JPS60124176A - Correcting system of shading - Google Patents

Abstract

PURPOSE:To remove noises generated at the formation of correcting data effectively and to obtain an excellent picture signal by connecting a memory for storing a signal obtained by reading out a reference surface and arithmetically processing the signal stored in the memory to form a corrected signal. CONSTITUTION:Prior to scanning, a reference white plate to be a reference is read out and the read-out picture is A/D converted in each line of main scanning and stored in an RAM52. The stored signal is read out synchronously with the real picture read out from the original and applied to an address signal line of an ROM54. A signal obtained by matching the timing of an input picture signal through a type flip-flop 50 is inputted to the ROM54 and the ROM54 executes the arithmetic processing for the correction of shading and stores the processed result. When the arithmetic result for the shading correction which is stored in the ROM54 is read out, a signal from which shading caused by the uneven light emitting of a fluorescent lamp as an illuminating light source, uneven density due to the dirt or the like of a reflecting mirror and the uneven distribution of luminance intensity of an optical lens is removed is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an image processing apparatus, and particularly to an image processing apparatus for forming faithful image signals.

[Prior art]

In recent years, manuscripts have been read using solid-state imaging devices such as COD, and the read calyx is further converted into analog/digital signals, subjected to various digital processing, and then formed into images with printers or sent to remote locations. A device has been put into practical use. In order to stabilize the operation of the equipment in this building, we take measures to prevent uneven light emission from the fluorescent lamp, uneven light intensity distribution of the optical system,
An image signal correction circuit is often used that uses digital signals to correct image signal variations such as unevenness in sensitivity. Conventionally, this type of circuit, especially in devices that handle high-speed image signals.

In order to perform high-speed processing, an expensive circuit element must be used, and therefore, when complex correction processing or high accuracy is required, the scale of the nine circuits becomes large, making it extremely expensive. there were.

For example, in a correction method that stores the image signal of a standard white board as a digital correction signal in a memory, etc., and corrects the image signal of the read document based on this data, high-speed processing is performed to store the image signal in the memory. A large amount of noise will be mixed into the corrected signal. Therefore, in order to remove this noise, it was necessary to take the average value of neighboring pixels.

For this reason, an additional circuit such as an adder circuit, a multiplication circuit, a circuit for controlling the timing of calculations, etc. is required, and since it is necessary to use a circuit capable of high-speed operation, the cost is extremely high.

In addition, a method has been proposed in which one pixel is sampled every few pixels and shading correction is performed based on that data, but if the pixel has a defect, sensitivity varies, or noise When abnormal data, such as disturbed data, becomes a sampling pixel, there is a drawback that all of the several pixels are disturbed.

[Item 09] The present invention has been made with consideration given to one or more of the above points, and an object thereof is to eliminate the drawbacks of the conventional example and to enable formation of a good image signal. .

That is, a memory for reading the reference plane and storing the f-star signal, means for arithmetic processing of the signal stored in the memory, and a reference signal subjected to the arithmetic processing.

The present invention provides an image processing device capable of correcting an image reading signal, and corrects the captured signal by one stroke 'l'4fJ using the average value of the signals obtained by reading the reference plane a plurality of times while sub-scanning the reference surface. The present invention aims to provide an image processing device that can perform the following functions.

〔Example〕

The present invention will be explained below based on drawings of embodiments.

FIG. 1 is a simplified configuration diagram of a document reading device to which the present invention can be applied.

A document placed face down on a document table 9 is illuminated with a fluorescent lamp 2, and reflected mirrors 3, 5. A document image is formed on the line reading 0ODZ through the optical lens 6.

Reads the original in the main scanning direction. The fluorescent lamp 2° reflecting mirrors 3 and 5 are moved along a guide rail 8 by an optical system motor (not shown) to scan the document table 9 and perform reading in the sub-scanning direction. At 0OD7, the original image is converted into an electrical signal. In this embodiment, so-called shading, such as uneven light emission of the fluorescent lamp 2, uneven density due to dirt on the reflecting mirror 3.5, uneven light intensity distribution of the optical lens 1, etc., is removed. In this embodiment, a standard white plate 1 serving as a reference is read prior to the scanning, scanning is performed after scanning, and image signal correction is performed based on the read signal of the standard white plate 1. Previous self-standard white board 1.

