JPH01109964A - Shading correction method in picture reader - Google Patents

Abstract

PURPOSE:To attain the shading correction with high accuracy by providing plural image sensors in a direction in crossing with the main scanning direction and applying the shading correction of plural image sensors at the same position in the subscanning direction on an object face. CONSTITUTION:When the preparation of offset correction and shading correction of a CCD 103R is finished, the optical system is moved up to the G home position by a command of a CPU 212. Then it is confirmed that the optical system is at the G position by using a pulse of a rotary pulse generation section 272 to apply the correction. Moreover, the optical system is moved till the B home position by the command of the CPU 212 to apply the operation similar to that of the G. Then the optical system is moved laterally and the original picture is read by the CCD 103 to apply correction and the result is outputted to a printer 209. Thus, the shading correction is applied by the same condition to attain the correction with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a shading correction method in an image reading device that reads an image of an object as image information using an image sensor such as COD.

[Prior art]

In recent years, with the development of electronic technology, various image transmission or processing devices have become popular.
A part that converts images of objects into electrical signals, that is, an image sensor, is essential. Image sensors typically have a plurality of pixels lined up in many models such as facsimile machines, and when this line moves in a direction approximately perpendicular to the direction of the line, it detects objects. Image sensors and line sensors that read pixels are widely used because they are relatively easy to manufacture.

Recently, line sensors that can read color images have appeared.

On the other hand, with digital image input devices, a common method is to read a shading correction chart, for example data from a standard white board, and then apply electrical shading correction to adjust the output to a constant level by applying a gain according to the unevenness of the output. is known for.

FIG. 7 is a schematic diagram showing a conventional color image reading device.

In the figure, 101 is a document table, 102 is a document holder, 1
03 is a CCD for image reading consisting of a plurality of light receiving elements arranged in a line; 104 is a halogen for illuminating the original; 105 to 107 are mirrors; 108 is a lens for imaging;
109 is a motor. Dihalogen 1 by motor 109
04, the original is sub-scanned in the Y direction by moving the mirrors 105 to 107, and the original images are sequentially focused on the CCD 103. Reference numeral 111 denotes a standard white plate for obtaining data for shading correction.A halogen 104 illuminates this standard white plate 111, and a halogen 104 and a mirror are placed at a position where reflected light from the standard white plate 111 is guided to a CCD 103. The state where 105 to 107 are present is called the home position. CCD 103 for color reading υ is a 3-line CC
The first line is an R filter, the second line is a G filter, and the third line is an ldB filter, which are arranged on the first chip at a distance of 200 μm. Furthermore, the pixels of each CCD have a pitch of 10 μm, and the imaging lens is for reduction of 1:10. Therefore CC
10 μm on the D side is 100 μm on the standard white plate 111
becomes. Therefore, the distance between each COD on the standard white plate 111 is 2I+Im. FIG. 8 is a diagram showing the situation. 103R is a CCD with an R filter, 103G is a CCD with a G filter, and 103El is a COD with a B filter. Here, as described above, the reading positions of each CCD on the standard white plate 111 are shifted in the sub-scanning direction. Therefore, if shading correction is attempted in this state, there will be the following drawbacks.

(1) It is necessary to ensure the same conditions over a wide range of standard white plates 111, which causes an increase in costs such as sorting.

(2) Density unevenness and flatness of the white coating on the standard white board 111,
CCD103R, CCD1 if there is foreign matter mixed in.
If you perform shading correction for 03G and CCD103B at the same time, for example, if there is a foreign object 112 at the reading position of C0D103G, the output result of C0D103G will be A.
The output area becomes weak magenta. Ma72C
If the flatness of the reading position 113 of the CD 103B is poor and there is a scratched area, the overall color balance of the output result of the CCD 103B will be disrupted, resulting in a yellowish output. Therefore, the quality of the read image information deteriorates. [Summary of the Invention] An object of the present invention is to provide a shading correction method for an image reading device that solves the drawbacks of the above-described shading correction method and is capable of performing highly accurate shading correction with a simple configuration.

