JPH04373259A - Picture reader - Google Patents

Abstract

PURPOSE:To obtain a read data in which picture quality is constant regardless of the quantity fluctuation of light of a light source without provision of an automatic adjustment means to keep the quantity of light of the light source constant. CONSTITUTION:An image sensor 2 receives a reflecting light from an original 4 and part of read elements receive a reflecting light from a reference white level plate 3 and outputs an electric signal in response to the received quantity of light. A subtractor circuit 6 subtracts an output of the image sensor 6 when a lighting lamp 5 goes off from an output signal of the image sensor 2. Thus, the relative relation between the output signal of the image sensor 2 with respect to the reference white level plate 3 subjected to subtraction processing at the output side of the subtractor circuit 6 and the other part of the output signal of the subtractor circuit 6 is constant regardless of the quantity fluctuation of light of the lighting lamp 5 and the digital value as a final output is constant regardless of the quantity fluctuation of light.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an image reading device that converts an image of a document into an electrical signal and outputs the electrical signal. The present invention relates to an image reading device that can always output stable image signals without being affected by changes in the amount of light.

0002

[Prior Art] Conventionally, this type of image reading device has
For example, as shown in Japanese Unexamined Patent Publication No. 2-16861, a reference plate having a predetermined reflectance is provided, and an output signal of an image sensor obtained when this reference plate is irradiated with a light source; Compare the output value of the image sensor with a predetermined target value, and if the output value of the image sensor is less than the target value, the light intensity of the light source is returned to a predetermined level to prevent image quality from deteriorating due to changes in the light intensity of the light source. It is already known that
It is well known.

0003

[Problems to be Solved by the Invention] However, in the conventional device described above, since the target value with which the output value of the image sensor is compared is fixed, the output value of the image sensor may fall below the target value. Until now, even if the light intensity of the light source decreased, the light intensity of the light source was not adjusted, so during that time, a scanned image with degraded image quality would be output.
Not only is there the problem of not being able to respond immediately to changes in the light intensity of the light source, but furthermore, the above configuration naturally requires hardware to adjust the light intensity of the light source. Since the hardware generally requires a relatively large amount of mounting space, there has also been a problem in that it runs counter to recent market demands for smaller devices. The present invention has been made in view of the above circumstances, and provides an image reading device that does not require an adjustment means for automatically adjusting the light intensity of a light source, has a simple configuration, and can always obtain constant image quality. The purpose is to provide the following.

0004

[Means for Solving the Problems] An image reading apparatus according to the present invention includes at least an irradiation means for irradiating a document, and an image reading means for converting reflected light from the document into an electrical signal. Dark data storage means that stores an output signal of the image reading means when the irradiation operation of the irradiation means is stopped, and a bright data storage means that stores the output signal of the image reading means when the irradiation means irradiates a blank document. - a white reference white plate irradiated by the irradiation means and arranged so that the reflected light reaches a predetermined reading element constituting the image storage means; and an output of the image reading means; A subtraction means for subtracting the output from the dark data storage means, and a subtraction means for subtracting the dark data from the output signal of the image reading means for the reflected light from the reference white plate among the output signals of the subtraction means. The output signal corresponding to the result of subtracting the dark data stored in the data storage means is used as a reference value for analog-to-digital conversion, and other signals excluding the part that becomes the reference value among the output signals of the subtraction means are an analog-to-digital converter for converting analog to digital; and an analog-to-digital converter for outputting a maximum digital value when the output value of the analog-to-digital converter is equal to the data stored in the clear data storage means; A correction means for correcting the output value of the digital conversion means.

[0005]

[Operation] Therefore, the output signal of the image reading means is composed of a signal for the reflected light from the reference white plate and a signal for the reflected light from the original, and these are processed by the subtracting means.
At the same time, the output signal (dark signal) component of the image reading means when the image reading means receives light corresponding to the amount of light reflected from the black plate is removed. Then, the standard white play
If we look at the signal for the reflected light from the reference white plate and the signal for the reflected light from the original at the output side of the subtraction means, we can see the relative relationship between them, that is, the signal for the reflected light from the reference white plate and the signal for the reflected light from the original. The relative ratio to the irradiation means remains constant even if the output light amount of the irradiation means fluctuates. Therefore, in the analog-to-digital conversion means, among the output signals of the subtraction means, the signal corresponding to the reflected light from the reference white plate mentioned above is used as the reference signal for analog-to-digital conversion, that is, the maximum of the input signals. Among the output signals of the subtraction means, the signal corresponding to the reflected light from the original is converted into an analog-to-digital value, so this analog-to-digital conversion output is also approximately constant regardless of fluctuations in the light amount of the irradiation means. It is a value. Therefore, unlike the conventional art, there is no need for a means to automatically adjust the light intensity of the light source, and the final image quality is always constant even if the light intensity of the light source changes.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image reading apparatus according to the present invention will be described below with reference to FIG. Here, FIG. 1 is a configuration diagram showing a schematic configuration of main parts in an embodiment of an image reading apparatus according to the present invention.

