JPH1169154A - Method and device for correcting shading - Google Patents

Abstract

PROBLEM TO BE SOLVED: To speedily and precisely correct shading with a simple configuration by performing shading compensation by using a histogram mode detected by a histogram mode detecting means for every pixel. SOLUTION: Black shading compensation data and white shading compensation data are fetched before reading an original image. Next, the original image is read. Read original image data is supplied to a shading compensating circuit 106, a subtracter 109 performs black shading compensation and a multiplier 110 performs white shading compensation receptively with an the shading compensation data that is fetched before reading. In such cases, shading compensation is performed by using a histogram mode that is detected by a histogram mode detection circuit 102 and in each pixel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to an image reading apparatus using a solid-state image pickup device such as a CCD (image pickup device) line sensor such as a copying machine. The present invention relates to a shading correction method and apparatus for correcting shading by a machine and an optical system performed as light distribution correction of a light source body or generated in read data by shading data read from a white correction plate.

[0002]

2. Description of the Related Art The configuration of a conventional shading correction device is shown in FIG. In the figure, the output of an n-pixel CCD line sensor (hereinafter referred to as CCD) 1001 is a sample-and-hold circuit (hereinafter referred to as SH circuit) 10.
02, a gain control amplifier (hereinafter, referred to as GCA) 1003, a clamp circuit (hereinafter, referred to as a CP circuit) 1004, which is converted to a predetermined level by an A / D converter 1005, and is converted to digital data and shaded. It is supplied to the correction circuit 1006.

The shading correction circuit 1006 includes a black shading correction unit 1011 and a white shading correction unit 1026.

The black shading correction unit 1011 has nx
13-bit black memory 1007, black memory 1007
Adder 100 for adding output data and input data of
8. an averaging circuit 1099 for averaging the output data of the black memory 1007 for each pixel;
It comprises a subtractor 1010 for performing a subtraction process on the output data of 99, and performs a black shading correction process by the following operation.

The input data is added by a predetermined number of lines,
It is taken into the black memory 1007. In general, a black signal can be sufficiently expressed by using 32 gradations with respect to a quantization size of 8 bits and 256 gradations of the A / D converter 1005. Therefore, when a 13-bit black memory 1007 is used,
Addition processing up to 256 lines is possible.

The data fetched into the black memory 1007 becomes black shading correction data. The black shading correction data is averaged by the averaging circuit 1099, the subtraction of the input data from the corresponding pixel is performed by the subtractor 1010, and the black shading correction is completed. The signal data after the black shading correction is (00) h.

The white shading correction unit 1026 has n ×
13-bit white memory 1020, white memory 1020
Adder 102 for adding the output data and input data of
1. An averaging circuit 1022 for averaging the output data of the white memory 1020 for each pixel, a correction coefficient operation circuit 1023 for obtaining a correction coefficient for a blank target 1024 set by a system controller (not shown), and an input data and correction coefficient operation circuit 1023. The input data is added by a predetermined number of lines in the same manner as in the black processing for performing white shading correction processing by the following operation, and is taken into the white memory 1020. Since the expression of a white signal requires 8 bits and 256 gradations, when a 13-bit white memory 1020 is used,
Addition processing for up to 32 lines is possible.

The data fetched into the white memory 1020 becomes white shading correction data. The white shading correction data is averaged by the averaging circuit 1022, and the output data of the correction coefficient calculation circuit 1023 is multiplied by the corresponding pixel of the input data to complete the white shading correction. The signal data after the white shading correction can be set by the white target 1024.
Generally, it is set to (FF) h.

In a document reading apparatus, shading correction is to normalize the white and black levels of a document to white and black levels in image processing for each pixel. Generally, a standard white plate is provided as a standard for normalization. I have. The target level of the standard white plate for normalization is white target 102
4 is set as the data.

In the document reading apparatus, shading correction is performed according to the following procedure.

(1) Capture of black signal when exposure lamp is off The data for black shading correction is captured. In this conventional example, an averaging operation for a maximum of 256 lines can be performed. The average number of calculations is appropriately set based on the SN.

(2) Capture of white signal from standard white plate The exposure lamp is turned on at a predetermined voltage to capture data from the standard white plate. In this conventional example, a maximum of 32
Average calculation up to the line can be performed. The standard white plate is one in which the density does not change much with time, or the density is controlled by a bar code or the like.

