JP3076692B2 - Image reading device - Google Patents

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 having a configuration for reading image data with an image sensor, and more particularly to an image reading apparatus for reading high quality image data.

In an image reading apparatus such as a facsimile or an image scanner, a fluorescent light or the like is used as an illumination light source, and image data is read using a CCD line image sensor or the like. In such an image reading apparatus, it is necessary to construct a configuration for reading high-quality image data.

[0003]

2. Description of the Related Art In an image reading apparatus using a line image sensor, as shown in FIG. 18, a document to be read is placed on a glass plate, and a carrier composed of a fluorescent lamp and a line image sensor is moved. Thus, a configuration is adopted in which the original is read by the line image sensor.

In adopting this configuration, in the image reading apparatus, in order to correct so-called shading, a reference white plate is provided in front of a glass plate as shown in FIG. The image sensor reads a white level value at a specific position (home position) of the reference white plate, and uses the read white level value to correct the signal level of image data of a document to be read. ing.

In a conventional image reading apparatus, such a white level value of the reference white is read once, and is used without changing the value until the next reading opportunity. .

On the other hand, resolution is one of the quality of image data. This resolution is mainly defined by the lens system when the number of sensor elements of the image sensor is determined.

In the conventional image reading apparatus, it is difficult to adjust the lens system. Therefore, if the lens system is adjusted at the time of shipment from a manufacturer, the resolution is left to the user and the resolution is adjusted at all. It had a configuration that did not exist.

[0008]

However, as in the prior art, once the white level value of the reference white is read, it is used without changing the value until the next reading opportunity. However, when reading the image data takes a long time, the quality of the image data to be read deteriorates.

For example, when the image processing capability of a data processing device connected downstream of the image reading device is low, the data processing device forcibly stops the movement of the carrier of the image reading device while reading the image data. In such a case, it takes time to read one piece of image data. In such a case, the white level value of the initial reference white is originally appropriate due to a change in the amount of light source during this time. Deviated from the above, there is a problem that image data to be read becomes uneven.

Further, as shown in FIG. 20, if a configuration is adopted in which a white level value at a specific position of a reference white plate is detected and shading correction is performed using the detected white level value as in the prior art, In addition, when dust adheres to the specific position, there is a problem that the quality of image data to be read deteriorates because a normal white level value cannot be obtained.

In order to cope with such a problem, a configuration is adopted in which a white level value around a specific position of the reference white plate is also sampled, and the sampled white level value is used to detect at a specific position of the reference white plate. In some cases, a method of correcting the obtained white level value is adopted.

However, even if such a method is adopted, if the attached dust is large enough to spread to the correction sampling point, a normal white level value cannot be obtained. The problem of quality degradation still remained.

Further, if a configuration having no means for adjusting the resolution as in the prior art is adopted, the adjustment of the lens system is disturbed due to vibrations at the distribution stage and various environmental conditions at the stage of use. As a result, there is a problem that the resolution is reduced from that at the time of shipment from the manufacturer, and the quality of image data is deteriorated.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a new image reading apparatus which realizes reading of high quality image data.