This is a board for measuring the above-mentioned image signal, and the entire surface is uniformly painted, for example, white.

FIG. 2 is a block diagram showing an example of the circuit configuration of an original reading device for performing image signal shading correction according to the present invention.

The document is illuminated by a fluorescent lamp 5, and the reflected light forms an image of the document on OcI) 7 through an optical lens 6. At 0OD7, this original image is converted into an electrical signal, and the main scanning line data is output as an analog fV (electrical signal) in accordance with the main scanning synchronization signal.

This signal is amplified by an amplifier circuit 10, converted to a digital signal by an A/I converter 11, and after being corrected by 7 degrees by an image correction circuit I2, it is connected to an external circuit as a digital image signal output. be done.

There are 1 external circuits, 2 such as a binarization circuit, a dither processing circuit, etc.
This is a value conversion circuit. The binary number is 1, for example, LBP
(Laser beam printer) One image electronic file, connected to equipment such as a transmission device and used.

In FIG. 2, a control circuit 21 is a control circuit for controlling the shading correction circuit 12 and the temperature adjustment and dimming of the fluorescent lamp 15, and operates upon receiving instructions from the main body control circuit 23. An operation section 24 is connected to the main body control circuit 23, and provides instructions to start reading the document and displays the status of the apparatus.

The adjustment C circuit 18 is a control circuit for controlling the members of the fluorescent lamp 15, and performs dimming by lighting time control using pulse width modulation according to instructions from the control circuit 21.1. The thermistor 13 is a temperature sensor for measuring the tube wall temperature of the fluorescent lamp 15. The measured output of this thermistor 13 is A
A/D converter 22 performs A/D conversion and inputs the data to the control circuit 21, and the temperature control circuit 19. Driver circuit 20. Heater I4 for heat retention, fan motor 16 for cooling
By controlling the tube wall temperature of fluorescent lamp I5 to 40"
Control is performed so that the most fluorescent lamps before and after C emit light efficiently and stably. Specifically, the thermistor 13 measures the tube wall temperature of the fluorescent lamp 15, and when the measured temperature is below 40°C, the heater 14 is turned on and the fan motor 16 is turned off.
Turn off the heater 14 when the temperature is above ℃.

Temperature control is performed by turning on the fan motor 16.

In reality, there is also heat generation due to the light emission of the fluorescent lamp itself, so it is necessary to take measures such as giving hysterence characteristics to the above-mentioned on/off temperature settings.

FIG. 3 is a more detailed block diagram of the noeding correction circuit 12 and control circuit 21.

The image signal output from the A/D converter 11 in FIG. 2 is timed by the D type Noritsubu flop 50 in FIG. Ru. The output signals of the D-type frigs 70 and 150 are sent to one main scanning line, that is, 0O
It is possible to store one image signal for D1 line in It and AM52. This AM52 stores the image read from the standard white plate l, outputs it in synchronization with the actual original read image, and stores it in the R,0M54 by feeding it to the address signal line of the FLOM54. By reading out the calculated shading correction results, the fluorescent lamp 2
Calculations are performed to remove uneven light emission (FIG. 1) caused by density unevenness due to dirt on the reflecting mirrors 3 and 5, uneven light intensity distribution of the optical lens 1, and the like. The D-type clip-flop 53 is a circuit for adjusting the timing of the image signal read out from the RAM 52.

The selector 57 is a switching circuit for switching between the address signal output from the 0PU60 and the count signal (=horizontal address signal) of the counter 58 that counts the CLOCK signal when reading the pixel signal from the 00D7. That is, when writing the image signal data of the standard white plate 1 to the AM 52 and when reading it out and performing shading correction, it is switched to the horizontal address signal of the counter 58.

1 directly with 0PU60 (when reading the contents of AM52,
It is used by switching to the address signal output from 0PU60. The counter 58 is initialized by a synchronizing signal H8YNC signal indicating the start of reading one main scanning line, and repeats the counting operation every one line. Counter 59, this HS
It is a counter that counts YNC signals, for example,
This is used when changing the pattern in the sub-scanning direction when performing dither processing.

Upon receiving the command from timing control circuit 66fd, OP[J5Q, selector 57. Gate circuit 51° is a circuit that controls 6111 the bidirectional bus driver 56.

This timing circuit 66 controls the following three types of operation modes.