The above-mentioned object of the present invention is to form an image of an object using an imaging optical system, and while main scanning the image using an image sensor, sub-scanning the image in a direction substantially orthogonal to the main scanning direction. Preferably, in the image reading device that obtains image information from the object, a plurality of the image sensors are provided in a direction intersecting the main scanning direction, and the shading correction of the plurality of image sensors is performed at the same position on the object surface in the sub-scanning direction. This is achieved by doing this.

〔Example〕

The present invention will be described below based on preferred embodiments with reference to the drawings.

FIGS. 1(A), (B), and (C) are diagrams for explaining the principle of the shading correction method of the present invention. The same diagram as FIG. 8 is used for comparison with the conventional method. FIG. 1A shows how only the CCD 103R equipped with an R filter is subjected to shading correction at the home position P of shading correction. At this time, there is a foreign object 112 at the reading position of C ('D103G), and the output result of CCD 103B is that part A is a weak magenta output.
The flatness of the reading position 113 of the CD 103B is poor and there are scratches in the scratched area, and the overall output result of the CCD 103B is unbalanced and has a yellowish tinge.

However, this state tc' is ccDt oao, CC
There is no problem since shading correction of DIO3B is not performed. Figure 1 (B) shows the home position P for shading correction, and then the CCD 10 with the G filter attached.
This shows how only 3G is subjected to shading correction. At this time, the shading correction of the CCD 103R has been completed. Also, there is a foreign object 11 at the reading position of C0D103B.
2, the output result of C0D103B is a weak output of 1 zenta in the A part. However, in this state, shading correction of the CCD 103B is not performed, so there is no problem. Figure 1 (C) is the home position P for shading correction, and then the CCD with the B filter attached.
103 shows that only shading is corrected for B. At this time, CCDIQ3.

Shading correction of the CCD 103G has been completed.

As explained above, the present invention performs the shading correction of the image sensors consisting of multiple rows in the main scanning direction at the same position on the object plane in the sub-scanning direction, thereby making the shading correction of the multiple rows of image sensors exactly the same. This can be achieved under the following conditions and enables highly accurate shading correction.
Therefore, high quality image reading is possible.

FIG. 2 is a block diagram showing the circuit configuration of a color image reading device using the shading correction method of the present invention. Further, the circuit shown in the same figure will be explained below assuming that it is connected to the color image reading device shown in FIG. 3 line CCD 103 is C with R filter
CD103R, CCD193G with G filter,
It consists of a CCD 103B with a B filter and is constructed on the same chip, but the circuits are made independently.

Therefore, the processing circuit below consists of CCD 103, (,'CD
Same for both 1oa() and CCD103B (20OR.

200G, 200B), only the processing circuit 200 of the CCD 103R will be described below. Each processing circuit 200R+, 200G, 200B is a drive signal generation circuit 211. It is connected to the CPU circuit section 212 and selector 269.

The CCDIQ3R is provided with two separate output systems (251a, 251b) corresponding to even and odd pixels, respectively, so that signal processing can be performed independently. Note that a processing circuit for even-numbered pixels is indicated by a, and a processing circuit for odd-numbered pixels is indicated by b.

Since the signal processing for even-numbered pixels and odd-numbered pixels is exactly the same, image processing for the output 251a corresponding to even-numbered pixels will be described below.

The image signal obtained by reading the image line by line by the CCD 103R has its noise component removed by the sample hold 201, and only the signal component is extracted. Further, the DC clamp circuit 202 reproduces the black level. The output of CCDIQ3R is extracted as an output relative to the black level, so the black level signal is detected for each line and the black level is always kept constant (for example, Ov
), this circuit corrects the output of the CCD 103R to an absolute level. 266 is CCD103R
This signal indicates the period during which a black level signal is output from the . The level-corrected image signal is then sent to the amplifier 203.
Signal names suitable for being A/D converted are amplified. EF8308 (manufactured by Thomson) is used as the A/D converter 204 in this example, and converts an analog input of 0 to 2 V into a digital signal of 0 to FFH. Level corrected CCD 1o3R.

