JP2012124711A - Image processor, image forming apparatus, control method of image processor, and control program of image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processor capable of executing screen processing in order to improve readability while holding more information of input images.SOLUTION: A control part of the image processor executes screen processing for the input image read by an original read part. The control part reads the input image and detects a character region and a background region (S100, S101). The control part calculates edge intensity for pixels in the character region and executes edge determination (S102, S103). When the edge is not determined for a target pixel at the boundary part of the character region and the background region (S104:YES, S105:NO), the control part extends an outer edge region (S107), and replaces image data in the extended region (S108). Thus, the character region and the background region are separated and the readability of output images is improved. When the edge is determined for the target pixel at the boundary part (S105:YES), edge emphasis processing is executed (S106).

Description

  The present invention relates to an image processing apparatus, an image forming apparatus, an image processing apparatus control method, and an image processing apparatus control program, and more particularly to an image processing apparatus that performs screen processing on image data, an image forming apparatus, and an image processing apparatus control. The present invention relates to a method and a control program for an image processing apparatus.

  Image processing performed in an image forming apparatus (MFP (Multi Function Peripheral), facsimile apparatus, copying machine, printer, etc.) having a scanner function, a facsimile function, a copying function, a printer function, a data communication function, and a server function In particular, there are error diffusion suitable for resolution reproduction and screen processing with excellent graininess. For example, in an image processing apparatus that performs screen processing provided in an image forming apparatus, after performing rasterization processing that generates image data for each page, image processing for image formation is performed by performing screen processing on the image data. Is generated.

  Patent Document 1 below discloses an image processing apparatus that performs a process of separating a character area and a background area among character area candidates. In this image processing apparatus, an edge of an input image is extracted, and a character area and a natural image area of a background are separated from a rough character area extracted by binarization by deleting pixels around the extracted edge. Processing is performed.

  In Patent Document 2 below, image processing is performed in which edge enhancement processing is performed on the background region and the non-character edge region, and processing is performed on the non-background region and the non-character edge region with an average value of the surrounding region existing therearound. An apparatus is disclosed. These processes are carried out for the purpose of preventing white borders from being formed around the characters and color turbidity from occurring.

JP-A-6-334857 JP 2003-018409 A

  By the way, in the image processing apparatus as described above, when screen processing of image data is performed, the screen line number and the resolution are in a trade-off relationship. That is, for example, in order to maintain a high resolution in a continuous tone region, it is necessary to keep the number of screen lines below a certain level. However, when image data including characters is printed on the screen, if the screen processing is performed with the same number of screen lines in the continuous tone area and the character area, the reproducibility of the image is reduced in a small-point character portion or the like. There are things to do.

  As a solution to the above problem, when screen processing is performed on an image including a character region and a background region surrounding the character region, the character region may be screened by a high-frequency screen dedicated to the character region. Conceivable. Thereby, the reproducibility of the character area is maintained. In this case, when screen processing is performed on an image including a character area and a background area around the character area, the edge of the character area that is a boundary with the background area is determined, and the inner edge of the character area is filled. Processing (solid processing, FEET processing) is performed. Thereby, a character area can be reproduced more sharply.

  However, the above solution has another problem. That is, for example, when there is a character on a colored background region, and the brightness difference (density difference) between the character region and the surrounding (background) region is small, the inner edge of the character region cannot be determined. For this reason, the process of filling the edge cannot be performed, and a pattern (texture) may occur at the boundary between the screen of the character area and the screen of the base area.

  Even if the inner edge is detected and the filling process is performed, or the filling process is performed using the detected character attribute, a satisfactory processing result cannot be obtained. In other words, when performing the filling process, fine gradation reproduction cannot be originally expected, but there is no choice but to paint more deeply than the desired density. For this reason, when the brightness difference between the character area and the background area is small, the outline of the part becomes very conspicuous and poor in appearance by performing the painting process.

  FIG. 19 is a first diagram illustrating an example of conventional screen processing.

