JP2012160883A - Image processing apparatus and image forming apparatus provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly remove a shown-through portion from image data by performing showing-through removal processing, focusing on a dispersion value.SOLUTION: An image processing apparatus comprises: an image input part for inputting image data of a document to the apparatus; a target pixel setting part which determines a target pixel from among pixels included in the image data; a dispersion value calculation part which obtains the dispersion value of the region of a certain range including the target pixel determined by the target pixel setting part; a shown-through pixel setting part which determines the target pixel as a shown-through pixel if the calculation result of the dispersion value calculation part is a predetermined dispersion reference value or less; and a shown-through correction part which performs the shown-through removal processing on the shown-through pixel determined by the shown-through pixel setting part.

Description

  The present invention relates to an image processing apparatus that corrects (removes) show-through of image data, such as an image forming apparatus such as a multifunction peripheral or a copying machine.

  When a document printed on both sides is read with a scanner, a show-through may be included in the image data. “Back-through” means that the contents (for example, characters) of the back surface of the reading surface appear in the image data of the reading surface. The show-through occurs due to factors such as a high density portion on the back surface, the irradiation intensity of the light source, and the degree of transparency of the paper. The show-through portion reduces the reproducibility of the content (original) on the reading surface, makes it difficult to see the copy, and deteriorates the image quality. Therefore, image processing for removing show-through may be performed.

  An image processing apparatus that shows one method of removing such show-through is described in Patent Document 1. Specifically, Patent Document 1 reads an image on the front side and an image on the back side of a document, stores the read image data on the front side and image data on the back side in a memory, and outputs them when outputting the stored image data. For each pixel of the image data, the flatness indicating the density change is detected from the density difference with the adjacent pixel, and the detected flatness is less than a certain value and the density of the image data whose density is less than the certain value is changed. An image processing apparatus that erases a show-through image is described. With this configuration, an attempt is made to erase the back-faced image by a simple process without using a complicated algorithm (see Patent Document 1: Claim 1, paragraph [0029], etc.).

JP 2001-346046 A

  The paper color of the original is often white. For this reason, in image data obtained by reading an original, pixels corresponding to the original paper itself (background, background) are often brightest in terms of density. It has been confirmed (experientially) that the show-through portion tends to appear in the image data at a slightly higher density than the density of the paper itself. In other words, a show-through portion often exists in a density band where the density of the paper is slightly increased.

  Therefore, a histogram may be generated for the pixel value of each pixel in the image data, and the show-through removal process may be performed. For example, in the histogram, the pixel value at the peak position is defined as the density (pixel value) of the paper itself. Then, there may be a show-through removal process in which pixels within a certain range of pixel values are uniformly converted into pixel values of the paper itself, centering on the pixel value determined as the density of the paper itself.

  On the other hand, in the image data, for example, a low density portion (halftone portion, for example, light gray) that is not show-through may be close to the density of the paper itself. Therefore, there is a case where the density conversion process is performed on the low density part by the image process of the show-through removal process. In particular, when the document of image data includes a photograph or a pattern, if the show-through removal process is performed, the thin portion is replaced with white, and smooth gradation expression may be lost.

  Here, the low density portion may be expressed as a halftone dot in the document. In the image data of the area that is intentionally expressed as a halftone dot, a feature that the variance value becomes high is confirmed. In other words, the dot portions (dark pixels) at the halftone dots are arranged according to a predetermined pattern in the printing press and become regular and periodic. However, with regard to the show-through removal process, there is a problem that show-through removal focusing on the dispersion value has not been performed.

  In the invention described in Patent Document 1, since the detected flatness is less than a certain value and the density of the image data whose density is less than a certain value is changed to erase the back image, the low density part is removed. There is a possibility that it is uniformly converted to the same density. Moreover, it does not focus on the dispersion value. Therefore, the invention described in Patent Document 1 cannot solve the above problem.

  An object of the present invention is to perform a show-through removal process by paying attention to a dispersion value in view of the above-described problems of the related art and appropriately remove a show-through portion from image data.

  To solve the above problem, an image processing apparatus according to claim 1 includes an image input unit for inputting image data of a document to the apparatus, and a target pixel setting unit that determines a target pixel among pixels included in the image data. A variance value calculation unit for obtaining a variance value of a certain range of region including the target pixel determined by the target pixel setting unit, and a calculation result of the variance value calculation unit is equal to or less than a predetermined variance reference value, A show-through pixel setting unit that determines a pixel of interest as a show-through pixel, and a show-through correction unit that performs a show-through removal process on the show-through pixel.

  According to this configuration, the show-through pixel setting unit determines the target pixel as the show-through pixel when the calculation result of the variance value calculation unit is equal to or less than a predetermined dispersion reference value, and is determined by the show-through pixel setting unit. The show-through removal process is performed on the show-through pixels. Thereby, a place where the variance value is small is determined as a show-through pixel (show-through portion). Therefore, the show-through removal process can be performed by paying attention to the dispersion value, and the show-through removal can be appropriately performed. In addition, because of the low density, it is possible to prevent the show-through removal processing for the portion expressed as a halftone dot in the original and leave it as a halftone dot.

  According to a second aspect of the present invention, in the first aspect of the invention, the target pixel setting unit is predetermined from pixel values indicating the highest density among pixel values of each pixel included in the image data. A pixel having a pixel value equal to or smaller than the difference is determined as the target pixel.

  The show-through part often appears as a density slightly higher than the density of the paper. According to this configuration, the pixel-of-interest setting unit has a pixel value indicating the highest density among the pixel values of each pixel included in the image data. Rather, a pixel having a pixel value equal to or smaller than a predetermined difference is determined as a target pixel. Thereby, the show-through portion can be surely included in the target pixel. In addition, to a certain extent, pixels with high density can be removed from the target pixel, the number of target pixels can be reduced, and the processing speed can be increased.

