JPS62277857A - Video signal binarization device - Google Patents

Abstract

PURPOSE:To obtain a binarization signal giving the reproducibility of a prescribed picture at all times even when an instable light source such as a fluorescent light is used by sampling and holding a white level obtained by reading a white level reference detecting means by means of a line image sensor. CONSTITUTION:White level reference detection means AS1, C1, OP1 provided in a picture frame in a direction orthogonal to the line direction of a line image sensor, white sampling circuits AS2, C2 and OP2 sampling and holding the white level voltage of an analog video signal VDO, means R3, C3, OP3 forming a threshold level and a comparator CP comparing the analog video signal VDO with a threshold level and outputting the binarization signal B of the analog video signal are provided. Then the white level voltage obtained by reading the white level reference detected means provided in the picture frame is subjected to sample holding. Thus, the binarization signal B giving always constant picture reproducibility is obtained regardless of the fluctuation of the luminous quantity of an original lighting source.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a video signal binarization device, and particularly to a video signal binarization device used in facsimiles, digital copying machines, etc. Regarding.

[Conventional technology]

As is well known, video signal binarization devices used in facsimile machines, digital copying machines, etc. generally use an unstable light source such as a fluorescent lamp whose light intensity fluctuates over time as a light source for illuminating documents. . For this reason, analog video signals read from a line image sensor consisting of a charge-coupled device (CCD) or MO3 type image sensor are converted into digital video signals.
When converting to a digital signal, comparing the analog video signal with a certain threshold level to determine whether it is white or black, even if the image is in the same document, it can be judged based on a certain standard. No determination of white or black was made, and a binarized signal that would provide a certain level of image reproducibility could not be obtained.

Therefore, conventionally, video signal 2 has been developed to eliminate such problems.
As a value conversion device, there is a device that uses an automatic gain control circuit to keep the white level voltage of an analog video signal read out from a line image sensor at a constant level (see Japanese Patent Application Laid-Open No. 56-37770, etc.), and a device that uses a pixel The threshold level is corrected by calculating the average value of the concentration of
(see Publication No. 68, etc.) have already been proposed.

[Problem that the invention seeks to solve]

However, even with the conventional video signal binarization device described above, the binarization signal that completely compensates for fluctuations in the amount of light on the document surface caused by unstable light sources such as fluorescent lights and always provides constant image reproducibility is generated. The problem was that it could not be obtained.

In view of the above-mentioned points, an object of the present invention is to sample and hold a white level voltage obtained by reading a white level reference detection means provided within an image frame, thereby changing the amount of light from a light source for illuminating an original. It is an object of the present invention to provide a video signal binarization gW capable of obtaining a binarized signal that always provides constant image reproducibility regardless of the image reproducibility.

Another object of the present invention is to sample and hold the black level voltage output by the line image sensor itself, thereby eliminating the influence of variations in the characteristics of the line image sensor itself and temperature fluctuations on the binary signal. It is an object of the present invention to provide a video signal binarization device.

[Means for solving problems]

The video signal binarization device of the present invention includes a white level 7f, f% detection means provided within an image frame read by a line image sensor along a direction orthogonal to the line direction of the line image sensor. , a white sampling circuit that samples and holds the white level voltage of the analog video signal output from the line image sensor by reading this white level JJ'<4 liquid detection means; and a white sampling circuit that samples and holds the white level voltage of the analog video signal output from the line image sensor; a threshold level forming means for forming a threshold level based on a level voltage value; and a comparator for comparing the analog video signal and the threshold level and outputting a binary signal of the analog video signal. Equipped with.

Further, the video signal binarization device of the present invention includes a white level reference detection means provided within the image frame read by the line image sensor along a direction perpendicular to the direction of the nXj line image sensor sign. , a white sampling circuit that samples and holds the white level voltage of the analog video signal output from the line image sensor by reading this white level reference detection means; and a white sampling circuit that samples and holds the white level voltage of the analog video signal output from the line image sensor. a black sampling circuit for holding; a threshold level forming means for forming a Threnjord level based on the white level voltage output from the white sampling circuit and the blank level voltage output from the black sampling circuit; , a comparator that compares the analog video signal with the threshold level and outputs a binary signal of the analog video signal.

[Effect]

In the video signal binarization device of the present invention, the line image sensor reads the white level reference detection means provided in the image frame in a direction perpendicular to the line direction, and the white sampling circuit converts the analog video signal into The white level voltage is sampled and held, the threshold level forming means forms a threshold level based on the white level voltage output from the white sampling circuit, and the comparator compares the analog video signal and the threshold level. A binary signal of the analog video signal is output.