  In FIG. 19, of the two upper and lower images, the upper part shows the input image 500, and the lower part shows the output image 510 output as a result of the conventional screen processing. Referring to the figure, an input image 500 is assumed in which a character area 502 is arranged on a colored background area 501 in a color different from that of the background area 501. Here, the color of the background area 501 is brown, and the color of the character area 502 is a khaki color brighter than the background. The input image 500 has a small brightness difference between the background area 501 and the character area 502.

  When screen processing is performed on such an input image, an output image 510 including a base area 511 and a character area 512 is obtained. The background area 511 has brightness corresponding to the background area 501. The character area 512 has brightness corresponding to the character area 502. Since an edge is not determined at the boundary portion between the character region 512 and the background region 511, a process of filling in this portion is not performed. Therefore, in the output image 510, texture noise with the background region 511 is conspicuous in the outline portion of the character region 512.

  FIG. 20 is a second diagram for explaining another example of the conventional screen processing.

  In FIG. 20, among the two upper and lower images, the upper part shows the input image 600, and the lower part shows the output image 610 output as a result of the conventional screen processing. Referring to the figure, an input image is assumed in which a character area 602 is arranged on a colored background area 601 in a color different from that of the background area 601. Here, the color of the background area 601 is gray, and the color of the character area 602 is slightly lighter gray than the background area 601. The input image 600 has a small brightness difference between the background area 601 and the character area 602.

  When screen processing is performed on such an input image 500, an output image 610 including a base area 611 and a character area 612 is obtained. The background area 611 has brightness corresponding to the background area 601. The character area 612 has brightness corresponding to the character area 602. Since an edge is not determined at the boundary portion between the character region 612 and the background region 611, the process of filling in this portion is not performed. In this case, since there is almost no difference in brightness between the background area 611 and the character area 612, it is difficult to distinguish the background area 611 from the outline portion of the character area 612 in the output image 610, and it is difficult to read the characters indicated by the character area 611. End up.

  Regarding the above problem, in the image processing apparatus described in Patent Document 1, when an input image is processed, a character region is separated from the background by deleting pixels around the extracted edge. However, since the peripheral pixels are similarly deleted regardless of whether the edge strength is high or low, there is a problem that the information of the input image is always lost to some extent.

  Regarding the above problem, the image processing apparatus described in Patent Document 2 improves the readability of characters by performing a process of replacing the outer edge region of the character region. However, this image processing apparatus cannot solve the problems that occur when the brightness difference between the background and the character is small, such as noise due to screen interference and the inability to identify the boundary between the character and the background.

  The present invention has been made to solve such problems, and an image processing apparatus, an image forming apparatus, and an image processing apparatus capable of executing screen processing so as to improve readability while retaining more information of an input image. It is an object of the present invention to provide an image processing apparatus control method and an image processing apparatus control program.

  In order to achieve the above object, according to one aspect of the present invention, an image processing apparatus that performs screen processing and outputs a screen image printed in an image forming apparatus is read by an input image and read by the reading means Based on the boundary detection means for detecting the boundary between the character area and the background area other than the character area, the strength calculation means for calculating the edge strength of the character area, and the edge strength calculated by the strength calculation means. First edge determination means for determining the outer edge area on the background area side of the boundary between the character area and the background area, and based on the detection result by the boundary detection means and the determination result of the first edge determination means An expansion means for extending the area to the base area, a replacement means for replacing the image data of the outer edge area expanded by the expansion means with replacement data, and an input Evaluation means for evaluating whether or not a condition relating to the characteristics of the boundary portion between the character area and the background area in the image is satisfied, the expansion means expands based on the evaluation result by the evaluation means, and the replacement means Perform replacement.

  Preferably, the image processing apparatus further includes a second edge determination unit that performs edge determination based on the edge strength calculated by the strength calculation unit, and the evaluation unit performs the second edge determination on the contour pixel of the character region. It is evaluated whether or not the edge determination is performed by the means, and when it is evaluated that the edge determination is not performed by the evaluation means, the expansion means performs expansion and the replacement means performs replacement.

