JP2007143040A - Shading correction data generating method, image reader, image forming apparatus and printing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately perform shading correction using simple arithmetic even if there is abnormality in reference white board data. <P>SOLUTION: In an image reader, a document is irradiated with light from a light source, reflection light is made incident from a scanning optical system to a photoelectric conversion element, photoelectric conversion is performed on the reflection light by the relevant photoelectric conversion element, and a document image is read by a read section 101. The image reader comprises: a reference white board data computation section 102 for acquiring reference white board data in reading by reading the density of a reference white board before reading the document image in the read section 101; a determination section 103 and a reference white board data forming section 104 for determining an abnormal part of the acquired reference white board data in reading in a sub scanning direction on the basis of averaged variations for each sub scanning area and excluding the reference white board data in reading from an object to be computed; and a shading correction processing section 105 for performing shading correction processing based on the excluded reference white board data in reading. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a shading correction data creation method for creating a shading correction data by reading a reference white plate, an image reading apparatus for performing a shading correction process using this method, an image forming apparatus and a printing system provided with the image reading apparatus. .

  In an image reading device used in a scanner device, a copying device, a facsimile device or the like, an image sensor such as a CCD (Charge Coupled Device) is used to photoelectrically convert reflected light from a light source irradiated on a document. The original image is being scanned. When reading in this way, there is uneven illumination of the light source that irradiates the document and CCD sensitivity variations, so shading correction processing is performed based on the white reference data (reference white plate data) when the reference white plate is read from the past. ing. When normal, the distribution in the sub-scanning direction is uniform for each line in the main scanning direction as shown in FIG. 10A, and the main scanning distribution of the reference white plate data is the main scanning of the document as shown in FIG. 10B. The distribution is the same, and the shading correction result of the original image is output uniformly.

  On the other hand, for example, an invention described in Patent Document 1 is known as a technique related to this type of shading correction. In the present invention, the calculation coefficient can be set to an optimum value so that the influence of white reference noise such as scratches and dirt can be reduced, or shading correction data can be created with a small number of lines. An averaging means for obtaining shading correction data of each image by obtaining an average between lines of image data is provided, and calculation coefficients used when obtaining the average by this averaging means are set for each position in the sub-scanning direction of the image data. It is a thing.

In addition, the inventions described in Patent Documents 2 and 3 are also known as this type of technology.
JP 2002-300393 A JP-A-7-177314 JP-A-8-256264

  By the way, as in the above-described conventional example, the calculation coefficient is set to an optimal value in order to output the shading correction result of the original image uniformly and to reduce the influence of white reference noise such as scratches and dirt, Although shading correction is performed appropriately, if there is distortion of the rail of the traveling body under the reference white plate or reflection on the glass end surface over time, sub-scanning of the reference white plate as shown in FIG. The distribution of the reading level in the direction is shifted between the lines in the main scanning direction. FIG. 11A shows a case where there is an abnormality at the left end portion of the reference white plate as an example. Accordingly, as shown in FIG. 11B, the main scanning distribution of the reference white plate data is different from the main scanning distribution of the document, and appropriate reference white plate data cannot be obtained. As a result, the shading correction process cannot be performed appropriately, and the image quality deteriorates.

  The present invention has been made in consideration of such a conventional example, and an object of the present invention is to be able to appropriately perform shading correction using simple calculation even when there is an abnormality in the reference whiteboard data. Is to make it.

  In order to achieve the above object, the first means irradiates the original with light from a light source, makes the reflected light enter the photoelectric conversion element from the scanning optical system, and performs photoelectric conversion with the photoelectric conversion element to image the original. In the shading correction data creation method for creating shading correction data by reading the density of the reference white plate before reading the original, a plurality of areas are set in the sub-scanning direction, and the adjacent sub-scanning area areas are set. The amount of change in the average reading level obtained by reading the reference white plate is obtained, and when the amount of change is larger than a preset threshold, the sub-scanning direction area data read later is deleted from the shading correction data. Features.

