KR100240069B1 - Image processing method - Google Patents

Abstract

The present invention is proportional to the amount of light reflected according to the state of an original in an image input apparatus having an image distortion correction unit for minimizing image distortion caused by circuit elements and components generated by color separation of the original for each color. In order to correct distortion of a CCD sensor or a light source for an analog signal, to adjust contrast and brightness for an original image, and to remove a background color of the original, reference data for image distortion correction of the original image is generated, and the original image The image distortion correction process and the set image which simultaneously set the upper and lower reference voltages for contrast adjustment, brightness adjustment and background color removal, and simultaneously perform black and white correction on the original image using the reference data. Image processing is performed on the original image using the lower limit voltage; An original image that has undergone image distortion correction processing and image processing is output as digital image data.

According to the present invention, an image distortion correction operation, a contrast adjustment, a brightness adjustment, and a background color can be removed with respect to an original image, so that an excellent output result can be obtained.

Description

Image processing method.

The present invention relates to an image processing method. More particularly, the image quality of an output image is improved by correcting distortion of an image reading sensor or a light source to digital data with respect to an analog signal proportional to the amount of reflected light according to the original state. In addition, the present invention relates to an image processing method for obtaining a clear output image by improving contrast, adjusting brightness, and removing a background color with respect to an original image.

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 apparatus 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, the distortion correction process of the color image input apparatus is composed of three steps.

First, the black correction process reads the magnitude of the dark current output from the pixel itself of the CCD sensor in the state that light is not input to the CCD sensor to obtain black correction data, 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 compared with the magnitude of the maximum pixel data value detected immediately before in the maximum value detector 206 to detect the maximum pixel data value and complete the maximum value detection 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 digital data from the A / D converter 208 into the digital data within the back correction memory 209 within the range of the maximum small value V _PEAK of the converted back reference plate 207. do.

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, 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 image processing, in order to adjust the contrast of the original image and to adjust the brightness, a predetermined value of a predetermined range is selectively designated and used as needed. On the basis of this, there was a difficulty in resetting the optimum variable by changing the control program of the image input apparatus.

Accordingly, the present invention has been made to solve the above problems, and an object of the present invention is to remove peripheral distortion elements in converting an analog signal into a digital image, and to provide a control program for the input device. It adds functions for contrast adjustment, brightness adjustment and background color removal to output an optimal image for the function selected by the user.

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

2 is a block diagram showing a circuit of a preprocessor for carrying out the present invention;

3 is a system configuration diagram of an apparatus for carrying out the present invention.

4 is a flowchart showing an image processing procedure of an original 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

The image processing method of the present invention for achieving the above objects is to read an original image using an image input apparatus having a preprocessor including a back correction memory, a black correction memory and a maximum value detector, wherein the image distortion of the original image Generating reference data for correction; setting respective upper / lower reference voltages for contrast adjustment, brightness adjustment, and background color removal; and using the reference data for the original image. Performing image processing on the original image using the image distortion correction processing for simultaneously performing black correction and white correction for the original and the set upper / lower reference voltages, and performing the image distortion correction processing and image processing. Outputting the original image 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 step of setting an upper / lower reference voltage for the contrast adjustment multiplies the contrast adjustment step value for the contrast adjustment with the contrast variation, and then multiplies the multiplication value from the back correction data output from the back correction memory. It is characterized by subtracting and using it as the upper limit reference voltage, and adding the multiplied value from the black correction data output from the black correction memory to use as the lower limit reference voltage.

Preferably, the contrast variation is obtained by dividing the small value of the back reference plate maximized value of the image input apparatus by the contrast adjustment step.

Preferably, the step of setting an upper / lower reference voltage for the brightness adjustment multiplies the brightness adjustment step value for the brightness adjustment with an upper limit variation, and then multiplies the value in the back correction data output from the back correction memory. It is characterized by using as the upper limit reference voltage by subtracting and using the black correction data output from the black correction memory as the lower limit reference voltage.

Preferably, the upper limit variation is obtained by subtracting the maximum value of the original detected during the prescan from the maximum value of the white reference plate of the image input apparatus and dividing the resultant value by the maximum brightness adjustment step number. It is done.

Preferably, the step of setting an upper / lower reference voltage to remove the background color uses the maximum and minimum values of the originals detected by the maximum detector as the upper limit reference voltage, and lowers the black correction data output from the black correction memory. It is characterized by using as a reference voltage.

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

2 is a block diagram showing a circuit of a preprocessor for carrying out the present invention.