First, in this embodiment, the image reading device is provided with, for example, an image sensor 2 as image reading means on the lower surface of the platen glass 1 (lower side of the paper in FIG. 1). This image sensor 2 is a known one having a so-called one-dimensional array configuration in which a plurality of photoelectric conversion elements (not shown) are arranged in the main scanning direction, and in this embodiment, its longitudinal axis The direction is arranged along the left-right direction on the paper surface of FIG. Note that a detailed explanation of the image sensor 2 will be omitted here. Of the plurality of photoelectric conversion elements of this image sensor 2, several of them are adapted to receive only the reflected light from a reference white plate 3, which will be described below. That is, a white reference plate 3 is provided at a predetermined position on the plan glass 1. The reference white plate 3 of this embodiment is formed in a rectangular shape, and is arranged so that its longitudinal axis direction runs along the front and back directions of the paper surface of FIG. On the other hand, the above-mentioned image sensor 2 and the irradiation lamp 5 as an irradiation means for irradiating the original 4 are both disposed in a moving mechanism (not shown) having a publicly known configuration (not shown). In the example, the document 4 is scanned by moving in the front and back directions of the paper surface of FIG. 1 (hereinafter, this scanning is referred to as "sub-scanning"). Therefore, some of the photoelectric conversion elements of the image sensor 2 always receive the reflected light from the reference white plate 3 during sub-scanning.

The output of the image sensor 2 is connected to a subtraction circuit 6 as a subtraction means, and this subtraction circuit 6 is connected to a digital/analog converter 7 ("D/A" in FIG. 1).
A" and hereinafter referred to as a "D/A converter." ) is connected, and a storage signal of a dark data memory 8 serving as a dark data storage means is inputted via this D/A converter 7. Here, the dark data memory 8
As a specific example, a so-called ROM, which is a well-known integrated circuit as a read-only memory, is suitable. Further, the dark data memory 8 stores the output value of the image sensor 2 measured in advance (hereinafter referred to as "dark data") when the above-mentioned irradiation lamp 5 is turned off as digital data. remembered. In addition, as dark data,
It is sufficient if it is equivalent to the measurement data as described above, and it is not necessary to be limited to this type of data. For example, when a black plate is irradiated with the irradiation lamp 5, the image sensor 2 receives the reflected light from the black plate.
It may also be an output signal of the digital sensor 2. The subtraction circuit 6 then outputs the result of subtracting the dark data converted into analog by the D/A converter 7 from the analog output signal of the image sensor 2. Among these subtracted outputs, a signal is obtained by subtracting the output of the image sensor 2 for the reflected light from the reference white plate 3 (hereinafter referred to as "reference white plate read bit output"). is input to the hold circuit 9, and while holding the signal value for a predetermined period of time (details will be described later), the signal is input to the analog-to-digital converter 10.
It is now output to .

An analog-to-digital converter 10 (“A/D” in FIG. 1) as an analog-to-digital conversion means
" and hereinafter referred to as "A/D converter." )
1 converts the analog output signal of the above-mentioned subtraction circuit 6 into a digital signal, and specifically, for example, a well-known so-called linear IC or the like is used. The output signal of the subtraction circuit 6 inputted to this A/D converter 10 as a signal to be converted is all the remaining signals except for the signal inputted to the above-mentioned hold circuit 9, that is, the reflected light from the original 4. This is the result of subtraction processing performed on the output of the image sensor 2 (hereinafter referred to as "image reading bit output"). On the other hand, the output signal of the hold circuit 9 is transmitted to the A/D converter 10.
It is input as a voltage signal (hereinafter referred to as "conversion reference voltage signal") that becomes a reference for conversion in . That is, the A/D converter 10 converts the value of the conversion reference voltage signal into the A/D converter 10.
This function is assigned to the maximum digital value that the D converter 10 can output, and converts the input signal into a digital signal using this value as a reference. This is not unique to the A/D converter 10 of this embodiment. And A/
The output of the D converter 10 is sent to a correction circuit 11 as a correction means.
It is connected to the.

