JP2020088661A - Image reader - Google Patents

Abstract

To solve the problem in which, in an ADF scan mode, if a variance value of an image reading sensor is large during document irradiation, print information on a back of a document becomes show-through and is erroneously detected as information printed on the front of the document and a blank document is erroneously detected, which causes discomfort for a user.SOLUTION: By measuring a variance value of an image reading sensor in advance and changing a blank sheet detection determination threshold value according to the variance value, it is possible to reduce a risk of false detection of blank sheet detection due to show-through.SELECTED DRAWING: Figure 4

Description

The present invention relates to an image processing technique for detecting a blank original in an image reading apparatus using an automatic document feeder that optically reads an image of an original while conveying the original.

As a conventional image reading apparatus, while a document placed on a document tray is conveyed one by one by an automatic document feeder (ADF), when a document passes over a reading glass at a reading position, a light source is used. 2. Description of the Related Art There is a document image reading apparatus that has a flow reading image reading unit that reads a document by irradiating the document, reflecting the reflected light on a mirror, and allowing the reflected light to enter an image sensor such as a CCD.

When an ADF is used to convey a document containing print information on the back side of the reading surface of the document, the print information on the back side of the reading surface may be transmitted when the document is illuminated at the document reading position, and is acquired by the image reading sensor. There is a case where a phenomenon called show-through occurs in which the printed image data includes print information on the back side.

In particular, the show-through of a document depends on the sensor characteristics such as the amount of light received (light receiving sensitivity) with respect to the amount of light emitted from the reading sensor and the ratio of the noise level and the amount of light received (S/N) of the sensor itself. There is a possibility that the show-through will be noticeable in the image data, or that the show-through will not appear in the image data.

Also, when a user puts a plurality of originals together on the original tray and mistakenly makes a copy without noticing that a blank original is included in the middle, the blank original will also be copied. There is known a blank paper detection technique in which a document that is determined to be blank as a result of scanning in step 1 is not copied and output.

If the show-through occurs, the print information on the back side of the document obtained by the show-through is erroneously detected as the print information on the front side of the document when it is detected whether or not it is a blank sheet, and it is printed on the front side of the document. A document without information may be erroneously detected as not a blank document.

In such a case, even though the original is a blank original, it is erroneously determined to be an original including print information, and the blank original is copied and output, which is not desirable for the user.

Therefore, in Patent Document 1, in a double-sided document reading apparatus capable of reading the front and back sides of a document by one-time document conveyance, a mark provided in advance on the back side of the document is printed and the mark is detected from the image reading result on the back side. However, a method has been proposed in which the image data on the back side of the document is identified and used as a determination material for the blank sheet skip processing to suppress the influence of false detection of a blank sheet skip due to show-through.

JP, 2014-17547, A

However, in Patent Document 1, the configuration is limited to the double-sided document reading device. In addition, since it is necessary to previously provide a mark on the back surface of the document, the operation is troublesome for the user. In addition, it is difficult to implement this proposal when marking is not desirable for the user's application.

Therefore, according to the present invention, in a configuration not limited to the double-sided document reading device, when S/N is not good and show-through is prominent, the false detection of a blank sheet skip due to show-through without providing a mark on the document in advance. The purpose is to do.

In order to achieve the above object, the image reading device according to the present invention is
In an image reading device that acquires image data of a document,
A document feeder that feeds documents,
Having an image reading sensor for reading color image data using a plurality of line sensors,
From the image data acquired by the line sensor, a dispersion value acquisition unit that acquires a dispersion value of luminance based on the line sensor,
A variance value storage unit for storing the variance value obtained by the variance value acquisition unit,
A blank sheet detecting means for detecting whether or not the original is a blank sheet from the image data read by the line sensor;
It is characterized in that blank sheet detection is carried out based on the variance value of each line sensor stored in the storage means.

According to the image reading apparatus of the present invention, in a configuration not limited to the double-sided document reading apparatus, when the S/N is not good and the show-through appears remarkably, a blank sheet by the show-through is not provided on the document without a mark in advance. False detection of skip can be performed.

