JPS6384264A - Picture reader - Google Patents

Abstract

PURPOSE:To attain accurate shading correction even if a white reference part has a defect by setting a photoelectric conversion output by one line as white level reference information constituted by a maximum photoelectric conversion output at each photodetector. CONSTITUTION:A CPU 10 starts the subscanning movement of a read section at the operation start and a line sensor 21 stores a picture signal PD by one line in a white level reference information area of a RAM 13. Similarly, the picture signal PD of a 2nd one line is stored in a white level comparison information area of the RAM 13. The CPU 10 compares the level of both the picture signals and replaces the reference information into the compared information only when the compared information is larger. As a result, the maximum value of the n-line picture signal PD with different white reference part is stored in the reference information area of the RAM 13. When the set counter N of the RAM 13 is zero, the original read is started. The CPU 10 uses the white level reference information stored in the RAM 13 to apply shading correction in the read scanning of the original.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an image reading device used in a facsimile machine or the like.

(Prior Art) Generally, as shown in FIG. 4, a document stationary type image reading device has a transparent document table 2 on which a document 1 is placed facing an opening of a cover 3, and A reading section 4 is disposed below the document table 2 inside the document table 3.

Among these, the reading section 4 includes a reading scanning optical system consisting of a linear light source 40, a mirror 41, a lens 42, and a line sensor 43, and a driving source such as a stepping motor, which moves the entire reading scanning optical system in the side scanning direction (indicated by the arrow). (direction)) and a drive system (not shown).

In the image reading apparatus shown in FIG. 4, for example, the linear light source 40 is turned on from the reading start position P1, and the main scanning of the original 1 is started while illuminating the reading surface of the original 1 in a line. The document 1 is also sub-scanned while the entire document is moved at a constant speed in the direction indicated by the arrow.

The reflected light from the reading surface of the original 1 during such reading scanning is as follows:
Light is received by the light receiving surface of the line sensor 43 through the mirror 41 and the lens 42, and the line sensor 43 responds to the amount of light received.
The document 1 is read by processing the photoelectric conversion output.

By the way, in this type of image reading device, due to the influence of the cosine fourth power law peculiar to the pupil lens (lens 42) constituting the optical system, even if the illuminance of the reading surface of the original 1 is uniform, the illumination on the in-sensor 43 is Due to the property that the image surface illuminance becomes darker as it moves away from the optical axis, and the sensitivity of each light receiving element of the line sensor 43 varies, even if a portion of the reading surface of the original 1 with the same brightness is read. , line sensor 4
Generally, the output level of No. 3 has a different value for each of the light receiving elements.

For example, FIG. 5 shows the output level of each light-receiving element of the line sensor 43 obtained when the entire white portion of the reading surface of the original document 1 is scanned.

The output of the line sensor 43 shown by the characteristic diagram is corrected to be flat, that is, the output level of all the light-receiving elements of the line sensor 43 is the same when reading the same brightness portion of the reading surface of the original 1. This correction is called shading correction, and is one of the essential processes for improving the reading accuracy of an image reading device.

In the image reading apparatus shown in FIG. 4, the white reference portion 5 provided on the extending portion of the document table 2 outside the document reading area is also a mechanism for performing the shading correction.

Here, the white reference portion 5 coats the extending portion of the document table 2 with a paint having a white reflectance comparable to that of the entire white portion of the document 1 that is placed within the document reading area of the document table 2 and is to be read. It is made by coating the back surface of the cover 3 in.

The normal reading section 4 is at a standby position P. When the operation start signal is given, the linear light source 3 is turned on, and the line light source 3 is turned on to move to the standby position P before scanning the reading surface of the document 1. Then, the white reference section 5 is read and scanned.

The output of one line of the line sensor 43 obtained by this reading scan is stored in the storage section as own level reference information.

After the reading scanning of the white reference part 5 is performed in this way, the reading part 4 is moved 8vJ to the reading starting position P1, and from the reading starting position P1, it performs main scanning and sub-scanning by the method described above, and then moves to the document table. Reading and scanning of the document 1 placed on the screen is started.

The output of the line sensor 43 corresponding to arbitrary image information on the reading surface of the document 1 obtained by this reading scan is subjected to a calculation that calculates the ratio with the white level reference information described above for each light receiving element, and shading is performed. It is output as a corrected image signal.