  The second means, in the first means, after deleting the data of the area in the sub-scanning direction read later from the shading correction data, obtain the amount of change in the average reading level of the area in the next sub-scanning direction, If the amount of change is larger than the threshold value, it is deleted, and if it is within the threshold value, the average reading level of the area in the next sub-scanning direction is compared with the average reading level of the area in the next sub-scanning direction. Comparison for obtaining shading correction by repeating the operation of obtaining the amount of change and comparing the magnitude relationship with the threshold value, and keeping the average reading level obtained by reading the reference white plate in the region in the sub-scanning direction within a predetermined range It is characterized by data.

  The third means is characterized in that, in the first or second means, the area set in the sub-scanning direction is provided for each of the plurality of areas set in the main scanning direction.

  The fourth means is an image reading unit having a reading unit that irradiates light from a light source to the original, makes the reflected light enter the photoelectric conversion element from the scanning optical system, and photoelectrically converts the original image by the photoelectric conversion element. In the apparatus, before reading the original image by the reading means, a means for reading the reference white board density to obtain the reference white board data at the time of reading, and an abnormal portion in the sub-scanning direction of the acquired reference white board data at the time of reading is averaged And a means for making a determination based on the amount of change for each sub-scanning region and excluding it from the calculation target, and a means for performing a shading correction process based on the excluded reading reference whiteboard data. .

  The fifth means is arranged in the fourth means to update the correction reference whiteboard data by reading the reference whiteboard data at the time of reading immediately after the start of reading by the excluding means and determining an abnormal portion from the change amount. The means for performing the shading correction process performs the shading correction process with reference to the updated correction standard whiteboard data.

  The sixth means is the fourth or fifth means wherein the exclusion means judges the abnormal portion in the sub-scanning direction using a preset judgment formula, and the influence on the reference whiteboard data at the time of reading is determined. It is characterized by removing data in a certain area.

  The seventh means is any one of the fourth to sixth means, further comprising means for setting a threshold value, wherein the determination is made based on the threshold value set by the means for setting the threshold value. To do.

  The eighth means is characterized in that the image forming apparatus includes an image reading apparatus according to any one of the fourth to seventh means.

  The ninth means is characterized in that the printing system includes an image reading apparatus according to any one of the fourth to seventh means.

  In the embodiment described later, the document is denoted by reference numeral 2, the photoelectric conversion element is identified by the CCD 10, the means for acquiring the reference whiteboard data at the time of reading is determined by the reading unit 101, and the means for excluding it from the calculation target is determined by the determining unit 103. The means for performing the shading correction processing corresponds to the shading correction processing section 105, the means for setting the threshold to the threshold setting section 106, the image forming apparatus to 51, and the printing system to 61.

  According to the present invention, since the amount of change in the average reading level in the sub-scanning direction is obtained and the influence of the reference white plate data at the time of reading in the sub-scanning direction is removed based on this amount of change, there is an abnormality in the reference white plate data. Even at times, it is possible to perform shading correction appropriately using a simple calculation.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing a mechanical configuration of an image reading apparatus according to an embodiment of the present invention, which is a configuration of a generally used flat bed type image reading apparatus. In FIG. 1, the image reading apparatus 1 is of a flat bed type, and includes a contact glass 3 on which a document 2 is placed, a first carriage 6 including a halogen lamp 4 for exposing the document 2 and a first reflecting mirror 5. A second carriage 9 comprising a second reflecting mirror 7 and a third reflecting mirror 8, a CCD linear image sensor (hereinafter simply referred to as CCD) 10 as a photoelectric conversion element, and a lens unit 11 for forming an image on the CCD 10. And a reference white plate 12 serving as a white reference for white shading correction, and a stepping motor 14 for driving the first carriage 6 and the second carriage 9. The CCD 10 is provided on the sensor board substrate 13. The halogen lamp 4, the first, second and third reflection mirrors 5, 7, 8 and the lens unit 11 constitute a scanning optical system.

