JPH11234471A - Correction device for uneven light quantity in image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct uneven light quantities in a subscanning direction without causing changes in an image processing speed and to generate digital video data with excellent gradation. SOLUTION: A linear CCD image sensor in a read section 1 of an image reader scans an object image in a main scanning and a subscanning directions to generate a video signal corresponding to the object image. A light quantity correction section 4 of the image reader is means to eliminate uneven light quantities independent of the object image from the video signal and corrects the uneven light quantities in a subscanning direction by adjusting a reference voltage that is an input to an A/D converter section 3 that converts an analog signal outputted from the linear CCD image sensor into a digital signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image reading apparatus, and more particularly, to a non-uniform light amount correcting apparatus for an image reading apparatus for correcting uneven light amount in a sub-scanning direction.

[0002]

2. Description of the Related Art At present, various image reading apparatuses using a one-dimensional CCD image sensor are provided. In this type of image reading apparatus, light from an illumination lamp is applied to a document surface to be read, and reflected light from the document surface is sensed by a one-dimensional CCD image sensor. Then, while moving the irradiation position (sub-scanning) on the document surface, the reading (main scanning) of the output signal (analog signal) of each CCD sensor constituting the one-dimensional CCD image sensor is performed for each sub-scanning position. Then, a video signal corresponding to one row of pixels crossing the document surface is generated.

In order to read an image on a document surface with high fidelity, it is necessary to read the image over the entire surface of the document under the same conditions. However, one-dimensional CCD
The characteristics of each CCD sensor constituting the image sensor do not always exactly match each other.
The loss of the optical system up to the CD image sensor is not uniform. For this reason, for example, even when a document whose entire surface is white is read by the image reading device, when a video signal obtained by reading is reproduced, an image having a gray level is reproduced instead of an image having a uniform white level. It will be. This is uneven light quantity. In order to obtain a video signal that is faithful to the document, it is necessary to remove this uneven light amount by some means.

In a conventional image reading apparatus, a white document is read in advance by a one-dimensional CCD image sensor, and correction data corresponding to uneven light amount is created and stored in a memory. Is one-dimensional C
At the stage after the analog video signal obtained from the CD image sensor is converted into the digital video signal by the A / D converter, the digital video signal is corrected by software processing using the correction data in the memory to remove the uneven light amount. Was applied to A technique for correcting unevenness in light amount based on such a principle is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-227428.

[0005]

However, the above-mentioned conventional technique for correcting unevenness in light quantity has the following problems. (1) In the prior art, in an area of a medium to be read in which the amount of irradiation light is small and the output level from the one-dimensional CCD image sensor is small, the input voltage range of the A / D conversion unit when performing A / D conversion Cannot be used effectively, and the digital video signal having already lost gradation
/ D conversion unit. Since software processing for removing uneven light amount is performed on such digital video signals having originally deteriorated gradation, a digital video signal having deteriorated gradation is obtained. (2) Since it is necessary to perform an operation for removing the uneven light amount for all of the read digital video signals, much image processing time is spent on software processing for correcting the uneven light amount.

SUMMARY OF THE INVENTION The present invention has been made in view of the circumstances described above, and in a technique for correcting unevenness in light amount in the sub-scanning direction in an image reading apparatus, digital video data with good gradation is obtained without a change in image processing speed. It is an object of the present invention to provide a device for correcting unevenness in light amount of an image reading device capable of generating the image.

[0007]

The invention according to claim 1 is
The one-dimensional CCD image sensor scans the image to be read in the main scanning direction and the sub-scanning direction, and is provided in an image reading device that generates a video signal corresponding to each pixel constituting the image to be read. The present invention relates to a light amount unevenness correction apparatus for performing correction for removing extraneous light amount unevenness from a video signal, wherein an upper reference voltage of an A / D converter for converting an analog signal output from the one-dimensional CCD image sensor into a digital signal is adjusted. The present invention provides a non-uniform light amount correcting apparatus for an image reading apparatus, comprising: a reference voltage adjusting unit that performs correction to remove the non-uniform light amount in the sub-scanning direction by adjusting the upper reference voltage.

According to a second aspect of the present invention, the reference voltage adjusting means scans the white medium by the one-dimensional CCD sensor and the memory for storing correction data used for correcting the light quantity unevenness. And the one-dimensional CC is scanned by scanning the white medium.
Correction data storage means for generating, for each sub-scanning position, a digital signal representing a peak level of a white level of a video signal obtained by main scanning for a video signal obtained from the D sensor, and storing the digital data in the memory as the correction data And D / A conversion for converting the correction data stored in the memory by the correction data storage means corresponding to the sub-scanning position into an analog voltage and supplying the analog voltage to the A / D converter as the upper reference voltage. And a unit for correcting unevenness in light amount of the image reading apparatus according to claim 1.