Further, in the video signal binarization device of the present invention, the line image sensor reads the white level reference detection means provided within the image frame in a direction perpendicular to the line direction, and the white sampling circuit reads the analog The white level voltage of the signal is sampled and held, the blank sampling circuit samples and holds the blank level voltage output from the line image sensor, and the threshold level forming means is configured to sample and hold the white level voltage output from the white sampling circuit and the blank sampling circuit. A comparator compares the analog video signal with the threshold level and outputs a binary signal of the analog video signal.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of a video signal binarization device according to an embodiment of the present invention. This circuit uses, for example, a 4.2 MHz basic clock CLK (see Fig. 4 (al)) divided by 8 and a four-clock CCDφ (see Fig. 4 (see bl)).
2100 dots per line with a period of 4 ms (Fig. 3)
It is connected to a line image sensor (not shown) consisting of a CCD that outputs an analog video signal (see a)).

The effective data range of this line image sensor is
There are 2048 dots out of 2100 dots (see Figure 3 (bl)).

The analog video signal (hereinafter simply referred to as video signal) VDO read from the line image sensor is input to the input terminal of analog switch 8S, and the output terminal of analog switch AS is grounded via capacitor C1. and is connected to the non-inverting input terminal of the operational amplifier OP. The inverting input terminal of the operational amplifier OP is connected to its own output terminal.

Capacitor C4 and operational amplifier OP are connected to video signal V
It forms an impedance conversion circuit for DO, but as the analog switch Δs1 turns on and off, the video signal VD
It also serves as a sample hold for ○.

As shown in the timing chart in Figure 4 tdl, the analog switch AS is designed such that high level and low level signals are applied to its control terminal at the timing of one dot for half a cycle, and it is turned off in the second half of the cycle. There is. As shown in the timing chart of FIG. 4(C), this
7) Since the video signal VDO contains noise, the capacitor C is
This is to sample and hold the one-dot video signal VDO in an integrating circuit consisting of an operational amplifier ○P and an operational amplifier ○P.

The output terminal of the operational amplifier ○P is an analog switch A S
It is connected to the input terminal of analog switch A.
The output terminal of Sz is grounded via capacitor C2, and also connected to operational amplifier OP.

is connected to the non-inverting input terminal of operational amplifier OP,
The inverting input terminal of is connected to its output terminal.

The output terminal of the operational amplifier OP is connected to one end of the concentration adjustment variable resistor VR via a resistor R1.

Analog Sui Sochi AS2, capacitor C2, and operational amplifier ○P2 are a white sampling circuit that samples and holds the white level voltage read from the white level reference white tape 3, which will be described later, of the video signal VDO output from the operational amplifier OP. Form.

Referring to FIG. 2, in the video signal binarization apparatus of this embodiment, a line image sensor within the effective data range (image frame) of the line image sensor is placed on the back side of the transparent document table 2 on which the document 1 is placed. A white level reference white tape 3 is pasted near the left end along the direction perpendicular to the line direction of the line image sensor when viewed from the scanning direction (from left to right in the figure). Note that the white level reference white tape 3 may be pasted on the right side within the effective data range (image frame) of the line image sensor as viewed from the scanning direction of the line image sensor.

As shown in the timing chart in Figure 3 (C1), the analog switch A S2 is turned on for a short time by applying a high-level pulse signal to its control terminal at a timing (4 ms) for each line. This is to sample and hold the white level voltage until one line of video signal VDO is processed.The timing to sample and hold the white level reference white tape 3 is determined by As seen from the scanning direction of the line image sensor within the effective data range (image frame) of the line image sensor, it is closer to the left end, so as can be seen from the timing chart in Figure 3 +c+, it is within the effective data range (image frame). Toward the end of the series (toward the right end in the diagram)
This is the timing at which the white level voltage is first output from the video signal VDO.

On the other hand, the circuit that generates the black level voltage is, for example, 2
It is formed of a Zener diode ZD that generates the Zener voltage (2), and this Zener diode ZD has a cathode applied with a power supply voltage VCC and an anode grounded. The cathode of the Zener diode ZD, which generates a Zener voltage serving as a black level voltage, is connected to the other end of the density adjustment variable resistor VR via a resistor R2.

The variable resistance terminal of the concentration adjustment variable resistance VR is connected to the inverting input terminal of the comparator CP via a resistor R3.

Further, the output terminal of the operational amplifier OP is connected to one end of the resistor R3, and the other end of the resistor R3 is grounded via the capacitor C3, and is also connected to the non-inverting input terminal of the operational amplifier OPj. The inverting input terminal of the operational amplifier OP is connected to its own output terminal.

