JPH03171966A - Image reader - Google Patents

Abstract

PURPOSE:To amplify a read signal for reading a white reference surface by an optimal amplification factor and to decrease and error caused at the time of correction by setting an amplification factor of an amplifying means to a first (a second) amplification factors, when read signals of a first (a second) white reference surfaces are outputted. CONSTITUTION:In the case of amplifying a read signal of a first white reference surface 141 extended in the main scanning direction, an amplification factor of an amplifying means 22 is switched, for instance, to a first amplification factor being relatively large. On the other hand, in the case a read signal of a second white reference surface 142 extended in the sub-operating direction from a reading means 20 and a signal of document are outputted, the amplification factor of the amplifying means 22 for amplifying them is switched, for instance, to a second amplification factor being relatively small. In such a way, the read signal is amplified by an optimal amplification factor corresponding to the kind of a read output.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a document reading device, and particularly to a document reading device suitable for digital copying machines, facsimile machines, etc. that digitally process read data.

Prior Art> In a conventional digital copying machine, as shown in FIG. Before illumination scanning, illuminate with lamp 4 and set white reference surface 2.
The reflected light 5 is transmitted to a self-scanning type reading sensor 6 such as a line COD.
There are known devices that perform so-called bit correction that corrects the shading of the lamp 4 or corrects the sensitivity of a plurality of reading elements constituting the reading sensor 6.

Furthermore, as shown in FIG. 6, in Japanese Patent Application Laid-Open No. 63-117556, a white reference surface 7 extending in the sub-scanning direction is arranged beside the contact glass 1, and the reading sensor 6 performs self-scanning (main-scanning). ), an apparatus has been disclosed in which the read output of the document 3 is corrected for each main scan or for each plurality of main scans based on the read output of the white reference surface 7. According to this device, it is possible to correct the adverse effects caused by ripples that occur when a halogen lamp or fluorescent lamp that is lit by a commercial AC power source is used as the lamp 4.

BACKGROUND OF THE INVENTION By the way, in the former device introduced in the prior art section, the read output when the read sensor 6 reads the white reference surface 2 is appropriately amplified by an amplifier, and shading correction and bit correction are performed based on the output. is being done.

Further, in the latter device, the reading sensor 6 uses the white reference i1i.
The amplification factor of the composter is adjusted based on the read signal when i7 is read, and ribble correction is performed to prevent unevenness in the read signal from occurring.

Therefore, by combining the above-mentioned former and latter devices and adjusting the amplification factor of the amplifier to an appropriate value, it is possible to eliminate both of the corrections performed by the former and latter devices, that is, shedding correction, bit correction, and ribble correction. The applicant came up with the idea that it would be possible to create a document reading device that could do all of the above and would not cause density unevenness.

However, the amount of light reflected from the white background of the document may be greater than the amount of light reflected from the white reference surface 2.7.

Considering such a case, it has been found that when the former and the latter are combined, it is impossible to adjust the amplification factor of the amplifier so as to satisfy both conditions.

Let me explain more specifically.

The white reference surface 2.7 is usually composed of a white sheet made of vinyl chloride or the like, a white-painted metal plate, or the like. On the other hand, the paper quality of manuscripts is diverse, and some of them have a light reflection If more than a white reference surface.
There are also papers with good rates. When reading images recorded on such paper with good light reflectance, the following problems arise.

First, when the white reference surface 2 shown in FIG. 5 is illuminated by the lamp 4 and the reflected light reflected from the white reference surface 2 is read by main scanning of the reading sensor 6, the maximum value of the read signal The amplification factor is set to achieve the maximum output of the amplifier.

Next, the lamp 4 is moved in the sub-scanning direction, and the reflected light from the white reference surface 7 and the original 3 shown in FIG. 6 is read by the main scanning of the reading sensor 6, and is amplified by an amplifier.
As mentioned above, if the amplification factor is set so that the maximum reading value of the white reference surface becomes the maximum output of the amplifier, the white background reading signal of the original 3, which has a better light reflectance than the white reference surface 7, will be completely It may not be possible to amplify it, or it may become distorted.

Therefore, in this case, the amplification factor must be set relatively small so that the read signal when the reading sensor 6 reads the reflected light reflected from the white background of the document becomes the maximum output of the j-spanning device. I didn't get it.