As shown, the A / D converter 301 converts the analog output signal of the CCD sensor into a digital signal. The D / A converters 302 and 303 generate upper and lower reference voltages respectively while the A / D converter 301 performs the A / D conversion operation.

On the other hand, the latches 304 and 305 respectively store digital data for the upper and lower reference voltages. The selectors 306 and 307 operate to select the upper and lower limit reference voltages according to the operation mode and the selection signal, respectively.

Meanwhile, the black correction memory 308 stores black correction data output from the A / D converter 301. The back correction memory 309 stores back correction data output from the A / D converter 301. The maximum value detector 310 detects the maximum value using the digital image data output from the A / D converter 301.

The first adder 311 receives data output from the back correction memory 309. The second adder 312 receives data output from the black correction memory 308. The latches 313 and 314 store data provided through the data bus in the scanner control unit 101 and provide input values of the first adder 311 and the second adder 312, respectively.

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 101 generates timing signals necessary for performing a series of scan operations for reading an image of an original as digital data and controls the overall operation.

The ROM 102 stores programs and reference data having a certain flow so that the scanner controller 101 can control the scanner system in a predetermined order. The RAM 103 stores temporary data generated while the scanner control unit 101 controls the system.

On the other hand, the lamp 114 outputs R, G, B tricolor light in order to read the image information of the document as the reflected light amount by the lamp driver 113 which receives the control signal from the scanner control unit 101. The tricolor light output from the lamp 114 is reflected to the original through the optical module 116 to form a path for input to the photoelectric conversion element, and a focus is formed on the color CCD sensor 104.

On the other hand, the step motor 115 receives the drive signal from the scanner control unit 101 to move the optical module 116 in the sub-scanning direction of the original with a predetermined resolution. The color CCD sensor 104 photoelectrically converts the 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 116.

On the other hand, the sensor driver 112 receives a predetermined signal from the scanner controller 101 and supplies a clock signal to the color CCD sensor 104 so that the color CCD sensor 104 operates properly. The buffer 105 transmits the analog signal output from the color CCD sensor 104 to the rear stage and prevents the distortion of the CCD sensor signal by the circuit of the rear stage.

Meanwhile, the multiplexer 106 selects and outputs one of three color information signals simultaneously input according to a signal supplied from the scanner controller 101. The amplifying stage 108 converts the image signal selected and output from the multiplexer 106 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 109.

On the other hand, the analog switch 107 operates to amplify the image signal by selecting the amplification degree for each color according to the signal supplied from the scanner controller 101. The preprocessor 109 receives the signal converted from the amplification stage 108 into a signal of a predetermined level, performs monochrome correction processing, converts an analog signal, and outputs the digital image data.

On the other hand, the memory buffer 110 temporarily stores the image data digitally converted by the preprocessor 109. The interface 111 transmits the image data stored in the memory buffer 110 to the computer 117 according to a certain transmission rule.

4 is a flowchart showing a document image processing procedure according to the present invention.

First, reference data for image distortion correction of an original image is generated (step S10).

An upper and lower reference voltage is set for contrast adjustment, brightness adjustment and background color removal for the original image (step S20).

Image distortion correction processing and image processing are performed on the original image using the set upper and lower reference voltages while simultaneously performing black and white correction on the original image using the reference data (step: S30). )

An original image that has undergone the image distortion correction processing and image processing 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: black correction data generation operation, maximum value detection operation, back correction data generation operation and original image reading operation, contrast adjustment operation, brightness adjustment operation and background color removal operation In the original image reading operation, it is made according to the user's selection of the image processing function.

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. In the black correction data generation operation, 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 (step S11).

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, the black correction data stored in the black correction memory 308 is interlocked with the pixel synchronizing signal to output the correction data for each pixel, thereby simultaneously processing the black correction in the A / D converter 301.

The image data converted into digital data is input to the maximum value detector 310 to perform an operation of detecting the maximum value according to the magnitude comparison with the previous pixel value (step: S12). 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. The black correction data is selected and input so that the A / D converter 301 inputs 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. Converts to digital data.

The digital data generated in the process is sequentially stored in the back correction memory 309 to complete the back correction data generating operation (step S13).

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.

Also, 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.

When the original is fixed and the original reading operation is started, the selection signal provided from the scanner controller 101 to the preprocessor 109 is provided to the selectors 306 and 307 according to the contrast adjustment, brightness adjustment and background color removal operations. The selected value of each selector is input to two D / A converters 302 and 303 which set upper and lower reference voltages of the A / D converter 301 (step S20).