A bright data memory 12 as bright data storage means is connected to the correction circuit 11.
Based on the signal input from the data memory 12, the output signal of the A/D converter 10 is subjected to correction as described later, and then outputted as a reading signal of the original image. Here, the bright data memory 12 stores the results of pre-measurement of the output value of the image sensor 2 when the image sensor 2 reads a blank original as digital data, and its electrical configuration is as follows. It is basically the same as the dark data memory 8 described above. The above-described subtraction circuit 6, D/A converter 7, dark data memory 8, hold circuit 9, A/D converter 10, correction circuit 11, and bright data memory 12 are all connected to the microprocessor 13. The operating timing is determined by the microprocessor (hereinafter referred to as "MPU")1.
It is controlled by 3. Furthermore, MPU1
Since 3 itself is already well known, detailed explanation thereof will be omitted here.

Next, the operation of the present apparatus will be explained with reference to a control flowchart of the present apparatus by the MPU 13 shown in FIG. The control flow in FIG. 2 shows a series of operations of this apparatus for the original image in the main scanning direction. Basically, even if the irradiation lamp 5 and the image sensor 2 move in the sub-scanning direction, Each time, a series of operations based on the control flowchart shown in FIG. 2 is repeated. First, when the original 4 is placed on the platen glass 1 and a reading start switch (not shown) is turned on, the irradiation lamp 5 is turned on.
lights up and the document 4 is illuminated. When the reflected light from the document 4 along the main scanning direction is received by the image sensor 2, the image sensor 2 receives a control signal from the MPU 13 and generates an analog electrical signal corresponding to the detected reflected light. is output to the subtraction circuit 6 (see FIG. 2a). By the way, in FIG. 3(A), when the original 4 is blank, the waveform of the signal outputted by the image sensor 2 (corresponding to the bright data mentioned above) is shown as a solid line, and the irradiation lamp 5 is turned off. The waveforms of the output of the image sensor 2 (corresponding to the dark data mentioned above) obtained when the image sensor 2 is in use are shown by two-dot chain lines, respectively. In FIG. 3(A), the horizontal axis corresponds to the positions of the photoelectric conversion elements arranged along the longitudinal axis direction of the image sensor 2. In particular, the left side from the dotted line shown in the vertical axis direction is
This corresponds to the position of the photoelectric conversion element that receives only the reflected light from the reference white plate 3. Further, the vertical axis indicates the magnitude of the output signal.

Following the signal output of the image sensor 2, the MP
The dark data memory 8 outputs dark data based on the control signal from U13, and the D/A converter 7 converts this digital dark data into an analog signal and outputs it to the subtraction circuit 6. (see Figure 2b). Then, the subtraction circuit 6 subtracts the dark data from the output signal of the image sensor 2 in analog form and outputs the result (see FIG. 2c). In FIG. 3B, the signal waveform obtained as a result of subtraction when the original 4 is white is shown by a solid line. Now, if we pay attention to the dark output of the image sensor 2 shown by the two-dot chain line in FIG. Then, the signal from the dark data memory 8 that is input to the subtraction circuit 6 via the D/A converter 7 and the dark output actually output from the image sensor 2 are basically the same. Therefore, after passing through the subtraction circuit 6, the signals are canceled out and reach the zero level, that is, coincide with the horizontal axis in FIG. 3(B). Furthermore, among the bright outputs,
The reference white plate read bit output includes a dark output that fluctuates somewhat when input to the subtraction circuit 6.
On the output side of the subtraction circuit 6, this dark output component is removed, so the output waveform becomes approximately flat as shown in FIG. 3(B). Further, the portion corresponding to the reference white plate read bit output on the output side of the subtraction circuit 6 should serve as a reference value as the output value of the image sensor 2 for the white portion of the document 4. In other words, the image reading bit output value on the output side of the subtraction circuit 6 for the white portion of the original document 4 should originally be the same as the reference white plate reading bit output value.