(3) Reading of Original Image The shading correction data is stored in the black memory 1007 and the white memory 1024 by the operations (1) and (2) described above. Thereafter, the original image is read, and the subtractor 1
010 and the multiplier 1025 synchronize the address of the read signal with the addresses of the black memory 1007 and the white memory 1020 and perform a predetermined operation.

FIG. 11 is a diagram schematically showing shading correction. The horizontal axis indicates the amount of light incident on the CCD line sensor 1001, and the vertical axis indicates the output level.

In FIG. 11, a is a standard white plate, b is a predetermined document, and b 'is an output characteristic of the document after shading correction.
It can be seen that the black level is normalized.

FIGS. 12A and 12B show the configuration of a conventional image reading apparatus. FIG. 12A shows the time of reading a standard white plate, and FIG. 12B shows the time of reading a document image. . 12, reference numeral 1201 denotes a standard white plate; 1202, an original; 1203, an original platen glass; 1204, an exposure lamp; 1205, 1206, 1207, mirrors;
Denotes a lens and 1209 denotes a CCD line sensor.

Bar code data (not shown) representing reflection density data is attached to the standard white plate 1201.

When reading bar code data representing the reflection density data written on the standard white plate 1201, the state shown in FIG.
When reading the image of the document 1202 placed on the document 203, the state shown in FIG. The illumination light emitted from the exposure lamp 1204 is
The lens 1208 is reflected on the surface 01 or on the surface of the original 1202 and passes through mirrors 1205, 1206 and 1207.
To form an image on the CCD line sensor 1209. C
In the CD line sensor 1209, the formed image is input to an image processing unit (not shown) at the subsequent stage, subjected to predetermined image processing, sent to a printer (not shown), and output as a copy image on paper.

In the shading correction method in such a conventional image reading apparatus, shading data is read several times at a fixed position of a standard white plate, and the average value is used as shading correction data. A shading correction coefficient as shown in FIG. 13 is calculated from the ratio between the correction data and the shading target value, and the shading correction coefficient is multiplied by the data of the corresponding pixel of the image data as shown in FIG. Had gone.

In FIG. 13, reference numeral 1301 denotes a shading target value, and 1302 denotes shading data. In FIG. 14, reference numeral 1401 denotes image data before correction;
Reference numeral 2 denotes image data after correction.

[0021]

However, the above-mentioned conventional apparatus has a problem as shown in FIG. 15 when performing white shading correction.

FIG. 15 is a diagram showing a problem in performing white shading correction in a conventional apparatus. FIG. 15A shows an example of a histogram of output data of a standard white plate when white shading correction data is captured. The spread of the skirt is extremely large on the left. In this case, the average value becomes smaller than the peak value as shown in the drawing, and when the normalization is performed, as shown in FIG. 15B, the output characteristic d of the peak value is more than the output characteristic c of the average value. The slope is large and saturated at point e. Therefore, the image becomes an image in which white tends to fly after point e. In addition, depending on the distribution of the histogram, an image or the like that tends to be blackened may occur. Furthermore,
For a CCD having a plurality of outputs, the image quality may be degraded due to a mismatch in linearity of each output.

As described above, the conventional shading correction using the average value due to the asymmetric distribution of the histogram of the image data cannot prevent the deterioration of the image quality. Such problems are expected to increase with the speeding up of digital devices in recent years.

In the conventional example of reading the shading data at the fixed position described above, if there is dust, dirt, or the like in the place where the shading data is read on the standard white plate, the data necessary for reading the original image is required. There is a problem in that shading correction data cannot be obtained and the output image is affected as shown in FIG.

In FIG. 16A, reference numeral 1601 denotes a shading target value, and 1602 denotes shading data. In FIG. 16B, reference numeral 1603 denotes image data before correction;
Reference numeral 1604 denotes image data after correction.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and a first object of the present invention is to provide a simple configuration, a high-speed and high-precision shading correction. It is an object of the present invention to provide a shading correction method and apparatus capable of performing the following.

A second object of the present invention is to reduce the influence on the image data even if the standard white plate has dust or dirt, and to reduce the production cost of the apparatus. It is an object of the present invention to provide a shading correction method and a shading correction method.