  According to a third aspect of the present invention, in the first aspect of the invention, the pixel-of-interest setting unit has a predetermined range based on a pixel value having the highest appearance frequency among pixel values of each pixel included in the image data. A pixel having a pixel value within the range is determined as a target pixel.

  The show-through portion often appears as a density slightly higher than the density of the paper. According to this configuration, the pixel-of-interest setting unit is a pixel having the highest appearance frequency among the pixel values of each pixel included in the image data. A pixel having a pixel value within a predetermined range based on the value is determined as a target pixel. This makes it possible to reliably include the show-through portion in the target pixel while recognizing the pixel value having the highest appearance frequency as the paper density. In addition, pixels that have a certain density difference from the paper can be removed from the target pixel, and the number of target pixels can be reduced to increase the processing speed.

  According to a fourth aspect of the present invention, in the first to third aspects of the invention, the ratio of the show-through pixel to the number of pixels of the entire image data, or the show-through for the total number of pixels in a region into which the image data is divided. A ratio calculation unit for obtaining a ratio of pixels, wherein the show-through correction unit performs a show-through removal process when a ratio of the show-through pixel to the number of pixels of the entire image data is equal to or less than a predetermined reference ratio; The show-through removal process is not performed on the show-through pixels included in a region that is not included or has a ratio equal to or lower than a predetermined reference ratio.

  In the show-through removal process, there is a possibility that the process (pixel) other than the show-through part may be processed. According to this configuration, the show-through correction unit is based on the ratio calculated by the ratio calculation unit. Determines whether or not the show-through removal process can be executed. As a result, if the calculated ratio is less than the reference ratio and the show-through portion is narrow and does not affect the reproducibility and visibility of the document, the show-through removal process may not be performed. it can. Note that the “reference ratio” can be arbitrarily determined, but can be determined based on whether the reproducibility of the document and the visibility are not affected.

  According to a fifth aspect of the present invention, in the first to fourth aspects of the invention, the show-through correction unit applies a reverse to the show-through pixels in a predetermined first area of the image data. The show-through removal process is performed, and the show-through removal process is not performed on the show-through pixels in the predetermined second region.

  According to this configuration, the show-through correction unit performs the show-through removal process on the show-through pixels in the predetermined first area of the image data, and the back-out in the predetermined second area. The show-through removal process is not performed on the reflected pixels. As a result, the show-through removal process can be performed only on pixels included in a predetermined area of the image data.

  In addition, although it can determine arbitrarily which part is made into 1st area | region and 2nd area | region among image data, you may determine from a viewpoint of the need for show-through removal. For example, a square region having a certain width from the edge of the image data may be the second region (for example, a blank portion), and the inside of the second region may be the first region. As a result, the show-through portion in the central portion that is conspicuous is removed, and the show-through removal process does not have to be performed on the show-through portion in the peripheral portion that has a weak influence on the reproducibility and visibility of the document.

  According to a sixth aspect of the present invention, in the first to fifth aspects of the present invention, the image recognition apparatus further includes a character recognition unit that performs processing for recognizing a character portion of the image data, and the show-through correction unit includes the show-through pixel. Among them, the show-through removal process is not performed on the show-through pixels included in the character portion and / or in contact with the character portion.

  If it is close to the character part, the part (pixel) recognized as show-through may be a part of the character. Therefore, according to this configuration, the show-through correction unit does not perform the show-through removal process on the show-through pixels included in the character portion and / or in contact with the character portion among the show-through pixels. Thereby, it is possible to prevent the character portion from being corrected and removed by mistake due to the show-through removal processing.

  An image forming apparatus according to a seventh aspect includes the image processing apparatus according to any one of the first to sixth aspects.

  According to this configuration, the image forming apparatus can appropriately remove the show-through portion from the image data by paying attention to the dispersion value.

  As described above, according to the present invention, the image processing for determining the place where the variance value is small as the show-through pixel (show-through portion), performing the show-through removal process focusing on the dispersion value, and appropriately removing the show-through. An apparatus and an image forming apparatus can be provided. In particular, it is possible to provide an image processing apparatus and an image forming apparatus that do not perform a show-through removal process on a portion expressed as a halftone dot at a low density.

1 is a schematic cross-sectional view illustrating an example of a multifunction machine according to a first embodiment. FIG. 2 is a block diagram illustrating an example of a hardware configuration of a multifunction machine according to the first embodiment. 3 is a block diagram for explaining image data processing in the multifunction peripheral according to the first embodiment; FIG. It is explanatory drawing which shows the outline | summary of the show-through removal process which concerns on 1st Embodiment. It is a histogram for demonstrating the show-through removal process which concerns on 1st Embodiment. It is a detailed setting screen of the show-through removal process according to the first embodiment. (A)-(c) is explanatory drawing which shows an example of the form of the show-through removal process which concerns on 1st Embodiment. 6 is a flowchart illustrating an example of a show-through removal process performed by the image processing apparatus and the multifunction peripheral according to the first embodiment. It is a histogram for demonstrating the show-through removal process which concerns on 2nd Embodiment.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 8, taking as an example a multifunction peripheral 100 including an image processing apparatus 1 (corresponding to an image forming apparatus). However, each element such as the configuration and arrangement described in the embodiment does not limit the scope of the invention and is merely an illustrative example.

(Outline of MFP 100)
First, the multifunction peripheral 100 according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view showing an example of a multifunction machine 100 according to the first embodiment of the present invention.

  As shown in FIG. 1, a document cover 101 that holds documents is provided at the top, and an image reading unit 2 (corresponding to an image input unit), a sheet feeding unit 3a, a conveyance path 3b, An image forming unit 4a, a fixing unit 4b, and the like are provided.

  The document cover 101 suppresses a document placed on the contact glass 21 provided on the upper surface of the image reading unit 2 as a document table during copying. Therefore, the document cover 101 has a fulcrum on the back side in FIG. 1 and can be opened and closed in the vertical direction.