At this time, if the user-specified image processing operation is a contrast adjustment process (step S21), as shown in Table 1, the input value of the selection signal has a value of three.

Accordingly, the adder 311 adds the back correction data V _WHT output from the back correction memory 309 and the first data (-mα) stored in the latch 313 via the data bus to the upper limit reference. It is input to the D / A converter 302 for use as a voltage. (Step S22)

In addition, the black correction data V _BLK output from the black correction memory 308 and the second data (+ mα) stored in the latch 314 through the data bus are added by the adder 312 to lower the reference voltage. It is input to the D / A converter 303 for use as a step (S22).

Accordingly, the A / D converter 301 converts the image signal input in the range of the lower limit reference voltage V _BLK + mα and the upper limit reference voltage V _WHT -mα into digital data.

Where m is the contrast adjustment step.

The digital data generated in the above process is performed simultaneously with the black correction process by the black correction voltage, the back correction process by the white correction voltage, and the contrast adjustment process, so that the desired correction operation and the image processing operation can be performed with a simple circuit configuration. (Step: S30).

Here, assuming that the contrast adjustment step (m) is controlled in 128 steps on the white side and 128 steps on the black side, the contrast variation can be obtained as follows.

α = maximum value of the white reference plate / 256

Where α is the contrast variation.

Here, in order to execute the contrast adjustment, if the user selects and performs an arbitrary adjustment step divided into (+) and (-) steps (here, 128 steps each), the brightness of the white side is further increased for the (+) step. The image is processed toward the brighter, and the image is processed toward the darker the brightness on the black side in the (-) step.

That is, if three steps are selected for the white side and four steps are selected for the black side, the white side variation amount is 3α and the black variation amount is 4α.

Accordingly, in order to select the upper limit reference voltage (V _WHT -3α) and the lower limit reference voltage (V _BLK + 4α) before the contrast adjustment process starts, the latch 313 stores a complement value of 3α through the data bus. The latch 314 stores data of 4α through the data bus.

In this manner, the third data (the complement value of 3α) stored in the latch 313 is added by the adder 311 with the back correction value to generate the upper limit reference voltage of the A / D converter 301, and the latch The fourth data 4α stored in 314 is added with the black correction value by the adder 312 to generate the lower limit reference voltage of the A / D converter 301.

At this time, if the user-specified image processing operation is the brightness adjustment processing (step S23), as shown in Table 1, the input value of the selection signal has a value of three.

Accordingly, the back correction data V _WHT output from the back correction memory 309 and the data (± nβ) stored in the latch 313 through the data bus are added by the adder 311 to the upper limit reference voltage. It is input to the D / A converter 302 for use (step: S24).

Further, the black correction data V _BLK output from the black correction memory 308 is input to the D / A converter 303 to use the lower limit reference voltage (step: S24).

Accordingly, the A / D converter 301 converts the input image signal within the range of the lower limit reference voltage V _BLK and the upper limit reference voltage V _WHT ± nβ into digital data.

The digital data generated in the above process is performed by the back compensation voltage included in the upper limit voltage and the black compensation process by the black correction voltage inputted as the lower limit voltage. The processing operation can be performed (step S30).

Here, the value nβ latched from the data bus of the scanner control unit 101, which is provided to one input of the adder 311 to set the upper limit reference voltage in the original image reading mode, is determined in the following manner.

In other words, the upper limit variation β used to adjust the brightness of the output image is the maximum small value V of the original acquired in the prescan mode performed by all operations of the original image reading mode from the maximum small value V _PEAK of the white reference plate. _The result of subtracting _PEAK ') is divided by the number of brightness adjustment steps.

β = (Minimum value of the white platen-original maximum value of the prescan) / n

Here, n is the brightness adjustment step.

The variation of the upper limit value determined by the above equation is performed according to the user's output image brightness adjustment step.

That is, when the user wants to darken the output image, the upper limit reference voltage is increased to output the dark image.

For example, the upper limit variation amount 3β is stored in the latch 313 through the data bus according to a user-specified brightness adjustment step (e.g., dark level 3), and is output from the back correction memory 309 by the adder 311. In addition to the back correction data V _WHT , an upper limit reference voltage V _WHT + 3β is generated and provided to the D / A converter 302 via the latch 304.

In addition, when the user wants to brighten the output image, the upper limit reference voltage is reduced to output the image brightly.

For example, a complementary value of the upper limit variation amount 5β is taken in accordance with a user-specified brightness adjustment step (e.g., bright five steps) and stored in the latch 313 through the data bus.