  Preferably, the image processing apparatus further includes an enhancement processing unit that performs an enhancement process for enhancing the edge determined by the second edge determination unit, and when the evaluation unit evaluates that the edge determination is performed, the enhancement processing unit Perform enhancement processing.

  Preferably, the image processing apparatus further includes a filling unit that performs a filling process of the region to be processed, and the filling unit applies the contour pixel of the character region when the edge strength calculated by the strength calculating unit is higher than a predetermined strength. The fill process is performed on the image.

  Preferably, the expansion unit determines an expansion size according to the edge strength calculated by the strength calculation unit, and performs expansion according to the determined expansion size.

  Preferably, the replacement unit generates replacement data according to the edge strength calculated by the strength calculation unit, and performs replacement with the generated replacement data.

  Preferably, the image processing apparatus further includes a brightness calculation unit that calculates the brightness of each pixel of the input image read by the reading unit, and the evaluation unit includes the contour pixel of the character region calculated by the brightness calculation unit and the contour pixel thereof. Whether or not the brightness difference with a pixel in the background region adjacent to the predetermined value is equal to or smaller than a predetermined value, and when the evaluation means evaluates that the brightness difference is equal to or smaller than the predetermined value, the expanding means expands and replaces Performs the replacement.

  Preferably, the extension means determines an extension size according to the brightness of the pixel in the background area adjacent to the contour pixel of the character area calculated by the brightness calculation means, and performs extension according to the determined extension size.

  Preferably, the replacement means generates replacement data according to the lightness of the pixel in the background area adjacent to the contour pixel of the character area calculated by the lightness calculation means, and performs replacement with the generated replacement data.

  Preferably, the image processing apparatus further includes lightness calculation means for calculating the lightness of each pixel of the input image read by the read means, and the expansion means includes the lightness and the contour of the contour pixel of the character area calculated by the lightness calculation means. The expansion size is determined according to the brightness of the pixel in the background area adjacent to the pixel, and the expansion is performed according to the determined expansion size.

  Preferably, the image processing apparatus further includes lightness calculation means for calculating the lightness of each pixel of the input image read by the reading means, and the replacement means includes the lightness and the contour of the contour pixel of the character area calculated by the lightness calculation means. Replacement data is generated according to the brightness of the pixel in the background area adjacent to the pixel, and replacement is performed with the generated replacement data.

  Preferably, the first edge determination unit determines an inner edge region on the character region side of the boundary between the character region and the background region based on the edge strength calculated by the strength calculation unit, and the image processing apparatus includes the strength calculation unit. Processing for determining the image data of the inner edge region and the image data of the contour region of the character region based on the calculation result of, the detection result of the boundary detection unit, and the determination result of the inner edge region by the first edge determination unit A boundary processing unit is further provided.

  According to another aspect of the present invention, an image forming apparatus includes any of the image processing apparatuses described above and an image forming unit that forms a screen image based on image data processed by the image processing apparatus.

  According to still another aspect of the present invention, a method for controlling an image processing apparatus that performs screen processing and outputs a screen image printed in an image forming apparatus includes a reading step of reading an input image, and an input read by the reading step Based on the boundary detection step for detecting the boundary between the character region and the background region other than the character region existing in the image, the strength calculation step for calculating the edge strength of the character region, and the edge strength calculated by the strength calculation step An edge determination step for determining the outer edge region on the background region side of the boundary between the character region and the background region, and the outer edge region is extended to the background region based on the detection result of the boundary detection step and the determination result of the edge determination step. The expansion step and the image data of the outer edge area expanded by the expansion step are placed in the replacement data. A replacement step, and an evaluation step for evaluating whether or not a condition related to the feature of the boundary portion between the character region and the background region in the input image is satisfied. The expansion step is expanded based on the evaluation result of the evaluation step. And the replacement step performs the replacement.