  The image reading unit 2 reads a document and generates image data of the document. A contact glass 21 is provided on the upper surface of the image reading unit 2, and an exposure lamp 23 and a first mirror 241 are provided in the first moving frame 221 in the image reading unit 2, and the second moving frame 222 is provided. Are provided with a second mirror 242 and a third mirror 243. When reading a document placed on the contact glass 21, the first moving frame 221 and the second moving frame 222 are moved in the horizontal direction by winding the wire 251 connected to each moving frame with the winding drum 252. Let Then, the reflected light of the light irradiated on the document is incident on the lens 26 by each mirror. The lens 26 guides the reflected light to the image sensor 27 (for example, CCD). Using these optical system members, light is applied to the placed original, and the output value of each pixel of the image sensor 27 receiving the reflected light of the original is A / D converted to generate image data.

  The paper feed unit 3a accommodates a plurality of papers (for example, various papers such as copy paper, recycled paper, and OHP sheet) as recording media, and sends them one by one to the conveyance path 3b during printing. The paper supply unit 3a includes cassettes 31 on which sheets are stacked and can be attached and detached (in the present embodiment, two units 31a and 31b). Paper feed rollers 32 (two in total, 32a and 32b) are provided in each cassette 31. When printing, one of the paper feed rollers 32 is rotationally driven to feed the paper one by one to the transport path 3b.

  The transport path 3b is a path for transporting paper fed from the paper feed unit 3a. In the conveyance path 3b, a guide plate 33 for guiding the sheet, a plurality of conveyance roller pairs 34 that are rotationally driven during sheet conveyance (in FIG. 1, a total of two of 34a and 34b are shown from above), A pair of registration rollers 35 and the like are provided for waiting the conveyed paper in front of the image forming unit 4a and feeding the paper in accordance with the transfer timing of the toner image.

  The image forming unit 4a forms a toner image based on the image data, and transfers the toner image to the conveyed paper. Therefore, each configuration of the image forming unit 4a and a toner image forming process will be described. A photosensitive drum 41 supported so as to be rotatable is provided at substantially the center of the image forming unit 4a. The charging device 42 charges the photosensitive drum 41 with a predetermined potential. The exposure device 43 irradiates (scans and exposes) laser light to the photosensitive drum 41 while turning it on and off based on the image data to form an electrostatic latent image corresponding to the image data. The developing device 44 supplies toner and develops the electrostatic latent image as a toner image. The transfer roller 45 is pressed against the photosensitive drum 41 to form a nip. When the sheet and the toner image enter the nip, a voltage having a polarity opposite to the charging polarity of the toner is applied to the transfer roller 45. As a result, the toner image is transferred to the paper. The cleaning device 46 cleans residual toner and the like remaining on the photosensitive drum 41 after the transfer, and prepares for the next toner image formation.

  The fixing unit 4b fixes the toner image transferred to the paper. The fixing unit 4b of the present embodiment includes a heating roller 47 and a pressure roller 48 that incorporate a heating element. The heating roller 47 and the pressure roller 48 are pressed to form a nip. After passing through this nip, the toner on the paper is melted and heated. As a result, the toner image is fixed on the paper. The sheet after toner fixing is discharged to the discharge tray 36. When using the copy function and the printer function, a series of image forming processes (printing) is performed.

(Hardware configuration of MFP 100)
Next, based on FIG. 2, the hardware configuration of the multifunction peripheral 100 according to the first embodiment of the present invention will be described. FIG. 2 is a block diagram illustrating an example of a hardware configuration of the multifunction peripheral 100 according to the first embodiment of the present invention.

  First, the control unit 5 is provided in the multifunction peripheral 100. The control unit 5 controls the operation of the multifunction device 100. For example, the control unit 5 includes a CPU 51, a storage unit 52, an image processing unit 7, and the like. The control unit 5 controls the main control unit that performs overall control and image processing, and the part that performs image formation processing, and controls, for example, ON / OFF of a motor that rotates various rotating bodies for printing. A plurality of types of engine control units and the like may be provided for each function.

  The CPU 51 is a central processing unit. The CPU 51 controls each unit of the multifunction peripheral 100 based on a control program stored in the storage unit 52 and developed. The image processing unit 7 performs image data read by the image reading unit 2, image data input from the outside, and various types of image processing to be transmitted to the outside. The storage unit 52 is configured by combining nonvolatile and volatile storage devices such as ROM, RAM, and HDD. The storage unit 52 can store various data such as a control program, control data, setting data, and image data of the multifunction peripheral 100.

  The control unit 5 is connected to the operation panel 6, the image reading unit 2, the paper feeding unit 3 a, the conveyance path 3 b, the image forming unit 4 a, the fixing unit 4 b, and the like through signal lines and the like. Control.

  The operation panel 6 is provided, for example, above the front surface of the multifunction machine 100. The operation panel 6 includes a liquid crystal display unit 61 that displays one or a plurality of keys for selecting the state of the multi-function device 100, various messages, functions, and setting. The liquid crystal display unit 61 is provided with a touch panel unit 62. The touch panel unit 62 recognizes the coordinates of the position pressed by the liquid crystal display unit 61. The control unit 5 compares the coordinate recognition by the touch panel unit 62 with the screen and image data displayed on the liquid crystal display unit 61 to recognize the contents of various setting inputs.

  Further, the control unit 5 is connected to a communication unit 8 (corresponding to an image input unit) provided with various connectors, sockets and the like. The communication unit 8 can communicate with a plurality of computers 200 (for example, a personal computer or a server; only one is shown in FIG. 3 for convenience) via a network or the like. Further, the communication unit 8 can communicate with the counterpart FAX apparatus 300 via a public line. For example, the image data obtained by the image reading unit 2 and processed by the image processing unit 7 can be transmitted to the computer 200 or the counterpart FAX apparatus 300 (scan function, FAX function). Also, printing, FAX transmission, and the like can be performed based on image data transmitted from the computer 200 or the partner FAX apparatus 300 (printer function, FAX function).

