the side of the screen where each bit is detected by the use of photoresistors 1...11. Each photoresistor is so placed that either a black square or a clear square is projected upon it depending upon whether a 1 or a 0 is desired. For example, a 1 bit is clear and a 0 bit is opaque.

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Photosensed Film Compensating Arrangement

Film strips frequently are addressed by binary coding bits on an edge of each film frame. This binary coding is then projected upon the side of the screen where each bit is detected by the use of photoresistors 1...11. Each photoresistor is so placed that either a black square or a clear square is projected upon it depending upon whether a 1 or a 0 is desired. For example, a 1 bit is clear and a 0 bit is opaque.

The detection of a 1 or a 0 is complicated by the fact that the film density often varies over a fairly wide range. This detection system operates as follows.

The on drive current and off drive current are established for a 1 and a 0 into an interface output circuit 13. These drive currents are established with a certain value of resistance for each photoresistor circuit and at a certain voltage Vb. Now as the film density is reduced the light intensity changes on each photocell causing the photodetector cell to be reduced in resistance and in turn increases the drive current into interface 13. Reference photocell 12 is connected to a feedback amplifier 14 to vary the voltage Vb inversely with the light intensity to reference cell 12. The latter is always at a 1 condition so that the drive currents remain constant at the 1 and 0 values already established.

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