Method for correcting nonuniformities in pixel output level for

Details Method for correcting nonuniformities in pixel output level for Method for correcting nonuniformities in pixel output level for

1989-05-11

1990-12-25

Coles, Sr., Edward L.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358461, 358475, H04N 140

Patent

active

049807781

ABSTRACT:
Scanning equipment for a low-cost facsimile machine which includes a variable gain amplifier and a comparator circuit for correcting nonuniformities in lighting, lenses, light sensors and the like. Each line of a document being scanned is subdivided into a number of picture elements that individually suffer from different degrees of nonuniformity. Stored correction signals, associated with each picture element, are used by the variable gain amplifier and the comparator in processing an analog output signal from the line scanner to thereby correct nonuniformities. In one illustrative embodiment of the invention, the stored correction signals regulate the magnitude of the line scanner's analog output signal which is then compared with a fixed black/white threshold voltage. In another illustrative embodiment of the invention, the stored correction signals are used to generate a number of black/white threshold voltages which are then compared with the line scanner's analog output signal. In all embodiments, correction signals are set during a calibration procedure that uses an illumination level which corresponds to the threshold between black and white.

REFERENCES:
patent: 4133008 (1979-01-01), Tisue
patent: 4408231 (1983-10-01), Bushaw et al.
patent: 4554583 (1985-11-01), Saitoh et al.
patent: 4633314 (1986-12-01), Kurato et al.
patent: 4760464 (1988-07-01), Sakano

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