JP2552315B2 - Image reader - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus that simplifies correction of shading phenomenon, sensitivity variation between photoelectric elements, and sensitivity secular change.

[Prior Art] Generally, as shown in FIG. 5, an image reading apparatus for reading an image drawn on a document includes a linear image reading sensor 2 and a document 1 whose arrangement direction matches the width direction of the document 1. While moving the relative position of, the image reading sensor 2 sequentially reads the image of the original 1 line by line in the horizontal direction, converts the read image data into a serial image data signal, and sends it to the image reading circuit 3. To do. The image reading circuit 3 binarizes the input serial image data signal and outputs it as binarized image data to the control device 4 such as a computer.

FIG. 6 shows the image reading sensor 2 when the original 1 is irradiated by the irradiation lamp 5 and the image reading sensor 2 reads an image line by line in the width direction of the original 1 in such an image reading apparatus. Is an image data signal for one line which is sequentially transmitted from the image reading circuit 3 to the image reading circuit 3. FIG. 6 (a) shows a logical image data signal waveform when a white (reference white) document in which no characters are drawn is read, for example. As shown in the figure, the signal level indicating the reference white is a complete rectangular waveform with Vs.

However, generally, the illuminance in the width direction of the document 1 irradiated by the irradiation lamp 5 is not constant, and both ends tend to be dark. Therefore, as shown by the solid line waveform in FIG. 6 (b), the waveform of the image data signal obtained by reading the original 1 shows the original 1
A shading phenomenon occurs in which both ends have a dark mountain shape.

Further, the sensitivity of each photoelectric element forming the image reading sensor 2 cannot be said to be completely uniform. Therefore, the waveform of the image data signal obtained by reading the original 1 does not have a uniform waveform as shown by the solid line in FIG. 6C, but contains many high frequency components. This high-frequency component includes noise components in the signal system in addition to the above-mentioned variation in sensitivity between photoelectric devices.

Further, when the image reading device is used for a long period of time, the average illuminance of the irradiation lamp 5 is lowered and the sensitivity of each photoelectric element of the image reading sensor 2 is lowered on average due to aging and environmental changes. As a result, in the waveform of the image data signal obtained by reading the original 1, there occurs a phenomenon that the signal level of the waveform as a whole is lowered as shown by the solid line in FIG. 6 (d).

When each of the above-mentioned phenomena occurs in the image data signal, the image data signal cannot be binarized correctly, so a white document (reference white) serving as a reference before the actual document is read.
Is read and the waveform of the reference white image data is once stored in the correction data memory formed in the storage section. Then, when the actual document is read, the read image data is corrected by the standard white image data stored in the correction data memory, and the corrected image data is compared with the determination reference level to obtain 2 Quantize and output as correct image data.

Further, in addition to the above-mentioned electrical means for binarizing the image data read by the arithmetic processing using the correction data memory, a shading mask, a slit, and a reflection for mechanically limiting the amount of light input to the image reading sensor 2. There are also mechanical methods such as adjusting the shape and characteristics of the mirror and the like.

[Problems to be Solved by the Invention] However, there are still the following problems in the image reading apparatus in which the image data signal is corrected by the electrical method or the mechanical method as described above. That is, in the means for electrically correcting, a correction data memory and a microprocessor (MP
U) is required, a more complicated control program is required, and the manufacturing cost is significantly increased. Further, since it is necessary to execute the arithmetic processing every time the image for one line is read,
There is also a problem that the reading speed decreases.

Further, in the case of performing the correction by the mechanical method, it is necessary to perform detailed adjustment in advance for each image reading device, and the adjustment work requires a great deal of labor. Moreover, in order to correct the secular change, it was necessary to carry out a regular adjustment work.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image reading device that can correctly binarize an image data signal output from an image reading sensor with a simple circuit configuration, improve reading speed, and significantly reduce manufacturing costs. And

[Means for Solving Problems] In the present invention, the image reading sensor is used to shift the relative position between the image reading sensor formed by linearly arranging a plurality of photoelectric elements and the document, and each one of the original is read by the image reading sensor. The image for one line is sequentially read, and the read image data for each line is used as a serial image data signal.
In an image reading apparatus that binarizes and outputs as binarized image data, an image data signal output from an image reading sensor is input, and an amplification circuit whose amplification factor decreases as the input signal level rises, and this amplification circuit. A peak value of the waveform of the image data signal amplified by the first peak hold circuit for holding the peak value of the waveform of the image data signal for a first holding time longer than the duration of the image data signal for one line, and the waveform of the image data signal amplified by the amplifier circuit. Second peak hold circuit that holds the peak value of the image data signal for one line for a very short second holding time, and the level of the image data signal output from the amplifier circuit is When the output signals of the first and second peak hold circuits are both divided and the levels of the determination reference signals are both higher, the image is determined to be white or black, It is obtained by a binarization circuit to obtain a binary image data for the data signal.