In order to achieve this object, according to the present invention, image data is read by a line image sensor, and a white level value is read by a line image sensor prior to reading the image data. Instructing means for instructing movement of a line image sensor in a zone in which the white level value is generated, in an image reading apparatus configured to read and perform shading correction on image data to be read in accordance with the white level value And evaluating the smoothness of the white level value read in response to the instruction of the instruction means for each detection line to determine whether each detection line of the white level value is a detection line of an appropriate white level value. Determining means for determining whether or not an appropriate white level value is detected in the zone while referring to the determination result of the determining means. Detecting means for detecting a continuous area; determining means for determining a specific detection line from the area detected by the detecting means; and a white level value read from the detecting line determined by the determining means for shading correction. Setting means for setting a white level value. And to achieve this goal,
According to the present invention, in an image reading apparatus having a configuration for reading image data with an image sensor, a configuration is adopted in which a chart of a monochrome edge image can be read by the image sensor, and a monochrome edge image of the chart read by the image sensor is provided. Calculate the differential value of the image data of
Detecting means for detecting an MTF characteristic indicated by the apparatus by performing a Fourier transform on the differential image data; calculating means for modulating the degree of enhancement of the image data read by the image sensor according to a set parameter; From the MTF characteristics detected by the detection means and the prescribed MTF characteristics,
Setting means for specifying the parameter for setting the resolution of the image data output by the calculating means to a specified value and setting the parameter in the calculating means.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle configuration of the present invention will be described with reference to FIGS. In FIG. 1A, reference numeral 1 denotes a document surface of the image reading apparatus on which a document to be read is placed, 2a is a reference white plate, and a position of the document surface 1 before scanning is, for example, The one that is provided at both left and right ends of the document surface 1 and generates a reference white for shading correction;
Reference numeral 0 denotes a line image sensor which is moved in the sub-scanning direction (the moving direction of the line image sensor 10) and reads image data in the main scanning direction (the direction of the broken line in the figure);
Reference numeral 11 denotes an amplifying unit that amplifies an electric signal of image data read by the line image sensor 10, 12a
Is a reference white level value storage means, which is a first storage area 1
20 and a second storage area 121 for storing a white level value of a reference white used for shading correction.
Reference numeral 3 denotes shading correction means for performing shading correction using the reference white level values stored in the reference white level value storage means 12a. Reference numeral 14 denotes comparison white level value extraction means for storing reference white level values. A signal level value necessary for correcting the reference white level value stored by the means 12a; and 15 a calculating means, which is a ratio used for correcting the reference white level value stored in the reference white level value storing means 12a. A correction means 16 for calculating the value corrects the reference white level value stored in the reference white level value storage means 12a.

In FIG. 1B, the same components as those shown in FIG. 1A are denoted by the same symbols. Reference numeral 2b denotes a reference white plate which is provided at a position before the scanning of the document surface 1 and generates a reference white for shading correction.
Reference numeral 2b denotes a reference white level value storage unit which stores a reference white level value used for shading correction.
Reference numeral 7 denotes first instructing means for instructing the movement of the line image sensor 10 in the area of the reference white plate 2b.
Reference numeral 8 denotes second instruction means, which is a line image sensor 1
Reference numeral 19 designates an instruction to move to a specific position of 0. Reference numeral 19 denotes a determination unit which determines whether a detection line of a white level value read in response to an instruction of the first instruction unit 17 is appropriate. The detecting means 20 is a detecting means for detecting a continuous area of a detection line of an appropriate white level value while referring to the determination result of the determining means 19, and the determining means 21 is a detecting means 20. , A setting means 22 for setting a reference white level value stored in the reference white level value storage means 12b. Things.

In FIG. 2, the same components as those described with reference to FIG. 1 are indicated by the same symbols. Reference numeral 3 denotes a chart, which is, for example, a black-and-white edge image provided at a position before scanning of the document surface 1, reference numeral 23 denotes an image sensor such as a line image or area image sensor, which reads image data, and reference numeral 24 denotes an amplification. Means for amplifying an electric signal of image data read by the image sensor 23; 25, a chart image storage means for storing a black and white edge image of the chart 3 read by the image sensor 23; Means for detecting the MTF characteristic (Modulation Transfer Function) indicated by the apparatus; 27, an arithmetic means for modulating the degree of enhancement of the image data read by the image sensor 23 in accordance with the set parameters; , 28 are setting means for setting parameters to the calculating means 27. .

In the image reading apparatus of the present invention shown in FIG. 1A, prior to reading a document, the line image sensor 10 detects a reference white color generated by a reference white plate 2a provided at a position before scanning of the document surface 1. The level value is detected, and the detected reference white level value is stored in the first and second storage areas 120 and 121 of the reference white level value storage means 12, and then, the reading of the document is started. At this time, the shading correction unit 13 performs the shading correction using the reference white level value stored in the first storage area 120.