According to a third aspect of the present invention, the reference voltage adjusting means scans the white medium by the one-dimensional CCD sensor and the memory for storing correction data used for correcting the light quantity unevenness. And the one-dimensional CC is scanned by scanning the white medium.
Correction data storage means for generating, for each sub-scanning position, a digital signal representing a peak level of a white level of the video signal obtained by the main scanning for the video signal obtained from the D sensor, and storing the digital data in the memory as the correction data Amplifying circuit that amplifies a reference power supply voltage and supplies it as an upper reference voltage to the A / D conversion unit; and a correction data storage unit that stores the correction data stored in the memory in a sub-scanning position. 2. An apparatus according to claim 1, further comprising an amplification factor switching means for switching an amplification factor of said amplification circuit according to a corresponding one.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. A. First Embodiment FIG. 1 is a block diagram showing a configuration of an image reading apparatus to which a light amount unevenness correction apparatus according to a first embodiment of the present invention is applied. An image reading apparatus according to the present embodiment includes a reading unit 1 for inputting an image of a medium to be read, and a reading unit 1
An analog signal processing unit 2 for performing predetermined signal processing on the analog video signal output from the A / D converter, an A / D conversion unit 3 for converting the analog video signal output from the analog signal processing unit 2 into a digital video signal, A digital unit for supplying a digital video signal to an upper interface and controlling each unit in the image reading apparatus;
A light amount unevenness correction unit 4 that performs light amount unevenness correction by changing the input voltage range of the conversion unit 3 is provided. Among these components, the uneven light amount correction unit 4 is an embodiment of the uneven light amount correction device according to the present invention.

In this embodiment, the A / D converter 3 converts an analog video signal into a digital video signal. The light amount unevenness correcting unit 4 reads the upper reference voltage of the A / D converter 3 and reads the upper reference voltage of the target medium. The intensity is changed in accordance with the intensity unevenness of the light amount on the irradiation surface in the scanning direction. As a result, the digital video signal corrected for the uneven light amount is output from the A / D converter 3. Further, since the correction of the light quantity unevenness is performed only by hardware, no image processing time is spent.

FIG. 2 shows a specific configuration example of the present embodiment. 2, the reading unit 6 corresponds to the reading unit 1 in FIG. 1, and includes a light source 6a and a one-dimensional CCD image sensor 6b. The analog signal processing section 7 corresponds to the analog section 2 in FIG. 1, and the A / D conversion section 8 corresponds to the A / D conversion section 3 in FIG. One-dimensional CCD image sensor 6
The analog video signal output from b is subjected to predetermined signal processing by an analog signal processing unit 7, and the analog video signal that has undergone this signal processing is converted to a digital video signal by an A / D conversion unit 8.

The uneven light amount correcting section 9 corresponds to the uneven light amount correcting section 4 in FIG. 1, and includes a D / A converter 9a and a memory 9b. Here, the D / A converter 9
The analog output terminal “a” is connected to the input terminal of the upper reference voltage of the A / D converter 8 and the D / A converter 9
The digital input port a is connected to the data bus line of the memory 9b. This memory 9b stores correction data corresponding to the intensity unevenness of the light amount in the sub-scanning direction.

The digital circuit 10 and the CPU 11
This corresponds to the digital section 5 in FIG. here,
The digital circuit 10 is composed of digital components such as a memory and an LSI, and performs a data buffer, a generation of a control signal, a data transfer to an upper interface, and the like. The CPU 11 is a means for controlling the image reading device. One of the control contents performed by the CPU 11
One is control of main scanning and sub-scanning. And
The CPU 11 has a function of supplying an address for reading out the correction data corresponding to the current sub-scanning position to the memory 9b during the sub-scanning.

Next, the operation of this embodiment will be described with reference to the flowchart shown in FIG.

When the power of the image reading apparatus is turned on,
Under the control of the CPU 11, white level peak data used when correcting the intensity unevenness of the light amount by the reading unit 6, the analog signal processing unit 7, the A / D conversion unit 8, the digital circuit 10, and the light amount unevenness correction unit 9. Is performed (step 30).

The details are as follows. First, with the light source 6a turned on, pre-scanning (main scanning and sub-scanning) for reading a white image (for example, in the case of a copying machine, a white surface on the back side of a cover for holding a document) by the one-dimensional CCD image sensor 6b is performed. Then, an analog video signal corresponding to the white image is output from the one-dimensional CCD image sensor 6b. This analog video signal is subjected to signal processing by an analog signal
The data is converted into a digital video signal by the D conversion unit 8 and stored in a memory in the digital circuit 10.