[Operation] In the image reading apparatus configured as described above, the image data signal for one line in the width direction of the document output from the image reading sensor is amplified by the amplifier circuit. Since the amplification factor of this amplifier circuit has the above-mentioned characteristic, as shown by the alternate long and short dash line in FIG. 6 (b), the portions where the signal level is low at both ends of the image data signal waveform are greatly amplified. Therefore, the shading phenomenon included in the image data signal is corrected.

Also, the image data signal shading-corrected by the amplifier circuit is held by the first peak hold circuit for the first hold in which the maximum value corresponding to the white level in the image data signal is longer than the duration of the image data signal for one line. Holds only for hours. Then, the signal level of the judgment reference signal waveform obtained by dividing the output signal of the first peak hold circuit is equal to the signal level of the image data signal shown by the solid line as shown by the constant chain line in FIG. 6 (d). Respond. Therefore, the first peak hold circuit corrects a decrease in the signal level of the entire image data signal waveform due to secular change or the like.

Further, the image data signal whose shading has been corrected by the amplifier circuit has the maximum value corresponding to the white level in the image data signal, which is extremely shorter than the duration of the image data signal for one line, by the second peak hold circuit. Will be retained for the retention time of. That is, the fluctuation of the signal level due to the sensitivity variation of each photoelectric element is held for an extremely short time. Therefore, the signal level of the judgment reference signal waveform obtained by dividing the output signal of the second peak hold circuit is the fluctuation of the signal level of the image data signal shown by the solid line as shown by the alternate long and short dash line in FIG. 6 (c). Change according to. Therefore, the second peak hold circuit corrects the fine fluctuation of the signal level of the image data signal waveform due to the sensitivity variation of the photoelectric element.

Therefore, the binarization circuit compares the image data signal shading-corrected by the amplifier circuit with each judgment reference signal obtained from the first and second peak hold circuits to obtain correct binarized data. .

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing an electronic blackboard to which the image reading device 12 of the embodiment is applied. As is well known, in the electronic blackboard, characters (graphics) drawn on a sheet (original) are displayed on the image reading device 12.
And is printed by the printing device 19. That is, in the control device 11, the power supply 15 is turned on and the key input device 14
When the copy key operation is executed at, the irradiation lamp 13 is turned on, and the sheet (original) is moved by the sheet motor 16 at a constant speed. Then, the image reading device 12 reads the character graphic drawn on the sheet (original). Then, the read image data is sent to the printing device 19. Next, the paper is fed to the paper feed motor 17 so as to have the designated copy magnification. When the paper detection device 18 detects the paper, the printing device 19 operates to print out the image data read on the paper.

FIG. 1 is a block diagram showing a schematic configuration of the image reading device 12. An image reading sensor 21 having a plurality of photoelectric elements arranged in a line reads serially image data for each line in the horizontal direction of a moving original 1 (sheet) as shown in FIG. Output as a data signal. The image data signal output from the image reading sensor 21 is directly binarized 23
Is input to the first peak hold circuit 24 and the second peak hold circuit 25. The output signal of the first peak hold circuit 24 is divided by the voltage dividing circuit 24d and input to the binarizing circuit 23 as the first determination reference signal. Further, the output signal of the second peak hold circuit 25 is 2 as the second determination reference signal divided by the voltage dividing circuit 25d.
It is input to the digitization circuit 23. The binarization circuit 23 compares the shading-corrected image data signal output from the logarithmic amplification circuit 22 with the first and second determination reference signals input from the voltage dividing circuits 24a and 25a, and binarizes the image data signal. Image data is obtained and sent to the control device 11.

