JPH10164360A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform optimum shading correction corresponding to conditions at the time of read by selecting a correction data read mode corresponding to the read speed of original images. SOLUTION: The high speed/low speed of a read mode are judged by a transmission resolution set by input from an operation part 43 by a user. In the case of being the high speed, the gathering of shading distortion correction data is turned to a one-time read mode and a CPU 40 copies the shading distortion correction data for the one-time read mode read and stored in a system RAM 42 beforehand to a shading RAM 31. The copying operation is faster than newly taking the shading distortion correction data again. In the case of being the low speed, the gathering of the shading distortion correction data is turned to an every-time read mode and the CPU 40 stores data DW obtained from analog signals AV obtained by reading a white reference board by a line image sensor 13 in the shading RAM 31 as the shading distortion correction data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus, and more particularly, to a method of reading a reference white image before starting reading of a document image by determining a signal level of each pixel of an original image signal obtained by reading a document image by an image sensor. The present invention relates to an image reading apparatus that obtains a sensitivity-corrected image signal by performing correction using shading distortion correction data stored and stored.

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus provided for reading a document in a facsimile apparatus or the like, a document to be sub-scanned is read one by one main scanning line by a line image sensor arranged in a main scanning direction. An original image signal for the entire original is obtained.

However, the original image signal is subject to optical distortion due to the characteristics of the reading optical system in the main scanning direction of the line image sensor and variations in the sensitivity of each pixel (light receiving element) constituting the line image sensor. Includes electrical strain caused.

The optical distortion can be corrected to some extent by interposing a shading correction plate or the like in the reading optical system, but the correction accuracy is not sufficient, and the electric distortion is corrected with high accuracy. It is not possible.

Therefore, every time a document image is read, an image signal of a reference white image obtained by reading a white reference plate or the like is stored as shading distortion correction data before the reading of the document image is started. By correcting the original image signal for each main scanning line obtained at the time of actual reading of the original image by the shading distortion correction data for each pixel, the signal level of each pixel constituting the original image signal is set to a reference white level. Normalization is performed by reading as a level relative to the signal level output by each pixel with respect to the image, and variations in the amount of received light for each pixel with respect to the reference white image, and variations in sensitivity for each pixel, The influence on the image signal obtained from the read original image is offset. Such a technique of correcting an original image signal using shading distortion correction data is called electrical shading correction.

[0006] Such electric shading correction is performed by:
It is a very effective technique to correct variations in optical and electrical sensitivities of each pixel of an original image signal obtained from a read original image.

[0007]

However, as a white reference plate for obtaining a reference white image, an original pressing plate at the back of a reading position (scan line) of a line image sensor is usually used. Therefore, ideally, the white reference plate (document pressing plate) that needs to maintain uniform whiteness in any case becomes dirty due to the contamination of the document and the attachment of pencil powder.

For this reason, the shading distortion correction data is not based on a uniform white reference white image because of contamination of the white reference plate (document pressing plate). Therefore, when sensitivity correction is performed by electrical shading correction on an original image signal obtained by reading an original image using such shading correction data based on a non-uniform white image, the corrected image signal However, there is a problem that black stripes and white stripes occur in the sub-scanning direction.

As a technique for preventing the occurrence of such black streaks and white streaks, a technique proposed by the inventor of the present invention has been proposed.
When the difference between the value of a specific pixel of the shading correction data and the value of an adjacent pixel exceeds a certain value, as in the technique disclosed in Japanese Patent Application Laid-Open No. Sho 60-263574, the value of the specific pixel is In some cases, the influence of the contamination of the white reference plate during shading storage is avoided by replacing the value with a value.

However, even with this technique, if the entire white reference plate is dirty, or if the input sensitivity of each pixel (each light receiving element) constituting the image sensor is large, as in the case of a contact type image sensor, the white reference plate is not white. There was a problem that it was not possible to effectively deal with the contamination of the reference plate.

In the electric shading correction, since the shading distortion correction data is unconditionally read before starting the reading of the document image each time, the speed of reading the document is increased when reading the shading distortion correction data. There is a problem that the time is limited by the time required.