However, if the amplification factor is set relatively small, the amplified output of the read signal when reading the white reference surface 2 will be at a relatively low level, and the dynamic range of the signal will be small, so the shading correction will be performed based on this. etc., errors are likely to occur.

Of course, in order to eliminate this drawback, two dedicated amplifiers may be provided, but this would make the overall structure of the device expensive and large.

The present invention has been made against the above background, and provides an image reading system that eliminates the above-mentioned drawbacks and can optimally amplify the reading output of a white reference plane and a document using a single amplifier. The purpose is to provide equipment.

[Structure of the Invention] The present invention provides a placing means for placing an original at a predetermined original placing position, a placing means that is provided close to the original placing position of the placing means, and is arranged in a predetermined main scanning direction. a first white reference surface that extends, a second white reference surface that extends in a sub-scanning direction orthogonal to the main scanning direction, a reading means that reads the mounting means in the main scanning direction by self-scanning, and a combination of the reading means and the mounting means. a driving means for moving the relative positional relationship at a constant speed in the sub-scanning direction; an amplifying means for amplifying the read signal of the reading means;
Also, when the reading signal of the first white reference surface is output from the reading means, the amplification factor of the amplification means is set to the first amplification factor, and the amplification factor of the amplification means is set to the second amplification factor.
The image reading apparatus is characterized in that it includes an amplification factor switching means that sets the amplification factor of the amplification means to a second amplification factor when a reading signal of a white reference plane is output.

Further, the present invention is characterized in that, in the image reading device, the first amplification factor switched by the amplification factor switching means is relatively large, and the second amplification factor is relatively small.

Effect> According to the present invention, when amplifying the read signal of the first white reference surface extending in the main scanning direction, the amplification factor of the amplification means is switched to, for example, a relatively large first amplification factor.

On the other hand, when the reading means outputs a reading signal of the second white reference surface extending in the sub-scanning direction and a reading signal of the document, the amplification factor of the amplifying means for converting the signals is, for example, relatively small. 2 amplification factor.

Therefore, the read signal is amplified with the optimum amplification factor depending on the type of read output.

<Embodiment> FIG. 1 is an illustrative diagram showing a schematic configuration of an image reading device according to an embodiment of the present invention.

In the figure, reference numeral 11 denotes a contact glass as a document placement means, and a placement position for placing the document is determined in advance. In this embodiment, the document 3 is placed on the leading edge 12 and the side edge 13 so that two adjacent sides of the document 3 are aligned.

A flat L-shaped white reference surface 14 is provided on the lower surface side of the contact glass 11 along the tip edge 12 and side edge edge 13 of the contact lath 11 . This white reference surface 1
4 includes a first white reference surface 141 extending in the main scanning direction and a second white reference surface 142 extending in the sub scanning direction. The first white reference surface 141 and the second white reference surface 142 are made of the same material (for example, white vinyl chloride sheet). A contact lamp 15 is provided on the lower surface side of the lath 11. The lamp 15 is formed of, for example, a halogen lamp or a fluorescent lamp, and has a longitudinal cylindrical shape extending in the main scanning direction. This lamp l5 illuminates the contact glass 11 and the white reference surface 14 from end to end in the main scanning direction. When the original 3 on the white reference surface 14 and the contact glass 11 is illuminated by the lamp 15, the reflected light is guided by the mirrors 16, 17, and 18, and is applied to the reading sensor 20 via the lens 19. The reading sensor 20 is a self-scanning line sensor that is elongated in the main scanning direction and is capable of reading one line or several lines. For example, several thousand light receiving elements are arranged in one line of the reading sensor 20, and the reflected light given to each light receiving element is photoelectrically converted and reading is performed by self-scanning.

The lamp 15 and the mirror 16 are moved at a constant speed in the sub-scanning direction, and illuminate the second white reference surface 142 and the original 3 in the sub-scanning direction. As the lamp 15 and mirror 16 move, the mirrors 17 and 18 move to the lamp 15 and mirror 1.
It follows and moves at half the speed of 6. As a result, the reading sensor 20 reads the image in the main scanning direction by self-scanning, and is sequentially moved in the sub-scanning direction, so that the document image on the contact glass 11 that is spread two-dimensionally can be read.

The output of the reading sensor 20 is given to a signal processing circuit 21 . The signal processing/processing circuit 21 includes an amplifying circuit 22 for amplifying the output of the reading sensor 20 and an A/D converter 23 for converting an analog signal multiplied by 1 into a digital signal.