At the time of reading this document, the line image sensor 10 detects the reference white level values generated by the reference white plates 2a provided at the left and right ends of the document surface 1, so that the comparison white level value extraction means 14 By specifying the sensor element of the line image sensor 10, a reference white level value generated by the reference white plate 2a is extracted from the image data read by the line image sensor 10.

Receiving this extraction result, the calculating means 15
Calculating a ratio value between the reference white level value extracted by the comparison white level value extracting means 14 and the reference white level value before reading the document corresponding to the extracted white level value stored in the second storage area 121; The correction unit 16 calculates a multiplication value of the calculated ratio value and the reference white level value stored in the second storage area 121, and updates the reference white level value stored in the first storage area 120. I will do it.

As described above, the image reading apparatus of the present invention shown in FIG. 1A employs a configuration in which a white level value is always input to a specific sensor element of the line image sensor 10 during reading of image data. From the ratio between the white level value of the image data detected by the specific sensor element before reading the image data and the white level value of the image data detected by the specific sensor element during the reading, the image data is detected before the image data is read. Since the configuration for correcting the reference white level value for shading correction is employed, even if it takes time to read the image data, the quality of the read image data does not deteriorate.

On the other hand, in the image reading apparatus of the present invention shown in FIG. 1B, the first indicating means 17 controls the movement of the line image sensor 10 in the area of the reference white plate 2b before reading the original. To instruct. Since the white level value is read by the line image sensor 10 in response to this instruction, the judging means 19 evaluates the smoothness of the read white level value for each detection line, thereby obtaining the white level value. It is determined whether or not each detection line of the value is an appropriate one showing a smooth characteristic with no dust attached.

In response to the result of this determination, the detecting means 20
In the area of the reference white plate 2b, a continuous area of a detection line of an appropriate white level value is detected (if there are a plurality of areas, for example, the longest continuous area is detected), and the determination unit 21 For example, a specific detection line is determined from the detected area, such as a detection line at the center.

In response to this determination, the second instructing means 18 instructs the movement of the line image sensor 10 to the detection line position determined by the determining means 21, and the setting means 22
Stores the white level value read in response to this instruction in the reference white level value storage means 12b, so that the white level value read from the detection line determined by the determination means 21 is used as the reference white level for shading correction. Set as a level value. At this time, the setting means 22
A white level value read from the detection line determined by
A white level value for shading correction is calculated by calculating an average value and the like of white level values read from one or more appropriate white level value detection lines existing in the vicinity of the detection line. May be set.

As described above, in the image reading apparatus of the present invention shown in FIG. 1 (b), the area of the reference white plate 2b to which dust is not attached is detected, and the white level read from the area is detected. Since a configuration is used in which the reference white level value for shading correction is set using the values, the reference white plate 2
Even if dust adheres to b, the quality of image data to be read does not deteriorate.

On the other hand, in the image reading apparatus of the present invention shown in FIG. 2, when the image sensor 23 detects, for example, that a certain adjustment cycle has been reached, the image sensor 23 reads the monochrome edge image of the chart 3 and stores it in the chart image storage means 25. I do.

In this way, the chart image storage means 2
When the black-and-white edge image of the chart 3 is stored in 5, the detecting means 26 calculates a differential value of the image data of the black-and-white edge image, and performs a Fourier transform on the differential image data to obtain an MTF characteristic indicated by the apparatus. The setting means 28 detects the MTF detected by the detecting means 26 and receives the detection result.
From the characteristics and the specified MTF characteristics, a parameter that makes the resolution of the image data output by the calculating means 27 specified is specified and set in the calculating means 27.

As described above, in the image reading apparatus of the present invention shown in FIG. 2, the resolution of the image data to be read can be kept constant, for example, at the stage of shipment from the manufacturer. There is no degradation of quality.

Next, the details of the present invention will be described with reference to FIGS. First, an embodiment of an image reading apparatus whose principle configuration is illustrated in FIG. 1A will be described.