(Image data processing flow)
Next, an example of the flow of image data processing in the multifunction peripheral 100 according to the first embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram for explaining image data processing in the multi-function peripheral 100 according to the first embodiment of the present invention.

  First, as an image input unit for inputting image data to the multifunction device 100, the multifunction device 100 includes an image reading unit 2 and a communication unit 8.

  For example, the image reading unit 2 is provided with a controller 20 that actually controls reading by the image reading unit 2. For example, an IC or CPU is used for the controller 20. When a copy or scan execution instruction is issued on the operation panel 6, the control unit 5 issues a document reading execution instruction to the controller 20. In response to the reading execution instruction, the controller 20 operates the winding motor M2 to turn on the lamp 23 for irradiating the document.

  The controller 20 operates the image sensor 27. The image sensor 27 is, for example, a line sensor. The image sensor 27 outputs an analog voltage (current) corresponding to the reflected light for each pixel (photoelectric conversion). Then, as shown in FIG. 3, the amplifying unit 28a amplifies the analog voltage (current) of each pixel. The image sensor 27 may be provided with an amplification function.

  Then, the A / D conversion unit 28b performs A / D conversion for each pixel and converts it to digital data. For example, when the original is read in gray scale, the A / D converter 28b quantizes each pixel to 8 bits (256 gradations, which may be 9 bits or more) according to the magnitude of the analog voltage (current). To do. Thereby, a pixel value indicating density (brightness) is given to each pixel. In the following, an example of performing various image processing such as show-through removal processing using grayscale image data will be described.

  The image sensor 27, the amplification unit 28a, and the A / D conversion unit 28b according to the present embodiment may be compatible with color reading. In the case of reading in color, the A / D converter 28b quantizes, for example, each color of R (red), G (green), and B (blue) with 8 bits (24 bits in total). Since image data (gray rail) indicating luminance can be generated from image data of each color of R, G, and B, first, after generating image data of each color of R, G, and B, the image Gray scale image data may be generated by the reading unit 2 or the image processing unit 7.

  The output of the A / D conversion unit 28b is input to the correction unit 28c. The correction unit 28c improves distortion caused by the reading characteristics of the image reading unit 2 (individual differences among pixels of the image sensor 27, variations in the light amount distribution of the lamp 23, and the like). For example, the correction unit 28c performs shading correction, γ correction, and the like. If various corrections are performed by the image processing unit 7, the correction unit 28c may not be provided. The corrected document image data is input to the image processing unit 7, for example. Alternatively, it may be given to the image processing unit 7 after passing through the storage unit 52.

  A communication unit 8 is an input destination of image data to the image processing unit 7. The communication unit 8 receives image data from the computer 200 or the FAX apparatus 300. Then, the communication unit 8 gives the received image data to the image processing unit 7 to perform image processing.

  A storage unit 52 is also an input destination of image data to the image processing unit 7. The storage unit 52 can store image data obtained by reading by the image reading unit 2 and image data received by the communication unit 8. For example, when an operation or instruction to use the stored image data is given to the operation panel 6, the storage unit 52 transmits the image data to the image processing unit 7.

  The image processing unit 7 includes, for example, an ASIC 70 and an image memory 71 that temporarily stores image data before and after image processing. The ASIC 70 is an integrated circuit designed exclusively for image processing. The ASIC 70 can perform various image processing (for example, enlargement, reduction, density conversion, etc.). The image processing unit 7 is provided with a setting memory 72. The setting memory 72 stores various programs and data related to image processing in a nonvolatile manner. The ASIC 70 confirms the stored contents of the setting memory 72 and performs image processing.

  As the show-through removal processing circuit, the target pixel setting unit 73, the variance value calculation unit 74, the show-through pixel setting unit 75, the show-through correction unit 76, the ratio calculation unit 77, and the character recognition unit 78 are included in the image processing unit 7. Is provided. For example, the pixel-of-interest setting unit 73, the variance value calculation unit 74, the show-through pixel setting unit 75, the show-through correction unit 76, the ratio calculation unit 77, and the character recognition unit 78 are configured as hardware (dedicated circuit) as the image processing unit 7. Can be provided. Further, the target pixel setting unit 73, the variance value calculation unit 74, the show-through pixel setting unit 75, the show-through correction unit 76, the ratio calculation unit 77, and the character recognition unit 78 are stored in the ASIC 70, the image memory 71, and the ASIC 70. It may be realized functionally and software by an image processing program.

  Since the image processing apparatus 1 according to the present invention includes the image input unit (the image reading unit 2 or the communication unit 8) and the image processing unit 7 that performs the show-through removal process, the MFP 100 according to the present embodiment includes the image processing device. It can be said that 1 is included. In other words, the image processing apparatus 1 constitutes a part of the multifunction peripheral 100.

  The image data that has been subjected to image processing by the image processing unit 7 is output from the output unit 79. The output destination of the image data includes the exposure device 43, the storage unit 52, and the communication unit 8. For example, image data is output to the exposure device 43 during copying or printing. When storing the image data scanned by the image reading unit 2, the image data is output to the storage unit 52. Further, when transmitting to the computer 200 or the FAX apparatus 300, the image data is output to the communication unit 8. Since the usage modes of the image data are various, the output unit 79 may perform a format conversion process of the image data as necessary.

(Outline of show-through removal processing)
Next, an example of the show-through removal process according to the first embodiment of the present invention will be described with reference to FIG. FIG. 4 is an explanatory diagram showing an outline of the show-through removal process according to the first embodiment of the present invention.