Further, in the electric shading correction, the shading distortion correction data can be obtained before starting the reading of the original image each time without considering the image quality such as whether the original to be read is a halftone image or a binary character image. Since the reading is performed unconditionally, there is a problem that the electrical shading correction does not necessarily contribute to the improvement of the image quality of the image signal obtained by sensitivity correction of the original image signal obtained by reading the original image.

The present invention has been made in view of the above circumstances, and it is possible to perform optimal shading correction on an original image signal obtained by reading an original image in accordance with conditions for reading the original image. It is an object to provide an image reading device.

[0014]

According to an aspect of the present invention, there is provided an image reading apparatus, comprising: reading an original image signal obtained by reading an original image with an image sensor; In an image reading apparatus that obtains a sensitivity-corrected image signal by reading a reference white image and correcting it with shading distortion correction data that has been stored before starting reading, every time a document image is read, the image is read before starting the reading. The reading mode is one of two modes: a reading mode in which the shading distortion correction data is newly read and stored every time, and a single reading mode in which the previously read shading distortion correction data is used as it is when reading the document image each time. Correction data reading mode selecting means for selecting according to the image reading speed; and When the correction data reading mode selecting means selects the reading mode every time, the shading distortion correction data is newly read and stored before the reading of the document image is started, while the correction data reading mode selecting means reads once. When the mode is selected, correction data storage that uses the previously read and stored shading distortion correction data as it is as the shading distortion correction data for reading the original image without reading new shading distortion correction data. Means.

In the image reading apparatus according to the present invention, the signal level of each pixel of the original image signal obtained by reading the original image by the image sensor is read and stored before the reading of the original image is started. In an image reading apparatus that obtains a sensitivity-corrected image signal by correcting with shading distortion correction data, each time a document image is read, before shading distortion correction data is newly read and stored every time an original image is read. One of a reading mode and a single reading mode in which the previously read shading distortion correction data is used as it is at the time of reading the document image each time, according to whether the reading image quality of the document image is halftone or not. Means for selecting a supplementary data reading mode, and selecting the correction data reading mode at the start of reading a document image. When the reading means is selected every time, the shading distortion correction data is newly read and stored before the reading of the document image is started, while the correction data reading mode selecting means selects the single reading mode. In this case, the apparatus further comprises a correction data storage unit that uses the previously read and stored shading distortion correction data as the shading distortion correction data for reading the original image without reading new shading distortion correction data. It is characterized by.

According to a third aspect of the present invention, there is provided an image reading apparatus.
3. The image reading apparatus according to claim 2, wherein the correction data storage means reads and stores the shading distortion correction data for the single reading mode in advance and stores the shading distortion correction data in accordance with the reading mode each time. The shading distortion correction data is compared with each pixel, and a specific pixel detection unit that detects whether there is a specific pixel whose difference value is greater than a predetermined set value, and the specific pixel detection unit determines whether the specific pixel is And further comprising a message display unit for displaying a message prompting cleaning of the white reference plate for reading the reference white image when it is detected,
The correction data reading mode selecting means selects the single-time reading mode as the reading mode regardless of the reading speed and the reading quality of the original image when the specific pixel detecting means detects the presence of the specific pixel. It is characterized by.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image reading apparatus according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Several techniques are already known as techniques for implementing shading correction in an image reading apparatus. One technique is to correct an original image signal obtained by reading an original image in an analog video waveform state. One that changes a reference voltage that is a reference when an analog video waveform is converted from analog to digital by an A / D converter, and one that performs a correction operation on multi-valued digital image information obtained after A / D conversion. It can be roughly divided into three.

Although the present invention can be applied to any of these technologies, in the embodiment described below, the present invention is applied to an A / D converter for converting an analog video waveform into an analog / digital signal. An example in which the present invention is applied to a device that changes a reference voltage serving as a reference when performing digital conversion will be described.

Before explaining the configuration of the image reading apparatus according to the present invention, for comparison, an image reading apparatus shown in FIG. 1 which unconditionally reads shading distortion correction data before starting the reading of an original image every time. A waveform shaping circuit as a part of the configuration will be described.