As described with reference to FIG.
The image reading apparatus whose principle configuration is illustrated in FIG. 1 employs a configuration in which a white level value is always input to a specific sensor element of the line image sensor 10. For example, as shown in FIG. 3, by providing a reference white plate 2a on the back side of the document surface 1 so as to surround the document surface 1, a white level value is always input to a specific sensor element of the line image sensor 10. It adopts a configuration.

Then, a change in the light source light amount is detected in real time according to the detected value of the specific sensor element,
According to this detection value, a configuration is adopted in which the reference white level value for shading correction read prior to reading of image data is corrected.

This processing configuration can be realized by using either a hardware configuration or a software configuration. FIG. 4 shows an embodiment of a processing flow in the case where the processing is realized by a software configuration.

Next, according to this processing flow, FIG.
The processing executed by the image reading apparatus whose principle configuration is illustrated in FIG. As shown in the processing flow of FIG. 4, first, in step 1, prior to reading the document, the image reading apparatus calculates the white level value generated by the reference white plate 2 a located before the scanning of the document surface 1. By reading, the reference white level value is recorded for all pixels (all sensor elements) of the line image sensor 10. Next, in step 2, from among the recorded reference white level values, white level values detected by one specific left and right pixel of the line image sensor 10 are extracted and recorded.

Then, in step 3, the original is read by moving the line image sensor 10 by one detection line in the sub-scanning direction. Subsequently, in step 4, when reading the original, the white level values detected by the left and right one pixels of the line image sensor 10 specified in step 2 are monitored.

Then, in step 5, the left and right sides of the line image sensor 10 specified in step 2 are determined from the white level values at the start of reading recorded in step 2 and the white level values during reading monitored in step 4. The change rate of the white level value detected by the pixel is calculated. In this calculation process, specifically, if the white level values recorded in step 2 are A and B, and the white level values monitored in step 4 are A _{N and} B _N , C = (A _N / A + B _This is performed by calculating the rate of change C according to _N / B) / 2. This change rate C
Correspond to the change rate of the light source light amount.

Subsequently, in step 6, by multiplying the change rate C calculated in step 5 by the reference white level value recorded in step 1, a reference white level value for shading correction is calculated and set. . The shading correction of the image data of the document to be read is performed using the reference white level value set in step 6. Then, Step 7
Then, it is determined whether or not the reading of the document has been completed. When it is determined that the reading has not been completed, the process returns to step 3 to perform the reading of the document.

As described above, the image reading apparatus of the present invention shown in FIG. 1A executes the processing flow of FIG. 4 so that the reference white level value used for the shading correction according to the change in the light source light amount. Is changed. From this, in the related art, as shown in FIG. 5A, there has been a disadvantage that the motion between the video output of the image sensor 10 and the reference white level value used for shading correction does not match. Therefore, as shown in FIG. 5B, the two movements coincide with each other, so that even if it takes a long time to read the original, accurate shading correction can be performed. Become.

Next, an embodiment of the image reading apparatus whose principle configuration is shown in FIG. 1B will be described. As described with reference to FIG. 1B, in the image reading apparatus whose principle configuration is illustrated in FIG. 1B, by evaluating the smoothness of the white level value of the reference white plate 2b, an area where dust is not attached is obtained. Is detected, and a reference white level value for shading correction is read from among them.

This processing configuration can be realized by using either a hardware configuration or a software configuration. FIG. 6 shows an embodiment of a processing flow when the processing is realized by a software configuration.

Next, according to this processing flow, FIG.
The processing executed by the image reading apparatus whose principle configuration is illustrated in FIG. Here, as shown in FIG. 7, the detection line at the forefront position of the reference white plate 2b is set to WP
1. The detection line at the last position is defined as WP2.

As shown in the processing flow of FIG. 6, the image reading apparatus first moves the line image sensor 10 to the position of the detection line WP1 in step 1. That is, the line image sensor 10 is moved to the detection line position at the forefront position of the reference white plate 2b. Next, in step 2, a variable WP indicating the current detection line position is displayed.
Is set to 0, a variable Y for displaying the number of continuous detection lines is set to 0, and a variable WP _n for displaying the position of the top detection line in the continuous detection line area is set to 0.