  In recent years, double-sided printing is frequently performed from the viewpoint of effective utilization of paper resources. However, when a document printed on both sides is read, the contents on the back side of the reading surface may also be read. In the image data, the portion where the contents of the back surface appear is a portion called “show-through”. An example of the show-through is shown in the upper diagram of FIG. In FIG. 4, the “AAAAAA” portion (portion surrounded by an ellipse) that appears thinly is a show-through portion.

  Conventionally, there exists image processing for removing show-through. The show-through part often appears slightly darker than the paper color so that it overlaps the paper color of the original. Therefore, for example, the paper color in the image data is determined, and pixels having pixel values close to the determined paper color (for example, paper pixel values ± 5 to 10 for 256 gradations) are set to the same pixel value. A show-through removal process for conversion into (for example, a pixel value of a sheet) is performed.

  However, in such a process, the portion of the reading surface that originally has a low density and is expressed as a halftone dot is not a show-through, but is a processing target. Therefore, for example, a low density (for example, light gray) portion in the document may be removed. For example, in the example of FIG. 4, the show-through removal process may be performed on the background of the figure or the halftone dots of the body portion. However, such image processing is excessive show-through removal processing, and the reproducibility of the document is impaired. Therefore, the image processing apparatus 1 and the multifunction peripheral 100 according to the present embodiment accurately perform the show-through removal process without impairing the low density portion (halftone dot expression) as illustrated in the lower diagram of FIG.

(Back-through removal processing)
Next, details of the show-through removal process according to the first embodiment of the present invention will be described with reference to FIGS. 3 and 5. FIG. 5 is a histogram for explaining the show-through removal process according to the first embodiment of the present invention.

  In order to perform the show-through removal of the present invention, the image processing unit 7 includes a target pixel setting unit 73, a variance value calculation unit 74, a show-through pixel setting unit 75, a show-through correction unit 76, a ratio calculation unit 77, a character recognition unit. 78 etc. are provided (refer FIG. 3).

  First, the pixel-of-interest setting unit 73 sets a pixel (a pixel of interest) to be calculated among pixels included in the image data. For example, as illustrated in FIG. 5, the target pixel setting unit 73 generates a histogram indicating the pixel values and the number of pixels included in the image data. FIG. 5 shows an example of a histogram of image data of 256 gradations (0 to 255) obtained by reading a document with the image reading unit 2, for example.

  Then, the pixel-of-interest setting unit 73 determines, as the pixel of interest, a lighter (brighter) pixel that is equal to or less than a predetermined difference (hereinafter referred to as “predetermined difference Δ”) than the pixel value of the highest density in the histogram. This is because the show-through part often appears thin. The predetermined difference Δ can be arbitrarily determined. Further, for example, a plurality of types of predetermined differences Δ may be provided according to the value of the highest density in the image data, such as increasing the predetermined difference Δ as the maximum density is higher. That is, the pixel-of-interest setting unit 73 selects a pixel having a pixel value equal to or less than a predetermined difference (predetermined difference Δ) from the pixel value indicating the highest density among the pixel values of each pixel included in the image data. It is determined.

  Next, the variance value calculation unit 74 calculates a variance value for each target pixel in a certain range centered on each target pixel. The fixed range is arbitrarily determined. For example, the range can be an odd dot × odd dot range such as 3 × 3, 5 × 5, 7 × 7, 9 × 9, etc. with the target pixel as the center.

The variance value calculation unit 74 obtains a variance value based on the following formula, for example.
(formula)
Dispersion value = 1 / (n−1) × ((X ₁ −Xa) ² + (X ₂ −Xa) ² +... + (X _n −Xa) ² )
Where n = number of pixels in a certain range
Xa = average pixel value of pixels within a certain range
Xn = pixel value of each pixel included in a certain range

  The show-through pixel setting unit 75 performs a process of determining whether or not the target pixel is a show-through portion based on the obtained dispersion value and a predetermined dispersion reference value. The dispersion reference value is stored in a non-volatile manner in the show-through pixel setting unit 75 or the setting memory 72 in the image processing unit 7.

  In the first place, the variance value is a value indicating the extent of data spread and variation. On the other hand, in the portion expressed as a halftone dot, dots are regularly dispersed. Further, a portion expressed as a halftone dot (a portion printed as a halftone dot) has a periodic dot distribution if it has the same density. Therefore, the variance value of the portion printed as a halftone dot on the original is high.

  Therefore, the show-through pixel setting unit 75 compares the dispersion value obtained by the calculation with the dispersion reference value. Then, the show-through pixel setting unit 75 determines the pixel of interest as a show-through pixel if it is equal to or less than the dispersion reference value (if it does not vary so much). On the other hand, the show-through pixel setting unit 75 determines that the pixel of interest is not a show-through pixel if the dispersion reference value is exceeded (if it varies). Note that the dispersion reference value is an arbitrarily determined value, but a suitable value is determined by repeated experiments and the like while taking into account the difference between the models of the image reading unit 2.

  The show-through correction unit 76 performs a show-through removal process on the pixels determined by the show-through pixel setting unit 75 as the show-through pixels. For example, the show-through correction unit 76 generates a histogram of the image data, and determines the pixel value of the lightest (brighter) peak among the peaks in the histogram as the paper color. Then, the show-through correction unit 76 converts the pixel value of the show-through pixel into a pixel value determined as the paper color, and performs a show-through removal process. Alternatively, the show-through correction unit 76 may perform image processing that brightens the pixel value of the show-through pixel by a predetermined value.

(Detailed settings for show-through removal processing)
Next, detailed settings in the show-through removal process according to the first embodiment of the present invention will be described with reference to FIGS. 3, 6, and 7. FIG. 6 is a detailed setting screen 9 of the show-through removal process according to the first embodiment of the present invention. FIGS. 7A to 7C are explanatory diagrams illustrating an example of the form of the show-through removal process according to the first embodiment of the present invention.