Referring to FIG.
Output from the analog image signal AV is amplified by an amplifier 21 and a peak hold circuit 22 and an A / D converter 23
Is input to

At the time of reading a reference white image (white reference plate, not shown), which is performed before the start of reading each original image, the logic level of the control signal CS output from the control unit, not shown, is set to H, and A peak signal AP output from the peak hold circuit 22 is input to the A / D converter 23 via the switch 24 as a reference voltage, and the line memory control circuit 2
5 is set in the write permission state.

Therefore, the analog image signal AV output from the line image sensor 13 has its peak value AP
Is converted into a digital image signal DV for each pixel by the A / D converter 23 using the reference voltage as a reference voltage. The converted digital image signal DV is latched by the latch circuit 30 in synchronization with the clock signal CP synchronized with the timing of each pixel,
It is input to the line memory control circuit 25.

The line memory control circuit 25 controls the control signal C
Since the write permission state is set by S, the latch circuit 30
Image signal for each pixel from the shading RAM 31
Are given as addresses to be sequentially counted up and output as data to be recorded. Thus, the shading RAM 31 stores shading distortion correction data for one main scanning line.

After the shading distortion correction data is stored in the shading RAM 31 in this manner, when reading the actual document image, the logic level of the control signal CS is set to L, so that the switch 24 is switched to the D / A mode. The analog signal DR output from the converter 26 is converted to an A / D converter 2
The connection is switched to the connection input as the reference voltage of No. 3.

The D / A converter 26 has a clock signal CP
, The shading distortion correction data read out from the shading RAM 31 in pixel units by the line memory control circuit 25 is input as a digital signal to be D / A converted.

Accordingly, the analog image signal for each pixel inputted to the A / D converter 23 is A / D as a signal of a level relative to a reference white image level corresponding to each pixel.
By performing the D conversion, the shading distortion is normalized, and the shading distortion based on the variation in the sensitivity of the reading optical system and the sensitivity of each pixel (light receiving element) of the line image sensor 13 is corrected.
The shading-corrected digital image signal DV output from the A / D converter 23 is output for further processing by a binarization circuit, a pseudo halftone processing circuit, or the like at a subsequent stage.

As described above, the waveform shaping circuit shown in FIG. 1 newly reads the reference white image again before starting reading the original image and stores the shading distortion correction data in the shading RAM 31, as shown in FIG. As described above, the shading distortion correction data is collected at the time of assembling the apparatus, written into the shading ROM 32 and converted into a ROM, so that the reference white image is newly read again before each reading of the original image, and the shading distortion correction data is read. In some cases, the fixed shading distortion correction data written in the shading ROM 32 is used every time without collecting the data.

In this case, as can be seen by comparing FIG. 2 with FIG. 1, the latch circuit 30 for reading the shading distortion correction data every time is omitted, and the line memory control circuit 25 outputs the output permission signal. The fixed shading distortion correction data is read out from the shading ROM 32 in synchronization with the clock signal CP input as a
/ A converter 26.

In the configuration shown in FIG. 1 in which the shading distortion correction data is unconditionally read before starting the reading of the document image each time, the contents stored in the shading RAM 31 are controlled in the waveform shaping circuit every time the document image is read. Is automatically read out or rewritten, and the contents stored in the shading RAM 31 cannot be read from the outside of the circuit, or conversely, the data cannot be written into the shading RAM 31, and the contents stored in the shading RAM 31 can be rewritten at any time. Therefore, as in the configuration using the shading ROM 32 shown in FIG. 2, it is impossible to perform shading correction using fixed shading distortion correction data as it is.

Therefore, in the configuration according to the present invention shown in FIG. 3, reading and writing of the contents stored in the shading RAM 31 can be performed from outside the waveform shaping circuit.

The configuration shown in FIG. 3 is a facsimile apparatus as an image reading apparatus including the waveform shaping circuit shown in FIG. 1 as a part of the configuration. In FIG. 3, the configuration is the same as that of the waveform shaping circuit shown in FIG. Are denoted by the same reference numerals, and detailed description is omitted.