  According to still another aspect of the present invention, a control program of an image processing apparatus that performs screen processing and outputs a screen image printed in an image forming apparatus includes a reading step for reading an input image, and an input read by the reading step Based on the boundary detection step for detecting the boundary between the character region and the background region other than the character region existing in the image, the strength calculation step for calculating the edge strength of the character region, and the edge strength calculated by the strength calculation step An edge determination step for determining the outer edge region on the background region side of the boundary between the character region and the background region, and the outer edge region is extended to the background region based on the detection result of the boundary detection step and the determination result of the edge determination step. The expansion step and the image data of the outer edge area expanded by the expansion step are replaced with the replacement data. Based on the evaluation result of the evaluation step, the computer executing a replacement step for replacing the input image and an evaluation step for evaluating whether or not a condition relating to the characteristics of the boundary portion between the character region and the background region in the input image is satisfied. The expansion step performs the expansion, and the replacement step performs the replacement.

  According to these inventions, the outer edge region is expanded to the background region based on the evaluation result as to whether or not the condition regarding the characteristics of the boundary portion between the character region and the background region in the input image is satisfied, and the outer edge is expanded by the replacement unit. The image data of the area is replaced. Therefore, an image processing apparatus, an image forming apparatus, an image processing apparatus control method, and an image processing apparatus control program capable of executing screen processing so as to improve readability while retaining more information of an input image are provided. be able to.

1 is a side view showing an image forming apparatus including an image processing apparatus according to a first embodiment of the present invention. It is a block diagram which shows the structure of a control part. It is a flowchart which shows operation | movement of the control part when performing a screen process. It is a figure which shows the 1st example of the relationship between the input image in this Embodiment, and the output image after a screen process. It is a figure which shows the 2nd example of the relationship between the input image in this Embodiment, and the output image after a screen process. It is a figure which shows an example of the relationship between the input image and the edge strength of an input image. It is a graph which shows the relationship between the edge intensity | strength and outer edge expansion amount in a 1st modification. It is a figure which shows the output image in the 1st modification. It is a graph which shows the relationship between the edge strength in the 2nd modification, and the gradation of replacement data. It is a figure which shows the output image in the 2nd modification. It is a figure which shows the 1st example of the relationship between the input image in 2nd Embodiment, and the output image after a screen process. It is a figure which shows the 2nd example of the relationship between the input image in 2nd Embodiment, and the output image after a screen process. It is a figure which shows an example of the relationship between the input image in the 3rd Embodiment, and the lightness and brightness | luminance conversion value of an input image. It is a graph which shows the relationship between the lightness of a base area | region and the lightness of a character area | region, and an outer edge expansion amount in 3rd Embodiment. It is a figure which shows an example of the output image in 3rd Embodiment. It is a graph which shows the relationship between the lightness of a base area | region and the lightness of a character area | region, and the gradation of replacement data in 4th Embodiment. It is a 1st figure explaining an example of the output image after a screen process. It is a 2nd figure explaining another example of the output image after a screen process. It is a 1st figure explaining an example of the conventional screen processing. It is a 2nd figure explaining another example of the conventional screen processing.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described.

  The image forming apparatus is an MFP (Multi Function Peripheral) having a scanner function, a copying function, a printer function, a facsimile function, a data communication function, and a server function. The scanner function is a function for reading an image of a set original and storing it in an HDD (Hard Disk Drive) or the like. The copying function is a function of printing (printing) it on paper or the like. The function as a printer is a function for printing on a sheet based on an instruction received from an external terminal such as a PC. The facsimile function is a function for receiving facsimile data from an external facsimile machine or the like and storing it in an HDD or the like. The data communication function is a function for transmitting / receiving data to / from a connected external device. The server function is a function that allows a plurality of users to share data stored in the HDD or the like.

  The image forming apparatus can form an image based on drawing data described in, for example, PDL (Page Description Language). The drawing data is interpreted by a data conversion processing unit (PDL interpreter), converted into generated image data for each page, and output to the print engine. The PDL interpreter includes a language analysis unit that interprets drawing data described in PDL and converts it into intermediate data, and a rasterization unit that converts intermediate data into frames. The frame is output to the printer engine after screen processing.

