JP2020068474A - Image processing apparatus and image correction method - Google Patents

Abstract

To provide an image processing apparatus and an image correction method, allowing for suppression of the occurrence of such a trouble that a density value of a background area of an image of a document read by an image reading unit is partially darkened in an area near a high-density area.SOLUTION: An image reading unit of an image processing apparatus 1 reads an image of a document. A first detection processing unit detects a density value of a background area in a read image read by the image reading unit. A second detection processing unit detects a high-density area in the read image. An identification processing unit identifies, as a pixel to be corrected, a neighboring pixel satisfying a predetermined correction condition among neighboring pixels located in a neighboring area of the high-density area. A correction processing unit corrects a density value of the pixel o be corrected.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image processing device and an image correction method.

  A background density is detected from an image of a document read by an image reading unit such as a CCD (Charge Coupled Device), and the background is removed from the image using a threshold value determined according to the detected background density. An image processing device capable of performing the above is known (for example, refer to Patent Document 1).

JP-A-4-37258

  By the way, in an image of a document optically read by an image reading unit such as a CCD, the density value of the background area may be darker than the original density value in the vicinity of a high density area such as a character. . This is because the density value of each pixel read by an image reading unit such as a CCD is affected by the reflected light from the area near the area in addition to the reflected light from the area on the document corresponding to the pixel. Because.

  An object of the present invention is to provide an image processing apparatus and an image correction capable of suppressing the density value of the background area of the image of the document read by the image reading unit from being partially dark in the vicinity of the high density area. To provide a method.

  An image processing apparatus according to one aspect of the present invention includes an image reading unit, a first detection processing unit, a second detection processing unit, a specific processing unit, and a correction processing unit. The image reading unit reads an image of a document. The first detection processing unit detects the density value of the background area in the read image read by the image reading unit. The second detection processing unit detects a high density area in the read image. The identification processing unit identifies, as a pixel to be corrected, a neighboring pixel satisfying a predetermined correction condition among the neighboring pixels located in the neighboring region of the high density region. The correction processing unit corrects the density value of the correction target pixel.

  An image correction method according to one aspect of the present invention includes an image reading step, a first detecting step, a second detecting step, a specifying step, and a correcting step. In the image reading step, the image of the document is read. In the first detecting step, the density value of the background area in the read image read in the image reading step is detected. In the second detecting step, a high density area in the read image is detected. In the specifying step, among the neighboring pixels located in the neighboring region of the high-density region, neighboring pixels satisfying a predetermined correction condition are designated as correction target pixels. In the correction step, the density value of the correction target pixel is corrected.

  According to the present invention, the image processing apparatus and the image correction capable of suppressing the density value of the background area of the image of the document read by the image reading unit from being partially dark in the vicinity of the high density area. A method is provided.

FIG. 1 is a block diagram showing the system configuration of an image processing apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of a document and a read image used in the image processing apparatus according to the embodiment of the present invention. FIG. 3 is a flowchart showing an example of the procedure of the image correction processing executed by the image processing apparatus according to the embodiment of the present invention. FIG. 4 is a diagram showing an example of a read image before correction and a read image after correction used in the image processing apparatus according to the embodiment of the present invention. FIG. 5 is a diagram for explaining an example of a second threshold value changing method used in the image processing apparatus according to the embodiment of the present invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention. The following embodiments are examples of embodying the present invention and do not limit the technical scope of the present invention.

[Configuration of image processing device]
As shown in FIG. 1, an image processing apparatus 1 according to an embodiment of the present invention includes an operation display unit 10, an ADF (Auto Document Feeder) 11, an image reading unit 12, an image forming unit 13, a communication I / F 14, and a storage. The unit 15 and the control unit 16 are provided. Specifically, the image processing apparatus 1 is a multifunction machine having a printer function, a scanner function, a copy function, a facsimile function, and the like. The present invention is not limited to the multi-function peripheral, and can be applied to any image processing apparatus including the image reading unit 12.

  The operation display unit 10 includes a display unit such as a liquid crystal display that displays information, and an operation unit such as a touch panel and operation buttons that accept user operations.

  The ADF 11 is an automatic document feeder that includes a document setting unit, a transport roller, a document retainer, and a paper discharge unit, and transports a document to be read by the image reading unit 12.

  The image reading unit 12 includes a document table, a light source, a mirror, an optical lens, and a CCD, and can read an image of the document D1 (see FIG. 2) and output it as a read image G1 (see FIG. 2).

  The image forming unit 13 can execute a printing process based on image data by an electrophotographic system or an inkjet system, and forms an image on a sheet based on the image data. For example, when the image forming unit 13 executes the printing process by the electrophotographic method, the image forming unit 13 includes a photosensitive drum, a charger, an exposure device, a developing device, a transfer device, a fixing device, and the like.