From the digital video signal of the white image stored in the memory, the CPU 11 determines the peak level of the white level in the sub-scanning direction for each main scanning line or every several lines (even for several lines at once). The calculated data is stored in the memory 9b as correction data representing the intensity unevenness of the light amount in the sub-scanning direction.

Next, the actual reading operation will be described. When reading, first, the light source 6a of the reading unit 6 is turned on (step 31). As a result, the output light of the light source 6a is applied to the medium to be read. The reflected light from the medium to be read enters the one-dimensional CCD image sensor 6b, is subjected to photoelectric conversion by the one-dimensional CCD image sensor 6b, and outputs an analog video signal (step 32).

The analog video signal output from the one-dimensional CCD image sensor 6b is input to an analog signal processor 7. Then, the analog video signal is supplied to the A / D converter 8 through analog signal processing such as clamp, sample hold, and amplification performed in the analog signal processor 7 (step 33).

On the other hand, while the sub-scanning is performed, the CPU 11 supplies an address for reading out the correction data corresponding to the sub-scanning position to the memory 9b. As a result, the correction data corresponding to the current sub-scanning position is stored in the memory 9.
b, is converted into an analog voltage by the D / A converter 9a (step 34), and is supplied to the A / D converter 8 as an upper reference voltage. For this reason, the upper reference voltage of the A / D converter 8 changes according to the intensity unevenness of the light amount in the sub-scanning direction.

The A / D converter 8 performs A / D conversion of the analog video signal using the upper reference voltage (step 35). As a result, the digital video signal which does not include the intensity unevenness in the sub-scanning direction is A
Output from the / D converter 8.

The digital video signal corrected for the intensity unevenness of the light quantity is transferred to the upper interface via the digital circuit 10 (step 36). When the reading operation is completed, the light source 6a is turned off (step 37).

B. Second Embodiment Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 4 shows a light amount unevenness correction unit 1 according to this embodiment.
8 is a block diagram showing the configuration of FIG. This light amount unevenness correction device 18 is a modification of the light amount unevenness correction unit 9 shown in FIG.

In FIG. 2, the upper reference voltage of the A / D converter is generated by the D / A converter 9a. On the other hand, in FIG. 4, the D / A converter 9a
Operational amplifier 18c, analog multiplexer 18a, resistor R, feedback resistors R1 to RX, and reference power supply V
Has been replaced by a circuit consisting of Note that the memory 18b corresponds to the memory 9b in FIG.

In this embodiment, the operational amplifier 18c,
A circuit including the feedback resistors R1 to RX, the analog multiplexer 18a, and the resistor R constitutes a non-inverting amplifier circuit that amplifies the output voltage of the reference power supply V and supplies the output voltage to the A / D converter as an upper reference voltage. Here, the amplification factor of the non-inverting amplifier circuit is the feedback resistance R
The amplification factor is switched by supplying a switching signal for that purpose from the memory 18b to the analog multiplexer 18a.

That is, in this embodiment, the correction data for the intensity unevenness of the light amount in the sub-scanning direction is stored in the memory 18b in advance, and when reading an image, the correction data corresponding to each sub-scanning position is read from the memory 18b. The feedback resistance required to output the upper reference voltage corresponding to the correction data is output from the analog multiplexer 18.
It is selected by a.

According to the present embodiment, basically the same effects as in the first embodiment can be obtained, but the step of changing the upper reference voltage is coarser than in the first embodiment. Therefore, the present embodiment is suitable for applications in which unevenness in light amount may be corrected in coarse steps. In this case, there is an advantage that it can be implemented at lower cost than in the first embodiment.

[0029]

According to the present invention, the following effects can be obtained. (1) Uneven light amount can be corrected without deteriorating the gradation of digital video data, and good digital data can be obtained. This is because the upper reference voltage of the A / D converter for converting an analog video signal into a digital video signal is changed in accordance with the intensity variation of the light amount on the irradiation surface in the sub-scanning direction of the medium to be read. . (2) Deterioration of image processing speed does not occur when correcting unevenness in light amount. This is because, because the light amount unevenness is corrected by hardware, it is not necessary to perform arithmetic processing on all the video data of the read digital video data.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a light amount unevenness correction device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a detailed configuration of the embodiment.

FIG. 3 is a flowchart showing an operation of the embodiment.

