Method and apparatus for correcting an image signal

Details Method and apparatus for correcting an image signal Method and apparatus for correcting an image signal

1990-02-20

1992-07-14

Coles, Sr., Edward L.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358463, H04N 140

Patent

active

051308223

ABSTRACT:
A digital signal is provided by correcting image signal distortions contained in an image signal outputted from an elongated direct contact type image sensor in an image reader such as a facsimile device, which image sensor reads patterns on a document in contact with the document. The image signal distortions of the sensor output are so-called shading distortions due to sensitivity distribution of sensor elements or distribution of light from light sources onto the document. Signal distortions are corrected from both a white signal outputted from the sensor when a white document is read and a black signal outputted when a black document is read. The white signal and the black signal are stored and reproduced to generate a reference signal which is obtained by dividing the voltage range across both the signals at a predetermined ratio. The digital signal is obtained by comparing the sensor output with the reference signal. If necessary, a pseudo-black signal may be produced by dividing the voltage of the white signal.

REFERENCES:
patent: 3723649 (1973-03-01), Pitegoff et al.
patent: 4525741 (1985-06-01), Chahal et al.
patent: 4578711 (1986-03-01), White et al.
patent: 4961117 (1990-10-01), Rumley

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