(1) Shading data sampling mode This is an operation mode in which the standard white plate 1- is read and nine image signals are stored in It and AM52. Gate circuit 51 H3YN
It operates for one main scanning line indicated by the C signal, switches the selector 57 to the address signal of the counter 58, and writes an image signal to the AM 52.

(2) Shading correction mode Based on the border signal written in ILAM52, D type
This is an operation mode in which both signals input to the flip-flop 50 are corrected. At this time, the selector 57 is operated by the address signal of the counter 58, sequentially reads out the data written in the shading data sampling mode il+ from the AM 52, and adjusts the timing using the D type 7 rig 70 ug 53. Tori, l'tOM54
Make a correction for 7 edging. Gate circuit 51: does not operate at this time.

(3) CPU mode 0 This is an operation mode in which the PU 60 can directly read and write the contents of the AM 52. At this time.

Bidirectional bus driver 56 is activated and direct 0P
It is connected to the data bus of U60 and is used to read the contents of RAM 52 and perform arithmetic processing, or conversely change the contents. At this time, the selector 51.

It is switched to the address signal line of 0PU60, and also.

Only gate circuit 51 does not operate.

Further, the sampling write clock control circuit 69.

J (This is a circuit that controls the image data manually input to the AM54. In other words, all pixels in the main scanning direction are transferred to the RAM54 at once.
4, without any manual input, a side slope signal is generated so that every 8 bits from the n-th bit instructed by the spo~8P3 signal manually inputted from the 0PU60 via the I10 boat 63 are stored in the RAM 54 as data, and then the 0PU60
According to the instructions of SPθ~8P3 from
This is a control signal generation circuit that samples every 8 bits starting from the pit and repeats the process 8 times to input all bits to the memory.

Now, the circuit described above operates from the working RAM 62 according to the control program stored in the 0PU 60 or the ROM 61.
, I10 boat 63. Control is performed using the serial circuit 641 and display circuit 6'5. The timer 67 is a circuit that provides pulses to the 0PU 60 at regular time intervals. 0PU60
performs time management by using this pulse signal as an interrupt signal.

Next, using FIG. 4, the principle of the "C" correction will be explained. In FIG. 4, the r and fM axes indicate the interval of 1 frame, and the vertical axis Fi indicates the gray level of the image signal. In this embodiment, this corresponds to the data read from the standard white board 1 and stored in the RAM 52 in the seven-edition data sampling mode. In this embodiment, the data stored in the RAM 52 is 6 bits, with the value 63 being the blackest level and the value O being the whitest level.

In Fig. 4, curve 1 frMaf'i indicates a state where the scene of the fluorescent lamp 15 is insufficient, curve 1 indicates a state where the light is adequate, and curve 1 C indicates a state where the amount of light is too large. There is. The aging correction method in this embodiment is as follows:
Since the correction is performed based on the data read from the standard white plate 1, when the reading is saturated as in curve 1 C, correction cannot be made, and as in curve 1 a. If the first arrival is insufficient, there is a drawback that the amount of correction by calculation increases, and the 8N ratio of the staked image signal deteriorates. Therefore, the light end of the fluorescent lamp 15 needs to be controlled so that the whitest point χ of the read data becomes the value O once, as in the case of one curve.

FIG. 5 shows an example of data stored in the RAM 52 when the fluorescent lamp 15 deteriorates after the fluorescent lamp 15 is dimmed using the standard white plate 1.

Curve d shows a state in which the fluorescent lamp 15 has deteriorated so much that even when it is fully lit, the black level remains by a value a, and the A light is insufficient. Curve e shows a state in which blackening progresses at both ends of the fluorescent lamp 15 and brightness at the ends of the tube decreases. Let the curve f be normal data, and let the density levels at both ends of the valid section in one frame be the values n and value, respectively.Similarly, let the density levels at both ends of the valid section of the curve e be the values m and J.

As explained above, in the shape ink correction in this embodiment, when the read value of the standard white board 1 is dark, as shown by the curve a in FIG. 4, the S/N ratio deteriorates by t. Therefore, in order to prevent this, the limit of the darkness is defined as a predetermined value α, and this.

It is possible to know the deterioration of the fluorescent lamp 15 by comparing the density levels in the effective sections.

In the example of FIG. 5, the conditions 1m>α>n and j>α>k are shown. Of course, regarding the above deterioration determination in 2, it is possible to determine that the fluorescent lamp 15 has deteriorated even if only one end exceeds the value α, for example, m)α, j〉α. Not even.