Subsequently, in step 3, the white level value of the detection line indicated by the value of the variable WP is read. In this case,
The white level value on the detection line WP1 is read. Subsequently, in step 4, the smoothness of the white level value read in step 3 is evaluated. That is, the smoothness of the read white level value is evaluated by calculating the difference value between the adjacent white level values and evaluating whether the difference value changes smoothly.

Subsequently, in step 5, it is determined whether the evaluation in step 4 is successful or not, and when it is determined that the evaluation is appropriate for the detection line, that is, when a smooth white level value is detected. If it is determined that the line is to be evaluated, the process proceeds to step 6, where it is determined whether or not the value of the variable Y is 0. When it is determined to be 0 in step 6,
To set the value of the variable WP to variable WP _n, the next step 8
Then, the value of the variable Y is counted up by one. On the other hand, if it is determined in step 6 that the value is not 0,
Is skipped and the process immediately proceeds to step 8 to increment the value of the variable Y by one.

That is, the fact that the value of the variable Y is 0 means that the detection line at the start of processing is an appropriate detection line, or that the previous inappropriate detection line is changed to an appropriate detection line. Variable W
After setting the current detection line position in P _n , the value of the variable Y is incremented by one. On the other hand, the fact that the value of the variable Y is not 0 means that the appropriate detection line up to that point is continuous. it means, for the value of the variable WP _n without updating is going to incremented by one only the value of the variable Y.

On the other hand, when it is determined in step 5 that the detection line is evaluated as an inappropriate detection line in step 4, it means that the detection line at the start of processing is an inappropriate detection line, or the appropriate detection line is interrupted. Or that the improper detection line is continuous, the process proceeds to step 9 and the value of the variable Y _MAX indicating the maximum number of continuous detection lines is larger than the value of the variable Y. When it is determined whether or not it is small, step 10
Proceed to, as well as set the value of the variable Y to variable Y _MAX, and set the value of the variable WP _{MA X} variable WP _n for displaying the head detection line position of the maximum continuous detection line region, in the subsequent step 11, a variable When Y is set to 0, and when it is determined that Y is large, the process of step 10 is omitted and the process immediately proceeds to step 11 to set 0 to the variable Y.

That is, the variable Y_MAXIs the value of the variable Y
Is smaller than the appropriate detection line
The number of continuous detection lines is larger than before.
The appropriate detection line
Is the variable Y _MAXAnd set it to
The position of the head detection line is stored in the variable WP_MAXSet to
And then set variable Y to 0, while variable Y_MAXIs the value of
The fact that it is larger than the value of the variable Y
The number of continuous detection lines
Variable Y_MAX,WP_MAXof
Set the variable Y to 0 without updating the value
Go.

Thus, step 8 / step 1
When the process of step 1 is completed, the process proceeds to step 12, in which the value of the variable WP is counted up by one in response to the reading of the white level value of one detection line in step 3, and in step 13, the variable WP is Is determined to be larger than WP2 at the last stage position of the reference white plate 2b,
When it is determined that it has not become larger, the process returns to step 3. On the other hand, when it is determined that becomes large, the routine proceeds to step 14, the value of the variable Y _MAX is determined whether greater than the value of the variable Y, when determined to be smaller, the process proceeds to step 15, a variable Y as well as set the value of the variable Y to _MAX, and set the value of the variable WP _n variable WP _MAX, whereas, when it is determined that large omits the processing in step 15.

Finally, at step 16, the line image sensor 10 detects the detection line " _YMAX / 2 + WP".
_MAX ", read the white level value there, set it as the reference white level value for shading correction, and end the process. At this time, the detection line “Y
All _MAX / 2 + from WP _MAX "" ± Y _MAX / 2 detection line that fits the number of detected lines of "than is appropriate detection line, reads the white level value of the detection lines included in this region, the average value is obtained It is also preferable to set the reference white level value for shading correction.