  The halogen lamp 4 irradiates light at a certain angle with respect to the reading surface of the reference white plate 12 or the contact glass 3, and the light reflected by the reference white plate 12 or the document 2 is reflected by the first, second, and third reflecting mirrors 5, 5. The light enters the CCD 10 via the lens units 7 and 8 and the lens unit 11. The CCD 10 outputs a voltage corresponding to the amount of incident light as analog image data. The first and second carriages 6, 9 are moved in the sub-scanning direction while the distance between the reading surface of the document 2 and the CCD 10 is kept constant by driving the stepping motor 14, and the document 2 is exposed and scanned.

  FIG. 2 is a block diagram showing an electrical configuration of the image reading apparatus according to the embodiment of the present invention. The image reading apparatus according to the present embodiment includes a reading unit 101 corresponding to a reading optical system including the CCD 10, a reference white plate data calculation unit 102, a determination unit 103, a reference white plate data forming unit 104, a shading correction processing unit 105, and a threshold setting unit. 106. In this configuration, first, analog data read by the CCD 10 by the reading operation in the reading unit 101 is converted into digital data. The reading data of the reference white plate 12, that is, the reference white plate data is stored in the reference white plate data calculation unit 2. In the case of reading with the flat bed method, the reference white plate 12 is installed on the upstream side of the reading direction from the reading start position as shown in FIG. 1. In the sheet-through type image reading apparatus, the reference white plate 12 is provided behind the document reading window. It has been.

As shown in FIG. 3, the reference white plate data calculation unit 2 divides the reference white plate data into 5 blocks in the main scanning direction (x direction) and 10 blocks in the sub scanning direction (y direction). Find the simple average value. Then, the reading level sub-scanning distribution shown in FIG. 11A is expressed as shown in FIG. 4 for 1 to 10 sub-scanning blocks. When calculating the reading level for each sub-scanning block as shown in FIG. 4, the amount of change in the simple average value of the reading level from the y-1th block to the y-th block in the sub-scanning direction as shown in FIG. Is calculated for each line in the main scanning direction. This amount of change is assumed to be ΔI (x, y). ΔI (x, y) is I (x, y) −I (x, y−1) = ΔI (x, y) (1 ≦ x ≦ 5 2 ≦ y ≦ 10) (1)
Is required.

ΔI (x, y) in the equation (1) is obtained for each main scanning range, and an average value Ia (y) is obtained. The calculation formula is
ΣΔI (x, y) / 5 = Iay (2)
However, Σ adds 5 from x = 1.
become that way.

Then at each of the 5 points in each main scanning range,
ΔI (x, y) −Iay = S (x, y) (1 ≦ x ≦ 5 2 ≦ y ≦ 10) (3)
In this manner, the difference S (x, y) between ΔI (x, y) and Ia (y) is calculated.

  Further, in the determination unit 103, a threshold value obtained by the product of the difference S (x, y) expressed by the equation (3) and the value S0 and the average value Ia (y) determined in advance by the threshold value setting unit 6. Compare with Sth (y). If the absolute value | S (x, y) | of this difference is smaller than the threshold value Sth (y) in each line in the main scanning direction in a certain sub-scanning block, that line has an amount of change in the reading level in the main scanning direction. It can be determined that each line is almost uniform. Therefore, this portion can be used as shading correction processing as appropriate reference white plate data.

  On the contrary, when there is a line having an absolute value | S (x, y) | of the difference larger than the threshold value Sth (y), the portion extends from the (y−1) th block to the yth block, and other lines in the main scanning direction. The amount of change in the reading level is extremely different compared to the sub-scanning block, so the sub-scan block has an influence on the reference whiteboard data due to the distortion of the rail of the traveling body of the reading unit and the reflected light on the glass end face. It can be determined that the given block, that is, an abnormal part. At this time, the reference white plate data of this sub-scanning block is removed without being used as the reference white plate data. As shown in FIG. 6, for the next block after the removed block, the amount of change is calculated by the previous block (sub-scan block 5) in the removed block (sub-scan block 6 in the example of FIG. 6). Go. That is, in FIG. 6, after the abnormality is detected from the 5th line to the 6th line and the 6th line is removed, the next 7th line is calculated for the 5th line, not the 6th line. ing.

  This calculation is performed in order from the original 2 side to the leading side of the reference white plate 12 for each sub-scanning block. Since the determination degree of the block having an abnormality is determined by the threshold value S0, the adjustment of the threshold value S0 in the threshold value setting unit 106 is the sensitivity adjustment of the abnormality detection.

