JPH02146869A - Image pickup device - Google Patents

Abstract

PURPOSE:To attain sure binarizing processing without being affected by uneven lighting by setting a comparison reference for discriminating a binary value properly when a character or a graph drawn on a dark background such as a blackboard is picked up and outputted to a printer or the like. CONSTITUTION:Since most of first parts of image pickup signals in the case of picking up a black board is a black level signal, the black signal level is held in capacitors C1, C2 of a reference signal section 11 for a low frequency, a minimum level of the pickup signal is held in the capacitor C1 and a terminal voltage of the capacitor C2 in interlocking with a change in the video signal is fed to an input terminal of a buffer IC3, a video signal is subject to binary processing based on the relation of quantity by using a comparator IC4 from the terminal voltage of the capacitors C1, C2. Thus, the part filled in a while level is functioned surely for binarizing processing and even if the image pickup signal transits from lots of thin character parts into white level filling part, since the image pickup signal level does not exceed the level of a comparison reference signal, the correspondence of processing is ensured.

Description

[Detailed Description of the Invention] (Objective of the Invention) (Industrial Application Field) The present invention derivates characters, figures, etc. drawn on a dark background such as a blackboard, and converts it into a binary form for output to a printer etc. It relates to an image carrier that obtains data.

(Prior technology) Characters and figures drawn on various walls such as blackboards and whiteboards are incident through a lens, the angle of view is determined while being monitored by a viewfinder, and the image is scanned by a one-dimensional image sensor. The applicant has proposed in Japanese Patent Application No. 175548/1983 a so-called imaging printing device which operates a printer based on the resulting image signal and prints out the characters, figures, etc. on paper.

In such imaging [2], the imaging signal output from the one-dimensional image sensor is binarized and used as an image signal for the subsequent printer or the like.

When converting the image signal into two values, the image signal of the white board is converted into two values.
It is more difficult to binarize a blackboard image signal than to convert it into a value. In other words, in the case of a white board, impulse-like character signals (including figures, etc.) are included in the white signal as the background in the carrier signal, so when converting into binarization, As shown, the white signal level in the 1liita signal is set to the maximum level by the AGC circuit,
It is only necessary to use a smoothed wi image signal of a level slightly lower than this as a comparison reference value of the comparator, and the background and characters can be reliably output as binary signals.

On the other hand, in the case of a blackboard, the level of the black signal as a background signal in the carrier signal is moved up and down by the AGC circuit. That is, since the m-image signal to be binarized is gain-controlled by the AGC circuit, the black signal rises or falls depending on how much white signal is included in the black signal, which is the background.

For this reason, an absolute value cannot be used as a comparison IQ-value of a binary determination comparator. In other words, it is not possible to use a method of determining that a DC voltage below a certain DC voltage is black.

Therefore, as the comparison reference value, as shown in FIG. 8, a voltage value obtained by adding a DC component to a smoothed imaging signal is used.

However, if such a comparison standard value is used, if there are many white characters or a figure filled with white is transferred,
The comparison Ft and the quasi-value continue to be Ueno, and the comparison reference value becomes higher than the original white level, making it impossible to perform binarization.

Furthermore, in a high frequency range where the wavelength of the imaging signal is short, the output characteristics generally deteriorate depending on the performance of the imaging lens, the number of imaging probes, etc. For example, when carrying an image of a subject such as a large number of fine letters or checkered stripes, the wavelength of the imaging signal becomes short, so the signal level cannot be changed sufficiently from pure white to pure black, and the amplitude becomes small. In other words, the waveform has a small amplitude floating at an intermediate level between pure white and pure black, and in order to binarize it, a comparison reference value must be set at this small amplitude intermediate level.

However, with the comparison reference value obtained by flattening the carrier signal mentioned above and adding a DC component to it, for the high frequency region of the imaging signal,
It is not immediately set to an appropriate comparison standard level;
It was difficult to perform reliable binarization.

(Problems to be Solved by the Invention) As mentioned above, when capturing images of characters and figures drawn on a blackboard and converting them into binarization, it is difficult to set the comparison reference value of the comparator for binary judgment, and it is difficult to set the comparison standard value for the binary judgment comparator. was difficult.

An object of the present invention is to provide an image carrier that can perform binarization of Jla image signals reliably and well under various environments by appropriately setting comparison reference values for binary determination. It's about doing.