The logarithmic amplifier circuit 22 has a characteristic that its amplification factor decreases as the input signal level increases. For example, the third
When a signal waveform that monotonically increases with time is input as shown in FIG. 6A, a low signal level portion of the signal waveform is greatly amplified, and a high signal level portion is hardly amplified. As a result, the output waveform becomes a signal waveform of a substantially rectangular wave shape with a short rise time and a flat shape thereafter, as shown in FIG. Therefore, as shown in FIG. 4 (a), the image data signal waveform input to the logarithmic amplifier circuit 22 in which the shading phenomenon is occurring is caused by the logarithmic amplifier circuit 22 to be a rising portion with a low signal level. Since the falling portion is greatly amplified and the central portion having a high signal level is hardly amplified, the waveform is corrected to a substantially rectangular waveform as shown in FIG.
That is, only the dark portions corresponding to both ends of the original of the shading phenomenon are amplified to a level close to the original white, so that the shading correction is performed.

The first peak hold circuit 24 holds the peak value in the input shading-corrected image data signal waveform for a first holding time longer than the duration of the image data signal for one line. That is, the maximum value corresponding to the white level in the image data signal is held for the first holding time. Then, the first peak hold circuit 24
The output signal of is divided by the voltage dividing circuit 24a at a predetermined magnification.

This partial pressure ratio is set to about 1/2. That is, with this voltage dividing circuit 24a, the first peak hold circuit 24a
The output signal of is converted into the first determination reference signal indicated by the alternate long and short dash line in FIG. The signal level of the judgment reference signal waveform obtained by dividing the output signal of the first peak hold circuit 24 responds to the overall signal level of the image data signal shown by the solid line. Therefore, the first peak hold circuit 24 and the voltage dividing circuit 24a respond to the overall signal level of the actually obtained image data signal,
Since the signal level of the first determination reference signal is generated and changed, it is possible to correct the first determination reference signal in response to a decrease in the overall signal level of the image data signal due to aging or the like. Become. That is, according to the first determination reference signal, it is possible to correctly binarize the signal level of the image data signal even if the signal level of the image data signal is entirely lowered due to aging or the like.

The second peak hold circuit 25 holds the peak value in the input shading-corrected image data signal waveform for a second holding time which is much shorter than the duration of the image data signal for one line. That is, the maximum value corresponding to the white level in the image data signal has a very short second value.
Will be retained for the retention time of. That is, the fluctuation of the signal level due to the sensitivity variation of each photoelectric element and the noise of the signal system is held for an extremely short time. Then, the output signal of the second peak hold circuit 25 is divided by the voltage dividing circuit 25a at a predetermined magnification. This partial pressure ratio is set to about 1/2. That is, by the voltage dividing circuit 25a, the output signal of the second peak hold circuit 25 is converted into the second determination reference signal shown by the alternate long and short dash line in FIG. 6 (c). The signal level of the second determination reference signal waveform obtained by dividing the output signal of the second peak hold circuit 25 responds to the local signal level of the image data signal indicated by the solid line. Therefore, the second peak hold circuit 25 and the voltage dividing circuit 25a generate and change the signal level of the second determination reference signal in response to the local signal level of the actually obtained image data signal. Therefore, the second determination reference signal is corrected in accordance with the sensitivity variation of each photoelectric element and the fine fluctuation of the signal level due to the noise of the signal system.
That is, according to the second determination reference signal, even if the signal level of the image data signal waveform fluctuates finely due to the sensitivity variation of each photoelectric element and the noise of the signal system, it can be correctly binarized.

The binarization circuit 23 includes the shading-corrected image data signal output from the logarithmic amplification circuit 22, the first determination reference signal input from the first peak hold circuit 24 via the voltage dividing circuit 24a, and the first determination reference signal. The second judgment reference signal input from the second peak hold circuit 25 via the voltage dividing circuit 25a is compared. The level of the image data signal is the first
If the level of any of the second determination reference signals is higher, it is determined to be white, and if the level of the image data signal is lower than the level of one of the first and second determination reference signals, it is determined to be black. To do. Then, the binarized image data of white (H level) or black (L level) is sent to the control device 11.

As described above, since the first determination reference signal responds to the overall signal level of the image data signal, it is used for the basic determination of binarization between white and black, and the second determination reference signal is used. Since the reference signal responds to the local signal level of the image data signal, it is used to stably binarize white and black.