Image reading device cross-section Device block diagram Document detection sensor Read image processing block diagram Main scanning digital value of color line sensor when dust is present Digital value before and after dust streak correction Cross section of dust and color line sensor Image diagram before and after dust streak correction Digital value before and after dust streak correction Blank manuscript Histogram of blank document Originals with text printed Histogram of the original printed with text Block division of the reading area used for the edge detector Flowchart of Example 1

Hereinafter, modes for carrying out the present invention will be described with reference to the drawings. The configuration of the apparatus and the procedure for determining the reading position described in this embodiment are examples for explaining the proposed content, and are not limited to the described content.

FIG. 1 is a sectional view of an embodiment of the device of the present invention.

Reference numeral 101 is a housing of the document reading apparatus, and 102 is an automatic document feeder for feeding a document.

The original 103 is placed on the original tray 104. The original 103 is brought into contact with the original by the width regulating plate 105, so that the oblique conveyance of the original is suppressed.

The original 103 is delivered by the pickup roller 106 to the separating unit as a bundle of originals placed on the original tray 104. In the separation unit, the separation pad 107 and the separation roller 108 separate the uppermost sheet of the original bundle one by one.

One separated original is corrected by the first registration roller 109 to correct the oblique conveyance of the original, and is conveyed to the second registration roller 110, the first conveyance roller 111, the second conveyance roller 112, and the third conveyance roller 113. To be done.

After passing through the third transport roller 113, the document is transported by the fourth transport roller 115 and the paper discharge roller 116, and is discharged to the paper discharge tray 117.

When the document passes over the document reading position set between the second transport roller 112 and the third transport roller 113, the document is illuminated by the light sources 119 and 120. Then, the reflected light from the document is guided to the imaging lens 124 by the mirrors 121, 122, 123.

A white guide member 114 is attached at a position opposite to the document reading position. The white guide member 114 serves to hold the document away from the reading glass 118 and prevent it from floating when the document is conveyed to the document reading position. When it does not exist on the position, it has a role of determining whether or not dust is attached to the reading position from the scan image of the white guide member 114.

The guided light is converged by the image forming lens 124 and imaged on the color line sensor 125 in which an image pickup device such as a CCD is arranged on the line.

The imaged optical signal is converted into an electric signal by the color line sensor 125 and converted into a digital signal by the signal processing board 126 to obtain image data.

By contacting the actuator 127 with the conveyed original, it is detected that the original has been conveyed to the vicinity of the reading position, and the reading start timing of the original is controlled.

Further, since the color line sensor 125 has manufacturing variations for each pixel and it is difficult to make the reflected light amounts of the light sources 119 and 120 uniform depending on the main scanning position, it is assumed that a member having the same density is read. However, the digital value of the image data of the color line sensor 125 varies for each main scanning position.

To correct this, a shading reference plate 128 manufactured so that the density becomes uniform in the main scanning direction is provided at the end of the apparatus, and when the shading reference plate 128 is read by the color line sensor, the main scanning is performed. A process called shading correction that corrects the luminance in the direction to be uniform to a specific digital value is used to correct the manufacturing variation of the sensor and the variation of the light amount.

FIG. 2 is a block diagram for realizing this embodiment.

The CPU 202 detects that the user places a document on the document table 104 and presses the copy button from the operation unit panel 201.

The CPU 202 drives the light sources 119 and 120 and the reflection mirror 121 with a reading unit drive motor to move the shading reference plate 128 to a readable position.

Then, the light sources 119 and 120 are turned on, and the color line sensor 125 is shaded.

In the shading process, the analog image signal based on the light amount of each of R, G, and B colors acquired by the color line sensor 125 is transmitted to the AD converter 206.

The AD converter 206 converts the analog signal into a digital signal based on the acquired analog value, and transmits the digital signal to the read image processing unit 207.

The read image processing unit 207 performs shading correction so that the digital values of the image data when the shading reference plate 128 corresponding to each pixel of the color line sensor 125 is read are substantially the same.

When the shading correction is completed, the light sources 119 and 120 and the reflection mirror 121 are moved by the reading unit drive motor 204 to a position where the conveyed document can be read. Subsequently, in order to convey the original placed on the original placing table 104, the original conveying motor 205 starts conveying the original.