(Structure of the Invention) (Means for Solving the Problems) An image carrier according to the present invention includes a low-frequency reference signal section, a high-frequency reference signal section, and a comparator, and the low-frequency reference signal section includes: i! ! It has a charging/discharging section with a time constant set to gradually increase or decrease the output level in response to the long wavelength component of the imaging signal obtained by the i-image means, and does not increase the output level above a predetermined level. It is configured as follows. Further, the high frequency reference signal section has a charging/discharging section with a time constant set so as to respond to the short wavelength component of the imaging signal, and outputs an output at an intermediate level in response to the amplitude of the short wavelength component. and is configured to generate an output at a lower level than the signal level for long wavelength components. Furthermore, the comparator is
Of the outputs from the low-frequency reference signal section and the high-frequency reference signal section, the one with the higher output level is configured to be used as a comparison reference signal for binary determination with respect to the eta signal.

Further, the invention of claim 2 provides a low frequency reference signal section that includes:
A configuration having a background level charging circuit that charges the imaging signal with a time constant shorter than a set time constant for a predetermined period of time from the start of imaging is used.

(Function) In the present invention, a comparison reference signal having a level corresponding to the black signal as the background in the carrier signal is generated in the low frequency reference signal section, and this is used for binary judgment in the low frequency range. At the same time, a high-frequency reference signal section generates a comparative reference signal with a floating level corresponding to the high-frequency component in the carrier signal, and this is used for binary determination in the high-frequency range. Therefore, it is possible to reliably binarize anything drawn on the subject, such as fine letters, checkered patterns, or white filled figures. In addition, the comparison reference signal generated by the low-frequency reference signal section slowly follows the level change of the carrier signal with a large time constant, so even if the blackboard is not evenly illuminated, it will follow the change in brightness. Gradual increase/decrease. Therefore, binarization can be reliably performed without being affected by uneven illumination or the like.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 11 denotes a low-frequency reference signal section which inputs an imaging signal and generates a low-frequency comparison reference signal. A charging path consisting of D3 and a discharging path consisting of resistor 1 and 3 and diode D2 are independently connected to constitute charging/discharging section 12. The above charging resistor R4
is set to a larger value than the discharging resistor R3, and is configured to charge the imaging signal slowly. Further, a background level charging circuit 13 consisting of an analog switch SW2 and a protection resistor R2 is provided between the capacitor C2 and the input point of the imaging signal. Above analog switch SW
2 starts from the start of imaging! ! 13 It is turned on by an area pulse that is at the "O" level for the first few μs of the effective range of the image, and the black signal level for the first 20 pixels of the l1il image signal, that is, the background, is transferred to the capacitor C2 with a short time constant. Charge.

14 is a charging stop circuit that detects a sudden rise of the 1Iil image signal and stops charging the capacitor C2, which connects the comparator IC2 and the resistors KRs and Re provided between the m image signal input point and the ground. have The ←) input terminal of the comparator IC2 is connected to the midpoint between the resistors Rs and Rs, and the +fri due to these resistors Rs and Re
Input the divided voltage of the image signal.

Further, the (+) input terminal is connected to the upper end of the capacitor C2 in the drawing, and the terminal voltage of this capacitor C2 is input.

Furthermore, the output end is connected to the anode side of the diode D3.

When the rise of the imaging signal is slow, the comparator IC2 detects the terminal voltage of the capacitor C2, that is, (+
) Since the input terminal voltage is higher than the voltage divided by the resistors R5 and R6, that is, the (-) input terminal voltage, the output terminal becomes rHJ level and J3 does not prevent charging of the imaging signal to the capacitor C2. On the other hand, when the carrier signal rises rapidly, the voltage divided by the resistors Rr+ and Rs becomes higher than the terminal voltage of the capacitor "j-02" which has a large charging time constant, so the output terminal becomes the rLJ level. The anode side of the diode D3 in the charging path is grounded to stop charging the capacitor C2.

Reference numeral 15 denotes a lowest level holding circuit for holding the lowest level of the image carrier signal, which includes an analog switch SW1, a resistor R1e, and a capacitor C1 between the input point of the m-image signal and the ground. In addition, in parallel with the analog switch SW1,
A diode D1 for discharging the capacitor C1 is provided.

The illustrated upper end of the capacitor C1 is connected to the (+) input terminal of the buffer 71C1, and the terminal voltage of the capacitor -01 is applied to this (+) input terminal. Further, the output end is connected to the input end (←), and is also connected to the upper end of the capacitor→jC2 in the figure via diodes D4 and Ds in the opposite direction.