In FIG. 3, a control signal CS is output from an I / O port 47, and a digital image signal DV is output from an I / O port 47.
Input to port 47. A control bus is provided between the line memory control circuit 25 and the I / O port 47. The CPU 40 operates the I / O port 47 via the system bus 48 to connect the line memory control circuit 25 to the I / O port 47. It exchanges control signals, fetches digital image signals DV and outputs control signals CS, and controls each unit of the device accommodated in the system bus 48.

Here, the components accommodated in the system bus 48 will be described.

First, the CPU 40 is a microcomputer for controlling each section of the apparatus as described above. The system ROM 41 is a read-only memory that is read as needed by the CPU 40, and stores various control procedures and a data table for control. System R
The AM 42 is used as a work area of the CPU 40 and stores rewritable data.
It is backed up by the battery E and keeps its stored contents even when the apparatus power is off.

The operation section 43 has other keys such as various setting keys in addition to basic keys such as a numeric keypad and a transmission start key, and is used to receive an operation input by a user. The display unit 44 is for displaying the operation state of the apparatus and displaying a message to be notified to the user. The modem 45 converts the digital image signal DV read by the line image sensor 13 input through the I / O port 47 and subjected to shading correction into a CPU.
40 modulates image information obtained by the binarization process or the pseudo halftone process or a control signal based on a predetermined protocol such as the G3 facsimile protocol and passes the modulated signal to the network control unit 46;
It demodulates received image information and control signals passed from the network control. The network control unit 46 controls the connection of the line, and sends out the modulated signal passed from the modem 45 to the line, and passes the modulated signal received from the line to the modem 45. The received image information is recorded and output by a plotter (not shown). The system bus 48 includes a CPU 40, a system ROM 41, a system RAM 42, an operation unit 43, a display unit 44, a modem 45, a network control 46, and an I / O port 47.
Are for exchanging signals between each other.

The first example of the original image reading process performed by the facsimile apparatus shown in FIG. 3 as the image reading apparatus according to the present embodiment configured as described above.
4 and 5 show the procedures of the embodiment and the second embodiment, respectively.

Before describing the reading processing procedures of the first and second embodiments, the processing performed prior to the processing procedures will be described.

The facsimile apparatus shown in FIG. 3 is a mode in which the shading distortion correction data is newly read and stored in the shading RAM 31 each time a document image is read (reading mode every time).
And a mode in which the previously read shading distortion correction data is used as it is at the time of reading the document image each time (one-time reading mode).

When reading a document image, whether to select the reading mode every time or the once reading mode is determined by:
In the reading processing procedure of the first and second embodiments shown in FIGS. 4 and 5, respectively, which will be described later, the reading processing is performed according to a predetermined document image reading condition.

In the reading mode every time, similarly to the waveform shaping circuit shown in FIG. 1, every time a document image is read,
The shading distortion correction data may be re-acquired. In the case of the one-time reading mode, the shading distortion correction data for the one-time reading mode which has been read in advance is used for reading a document later. It is necessary to hold the state even when the state is in the state, and when reading the document image, the state must be stored in the shading RAM 31.

On the other hand, the shading RAM 31 is also used to store shading distortion correction data for the reading mode every time. Therefore, the shading distortion correction data for the single reading mode is stored in the shading RAM.
31 must be stored in a different storage area and copied to the shading RAM 31 as needed.

Therefore, the shading distortion correction data for the one-time reading mode is output from the operation unit 43 when the white reference plate is in a clean state, such as during a production process or during maintenance by a service person. The data is stored in the system RAM 42 in response to a specific key operation for storing shading distortion correction data. Specifically, the CPU 40 gives an instruction to the line memory control circuit 25, and stores the shading distortion correction data obtained by reading the reference white image in the shading RAM 31 every time as in the reading mode. Next, the CPU 40 instructs the line memory control circuit 25 to read out the shading distortion correction data from the shading RAM 31, and reads the read shading distortion correction data by the battery E via the I / O port 47 and the system bus 48. The data is transferred to the backed-up system RAM 42 and stored. Thus, even if the contents of the shading RAM 31 are rewritten, the one-time reading mode shading distortion correction data is saved and held in the system RAM 42.

As will be described later, the shading distortion correction data for the one-time reading mode stored in the system RAM 42 is used as needed in the reading processing procedures of the first and second embodiments shown in FIGS. 4 and 5, respectively. Is copied to the shading RAM 31.

