JPH07264401A - Image reader - Google Patents

Abstract

PURPOSE:To reduce the capacity of a memory required to obtain a white level information mean value in the image information reader in which a white level reference face is scanned to obtain a correction value for shading. CONSTITUTION:The image reader is provided with a shading correction arithmetic section 7 consisting of an adder/subtractor circuit 71 in which a difference is obtained by subtracting a reference value from white level information obtained through scanning of a white level reference plane and a white level information mean value obtained by adding the reference value and a white level reference offset, of a division circuit 72 obtaining the white level information offset by dividing an integrated difference by a reference line number, and of a shading correction arithmetic section 73 correcting shading of the image information based on the white level information mean value to obtain an image correction signal, and with a correction value memory 11 integrating and storing the differences.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shading distortion correction function for image signals of a digital copying machine or the like.

[0002]

2. Description of the Related Art A white reference information calculating method for shading correction of a conventional digital copying machine is disclosed in Japanese Patent Laid-Open No. 59-59.
As described in Japanese Patent No. 223062 and Japanese Patent Laid-Open No. 60-246176, in order to improve the accuracy of white reference information, a plurality of pieces of white information obtained by reading a reference plane a plurality of times or by a plurality of lines are added, and the sum is added. A method has been proposed in which the number of readings is divided and averaged, and the average value is used as white reference information. However, since this method stores the white information for the number of times of reading, there is a problem that it is necessary to use a memory having a very large capacity and the cost cannot be kept low. Further, a method of sequentially adding the white information corresponding to the number of times of reading and storing the white information for each reading and dividing by the number of times of reading is also considered. However, since the added result is maximum one line of white information × the number of times of reading. , It is necessary to use a very large capacity memory to store the addition result. Therefore, this method has the same problem that the cost cannot be kept low.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a stable shading correction function at low cost in an image reading apparatus without increasing the memory capacity.

[0004]

A reading means for scanning a white reference plane and a document to obtain white information and image information, an average value calculating means for obtaining an average value of white information, and the white information average value are stored. In the image reading including a storage unit and a correction unit that performs shading correction on the image information obtained by scanning the document using the white information average value as the white reference information, the average value calculation unit includes the reference value and the reading unit. An adding and subtracting means for sequentially adding the difference between the white information and the reference value on the self-reference plane for a plurality of lines which are sequentially read at different positions,
Addition result storage means for storing the result of the addition and subtraction means,
A division means for dividing the value finally stored in the addition result storage means by the number of reading lines to obtain a white information offset amount, and an addition / subtraction means for adding the white offset amount and the reference value to obtain a white information average value. With.

[0005]

Since the white information offset amount is calculated by integrating the difference between the white information obtained by the reading means and the reference value, the capacity of the memory for storing the white information can be reduced.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a main part of an overall configuration of an image reading apparatus according to the present invention. The image reading apparatus includes an exposure lamp 1 serving as a light source, an optical system including a reflection mirror 2, an imaging lens 3, and a solid-state image sensor 4 such as a CCD, an amplifier 5, and an analog-digital converter 6 (hereinafter, referred to as A / D converter), a shading correction circuit 7, a digital filter 8, a reduction / enlargement unit 9, an image forming unit 10, a correction memory 11, a memory 12 and a memory 13, a CPU 14, and a timing generation circuit. 15, a sensor drive circuit 16, a platen 20 on which a document 21 is placed, and a white reference surface 24.

The light information of the original 21 irradiated by the light source 1 is imaged on the solid-state image pickup device 4 via the reflection mirror 2 and the lens 3 and converted into an analog electric signal to obtain image information. This image information is sent to the A / D converter 6
Then, the analog signal is converted into an n-bit digital signal and sent to the image processing section. In the image processing unit, the shading correction circuit 7 corrects the unevenness of the optical information generated based on the unevenness of the illumination of the light source 1 and the unevenness of the sensitivity of the solid-state image sensor. The image signal subjected to the shading correction by the shading correction circuit 7 is reduced / scaled by the MTF correction processing such as edge enhancement and smoothing of the image by the digital filter 8.
Image processing for reducing / enlarging an image is performed by the enlarging unit 9, and then the image data is sent to an image forming unit 10 such as a printer and printed on a sheet. The series of processes is controlled by the CPU 14. The solid-state image sensor 4 is driven by the sensor drive circuit 16 controlled by the timing from the timing generation circuit 15 and executes main scanning. The sub-scanning is performed by moving the light source and the optical system by a motor (not shown) controlled by the CPU 14.