However, in reality, as shown in FIG. 3(B), the output value may be lower than the reference white plate read bit output value (the level indicated by the dotted line in the horizontal axis direction in FIG. 3(B)). The main causes of such a decrease in the output value include a decrease in the amount of light from the irradiation lamp 5 and a lower degree of whiteness of the white portion of the document 4 than that of the reference white plate 3. Incidentally, such a decrease in the image reading bit output on the output side of the subtraction circuit 6 is corrected by the correction circuit 11 as described later. Next, after the subtraction circuit 6 outputs the subtraction result, the portion of the output signal that has been subjected to the subtraction process on the reference white plate reading bit output described above is input to the hold circuit 9, and is input to the subtraction circuit 9. Of the 6 output signals, the image reading bit output is A.
While being digitally converted by the A/D converter 10, it is input to the A/D converter 10 as a conversion reference voltage (denoted as Vc in FIG. 1) while being held (see FIG. 2d). Then, in the A/D converter 10, using the voltage input from the hold circuit 9 as a conversion reference voltage, a signal corresponding to the image reading bit output signal among the output signals of the subtraction circuit 6 is converted into a digital signal ( (see Figure 2d).

Here, among the outputs of the subtraction circuit 6, a signal corresponding to the part obtained by subtracting the reference white plate reading bit output is used as the conversion reference voltage, and among the outputs of the subtraction circuit 6, the signal corresponding to the part of the image reading bit output The physical meaning of digitally converting the output portion subjected to subtraction processing will be explained with reference to FIG. 4. The vertical axis in FIG. 4 represents the voltage output of the subtraction circuit 6, and the horizontal axis represents the longitudinal axis direction of the image sensor 2, that is, the position of the photoelectric conversion element. First, when the brightness of a certain part of the document 4 in the main scanning direction is smaller than that of the reference white plate 3, the signal corresponding to the image reading bit output at the output side of the subtraction circuit 6 of that part is naturally However, it will be lower than the conversion reference voltage. Suppose that the conversion reference voltage at a certain point in time is Ya, and the signal corresponding to the image reading bit output on the output side of the subtraction circuit 6 (signal obtained by subtracting dark data from the image reading bit output) is Xa. Generally, Ya is expressed as Xa multiplied by a proportionality coefficient K (see FIG. 4(A)). This is because the output of the image sensor 2 is approximately proportional to the brightness of the original 4 or the reference white plate 3.

If the light intensity of the irradiation lamp 5 decreases and the conversion reference voltage changes to Yb and the image reading bit output on the output side of the subtraction circuit 6 changes to Xb, in this case as well, Yb is expressed as Xb multiplied by a proportionality coefficient K before the light amount of the irradiation lamp 5 changes. That is, the relative relationship between the conversion reference voltage and the image reading bit output on the output side of the subtraction circuit 6 is kept constant. The reason why the relative relationship between the two is kept constant in this way is that by subtracting the dark output from the output of the image sensor 2 in the subtraction circuit 6, the reference for both always matches zero potential. be. Since the relative relationship between the conversion reference voltage and the image reading bit output on the output side of the subtraction circuit is constant, the output of the A/D converter 10 is also constant regardless of changes in the light amount of the irradiation lamp 5. A constant digital signal value will be obtained. For example, A/
When the D converter 10 has a 4-bit output, the maximum value of the digital output is "1111", but when the input signal is equal to the conversion reference voltage, the absolute value of the conversion reference voltage and the input signal are different. However, if the relative relationship between the two is constant as described above, the digital output value will always be "111".
1”. The fact that the output of the A/D converter 10 is constant even when the light intensity of the irradiation lamp 5 changes in this way means that there is no deterioration in image quality, that is, the output signal of this device is Based on this, it means that when a so-called hard copy of the original document 4 is made, its image quality remains the same before and after changes in the light amount of the irradiation lamp 5.