Resistor R3, capacitor C3, and operational amplifier OP form an integrating circuit for taking a moving average of video signal VDO. This integration circuit is for moving the threshold level toward white or black in accordance with the integral value so that a small number of men or white can be clearly identified in an image portion biased towards white or black. The output terminal of the operational amplifier ○P3, which serves as the output terminal of this integrating circuit, is connected to the inverting input terminal of the comparator CP via a resistor R4.

The inverting input terminal of the comparator CP is connected to the moving average obtained by integrating the voltage value obtained by adjusting the density of the white level voltage and the black level voltage by the variable resistance VR for density adjustment via the resistors R1 and R2, and the video signal VDO. The voltage value and the resulting threshold level are further applied via resistors R2 and R4. In addition, variable resistor VR for concentration adjustment
By providing this, a user or the like can freely adjust the density of an image from the outside.

Further, the output terminal of the operational amplifier OP is connected to and branched to the non-inverting input terminal of the comparator CP, and the video signal VDO applied to the non-inverting input terminal of the comparator CP is applied to the inverting input terminal of the comparator CP. compared to a threshold level. If the video signal VD○ is lower than the threshold level, it is determined to be black, and if it is higher than the threshold level, it is determined to be white, and a rectified signal B is output from the comparator CP, which takes either a low level or a high level.

Next, regarding the operation of the video signal binarization apparatus of this embodiment configured as described above, the line scale timing charts shown in FIGS.
This will be explained with reference to the dot scale timing chart shown in (d).

The video signal VDO (see Fig. 4 fcl) transferred and outputted from the line image sensor in the 111st order is sent to the analog switch AS at the timing shown in Fig. 4 +d+.
When 1 is turned on, the capacitor CI is charged and held, and since the input impedance of the operational amplifier OP is high impedance, the analog switch A S
+ is sampled to capacitor C0 at the same time as it turns off. Since the operational amplifier OP is connected as a voltage follower, the one-dot video signal VD○ sampled and held in the capacitor C1 is impedance-converted and outputted to the output terminal, and is output to the input terminal of the analog switch ASz, one end of the resistor R3, and the comparator CP. The non-inverting input terminals of the two input terminals are respectively input manually.

When the analog switch A S z is turned on for a short time at the timing shown in FIG. 3 tel, the white sampling circuit samples and holds the white level voltage in the capacitor C 7 and outputs it to the output terminal of the operational amplifier OP x. The output of the operational amplifier OPt, that is, the white level voltage, is applied to the density adjustment variable resistor V through the resistor R3.
applied to one end of R.

On the other hand, by applying the electric affi voltage VCC, the blank level voltage generated at the cathode of the Zener diode ZD is applied to the concentration level through the resistor R2. It is applied to the other end of the J4 adjustment variable resistor VR.

The white level voltage and the black level voltage applied to one end and the other end of the density adjusting variable resistor VR are level-adjusted by the density adjusting variable resistor VR, and are input to the inverting input of the comparator 1/-cp via the resistor R3. Applied to the terminal.

If the variable resistor VR for density adjustment is brought closer to the operational amplifier ○P2 side, the voltage value applied to the inverting input terminal of the comparator CP, that is, the threshold level, will be increased to make the image darker as a whole, and the Zener When it is brought closer to the diode ZD side, the threshold level is lowered and the image becomes brighter as a whole.

In addition, the video signal VDO applied from the output terminal of the operational amplifier OP to one end of the resistor R3 is integrated by an integrating circuit consisting of the resistor R1, the capacitor C3, and the operational amplifier OP3, and a moving average is taken. Applied to the inverting input terminal of CP.

Tooth tJ! is connected to the inverting input terminal of the comparator CP from the variable resistor VR for concentration adjustment. A threshold level is formed by the voltage applied via i'R5 and the voltage applied from the operational amplifier OP:l via the resistor R4.

Furthermore, the video signal VDO applied from the output terminal of the operational amplifier OP to the non-inverting input terminal of the comparator CP is
The comparator CP compares it with the threshold level applied to the inverting input terminal.

If the video signal VDO is higher than the threshold level, the comparator CP outputs a high level signal, and if the video signal VDO is lower than the threshold level, the comparator CP outputs a low level signal. That is, the comparator CP determines a high level as white and a low level as black based on the threshold, and outputs a binary signal B obtained by digitizing the video signal VDO.

In the above embodiment, the white tape 3 for the white level standard was pasted on the back side of the transparent document table 2 as a means to be detected for the white level standard, but this could be replaced by applying white paint or the like. Alternatively, it may be provided on a reflecting mirror or the like in the optical path between the line image sensor and the document table.

