KR100248751B1 - The preprocessor of an image input apparatus and image distortion correcting method - Google Patents

Abstract

According to the present invention, in the image input device having an image distortion correction unit for minimizing image distortion caused by circuit elements and components generated when color-coded originals are read by color, the image distortion correction unit corrects distortion of an original image. Generate the reference data for the image and use the generated reference data to simultaneously perform black and white correction on the original image. The apparatus further includes an adjusting unit for obtaining a clear output image as the contrast between the dark and bright portions of the output image of the original read by color separation is expanded.

According to the present invention, only one analog / digital converter can be used to correct an original image and to adjust color contrast. Therefore, when the application-specific integrated circuit is used, the chip size can be reduced and the cost can be reduced. Since the error due to the individual characteristics of the circuit element can be minimized, excellent output results can be obtained.

Description

A preprocessor of an image input device and an image distortion correction method using the same.

The present invention relates to a color image input device. More particularly, the image quality of an output image is obtained by correcting distortion of an image reading sensor or a light source to digital data for an analog signal proportional to the amount of reflected light according to the original state. At the same time, the preprocessor of the image input device and the image distortion correction method for obtaining a clear output image by extending the contrast between the light and dark areas of the output image displayed on the output device such as a monitor or a printer It is about.

In general, a scanner reflects light from a light source onto a document and reflects the reflected light to an image reading such as a charge coupled device (CCD) or a contact image sensor (CIS). The sensor converts it to an electrical output. On the other hand, the converted output value generally serves to be stored in a data storage device such as a hard disk of a computer.

As such, a scanner that reads document contents such as documents and books may be manufactured as a single piece to be used exclusively for scanning, or may be configured as a single device of a multifunction device together with a copy machine and a fax machine.

The analog signal output from the CCD sensor, a photoelectric conversion device of a general color image processing apparatus, includes variations due to individual differences between pixels of a CCD sensor, a semiconductor element, and emits light such as a fluorescent lamp or a halogen lamp used as a light source. And deterioration of image quality in reading an input image due to distortion of the white reference plate or the like.

In order to prevent the deterioration of the image quality due to such circuit elements and components, the color image input device performs black correction to correct individual differences according to the device characteristics of the CCD sensor, a light source (fluorescent lamp or halogen lamp) and a white reference plate. Back correction is performed to remove the effects of distortion.

In general, a distortion correction process of a color image input device is performed in three steps.

First, black correction processing for acquiring black correction data that reads the magnitude of the dark current output from the pixel itself of the CCD sensor when no light is input to the CCD sensor, and subtracts the analog signal output from the CCD sensor by the correction data size. And a maximum value detecting step of applying power to the light source, performing a black correction process on the analog signal reflected on the white reference plate, and reading the maximum value of the output image signal; The back of the analog signal reflected on the back is detected by detecting the distortion of the light source and the white reference plate within the range of the maximum value detected in the maximum value detection step and the black reference voltage, and performs a uniform operation based on the back correction data generated. There is a correction process step.

1 is a configuration diagram showing a conventional preprocessor circuit configuration.

As shown, conventionally, while driving a CCD sensor in a state in which no power is applied to a light source and outputting an analog image signal, an analog-to-digital converter (abbreviated as 'A / D converter' hereinafter referred to as 'A / D converter') 201 ) Performs an operation for acquiring black correction data, and converts the analog image signal output from the CCD sensor into digital data within the range of the black reference voltage (V _Bref ) and the black maximum voltage (V _Bmax ) and converts it into digital data. Save at 202.

The black correction memory 202 has a capacity equal to the number of effective pixels of the CCD sensor, and the black correction data is sequentially stored according to the output synchronization signal of the CCD sensor. The A / D converter 201 operates to be used only in the black correction data detection operation.

Next, power is supplied to the light source so that the reflected light reflected on the white reference plate is input to the CCD sensor, and the data detected in the black calibration data detection operation is converted into a digital / analog converter (DAC: D / A converter or less). After converting the analog value into an analog value, the black compensator 204 performs a black correction operation by subtracting the magnitude of the black correction data from the output signal of the CCD sensor.

The analog image signal of which black correction processing is completed is input to the A / D converter 205 for detecting the maximum value, and converted into a digital value within the range of the white maximum voltage (V _Wmax ) and the black reference voltage (V _Bref ) and converted. The obtained data is sequentially compared with the magnitude of the pixel data value output just before the maximum value detector 206 to detect the maximum pixel data value to complete the maximum value detecting operation.