After the above-mentioned A/D conversion is completed, the output signal is input to the correction circuit 11, and the data correction as described below is performed (see FIG. 2e). First, in the correction circuit 11, A
A digital signal is input from the /D converter 10, and then based on the control signal of the MPU 13, the bright data memory 12
Bright data is read from. And A/D converter 1
The signal input from 0 is divided by the bright data to find the ratio of the output value of the A/D converter 10 to the bright data, and the value obtained by multiplying it by a predetermined calculation coefficient is the final value of the original image. Output as read data. Here, the above-mentioned calculation coefficient is the maximum value of the digital output of the A/D converter 10 in this embodiment. More specifically, for example, A/D
If the digital output of the converter 10 is 4 bits, the maximum value of this 4-bit digital signal is "111".
1" is used as the calculation coefficient. Therefore, when the image reading bit output value on the output side of the subtraction circuit 6 matches the bright data, the image reading bit output value on the output side of the subtraction circuit 6 for the white part of the original 4 is the same as that of the correction circuit 11.
The data is corrected to "1111" and output to an external device as output data of this device. Figure 3(C)
As mentioned above, when the original 4 is white, there is some variation in the output value of the A/D converter 10, but this variation has been eliminated by correction in the correction circuit 11. has been done.

By the correction in the correction circuit 11 described above,
The data processing in the main scanning direction of the document 4 is completed, and the M
The PU 13 once returns to the main control flow (not shown).
After performing the processing necessary to read the next line of the document 4, such as moving the image sensor 2 in the sub-scanning direction, the series of processing described above (Fig. 2a to f) is performed.
will be repeated again. In this embodiment, the correction circuit 11 is constructed as hardware, but it goes without saying that this part may be constructed using software using the MPU 13. For example, the A/D converter 10
The output signal and the data in the bright data memory 12 are sent to the MPU 1.
It is also possible to input data from the input port No. 3 (not shown) and perform correction calculations as explained in this embodiment using a program.

[0018]

According to the present invention, the image reading means receives light corresponding to the amount of light reflected from the black plate based on the output value of the image reading means with respect to the light reflected from the white reference plate. Output value (dark output value) of the image reading means when
is subtracted in analog form, and the subtraction result is used as the reference voltage for A/D conversion, and the previous dark output value is subtracted from the output value of the image reading means for the light reflected from the original, and the result is used as the read data for the original image. By performing A/D conversion, the reference voltage for A/D conversion (the result of analog subtraction of the dark output value from the output value of the image reading means for the reflected light from the white reference plate) and the A/D conversion The relative relationship with the converted signal (the output value of the image reading means minus the dark output value with respect to the light reflected from the document) remains constant even if the light amount of the irradiation means changes, so the light amount of the irradiation means This has the effect that a constant image quality can always be obtained without being affected by fluctuations in the amount of light from the irradiation means, without having to provide means for adjusting the amount of light to a constant value.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a schematic configuration of main parts in an embodiment of an image reading device according to the present invention.

2 is a control flowchart showing the flow of control of device operations by a microprocessor used in the image reading device shown in FIG. 1. FIG.

3 is a waveform diagram showing signal waveforms in each main part of the image reading device shown in FIG. 1. FIG.

4 is an explanatory diagram for explaining the relationship between the reference white plate reading bit output and the image reading bit output as seen from the output side of the subtraction circuit constituting the image reading device shown in FIG. 1. FIG.

[Explanation of symbols]

2... Image sensor, 3... Reference white plate, 5... Irradiation lamp, 6... Subtraction circuit, 7... Digital/analog converter, 8... Dark data memory, 9... Hold circuit, 10... Analog... Digital converter, 11... Correction circuit, 12... Dark data memory

Claims (1)

[Claims] 1. An image reading device comprising at least irradiation means for irradiating a document, and image reading means for converting light reflected from the document into an electrical signal, wherein the image reading means is configured to emit light reflected from a black plate. dark data storage means storing an output signal of the image reading means when light corresponding to an amount of light is received; and a dark data storage means storing an output signal of the image reading means when the irradiation means irradiates a blank document. bright data storage means; a white reference white plate irradiated by the irradiation means and arranged so that the reflected light reaches a predetermined reading element constituting the image storage means; subtraction means for subtracting the output from the output of the dark data storage means;
The subtraction means uses an output signal corresponding to the result of subtracting the dark data stored in the dark data storage means from the output signal of the image reading means with respect to the light reflected from the image as a reference value for analog-to-digital conversion. an analog-to-digital conversion means for converting from analog to digital a signal other than the part serving as the reference value among the output signals of the above-mentioned output signal; - correction means for correcting the output value of the analog-to-digital conversion means so as to output a maximum digital value when the digital value is equal to the digital value.