Next, the configuration and operating principle of the shading correction circuit 7 which characterizes the present invention will be described with reference to FIG.

The shading correction circuit 7 of this embodiment is
For example, a reference value set in the CPU 14 is subtracted from the white reference plane information obtained by reading the white reference plane output from the solid-state image sensor 4 to calculate the difference, and the division circuit 72 is also provided.
An addition / subtraction circuit 71 for obtaining the white information average value by adding the white information offset amount from the reference value and the reference value;
A division circuit 72 for dividing the accumulated difference information stored in 1 by the number of reference lines and outputting a white information offset amount.
And a shading correction calculation unit 73 that performs shading correction calculation on the image information obtained by reading the document based on the white information average value.

In the image reading apparatus having such a structure, the light source 1 of the optical system moves below the white reference surface 24 and illuminates the white reference surface before reading the original 21.
The solid-state image sensor 4 performs main scanning in the direction perpendicular to the paper surface of FIG. 1 to obtain white information of the number of pixels for one line. This white reference plane reference scanning is performed a plurality of times to reduce errors in the white reference plane due to stains on the white reference plane.

The white information of the white reference plane of the read line is converted into a digital amount by the A / D converter 6 and then input to the addition / subtraction circuit 71. In the addition / subtraction circuit 71, the white information is subtracted from the reference data output from the CPU 14 for each pixel, and the difference is sequentially stored in the correction value memory 11 corresponding to each pixel. The white information of the subsequent lines is converted into a digital amount by the A / D converter 6, and then the reference data output from the CPU 14 is subtracted by the adder / subtractor circuit 71, and the difference is stored in the correction value memory 11. Are sequentially added to. This reading of the white reference plane is repeated a predetermined number of times. The reference scan of the white reference plane ends when the reading is performed a predetermined number of times. Next, the correction value memory 11
The integrated data of the difference data stored in is read out corresponding to each pixel, divided by the number of reference lines in the division circuit 72, and the white reference offset amount is output. Next, in the adder / subtractor circuit 71, the reference data output from the CPU 14 and the white reference offset amount corresponding to each pixel are added to obtain the white information average value. The average value of the white information is replaced with the integrated data stored in the correction value memory 11 corresponding to each pixel and sequentially stored. Thereafter, the document image information obtained by scanning the surface of the document 21 is A
After being converted into a digital amount by the / D converter 6, it is input to the shading correction calculation unit 73 and the white information average value that is the average value of the white information of the corresponding pixels stored in the correction value memory 11 is used to copy the document. An image correction signal obtained by shading-correcting the image information is calculated.

Next, a second embodiment of the present invention will be described with reference to FIG. This embodiment differs from the above-described embodiments in that the white information of the first line obtained by performing reference scanning on the white reference plane is used as the reference value and the reference value memory 17 for storing the reference value is provided. There is. Prior to reading a document, the light source 1 of the optical system moves below the white reference surface 24 and illuminates the white reference surface. The solid-state image sensor 4 scans in the direction perpendicular to the paper surface of FIG. 1 to obtain white information of the number of pixels for one line.

The read white information of the white reference plane of the first line is converted into a digital amount by the A / D converter 6 and then sequentially stored in the reference value memory 17. Next, the optical system performs sub-scanning in the right direction in FIG. 1, and the obtained white information of the second line is converted into a digital amount by the A / D converter 6. After that, the reference value including the white information of the first line stored in the reference value memory 17 is subtracted from the white information obtained in the adder / subtractor circuit 71. The difference is
The correction value memory 11 is sequentially stored for each pixel.
Similarly, the third line white information is also subtracted by the addition / subtraction circuit 71 by the reference value consisting of the white information of the white reference plane of the first line, and the difference is the difference data of the corresponding pixel stored in the correction value memory 11. Are sequentially added to. This reading is repeated a predetermined number of times. When the reading is performed a predetermined number of times, the reference scanning of the white reference plane ends.