For example, as described above, each judgment reference signal basically has the signal level as a reference when white of the image data signal is detected, and therefore, is not the image data signal when white is detected. Although a clear signal level difference is secured,
A signal level difference is not ensured with respect to the signal level of the image data signal when black is being detected, and the image data may be affected by noise generated in the signal system while black is being continuously detected. The signal may fluctuate and exceed the first criterion signal. However, since the second determination reference signal responds to the noise of the signal system, it does not exceed the image data signal while black is continuously detected,
It is possible to continue to send the binarized image data that accurately represents black.

In the case of the image reading apparatus configured as described above, the occurrence of the shading phenomenon due to the unevenness of the irradiation by the irradiation lamp 13 in the width direction is corrected by the logarithmic amplifier circuit 22, and the entire image data signal due to the secular change is corrected. The signal level of the first peak hold circuit 24 and the voltage dividing circuit 24
The first determination reference signal corrected from a is generated, and the fine signal level response of the image data signal is caused by the sensitivity variation between the photoelectric elements forming the image reading sensor 21 and the noise generated in the signal system. Is corrected by the second peak hold circuit 25 and the voltage dividing circuit 25a.
Is generated.

Therefore, since the shading-corrected image data signal and the determination reference signal corrected for various variations of the image data signal are obtained, the image data signal can be correctly binarized.

Since the logarithmic amplifier circuit 22, the first and second peak hold circuits 24 and 25 described above can be configured by simple analog circuits, the reference white is read and stored in the correction data memory before the measurement is started. The manufacturing cost can be significantly reduced as compared with the conventional image reading apparatus in which the image data input using the correction data is binarized by the arithmetic processing.

Further, unlike the conventional apparatus, it is not necessary to execute the arithmetic processing based on the control program on the image data output from the image reading sensor, so that the image reading sensor 21 reads the image of the original and then the binarized image data. As control device 11
The time required to send to can be greatly reduced. Therefore, the image reading speed of the entire apparatus can be improved.

As described above, according to the image reading apparatus of the present invention,
By passing the image data signal output from the image reading sensor through a hard circuit such as a logarithmic amplifier circuit and a peak hold circuit, shading phenomenon, signal level fluctuation due to aging, and sensitivity variation among photoelectric elements are corrected. . Therefore, the correct determination reference signal for binarization can be obtained, the image data signal can be binarized correctly with a simple circuit configuration, the reading speed can be improved, and the manufacturing cost can be significantly reduced.

[Brief description of drawings]

1 to 4 show an image reading apparatus according to an embodiment of the present invention. FIG. 1 is a block diagram showing a schematic structure, and FIG. 2 is an electronic blackboard incorporating the embodiment apparatus. FIG. 3 is a block diagram showing the amplification characteristic of a logarithmic amplifier, FIG. 4 is a diagram showing image data signal waveforms inputted to and outputted from the same logarithmic amplifier circuit, and FIG. 5 is a general image reading apparatus. And FIG. 6 are diagrams showing general image data signal waveforms. 1 ... manuscript, 11 ... control device, 12 ... image reading device, 21
... Image reading sensor, 22 ... Logarithmic amplifier circuit, 23 ... Binarization circuit, 24 ... First peak hold circuit, 24a, 25a ...
… Voltage divider circuit, 25 …… Second peak hold circuit.

Claims (1)

(57) [Claims] 1. An image for each line of the original is sequentially read by the image reading sensor while shifting the relative position between the image reading sensor formed by arranging a plurality of photoelectric elements linearly and the original. In the image reading device that outputs the read image data for each line as a serial image data signal, and binarizes the image data signal and outputs the binarized image data, the image reading sensor outputs the image data. An amplifier circuit in which an image data signal is input and the amplification factor decreases as the input signal level rises, and the peak value of the image data signal waveform amplified by this amplifier circuit is used as the duration of the image data signal for one line. A first peak hold circuit for holding a longer first holding time, and a peak value of the image data signal waveform amplified by the amplifier circuit for the image data for one line. A second peak hold circuit that holds a second hold time that is extremely short compared with the duration of the digital signal, and the level of the image data signal output from the amplifier circuit is the first and second peak hold circuits. A binarization circuit for determining whether the output signal of the circuit is white or black when it is higher than any of the levels of the determination reference signals obtained by dividing the output signal, and obtaining binary image data for the image data signal; An image reading apparatus comprising: