JPS60157376A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To obtain proper binary signals without making adjustment according to irregularity in the amount of light and the kind of originals by preparing a reference signal that performs envelope detection of video signals photoelectrically converted by line scanning and makes the video signals binary. CONSTITUTION:Video signals obtained by a line sensor 1 obtain envelope signal waveform A by a low-pass filter 20, and this signal waveform A is given to an envelope detector circuit 30. The envelope detector circuit 30 consists of an operational amplifier 11, a diode 12, a resistor 13 and a capacitor 14, and an envelope-detected reference signal B shown by a broken line is obtained by this circuit. The reference signal 13 and video signal A are inputted to a comparator 15 of a binary-coding circuit 40 and compared, and thereby, variation at the signal level of the video signal A corresponding to white ground and black characters is converted accurately to binary-coded signals.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a video signal processing circuit that binarizes video signals such as characters and codes photoelectrically converted by line scanning in a facsimile machine, a copying machine, or the like.

(Background of the Invention) Conventionally, in this type of device, a video signal charged and converted by a line sensor, etc. is input to a comparator, and the video signal is converted into a binary signal with a logic level of 1-1,1 by comparison with a predetermined reference level. It performs processing to convert it into a signal.

However, such conventional devices perform binarization using a fixed reference level setting, so the video signal converted due to conditions such as uneven light intensity of the light source or the use of colored paper, etc. If the signal level fluctuates, malfunction may occur,
There was a problem that the quality of the reproduced image deteriorated.

(Purpose of the Invention) The present invention has been made in view of the above-mentioned problems in the prior art.Even if the signal level fluctuates due to uneven light intensity, the type of document, etc., the present invention does not require adjustment each time, and can be used appropriately. An object of the present invention is to provide a video signal processing circuit that can obtain a binary value code.

(Summary of the Invention) In order to achieve this object, the present invention performs envelope detection on a video signal photoelectrically converted by line scanning to generate a reference signal for binarizing the video signal.

(Example) FIG. 1 is a circuit diagram showing an embodiment of the present invention.

First, to explain the configuration, reference numeral 1 is a line sensor in which photoelectric conversion elements such as CCDs are arranged in a line. The mechanical movement of the machine scans lines of characters, figures, etc. drawn on a recording medium such as manuscript paper and converts them into video signals. The output of the line sensor 1 is input to an active low-pass filter 20 including an operational amplifier 6.

This active low-pass filter 20 includes resistors 2.3.
7.8, a capacitor 4.5 and an operational amplifier 6.

The output of the active low-pass filter 20 is given to the envelope detection circuit 30, the level of the filter output is lowered by the variable resistor 9, and a DC component is added by the DC voltage 110 to undergo a voltage shift. given to the input terminal.

The output of the operational amplifier 11 is connected to the diode 12. The output of this envelope detector is applied as a reference signal B to the positive input terminal of a comparator 15 in the binarization circuit 40, and the negative input terminal of the comparator 15 is applied to an envelope detector consisting of a resistor 13 and a capacitor 14. is directly given the video signal A that is the output of the active low-pass filter 20,
The comparison operation of the comparator 15 converts and outputs the binary signal C.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

FIG. 2 shows the video signal A in the embodiment of FIG.

2 is a signal waveform diagram when a reference signal B and a binary signal C are photoelectrically converted by line scanning of black characters drawn on a white manuscript paper. FIG.

That is, when the line sensor 1 scans a line of black characters drawn on a white paper, a signal waveform is obtained through the active low-pass filter 20 in which the signal level is high in the white part and the signal level is low in the black part. , and an envelope signal waveform having a predetermined time constant at the rise and fall of line scanning is obtained.

At the same time as this signal waveform A, the signal level of the video signal A is lowered by the variable resistor 9 of the envelope detection circuit 30, and the voltage-shifted signal is output from the A amplifier 11 by adding the DC voltage of the DC power supply 10. Diode 12. The reference signal B is applied to an envelope detector 30 consisting of a resistor 13 and a capacitor 14, and an envelope-detected reference signal B shown by a broken line in FIG. 2 is obtained. This video signal A and the reference signal B subjected to envelope detection are input to the comparator 15 of the binarization circuit 40 and compared, and the portion of the video signal that exceeds the base standard signal B obtained by line scanning of the white area is converted into a video signal. The output of the comparator 15 becomes L level, and the part of the video signal A that scans the black text part becomes the comparator 1.
Since the reference signal @B also changes following the level change of the video signal A, the change in the signal level of the video signal A according to the white background and black text can be accurately detected at H and L.
can be converted into a binary signal with a logic level of

Furthermore, due to the voltage shift by the DC power supply 10, the level of the reference signal B when the video signal A is not satisfied is always the same as the video signal @A.
Since it is shifted to a larger value, it is possible to reliably prevent malfunctions that would produce erroneous binarized signals before and after line scanning.

Figure 3 is a signal waveform diagram showing the signal waveforms of various parts obtained by line scanning of paper with white characters drawn on a black background.In this case, the video signal A has a low signal level in the black part, and the white A waveform change occurs in which the signal level becomes higher in the character part, and the envelope detection circuit 30 causes! ! In order for the quasi-signal B to follow changes in the video signal A and maintain a value lower than the video signal A by a predetermined level, the comparator 15 of the binarization circuit 40 sets the H level in the black part and the 1-level in the white part. It is possible to accurately convert and output a binary signal. In addition, by voltage shifting by the DC power supply 10, the reference signal B is always kept at a higher level than the video signal A before and after line scanning,
This reliably prevents the output of erroneous binary signals before and after line scanning.

(Effects of the Invention) As described above, according to the present invention, since a reference signal for binarizing the video signal is generated by envelope detection of a video signal photoelectrically converted by line scanning, illumination unevenness caused by a light source is Even if the signal level of the video signal obtained by line scanning changes due to the color of the original, etc., it is possible to create a reference signal for conversion to a binary signal that follows the fluctuations in the signal level, and the reference signal An extremely accurate binarized signal can be obtained compared to the case where the level of is fixedly determined.

In addition, in envelope detection to obtain a reference signal, by adding DC components and performing a voltage shift, in addition to regular paper, that is, manuscript paper with black characters on a white background, Issada characters on a black background or a colored background. It is possible to realize a stable conversion operation of a binary signal even on a manuscript paper with a drawing on it.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a signal waveform diagram showing signals at various parts when a sheet of paper with black characters drawn on a white background is line-scanned according to the embodiment of FIG. 1. FIG. 3 is a signal waveform diagram showing signals from the isolation section when a sheet of paper with white characters drawn on a black background is line-scanned in the embodiment shown in FIG. 1 Ni-line sensor 2.3, 7.8.13: Resistor 4.5.14': Capacitor 6.11: Operational amplifier 9: Variable resistor 12: Diode 15: Comparator 20 Near-act low-pass filter 30: Envelope detection Circuit patent applicant Nippon Kogaku Kogyo Co., Ltd. Agent Patent attorney Susumu Takeuchi

Claims (2)

[Claims] (1) In a video signal processing circuit that binarizes a video signal obtained by photoelectrically converting characters, codes, etc. on a recording medium by line scanning, the video signal is envelope-detected, and the detected signal is converted from the video signal. Video signal processing characterized by comprising: an envelope detector that outputs the output at a predetermined level lowering; and a binarization circuit that binarizes the output of the envelope detector as a reference signal by comparing it with the video signal. circuit. (2) The video signal processing circuit according to claim 1, wherein the reference signal of the binarization circuit is voltage-shifted by applying a DC voltage.