The reading procedure of the first embodiment shown in FIG. 4 will be described.

In the figure, the CPU 40 monitors the setting of the document to be read by monitoring the input from a document detection sensor (not shown) (decision 101).
No loop). When the document is set (Yes in determination 101), it is determined whether the reading mode of the document is high speed (low speed) (determination 102).

The high / low speed of the reading mode is determined based on the transmission resolution set by an input from the operation unit 43 by the user. Specifically, the transmission resolution is
If the standard resolution in facsimile communication is 8 pixels / mm in main scanning and 3.85 lines / mm in sub-scanning, it is determined to be “high speed”, and 8 pixels / mm in main scanning and sub-scanning are used.
If the resolution is high, such as 7 lines / mm, 8 pixels / mm in the main scanning, and 15.4 lines / mm in the sub-scanning, it is determined to be “low speed”.

This is because in facsimile communication, the transmission resolution is 8 pixels / mm in main scanning and 3.85 lines / m in sub-scanning.
In the standard resolution of m, the reading time is required to be shorter than the image quality. Therefore, recently, a high-speed reading mode in which the reading speed is increased and, for example, an A4 size document is read in 1 second or less has been commercialized. In such high-speed reading, if shading distortion correction data is collected every time before reading, several hundred milliseconds of time are consumed for each page, which is a barrier to further increasing the reading speed. It is in consideration of what had become.

When the reading mode is high speed in the judgment 102 (Yes in the judgment 102), the one-time reading mode is set for collecting the shading distortion correction data. Is copied to the shading RAM 31 for the one-time reading mode (step 103). This copying operation is much faster than re-shading distortion correction data.

Then, the original is fed by an original transport mechanism (not shown) (process 104), the original image is also read by the line image sensor 13 in the same manner as in the prior art, and the digital image signal which has been subjected to shading correction by the shading distortion correction data of the shading RAM 31 is used. A document reading operation for obtaining a DV is performed (process 105). And
One page of the original is discharged (process 106), and if there is a next page to be read (Yes in decision 107), the operation from process 104 is repeated, and if there is no next page to be read (No in decision 107). ) Terminates the reading.
In this case, since the copy in the process 103 is performed only once regardless of the number of pages of the document to be read, high-speed reading can be performed.

In this case, the amount of light received by each pixel (light receiving element) of the line image sensor 13 is larger than the amount of light received by each pixel (light receiving element) of the line image sensor 13 due to a temporal change in the intensity distribution of the light source, as compared with the case where the shading distortion correction data is collected every time the original is read. Although there is a problem of undulation, such undulation has an advantage that is not noticeable in the high-speed reading / low-resolution mode. When an image sensor having a large variation in sensitivity for each pixel (light receiving element), such as a contact image sensor, is used as the line image sensor 13 or when a white reference plate for reading a reference white image is stained. Even if the device is placed in an environment that tends to be bad in a short period of time, the quality of the read image can be ensured.

On the other hand, when the reading mode is not high speed (low speed) in the judgment 102 (No in the judgment 102).
Is set to the reading mode each time as described above with respect to collection of shading distortion correction data, and the CPU 40 feeds a document by a document transport mechanism (not shown) (step 10).
8) The analog image signal AV obtained by instructing the line memory control circuit 25 to read the white reference plate by the line image sensor 13 similarly to the waveform shaping circuit shown in FIG.
Is the operation of storing the data DW obtained by A / D conversion by the A / D converter 23 using the peak signal AP from the peak hold circuit 22 as the reference voltage in the shading RAM 31 as shading distortion correction data. Perform the distortion correction data storage operation (Process 10
9).

The original image is read by the line image sensor 13 in the same manner as in the prior art.
An original reading operation, which is an operation of obtaining a digital image signal DV that has been subjected to shading correction by the shading distortion correction data 31 (step 110). Then, one page of the document is discharged (step 111), and if there is a next page to be read (Yes in decision 112), the operation from step 108 is repeated, and if there is no next page to be read (decision 112). No), the reading ends. in this case,
The shading distortion correction data storage operation of the processing 109 is as follows.
Since the reading is performed for each document of each page to be read, precise shading correction is performed at the time of low-speed / high-resolution reading, so that a highly uniform image can be read.