Next, the control means will be explained using the flowcharts shown in FIGS. 6 to 9.

FIG. 6 is a flowchart showing the main side diagonal procedure of the main body control 1 circuit 23 in FIG. first.

When It_rli is turned on, the operation unit 24 and each drive circuit are initialized in step SPI, and a polling operation is started to start reading. In step SP2, it is determined whether or not the reading start switch of the plagiarism section 24 has been pressed, and one branch is performed. In case of read restart,
Proceed to step SP3.

After confirming that the reading position of the optical system is at the position of quasi-white plate I (= home position).

Proceed to step SP4. In step SP4, fluorescent lamp 1
It is determined whether the temperature adjustment control for maintaining the tube wall taU of No. 5 at a predetermined shortening is completed, and if not, stable reading cannot be guaranteed, so the start of document reading is prevented. If the temperature control has been completed, the process advances to step SP5. In step SP5.

Abnormal pixels are detected in the state Q, +4 with the fluorescent lamp 15 turned off, and in step SP6, the fluorescent lamp 15 is turned on, and in step SP7, dimming control of the fluorescent lamp 15 is performed.

In step SP8, it is determined whether there is an error in the dimming control, and if there is an error, an error is displayed and reading of the document is prevented. N'''3 If there is no optical control error, proceed to step SP9.

An abnormal pixel is detected in the state 111 in which the fluorescent lamp 15 is turned on, and the process proceeds to step 5PIO-\. 2. If there are too many abnormal pixels, an error is displayed and the reading operation is prohibited. In step 5P11), the value read from the standard white board 1 is stored in the H, ILAM 52.

Fi in Step 5 PII, Step SP5. Step S
The abnormal pixels detected in P9 are corrected, and then, in step S5P12, scanning of the document is started. Step 5P
In step 13, it is determined whether or not the required number of document reading scans have been completed, and if not, the process returns to step SP7 and the operations described above are repeated. On the other hand, when the required number of original reading scans have been completed, the fluorescent lamp 15 is turned off, the original reading is completed, and a new operation of the reading start switch is awaited.

7 and 8 are flowcharts showing the control procedure of the CPU 60 of the control circuit 21. FIG.

In FIG. 7, after turning on the power, in step 5P50,
72g, I/'0 boat 63. Serial circuit 64. After initializing the display circuit 65 and the like, the process proceeds to step SP51. In step SP51.

It is determined whether or not there is human power for operating commands from the main body control circuit 23, and if not, the status of light adjustment, temperature adjustment, etc. is displayed on the 1 display circuit 65. If there is a command input, the process proceeds to step 5P52, and the process branches to each step depending on the presence of a command.

The details of each process are as follows.

Step SP53...Turn on the fluorescent lamp 15, set the flag FLON to 1, and similarly set the flag ICFt ROM
' Set r to O. 701 Flag when explaining Chigito, power +
77ri, cheetah and f-1, ILAM62KOPU6
0 indicates data to be read and written for processing.

Step 5P54---Turn off the fluorescent lamp 15 and set the flag FLON to the value ().

Step 5P55...Perform dimming control.

Step 5P56...The detected error information is transferred to the main body control circuit 23.

Step 5P57... Abnormal pixels in l frame are detected.

Step 5P5B... Performs correction processing for the abnormal pixel detected in step 5P57.

Step 5P59: The image signal read from the standard white board 1 is stored in the R and AM 52 after removing noise.

Step 5P60...R, 9 data stored in AM52 are transferred to an external circuit via serial circuit 64.

After all of the above processing steps are completed, the process returns to step SP1 and the control procedure described above is repeated.

FIG. 8 is a flowchart of timer processing executed at regular time intervals using pulse signals provided by the timer 67. Execution of this process is started after initialization in step 5P50 is performed. In step 5P61, a process is performed to control the temperature of the tube wall of the fluorescent lamp 15 to around 40° C. at which stable light emission is possible.

Next, the processing contents explained in FIGS. 7 and 8.