The principle of this shading correction will be explained in more detail.

For example, if the light-receiving element rows of the line sensor 43 are arranged in the horizontal axis direction and the output of each light-receiving element of the line sensor 43 is taken in the vertical axis direction, following the characteristic diagram shown in FIG.
The output of the line sensor 43, that is, the white level reference information obtained by reading the white reference section 5, is shown in FIG. 6(a).
It will be as shown below.

In the characteristic diagram of FIG. 6(a), the drop in output at both ends is due to the characteristics of the lens 42, and the depression in the output at the center is due to variations in sensitivity of each light receiving element of the crawler sensor 43.

After that, if the output of the line sensor 43 as shown in FIG. 6(b) is obtained by reading and scanning the reading surface of the original 1, the output may be based on the characteristics of the lens 42 or the line sensor 43 as described above. Each light receiving element 43 of the sensor 43
This can be considered to be influenced by variations in the sensitivity of the original 1, and cannot be treated as an accurate read image signal of the original 1.

Therefore, the output of the line sensor 43 shown in FIG. 6(b) is
Divide by the white level reference information shown in FIG. 6(a) for each corresponding light receiving element, take the ratio, and calculate what percentage of the white level reference information the output of the line sensor 43 corresponds to for each light receiving element. Shading correction is performed by adjusting.

As a result of this calculation, the output of the line sensor 43 as shown in FIG. 6(b) is corrected to the output level as shown in FIG. The signals will each be read as the same level.

By the way, in order to improve the reading accuracy in this type of image reading device, it is necessary to eliminate not only the effects of the above-mentioned characteristics of the lens 42 and variations in sensitivity of each light receiving element of the line sensor 43, but also the effects of the characteristics of the linear light source 3. It is also necessary to consider

That is, the linear light source 3 has a characteristic that the light intensity tends to become unstable immediately after being turned on, and when the output of the in-sensor 43 obtained by reading and scanning the white reference section 5 only once is set as the white level reference information. , depending on the light intensity of the linear light source 3, white level reference information lower than the original level is set;
Correct shading correction may not be performed.

In order to eliminate such inconveniences, some conventional image reading apparatuses of this kind have a standby position P before scanning the reading surface of the original 1. The white reference section 5 is read and scanned multiple times, and the image signal for one line consisting of the maximum value of the output of each light receiving element of the inner sensor 43 obtained by each reading scan is set as white level reference information. was there.

For example, FIG. 7 is a characteristic diagram for explaining an example of setting the white level reference information when the number of reading scans of the white reference section 5 is set to three times, and the first, second, and third The outputs of the wafer sensor 43 obtained by the reading scan are shown in FIGS.

In the conventional image reading device, the maximum value for each light receiving element of the line sensor 43 obtained with the characteristics as described above is combined to set white level reference information having the characteristics as shown in FIG. This compensates for the drop in the level of the white level reference information during the unstable period of the light amount of the linear light source 3, thereby ensuring accuracy in shading correction.

However, in this type of conventional image reading device, multiple reading scans are performed on the same location of the white reference section 5 to obtain white level reference information, and dust may adhere to the reading scanning line. If there is a defect such as a scratch or the like, the output level of the light receiving element of the line sensor 43 that scans and reads the defective location will inevitably decrease.

For example, FIG. 8(a) shows the characteristics of the white level reference information obtained when the reading scanning line of the white reference section 5 includes a defective portion as described above.
A significant decrease in the output level is observed in the light receiving element near the center of No. 3.

Based on the white level reference information obtained in this way, Figure 8 (
When shading correction is applied to an image signal having the characteristics as shown in b) (obtained by scanning the reading surface of the original 1), the defective portion is targeted for scanning as shown in FIG. 8(C). An image signal having an abnormally high output level was obtained at the light receiving element, making it impossible to perform correct shading correction.

(Problems to be Solved by the Invention) As described above, in the conventional image reading device described above, the white reference portion is read and scanned multiple times in order to prevent the level of white level reference information from decreasing due to instability of the light amount of the light source. Although the white level reference information is set from the read output obtained by There is a problem in that correct shading correction cannot be performed due to the influence of output fluctuations of the light-receiving element that scans and reads the image.

The present invention has been made in view of the above circumstances.

To provide an image reading device that can perform accurate shading correction even when there is a defect such as adhesion of dust or scratches in a white reference part and can contribute to improvement of reading accuracy.