  The user can display the detailed setting screen 9 shown in FIG. 6 on the liquid crystal display unit 61 by operating the operation panel 6. On this detail setting screen 9, the details of the show-through removal process can be set.

  For example, as shown in FIG. 6, it is possible to set whether or not to perform the show-through removal process on the show-through pixels existing in the peripheral area in the image data. Regarding this setting item, a Yes key K1 and a No key K2 are provided. For example, the liquid crystal display unit 61 displays the selected key in a black and white reversed state (black background, white characters) (hereinafter the same).

  The show-through removal processing for the show-through pixels in the peripheral area will be described with reference to FIG. As shown in FIG. 7A, the image data is divided into a first region R1 in the central portion and a second region R2 in the peripheral portion. The number of dots wide from the edge of the image data is determined in advance as the second region R2. For example, the setting memory 72 in the image processing unit 7 stores the setting for setting the second region R2 for dots corresponding to a width of several mm to several cm (for example, 2 to 3 cm) from the edge of the image data. The inside of the square shape is the first region R1.

  The second region R2 often corresponds to a margin, and the need to perform the show-through removal process is inferior to the first region R1 at the center. Further, even if the show-through portion of the second region R2 is not removed, there may be no problem in terms of readability. Therefore, when setting is made not to perform the show-through removal process for the second region R2, the image processing unit 7 (the pixel-of-interest setting unit 73, the variance value calculation unit 74, the show-through pixel setting unit 75, and the show-through correction unit 76). Does not perform the process on the second region R2. Thereby, the processing speed can be improved.

  That is, the show-through correction unit 76 performs show-through removal processing on the show-through pixels in the predetermined first region R1 in the image data, and shows-through in the predetermined second region R2. The show-through removal process is not performed on the pixel.

  For example, as shown in FIG. 6, when the ratio of the show-through pixel to the total number of pixels in a certain range (area) is small in the image data, it can be set not to perform the show-through removal process. Accordingly, if there are not so many show-through pixels that are relatively difficult to see, the show-through removal process is skipped.

  Regarding this setting item, a Yes key K3 and a No key K4 are provided. Further, the overall key K5 that is pressed when obtaining the ratio of the show-through pixel with respect to the entire image data, or the ratio of the show-through pixel with respect to each area obtained by dividing and subdividing the image data. There is provided a partial key K6 that is pressed when turning on.

  And as shown in FIG. 3, the ratio calculating part 77 is provided as a part which performs the calculation which calculates | requires a ratio. In accordance with the setting on the operation panel 6, the ratio calculation unit 77 obtains the ratio of the number of show-through pixels to the number of pixels in the area.

  The show-through removal process based on the ratio calculation will be described with reference to FIG. As shown in FIG. 7B, when the partial key K6 is pressed, the ratio calculation unit 77, for example, for each area obtained by dividing the image data into a plurality of areas (FIG. 7B). In this example, the image data is divided into 42 areas), and the ratio of the number of show-through pixels to the total number of pixels in the area is obtained. On the other hand, if the overall key K5 is pressed, the ratio calculation unit 77 obtains the ratio of the number of show-through pixels to the total number of pixels of the image data.

  The show-through correction unit 76 performs the show-through removal process on the entire region or the whole because the show-through has little influence on the visibility when the obtained ratio is equal to or less than a predetermined reference ratio. Absent. In the show-through removal process, there is a possibility that pixels in a portion that is not show-through are erroneously converted. However, according to this setting, if the show-through is small, the show-through removal process is not performed. Thereby, it is possible to prevent the show-through removal process from being performed excessively. Even when the show-through removal process is not performed, the pixel-of-interest setting unit 73, the variance value calculation unit 74, and the show-through pixel setting unit 75 of the image processing unit 7 perform the process.

  That is, the image processing apparatus 1 includes a ratio calculation unit 77 that calculates the ratio of the show-through pixel to the total number of pixels of the image data or the ratio of the show-through pixel to the total number of pixels in the divided area of the image data. The show-through correction unit 76 does not perform the show-through removal process when the ratio of the show-through pixel to the total number of pixels of the image data is equal to or less than a predetermined reference ratio, or a ratio equal to or less than a predetermined reference ratio. The show-through removal process is not performed on the show-through pixel included in the region.

  Further, for example, as shown in FIG. 6, it is possible to set so that the show-through removal process is not performed on the show-through pixel close to the character in the image data. Thereby, it is possible to avoid performing the show-through removal process by mistake on a part of the character. Regarding this setting item, a Yes key K7 and a No key K8 are provided.

  And as shown in FIG. 3, the character recognition part 78 is provided as a part which recognizes the character part RT. For example, the character recognition unit 78 performs image processing for edge enhancement, recognizes the outline of the character by connecting the edge portions, and recognizes the character portion RT in the image data. Alternatively, the character recognition unit 78 may use pattern matching or an existing OCR (Optical Character Recognition) technique. As described above, the character recognition unit 78 recognizes and specifies the region of the character portion RT in the image data.

  The show-through removal process after character recognition is described with reference to FIG. In FIG. 7C, a part of the image data is enlarged. And the character recognition part 78 recognizes each character as it expands and shows in FIG.7 (c). And the character recognition part 78 recognizes the character part RT as shown with a broken line in FIG.7 (c), for example. In this example, an example will be described in which the character recognizing unit 78 recognizes a plurality of characters as a group of character portions RT. However, the region occupied by the characters may be determined for each character.

  Then, the show-through correction unit 76 performs show-through removal only for show-through pixels that are away from the area recognized as a character. For example, in the example of FIG. 7C, the show-through correction unit 76 performs a show-through removal process on the dot-like show-through pixels positioned on the characters “Shin”. On the other hand, the show-through correction unit 76 does not remove the show-through pixel in the “mouth” in the character “Shin”. For example, the show-through correction unit 76 may not remove the show-through pixels in contact with the region. As a result, it may be difficult to determine whether the character part is a part or a show-through part, but it is possible to prevent the show-through removal process from being performed excessively. Even when the show-through removal process is not performed, the pixel-of-interest setting unit 73, the variance value calculation unit 74, and the show-through pixel setting unit 75 of the image processing unit 7 perform the process.