FIG. 9 is a flowchart illustrating the control procedure of the aging process. In step 5P200,
The counter ONT for counting the number of main scans is set to the value 0, the 3-bit signal 5PO-8P2 indicating the starting position of the Sangrinder IIIj element is set to 0, and all the shading buffer portions of the AM62 are set to the value 0. In step SP20l, the image signal read from 4 and whitening plate 1 is stored in the AM52 in the shape ink data sampling mode, and the pixel 11f corresponding to the contents of the previous 7 aging buffer is multiplied by II11. , shading back rK is stored. In step 5P203, u, Karan lON'J" and 8PO-8PZcD value are set to 1.
Increment until the value reaches 8, that is, until 8 main scans are completed Step 5P201 to Step SP203
Repeat.

In step 5P204, the contents of the shading buffer are divided by 8, the average value is calculated, and the average value is stored in the RAM 52 (It, AM for shading correction), and the shading process is ended.

According to the 7-aging process explained above.

RAM52. By simply processing the data in the RAM 62 with the 0PU 60, it is possible to average both signals read from the standard white board 1, remove noise, and measure it at an extremely low cost without using any special adders, dividers, etc. I'm there. , -i: I finished the algorithm. A more advanced noise removal method can also be easily applied by simply changing the control system stored in the I'LOM 61.

Figure io shows LLAM52. Around ROM54.

It is a circuit block diagram described in more detail. D type・
The flip 70 ring 68 is 1 e.g. 8N74LS174 (
This is a 6-bit D-type flip 70, such as that manufactured by TI Corporation, which captures and outputs the data input to the data input terminal at the rising edge of the signal input to the clock terminal. Therefore, the sampling clock control circuit 6
The image signal is latched in synchronization with the clock signal 5SCK output from 9. Sampling clock control circuit 69
To explain, the shading data is stored in RAM5.
When writing to 2, a sampling pulse 5SCK is output once every 8 bits in synchronization with the horizontal synchronizing signal H5YNC. The bit at which the sampling pulse is first output from HSYNC is determined by the value of the 3-bit signal SPO~2 from 0PV60.1For example,
If the value of SPO~2 is O, a sampling pulse is output at the same time as H5YNC, and then 8 bits, &? At this time, sampling pulse 5SCK is output. Also, SP
If the value of o7-z is 1, sampling starts from the next pixel of H5YNC, and a sampling pulse SSC is similarly output every 18 bits.

Also, in the case of key nine system fullllll, in order to sample all the image data at any location specified by cPu.

The sampling pulse SSC is output at only one location on one line.

Gate circuit 51 (e.g. 5N74LS374 (TI company)) f'i, 7x-tin f data 1LAM52
When writing to Q, the gate is opened and D flip 7a
Tsub is produced in synchronization with Kupu 68. Also, data is read out from the RAM 52 and one stroke is 14! When actually correcting the signal, the enable signal is turned off and the output is in a high impedance state. Further, during dimming control, image data of arbitrary bits is captured by the D-flip 70 knob 68, and then the gate is opened only when reading it into the microcopy computer. D noise flip 70 ring 53 is R
The 7 aging correction data read from AM52 is converted into the actual image l#! This is a launch to match the signal and phase.

The bidirectional bus driver 56 connects the LLAM52 to 0PU60.
When accessing, the gate is opened.

Other than that time, that is, the shading data is in RAM5.
The gate is closed when data is written to 2 and when shading correction is actually performed.

Gates 70, 71, and 72 are for controlling the opening and closing of the gates of the bidirectional cross driver 56. When the address of the microcomputer is decoder 79 and a certain address is accessed, the gate opens. It was designed so that

Further, the selector 57 selects the address of the microcomputer and the main scanning address of the COD.

This is to supply the tLAM52, and the CO2 is used except when the microcomputer accesses the RAM52.
Address D has been selected. Also.

This R, AM52I:j:, 2 kX8 bit
If you sample 11 pieces of data at 29.81 degrees using the
1 line (4,752 bytes) is sufficient. However, the areas that have more than twice the memory capacity are the area for storing 1-shading data (138 NKI), the area for performing multiple renderings (HANK2), and 1. This is because

Gates 75, 76, and 77 pass the shading data to R.
When writing to AM52, each gate l+ll generates a write signal to Aiv152.

The flip 70 knobs 80 and 81 are horizontal synchronization signals HSY
This is for generating a write signal; 4'r-4 signal in synchronization with the NC.

