Dr. Ing. Rudolf Hell Gmbh

Dr.-ing. Rudolf Hell Gmbh, Firma

Hermann Wischer

Rudiger Sommer

Ruediger Sommer

The invention relates to facsimile reproduction and particularly to a method for converting a video signal obtained by scanning an original dot by dot and line by line, into a bilevel black/white signal. In the black/white recording of colored originals in which both the background and the information can be white, black, grey or colored, grey/black transitions coming from 'white' and grey/white transitions coming from 'black' are frequently not evaluated correctly by the dynamic threshold so that information is lost in the copy. In order that these types of transitions are also detected, it is suggested to eliminate the DC component of the video signal and to compare the video signal modified in this way with a second dynamic threshold signal derived from it. The comparison signal is logically linked to the customary black/white signal in such a manner that the black/white signal is flipped to 'white' at a grey/black transition and to 'black' at a grey/white transition in each case for a specified time interval. In this manner, for example between a colored area in the original recorded as 'black' and a black letter in this area, a white boundary line is created which makes the front contour of the letter visible. Similarly, between a colored area in the original reproduced as 'white' and the white edge of the original copy a black boundary line is generated which makes the contours of the colored area in the original clearly recognizable.

Methods for converting a video signal into a black/white signal

This invention relates to a method of boosting a discontinuous-value video signal (in pulse or stepped form). From the video signal there is derived an upper accompanying signal extending above it and a lower accompanying signal extending below it, which follow the video signal dynamically. First differential values are formed between the upper accompanying signal and the video signal and second differential values are formed between the video signal and the lower accompanying signal. To boost the discontinuous-value video signal, multiples of the first differential values are subtracted continuously from the video signal and multiples of the second differential values are added to the video signal.

Boosting video signals

A facsimile scanning method for converting a video signal, generated by opto-electronic scanning of an original copy, into a bilevel black/white signal in facsimile reproduction. In the black/white recording of colored originals in which both the background and the information can be white, black, grey or colored, white/grey (colored)/black transitions in the original are frequently not picked up correctly so that information is lost in the copy. The invention solves this problem by recording colored, grey or black areas in the original as 'white' with black boundary lines, by means of suitable electronic circuits. If the colored area in the original is a background area without information content of its own but containing a black item of information (letter), the legibility of the black letter in the area is increased in the copy by reproducing the background area as 'white'. On the other hand, the background area remains recognizable in the copy with respect to the white of the paper by virtue of its surround. If the colored area in the original, however, is itself an item of information, e.g. a broad letter, the line-boundary according to the invention causes at least the contour of the letter to be recorded in the copy, making the letter legible. In general, black areas in the original can be reproduced in the copy as white areas with black surround. This has the advantage that overheating of thermal print of needle print recording devices is avoided due to the reduced black component in the copy.

Method for converting a video signal into a black/white signal

A facsimile scanning method for converting a video signal obtained by opto-electronic scanning of an original into a two-level signal suitable for transmission. A first companion signal is first generated which lies essentially above the video signal and which follows the video signal when it rises but when the video signal declines remains at the voltage reached when the video signal was at a maximum until a difference value between the first companion signal and a reference signal is reached, which then comes close to the declining video signal until the difference value is reached, which remains at the voltage value then reached until the first companion coincides with the video signal, and which then follows the rising video signal. At the same time a second companion signal is generated which lies substantially below the video signal and which progresses accordingly. From the first and second companion signals is derived a threshold signal which follows the video signal dynamically. The two-level signal is obtained by comparing the threshold signal with the video signal. The reference signal may be the video signal or one of the companion signals. The difference values are preset at constant levels or are proportional to the mean brightness of the background of the original.

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Kiel, Germany

Hermann Wischer