The determination of the high / low speed of the reading mode according to the resolution can be arbitrarily set, and the setting can be changed at any time by an input from the operation unit 43 by the user. .

Next, the reading procedure of the second embodiment shown in FIG. 5 will be described.

In the figure, the CPU 40 monitors input from a document detection sensor (not shown) to monitor setting of a document to be read (decision 201).
No loop). When an original is set (Yes in determination 201), it is determined whether the read image quality is halftone (binary character mode) (determination 202).

The halftone / binary character mode of the read image quality is determined based on the read image quality set by an input from the operation unit 43 by the user. Specifically, when the original image to be transmitted is a halftone image such as a photograph, the read image quality is set to halftone,
In the case of a character image, the read image quality is set to the binary character mode. Therefore, the read image quality can be determined by checking the setting state.

In the judgment 202, the read image quality is 2
In the case of the value character mode (No in determination 202),
As for the collection of the shading distortion correction data, the above-described one-time reading mode is set, and the CPU 40 reads the one-time reading mode shading distortion correction data that has been read in advance and stored in the system RAM 42.
1 (process 203).

Then, the original is fed by an original transport mechanism (not shown) (step 204), and the original image is read by the line image sensor 13 in the same manner as in the prior art, and the digital image signal DV which has been subjected to shading correction by the shading distortion correction data in the shading RAM 31. Is performed (process 205). And
One page of the original is discharged (step 206), and if there is a next page to be read (Yes in decision 207), the operation from step 204 is repeated, and if there is no next page to be read (No in decision 207). ) Terminates the reading.
In this case, since the shading distortion correction data at the time of reading the document of each page is collected in advance when the white reference plate is clean, it is caused by dirt on the white reference plate that is conspicuous in a binary image. Streaks are less likely to occur, and fluctuations in the reading density due to changes over time in the characteristics of the reading optical system and the light receiving element, which can be caused by not collecting the distortion correction data each time the document is read, are not binarized. Inconspicuous.

On the other hand, when the read image quality is halftone in the determination 202 (Yes in the determination 202), the collection mode is set to the above-described reading mode with respect to the collection of shading distortion correction data, and the CPU 40 is provided with a document transport mechanism (not shown). 1 (process 208), and instructs the line memory control circuit 25 to read the white reference plate by the line image sensor 13 in the same manner as the waveform shaping circuit shown in FIG. Is the operation of storing the data DW obtained by A / D conversion by the A / D converter 23 using the peak signal AP from the peak hold circuit 22 as a reference voltage in the shading RAM 31 as shading distortion correction data. A distortion correction data storage operation is performed (process 209).

The original image is read by the line image sensor 13 as in the prior art, and the shading RAM is used.
A document reading operation for obtaining a digital image signal DV that has been subjected to shading correction by the shading distortion correction data 31 is performed (process 210). Then, one page of the document is discharged (process 211), and when there is a next page to be read (Yes in decision 212), the operation from process 208 is repeated, and when there is no next page to be read (decision 212). No), the reading ends. in this case,
The shading distortion correction data storage operation of the process 209 is as follows.
Since the reading is performed for each document of each page to be read, unevenness in the reading density of the halftone image is suppressed as much as possible, and a uniform halftone image can be obtained. Also, by performing the collection of the shading distortion correction data again each time the original is read, the stripes due to the contamination of the white reference plate are likely to be generated. There is no problem because it is much less noticeable than in the case of the character image.

Next, FIG. 6 shows another configuration of the facsimile apparatus as the image reading apparatus according to the embodiment of the present invention, which is different from that shown in FIG.

The configuration shown in FIG. 6 differs from the configuration shown in FIG. 3 in that a subtractor 33, a constant generator 34, and a comparator 35 are provided. The same reference numerals are given and the detailed description is omitted.

