Photosensor circuit for photographic printer

Details Photosensor circuit for photographic printer Photosensor circuit for photographic printer

1979-09-06

1981-06-02

Hix, L. T.

Photocopying

Projection printing and copying cameras

Multicolor picture

355 68, G03B 2773, G03B 2780

Patent

active

042708613

ABSTRACT:
A photographic printer includes large area transmission density (LATD) sensors and a digital processor, such as a microprocessor, which calculates red, green and blue exposure times based upon the LATD sensor readings. The LATD sensors provide analog photosignals which are a function of light received. Voltage controlled oscillators for each color channel provide red, green pulse signals which have durations which are a function of the red, green and blue analog photosignals, respectively. Red, green and blue gate circuitry receives red, green and blue enable signals from the microprocessor together with the red, green and blue pulse signals from the voltage controlled oscillators. The outputs of the gate circuitry are red, green and blue gate signals which are supplied to red, green and blue counters, respectively, and permit the counters to count in response to a high frequency clock signal. The resulting count in each counter, therefore, is a function of the duration of the gate signal which it received. Each time one of the gate signals is completed, an interrupt circuit provides signals to the microprocessor indicating that a count is complete for one of the color channels and the microprocessor retrieves the count from the appropriate counter.

REFERENCES:
patent: 3795444 (1974-03-01), Gliddenet al.
patent: 3992098 (1976-11-01), Wirtz
patent: 4125326 (1978-11-01), Baert
patent: 4140391 (1979-02-01), Laciak et al.

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