Next, the data obtained by integrating the differences for each pixel stored in the correction value memory 11 is divided by the number obtained by subtracting 1 from the reference line number in the division circuit 72 to obtain the white reference offset amount. This white reference offset amount is output to the adder / subtractor circuit 71, where the reference value memory 1
The white information of the white reference plane of the first line stored in 7 is added to obtain the white information average value. The obtained white information average value is replaced with the integrated value of the difference data of the corresponding pixel stored in the correction value memory 11, and is sequentially stored. When the reference scanning of the white reference surface is completed, the optical system moves below the document 24 and scans the document surface. The original image information obtained as a result of scanning is converted into a digital amount by the A / D converter 6, and the white information average value which is the average value of the white information corresponding to each pixel stored in the correction value memory 11 is calculated. An image correction signal that has been subjected to shading correction using the shading correction calculation unit 73 and the original image information has been corrected is output.

[0015]

According to the present invention, when the white reference information for shading correction of the digital copying machine is calculated, the position of the white reference plane is moved and a plurality of lines are scanned to obtain the white information average value. It is possible to obtain an appropriate shading correction function that eliminates an inappropriate reference signal due to dirt or scratches on the reference surface. Further, since the difference between the white information obtained when obtaining the white information average value and the reference value is added and stored in the correction value memory, it is possible to store the read white information and the calculation result. The capacity of the storage device can be reduced, and the white information average value can be obtained at low cost. Therefore, an accurate and stable image signal can be obtained at low cost, and the white reference plane is held, and the assembly and processing of the apparatus do not require accurate accuracy, which enables cost reduction, etc. Its industrial value is great.

[Brief description of drawings]

FIG. 1 is a block diagram showing a concept of image reading including a shading correction circuit according to the present invention.

FIG. 2 is a block diagram showing a shading correction circuit according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing a shading correction circuit according to a second embodiment of the present invention.

[Explanation of symbols]

1 exposure lamp (light source), 4 solid-state image sensor, 6
A / D exchanger, 7 shading correction circuit, 10
Image forming unit, 11 correction value memory, 14 CPU,
21 manuscript, 24 white reference plane.

Claims (2)

[Claims] 1. A reading means for obtaining white information and image information corresponding to the original by scanning the white reference surface and the original, a storage means for storing an average value of the white information, and a plurality of arbitrary locations on the white reference surface. Shading correction means for performing shading correction of image information obtained by scanning the document by the reading means using white information average value obtained from a plurality of white information obtained by scanning once or a plurality of lines as white reference information. In the image reading apparatus described above, the shading correction unit subtracts a reference value from the white information on the white reference plane for a plurality of lines sequentially read by the reading unit while changing the position and sequentially adds the difference, and also the white information offset. The addition and subtraction means for adding the amount and the reference value to obtain the white information average value, and the storage means for storing the addition result An image reading apparatus comprising: a dividing unit that divides the finally added value that has been stored by the number of reference lines to obtain the white information offset amount. 2. A reading means for obtaining white information and image information corresponding to the original by scanning the white reference surface and the original, a storage means for storing an average value of the white information, and a plurality of arbitrary locations on the white reference surface. Shading correction means for performing shading correction of image information obtained by scanning the document by the reading means using white information average value obtained from a plurality of white information obtained by scanning once or a plurality of lines as white reference information. In the image reading apparatus described above, the shading correction means stores the white information of the first line of the white information on the white reference plane for a plurality of lines sequentially read by the reading means at different positions, and the reading means. Subtracts the white information of the first line from the white information on the white reference plane for multiple lines that are sequentially read at different positions. And add the difference in sequence,
From the number of reference lines, the addition / subtraction means for adding the white information offset amount and the white information of the first line to obtain the white information average value, and the finally added value stored in the storage means for storing the addition result. An image reading apparatus, comprising: a division unit that divides by 1 to obtain a white information offset amount.