Next, power is supplied to the light source so that the reflected light reflected by the white reference plate is inputted to the CCD sensor, and the black correction signal is input to detect the black reference voltage (V _Bref ) and the maximum value detector to detect the D / A converter ( The back correction data detection operation is performed by converting the A / D converter 208 into digital data and storing it in the back correction memory 209 within the range of the maximum value V _PEAK converted by 207.

Therefore, in the case of performing the operation of reading the actual document image, the power is supplied to the light source so that the reflected light reflected on the original is input to the CCD sensor, and the analog signal output is converted into photoelectric conversion according to the reflected light to receive the black light. In order to perform the correction, data stored in the black correction memory 202 is provided to the black corrector 204 via the D / A converter 203 to perform a black correction operation.

In addition, in order to perform back correction, data stored in the back correction memory 209 is provided to the back corrector 211 through the D / A converter 210 to perform the back correction operation.

The distortion-corrected image signal is the black reference voltage (V _Bref ) and data bus which finally converted the data stored in the latch 215 through the data bus in the A / D converter 212 in the D / A converter 214. By converting the data stored in the latch 216 into digital image data within the range of the _white reference voltage V _Wref converted by the D / A converter 213, the operation of reading the original image as digital data is performed. .

Here, the reference voltage of the A / D converter 212 that finally converts the image signal into digital data is configured to use an arbitrary value provided by the scanner controller 101 so that the reference voltage is output as the reference voltage is raised or lowered. The picture can be adjusted to lighten or darken.

Here, in the case of a color image input device that is currently being commercialized, a circuit for performing distortion correction processing, which is essentially used, is made into an application specific integrated circuit (ASIC). Applied as circuit elements.

However, in the conventional distortion correction processing circuit, when a large number of A / D converters and D / A converters are used and ASIC is used, the circuit configuration becomes complicated, and as the size of the chip increases, power consumption increases, and the chip The die size, which is closely related to the manufacturing cost of, increases, which contributes to the cost increase.

In addition, the current trend that the image quality of the color image input device is mainly focused on, the resolution of the A / D converter converting an analog signal to a digital signal is increasing, the resolution of the A / D converter is usually 1 bit If the chip size increases, the chip size may be doubled up to two times. Therefore, using a plurality of A / D or D / A converters may not reduce the chip size.

Accordingly, the present invention was devised to solve such problems, and an object of the present invention is to simply design and apply a circuit that performs the same function, thereby reducing the burden of cost and stably performing circuit operation. Especially, in case of A / D converter, since it has close correlation with chip area according to the bit resolution applied to the circuit, it is possible to design a chip with multifunctional addition by reducing the number of A / D converters to a minimum. In addition, the interference effect between each other is small to achieve a stable signal processing effect.

1 is a block diagram showing a circuit configuration of a conventional preprocessor,

2 is a block diagram showing a circuit configuration of a preprocessor according to the present invention;

3 is a system configuration diagram of an apparatus to which the present invention is applied.

4 is a flowchart showing an image data correction processing procedure according to the present invention.

<Description of the code | symbol about the principal part of drawing>

101: scanner control unit 102: ROM

103 RAM 104 Color CCD Sensor

105: buffer 106: multiplexer

107: analog switch 108: amplification stage

109: preprocessor 110: memory buffer

111: interface 112: sensor driver

113: lamp driver 114: lamp

115: step motor 116: optical module

117: computer

201,205,208,212,301: Analog / Digital Converter (ADC)

202,308: Black correction memory

203,207,210,213,214,302,303: Digital / Analog Convertor (DAC)

204 black compensator 206,310 maximum value detector

209,309 Back correction memory 211 Back correction device

215,216,304,305,313,314: Latch 306,307: Selector

311,312: Adder

According to an aspect of the present invention, a control signal input from a control unit of an image input apparatus and an analog image signal detected and input by an image reading sensor of the image input apparatus using color contrast adjustment data input from the control unit. An A / D converter for converting to digital data, a D / A converter for generating an upper / lower reference voltage when the A / D converter performs an A / D conversion operation and providing the A / D converter to the A / D converter; A black correction memory for storing black correction data output by performing an A / D conversion operation in the A / D converter, and a back storing data for back correction data output by performing an A / D conversion operation in the A / D converter. A correction memory, a maximum value detector for detecting a maximum pixel data value from the digital image data output from the A / D converter, a control signal input from the control unit and the A / D converter; A selector for setting an upper / lower reference voltage according to an operation mode of the device, and subtracting the color contrast adjustment data from a data value input from the back correction memory to provide the input value of the selector for selecting the upper limit reference voltage. And a second adder for adding the color contrast adjustment data to a data value input from the black correction memory and providing the lower limit reference voltage as an input value of the selector.