  The communication I / F 14 performs communication processing according to a predetermined communication protocol with an external facsimile device or an information processing device such as a personal computer via a communication network such as a telephone line, the Internet, or a LAN. It is a communication interface that can.

  The storage unit 15 is a non-volatile storage unit such as a hard disk or an EEPROM (registered trademark). The storage unit 15 stores various control programs executed by the control unit 16 and various data. The control program includes a control program for causing the control unit 16 to execute an image correction process (see FIG. 3) described later.

  The control unit 16 includes control devices such as a CPU, a ROM, and a RAM. The CPU is a processor that executes various arithmetic processes. The ROM is a non-volatile storage unit in which information such as a control program for causing the CPU to execute various processes is stored in advance. The RAM is a volatile or nonvolatile storage unit used as a temporary storage memory (work area) for various processes executed by the CPU.

  By the way, in the case where the original is a white paper with black characters printed, the image of the original optically read by the image reading unit 12 (for example, the read image G1 shown in FIG. 2) is an image representing the characters. In the vicinity area A3 (hatched portion in FIG. 2) of the high-density area A1 (black portion in FIG. 2) corresponding to, the density value of the vicinity area A is smaller than the original density value (that is, the density value of the background area A2). May get dark. This is because the density value of each pixel read by the image reading unit 12 is affected by the reflected light from the area near the area in addition to the reflected light from the area on the original corresponding to the pixel. . On the other hand, according to the image processing apparatus 1 according to the present embodiment, the density value of the background area A2 of the image of the document read by the image reading unit 12 is partially dark in the vicinity area A3 of the high density area A1. It is possible to suppress that.

  Specifically, the control unit 16 includes a first detection processing unit 161, a second detection processing unit 162, a specific processing unit 163, and a correction processing unit 164. The control unit 16 functions as each of these processing units by executing various processes according to the control program. Further, the control unit 16 may include an electronic circuit that realizes a part of these processing units or a plurality of processing functions.

  The first detection processing unit 161 detects the density value of the background area A2 in the read image G1 (see FIG. 2) read by the image reading unit 12. For example, when the original is an original in which characters are printed on a blank sheet (for example, the original D1 shown in FIG. 2), a density value corresponding to white is detected as the density value of the background area A2. When the original is a newspaper, a density value corresponding to gray is detected as the density value of the background area A2. As a method for detecting the density value of the background area A2, any known method can be adopted. For example, the first detection processing unit 161 generates a density histogram of the image (that is, a histogram indicating the number of pixels for each density value), and calculates the density value corresponding to the peak in the density histogram as the density value of the background area A2. May be detected as

  The second detection processing unit 162 detects the high density area A1 in the read image. The high-density area A1 may be, for example, an area whose density value is equal to or larger than a predetermined threshold value, or may be an area darker than the background area A2 by a predetermined threshold value or more. For example, when the original is an original in which black characters are printed on white paper (for example, the original D1 shown in FIG. 2), the high density area A1 in the read image G1 is an area of a character portion. The second detection processing unit 162 may detect an edge of the high-density area A1 (that is, a portion adjacent to the background area A2) by using a known arbitrary edge extraction method (for example, Sobel filter). Good.

  The identification processing unit 163 identifies, as the correction target pixel, a neighboring pixel satisfying a predetermined correction condition among the neighboring pixels located in the neighboring area A3 of the high density area A1. The neighboring area A3 is, for example, an area within a range of a × b pixels (where a and b are arbitrary integers) centered on an arbitrary pixel on the edge of the high-density area A1. For example, the neighborhood area A3 may be an area within a range of 3 × 3 pixels centered on an arbitrary pixel on the edge of the high-density area A1. The neighborhood area A3 may be appropriately changed depending on the situation. For example, the larger the density difference between the high density area A1 and the background area A2, the wider the neighboring area A3 may be.

  The correction condition includes that the density value of the neighboring pixel is within a predetermined first density range based on the density value of the background area A2 detected by the first detection processing unit 161. May be. The first density range is, for example, a density range darker than a density value of the background area A2 detected by the first detection processing unit 161 by a predetermined threshold or more (that is, darker than the background area A2 and the background area A2). The density range may be such that the density difference from A2 is equal to or more than the first threshold value. The first threshold is an arbitrary value greater than 0, for example. The first threshold value may be a preset fixed value, or may be appropriately changed depending on the situation. For example, the first threshold value may be automatically changed according to the density value of the background area A2, the density difference between the high density area A1 and the background area A2, and the like.