The meaning that the complement value of the change amount 5β is added to the back correction data V _WHT output from the back correction memory 309 by the adder 311 is to subtract the change amount 5 β from the back correction data V _WHT . Same result.

That is, the upper limit reference voltage V _WHT -5β is generated according to the above process and is provided to the D / A converter 302 through the latch 304.

At this time, if the user-specified image processing operation is the background color removing process (step S25), as shown in Table 1, the input value of the selection signal has a value of 2.

Accordingly, the _smallest value V _PEAK 'of the original detected by the maximum value detector 310 is selected and input to the D / A converter 302 through the selector 306 and the latch 304 to perform background color processing. An upper limit reference voltage V _PEAK ′ is generated (step S26).

Also, the black correction data V _BLK output from the black correction memory 308 is selected to the latch 314 and input to the D / A converter 303 through the selector 307 and the latch 305 to perform background color processing. A lower limit reference voltage V _BLK is generated (step S26).

Accordingly, the A / D converter 301 converts the image signal input in the range between the lower limit reference voltage V _BLK and the upper limit reference voltage V _PEAK 'to digital data.

Here, the back correction operation is not performed during the background color removal process. This is because the output image when scanning for character recognition typically uses binarization image data, so that the pixels are not affected by the back correction process. This is to simplify the processing operation because it depends on how precisely the background color is removed and how the binarization reference level is determined.

When the upper / lower reference voltage is determined according to the above operation, and the original reading operation is performed with the upper / lower reference voltage, the black correction process and the background color removal operation are performed at the same time. It may be performed (step: S30).

In accordance with the above operation, the data which has undergone image distortion correction and image processing on the original image is finally output as digital image data (step: S40).

Mode, high and low reference voltage according to input value of selector. division Selection value 0 One 2 3 3 2 Operation mode Create black correction value Maximum value detection Create Back Compensation Contrast adjustment Brightness adjustment Remove background color Upper limit voltage V _Bmax: A V _Wmax: B V _PEAK V _WHT -mα V _WHT ± nβ V _PEAK '' Lower limit voltage V _Bref: C V _BLK V _BLK V _BLK + mα V _BLK V _BLK

Where m is the contrast adjustment step and n is the brightness 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, in the conversion of an analog signal from an original image to a digital signal, image distortion correction operations and various operations are performed by removing peripheral image distortion elements, contrast adjustment, brightness adjustment, and background color of the original image. By performing the image processing operation, errors due to individual characteristics of the circuit elements can be minimized, so that an excellent output image can be obtained.

Claims (7)

In reading an original image using an image input device having a preprocessor including a back correction memory, a black correction memory, and a maximum value detector, Generating reference data for image distortion correction of the original image; Setting respective upper and lower reference voltages for contrast adjustment, brightness adjustment, and background color removal for the original image; Performing image distortion correction processing for simultaneously performing black and white correction on the original image using the reference data, and performing image processing on the original image using the set upper / lower reference voltages; and And outputting the original image which has undergone the image distortion correction processing and image processing as digital image data. The method of claim 1, 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 on the image input apparatus. The method of claim 1, wherein the setting of the upper and lower reference voltages for the contrast adjustment is performed. After multiplying the contrast adjustment step value for the contrast adjustment by the contrast variation, the multiplied value is subtracted from the back correction data output from the back correction memory and used as the upper limit reference voltage, and the black output from the black correction memory. And multiplying the multiplied value from correction data to use the lower limit reference voltage. The method of claim 3, wherein the contrast variation is And dividing the small value of the back reference plate maximized of the image input device by the contrast adjustment step. The method of claim 1, wherein setting the upper and lower reference voltages for adjusting the brightness is performed. After multiplying the brightness adjustment step value for the brightness adjustment with the upper limit variation, the multiplied value is subtracted from the back correction data output from the back correction memory and used as the upper limit reference voltage, and the black output from the black correction memory is performed. An image processing method comprising using correction data as a lower limit reference voltage. The method of claim 5, wherein the upper limit variation And subtracting the subtracted value of the original detected during prescan from the submaximal value of the back reference plate of the image input apparatus, and dividing the subtracted result value by the maximum brightness adjustment step number. The method of claim 1, wherein setting the upper and lower reference voltages to remove the background color is performed. And using the smallest reference value of the original detected by the maximum detector as the upper limit reference voltage, and using the black correction data output from the black correction memory as the lower limit reference voltage.

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