Preferably, the control signal is a black correction value generation mode selection signal, a maximum value detection mode selection signal, a back correction value generation mode selection signal, and an original image read mode selection signal.

Advantageously, the D / A converters comprise a first D / A converter for generating an upper limit reference voltage while the A / D converter performs an A / D conversion, and the A / D converter performs an A / D conversion. And a second D / A converter for generating a lower limit reference voltage during performance.

Preferably, the selectors include a first selector for selecting an upper limit reference voltage provided to the A / D converter according to a control signal input from the controller and an operation mode of the A / D converter, and the A / D converter. And a second selector configured to select a lower limit reference voltage according to a control signal input from the controller and an operation mode of the A / D converter.

The image distortion correction method of the present invention for achieving the above objects comprises the steps of setting a white brightness adjustment step value for an original image, setting a black brightness adjustment step value for the original image, and an image of the original image Generating reference data for distortion correction; and simultaneously performing black and white correction on the original image using the reference data, using the white brightness adjustment step value and the black brightness adjustment step value. And adjusting the color contrast with respect to the digital image data, and outputting the original image having the color contrast, black correction, and white correction as digital image data.

Preferably, the generating of the reference data includes generating black correction data for correcting a deviation due to individual difference according to device characteristics of an image reading sensor mounted in the image input device, and maximum pixel data in the black correction data. Detecting a value, and generating back correction data for removing the influence of distortion of the light source and the white reference plate mounted on the image input apparatus.

Preferably, the adjusting of the color contrast with respect to the original image comprises multiplying an upper limit variation that can adjust the color contrast of the output image with the set back brightness adjustment step value, and then, in the back correction data output from the back correction memory. Using the value obtained by subtracting the multiplied value as the upper limit reference voltage, the white brightness of the original image is adjusted, and the lower limit variation that can adjust the color contrast of the output image is multiplied by the set black brightness adjustment step value. The black brightness of the original image is adjusted by using the value obtained by adding the multiplied value from the black correction data output from the black correction memory as the lower reference voltage.

Preferably, the upper limit value and the lower limit value change amount is used to reset the color contrast for the original image based on the maximum pixel value of the original detected by the maximum value detector = upper limit value change value = lower limit value change value = (maximum pixel value of the document / 100) It is characterized by obtaining.

Hereinafter, the objects, features, and advantages of the present invention described above will be described in detail with reference to preferred embodiments of the present invention shown in the accompanying drawings.

2 is a block diagram showing a circuit configuration of a preprocessor according to the present invention.

As shown, the A / D converter 301 for converting the analog output signal of the CCD sensor into a digital signal, and the upper and lower reference voltages during the A / D conversion operation of the A / D converter 301 are performed. The D / A converters 302 and 303 respectively generate the latches 304 and 305 which store digital data for the upper and lower reference voltages respectively, and the upper and lower reference voltages can be selected according to the operation mode and the selection signal. Black correction memory 308 for storing the black correction data output from the selector 306 and 307, A / D converter 301, and back correction for storing the back correction data output from the A / D converter 301. A maximum value detector 310 for detecting a maximum value using the digital image data output from the memory 309, the A / D converter 301, and data output from the back correction memory 309; 1 output from adder 311 and black correction memory 308 And a second adder for receiving the data, and the latches 313 and 314 for storing the data provided through the data bus from the scanner controller 101 and providing the input values of the first adder 311 and the second adder 312, respectively. do.

3 is a system configuration diagram of an apparatus to which the present invention is applied and illustrates a color image input apparatus by way of example.

