JPS61135276A - Shading corrector - Google Patents

Abstract

PURPOSE:To obtain the picture signals which are free from shading distortion by providing a memory means for the shading correction data which is delivered synchronously with the output of a photoelectric conversion element and re peating the shading corrections to set the optimum shading correction data. CONSTITUTION:The output signal S1 of a photoelectric conversion element is supplied to a variable attenuator 1 and attenuated by an attenuation factor decided by the shading correction data D4 read out of a data memory 6. Thus the signal S1 is turned into the picture signal S2. The signal S2 is digitized by an A/D converter 3 and stored in a signal memory 4. These digital signals are successively read out in the form of the picture signal D2 and synchronously with the read signal of an operator 5. The operator 5 compares the signal D2 with a desired level Y set previously. When the signal D2 has a higher level than the level Y, the shading correction data for the picture element corresponding to the signal D2 is read out of the memory 6 and added with '1' by the operator 5 to be stored in the memory 6. This processing is repeated until the signal D2 gets closest to the level Y and has the even value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a shading correction device for an image reading device such as a facsimile or a digital copier.

(Prior art) In general, the image signal obtained by optically scanning a document image such as a single character, symbol, figure, etc. is subject to variations due to the light intensity distribution of the light source that illuminates the document, the sensitivity of the photoelectric conversion element, etc. Shooting may occur. Since this shading causes image quality deterioration, various shading correction devices have been proposed.

For example, the method described in Japanese Patent Application Laid-Open No. 54-158115 stores the amount of shuding distortion of an image signal corresponding to each pixel, and converts the stored data into a shuding correction value by a calculation means. However, the output is used to electrically perform shooding correction. However, in this correction device, the accuracy of the shuding correction is determined by the calculation means, and the image signal after the shuding correction is not checked.

Furthermore, in the method described in Japanese Patent Application Laid-open No. 54-144807, once one line of image signal is read, one
Pixel data is taken in, this is repeated a number of times equal to or less than the number of pixels in one line, and the amount of shading is stored. However, even with this configuration, since the signal after shooding correction is not seen, it is not known whether the output signal is optimal.

(Purpose) The present invention scans an original with uniform density, repeats correction multiple times, detects the output image signal after each correction, sequentially creates more accurate shooing correction data, and finally The present invention provides a shooding correction device that obtains an image signal free of shooing distortion by setting optimal data.

(Structure) In order to achieve the above object, the shooing distortion of the image signal that appears in the output of the photoelectric conversion element by scanning a document surface with a uniform density is corrected by shooing distortion that corresponds to each pixel signal of the image signal. an image signal storage means for storing the image signal corrected by the correction means; and a predetermined reference value for the output image signal from the image signal storage means. The present invention is characterized by comprising a calculation means for comparing and calculating the calculation means, and a shuding correction data storage means for storing the calculation result of this calculation means and outputting the data as corrected shuding correction data. .

Hereinafter, a detailed explanation will be given based on one embodiment of the present invention.

(Embodiment) FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In FIG. 1, 1 is a variable attenuator which is an electrical shooing correction means, 2 is an amplifier, 3 is an A/D converter, and 4 is an image signal storage device (hereinafter referred to as signal storage device).
, 5 is an arithmetic unit, and 6 is a data storage device for shuding correction (hereinafter referred to as data storage device).

Next, the operation will be explained. The output signal S8 of the photoelectric conversion element containing the shuding distortion obtained by scanning a document surface of uniform density is inputted to the variable attenuator 1, where it is used for shuding correction read out from the data storage device 6. Data D
, and becomes one image signal S2. The variable attenuation a1 has a smaller attenuation rate as the value of D4 is smaller, and therefore the output signal level is larger. The shooding correction data D4 is synchronized with the output signal of the photoelectric conversion element and has one pair with the pixel signal. 1 is output from the data storage device 6 as data corresponding to 1.

The image signal S8 subjected to the shooding correction becomes an image signal S that is amplified by the amplifier 2 to the input signal level of the A/D converter 3, and is input to the A/D converter 3 manually. A
The image signal D1 digitized by the /D converter is stored in the signal storage device 4, and sequentially read out as a digital image signal in synchronization with an external read signal or a successive output signal from the arithmetic unit 5.