The feature of this embodiment is that the reading sensor 20 outputs the reading signal of the first white reference surface 141 and the reading signal of the second white reference surface 142 and the original 3, as described below. The amplification factor of the amplification circuit 22 can be switched at .

Next, a detailed explanation will be provided. FIG. 2 shows a circuit configuration of an amplifier circuit 22 for amplifying the output of the reading sensor 20 and an A/D converter 23 for converting the amplified analog signal into a digital signal according to an embodiment of the present invention. It is a diagram.

The video signal V output from the reading sensor 20 is supplied to the amplifier 24 and amplified, and the output of the amplifier 24 is output from the A/D.
A video signal of the converter 23 is given to the human power terminal V1,
It is converted into a digital signal within the A/D converter 23. The output of the amplifier 24 is also applied to a hold circuit 26 via a switch 25, and the output of the hold circuit 26 is applied to a gain control circuit 27. The power control circuit 27 controls the first reference voltage v,11 or the second reference voltage v,11.
The gain of the amplifier 24 is adjusted by comparing the reference voltage V v e I 2 and the hold voltage. First reference voltage V
Switching between +e,1 and the second reference voltage v,12 is performed by a switch 28.

In this circuit, the switch 25 is in a conductive state while the reading sensor 20 is outputting a reading signal of the second white reference surface 142, and is in a non-conductive state at other times. Which reading signal is output by the reading sensor 20?
For example, since it can be detected by counting the reference clock that serves as the operating reference for the reading sensor 20, the switch 25 may be switched based on that.

On the other hand, when the reading sensor 20 is outputting a reading signal of the first white reference surface 141, the switch 28 operates to apply the first reference voltages ■, . ．． side and the reading sensor 20 is outputting the reading signal of the second white reference surface 142 and the original 3, the second reference voltage V, . Switched to the 12 side.

Therefore, when the reading sensor 20 outputs the video signal V read by the second white reference plane 142 and the first white reference plane 141, the video signal V1 is equal to the first reference voltage V r * l I It is amplified by an amplifier 24 whose gain is adjusted based on. In this case, the switch 25 is turned on only when the read signal of the white reference surface 142 is output from the read sensor 20, and the voltage is held in the hold circuit 26 and applied to the gain control circuit 27. Here, the first reference voltages V, . ．． As shown by the solid line in Figure 3A, the maximum value is A/
Reference voltage V. of D converter 23 ．． The gain of amplifier 24 is adjusted so that it is equal to .

In addition, in FIG. 3A, the broken line is the video signal V1 before amplification.

On the other hand, when the reading sensor 20 reads the second white reference surface 142 and the opposite light of the original 3 and outputs the read video signal V2, the switch 28 is switched and the reference voltage of the gain control circuit 27 is set to the second reference level. The voltage is set to V,12. Also in this case, the switch 25 is turned on only when the reading sensor 20 outputs a reading signal of the second white reference surface 142.

Therefore, as shown in FIG. 3B, the second white reference surface 142
The read signal of document 3 is compared with a second reference voltage v,12.
The gain of the amplifier 24 is adjusted so that the maximum value of the white background read signal matches the reference voltage V t e l of the A/D converter 23 .

Note that in FIG. 3B, the broken line is the video signal V2 before being input to the amplifier 24.

In the above case, the first reference voltages v, . . is set at a relatively high potential compared to the second reference voltage V,12. This is done in consideration of the fact that the white background of the original 3 may have better light reflectance than the white reference surface 14.

Note that if the read video signal of the first white reference surface 141 is
If the gain of the amplifier 24 is adjusted based on the second reference voltage Vt*t2 when amplifying the amplified video signal V1. is an output as shown by the single point feed line in FIG. 3A, and its maximum value is the reference voltage V7. of the A/D converter 23. , it will be lower than . Therefore, when the digital signal is converted into a digital signal by the A/D converter 23 and used for shading correction or bit correction, the dynamic range of the data becomes small, which tends to cause errors in the correction contents. This embodiment does not have such drawbacks.

Furthermore, when amplifying the read video signal V2 of the second white reference surface 142 and the document 3, if the gain of the amplifier 24 is adjusted based on the first reference voltage Vre++, then the amplified video signal V2 ．． is shown by the dashed line in FIG. 3B, and the reading output of the white background of the original 3 is the reference voltage V, . , and accurate A/D conversion cannot be performed.