As shown, the scanner control unit 501 generates timing signals necessary for performing a series of scan operations for reading the image of the document as digital data and controls the overall operation. The ROM 502 stores a program and reference data having a certain flow so that the scanner controller 501 can control the scanner system in a predetermined order. The RAM 503 stores temporary data generated while the scanner controller 501 controls the system. The lamp 514 outputs R, G, and B tricolor lights in order to read the image information of the document as the reflected light amount by the lamp driver 513 which receives the control signal from the scanner control unit 501. The tricolor light output from the lamp 514 is reflected to the original through the optical module 516 to form a path for input to the photoelectric conversion element, and a focal point is formed on the color charge coupling element sensor 504.

On the other hand, the step motor 515 receives the drive signal from the scanner control unit 501 to move the optical module 516 in the sub-scanning direction of the document at a predetermined resolution. The color charge coupling device sensor 504 photoelectrically converts color information of each of the three primary colors R, G, and B into electrical analog signals in proportion to the amount of light input through the optical module 516. The sensor driver 512 receives a predetermined signal from the scanner controller 501 and supplies a clock signal to the color charge coupled device sensor 504 so that the color charge coupled device sensor 504 operates properly. The buffer 505 transfers the analog signal output from the color charge coupling element sensor 504 to the rear stage and prevents the distortion of the CCD sensor signal by the circuit of the rear stage. The multiplexer 506 selects and outputs one of three color information signals simultaneously input according to a signal supplied from the scanner controller 501. The amplifying stage 508 converts the image signal selected and output from the multiplexer 506 into an output signal of a predetermined level and amplifies it according to a predetermined amplification degree to be connected to the input of the preprocessor 509. The analog switch 507 operates to amplify the image signal by selecting an amplification degree for each color according to the signal supplied from the scanner controller 501. The preprocessor 509 receives a signal that is converted into a signal of a predetermined level by the amplifier stage 508, performs black and white correction processing, converts an analog signal, and outputs the digital image data. The memory buffer 510 temporarily stores image data digitally converted by the preprocessor 509. The interface 511 transfers the image data stored in the memory buffer 510 to the computer 517 according to a certain transmission rule.

4 is a flowchart showing an image data correction processing procedure according to the present invention.

First, a white brightness adjustment step value and a black brightness adjustment step value are set (step: S10).

Generate black calibration data (step: S21).

The maximum value of the image signal is detected from the generated black correction data. (Step S22)

After the maximum value is detected, back correction data is generated (step S23).

Color contrast adjustment operation and image distortion correction are simultaneously performed on the original image using the set white brightness adjustment step value and black brightness adjustment step value.

An original image which has undergone the color contrast adjustment operation and image distortion correction is output as digital image data. (Step S40)

Hereinafter, the operation of the color image input device of the present invention will be described in detail with reference to FIGS.

The overall operation is divided into four operation steps, which include a black correction data generation operation, a maximum value detection operation, a back correction data generation operation, and a read operation of the original image in parallel.

First, a selection signal provided from the scanner controller 101 to the preprocessor 109 in order to perform the black calibration data generation operation has a value of 0 and is provided to the selectors 306 and 307, and the selected value of each selector is A / D. Inputs are made to two D / A converters 302 and 303 which set the upper and lower reference voltages of the converter 301.

That is, as shown in Table 1, the D value for outputting the black maximum voltage is input to the D / A converter 302, and the C value for outputting the black reference voltage is input to the D / A converter 303. During the operation of generating black correction data, the A / D converter 301 digitally outputs the image signal input within the range of the black reference voltage V _Bref as the lower limit reference voltage and the black maximum voltage V _Bmax as the upper limit reference voltage. The operation is completed by converting the data into the black correction memory 308 sequentially.

Next, the selection signal provided from the scanner controller 101 to the preprocessor 109 has a value of 1 and is provided to the selectors 306 and 307 to perform the maximum value detecting operation, and the selected value of each selector is an A / D converter. Inputs are made to two D / A converters 302 and 303 which set the upper and lower reference voltages of 301.

That is, as shown in Table 1, the B value capable of outputting the white maximum voltage is selected and input to the D / A converter 302, and is output from the black correction memory 308 to the D / A converter 303. The black correction data is selected and input so that the A / D converter 301 receives the image signal input within the range of the black correction voltage V _BLK as the lower limit reference voltage and the white maximum voltage V _Wmax as the upper limit reference voltage. Convert to

At this time, as the black correction data stored in the black correction memory 308 is interlocked with the pixel synchronizing signal and the correction data for each pixel is output, the black correction is simultaneously processed by the A / D converter 301.