  When the image forming apparatus performs screen processing on image data and prints it, depending on the edge strength and the brightness information of the character part and the surrounding part, such as when the lightness difference between the character part and the surrounding (background) part is within a certain range, etc. Thus, a replacement area and replacement data are determined, and gradations of pixels around the character portion are replaced. Thereby, separation processing can be performed according to the edge strength or the like for the edge portion where the edge cannot be determined. For example, the separation process is performed only for a portion where the brightness difference is small. Since the separation process is performed, it is possible to improve the readability of the character portion of the document while maintaining the document information as much as possible. Even when the brightness difference between the background and the character portion is small, the occurrence of texture can be prevented, and the discrimination between the boundary portion between the character and the background can be improved.

  [First Embodiment]

  FIG. 1 is a side view showing an image forming apparatus including an image processing apparatus according to the first embodiment of the present invention.

  Referring to FIG. 1, an image forming apparatus 1 includes an automatic document feeder 10, a document reading unit (an example of a reading unit) 20, an image forming unit 30, an automatic duplex unit 40, a paper feeding unit 50, A paper feed cabinet 60, an operation panel 70, a facsimile unit 90, a communication interface (I / F) unit 91, a control unit (an example of an image processing apparatus) 100, and an HDD (Hard Disk Drive) 120 are provided. Yes.

  The document reading unit 20 is disposed on the upper part of the image forming apparatus 1. A platen glass (not shown) is disposed on the upper surface of the document reading unit 20. The document reading unit 20 has a reading sensor (not shown) disposed below the platen glass.

  The automatic document feeder 10 conveys a plurality of documents set on the document feed tray 12 to the document reading unit 20 one by one. The automatic document feeder 10 conveys each document to a predetermined document reading position set on the platen glass. When the document image is read by the reading sensor of the document reading unit 20, the automatic document feeder 10 discharges the document onto the document discharge tray 13.

  The automatic document feeder 10 includes a document set sensor 11. The document set sensor 11 is composed of, for example, a known tact switch. Document set sensor 11 detects whether or not a document is set on document feed tray 12 and transmits a detection signal to control unit 100.

  The document reading unit 20 scans a document image with a reading sensor in accordance with the size of the document conveyed to the document reading position. The reading sensor converts incident light from the document into an electrical signal. The document reading unit 20 transmits the image read by the reading sensor to the control unit 100 as image data.

  The document reading unit 20 includes a device lifting sensor 21. The device lifting sensor 21 is composed of, for example, a known magnetic sensor. The apparatus lifting sensor 21 detects whether or not the automatic document feeder 10 is lifted with respect to the document reading unit 20 and transmits a detection signal to the control unit 100.

  The operation panel 70 includes a touch panel input unit 71 and a key input unit 72. The operation panel 70 can accept a user's operation input through, for example, a known user interface. The operation panel 70 displays operation screens corresponding to various operation situations on the touch panel input unit 71 and accepts a user's touch operation. The key input unit 72 includes, for example, a key arranged so as to be pressed and a switch that is turned on / off in response to the pressing of the key, and receives a pressing operation of the user. The control unit 100 controls the operation of the image forming apparatus 1 according to the operation input received by the operation panel 70.

  The operation panel 70 is provided with a sub power switch 80. The sub power switch 80 is a switch operated by the user. When the sub power switch 80 is operated, the operation mode of the image forming apparatus 1 shifts from a normal operation mode in which an image forming operation or the like is performed to a sleep mode. Here, the sleep mode is a power saving operation mode in which only a limited part is driven as compared with the normal operation mode. The user can directly instruct the image forming apparatus 1 to shift to the sleep mode via the sub power switch 80.