As described above, the image reading apparatus of the present invention shown in FIG. 1B evaluates the smoothness of the white level value of the reference white plate 2b by executing the processing flow of FIG. Then, a configuration is adopted in which the maximum length area to which no dust is attached is detected from the area of the reference white plate 2b, and the reference white level value for shading correction is read from this area. Thus, in the related art, as shown in FIG. 8A, if there is dust at the home position of the reference white plate 2b, there is a disadvantage that an accurate reference white level value cannot be read. As shown in FIG. 8B, a configuration is adopted in which the reference white level value is read from the position of the reference white plate 2b without dust, so that an accurate reference white level value can be read. This makes it possible to perform an excellent shading correction.

Next, an embodiment of the image reading apparatus whose principle configuration is shown in FIG. 2 will be described. As described with reference to FIG. 2, the image reading apparatus whose principle configuration is illustrated in FIG. 2 employs a configuration that includes an arithmetic unit that enables detection of the MTF characteristic indicated by the apparatus and modulation of the degree of enhancement of image data. Then, the degree of emphasis is adjusted based on the detected MTF characteristics so that the resolution of the image data output from the arithmetic means becomes a specified one.

FIG. 9 shows an embodiment of the chart 3 shown in FIG. 2, and FIG. 10 shows an embodiment of the arrangement of the chart 3. The chart 3 shown in FIG. 9 includes the main scanning direction (the scanning direction of the line image sensor when the line image sensor is used as the image sensor 23) and the sub-scanning direction (the scanning direction of the line image sensor as the image sensor 23). Is composed of a black-and-white edge image having an inclination of 45 degrees with respect to both the moving direction of the line image sensor) and, as shown in FIG. Will be provided.

The image data of the chart 3 is taken into the image buffer provided in the image reading device according to the circuit configuration shown in FIG. The detecting means 26 shown in FIG. 2 detects the MTF characteristic indicated by the apparatus from the image data of the chart 3 stored in the image buffer as described in FIG. The process of detecting the MTF characteristic is as follows.
Specifically, as shown in FIGS. 12A and 12B, one line of the image data of the chart 3 is read in each of the main scanning direction (x) and the sub-scanning direction (y). FIG.
As shown in FIG. 12C, a differential value of the read image data is calculated for each of the main scanning direction (x) and the sub-scanning direction (y), and then, as shown in FIG. ,
In each of the main scanning direction (x) and the sub-scanning direction (y), the differential image data is subjected to Fourier transform to obtain a power value with respect to a spatial frequency.

The MTF characteristics thus obtained represent the resolution characteristics including the optical system of the device. The arithmetic means 27 shown in FIG. 2 modulates the degree of enhancement of the image data read by the image sensor 23 according to the set parameters, as described in FIG. The arithmetic means 27 employs a configuration in which the degree of enhancement of image data is modulated using, for example, Laplacian enhancement.
The pixel data S ₂ of the center pixel of the 5 × 5 matrix pixel shown in FIG.

[0054]

(Equation 1)

The image data value S_Two’
Calculation will be performed. Where K _xIs the main scanning direction
K is the emphasis parameter_yIs the emphasis parameter in the sub-scanning direction.
Data. It should be noted that the calculating means 27 is a one-dimensional Laplacian
When using image enhancement, the one-dimensional image shown in FIG.
Pixel data S of the central pixel of the pixel_TwoTo

[0056]

(Equation 2)

The operation of replacing the image data with the image data S ₂ ′ is performed. According to the Laplacian enhancement, the arithmetic means 27 performs a filtering process of changing the enhancement degree of the image data depending on the spatial frequency by the value of the enhancement parameter K as shown in FIG.

FIG. 15 shows a case where Laplacian enhancement is used.
The circuit configuration of the calculating means 27 in the case is shown. In the figure, 30 is
Four FIFOs connected in cascade, and image data
What is buffered, 31 is 5 × 5 flip-flops
, Which latches image data, 32
An adder, which is a pixel data S shown in FIG._0,S_FourAddition value of
Is an adder, which is a pixel of FIG.
Data S_Five,S₈34 is an adder.
32 is a multiplier which receives the output value of 32 as an input,
35 is an output of the adder 33.
A multiplier that takes a value as an input, wherein the third
The term 36 calculates pixel data S _TwoInput
A multiplier for calculating the first term on the right side of the equation (1)
And 37, the output values of the multipliers 34, 35, 36
Which calculates the value of the expression (1).
You.