The analog switch SW1 is a background level charging circuit 1.
It is turned on together with the analog switch SW2 of No. 3 by the area pulse. Therefore, the capacitor C1 is charged to the black signal level, which is the background of the blackboard, in the same way as the capacitor C2 at the start of image transport. After a predetermined time, the analog switch SW1 is turned off, and after that, if the R@other signal becomes small, it is discharged through the diode D1, but it is not charged, and the lowest level of the m-image signal is held in the capacitor C1. It is applied to the (+) input terminal of buffer IC1. Further, the terminal voltage of the capacitor C2 is connected to the (-) input terminal of the buffer IC1 through a diode Da.

It is applied with a voltage drop due to DB. Therefore, if the terminal voltage of capacitor C2 is below a certain level,
That is, the lowest voltage charged to capacitor C1 is connected to diode D4. Forward voltage of Ds (e.g. 0.5V
If the value is less than the sum of 2>, the diodes Da and D
s is in a non-conducting state and has no effect on the charging of the capacitor C2. On the other hand, when the terminal voltage of the capacitor C2 exceeds the above-described certain level, the diodes D4 and Ds become conductive.

Therefore, the terminal voltage of capacitor C2 will not rise above this constant voltage.

In this way, the capacitor C2 provided in the charging/discharging section 12 of the low frequency reference signal section 11 gradually increases or decreases the terminal voltage in response to gradual changes in the bounce image signal. When the imaging signal suddenly rises, charging is stopped by the operation of the charging stop circuit 14, and the terminal voltage does not rise. Also,
Even with a gentle Ueno, the diode DJ is connected to the lowest level of the imaging signal held by the lowest level holding circuit 15.

Since charging is stopped when the voltage exceeds the sum of the forward voltage of DB, the voltage does not rise any further.

Reference numeral 16 denotes a high-frequency reference signal section, and a charge/discharge section 17 includes a dividing resistor R7°R8 provided between the input point of the ms signal and the ground, and a capacitor C3 connected in parallel to this dividing resistor R8. has.

This charging/discharging section 17 has a capacitance of a capacitor C3 made small and is set to have a shorter time constant than the charging section 12 of the low frequency reference signal section 11 so as to respond to short wavelength components of the imaging signal.

Capacitor C3 constituting this high frequency charging/discharging section 17
The upper ends of the capacitors C2 and the upper ends of the capacitors C2 constituting the low frequency charge/discharge section 12 are connected to corresponding diodes D.
The terminal voltage of the capacitor C2 or C3, whichever is larger, is applied to the (-) input terminal of the buffer IC3.

The output end of this buffer 71C3 is connected to the input end (+) and also to the variable resistor VR provided between it and the power supply VCC.

IC4 is a comparator for binary judgment, and its (+) input terminal is! It is connected to the image signal input point Iil, and its (-) input end is connected to the operating contact of the variable resistor VR. Then, the comparison reference signal for binary determination outputted from the 2-value contactor is compared with the imaging signal, and a binary output is generated from the output end in accordance with the magnitude relationship between them.

In the above configuration, when an image is conveyed on a blackboard as a subject by an image conveying means (not shown), an imaging signal is input to each of the low frequency reference signal section 11 and the high frequency reference signal section 16 via an AGC circuit (not shown).

Here, when a blackboard is imaged, the image signal generally includes a black signal as a background and impulse-like white character signals interspersed with it, as shown in FIG. Therefore, the first part of the carrier signal is almost always a black signal, and first, the level of this black signal is set to the low frequency reference signal section 11.
is held by capacitors C1 and C2. For this purpose, the analog switch 5W1SW2 is turned on by an area pulse for a predetermined period of time from the start of image transport, that is, for the first few μs of the effective imaging range as shown in FIG. The signal for 20 pixels is transferred to capacitor C1.
, C2 is charged.

After this, the analog switch SW1.8W2 is turned off, so that the lowest level of the imaging signal is held in the capacitor C1 as described above. Furthermore, although the black signal level is temporarily held in the capacitor C2 as described above, after the analog switch SW2 is turned off, the imaging signal is transferred to the resistor R4.
It is charged via the diode D3 with a large time constant, and is discharged via the relatively small resistor R3 and the diode D2 as the imaging signal decreases. For this reason, capacitor C
The two-terminal voltage A1, that is, the charge level of the black signal gradually increases or decreases in conjunction with changes in the imaging signal.

The terminal voltage of this capacitor C2 is buffered via diode DB? Since it is applied to the ←) input terminal of lc3, a potential at a level corresponding to the terminal voltage of capacitor C2 is generated at the output terminal of buffer IC3.