[0028]

According to a first aspect of the present invention, there is provided a shading correction method for calculating a mode of a histogram for each pixel of a solid-state imaging device in an image reading apparatus. A mode calculation step; and a shading correction step of performing shading correction using the mode of the histogram calculated in the histogram mode calculation step.

According to another aspect of the present invention, there is provided a shading correction apparatus for calculating a mode of a histogram for each pixel of a solid-state image sensor in an image reading apparatus. Means, and shading correction means for performing shading correction using the mode of the histogram calculated by the histogram mode calculation means.

According to a third aspect of the present invention, there is provided a shading correction device according to the second aspect, wherein the histogram mode calculating means includes at least n pixels × m lines. Page memory means, a comparing means for comparing a plurality of gradations,
Measuring means for measuring the frequency of each tone of the comparing means, and judging means for judging the most frequent tone for each tone of the comparing means from the measurement result of the measuring means. .

In order to achieve the first object, a shading correction device according to a fourth aspect of the present invention is the shading correction device according to the third aspect, wherein the histogram mode calculation means includes the comparison means and the measurement means. A series of operations by the means and the determination means are performed for each pixel of the page memory means.

According to a fifth aspect of the present invention, there is provided a shading correction method according to the fifth aspect, wherein a white correction plate is scanned by an image sensor in a main direction and a sub direction to read the shading data. A shading correction method for an image reading apparatus for correcting shading of image data read by scanning an image in a main direction and a sub-direction by an image sensor, wherein an average value of the shading data is calculated from a plurality of data in the sub-direction of the shading data. And shading correction of the read image data using a shading correction coefficient calculated from a ratio of the data to a predetermined value.

According to a sixth aspect of the present invention, there is provided a shading correction method according to the fifth aspect, wherein the maximum value among a plurality of data in the sub-direction of the shading data is provided. The average value is obtained from the value excluding the minimum value and the minimum value.

According to a seventh aspect of the present invention, there is provided a shading correction method according to the fifth aspect, wherein the shading data is read at a plurality of locations in a sub-direction and is provided at each location. Is read a plurality of times.

According to another aspect of the present invention, there is provided a shading correction device for scanning a white color correction plate by using an image sensor in a main direction and a sub direction to read a shading data. What is claimed is: 1. A shading correction device for an image reading device, which scans an image in an image sensor in a main direction and a sub direction to correct shading of read image data, wherein an averaging device calculates an average value from a plurality of data in the sub direction of the shading data. Value calculation means, shading correction coefficient calculation means for using the average value calculated by the average value calculation means as shading data, and calculating a shading correction coefficient from a ratio of the shading data to a predetermined value; and the shading correction coefficient calculation means Using the shading correction coefficient calculated by And having a shading correction means for correcting the shading of the image data Tsu.

In order to achieve the second object, a shading correction device according to a ninth aspect of the present invention is the shading correction device according to the eighth aspect, wherein the average value calculating means includes a plurality of shading data sub-directions. The average value is obtained from the value obtained by excluding the maximum value and the minimum value from the data.

According to a tenth aspect of the present invention, there is provided a shading correction apparatus according to the tenth aspect, wherein the shading data is read at a plurality of locations in a sub-direction. And a reading means for reading a plurality of times.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS.

(First Embodiment) First, the first embodiment of the present invention will be described.
The embodiment will be described with reference to FIGS. FIG.
FIG. 1 is a block diagram illustrating a configuration of a shading correction device according to a first embodiment of the present invention, in which the same parts as those in FIG. 10 of the above-described conventional example are denoted by the same reference numerals.

FIG. 1 differs from FIG. 10 in that FIG.
And a shading correction circuit 106 having a configuration different from that of the shading correction circuit 1006.

The histogram mode detection circuit 102 includes a comparator 103, a group of counters 104, and a maximum value detection circuit 105. The shading correction circuit 106 includes a black memory 107, a white memory 108, and a subtractor 1.
09, a multiplier 110, a correction coefficient operation circuit 1023, and a white target 1024.

