JP3708888B2 - Scanner device and photoelectric gain output automatic gain adjustment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a scanner device using a gray reference plate and an automatic gain adjustment method for photoelectric conversion output.
[0002]
[Prior art]
A light source such as a fluorescent lamp used for an OCR scanner generally changes in light amount and spectral characteristics over time. For this reason, in a character reader or the like, there is a problem that an image having a constant density or a constant color cannot be obtained if the secular change of the fluorescent lamp is left unattended. In order to solve this problem, it is necessary to adjust the gain of the amplifier circuit provided in the photoelectric conversion unit in accordance with changes in the light amount and spectral characteristics of the light source. Therefore, the scanning unit scans a reference plate that serves as a reference for brightness and hue before scanning the read document, and the amplification unit performs the above amplification so that all the outputs of the photoelectric conversion unit when the reference plate is read have the same value. It is widely practiced to automatically adjust the gain of a circuit. At this time, as a reference plate to be used, white such as magnesium oxide is often used as a reference for brightness and hue.
[0003]
On the other hand, it is desirable to be able to easily detect the outline (edge) of the form from the image data obtained by scanning during the operation of performing the form reading process by the scanner. Since it is often a white background, it is required to make the periphery (background) of the form black.
[0004]
In order to achieve both of these, for example, in a document moving scanner of a character recognition device, before scanning a form, a white reference plate serving as a white reference appears in the image reading unit, and the amplification result is determined based on the read result. A mechanism is employed in which the gain is adjusted, and then the form is scanned after the black background plate, which is replaced with the white reference plate, appears as a black background in the image reading unit.
[0005]
Also, in a small scanner that does not have a moving part for moving the white reference plate and black background plate, a gray reference plate serving as a gray reference is fixed to the image reading unit instead of the white reference plate and black background plate. Before scanning the read form, the method of automatically adjusting the gain of the amplifier circuit so that the output of the photoelectric conversion unit when reading from the gray reference plate becomes a predetermined value, or the background of the gray reference plate as it is A method of scanning a read form is used.
[0006]
Also, in order to reduce the manufacturing cost of the gray reference plate, the gray reference is not manufactured so that its brightness (reflectance) and hue (spectral characteristics) are strictly constant. Using a measuring instrument calibrated with a reference plate (or the scanner device itself), measure the reflectance and spectral characteristics of each gray reference plate, and register the measurement results for each scanner that uses the gray reference plate ( And the value is set as a target value for gain adjustment of the amplifier circuit. At this time, the gray reference plate to be mounted needs to be as close to black as possible in order to obtain a sufficient difference in brightness between the white background of the form and the gray reference plate.
[0007]
As described above, in the conventional automatic gain adjustment of the amplification circuit provided in the photoelectric conversion unit of the scanner, in order to easily detect the outline of the form from the image data, that is, the white background and the gray of the form. In order to obtain a sufficient difference in brightness from the reference, the gray reference plate had to be made as black (dark) as possible. However, the blacker the gray reference plate is, the smaller the target value registered as gain adjustment becomes. For this reason, there is a problem that the accuracy of gain adjustment deteriorates due to noise caused by dust adhering to the form. there were.
[0008]
[Problems to be solved by the invention]
As described above, in the conventional automatic gain adjustment of the amplifier circuit provided in the photoelectric conversion unit of the scanner, in order to easily detect the outline of the form from the image data, that is, the white background of the form. In order to obtain a sufficient brightness difference from the gray reference plate, the gray reference plate must be black (darkened) as much as possible. However, the darker the gray reference plate, the more the target value registered as gain adjustment. There is a problem that the gain adjustment accuracy deteriorates due to noise caused by dust adhering to the form.
[0009]
The present invention has been made in view of the above circumstances, and in a scanner device using a gray reference plate, a scanner device capable of accurately adjusting the gain of an amplifier circuit provided in a photoelectric conversion unit, and a photoelectric conversion output It is an object of the present invention to provide an automatic gain adjustment method.
[0010]
[Means for Solving the Problems]
The present invention relates to an automatic gain adjustment mechanism of an amplifier circuit of a photoelectric conversion unit of a scanner device using a gray reference plate. At the time of shipment, maintenance or inspection, photoelectric conversion output at least when a white reference plate is scanned The target value is stored (set), and the automatic gain adjustment of the amplifier circuit of the photoelectric conversion unit is performed using the target value of the white reference plate when reading the image of the read form.
[0011]
That is, the present invention provides a photoelectric conversion when a white reference plate temporarily mounted is scanned in a scanner device that adjusts the gain of an amplification circuit of a photoelectric conversion unit using a gray reference plate when reading a form image. Storage means for storing the output target value (W) and the target value (G) of the photoelectric conversion output when the gray reference plate fixedly attached to the scanner device is scanned, and the gray before reading the form After scanning the reference plate and adjusting the gain of the amplifier circuit of the photoelectric conversion unit until the target value (W) obtained from the storage means is reached, the target value (W) obtained from the storage means wherein the ratio amount between the target value (G); and a gain adjustment means for reducing (G / W) only to read the document with the amplifier circuit of the photoelectric conversion unit, which is adjusted by the gain adjusting means and And it features.