  The correction condition may include that the density value of the neighboring pixel is within a predetermined second density range based on the density value of the high density region. The second density range is, for example, a density range brighter than a density value of the high-density area A1 by a predetermined second threshold or more (that is, brighter than the high-density area A1 and the density difference from the high-density area A1 is The density range may be a second threshold value or more). The second threshold is an arbitrary value greater than 0, for example. The second threshold value may be a preset fixed value or may be appropriately changed depending on the situation. For example, the second threshold value may be automatically changed according to the density value of the high density area A1 and the density difference between the high density area A1 and the background area A2.

  Further, the specification processing unit 163 may change the second density range according to the number of pixels in the high density area A1 in the specific range centered on the neighboring pixel. The specific range is, for example, a region within a range of c × d pixels (where c and d are arbitrary integers) centered on the neighboring pixels. When the specific range is an area within a range of 3 × 3 pixels centered on the neighboring pixel, pixels of the high-density area A1 in the specific range centered on the neighboring pixel P1 shown in FIG. The number is one. Further, the number of pixels in the high-density area A1 in the specific range centered on the neighboring pixel P2 shown in FIG. 5B is three. Further, the number of pixels in the high-density area A1 in the specific range centered on the neighboring pixel P3 shown in FIG. 5C is five.

  For example, the specific processing unit 163 may increase the second threshold value as the number of pixels in the high density region A1 in the specific range increases. This is because as the number of pixels in the high-density area A1 in the specific range increases, the density value of the neighboring pixels becomes darker than the original density value, and accordingly the second threshold value is increased (that is, darker). It is possible to appropriately correct the density value of the neighboring area A3 of the high-density area A1 by setting the neighboring pixels as the correction target pixels.

  The correction processing unit 164 corrects the density value of the correction target pixel. Specifically, the correction processing unit 164 corrects the density value of the correction target pixel so as to approach the density value of the background area A2. For example, the correction processing unit 164 may correct the density value of the correction target pixel to the same density value as the density value of the background area A2. As a result, as in the corrected read image G2 shown in FIG. 4, the density value of the background area A2 that is partially dark in the vicinity area A3 of the high density area A1 is the same as that of the original background area A2. Corrected to the density value.

  Note that in another embodiment, the control unit 16 may include the determination processing unit 165 (see FIG. 1). The determination processing unit 165 determines whether the high-density area A1 is a character or a diagram. For example, the determination processing unit 165 calculates the width of the high-density area A1 (that is, the distance between two opposing edges in the high-density area A1), and when the calculated width is less than or equal to a predetermined threshold value. Alternatively, it may be determined that the high-density area A1 is a character or a diagram. Then, the identification processing unit 163 may identify the correction target pixel from the neighboring pixels located in the neighboring region A3 of the high-density region A1 determined to be a character or a diagram by the determination processing unit 165. As a result, only the pixels located in the vicinity area of the character or diagram can be set as the correction target pixel, and the vicinity of the high density area A1 (for example, the high density area A1 in the photographic image) which is neither a character nor a diagram. It is possible to suppress unnecessary correction of pixels located in the area.

[Image correction processing]
Next, an example of the procedure of the image correction processing executed by the control unit 16 will be described with reference to FIG. Here, steps S1, S2, ... Show the numbers of the processing procedures (steps) executed by the control unit 16. The image correction process is started in response to an image reading start operation performed on the operation display unit 10, for example.

<Step S1>
First, in step S1, the control unit 16 controls the image reading unit 12 to read the image of the document D1 placed on the document table or the document setting unit of the ADF 11. Note that, here, a case will be described in which the document D1 is a blank sheet in which black characters are printed. The step S1 is an example of the image reading step of the present invention.

<Step S2>
In step S2, the control unit 16 generates a density histogram of the read image G1 read in step S1.

<Step S3>
In step S3, the control unit 16 detects the density value of the background area A2 in the read image G1 based on the density histogram generated in step S2. For example, the control unit 16 detects the density value corresponding to the peak in the density histogram generated in step S2 (that is, the density value having the largest number of pixels) as the density value of the background area A2. The step S3 is an example of the first detection step of the present invention. The process of step S3 is executed by the first detection processing unit 161 of the control unit 16.

<Step S4>
In step S4, the control unit 16 detects the high density area A1 in the read image G1. For example, the control unit 16 detects, as the high-density area A1, an area having a density value darker than the density value of the background area A2 detected in step S3 by a predetermined threshold value or more. The step S4 is an example of the second detection step of the present invention. The process of step S4 is executed by the second detection processing unit 162 of the control unit 16.

<Step S5>
In step S5, the control unit 16 selects any one of the neighboring pixels included in the neighboring area A3 of the high-density area A1 detected in step S4 as the target pixel.