(Structure of the Invention) (Means for Solving the Problems) The image reading device of the present invention uses a plurality of light receiving elements arranged in a line to receive light emitted from an illumination light source and reflected on the reading surface of a document. a document reading unit that receives light on a light receiving surface of a light receiving element array made up of a plurality of light receiving elements, and reads the original based on a photoelectric conversion output of the light receiving element array corresponding to the amount of received light; and a moving means that moves the manuscript reading unit in a side scanning direction. and a white reference portion provided outside the reading scanning range of the original, and driving the original reading portion and the moving means to read and scan the white reference portion multiple times at different locations prior to reading and scanning the original. one line consisting of the maximum value for each light receiving element among the photoelectric conversion outputs of the light receiving element array for multiple lines obtained by a driving means and a plurality of reading scans at different locations of the white reference section; At the same time, the photoelectric conversion output of the light receiving element row obtained by the reading scan of the document performed after the completion of the reading scan of the white reference section is set as the white level reference information. The image forming apparatus is configured to include a shading correction means for correcting shading.

(Function) In the image reading device of the present invention, the maximum value for each light receiving element among the photoelectric conversion outputs of the light receiving element rows for multiple lines, which are blued by multiple reading scans at different locations of the white reference part, is used. In order to set the photoelectric conversion output for one line constituted as white level reference information, each of the light receiving elements must perform a reading scan of a defect-free portion at least once among the plurality of reading scans of the white reference portion. For example, it is possible to avoid the influence of the defect when setting the white level reference information.

(Example) Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of an operating circuit of an image reading apparatus according to the present invention.

In FIG. 1, a control circuit (CPU) 10 consisting of a microprocessor is connected to a ROM 1 via a bus 11.
2, RAM 13, and I10 circuits 14 and 15.

Here, the ROM 12 stores a control program for the control circuit 10, and the RAM 13 stores control data, image data, etc. during control execution of the control circuit 10 based on the control program.

Also, I10 circuit 14 out of 14.15 I10 circuits is
An operation start signal S generated based on the operation of the start switch 16 to start the reading scan, and an image signal PA
This is an input circuit for inputting the image signal PD obtained by converting the output of the line sensor 21 (to be described later) by the A/D conversion circuit 17 into the control circuit 1o, and the I10 circuit 15 is connected to the line sensor drive circuit 18 and the light source. The main scanning control signal S8, light source control signal S1, and motor control signal SN for driving the line sensor 21, light source 22, and motor 23 through the lighting circuit 19 and motor drive circuit 20 are sent from the control circuit 10 to the line sensor, respectively. Drive circuit 18, light source lighting circuit 1
9. An output circuit for sending out data to the motor drive circuit 20.

Note that the external configuration of the image reading device of the present invention is similar to the device shown in FIG. 4 (the line sensor 21 in FIG.
The light source 22 is the line sensor 43 in FIG.
(corresponding to the linear light source 40), their operation is different.

Below, the restraint operation in the image flA reading device of the present invention is as follows.
This will be explained in detail with reference to the flowchart shown in FIG.

First, the control circuit 10 starts control when the main power of the image reading device is turned on (step 100).
The reading unit 4 is placed in the waiting position P. After performing the initial settings such as returning to
(step 102).

The control circuit 10 continues to monitor the operation start signal S obtained according to the operation status of the start switch 16 (
Step 103), the start switch 16 is operated and the operation start signal S is generated.

When it detects that it has become, it sends a light source control signal S and a motor control signal SH to the light source lighting circuit 19 and motor drive circuit 20, respectively. (Steps 104 and 105).

Here, the light source lighting circuit 19 turns on the light source 22 based on the light source control signal S, and the motor drive circuit 20 rotates the motor 23 based on the motor control signal SH to prevent the reading unit 4 from moving in the side scanning direction. Let it start.

Thereafter, the control circuit 10 measures the main scanning control signal SS @L to the line sensor drive circuit 18 at an appropriate timing.
(Step 106) Here, the line sensor drive circuit 18 drives the line sensor 21 based on the main scanning control signal S8, and the line sensor driving circuit 18 drives the line sensor 21 based on the main scanning control signal S8. The line sensor 21 starts the first reading scan of the corresponding location on the white reference section 5.