  When the calculation and determination are completed for all the sub-scan blocks, only the reference white plate data of the sub-scan block of these appropriate reference white plate data is sent from the determination unit 103 to the reference white plate data forming unit 104, and as shown in FIG. It is formed as appropriate reference white plate data that eliminates the influence of the scanning distribution. The reference whiteboard data formed by the reference whiteboard data forming unit 104 is input to the shading correction processing unit 105, and the shading correction processing unit 105 can perform appropriate shading correction processing.

  FIG. 8 is a diagram showing a schematic configuration of a digital copying machine as an image forming apparatus including the image reading apparatus according to FIG. As shown in FIG. 8, the digital copying machine 51 includes an image reading apparatus 1, a printer engine 52, and a control unit 53 including a microcomputer that controls the entire digital copying machine 51. The printer engine 52 forms an image on a recording medium such as paper, and the printing method is an electrophotographic method, an inkjet method, a sublimation type thermal transfer method, a silver salt photographic method, a direct thermal recording method, a melting method. Various known methods such as a mold thermal transfer method can be used. The control unit 53 controls the image reading device 1 and the printer engine 52 to read the document 2 with the image reading device 1 and form an image with the printer engine 52 based on the read image data. Since the image reading device 1 itself is the same as that shown in FIG. 1, the description of the image reading device 1 is omitted.

  FIG. 9 is a block diagram illustrating a schematic configuration of a printing system 61 including the image reading apparatus according to FIG. As shown in FIG. 9, the printing system 61 includes an image reading device 1, an information processing device 62 such as a PC (Personal Computer) capable of various information processing based on a given program, and a printer 63. The image reading apparatus 1 and the printer 63 are connected to the information processing apparatus 62 via a predetermined interface.

  The printer 63 performs image formation on a recording medium such as paper, and the printing method is an electrophotographic method, an ink jet method, a sublimation type thermal transfer method, a silver salt photography method, a direct thermal recording method, a fusion type. Various known methods such as a thermal transfer method can be used. Driver software for driving the image reading device 1 and the printer 63 is stored in the information processing device 62. By operating the information processing device 62, the image reading device 1 and the printer 63 are controlled based on the driver software. It is possible to read the document 2 with the image reading device 1 and form an image with the printer engine 52 based on the read image data.

  Since the image reading apparatus 1 itself is the same as that shown in FIG. 1, the description of the image reading apparatus 1 is omitted.

  As described above, according to the present embodiment, the following effects can be obtained.

1) The correction reference white plate data can be obtained by removing the influence on the sub-scanning direction of the reference white plate data at the time of reading due to the distortion of the rail of the traveling body of the reading unit 101, reflection on the glass end face, and the like by a simple calculation process. Therefore, the shading correction processing unit 105 can accurately perform shading correction based on the correction reference white plate data.

2) Since the abnormal portion of the reference whiteboard data at the time of reading generated due to the influence of the light source and the rail of the traveling body over time is updated every time at the time of reading, appropriate correction can be made as needed.

3) Since an abnormal portion in the reference white plate sub-scanning direction is detected using a simple arithmetic expression and the portion is not included in the reference white plate data, high-quality reference white plate data can be obtained.

4) Before the shading correction processing unit 105, the sub-scanning direction reference whiteboard data calculation unit 102, a determination unit 103 for determining and removing a sub-scan block having an abnormal part, a threshold setting unit 106 for determination, and a determination unit 103 Since the correction reference white plate data forming unit 104 for forming the correction reference white plate data used in the shading correction processing unit 105 is provided from the data removed in step S2, the unnecessary reference white plate data is prevented from being sent to the shading correction processing unit 105. Therefore, it is possible to speed up subsequent shading correction processing.

5) Since the threshold value setting unit 106 for setting the threshold value used for the determination is provided, it is possible to easily perform sensitivity adjustment for detecting an abnormal portion on the reference white plate 12.