  The control unit 100 includes a CPU 101 (shown in FIG. 2) described later, and controls the operation of the image forming apparatus 1 by executing various control programs. When the image data transmitted from the document reading unit 20 is input, the control unit 100 performs various data processing on the image data. As the data processing, for example, shading correction processing or the like is performed. The control unit 100 reads the data after the data processing and outputs a signal used for an image forming operation (for example, a signal for driving an exposure laser diode described later). Data reading is performed for each main scanning line in synchronization with the paper supply.

  The facsimile unit 90 is an interface for transmitting and receiving image data via a public telephone line. The image forming apparatus 1 is connected to a public telephone line via a facsimile unit 90.

  The communication I / F (interface) unit 91 is an interface for connecting to, for example, an external network (such as a local area network (LAN)) to which a personal computer or the like is connected. The communication I / F unit 91 may be configured to be connectable to an external network or an external device based on another communication standard such as a USB (Universal Serial Bus) standard.

  The HDD 120 stores image data sent from the control unit 100. Note that the image forming apparatus may have another type of storage device such as an SSD (Solid State Drive) instead of the HDD 120.

  The image forming unit 30 forms an image by a so-called electrophotographic method. The image forming unit 30 can form a color image. The image forming unit 30 includes photosensitive drums 31a, 31b, 31c, and 31d (these may be referred to as photosensitive drums 31) and exposure scanning units 32a, 32b, 32c, and 32d (representing them). An exposure scanning unit 32), a transfer belt 33, a fixing device (not shown), a front door cover (not shown) for protecting these units, and a front door sensor 34. . The photosensitive drums 31a, 31b, 31c, and 31d and the exposure scanning units 32a, 32b, 32c, and 32d correspond to yellow, magenta, cyan, and black, respectively.

  The image forming unit 30 performs the image forming operation as follows based on the control of the control unit 100. That is, the exposure scanning unit 32 generates laser light based on the drive signal output from the control unit 100. The exposure scanning unit 32 performs exposure scanning of the generated laser light on the photosensitive drum 31. The latent image formed on the photosensitive drum 31 is developed using each color toner. The developed toner images of respective colors are transferred onto the transfer belt 33 in an overlapping manner. When all the toner images of the respective colors are superimposed on the transfer belt 33, the toner images are transferred from the transfer belt 33 onto a sheet conveyed from the paper feeding unit 50. The transferred toner image is fixed on a sheet through a fixing process by a fixing device (not shown), and an image is formed on the sheet. The formed image is discharged outside the image forming apparatus 1.

  The front door sensor 34 includes a tact switch or the like. The front door sensor 34 detects whether or not the front door cover is opened, and transmits a detection signal to the control unit 100.

  The paper feed unit 50 includes paper feed cassettes 51 and 53 and pickup rollers 52 and 54. The paper feed cabinet 60 includes paper feed cassettes 61 and 63 and pickup rollers 62 and 64. In the paper feed cassettes 51, 53, 61, and 63, paper on which images are formed is stored. The pickup rollers 52, 54, 62, and 64 are provided so as to correspond to the paper feed cassettes 51, 53, 61, and 63, respectively. The pickup rollers 52, 54, 62, and 64 are rollers that feed out the paper stored in the paper feed cassettes 51, 53, 61, and 63. The paper feed unit 50 conveys (supplements) paper to the image forming unit 30 during an image forming operation. The paper feed cabinet 60 conveys (supplements) paper to the image forming unit 30 via the paper feed unit 50 during an image forming operation.

  The automatic duplex unit 40 is used when images are formed on both sides of a sheet (during duplex printing). The automatic duplex unit 40 is provided, for example, on the side of the image forming apparatus 1. The automatic duplex unit 40 has a paper inversion path. The reversing path is a path connecting a position where the sheet on which the image is formed is transported and a position where the sheet before the toner image is transferred is transported among the sheet transport paths inside the image forming apparatus 1. is there. During double-sided printing, the sheet on which an image is formed on one side via the fixing device is switched back on the sheet passing path before being completely discharged from the image forming apparatus 1. The switched-back paper is introduced into the automatic duplex unit 40. The automatic duplex unit 40 conveys the sheet on the reverse path, and sends the sheet to a position on the sheet conveyance path before the toner image is transferred. The sheet thus reversed is conveyed again to the image forming unit 30. Thereby, image formation is performed on the surface of the sheet on which the image is not formed. The paper on which images are formed on both sides is discharged from the image forming apparatus 1.