Until the original is conveyed, the color line sensor 125 causes the read image processing unit 207 to read on the reading glass based on the reflected light when the white guide member 114 facing the reading position is irradiated with the light sources 119 and 120. Specify the position of dust adhering to the.

Details of the dust detection process for specifying the dust position will be described later.

When the position of the dust is specified and the conveyed document comes into contact with the actuator 127, the fact that the document has reached the vicinity of the reading position is transmitted to the CPU 202.

FIG. 3 is an enlarged view of the actuator 127.

When the document comes into contact with the actuator 127, the actuator 127 falls down so as to block the transmissive sensors 301a and 301b attached to the apparatus. The transmissive sensor 301 has an irradiation unit 301a that irradiates infrared light on one side and a light receiving unit 301b that receives the irradiated light on the other side, and converts it into an electric signal based on the amount of light incident on the light receiving unit. To be done.

When the irradiation light is blocked by the operation of the actuator 127, the voltage level of the electric signal of the light receiving unit changes. Therefore, by transmitting this signal to the CPU 202, it can be detected that the document has reached the document detection sensor 127. ..

The original detection sensor 127 is attached at a predetermined distance from the original reading position, and after the original reaches the original detection sensor 127, the CPU 202 causes the original conveyance motor 205 to operate the original conveyance motor 205 for a predetermined number of pulses. By conveying the document, the timing at which the document reaches the reading position is managed.

The CPU 202 transmits a signal to the read image processing unit 207 at the timing when the document should reach the reading position, and controls the document reading to be effective, whereby the document can be read.

Similarly, when the CPU 202 detects that the trailing edge of the transported document reaches the document detection sensor 127, after the motor is transported by a predetermined number of pulses to the document transport motor, the document is sent to the read image processing unit 207. By giving an instruction to stop reading, the timing of ending reading of the document is controlled.

FIG. 4 is a detailed block diagram of the read image processing unit indicated by 207 in FIG. FIG. 5 is a chart drawing for measuring the dispersion value of the sensor.

As indicated by 501 to 505, the chart 500 has a plurality of density patches printed with different densities, and the variance value is calculated using the image data of each density patch.

The brightness value when the chart shown in FIG. 5 is read from the output value of the AD converter shown at 206 in FIG. 2 is input to the S/N calculation unit 401.

The S/N calculator calculates the average luminance value and the variance value of each of the density patches 501 to 505.

As an example, FIG. 6 shows luminance values for each main scanning line when the chart 500 is scanned.

In FIG. 6, the horizontal axis indicates the sub-scanning position, and the vertical axis indicates the average luminance value of all the main-scanning pixels acquired at each sub-scanning position.

Since the chart 500 is printed such that the density becomes lighter from 501 to 505 in order, the luminance value gradually changes so that the luminance value becomes higher.

The variation in the luminance value in each patch indicates the variation in luminance for each reading line of the sensor, and this appears as a variance value which is the measurement result of S/N.

Next, a method of calculating the variance value will be described.

In the evaluation area of each density patch, if the main scanning width is Width, the number of sub-scanning lines is Height, and the brightness values at the main scanning position X and the sub-scanning position Y are defined as I[X,Y], the brightness of each density patch The average value Average is represented by [Formula 1], and the variance value Evaluation is represented by [Formula 2] [Formula 1]
Average={I[0,0]+I[1,0]+I[2,0]+...
+I[Width-1, Height-1]}/{Width*Height}

The calculation results of the formulas 1 and 2 are calculated for each of the density patches 501 to 505 as a variance value, which is output.

The above is the processing performed by the S/N calculation unit 401 in FIG.

Note that the drawings of the charts shown in this embodiment are examples, and the drawings of the charts are not limited thereto.

Further, for example, when a blank sheet is conveyed, the analog output level of the sensor is controlled to change by gradually changing the amount of light emitted from the light source for illuminating the original during reading the original, and the variance value is acquired. Any method may be used.

The variance value calculated by the S/N calculation unit 401 is stored in the S/N value storage unit 402.

This value is transferred to the blank paper detection unit 407, transmitted to the edge detection unit 404 of the blank paper detection unit 407, and is calculated so that the variance value is reflected in the determination threshold of the edge detection unit 407.