The arithmetic unit 5 compares the digital image signal D2 with a predetermined desired level Y, and if D2 is larger than Y, reads out the shading correction data of the corresponding pixel of the image signal from the data storage device 6, The arithmetic unit 5 adds 1 to the shuding correction data and stores it in the data storage device 6.
to be memorized.

After this processing, when the output signal S1 of the photoelectric conversion element containing the shuding distortion is corrected again using the shuding correction data output from the data storage device 6, the correction data in this case is more than the previous correction data. Since the value is increasing, the attenuation rate of the variable attenuator 1 becomes large, and the value of the shooding-corrected image signal S2→D□ becomes small,
Therefore, the output image signal D2 approaches the value of Y.

When D8 is smaller than Y, 1 is subtracted from the shuding correction data and correction is performed using this as new correction data.

The above process is repeated, and when the output image signal D2 comes closest to the desired level Y and becomes a uniform value, the shuding correction data stored in the data storage device 6 is used for normal document reading. .

By performing shading correction, an image signal without shading can be obtained.

In the calculation of the shuding correction data in the above embodiment, addition or subtraction of 1 is performed. At first, addition or subtraction is performed with a large number, and as the number of processing increases, the number of additions or subtractions is decreased. By doing so, a uniform image signal can be obtained with fewer processing steps.

FIG. 2 shows the flow of the shooding correction process of the present invention. Here, rather than detecting the uniformity of the output image signal, the shading correction data is determined based on the number of times of processing.

Note that X in FIG. 2 is data for initial shooding correction, and may be data set corresponding to individual pixel signal levels of image signals obtained without initial correction, for example. .

Also, set X by assuming that all pixel signal levels output from the photoelectric conversion element are constant, perform shuding correction using this data, check the output image signal after correction, and adjust it to the desired level. You can modify the correction data for pixels that do not have the same value and repeat the correction, or, since the image reading device itself has a roughly fixed unique shading pattern, set X corresponding to that shading pattern. However, by performing subsequent corrections using the correction data as a starting point, the final shooding correction data can be determined in fewer steps.

As for the hardware configuration, the signal storage device 4 serves as a buffer for outputting to the next unit, and the arithmetic unit 5 can use the CPU (central processing unit) used to control the system. It is. This is because the arithmetic unit 5 and the signal storage device 4 are required only when performing the process of obtaining the data for snuding correction, but once the data for snuding correction is determined, the data is stored in the data storage device. This is because the arithmetic unit 5 and signal storage device 4 are no longer needed at this point, and can be used for other purposes.

(Effects) As explained above, according to the present invention, the output image signal is detected and the shuddling correction data is sequentially corrected, and finally the optimal multi-kneading correction data is obtained. It is possible to obtain an image signal free of distortion. In the traditional configuration.

If noise is included in the read image signal, etc., it will result in an inappropriate shading correction signal, but in the present invention.

Since the correction is repeated multiple times, there is an advantage that the influence of noise etc. is extremely small.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
FIG. 2 is a flowchart of the correction process. 1...variable attenuator, 2...amplifier, 3...
A/D converter, 4... image signal storage device, 5...
Arithmetic unit, 6... data storage device for shuding correction. Patent applicant Ricoh Co., Ltd. Figure 1 Figure 2

Claims (3)

[Claims] (1) In a shooding correction device that corrects shooding distortion contained in an image signal obtained by optically scanning a document image such as a character, symbol, or figure,
Shuding distortion in an image signal that appears in the output of a photoelectric conversion element by scanning a document surface of uniform density is electrically corrected using Shuding correction data corresponding to each pixel signal of the image signal. distortion correction means;
An image signal storage means for storing the image signal corrected by the shooding distortion correction means, a calculation means for comparing the output image signal from the image signal storage means with a predetermined reference value, and calculating the calculation means. and a shooding correction data storage means that stores the calculation results of , and outputs the corrected shooding correction data in synchronization with the output of the photoelectric conversion element, and repeats the correction multiple times to obtain the optimum shoeing correction data. A shooding correction device is characterized in that it sets data for shooding correction. (2) The shooding correction data initially set in the shooding correction data storage device is constant data determined by assuming that all pixel signal levels output from the photoelectric conversion elements are constant. A shooding correction device according to claim (1), characterized in that: (3) A patent characterized in that the shading correction data initially set in the shading correction data storage device is data determined in accordance with a unique shading pattern of the image reading device. A shooding correction device according to claim (1).