  That is, the image recognition unit 78 that performs processing for recognizing the character part RT of the image data is included, and the show-through correction unit 76 is included in the character part RT of the show-through pixels and / or the character part. The show-through removal process is not performed on the show-through pixel in contact with the RT.

  The various setting contents on the detailed setting screen 9 are stored when the OK key K9 is pressed. For example, the detailed setting in the show-through removal process is stored in the setting memory 72 of the image processing unit 7. Alternatively, the setting content may be stored in the storage unit 52 and the image processing unit 7 may check the data in the storage unit 52.

(Flow of show-through removal process)
Next, an example of the flow of the show-through removal process in the image processing apparatus 1 and the multifunction peripheral 100 according to the first embodiment of the present invention will be described with reference to FIG. FIG. 8 is a flowchart illustrating an example of a show-through removal process in the image processing apparatus 1 and the multifunction peripheral 100 according to the first embodiment of the present invention.

  First, the start is the time when the show-through removal process is to be performed. For example, it is the time when printing, transmission, or accumulation in the storage unit 52 is to be performed based on image data obtained by reading an original that has been duplex printed by the image reading unit 2 or image data received by the communication unit 8. It is possible to set whether or not to perform the show-through removal process on the operation panel 6, and the show-through removal process is performed only when the multifunction peripheral 100 (image processing apparatus 1) is set to the show-through removal processing mode. You may do it.

  First, image data is input to the multifunction peripheral 100 (image processing apparatus 1) (step # 1). Then, the image processing unit 7 confirms settings related to the show-through removal process. For example, the image processing unit 7 reads settings relating to the show-through removal process stored in the setting memory 72 or the storage unit 52. Thereafter, the following processing is performed as necessary according to the setting.

  Then, the target pixel setting unit 73 sets a target pixel among the pixels included in the image data (step # 2). Next, the variance value calculation unit 74 calculates a variance value for each pixel of interest (step # 3). Further, based on each calculated variance value, the show-through pixel setting unit 75 determines whether each pixel of interest is a show-through pixel (step # 4).

  Next, the show-through correction unit 76 performs a show-through removal process on the pixels determined as show-through pixels (step # 5). That is, the image processing apparatus 1 includes an image input unit (image reading unit 2 and communication unit 8) for inputting image data of a document to the apparatus, and a target pixel setting that determines a target pixel among pixels included in the image data. Unit 73, a variance value calculation unit 74 for obtaining a variance value of a region within a certain range including the target pixel determined by the target pixel setting unit 73, and a calculation result of the variance value calculation unit 74 is a predetermined variance reference value A show-through pixel setting unit 75 that determines a pixel of interest as a show-through pixel, and a show-through correction unit 76 that performs a show-through removal process on the show-through pixel determined by the show-through pixel setting unit 75; including. Depending on the setting, the show-through correction unit 76 may not perform the show-through removal process on pixels determined to be show-through pixels.

  Then, the image processing unit 7 (the output unit 79 thereof) outputs the image data (step # 6). This completes the show-through removal processing for one page of image data (end). When a new show-through removal process is performed on the image data, the process is executed again from step # 1.

  In this way, according to the image processing apparatus 1 of the present embodiment, the show-through pixel setting unit 75 sets the target pixel behind when the calculation result of the variance value calculation unit 74 is equal to or less than a predetermined variance reference value. The show-through pixel is determined, and the show-through removal processing is performed on the show-through pixel determined by the show-through pixel setting unit 75. Thereby, a place where the variance value is small is determined as a show-through pixel (show-through portion). Therefore, the show-through removal process can be performed by paying attention to the dispersion value, and the show-through removal can be appropriately performed. In addition, because of the low density, it is possible to prevent the show-through removal processing for the portion expressed as a halftone dot in the original and leave it as a halftone dot.

  In addition, the show-through portion often appears as a density slightly higher than the density of the paper. Therefore, the pixel-of-interest setting unit 73 determines that the pixel value of each pixel included in the image data is higher than the pixel value indicating the highest density. A pixel having a pixel value equal to or smaller than a predetermined difference is determined as a target pixel. Thereby, the show-through portion can be surely included in the target pixel. In addition, to a certain extent, pixels with high density can be removed from the target pixel, the number of target pixels can be reduced, and the processing speed can be increased.

  Further, in the show-through removal process, there is a possibility that the process (pixels) other than the show-through part may be performed. However, the show-through correction unit 76 performs the show-through based on the ratio calculated by the ratio calculation unit 77. Determines whether or not the removal process can be executed. As a result, if the calculated ratio is less than the reference ratio and the show-through portion is narrow and does not affect the reproducibility and visibility of the document, the show-through removal process may not be performed. it can. Note that the “reference ratio” can be arbitrarily determined, but can be determined based on whether the reproducibility of the document and the visibility are not affected.

  In addition, the show-through correction unit 76 performs show-through removal processing on the show-through pixels in the predetermined first region R1 in the image data, and shows-through in the predetermined second region R2. The show-through removal process is not performed on the pixel. As a result, the show-through removal process can be performed only on pixels included in a predetermined area of the image data. In addition, although it can determine arbitrarily which part is made into 1st area | region R1 and 2nd area | region R2 among image data, you may determine from a viewpoint of the necessity of a show-through removal. For example, a square region having a constant width from the edge of the image data may be the second region R2 (for example, a blank portion), and the inside of the second region R2 may be the first region R1. As a result, the show-through portion in the central portion that is conspicuous is removed, and the show-through removal process does not have to be performed on the show-through portion in the peripheral portion that has a weak influence on the reproducibility and visibility of the document.