1 is a schematic configuration diagram illustrating a mechanical configuration of an image reading apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating an electrical configuration of an image reading apparatus according to an embodiment of the present invention. It is explanatory drawing which shows the area | region division of the reading data of a reference | standard white board. FIG. 4 is a diagram illustrating an example of a relationship between a block in a main scanning direction and a sub scanning direction and a reading level for the region illustrated in FIG. It is explanatory drawing which shows the detection state of the difference of the average reading level in the area | region of an adjacent subscanning direction, and each main scanning direction. FIG. 10 is an explanatory diagram illustrating a detection state of a difference between an area in the next sub-scanning direction and an average reading level by removing data in a region where an abnormality is detected when abnormality is detected in the reading data of a reference white board. It is a figure which shows an example of the reference white board data obtained by deleting abnormal reading data from the state of FIG. 1 is a diagram illustrating an example of an image forming apparatus in which an image reading apparatus according to the present invention is used. 1 is a diagram illustrating an example of a printing system in which an image reading apparatus according to the present invention is used. It is a figure which shows the state of normal reference | standard white board data. It is a figure which shows the state of the reference white board data when abnormality has arisen.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image reader 2 Original 10 Photoelectric conversion element (CCD)
DESCRIPTION OF SYMBOLS 12 Reference white board 101 Reading part 102 Reference white board data calculating part 103 Judgment part 104 Reference white board data formation part 105 Shading correction process part 106 Threshold setting part

Claims (9)

When the original is irradiated with light from a light source and the reflected light is incident on the photoelectric conversion element from the scanning optical system and photoelectrically converted by the photoelectric conversion element to read the image of the original, the reference white plate is read before reading the original. In the shading correction data creation method of creating the shading correction data by reading the density,
Set multiple areas in the sub-scanning direction,
Obtain the amount of change in the average reading level obtained by reading the reference white plate in the adjacent sub-scanning direction area,
When the amount of change is larger than a preset threshold value, the shading correction data generation method is characterized in that data in a sub-scanning direction area read later is deleted from the shading correction data. After deleting the data of the area in the sub-scanning direction read later from the shading correction data, the amount of change in the average reading level of the area in the next sub-scanning direction is obtained, and if the amount of change is larger than the threshold, it is deleted. If it is within the range, the average reading level of the area in the next sub-scanning direction is compared with the average reading level of the area in the next sub-scanning direction to determine the amount of change in the average reading level, and the magnitude relationship with the threshold value is Repeat the operation of comparing,
2. The shading correction data generation method according to claim 1, wherein the average reading level obtained by reading the reference white plate in the region in the sub-scanning direction falls within a predetermined range and is used as comparison data for performing shading correction.   3. The shading correction data generation method according to claim 1, wherein the region set in the sub-scanning direction is provided for each of a plurality of regions set in the main scanning direction. In an image reading apparatus having reading means for irradiating light from a light source to a document, passing the reflected light from a scanning optical system and entering a photoelectric conversion element, photoelectrically converting the photoelectric conversion element, and reading the document image.
Means for reading a reference white plate density before reading the document image by the reading means to obtain reading reference white plate data;
Means for determining an abnormal portion in the sub-scanning direction of the acquired reference whiteboard data at the time of reading based on the amount of change for each sub-scanning area that has been averaged, and excluding it from the calculation target;
Means for performing shading correction processing based on the excluded reading reference whiteboard data;
An image reading apparatus comprising: The means for excluding reads the reference whiteboard data at the time of reading every time immediately after the start of reading, and determines the abnormal part from the change amount to update the correction reference whiteboard data,
5. The image reading apparatus according to claim 4, wherein the means for performing the shading correction processing performs the shading correction processing with reference to the updated correction reference white plate data.   The exclusion means determines an abnormal portion in the sub-scanning direction using a predetermined determination formula, and removes data in an area having an influence on the reference whiteboard data at the time of reading. The image reading device according to 4 or 5.   7. The image reading apparatus according to claim 4, further comprising means for setting a threshold value, wherein the determination is performed based on the threshold value set by the means for setting the threshold value.   An image forming apparatus comprising the image reading apparatus according to claim 4.   A printing system comprising the image reading device according to claim 4.

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