The image data converted into digital data is input to the maximum value detector 310 to detect the maximum value according to the comparison with the previous pixel value. As the processing for one line of the CCD sensor is completed, the maximum value detected in the area corresponding to the effective number of pixels of the CCD sensor is provided as one input value of the selector 306.

Next, the selection signal provided from the scanner controller 101 to the preprocessor 109 has a value of 2 and is provided to the selectors 306 and 307 to perform the back correction value generating operation, and the selected value of each selector is A / D. Inputs are made to two D / A converters that set the upper and lower reference voltages of the converter 301.

That is, as shown in Table 1, the maximum value detected by the maximum value detector 310 is selected and input to the D / A converter 302, and the output from the black calibration memory 308 to the D / A converter 303. When the black correction data is selected and input, the A / D converter 301 digitally converts the image signal input within the range of the black correction voltage V _BLK as the lower limit reference voltage and the maximum voltage V _PEAK as the upper limit reference voltage. Convert to

The digital data generated in the process is sequentially stored in the back correction memory 309, so that the back correction data generating operation is completed.

When the back correction data generation operation is completed, the color image input device is in a state where all preparation operations have been completed, and the input operation of the original image can be actually started.

Before giving a command to perform a scan operation, the user can actually select various processing operations to improve the image quality according to the state of the original image. A case of selecting and performing a color contrast adjustment operation for displaying an image clearly in accordance with the state of an original among such image processing operations will be described.

When the original is fixed and the document reading operation is started, the selection signal provided from the scanner control unit 101 to the preprocessor 109 has a value of 3 and is provided to the selectors 306 and 307, and the value selected by each selector is A. Inputs are made to two D / A converters 302 and 303 which set the upper and lower reference voltages of the / D converter 301.

That is, as shown in Table 1, the back correction data output from the back correction memory 309 and the data n α set by the user for color contrast adjustment stored in the latch 313 through the data bus are added to the adder ( The value added and output by 311) is selected and input to the D / A converter 302, and the color contrast stored in the latch 314 through the data correction bus and the black correction data output from the black correction memory 308. The user-set data nβ for adjustment is added by the adder 312 and the output value is selected and input to the D / A converter 303 so that the A / D converter 301 receives the lower limit reference voltage (V _BLK). V + _nβ) and the upper limit reference voltage (V _WHT - the image signal input in the range of _nα V) and converts it into digital data.

Here, the values nα and nβ latched from the data bus of the scanner controller 101 provided as inputs of the adders 311 and 312 to set the upper and lower reference voltages in the original image reading mode are as follows. Determined by the method.

That is, the adjustment range of the upper limit value α and the lower limit value β, which can adjust the color contrast of the output image, can be set to an arbitrary range.

For example, assuming that the adjustment range of the upper limit is adjusted in 100 steps (± 50) and the difference between the steps is 1% of the maximum pixel value of the original, the upper and lower limit variation that can adjust the color contrast of the output image (α) is obtained by calculating as follows based on the maximum pixel value of the original acquired in the prescan mode performed by the previous operation of the original image reading mode.

Upper limit variation (α) = Lower limit variation (β) = (Maximum pixel value of the original / 100)

If the user wants to perform the color contrast adjustment in an arbitrary step according to the number of steps determined by the above calculation formula, the operation is performed by specifying a separate step for the white side and a separate step for the black side. It is possible to control the contrast adjustment operation to be made.

In this case, in order to perform the color contrast adjustment step by step on the white side, a value nα multiplied by the upper limit variation α of the corresponding step n is subtracted from the maximum value of the original. The operation on the black side is in the form of adding the value nβ multiplied by the lower limit variation β to the corresponding step n.

To perform the color contrast adjustment, the user selects an arbitrary adjustment step divided into (+) and (-) steps, and in the (+) step, the image is processed to make the brightness of the white side brighter, ( In step-), the image is processed in a way that the brightness of the black side becomes darker.

The digital data generated in the above process is performed simultaneously with the black correction process, the white correction process and the color contrast adjustment process, so that the desired correction operation and the image processing operation can be performed with a simple circuit configuration.

Mode, high and low reference voltage according to input value of selector. division Selection value 0 One 2 3 Operation mode Create black correction value Maximum value detection Create Back Compensation Original image reading Upper voltage selection V _Bmax: A V _Wmax: B V _PEAK V _WHT + V _nα Lower voltage selection V _Bref: C V _BLK V _BLK V _BLK -V _nβ

Here, n is a color contrast adjustment step.