  In another embodiment, the control unit 16 determines whether or not the high-density area A1 detected in step S4 is a character or a diagram, and determines that the high-density area A1 is a character or a diagram. The target pixel may be selected only from the area A3 near the area A1.

<Step S6>
In step S6, the control unit 16 determines whether or not the density value of the target pixel is darker than the density value of the background area A2 detected in step S3 by a first threshold value or more. When it is determined that the density value of the pixel of interest is darker than the density value of the background area A2 by the first threshold value or more (S6: Yes), the process proceeds to step S7. On the other hand, if it is determined that the density value of the target pixel is not darker than the density value of the background area A2 by the first threshold value or more (S6: No), the process proceeds to step S9.

<Step S7>
In step S7, the control unit 16 determines whether or not the density value of the pixel of interest is darker than the density value of the high density area A1 detected in step S4 by a second threshold value or more. When it is determined that the density value of the target pixel is darker than the density value of the high density area A1 by the second threshold value or more (S7: Yes), the process proceeds to step S8. On the other hand, if it is determined that the density value of the pixel of interest is not darker than the density value of the high density area A1 by the second threshold value or more (S7: No), the process proceeds to step S9.

  In step S7, the control unit 16 may increase the second threshold value as the number of pixels in the high-density area A1 in the specific range centered on the target pixel increases.

  The step S6 and the step S7 are examples of the specific step of the present invention. The processing of steps S6 and S7 is executed by the specific processing unit 163 of the control unit 16.

<Step S8>
In step S8, the control unit 16 corrects the density value of the target pixel (that is, the correction target pixel). For example, the control unit 16 corrects the density value of the target pixel to the same density value as the density value of the background area A2 detected in step S3.

<Step S9>
In step S9, the control unit 16 determines whether or not there is a neighboring pixel that has not been selected as the target pixel in the neighboring area A3 of the high density area A1 detected in step S4. When it is determined that there is a neighboring pixel that has not been selected as the target pixel (S9: Yes), the process returns to step S5. On the other hand, when it is determined that there is no neighboring pixel that has not been selected as the target pixel (S9: No), the image correction process ends.

  By the image correction processing, for example, the read image G1 before correction shown in FIG. 2 or 4 is finally corrected like the read image G2 after correction shown in FIG.

  As described above, in the image processing apparatus 1 according to the present embodiment, the density values of the neighboring pixels that satisfy the predetermined correction condition among the neighboring pixels located in the neighboring area A3 of the high-density area A1 in the read image G1 are The density value is corrected to be the same as the density value of the background area A2 in the read image G1. Therefore, it is possible to prevent the density value of the background area A2 of the image of the document read by the image reading unit 12 from being partially dark in the area A3 near the high density area A1.

Reference Signs List 1 image processing device 12 image reading unit 16 control unit 161 first detection processing unit 162 second detection processing unit 163 specific processing unit 164 correction processing unit 165 determination processing unit

Claims (8)

An image reading unit that reads the image of the original,
A first detection processing unit that detects a density value of a background area in the read image read by the image reading unit;
A second detection processing unit that detects a high-density area in the read image;
A specific processing unit that specifies, as a pixel to be corrected, a neighboring pixel that satisfies a predetermined correction condition among neighboring pixels located in the neighboring region of the high density region,
A correction processing unit for correcting the density value of the correction target pixel;
An image processing apparatus including. The correction condition includes that the density value of the neighboring pixel is within a predetermined first density range based on the density value of the background region detected by the first detection processing unit,
The image processing apparatus according to claim 1. The first density range is a density range darker than a density value of the background region detected by the first detection processing unit by a predetermined threshold value or more.
The image processing apparatus according to claim 2. The correction condition includes that the density value of the neighboring pixel is within a predetermined second density range based on the density value of the high density region.
The image processing apparatus according to claim 1. The second density range is a density range brighter than a density value of the high density region by a predetermined second threshold or more.
The image processing apparatus according to claim 4. The specific processing section changes the second density range according to the number of pixels in the high density region in a specific range centered on the neighboring pixels.
The image processing apparatus according to claim 4. Further comprising a determination processing unit that determines whether the high-density region is a character or a diagram,
The identification processing unit identifies the correction target pixel from among the neighboring pixels located in the neighborhood region of the high-density region determined to be a character or a diagram by the determination processing unit,
The image processing device according to claim 1. An image reading step of reading the image of the original,
A first detecting step of detecting a density value of a background area in the read image read in the image reading step;
A second detection step of detecting a high density area in the read image;
A specifying step of specifying, as a pixel to be corrected, a neighboring pixel satisfying a predetermined correction condition among neighboring pixels located in the neighboring region of the high density region,
A correction step of correcting the density value of the pixel to be corrected,
Image correction method including.