FIG. 4 shows a reading sensor 20 according to another embodiment of the invention.
FIG. 2 is a circuit diagram of an amplifier circuit for amplifying the output of the circuit and a circuit for performing A/D conversion.

In the circuit shown in FIG. 2 described above, the video signal V is amplified by an appropriate amplification factor before being applied to the A/D converter 23, and the video signal V. The amplified video signal V. The maximum value of is the reference voltage V r * of the A/D converter 23
It was made to match I.

On the other hand, in the circuit shown in Section 4, the video signal V output from the reading sensor 20 is directly transmitted without being amplified.
The reference voltage V of the A/D converter 23 is supplied to the human power terminal V of the A/D converter 23.
．． , can be switched in proportion to the constant density signal value of the video signal V.

In other words, if you look at it from a different perspective, the circuit of FIG. 2 has the reference voltages V, . In contrast, in the circuit shown in FIG. /D converter 23
Reference voltage of ■,. , is arranged in one row.

Specifically, with reference to FIG.
While the read signal is being output, the switch 35 is turned on and the video signal V is held in the hold circuit 31.
The signal is applied to the gain control circuit 32. The gain control circuit 32 is provided with a switch 33.
The resistance value for gain adjustment is switched to the first resistance R or the second resistance R2. The switching of the switch 33 is the second
Similar to the switching of the switch 28 explained in the figure, the reading sensor 20 is connected to the second white reference surface 142 and the first white reference surface 1.
When the reading sensor 20 is outputting the reading signal of 41, switch to the first resistor R1 side, and when the reading sensor 20 outputs the reading signal of the second white reference surface 142 and the original 33, switch to the second resistor R2 side. It will be done.

The output of the gain control circuit 32 is the A/D
The reference voltage is applied to the human power terminal v31 of the converter 23.

According to the circuit shown in FIG. 4, when the reading sensor 20 outputs the reading signal of the second white reference surface 142 and the original 3, the output of the hold circuit 31 is caused by the ripple of the lamp 15, etc. for each line, for example. Even if there is a slight change, the output of the gain control circuit 32 is adjusted accordingly, so there is an advantage that the signal conversion in the A/D converter 23 is not adversely affected by ripples or the like.

Effects of the Invention> Since the present invention is structured as described above, the read signal read from the white reference plane can be multiplied by 1 with an optimum amplification factor for shading correction and bit correction, and the read signal A wide dynamic range can be obtained, and errors during correction can be reduced.

Furthermore, even if the light reflectance of the white background of the document is higher than that of the white base surface, the document reading signal can be amplified with the optimal amplification factor, and the subsequent circuit can accurately and noise-free document images. Less processing can be done.

Further, according to the present invention, even if there is aging or characteristic deterioration of the optical system included in the reading device, it is possible to correct the deterioration over time and to output a read signal accurately.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of a document reading device according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing the main part configuration of an embodiment of the present invention. FIGS. 3A and 3B are waveform diagrams representing amplification states of signals read by an embodiment of the present invention. FIG. 4 is a circuit diagram showing the main structure of a reading device according to another embodiment of the present invention. FIG. 5 and FIG. 6 are illustrative views for explaining the prior art related to this invention. In the figure, 3...Original, 11...Contact glass as document mounting means, 14...White reference surface, 14l
... first white reference surface, 142 ... second white reference surface,
15...Lamp, 20...Reading sensor, 21...
Signal processing circuit, 22... Amplification circuit, 23... A/D
Converter 27 shows a gain control circuit.

Claims (1)

[Scope of Claims] 1. A loading means with a determined document placement position for placing the document; a white reference surface and a second white reference surface extending in the sub-scanning direction perpendicular to the main scanning direction; a reading means that reads the mounting means in the main scanning direction by self-scanning; and a relative relationship between the reading means and the mounting means. a driving means for moving the positional relationship at a constant speed in the sub-scanning direction; an amplifying means for amplifying the read signal of the reading means; An image reading device comprising: an amplification factor switching device that sets the amplification factor to a first amplification factor and sets the amplification factor of the amplification device to a second amplification factor when the read signal of the second white reference surface is output. . 2. The image reading device according to claim 1, wherein the first amplification factor switched by the amplification factor switching means is relatively large, and the second amplification factor is relatively small.