Although the preferred embodiments of the present invention have been described in detail above, those skilled in the art will appreciate that the present invention may be modified without departing from the spirit and scope of the invention as defined in the appended claims. It will be appreciated that modifications or variations may be made. Therefore, changes in the future embodiments of the present invention will not be able to escape the technology of the present invention.

As described above, according to the present invention, the correction operation can be performed using only one A / D converter. Therefore, in case of ASIC, the chip size can be reduced as well as if the circuit is configured using a single product, depending on the model of the product. As products with different resolutions of A / D converters are developed, the same circuit can be applied to various products, resulting in cost reduction effects.

In addition, since all correction operations can be performed using one A / D converter, errors due to individual characteristics of the circuit elements can be minimized, so that excellent output results can be obtained and black correction and white correction operations can be performed simultaneously. Stable operation

In addition, in most cases, the color contrast adjustment process is often performed in software. However, since the color contrast adjustment operation is hardware-processed, no separate processing is required, and thus, there is an advantage in that a quick processing result can be obtained for the output image. .

Claims (8)

A / D converter for converting the analog image signal detected and input by the image reading sensor of the image input apparatus into digital data using the control signal input from the controller of the image input apparatus and the color contrast adjustment data input from the controller. ; D / A converters which generate upper and lower reference voltages when the A / D converter performs an A / D conversion operation and provide them to the A / D converter; A black correction memory for storing black correction data output by performing an A / D conversion operation in the A / D converter; A back correction memory configured to store back correction data output by performing an A / D conversion operation in the A / D converter; A maximum value detector for detecting a maximum pixel data value from the digital image data output from the A / D converter; Selectors for setting upper and lower reference voltages according to a control signal input from the controller and an operation mode of the A / D converter; A first adder for subtracting the color contrast adjustment data from the data value input from the back correction memory and providing the upper limit reference voltage as an input value of the selector; And a second adder which adds the color contrast adjustment data to a data value input from the black correction memory and provides the input value of the selector for selecting the lower limit reference voltage. The method of claim 1, wherein the control signal is Black correction value generation mode selection signal; A maximum value detection mode selection signal; Back compensation value generation mode selection signal and A preprocessor of an image input apparatus, characterized in that the original image reading mode selection signal. The method of claim 1, wherein the D / A converters A first D / A converter for generating an upper limit reference voltage while the A / D changer performs A / D conversion; And a second D / A converter for generating a lower limit reference voltage while the A / D converter performs A / D conversion. The method of claim 1, wherein the selectors are A first selector for selecting an upper limit reference voltage provided to the A / D converter according to a control signal input from the controller and an operation mode of the A / D converter; And a second selector for selecting a lower limit reference voltage provided to the A / D converter according to a control signal input from the controller and an operation mode of the A / D converter. Setting a back brightness adjustment step value for the original image; Setting a black brightness adjustment step value for the original image; Generating reference data for image distortion correction of the original image; Adjusting color contrast for the original image using the white brightness adjustment step value and the black brightness adjustment step value while simultaneously performing black and white correction on the original image using the reference data; and And outputting the original image having the color contrast, black correction, and white correction as digital image data. The method of claim 5, wherein the reference data generating step Generating black correction data for correcting a deviation caused by an individual difference according to an element characteristic of an image reading sensor mounted in the image input device; Detecting a maximum pixel data value from the black correction data; and And generating back correction data for removing the influence of the distortion of the light source and the white reference plate mounted in the image input apparatus. 6. The method of claim 5, wherein adjusting the color contrast for the original image The value obtained by subtracting the multiplied value from the back correction data output from the back correction memory after multiplying the upper limit variation that can adjust the color contrast of the output image and the set back brightness adjustment step value is used as the upper limit reference voltage. Multiplying the lower limit value change that adjusts the brightness of the original image to adjust the color contrast of the output image and the set black brightness adjustment step value, and then multiplies the black correction data output from the black correction memory; And adjusting the black brightness of the original image using the obtained value as the lower reference voltage. The method of claim 7, wherein the upper limit value and the lower limit change amount To reset the color contrast for the original image based on the maximum pixel value of the original detected by the maximum value detector An image distortion correction method characterized by obtaining the upper limit variation = the lower limit variation = (the maximum pixel value of the original / 100).

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