Since the white level output is 0.3■, the amplifier 203 performs amplification by 6.6 times. Although not shown, C0D1
Halogen 10 so that the output of 03R is white and 0.3V.
A circuit is provided to constantly adjust the amount of light in step 4. The image data A/D converted for each pixel by the A/D converter 204 is output to the image signal line 255 as pure white "OOH" and pure black "FFH".

The image data input to the offset correction circuit 205 is subjected to dark voltage correction, and is further sent to the shading correction circuit 206 for sensitivity correction.

The sensitivity-corrected data is sent to the γ correction circuit 207. The γ correction circuit 207 is a RAM that stores density conversion data, and allows the CPU 212 to write a desired conversion curve based on the user's density designation or the density characteristics of the recording unit.

Buffer memo! 7208 is 1 image recording unit (printer) 2
It is used to match the output speed of image data to the recording section when recording on 09, and has a storage capacity of two lines of image data.

The drive signal generation circuit 211 generates a lock as necessary to drive the CCD 103R, and further generates an address corresponding to each pixel position of the line image. Using this address, each circuit knows at which position in the main scanning direction the input image data is.

The CPU 212 has a microcomputer as its main component, and controls the operation section 213 and generates signals for controlling each section.

5 and 6 show the operating procedure of the CPU 212. This operating procedure is preprogrammed into the memory ROM of the microcomputer.

crty212 initializes the I10 port when the power is turned on,
The RAM is cleared (step 501). Next, R.A.
Self-diagnosis is performed by writing and reading a test pattern to M (step 502). If it is confirmed that there is no abnormality (step 5o3), initial settings necessary for image reading are performed (step 504).

Then, data is written to the shading correction RAM 403 of the shading correction circuit 206, which will be described later, and the CPU waits for the reading start key to be pressed on the operation unit (step 505).

Also, if an abnormality is found, there is an abnormality in the 1 display unit.
Display the problem and the location of the abnormality (step 507)
.

FIG. 3 shows a detailed configuration of the offset correction circuit 205.

A selector 301 alternately selects and outputs outputs corresponding to even-numbered pixels and outputs corresponding to odd-numbered pixels. Also, 302, 304 and 306 are D type flip 7
It is a zero block (D F/F), and it is used to match the timing of data, and if the circuit speed is slow, some of them can be removed.

Further, FIG. 4 shows a detailed configuration of the shedding correction circuit 206.

The operation of the circuits shown in FIGS. 3 and 4 will be explained in accordance with the flowchart shown in FIG.

When the reading start key is pressed on the operation unit, in FIG. 5 (step 506), the CPU 212 starts the reading operation shown in FIG. 6. That is, it is checked whether the optical system (halogen 104, mirrors 105 to 107) is at the R home position (step 601), and if it is not at the home position, the optical system is returned to the R home position. and,
CPU21 determines whether offset correction killing is set.
2 is searched (step 602). This offset correction killing setting is set for testing by a service person or the like before starting the reading operation, and the instruction is given through the operation unit 213.

If offset correction killing is not set, CPU2
12 sets the selectors 405 and 409 to A and instructs the shading correction RAM 408 to write the output data of the A/D comparator 204 (step 603).

As a result, the CCD 103R is operated for reading without the halogen 104 turned on, and all the image data at that time is written to the shading I (, AM 408) via the selector 405 and the buffer 406 according to the address specification of the drive signal generation circuit 211. The purpose of turning off the halogen at the home position is to eliminate the influence of external light and reproduce a pure black state.Also, this shading R
When writing to AM408, the offset correction section simply outputs input data.