[0012]
The present invention also provides a white reference temporarily mounted in a scanner device that adjusts the gain of an amplification circuit of a photoelectric conversion unit using a gray reference plate when reading an image of characters or figures printed on a form. Target value (W ) of photoelectric conversion output when scanning a plate, target value (W ) of this photoelectric conversion output and target value (G) of photoelectric conversion output when scanning the gray reference plate fixedly attached to the scanner device Storage means for storing the ratio (G / W) obtained from the above, and scanning the gray reference plate before reading the form, until the target value (W) obtained from the storage means is reached. Gain adjusting means for reducing the gain by a ratio (G / W) obtained from the storage means after adjusting the gain of the amplifier circuit, and the amplifier circuit of the photoelectric conversion unit adjusted by the gain adjusting means Using And reading the form.
[0013]
By providing the automatic gain adjustment function of the amplification circuit of the photoelectric conversion unit as described above, the gain of the amplification circuit of the photoelectric conversion unit in the scanner device using the gray reference plate can be accurately adjusted.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
FIG. 1 is a block diagram showing the configuration of the main part of the scanner device according to the first embodiment of the present invention.
[0016]
In the figure, reference numeral 11 denotes a light source such as a fluorescent lamp that illuminates a form to be read and a reference plate for photoelectric conversion output adjustment. Reference numeral 12 denotes a read form to be read by the image sensor. Reference numeral 13 denotes a gray reference plate that is fixedly mounted at the reading position of the image sensor and serves as a reference for brightness and hue, and serves as the background of the form 12 to be read when the form is scanned. Reference numeral 14 denotes brightness (reflectance) and hue (spectral characteristics) that are temporarily attached to the reading position of the image sensor to calibrate the reflectance and spectral characteristics of the gray reference plate when the scanner apparatus is manufactured. It is a white reference plate that is an absolute reference for An image sensor 15 scans the form 12 to be read and reads an image. Reference numeral 16 denotes an amplifier circuit that amplifies the read output (analog output voltage) of the image sensor 15. Reference numeral 17 denotes a gain adjustment circuit that performs automatic gain adjustment of the amplifier circuit 16 so that the photoelectric conversion output (A / D conversion output) of the gray reference plate 13 becomes a predetermined value. Reference numeral 18 denotes an A / D conversion circuit that performs analog / digital conversion on the image signal (analog output voltage) amplified by the amplifier circuit 16. An image memory 19 stores the image data output from the A / D conversion circuit 18. Reference numeral 20 denotes a parameter storage unit that holds data (reference value) for automatic gain adjustment of the photoelectric conversion unit.
[0017]
FIG. 2 is a flowchart showing a procedure of photoelectric conversion output adjustment before shipment and a procedure of automatic gain adjustment of the photoelectric conversion unit at the time of scanner reading after shipment in the first embodiment. It is operation | movement explanatory drawing of embodiment.
[0018]
Here, the operation in the first embodiment of the present invention will be described with reference to the respective drawings.
[0019]
First, the operation of FIG. 1 will be described. The read form 12, the gray reference plate 13, the white reference 14 plate, and the like are irradiated with light from the light source 11. Printed and / or handwritten characters / graphics, etc. are entered in the form 12 to be read, and image data such as the characters / graphics is read by the scanner device. In general, the form 12 is white. . The gray reference plate 13 serves as a reference for brightness and hue, and serves as the background (background color) of the form 12. The gray reference plate 13 is fixedly mounted at the reading position of the image sensor 15.
[0020]
On the other hand, the white reference plate 14 is an absolute reference for brightness (reflectance) and hue (spectral characteristics). The reflectance of the white reference plate 14 is always higher (brighter) than the reflectance of the form. The white reference plate 14 is detachably attached to the scanner device, and temporarily adjusts the reflectance and spectral characteristics of the gray reference plate 13 when the scanner device is manufactured. Install and use at the reading position. The white reference 13 plate is removed when the gain adjustment described later is completed, and is not mounted at the time of scanner shipment.
[0021]
The image sensor 15 is composed of a number of CCD sensors and the like, and photoelectrically converts the reflected light from the various reference plates 13 and 14 or the form 12 and outputs it to the amplifier circuit 16. The amplifying circuits 16 are provided as many as the number of CCD sensors constituting the image sensor 15, and amplify the analog output voltage output from the image sensor 15. The gain of the amplifier circuit 16 is given from the gain adjustment circuit 17. The A / D conversion circuit 18 converts the analog output voltage amplified by the amplification circuit 16 into digital data. The image memory 19 temporarily stores the digital data A / D converted by the A / D conversion circuit 18 and outputs the image data to a reading control unit (not shown).