Therefore, the potential difference with the power supply Vcc changes according to the change in the terminal voltage of the capacitor C2, and the movable contact of the variable resistor vR generates a long R image signal as shown in Figs. 3 to 6. In response to changes in the black signal level, which is the wavelength component,
Furthermore, a comparison reference signal A' is generated which is set to a higher value than this black signal level.

Then, this comparison reference signal A' becomes a comparison target for the image pickup signal in the comparator IC4, and a binary output is generated based on the magnitude relationship between these signals.

FIG. 3 shows a case where a white filled part drawn on a blackboard is imaged. In this case, the m-image signal rises rapidly due to the image of the white filled part, but since the charge to the capacitor C2 is stopped by the operation of the charge stop circuit 14 described above, the comparison reference signal A' does not rise to an upper limit. , maintains a value corresponding to the black signal level. Therefore, the white filled portion can be reliably binarized.

FIGS. 4 and 5 show a case where the black signal level of the m-image signal changes depending on the imaging location due to uneven lighting on the blackboard or the like. In this case, since the black signal level in the phantom signal changes slowly, the terminal voltage A of the capacitor C2 gradually increases/decreases in response to the large time constant of the charging/discharging section 12 of the low frequency reference signal section 11. do. For this reason,
It is possible to obtain a comparison reference signal @A' that corresponds to changes in the brightness of the blackboard surface, and it is possible to reliably double the image pickup signal without being affected by uneven illumination on the blackboard.

FIG. 6 shows a case where a large number of small letters or checkered patterns and white filled areas are drawn on a blackboard. In this case, when a large number of small characters or checkered patterns are imaged, the wavelength of the m-image signal becomes shorter, and as mentioned above, the amplitude of the m-image signal becomes smaller and floats to an intermediate level between the black level and the white level. The state will be as follows.

When the m-image signal becomes floating in this way, the terminal voltage of the capacitor C3 of the high-frequency reference signal section 16 immediately increases. Of course, the capacitor C of the low frequency reference signal section 11
The terminal voltage of the diode D4.2 also rises slowly, but due to the action of the lowest level holding circuit 15, the wt carrier signal reaches the lowest level. It does not rise above the value of the forward voltage of Ds, and the comparison reference signal A' is held at a low level as shown.

Terminal voltage B of capacitor C3 of high frequency reference signal section 16
The level of the comparison reference signal B' based on is lower than the signal level for long wavelength components of the imaging signal, but when carrying short wavelength components, many small characters, etc. The signal component is set to have an intermediate level of amplitude.

For short wavelength components of the imaging signal, a comparison reference signal B' having an intermediate level of amplitude is applied to the comparator I.
Since this is a comparison target in C4, this short wavelength component can be reliably binarized.

Furthermore, when the image carrier signal moves from a large number of small character parts to a white filled part, the comparison reference signal B' also rises, but it does not rise above the mt* signal level, and the two corresponding to white Continue to produce value output.

〔Effect of the invention〕

As described above, according to the present invention, image signals of all kinds of characters and figures including checkered stripes and filled parts drawn on a blackboard can be captured.
Binarization processing can be performed reliably without being affected by uneven lighting on the blackboard.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the imaging device according to the present invention, FIG. 2 is a characteristic diagram showing the m-image signal given to the device in FIG. 1, and FIGS. FIGS. 7 and 8 are characteristic diagrams showing the relationship between the carrier image signal and the comparison reference voltage in the apparatus, and are characteristic diagrams for explaining the prior art. 11...Low frequency reference signal section, 12...Charge/discharge section, 13
...Background level charging circuit, 16..High frequency reference signal section, 17..Charging/discharging section, IC4..Comparator.

Claims (2)

[Claims] (1) It has a charging/discharging section with a time constant set so as to gradually increase or decrease the output level in response to the long wavelength component of the imaging signal obtained by the imaging means, and the output level is raised to a predetermined level or higher. It has a low frequency reference signal section configured so as not to increase the amplitude, and a charging/discharging section whose time constant is set so as to respond to the short wavelength component of the image pickup signal, and has an intermediate level of the amplitude of the short wavelength component with respect to the amplitude of the short wavelength component. a high-frequency reference signal section configured to generate an output and generate an output at a lower level than the signal level for long wavelength components; An imaging device comprising: a comparator that uses the higher output level as a comparison reference signal for binary determination of an imaging signal. (2) The imaging device according to claim 1, wherein the low-frequency reference signal section has a background level charging circuit that charges the imaging signal with a time constant shorter than a set time constant for a predetermined time from the start of imaging. .