FIG. 4 is a block diagram showing a configuration of a light amount unevenness correction device according to a second embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 reading unit 2 analog signal processing unit 3 A / D conversion unit 4 uneven light amount correction unit 5 digital unit 6 reading unit 6a light source 6b one-dimensional CCD image sensor 7 analog signal processing unit 8 A / D conversion unit 9 uneven light amount correction unit 9a D / A conversion unit 9b Memory 10 Digital circuit 11 CPU 18 Light intensity unevenness correction unit 18a Analog multiplexer 18b Memory 18c Operational amplifier

[Procedure amendment]

[Submission date] February 22, 1999

[Procedure amendment 1]

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[Claims]

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[0007]

The invention according to claim 1 is
The one-dimensional CCD image sensor scans the image to be read in the main scanning direction and the sub-scanning direction, and is provided in an image reading device that generates a video signal corresponding to each pixel constituting the image to be read. The present invention relates to a light amount unevenness correction apparatus for performing correction for removing extraneous light amount unevenness from a video signal, wherein an upper reference voltage of an A / D converter for converting an analog signal output from the one-dimensional CCD image sensor into a digital signal is adjusted. A reference voltage adjusting means for adjusting the upper reference voltage, and performing a correction for removing the uneven light amount in the sub-scanning direction, wherein the reference voltage adjusting means comprises a white medium by the one-dimensional CCD sensor. Means for scanning uneven light amount, and a correction data used for correcting uneven light amount. A memory for storing data,
As the white medium is scanned, the one-dimensional C
Correction data storage means for generating, for each sub-scanning position, digital data representing the peak level of the white level of the video signal obtained by the main scanning for the video signal obtained from the CD sensor, and storing the digital data in the memory as the correction data Amplifying circuit that amplifies a reference power supply voltage and supplies it as an upper reference voltage to the A / D conversion unit; and a correction data storage unit that outputs the correction data stored in the memory to the sub-scanning unit. The invention is also directed to an apparatus for correcting an uneven light amount of an image reading apparatus, comprising: an amplification factor switching means for switching an amplification factor of the amplification circuit according to a corresponding one.

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[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an image reading apparatus to which the uneven light amount correcting device of the present invention is applied. The image reading apparatus according to the present embodiment includes a reading unit 1 that inputs an image of a medium to be read, an analog signal processing unit 2 that performs predetermined signal processing on an analog video signal output from the reading unit 1, An A / D conversion unit 3 for converting an analog video signal output from the signal processing unit 2 into a digital video signal, a digital unit for supplying the digital video signal to an upper interface and controlling each unit in the image reading apparatus; A light amount unevenness correction unit 4 that performs light amount unevenness correction by changing the input voltage range of the A / D conversion unit 3 is provided. Among these constituent elements, the uneven light amount correction unit 4 is an embodiment of the uneven light amount correction device according to the present invention.

[Procedure amendment 6]

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FIG. 2 shows a specific configuration example of the embodiment of the present invention. In this figure, the reading unit 6 is shown in FIG.
And comprises a light source 6a and a one-dimensional CCD image sensor 6b.
The analog signal processing section 7 corresponds to the analog section 2 in FIG. 1, and the A / D conversion section 8 corresponds to the A / D
It corresponds to the conversion unit 3. The analog video signal output from the one-dimensional CCD image sensor 6b is subjected to predetermined signal processing by an analog signal processing unit 7, and the analog video signal that has undergone this signal processing is converted into a digital video signal by an A / D conversion unit 8. Is done.

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The uneven light amount correcting section 18 corresponds to the uneven light amount correcting section 4 in FIG. 2 includes an operational amplifier 18c, an analog multiplexer 18a, a resistor R, and feedback resistors R1 to R
A variable amplification factor amplification circuit composed of X and a reference power supply V is configured. An analog output terminal of this circuit is connected to an input terminal of an upper reference voltage of the A / D converter 8 and a digital input terminal of the circuit is connected. The port is a memory 18
b is connected to the data bus line. This memory 1
8b stores correction data corresponding to the intensity unevenness of the light amount in the sub-scanning direction.

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The digital circuit 10 and the CPU 11
This corresponds to the digital section 5 in FIG. here,
The digital circuit 10 is composed of digital components such as a memory and an LSI, and performs a data buffer, a generation of a control signal, a data transfer to an upper interface, and the like. The CPU 11 is a means for controlling the image reading device. The content of control performed by the CPU 11 is 1
First, there is control of main scanning and sub-scanning, and
The CPU 11 has a function of supplying an address for reading out the correction data corresponding to the current sub-scanning position to the memory 18b during the sub-scanning.