  FIG. 2 is a block diagram illustrating a configuration of the control unit 100.

  Referring to the figure, the control unit 100 includes a CPU 101, a ROM 102, and a RAM 103.

  The CPU 101 is connected to each unit of the control unit 100 and the HDD 120 via a system bus or the like, and can communicate with each unit of the control unit 100 and the HDD 120. Further, the CPU 101 can communicate with the document reading unit 20, the operation panel 70, the communication I / F unit 91, the image forming unit 30, and the like.

  In addition to the image data, the HDD 120 stores setting information of the image forming apparatus 1, a control program 120a for performing various operations of the image forming apparatus 1, and the like. The HDD 120 can store a plurality of jobs transmitted from one client PC or a plurality of client PCs.

  The ROM 102 is, for example, a flash ROM (Flash Memory). The ROM 102 stores data used for operating the image forming apparatus 1. Like the HDD 120, the ROM 102 may store various control programs, function setting data of the image forming apparatus 1, and the like. The CPU 101 reads data from the ROM 102 and writes data to the ROM 102 by performing predetermined processing. The ROM 102 may be non-rewritable.

  A RAM 103 is a main memory of the CPU 101. The RAM 103 is used to store data necessary when the CPU 101 executes the control program 120a.

  The CPU 101 controls various operations of the image forming apparatus 1 by executing a control program 120a stored in the ROM 102, the RAM 103, the HDD 120, or the like. When an operation signal is sent from the operation panel 70 or an operation command is sent from an external personal computer or the like, the CPU 101 executes a predetermined control program 120a in response thereto. Thereby, a predetermined function of the image forming apparatus 1 is executed in accordance with the operation of the operation panel 70 by the user.

  The control unit 100 further includes a pixel attribute detection unit 104, a boundary detection unit (attribute boundary detection unit) 105, a brightness calculation unit (pixel brightness calculation unit) 106, an intensity calculation unit (edge intensity detection unit) 107, an edge determination unit ( An example of a first edge determination unit; an example of a second edge determination unit 108, an expansion unit (specific area expansion unit) 109, an enhancement processing unit (an example of a painting unit; an edge enhancement unit) 110, a replacement unit (image floor) A tone replacement unit) 111 and a screen conversion unit 112.

  The CPU 101 controls the pixel attribute detection unit 104, the boundary detection unit 105, the lightness calculation unit 106, the intensity calculation unit 107, the edge determination unit 108, the expansion unit 109, the enhancement processing unit 110, the replacement unit 111, the screen conversion unit 112, and the like. I do. Thereby, the control unit 100 operates as an image processing apparatus. As the image processing, the control unit 100 can perform screen processing on the image data as follows. That is, the control unit 100 outputs a screen image printed by the image forming unit 30. The image forming unit 30 forms an image on a sheet based on the screen image under the control of the CPU 101.

  The CPU 101 reads, for example, image data of a document read by the document reading unit 20 as an input image.

  The image attribute detection unit 104 determines a character area and a background area (image area or the like) other than the character area for the input image. The document attribute detection unit 104 assigns whether each pixel of the input image is a character area pixel or a background area pixel.

  The boundary detection unit 105 detects a boundary between the character region determined by the image attribute detection unit 104 and a base region other than the character region for the input image. That is, the boundary detection unit 105 detects a boundary between a character area and a base area other than the character area that exists in the input image.

  The lightness calculation unit 106 calculates the lightness or luminance (hereinafter sometimes simply referred to as lightness) of each pixel of the input image. The brightness is calculated by performing YCrCb conversion or Lab conversion on the RGB image data of each pixel of the input image.