Next, FIG. 7 shows image data when the chart 500 is read by a sensor having a good S/N characteristic.

In FIG. 7, the horizontal axis represents the sub-scanning position, and the vertical axis represents the average luminance value of all the main-scanning pixels acquired at each sub-scanning position.

When a sensor having a good S/N characteristic is used, the variance becomes small when the density patches 501 to 505 are read, so that the brightness variation in each density patch becomes small as shown in FIG. 7.

Therefore, also with respect to the brightness variation calculated by Expression 2, the brightness dispersion value of each of the density patches 501 to 505 becomes large in the image data shown in FIG. 6, and each of the density patches 501 to 501 in the image data shown in FIG. The luminance dispersion value of 505 tends to be small.

As an example, FIG. 8 shows dispersion values of the density patches 501 to 504 in the image data of FIG. 6, and FIG. 9 shows dispersion values of the density patches 501 to 504 in the image data of FIG. 7.

In the white paper detection unit 407, the histogram detection unit 405 calculates a histogram from the digital value when the original area is read. When the document does not include print information, the histogram of the digital values has a peak of the histogram only in the vicinity of the digital value corresponding to the paper color of the document itself. On the other hand, when the document includes print information, there are a plurality of peaks in the histogram.

The blank sheet determination unit 406 calculates a luminance distribution (histogram) for one original. The histogram is divided into groups at predetermined brightness intervals, and if there are two or more groups in which it is determined that the histogram value is larger than a preset value for each group, it is determined that the original includes print information. To do.

On the other hand, if there is only one group in which it is determined that the histogram value is larger than the preset value, it is determined that the original document is blank.

As an example, FIG. 11 shows an image diagram in which the histogram for one surface of the original is calculated for the blank original not including the print information shown in FIG.

In this embodiment, the digital values of the image data are 0 to 255, and the image data is classified into two groups (group A has digital values 0 to 170 and group C has digital values 171 to 255).

When the document does not contain any print information, the white background of the document has the highest histogram. Therefore, in the case of a document with high whiteness, the histogram with high digital values is displayed as shown in group B of FIG. Peak occurs.

In FIG. 11, a threshold value of the digital value 1101 is provided, and it is determined that the group exceeding the threshold value exists only in one of the groups A and C. You can judge whether or not.

Next, as shown in FIG. 12, in the case where there is print information such as a page number with a small number of characters in the right corner of the document, an image diagram in which a histogram for one surface of the document is calculated is shown in FIG.

Even if the print information is small, the peak of the histogram generated by the characters of the group A can be detected as long as the threshold is the threshold 1501.

By doing so, when a document on which a small amount of print information such as characters is printed is read, the histogram detection unit 405 determines whether the document contains print information or a blank document.

The above is the description of the histogram detection unit 405.

Next, the edge detection unit 404 of FIG. 4 will be described.

The edge detection unit 404 detects edges of print information such as characters and lines.

An original that does not include print information does not include data of different colors, such as characters, for the background of the original, so if no edge is detected and no edge occurs, it is a blank original. You can judge.

However, in recent years, there are documents such as recycled paper that include colored fibers in the document itself.

In the case of such an original, the colored fiber is detected as an edge, and even an original containing no print information is erroneously determined to be not a blank sheet.

Therefore, in this embodiment, the document is divided into blocks in the vertical direction and the horizontal direction, and it is determined whether the document is a blank sheet or not based on the variation in the number of edges in each block.

FIG. 14 is a diagram showing a document 1601 which is divided into blocks in the horizontal and vertical directions.

AREAy0, AREAy1, AREAy2,..., AREAyX in the horizontal direction
AREA0x, AREA1x, AREA2x,..., AREAYx in the vertical direction.
Is divided into blocks and the edge is detected in each block.

The edge is detected by using the difference between the pixel of interest and the adjacent pixel.

In this processing, as a result of calculation by the S/N calculation unit 401, if the variance value is large, the show-through image data may be detected as an edge.

Therefore, the value stored in the S/N value storage unit 402 is calculated to reflect the variance value in the determination threshold of the edge detection unit 404 of the blank sheet detection unit 407.