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When the power of the image reading apparatus is turned on,
Under the control of the CPU 11, the reading unit 6, the analog signal processing unit 7, the A / D conversion unit 8, the digital circuit 10, and the light amount unevenness correction unit 18 correct the white level peak data used when correcting the light intensity unevenness. A collection process is performed (Step 30).

[Procedure amendment 10]

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From the digital video signal of the white image stored in the memory, the CPU 11 determines the peak level of the white level in the sub-scanning direction for each main scanning line or every several lines (even for several lines at once). Then, it is stored in the memory 18b as correction data representing the intensity unevenness of the light amount in the sub-scanning direction.

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On the other hand, while the sub-scanning is performed, the CPU 11 supplies an address for reading out the correction data corresponding to the sub-scanning position to the memory 18b. As a result, the correction data corresponding to the current sub-scanning position is read from the memory 18b, and is converted into an analog voltage by an amplifier circuit having a variable amplification factor including an operational amplifier 18c, an analog multiplexer 18a, and feedback resistors R1 to RX ( Step 34), is supplied to the A / D conversion section 8 as an upper reference voltage. Therefore, A / D
The upper reference voltage of the conversion unit 8 changes according to the intensity unevenness of the light amount in the sub-scanning direction.

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[0029]

According to the present invention, the following effects can be obtained. (1) Uneven light amount can be corrected without deteriorating the gradation of digital video data, and good digital video data can be obtained. A / D for converting an analog video signal into a digital video signal
This is because the high-order reference voltage of the conversion unit is changed in accordance with the intensity unevenness of the light amount on the irradiation surface in the sub-scanning direction of the medium to be read. (2) Deterioration of image processing speed does not occur when correcting unevenness in light amount. This is because the light amount unevenness correction is performed by hardware, so that it is not necessary to perform arithmetic processing on all the video data of the read digital video data. (3) Since the variable step of the upper reference voltage is performed for each step by the feedback resistors R1 to RX, it is suitable for the use of correcting the light quantity unevenness in steps and can be performed at low cost.

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FIG. 2

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[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a light amount unevenness correction device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a detailed configuration of the embodiment.

FIG. 3 is a flowchart showing an operation of the embodiment.

[Description of Signs] 1 reading unit 2 analog signal processing unit 3 A / D conversion unit 4 light quantity unevenness correction unit 5 digital unit 6 reading unit 6a light source 6b one-dimensional CCD image sensor 7 analog signal processing unit 8 A / D conversion unit 10 Digital circuit 11 CPU 18 Light intensity unevenness correction unit 18a Analog multiplexer 18b Memory 18c Operational amplifier

Claims (3)

[Claims] An image to be read is scanned in a main scanning direction and a sub-scanning direction by a one-dimensional CCD image sensor,
In the image reading device that is provided in the image reading device that generates a video signal corresponding to each pixel constituting the image to be read, and in the light amount unevenness correction device that performs correction to remove light amount unevenness unrelated to the image to be read from the video signal, A reference voltage adjusting means for adjusting an upper reference voltage of an A / D converter for converting an analog signal output from the one-dimensional CCD image sensor into a digital signal; An uneven light amount correction apparatus for an image reading apparatus, wherein the correction is performed to remove the uneven light amount. 2. The method according to claim 1, wherein the reference voltage adjusting unit includes an uneven light amount scanning unit that scans a white medium by the one-dimensional CCD sensor, and a memory for storing correction data used for correcting the uneven light amount. For a video signal obtained from the one-dimensional CCD sensor by performing a scan of a medium, digital data representing a peak level of a white level of the video signal obtained by main scanning is generated for each sub-scanning position, and the correction is performed. Correction data storage means for storing the data as data in the memory; and correcting data corresponding to the sub-scanning position among the correction data stored in the memory by the correction data storage means, into an analog voltage. And a D / A converter for supplying the signal to the / D converter. The uneven light amount correction device of the image reading device. 3. The method according to claim 1, wherein the reference voltage adjusting unit includes: a light amount unevenness scanning unit that scans a white medium by the one-dimensional CCD sensor; and a memory that stores correction data used for correcting the light amount unevenness. For a video signal obtained from the one-dimensional CCD sensor by performing a scan of a medium, digital data representing a peak level of a white level of the video signal obtained by main scanning is generated for each sub-scanning position, and the correction is performed. Correction data storage means for storing data in the memory; amplifying circuit for amplifying a reference power supply voltage and supplying as an upper reference voltage to the A / D converter; and a variable amplification factor; Switching the amplification factor of the amplifier circuit according to the stored correction data corresponding to the sub-scanning position Light amount unevenness correction apparatus of the image reading apparatus according to claim 1, characterized in that it comprises an amplification factor switching means that.