[0022]
The gain adjustment circuit 17 is provided with an amplification circuit 16 (corresponding to the CCD sensor) so that the photoelectric conversion outputs (A / D conversion outputs) of the CCD sensor when the gray reference plate 13 is read all have the same value. Adjust the gain. The parameter storage unit 20 is read / written by the gain adjustment circuit 17 and adjusts the gain for each amplifier circuit so that the photoelectric conversion outputs of the CCD sensor when the gray reference plate 13 is read all have the same value. Are stored for each scanner device or each gray reference plate 13.
[0023]
Here, before shipping the scanner device, first, the white reference plate 14 is attached to the reading position of the image sensor 15. The white reference plate 14 is read by the image sensor 15. At this time, the gain adjustment circuit 17 sets the gains of all the amplification circuits 16 corresponding to the CCD sensors to one so that the photoelectric conversion outputs of the many CCD sensors constituting the image sensor 15 all have the same predetermined value [W]. Individual adjustment (as large as possible within the range where the output of the amplifier circuit 16 is not saturated) is set (step S1 in FIGS. 2 and 3).
[0024]
Next, the white reference plate 14 at the reading position is removed, the gray reference plate 13 is read by the image sensor 15 with the gain as it is, and the photoelectric conversion output of the CCD sensor constituting the image sensor 15 is measured. The gain adjustment circuit 17 stores the photoelectric conversion output value [G] at this time in the parameter storage unit 20 together with the predetermined value [W] obtained above (step S2 in FIGS. 2 and 3).
[0025]
The above adjustment is performed before shipping the scanner device. Note that the above-described gain adjustment is not limited to before the scanner device is shipped, and may be performed, for example, during regular adjustment or maintenance inspection.
[0026]
When the scanner device is subsequently operated, that is, before reading the image of the form 12 to be read, first, the gray reference plate 13 is read by the image sensor 15 and all photoelectric conversion outputs of the CCD sensors constituting the image sensor 15 are read. The gain adjustment circuit 17 adjusts the gain of the amplifier circuit 16 based on the [W] value obtained from the parameter storage unit 20 (step S11 in FIG. 2 and FIG. 3). ). The gain of the amplifier circuit 16 at this time is [A].
[0027]
Next, the gain R of the amplifier circuit 16 is set to R = [A × G / W] (step S12 in FIGS. 2 and 3). In this state, the form 12 is scanned and read by the image sensor 15, and the amplification circuit 16 performs amplification processing with the value of the gain R (step S13 in FIG. 2).
[0028]
The automatic gain adjustment according to the above-described embodiment of the present invention enables highly accurate gain adjustment.
[0029]
Here, a method of adjusting the gain of the amplifier circuit using only a gray reference plate that does not use the present invention (herein referred to as a general method) and a white reference plate and a gray reference plate as in the present invention are used. A comparison is made with a method for performing gain adjustment (herein referred to as the present invention method).
[0030]
In the general method, when scanning the form 12, first, the gray reference plate is read by the image sensor, and the photoelectric conversion outputs of the CCD sensors constituting the image sensor are all set to the same value [G]. Adjust the gain. Then, the form 12 is scanned and read by the image sensor 15, and the photoelectric conversion output is amplified by the amplification circuit 16 (with the gain obtained above) and output to the A / D conversion circuit. . On the other hand, in the method of the present invention, as the first step, the white reference plate 13 is read in advance, and the amplifier circuit 16 is configured so that the photoelectric conversion outputs of all the CCD sensors constituting the image sensor 15 have the same value [W]. The gray reference plate 14 is read next, and the photoelectric conversion output values [G] of all the CCD sensors constituting the image sensor 15 are measured while the gain of the amplifier circuit 16 is left as it is. . Then, as the second stage, the value [W] obtained by reading the gray reference plate 13 and reading the photoelectric conversion outputs of all the CCD sensors constituting the image sensor 15 in the first stage before reading the actual form 12. Thus, the gain (value [A]) of the amplifier circuit 16 is obtained so that the gain R = A × G / W when reading the actual form 12 is obtained.
[0031]
As a result, if the gain adjustment error e = WG of the amplifier circuit 16 is zero, substantially the same image data can be obtained regardless of the method of the present invention or the general method. However, actually, the same amount of light is not emitted from the fluorescent lamp of the light source 11 to the CCD sensor constituting the image sensor 15 due to aging.
[0032]
However, in general manner, the amplifier circuit 16 to be gain adjusted only photoelectric conversion output when scanning read gray reference plate 13, the light intensity deterioration due to aging of the values of the photoelectric conversion output, for example, the light source 11 not When an appropriate value is reached, the value is directly reflected in the output signal, affecting the character reading.