  If the character portion RT is close, the portion (pixel) recognized as show-through may be part of the character. Therefore, the show-through correction unit 76 does not perform the show-through removal process on the show-through pixels included in the character portion RT and / or in contact with the character portion RT among the show-through pixels. Thereby, it is possible to prevent the character portion RT from being corrected and removed by mistake due to the show-through removal processing. Further, the image forming apparatus (for example, the multifunction peripheral 100) can appropriately remove the show-through portion from the image data by paying attention to the dispersion value.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 9 is a histogram for explaining the show-through removal process according to the second embodiment of the present invention.

  In the first embodiment, the example in which a pixel having a pixel value equal to or smaller than the predetermined difference Δ with respect to the highest density of the image data is set as the target pixel has been described. The second embodiment is different in that a pixel having a pixel value in a predetermined range (hereinafter referred to as a predetermined range W) with a pixel value having the highest appearance frequency as a reference is determined as a target pixel.

  The second embodiment is different from the first embodiment in how to determine the target pixel. However, the multifunction peripheral 100 and the image processing apparatus 1 according to the second embodiment may be the same as those according to the first embodiment in terms of hardware configuration, processing in the image processing unit 7, and the like. Therefore, in the second embodiment, descriptions and illustrations of portions common to the first embodiment are omitted unless specifically described.

  Also in the present embodiment, the pixel-of-interest setting unit 73 sets a pixel (a pixel of interest) that is a calculation target among pixels included in the image data. For example, as illustrated in FIG. 9, the target pixel setting unit 73 generates a histogram indicating the pixel values and the number of pixels included in the image data. FIG. 9 shows an example of a histogram of image data of 256 gradations obtained by reading a document with the image reading unit 2, for example.

  In the image data, the paper color of the document often appears as the base color (background color) with the highest frequency (particularly a character document). In such a manuscript, the show-through portion tends to appear in a form that is thinly applied to the paper color of the manuscript.

  Therefore, in the present embodiment, the pixel-of-interest setting unit 73 determines a pixel value that appears again as a paper color, and determines a pixel of interest based on the pixel value that appears again. Specifically, as illustrated in FIG. 9, the target pixel setting unit 73 determines a pixel in a predetermined range W as a target pixel with reference to a pixel value that appears frequently. As a result, the show-through portion can be reliably included in the target pixel.

  That is, the pixel-of-interest setting unit 73 determines a pixel having a pixel value within a predetermined range W with the pixel value having the highest appearance frequency as the reference among the pixel values of each pixel included in the image data.

  In this way, the show-through portion often appears as a density slightly higher than the density of the paper. According to the invention of this embodiment, the pixel-of-interest setting unit 73 sets the pixel value of each pixel included in the image data. Among them, a pixel having a pixel value within a predetermined range W with a pixel value having the highest appearance frequency as a reference is determined as a target pixel. This makes it possible to reliably include the show-through portion in the target pixel while recognizing the pixel value having the highest appearance frequency as the paper density. In addition, pixels that have a certain density difference from the paper can be removed from the target pixel, and the number of target pixels can be reduced to increase the processing speed.

  Although the embodiment of the present invention has been described, the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

  The present invention is applicable to an image processing apparatus 1 having an image input unit such as the image reading unit 2 and an image processing unit 7 and an image forming apparatus.

DESCRIPTION OF SYMBOLS 1 Image processing apparatus 2 Image reading part (image input part)
7 Image processing unit 73 Pixel of interest setting unit 74 Variance calculation unit 75 Back-through pixel setting unit 76 Back-through correction unit 77 Ratio calculation unit 78 Character recognition unit 8 Communication unit (image input unit)
100 MFP (image forming apparatus) Δ predetermined difference W predetermined range

Claims (7)

An image input unit for inputting image data of a document to the apparatus;
Of the pixels included in the image data, a target pixel setting unit that determines a target pixel;
A dispersion value calculation unit for obtaining a dispersion value of a region in a certain range including the target pixel determined by the target pixel setting unit;
When the calculation result of the variance value calculation unit is equal to or less than a predetermined variance reference value, a show-through pixel setting unit that determines a target pixel as a show-through pixel;
An image processing apparatus, comprising: a show-through correction unit that performs a show-through removal process on the show-through pixels.   The pixel-of-interest setting unit determines, as a pixel of interest, a pixel having a pixel value equal to or less than a predetermined difference from a pixel value indicating the highest density among pixel values of each pixel included in image data. The image processing apparatus according to claim 1.   The pixel-of-interest setting unit determines a pixel having a pixel value within a predetermined range based on a pixel value having the highest appearance frequency among pixel values of each pixel included in image data as the pixel of interest. Item 6. The image processing apparatus according to Item 1. The ratio of the show-through pixel with respect to the number of pixels of the entire image data, or a ratio calculation unit for obtaining the ratio of the show-through pixel with respect to the total number of pixels in the area into which the image data is divided
The show-through correction unit does not perform a show-through removal process when the ratio of the show-through pixel to the number of pixels of the entire image data is equal to or less than a predetermined reference ratio, or is equal to or less than a predetermined reference ratio. The image processing apparatus according to claim 1, wherein the show-through removal process is not performed on the show-through pixels included in the ratio area.   The show-through correction unit performs a show-through removal process on the show-through pixels in the predetermined first area of the image data, and the show-through pixels in the predetermined second area. The image processing apparatus according to claim 1, wherein the show-through removal process is not performed on the image processing apparatus. A character recognition unit that performs processing for recognizing a character part of image data;
The show-through correction unit does not perform a show-through removal process on the show-through pixels included in the character part and / or in contact with the character part among the show-through pixels. Item 6. The image processing apparatus according to any one of Items 1 to 5.   An image forming apparatus comprising the image processing apparatus according to claim 1.