Next, the CPU 212 switches the selectors 405 and 409 to B, switches the shading R and AM to microcomputer access, and switches the CPU 212fd engineering RAM 40.
8 data is read through the buffer 407, and the average value NeVen of the data on the even number side is calculated (step 604).
).

Next, the average value Nodd of the data of odd-numbered pixels is obtained in the same manner (step 605). and step 604.60
The average values corresponding to the even and odd pixels obtained in step 5 are set as complementary values for the even and odd pixels in the DF/F 358 and 359 of the offset correction circuit 205 via the data bus 261, respectively (steps 606 and 607).
).

Next, the CPU 212 sets a certain offset value to DF/F3.
07 (step 604). This is CPU2
Data is latched into the DF/F 307 by the 12 data buses 261, and the latched data of the DF/F 307 is added to the image data on the signal line 354 as an offset. The purpose of this circuit is to change the density reproducibility of the black level. For example, it adjusts the density of 2.0 or more to be peta black, or the density of 1.2 or more to be peta black, etc., and adjusts the original density. You can adjust the black level accordingly. Further, the circuit constants of this circuit change depending on the temperature, making it possible to correct the amount of change when the document density changes.

With the above steps, the preparation for operation by the offset correction circuit 205 is completed.

Thereafter, the two systems of image data newly input from the CCD 103R are combined into one system of image data by the selector 301, and then input through the DF/F 302 to the signal line 352 and to the adder 303. On the other hand, in synchronization with the input of image data, the dark output data is DF/F358°359.
Read from either. That is, for input image data of even-numbered pixels, the dark output data corresponding to the even-numbered elements is output from the DF/F 358, and for input image data of odd-numbered pixels, the dark output data corresponding to the odd-numbered pixels is output from the DF/F 359. Each time output data is read out. The read dark output data is input to the adder 303 through the signal line 356. As a result, the offset (dark voltage) is corrected for each pixel. For example, an 8-bit signal is generated as image data and A/D converted so that black becomes F F H1 and white becomes OOH. Here DF/
When the n-th pixel data in the dark stored in F358.359 has a value of OCH, the adder 303 has OC
◇At the same time, the image signal line 352 is given image data that becomes F3H1 in a black state and OOH in a white state. Therefore, as a result of the adder 303, black is converted into data F' F H and white is OCH, which is sent to the DF/F 304 via the signal line 353, and further input to the adder 305 via the signal line 354. Ru.

As mentioned above, the function of the adder 305 is that the output data of the adder 303 is further instructed by the CPU 212 to be added to the DF/F3.
Add the latched value to 07. The adder 305 receives image data from the DF/F 304 (pure black FF)! , it is supposed to be sent as a pure white OCR, but the actual document is not completely black, but has a certain density. Therefore, when using a certain original, if FOR is black on the original, O
The FH is added to the image data according to instructions from the CPU 212. As a result, the black of the original is represented by FFH, and a black density corresponding to the original is obtained. However, adder 305,
303 will never exceed FFH no matter what addition you do, and if it exceeds FFH in calculations, it will all be FFH.
It is configured to be H. As described above, offset correction of the black level of image data is performed separately for even-numbered pixels and odd-numbered pixels, and the corrected data is sent to D via the signal line 355.
It passes through the F/F 306 and is further output to the signal line 256.

As mentioned above, the addition data given to the adder 305 is C
It is given to PU212.

The method for creating this addition data will be described below.

The reflected black density of a document varies greatly depending on the type of document (for example, the type of print, surface treatment, etc.). Therefore, depending on the manuscript, even solid black areas may not be expressed as black.

On the other hand, if you make the light areas black to a certain extent,
If the original has a high black density, the density gradation of the black part will be poor. Therefore, the image signal is set to be FFH when it is truly black, and an additional value is input from the operation section according to the black density of the original. For example, if the black level of the original is FOI-I, an additional value FH is added. As a result, black in the original will be read as black.