FIG. 5 is a circuit diagram showing a video signal binarization device according to another embodiment of the present invention. The video signal binarization device of this embodiment uses a field element based on a combined pressure provided in a line image sensor in place of the black level voltage generating Zener diode ZD in the video signal binarization device shown in FIG. The voltage output from the germ-destroying part of the child is sampled and held, and this voltage is used as a blank level voltage.

That is, the video signal binarization device of this embodiment is provided with a black sampling circuit consisting of an analog switch ASp, a capacitor C4, and an operational amplifier oP4 instead of the Zener diode ZD, and the input terminal of the black sampling circuit and Analog switch AS,
The input terminal of the operational amplifier OP + is the output terminal of the operational amplifier OP + , and the input terminal of the operational amplifier OP + is the output terminal of the blank sampling circuit.
The output terminal of No. 4 is connected to the variable resistance V for concentration adjustment via the resistance R2.
Connected to the other end of R. Is the analog switch AS2 that system? Timing for each line (4mS) for I19 child
), a high-level pulse signal is applied to turn it on for a short time. This sets the blank level voltage to 1
This is to sample and hold the line video signal VDO until it is processed. Note that the sample and hold timing is first from the video signal VDo which is within the output data range of 2100 dots of the line image sensor shown in FIG. 3 (al) and outside the effective data range of 2048 dots shown in FIG. This is the timing at which the black level voltage is output.

The other parts are configured exactly the same as the video signal 2 (i) of the embodiment shown in FIG. Omitted.

According to the video signal binarization device of this embodiment configured in this way, the black level voltage is also sampled and held, so that the black level voltage can be obtained in accordance with variations in characteristics of the line image sensor, temperature fluctuations, etc. This is reflected in the Threnjord level, resulting in a more accurate video signal VD.
A binary signal B of O is obtained.

〔Effect of the invention〕

As described above, according to the video signal binarization device of the present invention, the white level voltage outputted by reading the white level reference detection means with the line image sensor is sampled and held, and the white level voltage output from the white level reference detection means is sampled and held. By controlling the threshold level of the comparator according to the amount of light, it is possible to obtain a binary signal that always provides constant image reproducibility even when using unstable light sources such as fluorescent lights. .

In addition, the white level voltage output by reading the white level standard detection means with the line image sensor and the blank level voltage output from the line image sensor are sampled and held, and the light intensity of the document illumination light source and the line image sensor are Control the comparator threshold level according to characteristics? 11, it is possible to obtain a binarized signal that always provides constant image reproducibility even when an unstable light source such as a fluorescent lamp is used and the characteristics of the line image sensor vary.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a video signal binarization device according to an embodiment of the present invention, and FIG. A partially fragmented back view of the document table illustrating the detection means; FIG. +d+ is a dot scale timing chart showing the operation of the video signal binarization device of this embodiment, and FIG. 5 is a circuit diagram of a video signal binarization device according to another embodiment of the present invention. In the figure, l...Original, 2...Transparent document table, 3...White tape for white level reference, A S
l, A S z, A S x ・Analog switch, B...Binarized signal, CI~C4・Capacitor, CP...Comparator, OP, ~op, ・Operational amplifier, R3~R6・) VDO...analog video signal, VR...variable resistor, ZD...zener diode.

Claims (3)

[Claims] (1) A white level reference detection means provided along a direction perpendicular to the line direction of the line image sensor within the image frame read by the line image sensor, and reading this white level reference detection means. A white sampling circuit that samples and holds a white level voltage of an analog video signal output from the line image sensor; and a thread that forms a threshold level based on the white level voltage value output from the white sampling circuit. A video signal binarization device comprising: a threshold level forming unit; and a comparator that compares the analog video signal with the threshold level and outputs a binarized signal of the analog video signal. . (2) A white level reference detection means provided along a direction perpendicular to the line direction of the line image sensor within the image frame read by the line image sensor, and reading this white level reference detection means. a white sampling circuit that samples and holds a white level voltage of an analog video signal output from the line image sensor; a black sampling circuit that samples and holds a black level voltage that is output from the line image sensor; and the white sampling circuit. threshold level forming means for forming a threshold level based on the white level voltage output from the black level voltage and the black level voltage output from the black sampling circuit; and the analog video signal and the threshold level. A video signal binarization device comprising: a comparator that compares the analog video signal with a binarized signal of the analog video signal and outputs a binarized signal of the analog video signal. (3) The video signal 2 according to claim 1 or 2, wherein the threshold level forming means includes a density adjusting means that allows the threshold level to be adjusted from the outside. Value device.