[0033]
In contrast, in the present invention method, the gain R in amplifier 16 obtained before the time of reading the document 12 (when reading the document 12), since obtaining the A × G / W, a gray reference plate 13 even Even when the photoelectric conversion output [G] at the time of scanning reading becomes an inappropriate value, it can be suppressed to an extremely small influence by [G / W] (≦ 1). Therefore, the gain of the present invention can be adjusted with high accuracy.
[0034]
In the above-described embodiment, the photoelectric conversion output values [W] and [G] obtained above are stored in the parameter storage unit 20 (step S2 in FIG. 2). Instead, the target value [ W] and ratio [G / W] may be stored. Further, the photoelectric conversion output of the white reference plate or the gray reference plate may be any of an average value, a maximum value, a partial average value of the entire area of the image sensor, and the like. Further, in the color scanner, the hue (color balance) can be controlled by performing the same operation as that of the above embodiment for each of R, G, and B.
[0035]
【The invention's effect】
As described above in detail, according to the present invention, the gain of the amplifier circuit of the photoelectric conversion unit can be accurately adjusted in the scanner device using the gray reference.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a main part of a scanner device according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a procedure of photoelectric conversion output adjustment before shipment and photoelectric conversion output automatic gain adjustment at the time of form scanning in the embodiment.
FIG. 3 is an operation explanatory diagram of the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Light source 12 ... Form 13 ... Gray reference board 14 ... White reference board 15 ... Image sensor 16 ... Amplifier circuit 17 ... Gain adjustment circuit 18 ... A / D (analog / digital) conversion circuit 19 ... Image memory 20 ... Parameter memory | storage part

Claims (4)

In a scanner device that adjusts the gain of an amplifier circuit of a photoelectric conversion unit using a gray reference plate when reading an image of a form,
The target value (W) of the photoelectric conversion output when the white reference plate temporarily mounted is scanned and the target value (G) of the photoelectric conversion output when the gray reference plate fixedly attached to the scanner device is scanned. Storage means for storing;
The gray reference plate is scanned before reading the form, and after adjusting the gain of the amplifier circuit of the photoelectric conversion unit until the target value (W) obtained from the storage means, the gain is read from the storage means. Gain adjusting means for reducing the ratio (G / W) of the target value (W) and the target value (G) to be obtained;
A scanner apparatus that reads the form using an amplifier circuit of the photoelectric conversion unit adjusted by the gain adjusting means. In a scanner device that adjusts the gain of an amplifier circuit of a photoelectric conversion unit using a gray reference plate when reading an image of a form,
Target value (W) of photoelectric conversion output when scanning a white reference plate that is temporarily mounted, and photoelectric conversion when scanning the gray reference plate fixedly attached to the target value (W) and the scanner device Storage means for storing the ratio (G / W) obtained from the output target value (G);
The gray reference plate is scanned before reading the form, and the gain of the amplifier circuit of the photoelectric conversion unit is adjusted until the target value (W) obtained from the storage unit is obtained, and then the gain is obtained from the storage unit. A gain adjusting means for reducing the ratio (G / W),
A scanner apparatus that reads the form using an amplifier circuit of the photoelectric conversion unit adjusted by the gain adjusting means. In an automatic gain adjustment method for adjusting the gain of an amplifier circuit of a photoelectric conversion unit using a gray reference plate in a scanner device for reading an image of a form,
Target value (W) of photoelectric conversion output when scanning a white reference plate temporarily mounted, and target value (G) of photoelectric conversion output when scanning the gray reference plate fixedly attached to the scanner device Is stored in the storage unit,
Before reading the form, scan the gray reference plate, adjust the gain of the amplification circuit of the photoelectric conversion unit until the target value (W) obtained from the storage unit,
A gain obtained by reducing the gain of the amplifier circuit by a ratio (G / W) between the target value (W) and the target value (G) obtained from the storage unit is obtained. Gain adjustment method. In an automatic gain adjustment method for adjusting the gain of an amplifier circuit of a photoelectric conversion unit using a gray reference plate in a scanner device for reading an image of a form,
Target value (W) of photoelectric conversion output when scanning a white reference plate that is temporarily mounted, and photoelectric conversion when scanning the gray reference plate fixedly attached to the target value (W) and the scanner device The ratio (G / W) obtained from the output target value (G) is acquired and stored in the storage unit,
Scan the gray reference plate before reading the form, and adjust the gain of the amplification circuit of the photoelectric conversion unit until the target value (W) obtained from the storage unit,
An automatic gain adjustment method for a photoelectric conversion output, wherein a gain obtained by reducing the gain of the amplifier circuit by the ratio (G / W) obtained from the storage unit is obtained.

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