The image signal PA for one line of the white reference section 5 obtained from the line sensor 21 through such reading scanning is converted into an image signal P by the A/D conversion circuit 17. After being converted to Φ as I10
is input through circuit 14 (step 107) and bus 1
1 and is stored in the white level reference information area of the RAM 13 (step 108).

At the same time, the control circuit 10 monitors whether the reading scan for one line of the white reference section 5 has been completed (step 109), and when it is determined that the reading scan has been completed, the line sensor Main scanning control signal S to drive circuit 18
8 is output as H (step 110).

Through such control, the white reference section 5 by the line sensor 21
Although the reading scan is temporarily stopped, the lighting of the light source 22 and the rotation of the shutter 23 continue.

Next, the control circuit 10 automatically sets the reading scanning number counter N in the RAM 13 after the first reading scanning of the white reference section 5 is completed.
In step 111), it is determined whether or not a preset n number of reading scans of the white reference portion 5 has been completed, that is, whether or not the count value N is 0. (Step 112).

If it is determined in this judgment that the count value N is not O, the control circuit 10 outputs the main scanning control signal S@Lo to the line sensor drive circuit 18 again in the same manner as described above (step 113). , by driving the line sensor 21, the white reference section 50 starts the second reading scan.

As described above, since the lighting of the light source 22 and the rotation of the motor 23 continue once they are started, the first and second reading scan points of the white reference section 5 by the line sensor 21 are respectively It will be a different place.

The image signal P obtained by the second reading scan of the white reference section 5 is inputted through the I10 circuit 14 (step 114'), and then stored in the white level comparison information area of the RAM 13 via the bus 11. (Step 115
).

At the same time, the control circuit 10 monitors whether the reading scan for one line of the white reference section 5 has been completed (step 116), and when it is determined that the reading scan has been completed, the line sensor Main scanning control signal S to drive circuit 18
, is output as H, step 117), and the second reading scan by the line sensor 21 is stopped.

Subsequently, the control circuit 10 reads the image signal P stored in the white level comparison information area of the RAM 13 during the previous reading scan of the white reference section 5. and the image signal P stored in the white level reference information area are compared in level for each pixel corresponding to each light receiving element of the line sensor 21 (step 118).

Then, as a result of the comparison, only those pixels whose white level comparison information is larger than the white level reference information are replaced with the white level comparison information of the white level reference information (step 119).

Next, the control circuit 1o monitors whether or not the above-described comparison and replacement process between the white level reference information and the white level comparison information has been completed for one line (step 120).
), when it is determined that the processing for one line has been completed, the process returns to step 111 again, and after subtracting the count value N of the reading scan number counter N of the RAM 13,
It is determined whether the count value N is ◯ (step 12).

While it is determined in this judgment that the count value is not NtfiO, the control circuit 10 continues in steps 113 to
The process of step 120 is repeatedly executed, and as soon as the count value N becomes O, the process of step 121 and subsequent steps is proceeded.

The processing after step 121 shows the normal reading operation for the original 1 placed in the original reading area on the original table 2. The control circuit 10 first moves the reading unit 4 to the reading start position. Determine whether P1 has been reached (step 121
).

When it is determined in this judgment that the reading section 4 has reached the reading start position P1, the control circuit 10 sends the main scanning control signal S to the line sensor drive circuit 18. In step 122), the line sensor 21 is continuously driven in accordance with the movement of the reading section 4, which is moved in the 01 scanning direction (in the direction of the arrow in FIG. 4) by the rotation of the motor 23.
The original 1 is read and scanned (main scanning and sub-scanning).

An image signal P obtained by such reading scanning. is input from the I10 circuit 14 (step 123), and then stored in the image information area of the RAM 13 via the bus 11 (step 1).
24) In determining whether or not the reading process of the image signal Po for one line has ended (step 125), each time it is determined that the reading process has ended, shading correction is performed using the method described below. (step 126)
.

Next, the control circuit 10 receives the shading-corrected image signal P. Step 127) of storing the D in the storage unit or transferring it to the outside; Step 128) of monitoring the timing at which sub-scanning ends; Step 128)
Upon completion of the j scan, the process returns to step 101 to initialize the device.