Hereinafter, the variance value as the calculation result of the S/N calculation unit 401 and the determination threshold value of the edge detection unit 404 will be described.

With respect to the variance value which is the calculation result of the S/N calculation unit 401, the variance values obtained by reading the density patches 501 to 505 of FIG. 5 using the apparatus are EV[01] to EV[05]. .

Further, the standard of the dispersion value provided in advance is EV[11] to EV[15]. The reference value is a predetermined central dispersion value, for example, by measuring the dispersion value of a plurality of devices having the same configuration and adopting the average value thereof as the reference value.

Letting TH_DEF be a threshold value for edge detection that is provided in advance and TH_EDGE be a threshold value for edge detection that reflects the variance value, the relationship between the variance value and the determination threshold value of the edge detection unit 404 is shown in [Formula 3].

The brightness difference between TH_EDGE calculated by [Formula 3] and an adjacent pixel is compared for each pixel, and when the difference is larger than TH_EDGE, it is determined that the pixel has an edge.

In such processing, edge detection is performed for each of AREA00 to AREAYX in FIG. 14, and the total number of edges detected in each area is counted.

Next, the number of detected edges in each area is compared.

If there is a difference in the number of detected edges in each area and it is larger than a predetermined threshold value, it is determined that the print information varies in each area, and it is determined that the document is not a blank document.

On the other hand, even if the number of detected edges in each area is large, if the difference in the number of detected edges in each area is small and it is determined that there is little variation, it is determined to be a blank document.

By performing such processing, it is possible to determine that even an original document including colored fibers such as recycled paper is a blank original document if there is no print information.

Further, in the case where the show-through has occurred, the edge detection threshold detected by the edge detection unit 404 becomes high when the variance value is large, based on the result calculated by the mathematical formula 2. Even if the variance value of the image area is large, the risk of being erroneously determined as an edge is suppressed.

The above is the description of the edge detection unit in FIG.

Finally, the blank sheet determination unit 407 in FIG. 4 will be described.

The blank sheet determination unit 407 determines that the blank document is a blank document only when it is determined from the detection results of the edge detection unit 405 and the histogram detection unit 406 that they are not blank documents, and the image processing controller 404 determines the determination result. To send.

On the other hand, if it is determined by at least one of the edge detection unit 405 and the histogram detection unit 406 that the document is a blank document, the document includes print information, and therefore it is transmitted to the image processing controller 404 that the document is not a blank document. To do.

Next, the flowchart of this embodiment will be described with reference to FIG.

The CPU 202 of FIG. 2 detects that the user has pressed the copy button from the operation unit panel 201 of FIG. 2 (S001).

The CPU 202 requests the reading unit 204 of FIG. 2 to drive the motor, and moves the reading unit to below the shading reference plate 128 of FIG. 1 (S002).

After arriving under the shading reference plate, the light sources 119 and 120 of FIG. 1 are turned on, and shading correction is performed so that the white level becomes uniform (S003).

Next, whether or not the document is placed on the ADF is detected by the document detection sensor installed on the document table (S004).

It should be noted that in the case of the pressure plate scan, blank sheet detection is not performed.

When the document placed on the ADF is detected, the reading unit is moved to the ADF reading position (S005).

After moving to the reading position, the variance value calculated in advance by the S/N calculation unit 401 is acquired from the S/N value storage unit 402, and the edge detection threshold used in the edge detection unit 404 is calculated (S006), (S007). ..

When the edge detection threshold is determined, the document conveyance is started (S008).

When the arrival of the leading edge of the original at the original detection sensor 127 of FIG. 1 is detected as a result of the original being conveyed, the ADF reading position is located at a predetermined distance from that position. After the document is conveyed, the document reading is started (S011, S014, S015).

If the document detection sensor 127 of FIG. 1 does not detect the document even after a lapse of a predetermined time after the document is started to be conveyed, it is considered that the document JAM has occurred during the document conveyance, and a time-out error occurs (S012, S013). ).

When the document reading is started, the blank sheet detection unit 407 of FIG. 4 makes a blank sheet detection determination.

