Pulse-forming circuit for on/off conversion of an image analysis

Details Pulse-forming circuit for on/off conversion of an image analysis Pulse-forming circuit for on/off conversion of an image analysis

1979-08-30

1981-06-09

Britton, Howard W.

Facsimile and static presentation processing

Facsimile

Recording apparatus

H04N 140

Patent

active

042727898

ABSTRACT:
When a document is scanned, for example in a facsimile transmitter, an image analysis signal is formed. This signal has a level which varies between a maximum black level and a maximum white level and it is converted into an on/off (e.g. black and white) signal by comparison with a threshold. For good results on backgrounds of various tones it is necessary for the threshold to vary. The present pulse-forming circuit has a first detector 2 arranged over each scan line to detect and store a background level signal .DELTA.. It has a second detector 3 arranged over a few successive image points to detect an average value signal V'. These signals are combined by threshold determining circuit 4 to generate a threshold V.sub.d such that V.sub.d =K.DELTA.+K'.DELTA. where K and K' are two constants satisfying the relationships:

REFERENCES:
patent: 3566281 (1971-02-01), Baumann
patent: 3723649 (1973-03-01), Pitegoff
patent: 3987413 (1976-10-01), Wilmer

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