In FIG. 1, the output of a CCD line sensor 1001 of n pixels is output from an SH circuit 1002 and a GCA 100.
3. After being converted to a predetermined level by the CP circuit 1004, 8
The data is converted into digital data by a bit A / D converter 1005.

Prior to reading the original image, the loading of the black shading correction data and the loading of the white shading correction data are performed as follows.

(Retrieval of black shading correction data) The exposure lamp (not shown) is turned off, and the CCD
Signal reading from the line sensor 1001 is performed.
The digital data converted by the A / D converter 1005 is
It is stored in the page memory circuit 101. This page memory circuit 101 has a configuration of n × m × 8 bits, and can store the output of the n-pixel CCD line sensor 1001 for m lines. Here, m = 256.

The data stored in the page memory circuit 101 is read address controlled by the histogram mode detection circuit 102, and the stored data is sequentially transferred to the histogram mode detection circuit 102. In the read control, as shown in FIG. 2, data for the first pixel and m lines are sequentially transferred to the n-th pixel as one data series. First, the histogram mode detection circuit 102 determines whether the first pixel data of the page memory circuit 101 has 256 pixels (25 pixels).
6 lines of data) and read them out sequentially. The read data is subjected to data value discrimination by a 256-gradation comparator 103, and is supplied to a clock of a corresponding counter of an 8-bit counter group 104 so that the count value is 1
Go up. After 256 data are all processed by the comparator 103 and the counter group 104, the maximum value detection circuit 10
5, the mode is determined.

FIG. 3 shows a histogram mode detection circuit 102.
The above operation is schematically illustrated, and the horizontal axis is the comparator 1
And the vertical axis indicates the counter group 10
4 respectively. In this case, the maximum value is “4”. The output of the maximum value detection circuit 105 is stored at an address corresponding to the first pixel of the black memory 107 of the shading correction circuit 106. Next, data of the second pixel to the n-th pixel is processed in the same manner.

(Retrieval of White Shading Correction Data) A not-shown exposure lamp is turned on, and data for 256 lines of a standard white plate (not shown) is stored in the page memory circuit 1.
01. As in the case of the black shading correction data, the mode value is obtained for each pixel. The obtained mode is corrected by the correction coefficient calculation circuit 1023 for the white target 1024, and then the white memory 10
8 is stored at the corresponding address. Next, a document image is read.

The read original image data is supplied to a shading correction circuit 106, and the subtracter 10 uses the shading correction data taken in before reading.
9 and the white shading correction by the multiplier 110 are performed. The data after the shading correction is supplied to a subsequent image processing circuit (not shown).

FIG. 4 shows that the accumulation time of one line is 100 μsec.
9 is a timing chart showing the timing of reading a document image when the setting is c.

FIG. 4A shows the timing in the present embodiment. As shown in FIG. 4A, first, 256 lines × 100
μsec = 25.6 msec, and the time required for the calculation of the black data is 256 × n pixels as in the case of the input of the black shading correction data.
56 × 100 μsec = 25.6 msec is required, and the acquisition and calculation of white data are similarly performed for 25.6 ms.
ec required, 102.4msec from start
The reading of the document image is performed later.

FIG. 4B is a timing chart showing the timing of reading the original image when the histogram mode value is detected without using the page memory circuit 101. As shown in FIG. 4B, this is a case where 256 lines are taken in to perform the operation of the first pixel, and 256 lines need to be taken in the same manner for each pixel. In this case, from the start to the start of reading the original image, 2
It takes 5.6 msec × n pixels, and n = 50
Assuming that the time is 00, it takes 256 seconds and about 4 minutes. Also, half of this time is not desirable in terms of power, heat, and safety because the exposure lamp is turned on to capture the white shading correction data. Therefore, in this embodiment, the page memory circuit 101 is a minimum required.