The edge detection unit 404 counts the number of edges included in the image data from the edge detection threshold value based on the variance value calculated in S007 (S016).

Similarly, the histogram detection unit 405 of FIG. 4 calculates a histogram (S017).

This calculation is performed until the document detection sensor 127 detects the trailing edge of the document (S018).

After the document detection sensor 127 detects the trailing edge of the document, the document reading is stopped after a predetermined number of pulses have elapsed (S018, S021, S022).

When the document detection sensor 127 does not detect the document trailing edge even after a predetermined time has elapsed, it is determined that the document JAM has occurred, and the job is ended (S019, S020).

The blank sheet determination unit 407 in FIG. 4 determines that the copy document is blank sheet based on the detection results of the edge detection unit 404 and the histogram detection unit 405 when at least one of them is blank sheet. The image processing controller 404 notifies the user of the blank original through the operation unit (S025).

The above is the flowchart of the present embodiment.

By performing such processing, even in an image reading apparatus having a large sensor dispersion value, it is possible to prevent the false detection of a blank original due to show-through and perform original reading.

101 image reading device housing, 102 document feeder, 103 document stack,
104 original placing table, 105 width regulation plate, 106 pickup roller,
107 separation pad, 108 separation roller, 109 first resist roller,
110 second registration roller, 111 first transport roller,
112 second transport roller, 113 third transport roller, 114 white guide plate,
115 fourth conveyance roller, 116 paper ejection roller, 117 paper ejection tray,
118 reading glass, 119, 120 light source, 121, 122, 123 mirror,
124 imaging lens, 125 color line sensor, 126 sensor substrate,
127 original detection sensor, 128 shading reference member,
201 operation panel, 202 CPU, 204 reading unit drive motor,
205 document transport motor, 206 AD converter, 207 read image processing unit 301 reflective sensor, 401 dust streak detection unit, 402 dust position storage unit,
403 dust streak correction unit, 404 image processing controller, 405 edge detection unit,
406 Histogram detection unit, 407 Blank paper determination unit, 501 Adhesion dust,
502 Red sensor, 503 Green sensor, 504 Blue sensor 701 Dust position information stored in the dust stripe storage unit of the Red sensor,
702 Red sensor explanatory diagram near the pixel of interest,
703 Digital value near pixel of interest when dust streak of Red sensor occurs,
704 Red digital value of the vicinity of the pixel of interest when correcting dust streaks of the sensor
The dust position information stored in the dust stripe storage unit of the 711 Green sensor,
712 Green sensor explanatory diagram near the pixel of interest,
713 Green sensor digital value near the pixel of interest when dust streaks have not occurred,
714 Green sensor digital value near the pixel of interest at the time of dust streak correction of the Green sensor,
The dust position information stored in the dust stripe storage unit of the 721 Blue sensor,
Explanatory drawing of the pixel of interest vicinity of 722 Blue sensor,
723 Blue sensor digital value near the pixel of interest when dust streaks have not occurred,
724 Blue sensor digital value near the pixel of interest at the time of dust streak correction of the blue sensor,
1101 Histogram threshold,
1501 threshold 1, 1402 histogram threshold 2,
1601 Area division image diagram at the time of edge detection

Claims (3)

In an image reading device that acquires image data of a document,
A document feeder that feeds documents,
Having an image reading sensor for reading color image data using a plurality of line sensors,
From the image data acquired by the line sensor, a dispersion value acquisition unit that acquires a dispersion value of luminance based on the line sensor,
A variance value storage unit for storing the variance value obtained by the variance value acquisition unit,
A blank sheet detecting means for detecting whether or not the original is a blank sheet from the image data read by the line sensor;
An image reading apparatus, which performs blank sheet detection based on a variance value of each line sensor stored in the storage means. The blank sheet detecting means is a blank sheet based on the information acquired by the edge detecting means for detecting edge information from the image data and the histogram detecting means for detecting the histogram of the image data from the image data read by the line sensor. The image reading apparatus according to claim 1, wherein detection is performed. The image reading apparatus according to claim 1, wherein the edge detection unit is an edge detection unit that changes an edge detection threshold according to a variance value stored in the storage unit. .