In FIG. 6, a subtractor 33 outputs an output signal DW from the latch circuit 30 in the read mode each time.
And shading distortion correction data output as
The shading distortion correction data for the one-time reading mode stored in 31 is subtracted for each pixel, and the result of the subtraction is output to the input terminal B of the comparator 35. The subtracter 33 outputs a result obtained by subtracting the smaller value from the larger value of the two input values. The constant generator 34 outputs a predetermined positive set value to the input terminal A of the comparator 35. The comparator 35 compares the values input to the input terminals A and B for each pixel, and if it detects that the value of the input terminal B is larger than the value of the input terminal A, the detection result is I /
This is notified to the CPU 40 via the O port 47.

Here, a pixel whose value at the input terminal B is larger than the value at the input terminal A is the shading distortion correction data for the pixel read once for the reading mode in a state where the white reference plate is clean. And a shading distortion correction data for the pixel in the reading mode each time, which indicates that the pixel is a peculiar pixel having a difference equal to or more than a certain amount. That is, it is indicated that dirt has adhered to the position corresponding to the specific pixel on the white reference plate.

Therefore, the CPU 40 sets the comparator 35
When the detection of the unique pixel is notified from, the guidance for cleaning the white reference plate is displayed on the display unit 44, and at the time of reading the original, the shading correction in the single reading mode is performed. Specifically, in the reading process procedure of the first embodiment shown in FIG.
The following processing is performed, and in the reading processing procedure of the second embodiment shown in FIG.
The processing after 3 is performed. As a result, optimal shading correction can always be automatically performed.

In the above-described embodiment, the case where the present invention is applied to a facsimile apparatus has been described as an example. However, the present invention is not limited to this, and other apparatuses such as a scanner apparatus and a digital copying machine may be used. The same can be applied to the image reading apparatus described above.

[0068]

According to the first aspect of the invention, the correction data reading mode selection means selects the shading distortion before starting the reading each time the reading of the document image is performed in accordance with the reading speed of the document image. Depending on the reading mode selected, either a new reading mode in which the correction data is newly read and stored, or a single reading mode in which the previously read shading distortion correction data is used as it is when reading the original image each time. The correction data storage means may newly add shading distortion correction data before the reading of the document image starts when the correction data reading mode selecting means selects the reading mode each time at the time of reading the document image. While reading and storing, the correction data reading mode selecting means has selected the single reading mode. In this case, since the shading distortion correction data previously read and stored is used as it is as the shading distortion correction data for reading the original image without reading new shading distortion correction data, the original image is obtained by reading the original image. Optimal shading correction can be performed on the original image signal according to the reading speed of the original image as a condition for reading the original image. In other words, when the reading speed of the original image is relatively high, the correction data reading mode selecting means selects the single reading mode as the reading mode, and when the reading speed is relatively low, the reading mode is selected every time. The reading speed can be increased, and at the time of high-speed reading, since the influence of shading distortion is less likely to occur, the image quality can be maintained even in the one-time reading mode.

According to the second aspect of the present invention, the correction data reading mode selecting means reads the original image in accordance with whether the reading image quality of the original image is halftone or not as a condition for reading the original image. Every time the scanning is performed, the shading distortion correction data is newly read and stored before starting the reading, or the reading mode is used each time, or the shading distortion correction data read in advance is used as it is at the time of reading each original image. Select the reading mode as one of the reading modes. Therefore, the read image quality is halftone in which the overall density unevenness is conspicuous but local streaks are inconspicuous, or the overall density unevenness is inconspicuous due to binarization, but local streaks are inconspicuous in binary characters. By selecting the reading mode or the reading mode each time depending on whether the image is an image or not, it is possible to obtain an effect that optimal shading correction can be automatically performed for each of the halftone and binary character images.

According to the third aspect of the invention, the shading distortion correction data for the one-time reading mode, which is read and stored in advance by the correction data storage means, and the shading distortion correction data are read in accordance with the every-time reading mode. The shading distortion correction data is compared with each pixel, and the unique pixel detecting means for detecting whether there is a unique pixel whose difference value is larger than a predetermined set value has detected that the unique pixel is present. In the case, the message display unit displays a message prompting cleaning of the white reference plate for reading the reference white image, while the reading mode selection unit determines that the specific pixel detection unit has the specific pixel. If it is detected, the white reading mode is selected as the reading mode regardless of the reading speed and reading quality of the original image. If the each reading mode is dirty plate interfere, a single reading mode is automatically selected to obtain an effect that automatically perform always optimal shading correction. In addition, by displaying a message urging the cleaning of the white reference plate, it is possible to make the user recognize that the white reference plate is dirty, and to prompt an appropriate process.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a block configuration of a waveform shaping circuit as a partial configuration of an image reading apparatus configured to unconditionally read shading distortion correction data before starting reading a document image each time.