As described in detail above, according to the shading correction apparatus according to the present embodiment, the histogram mode detection circuit 102 for each pixel is provided, and the histogram mode detection circuit 102 detects the histogram mode. The shading correction is performed using the values. More specifically, by obtaining the histogram mode value for each pixel from the data fetched into the page memory circuit 101 by the histogram mode detection circuit 102, the shading correction with a simple configuration and at higher speed and with higher accuracy can be performed. It can be carried out.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
The embodiment will be described with reference to FIGS. FIG. 5 is a block diagram showing a configuration of a shading correction device according to the second embodiment of the present invention. In the figure, 501 is CC
A D linear sensor 502 is an A / D converter, which converts the output of the CCD linear sensor 501 into a digital value. A line memory circuit 503 stores the captured image data. Reference numeral 504 denotes a selector, and reference numeral 505 denotes a maximum / minimum value detection circuit which takes in shading data from a standard white plate (not shown) and removes the maximum value and the minimum value from data different in the main direction in the same direction in the sub-direction. is there. Reference numeral 506 denotes an averaging circuit for obtaining an average value of data from which the maximum value and the minimum value have been removed by the maximum value / minimum value detection circuit 505. A shading memory circuit 507 stores an average value of each position in the main direction. A shading correction circuit 508 multiplies a shading correction coefficient calculated from an average value in the shading memory circuit 507 corresponding to the main direction of image data obtained by fetching a document image and outputs the result.

The selector 504 is connected to the maximum value / minimum value detection circuit 505 when taking in shading data from the standard white plate, and is connected to the shading correction circuit 508 in taking in image data. .

Next, the operation of the shading correction apparatus according to the present embodiment having the above configuration will be described.

To load shading data from a standard white plate (not shown), the selector 504 is connected to the maximum / minimum value detection circuit 505 side. The maximum / minimum value detection circuit 505 detects the maximum value and the minimum value and outputs the sum separately. The averaging circuit 506 adds different data in the sub-direction at the same location in the main direction, subtracts the value obtained by the maximum / minimum value detection circuit 505 from the added value, and obtains a predetermined value (total data acquisition in the sub-direction). If the number is f, "f-2"
Divide by) to obtain the average value. The shading memory circuit 507 stores the average value.

Next, when fetching image data, the selector 504 is connected to the shading correction circuit 508 side. The image data output from the line memory circuit 503 is input to a shading correction circuit 508, and a shading correction coefficient calculated from the shading data stored in the shading memory circuit 507 and the shading target value is calculated. Is output.

FIG. 6 is a diagram showing the position where the shading data is taken in on the standard white plate. In the figure,
Data of n points is taken in the main direction, and data of one point is taken in the sub direction. Data is taken in j times at each point in the sub-direction. That is, each pixel takes in data of j × 1 time.

FIG. 7 shows shading data on the standard white plate and its effect. FIG. 7A shows a reading position on the standard white plate. E1 to Em in the main direction and L1 to Ln in the sub direction, the coordinates (Eh, Li), (Ej,
If dust is present at Lk), the shading data has waveforms as shown in FIGS. 7B to 7D. Taking the average value of the data in these sub-directions approximates an average waveform as shown by the dotted line in FIG. 7 (e), but the location where dust is present is affected to some extent.

When the output of the exposure lamp fluctuates, the shading data also fluctuates as shown by the vertical arrows in FIGS. 7B to 7D. In order to eliminate this effect, it is necessary to take shading data a plurality of times at the same place.

FIG. 8 shows an actual image reading sequence. In FIG. 8, when an image reading operation is commanded, a shading operation starts, and in step S801, the image reading position is moved to a standard white plate. Next, step S8
At 02, it is determined whether or not the shading sample operation has been completed. If the shading sample operation does not end, the acquisition of the shading data is repeatedly executed at the same location in the sub direction. Next, step S8
At 03, it is determined whether or not the capture of the shading data at the same location is completed. If the capturing of the shading data at the same location is completed, the image reading position is moved to a different location on the same standard white plate in step S805 to repeat the capturing of the shading data, and then the process returns to step S802. It is determined whether the shading sample operation has been completed.

If the loading of the shading data at the same location is not completed in step S803, the loading of the shading data is performed at step S804, and the process returns to step S803 to capture the shading data at the same location. It is determined whether the process is completed.

On the other hand, if the shading sample operation has been completed in step S802, the process proceeds to step S802.
At 806, shading data processing is performed, and an image capturing operation is started. The shading data processing here means detection of the maximum value and the minimum value of the maximum value / minimum value detection circuit 505 in FIG. 5, addition of the total data, and averaging by the value obtained by subtracting the maximum value and the minimum value by the averaging circuit 506. Calculating the value and storing the calculated value in the shading memory circuit 507.