FIG. 11 is a diagram showing the positions of sample pixels in the main and sub-scanning directions, and the circuit described above allows the bits indicated by diagonal lines in the diagram to be sequentially input to the memory. That is, n
For the line, 3 indicates the sampling pixel start position 1d.
If the bit signal, 5po-sP2, is 0, the 1st and 8th
*fn...The 8χth pixel data is manually transferred to the memory. Specifically, if SPO~8P2 is set to 1, the second, ninth, . . . (8χ+1) completed pixel data are manually input to the LLAM 52. Like this SPO
By changing .about.2 for each main scan, all pixels can be manually controlled by eight main scans. Actually, in the n-th fin, SPO~2 is set to O, the image data is manually inputted to l'l, A M 5 '1OBANKI, and the next n+ti-th image data T/'iit A
Manually input BANK2 of 1V152. Then, the microcomputer adds the values of BANK1 and BANK2, and adds up the values to 13ANK2(・2. Similarly, the added value is stored in BANK2.By repeating this operation 8 times, the image data of 14 adjacent 8 pixels can be added.Next, by dividing this by 8, the average level of the 8 pixels is calculated. can.

By using this method, all pixels are stored in memory,
Compared to performing shading correction IE for each pixel independently, it is possible to realize shading correction with a smaller memory capacity and slower speed, and with almost the same quality. In other words, if only 1 pixel out of 8 pixels is sampled and 7 aging correction data for 8:IIj pixels is determined, if there is a defect in that pixel, insufficient sensitivity, or data disturbance due to Q noise, 8 pixels I [Kore 16
However, according to this embodiment, since the actual 8 pixels are averaged, the above-mentioned noise is affected.

Adverse effects such as insufficient sensitivity can be extremely minimized.

Shiki et al. again. If there are 41 small stains on the standard white board, this will have a large effect on the special T pixels, but the present invention is also effective in removing them.

Further, in this embodiment, after sampling the bn#rth line, it can be handled in the same way as the fmn+1st line after an arbitrary number of lines have elapsed. In other words, spo~S
This can be easily realized by not changing P2. With this method, after capturing the n-th image data, it is possible to capture the pixel data after moving the optical system a little. Instead of reading the same location, read f1t at a different location.By this means, the standard white board is read smoothly and equivalently, and it is possible to read the standard white board smoothly and equivalently. Malfunctions can be significantly reduced.

〔effect〕

As described above using the embodiments, according to one aspect of the present invention, when reading a standard document, data for 7 aging correction is obtained from data sampled multiple times while sub-scanning the standard document. It is possible to remove the effects of noise etc. on the data. Furthermore, by dividing the main scanning data into multiple blocks and changing the sampling pixels within each block according to the sub-scanning direction, it is possible to more effectively remove noise when creating data for shape ink correction. It is now possible to form a good image defect signal.

[Brief explanation of drawings]

FIG. 1 is a simplified configuration diagram of a document reading device to which the present invention can be applied, FIG. 2 is a block diagram showing a circuit configuration for performing shading correction to which the present invention is implemented, and FIG.
A more detailed block diagram of FIG. 2, and FIG. 4 are h 1
Explanation of the principle of tfN light control V. Fig. 5 is an explanatory diagram of the deterioration detection principle of the fluorescent pair, Fig. 6 is a control flowchart of the main body control circuit, Figs. 7 and 8 are control 70-char of the control circuit 21, Fig. 9 7
70-Chart of engineering process control procedure-Part t
This figure is a more detailed block circuit diagram of FIG. 9, and FIG. 11 is a diagram showing the positions of Zangle pixels with respect to the main/sub-scanning directions. l・・・・・・・・・Standard white plate 2.15...
Fluorescent pair 1...C0D 13...Thermistor 14...Heater 18...Tune Optical circuit 19...@Sub circuit 21...Control circuit 23...Main control circuit 51... Gate circuit 54...... 0M 52.56...R/1 58.59......Counter Fig. 7 Fig. 9 (To )D

Claims (1)

[Claims] (11) When reading a standard document that serves as a reference for shading correction, the standard document is sampled and read multiple times while sub-scanning, and data for 7 edging correction is created using a plurality of sampling data obtained thereby. (2) When reading a standard document that is a reference for shading correction, main scanning data is divided into a plurality of blocks, and within each block, data is divided according to the sub-scanning direction. The shading correction method according to claim 1, wherein the fading correction data is created by changing sampling pixels.