According to the circuit configuration of FIG. 15, the arithmetic means 27 exerts a function of modulating the degree of enhancement of image data using Laplacian enhancement. The setting unit 28 shown in FIG. 2 is, as described with reference to FIG.
6, a parameter that makes the resolution of the image data output by the calculating means 27 specified is specified from the MTF characteristics detected by the calculating means 6 and the specified MTF characteristics and set in the calculating means 27.

That is, for example, when the MTF characteristic at the time of shipment from the manufacturer is as shown by the broken line in FIG. When it is detected that the MTF characteristic becomes as shown by the solid line in FIG. 16A which causes a decrease in the high spatial frequency component, the setting unit 28 sets the emphasis parameter used by the arithmetic unit 27 as shown in FIG. By selecting and setting one that emphasizes the high spatial frequency components as shown in FIG. 16 (c), the M of the image data output from the calculating means 27 is displayed as shown in FIG.
The processing is performed so that the TF characteristics are those at the stage of shipment from the manufacturer.

As described above, in the image reading apparatus of the present invention shown in FIG. 2, the resolution of the image data to be read can be kept constant, for example, at the stage of shipment. There is no degradation of quality.

Although the illustrated embodiment has been described, the present invention is not limited to this. For example, in the processing flow shown in FIG. 6, a configuration in which the reference white level value is obtained by moving the line image sensor 10 to the position of the detection line “Y _MAX / 2 + WP _MAX ” in step 16 is disclosed.
The present invention is not limited to this, but adopts a configuration in which a previously read white level value is stored, and a reference is made by selecting one of the detection lines “Y _MAX / 2 + WP _MAX ” from the white level values. It is also possible to adopt a configuration for obtaining a white level value.

In this processing flow, the reference white plate 2
Although the configuration for detecting the maximum length area where no dust is attached from the area b is disclosed, the present invention is not limited to this, and it is possible to detect a continuous area where dust is not attached. But it may be.

For example, in the embodiment shown in FIG.
Although a configuration in which one chart 3 is provided at a position before scanning of the document surface 1 is disclosed, the present invention is not limited to this.
As shown in FIG. 7, by adopting a configuration in which a plurality of charts 3 are prepared corresponding to different image portions of the image data to be read, the detecting means 26 detects the MTF characteristics of the optical system corresponding to each chart, It is also possible to adopt a configuration in which the setting means 28 specifies and sets an emphasis parameter for each chart.

[0065]

As described above, according to the image reading apparatus of the present invention, a configuration is adopted in which the white level value is always input to the specific sensor element of the line image sensor, and the detected value of this specific sensor element is used. The configuration in which the change in the light source light amount is detected in real time in accordance with and the white level value for shading correction is adopted, so that even if it takes time to read the image data,
The quality of the image data to be read does not deteriorate.

Further, according to the image reading apparatus of the present invention, by evaluating the smoothness of the white level value on the reference white plate, an area where dust is not attached is detected, and from among the areas, the shading correction area is determined. From the configuration that reads the white level value,
Even if dust adheres to the reference white plate, the quality of image data to be read does not deteriorate.

Further, according to the image reading apparatus of the present invention, the resolution of the image data to be read can be kept constant, for example, at the stage of shipment.
The quality of the image data to be read does not deteriorate.

[Brief description of the drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a principle configuration diagram of the present invention.

FIG. 3 is an example of a reference white plate.

FIG. 4 is an embodiment of a processing flow executed by the present invention.

FIG. 5 is an explanatory diagram of a correction process according to the present invention.

FIG. 6 is an example of a processing flow executed by the present invention.

FIG. 7 is an explanatory diagram of a position symbol of a reference white plate.

FIG. 8 is an explanatory diagram of a reference white level value obtaining process according to the present invention.

FIG. 9 is an example of a chart.