Upon entering the image capturing operation, first, in step S807, the image reading position is moved to the image capturing position. Next, in step S808, it is determined whether or not image capturing has been completed. Then, when the image capturing is completed, this processing operation ends without performing any processing. If image capture has not been completed in step S808, image capture is performed in step S809, and shading correction is performed using data in the shading memory circuit 507 in the next step S810. Next, in step S811, the data is output to an output device such as a printer. After moving the image capturing position in the next step S812, the process returns to step S808 to determine whether the image capturing is completed. These series of operations are repeated until image capturing is completed.

The shading correction here is to correct the image fetched data based on the ratio between the data in the shading memory circuit 507 and the shading target value.

As described in detail above, according to the shading correction apparatus according to the present embodiment, an average value is calculated by the averaging circuit 506 from a plurality of pieces of data in the sub-direction of the shading data, and the calculated average value is calculated. Since the read image data is shaded using the shading correction coefficient calculated by the shading correction coefficient calculation circuit 1023 from the ratio of the data to a predetermined value as the shading data, the fluctuation of the exposure lamp, for example, on the standard white plate The influence of dust and dust on the image data is reduced.

(Third Embodiment) Next, a third embodiment of the present invention will be described.
The embodiment will be described with reference to FIG. FIG. 9 is a block diagram showing a configuration of a shading correction device according to the third embodiment of the present invention. In the figure, reference numeral 901 denotes a CCD linear sensor; and 902, an A / D converter for converting the output of the CCD linear sensor 901 into a digital value. 9
A line memory circuit 03 stores the captured image data. Reference numeral 904 denotes a selector, and reference numeral 905 denotes a maximum / minimum value detection circuit which takes in shading data from a standard white plate (not shown) and removes the maximum value and the minimum value from data different in the main direction in the sub-direction at the same location. is there. An addition circuit 906 adds different data in the sub-direction at the same location in the main direction. 907 is a division coefficient, and 908 is a shading memory circuit for storing shading correction coefficients.

The selector 904 is connected to the maximum / minimum value detection circuit 905 when taking in shading data from the standard white plate, and connected to the output side when taking in image data.

Next, the operation of the shading correction device according to the present embodiment having the above configuration will be described.

When fetching shading data from a standard white plate (not shown), the selector 904 is connected to the maximum / minimum value detection circuit 905 side. The maximum / minimum value detection circuit 905 detects a maximum value and a minimum value. The addition circuit 906 adds different data in the sub-direction at the same location in the main direction. The shading memory circuit 9 subtracts the maximum value and the minimum value obtained by the maximum / minimum value detection circuit 905 from the addition result and divides the value by the division coefficient 907.
08.

Next, when fetching image data, the selector 904 is connected to the output side. Line memory circuit 903
Is output after being multiplied by the shading correction coefficient stored in the shading memory circuit 908.

[0072]

As described above in detail, according to the shading correction method according to the first aspect of the present invention and the shading correction apparatus according to the second to fourth aspects, the histogram detected by the histogram mode detection means for each pixel. Since the shading correction is performed using the mode value, there is an effect that the shading correction can be performed with higher speed and higher accuracy with a simple configuration.

According to the shading correction method according to claims 5 to 7 and the shading correction apparatus according to claims 8 to 10 of the present invention, an average value is calculated from a plurality of pieces of data in the sub-direction of shading data. Using the calculated average value as shading data, using a shading correction coefficient calculated from a ratio of the data to a predetermined value,
Since the read image data is shaded, there is an effect that fluctuation of the exposure lamp, for example, influence of dust or dust on the standard white plate on the image data is reduced.

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating a page memory configuration in the shading correction device according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating detection of a histogram mode value in the shading correction device according to the first embodiment of the present invention.

FIG. 4 is a timing chart showing image reading timings in the shading correction device according to the first embodiment of the present invention.

FIG. 5 is a block diagram illustrating a configuration of a shading correction device according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a shading data capturing position in a shading correction device according to a second embodiment of the present invention.

FIG. 7 is a diagram showing shading data at each position in a shading correction device according to a second embodiment of the present invention and the effect thereof.

FIG. 8 is a flowchart illustrating an image capturing sequence of the shading correction device according to the second embodiment of the present invention.