During execution of such a series of control operations, the condition N=O, which is satisfied in step 112, indicates that the reading scan of the white reference section 5 has been performed a preset number of times, that is, n times, and the white color By the time the reading scan of the reference section 5 is completed, the white level reference information area of the RAM 13 is filled n times by the comparison and replacement processing of the own level reference information and the white level comparison information performed in step 118 and step 119. One line of image formed by the maximum value of each light receiving element of the line sensor 21 when the image signal Po of n lines at different scanning points obtained by the reading scan of the white reference part 5 is extracted for each light receiving element of the line sensor 21. Signal PD will be stored.

For example, FIG. 3 is a characteristic diagram showing a setting example of white level reference information when the number of reading scans of the white reference section 5 is set to three in the image reading apparatus of the present invention. The outputs of the line sensor 21 obtained by the third and third reading scans are <a), (b) in the same figure, respectively.
The result is as shown in (C).

In addition, the output for one line, that is, the self-level reference information, which is composed of the maximum value of the output for each light receiving element of the line sensor 21 for three lines obtained in the three reading scans described above, is shown in FIG. It will be as shown.

Then, the control circuit 10 performs shading correction (step 126) during the reading scan of the original 1 based on the white level reference information obtained in this way.

Here, the white level reference information indicates that even if a defective part such as dust or scratches is read and scanned several times during multiple reading scans of the white reference part 5 performed by the line sensor 21, the defective part At least 1 light-receiving element has read and scanned the
If a portion without a defect is read and scanned, the influence of the defect can be avoided, so that the shading correction described above can be performed extremely accurately.

Moreover, this also eases the measures taken to prevent defects in the white reference portion 5, thereby making it possible to reduce manufacturing costs.

〔Effect of the invention〕

As explained above, according to the image reading device of the present invention, one line is formed by the maximum value of the output of each light receiving element of the line sensor obtained by multiple reading scans at different positions of the white reference part. The image signal for the white reference section is set as the self-level reference information, and shading correction is performed during document reading and scanning based on the white level reference information, making it extremely unlikely to be affected by defects such as dust or scratches on the white reference table. This has the excellent advantage that accurate shading correction can be performed and reading accuracy can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the operation circuit of the image reading device according to the present invention, FIG. 2 is a flowchart showing the control operation of the image reading device according to the present invention, and FIG. Picture of invention @
An output characteristic diagram of a line sensor to explain an example of setting white level reference information in a reading device, FIG. 4 is an external cross-sectional view showing an example of the configuration of a general image reading device, and FIG. 5 is an image reading device of this type. FIG. 6 is an output characteristic diagram of the line sensor in this type of image reading device to explain the principle of shading correction in this type of image reading device, and FIG. 7 is a diagram of the output characteristic of the line sensor in this type of image reading device. FIG. 8 shows an output characteristic diagram of a line sensor to explain the shading correction processing method in this type of conventional image reading device. It is. 1...Original, 2...Document stand, 3...Cover, 4...
...reading section, 40...linear light source, 41...mirror,
42...Lens, 43.21...Line sensor, 5
... White reference section, 10 ... Control circuit (CPU), 1
1...Bus, 12...ROM113...RAM,
14.15... I10 circuit, 16... Start switch, 17... A/D conversion circuit, 18... Line sensor drive circuit, 19... Light source lighting circuit, 20... Motor drive circuit , 22... light source, 23... motor. Representative Patent Attorney Rules Near Point Yudo Yamashita - Figure 1 ((1) (b) Figure 4 Father Mitsuru) - Child Dali Figure 5 (Q) (b) (C
) Figure 6

Claims (1)

[Claims] Light emitted from an illumination light source and reflected on the reading surface of a document is received by the light receiving surface of a light receiving element array formed by arranging a plurality of light receiving elements in a line, and the amount of light received is a document reading section that reads the document based on the photoelectric conversion output of the light receiving element array according to the response; a moving means that moves the document reading section in a side scanning direction; a white reference section provided outside the reading scanning range of the document; , driving means for driving the document reading section and the moving means to read and scan the white reference section multiple times at different locations prior to scanning the document; One line of photoelectric conversion output consisting of the maximum value for each light receiving element among the photoelectric conversion outputs of the plurality of lines of the light receiving element array obtained by the reading scan is set as white level reference information, and the The present invention is characterized by comprising shading correction means for performing shading correction on the photoelectric conversion output of the light receiving element array obtained by the reading scan of the document performed after the end of the reading scan of the white reference section, based on the white level reference information. Image reading device.