FIG. 2 is a diagram illustrating a block configuration of a waveform shaping circuit that uses fixed shading distortion correction data written in a shading ROM each time a document image is read.

FIG. 3 is a diagram showing a block configuration of a facsimile apparatus as an image reading apparatus according to the embodiment of the present invention.

FIG. 4 is a flowchart illustrating an image reading processing procedure according to the first embodiment of the present invention.

FIG. 5 is a flowchart illustrating an image reading processing procedure according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a block configuration different from FIG. 3 of the facsimile apparatus as the image reading apparatus according to the embodiment of the present invention;

[Explanation of symbols]

 13 Line Image Sensor 21 Amplifier 22 Peak Hold Circuit 23 Analog / Digital Converter 24 Switch 25 Line Memory Control Circuit 26 Digital / Analog Converter 30 Latch Circuit 31 Shading RAM 32 Shading ROM 33 Subtractor 34 Constant Generator 35 Comparator 40 CPU 41 System ROM 42 System RAM 43 Operation unit 44 Display unit 45 Modem 46 Network control unit 47 I / O port 48 System bus

Claims (3)

[Claims] 1. A signal level for each pixel of an original image signal obtained by reading an original image by an image sensor is corrected by shading distortion correction data stored by reading and storing a reference white image before starting to read the original image. An image reading apparatus for obtaining a sensitivity-corrected image signal by reading a shading distortion correction data each time a document image is read before starting the reading, and storing the shading distortion correction data each time. Correction data reading mode selecting means for selecting any one of a single reading mode and a single reading mode in which the distortion correction data is used as it is at the time of reading the document image in accordance with the reading speed of the document image, and reading the document image At the start, when the correction data reading mode selecting means has selected the reading mode every time, While the shading distortion correction data is newly read and stored before the reading of the original image is started, if the correction data reading mode selecting means has selected the single reading mode, the new shading distortion correction data is not read. And a correction data storage unit that uses shading distortion correction data read and stored in advance as shading distortion correction data for reading the original image. 2. A method for correcting a signal level of each pixel of an original image signal obtained by reading an original image by an image sensor using shading distortion correction data stored by reading a reference white image before starting to read the original image. An image reading apparatus for obtaining a sensitivity-corrected image signal by reading a shading distortion correction data each time a document image is read before starting the reading, and storing the shading distortion correction data each time. Complementary data reading mode selecting means for selecting any one of the single reading mode and the single reading mode in which the distortion correction data is used as it is at the time of reading the original image each time, depending on whether the image quality of the original image is halftone or not. And the correction data reading mode selecting means selects the reading mode every time when the reading of the original image is started. In this case, the shading distortion correction data is newly read and stored before the reading of the document image is started. On the other hand, if the correction data reading mode selecting means has selected the one-time reading mode, a new shading distortion correction data is stored. An image reading apparatus comprising: a correction data storage unit that uses shading distortion correction data read and stored in advance as it is, without reading data, as shading distortion correction data for reading the original image. 3. The method according to claim 1, wherein the correction data storage means reads and stores in advance the shading distortion correction data for the single reading mode and the shading distortion correction data read corresponding to the reading mode each time. For each comparison, a specific pixel detection means for detecting whether or not there is a specific pixel whose difference value is larger than a predetermined set value, and when the specific pixel detection means detects that the specific pixel is present, Message correction means for displaying a message prompting cleaning of the white reference plate for reading the reference white image, while the correction data reading mode selection means detects that the specific pixel detection means has the specific pixel. In this case, the one-time reading mode is selected as the reading mode regardless of the reading speed or the reading quality of the original image. The image reading device according to claim 1.