Further, as the temperature of the clamp circuit and amplifier circuit changes, the black level obtained even for the same document changes. For example, 0℃
If the black level is FOH at 10°C and becomes ECH at 10°C, it will fluctuate by about 4 levels per 10°C. In such a case, the ambient temperature is detected and the added value is changed at a rate of 4 levels/10°C. This makes it possible to eliminate concentration changes due to temperature.

Also, a plurality of these added values are stored in advance in the memo IJROM, and one of them is selected based on a command from the operating section or a temperature detection result. Further, instead of the addition operation, a similar level shift operation can be performed by a subtraction operation.

Note that if the offset correction killing described above is set, 0 is written to DF/F3s8.359 (step 6).
12.613). With this, it is possible to obtain input image data without performing an offset correction operation.

In the manner described above, the image data corrected for the black level is input to the 5-shading correction circuit 206 and processed.

Next, the operation of the shading correction circuit will be explained. After the power is turned on, the selector 402 is switched to B by the CPU 212 before the start of document reading, and conversion data, which will be described later, is written into the RAM 403 via the I10 buffer 410.

That is, when the reading start key is pressed and the preparation operation for offset correction as described above is completed, the halogen 104 is turned on and the light is adjusted to a constant light intensity (step 608).
). Next, it is determined whether shading correction killing is set (step 609). If shading correction killing is not set, selector 405.409
Select A as A.

In this state, the halogen 104 irradiates the standard white plate 111 at the R home position, reads the standard white plate 111 by the CCD 103R, and then the offset correction circuit 205
The offset-corrected data input via the signal line 256 is written into the all-pixel shading RAM 408 via the selector 405 according to the address designation of the drive signal generation circuit 211 (step 610).

Next, the output buffer 406 is set to zero impedance, the output of the selector 405 to the signal line 454 is cut off, and the shading RAM 408 is set to read mode.

This completes the standard operation of shape and ink correction by the shading correction circuit 206. After this, C
Image data representing a newly input document image from the CD 103R passes from the DF/F 401 via the signal line 451 to the selector 402, and is sent to the shading correction RAM 40.
3 is input to address AQ-A7. Further, shading data of the same pixel as the pixel of the input image data is read from the shading RAM 408. Shading data is sent to DF/F4 by signal line 455.
01, passes through the selector 402 via the signal line 451, and goes to the address 88 of the LAM 403 (shading correction).
~A12 is input.

At this time, the upper 3 bits of RAM 403 are not used.

According to this address AO-A12.

Corrected data from R and AM403 is sent to signal line 453
The signal passes through the DF/F 404 and is output to the signal line 257.

As described above, the shedding correction RAM 403 is set as a table so that after the power is turned on and before reading starts (step 505), the value calculated by is outputted as data y with x and z as addresses. Note that X is image data, 2 is shading data, and y is corrected data.

For example, when the standard white plate 111 is irradiated, R, AM4Q
If the nth pixel data stored in 8 is 0CHt):), the address of the shading correction RAM 403 is
0CXXH (XX is the currently output image data) is given.

The image data input to the RAM 403 is in the range of 0C-FFH due to offset correction, so R
The output data of AM4Q3 is as shown in the following table for each input image data.

Shading data, 2 OCR Therefore, a table as shown in this table is written in the shading correction RAM 403 by the CPU 212. As a result, even if the sensitivity of each pixel of the COD is non-uniform, the output data is made uniform for each pixel within the range of 0-F'FH.

As described above, the offset correction circuit 205 and the shading correction circuit 206 cause the output non-uniformity of the CCD 103R due to the variation in dark voltage that appears when it is dark, and the CC due to the sensitivity variation and dark voltage variation that appear when it is open.
I) Nonuniform output of 103R is corrected, and uniform output faithful to the original density can be obtained.

In addition, if shading correction kill is set,
Write “0” data to the shading RAM 408 (
step 614).

As a result, image data without shading correction can be obtained.