FIG. 9 is a block diagram illustrating a configuration of a shading correction device according to a third embodiment of the present invention.

FIG. 10 is a block diagram illustrating a configuration of a conventional shading correction device.

FIG. 11 is a diagram illustrating shading correction in a conventional shading correction device.

FIG. 12 is a side view showing a configuration of a conventional shading correction device.

FIG. 13 is a diagram showing shading correction coefficients in a conventional shading correction device.

FIG. 14 is a diagram showing image data in a conventional shading correction device.

FIG. 15 is a diagram illustrating a problem of average value shading in a conventional shading correction device.

FIG. 16 is a diagram for explaining a problem in a conventional shading correction device.

[Explanation of symbols]

 101 Page memory circuit 102 Histogram mode detection circuit 103 Comparator 104 Counter group 105 Maximum value detection circuit 106 Shading correction circuit 107 Black memory 108 White memory 109 Subtractor 110 Multiplier 501 CCD line sensor 502 A / D converter 503 Line memory Circuit 504 Selector 505 Maximum / minimum value detection circuit 506 Averaging circuit 507 Shading memory circuit 508 Shading correction circuit 901 CCD linear sensor 902 A / D converter 903 Line memory circuit 904 Selector 905 Maximum / minimum value detection circuit 906 Addition circuit 907 Division coefficient 908 Shading memory circuit 1001 CCD line sensor 1002 Sample hold circuit (SH circuit) 1003 Gain control amplifier (GCA) 1004 clamp circuit (CP circuit) 1005 A / D converter

Claims (10)

[Claims] 1. A histogram mode calculating step of calculating a mode of a histogram for each pixel of a solid-state imaging device in an image reading device, and a mode of a histogram calculated by the histogram mode calculating step is calculated. A shading correction step of performing shading correction by using the shading correction method. 2. A histogram mode calculating means for calculating a mode of a histogram for each pixel of a solid-state imaging device in an image reading device; and a mode of a histogram calculated by the mode calculating means. A shading correction device for performing shading correction using the shading correction device. 3. The histogram mode calculation means includes a page memory means for at least n pixels × m lines, a comparison means for comparing a plurality of gradations, and a measurement for measuring the frequency of each gradation of the comparison means. 3. A shading correction apparatus according to claim 2, further comprising: means for judging the most frequent gradation for each gradation of said comparing means from the measurement result of said measuring means. 4. The histogram mode calculating means, wherein a series of operations by the comparing means, the measuring means, and the determining means are performed for each pixel of the page memory means. 3. The shading correction device according to 3. 5. Shading of image data read by scanning a target image in a main direction and a sub-direction by an image sensor using a shading data read by scanning a white correction plate with an image sensor in a main direction and a sub-direction. A shading correction method for an image reading apparatus, wherein an average value is used as shading data from a plurality of data in the sub-direction of the shading data, and a shading correction coefficient calculated from a ratio of the data to a predetermined value is used. A shading correction method for correcting shading of read image data. 6. The shading correction method according to claim 5, wherein an average value is obtained from a value obtained by removing a maximum value and a minimum value from a plurality of pieces of data in the sub-direction of the shading data. 7. The shading correction method according to claim 5, wherein the shading data is read at a plurality of locations in the sub-direction and is read a plurality of times at each location. 8. Shading of image data read by scanning a target image in the main and sub directions by using an image sensor by using shading data read by scanning a white correction plate in a main direction and a sub direction by an image sensor. A shading correction device of an image reading device for correcting an average value from a plurality of data in the sub-direction of the shading data, an average value calculating means, and the average value calculated by the average value calculating means as shading data A shading correction coefficient calculating means for calculating a shading correction coefficient from a ratio of the shading data to a predetermined value; and shading for correcting shading of the read image data using the shading correction coefficient calculated by the shading correction coefficient calculating means. Correction means And a shading correction device. 9. The average value calculating unit according to claim 8, wherein the average value calculating means obtains an average value from a value excluding a maximum value and a minimum value among a plurality of data in the sub-direction of the shading data. Shading correction device. 10. The shading correction device according to claim 8, further comprising reading means for reading the shading data at a plurality of locations in the sub-direction and reading the shading data a plurality of times at each location.