FIG. 10 is an example of an arrangement form of a chart.

FIG. 11 is a configuration diagram of a circuit included in the image reading apparatus.

FIG. 12 is an explanatory diagram of a detection process executed by a detection unit.

FIG. 13 is an explanatory diagram of an arithmetic circuit configuration of the arithmetic means.

FIG. 14 is an explanatory diagram of calculation contents of a calculation means.

FIG. 15 is an embodiment of a circuit configuration of a calculating means.

FIG. 16 is an explanatory diagram of a correction process according to the present invention.

FIG. 17 shows another example of a chart layout.

FIG. 18 is a diagram illustrating a configuration of an image reading apparatus.

FIG. 19 is an explanatory diagram of a shading correction technique.

FIG. 20 is an explanatory diagram of a problem of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Original surface 2a Reference white plate 2b Reference white plate 3 Chart 10 Line image sensor 11 Amplifying means 12a Reference white level value storage means 120 First storage area 121 Second storage area 13 Shading correction means 14 Comparative white level value extraction means Reference Signs List 15 calculation means 16 correction means 17 first instruction means 18 second instruction means 19 determination means 20 detection means 21 determination means 22 setting means 23 image sensor 24 amplification means 25 chart image storage means 26 detection means 27 calculation means 28 setting means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-168 (JP, A) JP-A-3-112268 (JP, A) JP-A-3-131171 (JP, A) JP-A-5-131 14712 (JP, A) JP-A-3-34774 (JP, A) JP-A-3-120951 (JP, A) JP-A-1-160177 (JP, A) JP-A-62-35772 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (6)

(57) [Claims] An image data is read by a line image sensor, a white level value is read by a line image sensor prior to reading the image data, and shading correction is performed on the image data to be read according to the white level value. (17) instructing the movement of the line image sensor in the zone where the white level value is generated, and responding to the instruction of the instruction means (17). A judgment unit (19) for judging whether each detection line of the white level value is a detection line of an appropriate white level value by evaluating the smoothness of the white level value read for each detection line. A detecting means (20) for detecting a continuous area of a detection line of an appropriate white level value in the zone while referring to a result of the determination by the determining means (19); Determining means (21) for determining a specific detection line from the area detected by the detecting means (20); and a white level value read from the detection line determined by the determining means (21). An image reading apparatus, comprising: setting means (22) for setting a level value. 2. The image reading apparatus according to claim 1, wherein the detecting means performs processing so as to detect a continuous area of a detection line having the longest appropriate white level value. Image reading device. 3. An image reading apparatus according to claim 1 or 2, wherein determining means (21) to process to continue to determine the detection line of the central part of the detection region of the detecting means (20), Characteristic image reading device. 4. The image reading apparatus according to claim 1, 2 or 3, wherein setting means (22) includes a white level value to be read from the determined detecting line determining means (21), in the vicinity of the detection line Image reading characterized by processing to calculate and set a white level value for shading correction from a white level value read from one or more existing detection lines of an appropriate white level value. apparatus. 5. An image reading apparatus having a configuration in which image data is read by an image sensor, wherein a chart (3) of a black-and-white edge image is configured to be readable by the image sensor, and the chart read by the image sensor is provided. (3)
To calculate the differential values of the image data of the black-and-white edge image, the
Computation with detection means for detecting an MTF characteristic indicated by that the equipment for performing the Fourier transform on the differentiated image data (26), according to a parameter set, and can modulate the enhancement degree of the image data read by the image sensor Means (27), an MTF characteristic detected by the detecting means (26), and a specified MTF.
And setting means (28) for specifying the parameter that makes the resolution of the image data output from the calculating means (27) specified from the characteristics and setting the parameter in the calculating means (27). Image reading device. 6. The image reading apparatus according to claim 5 , wherein a plurality of charts are prepared corresponding to different image portions of the image data to be read, and the detecting means is an optical system corresponding to each chart. An MTF characteristic of the image reading apparatus, and a setting unit (28) performs processing for specifying and setting parameters corresponding to each chart.