As described above, the image data appearing on the signal line 257 after being linearly corrected with respect to the amount of reflected light from the original is as follows:
The image data is input to the r correction circuit 207 and converted into image data linear in density. Furthermore, the characteristic (curve) for density conversion can be changed by specifying the density using the operation unit 213 (step 615).

In this way, preparations for R offset correction, R shading correction, and γ correction operations are completed.

Next, according to instructions from the CPU 212, the motor drive unit 27
The motor 271 is driven by the pulse generator 272 connected to it, and the generated pulses are sent to the CPU 212 to check whether the optical system is at the G home position (Stella 7'617), if it is not at the G home position , move the optical system to the G home position. Then, as described above, the G offset operation, the G shading correction, and the γ correction operation are performed. Next, according to instructions from the CPU 212, the motor drive unit 270 drives the motor 2.
71 to move the optical system to the B home position (step 618).

A rotation pulse generator 272 is connected to the motor 271, and the generated pulses are input to the CPU 212 to check whether the optical system is at the B home position (step 619). If it is not at the B home position, Move the optical system to the B home position. Then, as described above, the B offset operation, the B shading correction, and the r correction operation are performed.

After the above operations, the optical system is moved in the y direction, the original image placed on the original platen 101 is read by the CCD 103 (step 620), and the read image data is offset corrected as described above. , performs shading correction and density correction, and outputs the corrected data to the printer 209 via the buffer memory 208 and selector 269.

When the image reading is completed, the apparatus is put into standby state and waits for new image reading (step 621).

Although the above embodiments have been described using a system in which the optical system is moved, the object of the present invention can also be achieved by fixing the optical system and moving a standard white plate for shading and correction.

Furthermore, if a pulse motor is used as the motor, the desired movement amount can be achieved without providing a rotational pulse generator, and the object of the present invention can be achieved.

Furthermore, in the above embodiments, the shading correction is performed after the optical system is moved and stopped sequentially, but the present invention also applies if the shading correction is performed at the same position with the timing set by the clock while moving and scanning in the same manner. objective can be achieved.

The object of the present invention can also be achieved by reading data at several positions for each of R, G, and B colors, averaging the data, and then performing shading correction.

Furthermore, although the above embodiments have been explained using a 3-line sensor for color reading, it is possible to apply the present invention to any reading device that uses multiple rows of image sensors in the main scanning direction. Not even.

〔Effect of the invention〕

As explained above, the present invention performs the shading correction of the image sensors consisting of multiple rows in the main scanning direction at the same position on the object plane in the sub-scanning direction, thereby making the shading correction of the multiple rows of image sensors exactly the same. This can be achieved under the following conditions, making it possible to perform highly accurate shading correction. Furthermore, there is no need to process the shading correction plate over a wide area with high precision, which is advantageous in terms of cost.

[Brief explanation of the drawing]

FIGS. 1(A), (B), and (C) are diagrams explaining the principle of the shading correction method of the present invention, and FIG. 2 shows the circuit configuration of a color image reading device using the shading correction method of the present invention. 3 is a block diagram showing the configuration of the offset correction circuit, FIG. 4 is a block diagram showing the configuration of the shading correction circuit, and FIGS. 5 and 6 (a
), (b) is a CPU. 7 is a schematic diagram showing a conventional color image reading device, and FIG. 8 is a diagram illustrating a conventional shading correction method. 101... Original table 103... CCD 108... Lens for imaging 111... Standard white plate

Claims (1)

[Claims] (1) An image of the object is formed by an imaging optical system, and while the image is main-scanned by the image sensor, the image is sub-scanned in a direction substantially perpendicular to the main-scanning direction. The image reading device obtains image information from a plurality of image sensors, wherein a plurality of the image sensors are provided in a direction intersecting the main scanning direction, and shading correction of the plurality of image sensors is performed at the same position on the object plane in the sub-scanning direction. A shading correction method for an image reading device.