  The intensity calculator 107 calculates the edge intensity at each pixel of the input image. The calculation of the edge strength is performed by, for example, a primary differential filter calculation and a secondary differential filter calculation.

  The edge determination unit 108 performs edge determination for each pixel based on the edge strength calculated by the strength calculation unit 107. That is, the edge determination unit 108 determines that each pixel is an edge (a pixel that is an edge) when the edge intensity exceeds a certain threshold value.

  Here, the edge determination unit 108 determines the inner edge region and the outer edge region of the character region based on the edge strength. The outer edge region of the character region is a region formed of pixels that form the outside of the outline of the character region. In other words, a pixel (outer edge) in the outer edge region is a pixel with a character boundary background attribute (a pixel on the background region side of the boundary between the character region and the background region). The inner edge area of the character area is an area composed of pixels that form the inside of the outline of the character area. In other words, the pixel (inner edge) in the inner edge region is a pixel having a background boundary character attribute (a pixel on the character region side at the boundary between the character region and the background region). The edge determination unit 108 can perform edge determination on the outline pixels of the character region and can determine the inner edge region and the outer edge region.

  Based on the detection result from the boundary detection unit 105 and the determination result from the edge determination unit 108, the expansion unit 109 performs an expansion process for extending the outer edge region of the character region to the base region. Whether or not to perform the extension process is determined based on an evaluation result of whether or not a condition regarding a feature of a boundary portion between the character area and the background area in the input image is satisfied. The evaluation is performed by the CPU 101 based on, for example, the determination result of the edge determination unit 108 and the calculation result of the brightness calculation unit 106. The expansion unit 109 expands the target pixel as a pixel in the outer edge region when it is evaluated that the predetermined pixel satisfies the predetermined condition.

  In the present embodiment, for example, the expansion process is performed when the following predetermined conditions are satisfied. That is, the pixel of interest is detected as a character area (having a character attribute) by the image attribute detection unit 104 and detected as a boundary between the character area and the background area by the boundary detection unit 105. Thus, when the edge determination unit 108 does not perform edge determination, an extension process is performed on the target pixel. In other words, the expansion unit 109 performs expansion processing when the edge determination unit 108 does not perform edge determination on the contour pixels of the character area. The extension process is performed when the edge intensity calculated by the intensity calculation unit 107 does not exceed a certain threshold value for the pixel detected as the boundary between the character area and the background area.

  The enhancement processing unit 110 performs edge enhancement processing (hereinafter, simply referred to as enhancement processing) for pixels that are determined to be edges (edge determination) by the edge determination unit 108. The enhancement processing unit 110 enhances the edge determined by the edge determination unit 108 by performing sharpness filter processing or the like. In the present embodiment, when the edge determination unit 108 performs edge determination on the outline pixel of the character area, the enhancement processing unit 110 performs enhancement processing.

  The enhancement processing may be performed after the screen conversion is performed on the input image by the screen conversion unit 112 and the screen conversion is performed. That is, the enhancement processing may be performed by printing only the edge enhancement target pixels of the screen-converted image with solid (filling) without performing screen conversion.

  The replacement unit 111 replaces the image data of the pixels in the outer edge region expanded by the expansion unit 109 with replacement data. That is, in the data replacement processing, the edge determination unit 108 is used for a pixel of interest that is detected as a character region by the image attribute detection unit 104 and is detected as a boundary between the character region and the background region by the boundary detection unit 105. This is executed when the edge is not judged in step. In other words, the replacement process is executed when the edge intensity calculated by the intensity calculation unit 107 does not exceed a certain threshold for the pixel detected as the boundary between the character area and the background area.

  The screen conversion unit 112 performs screen processing on the input image by a dither matrix method or the like according to the gradation of each part of the input image, and converts the input image into a screen image.

  FIG. 3 is a flowchart showing the operation of the control unit 100 when performing screen processing.

  Hereinafter, as an example of the screen processing, a flow of screen processing executed using an image read by the document reading unit 20 as an input image will be described. The image forming apparatus 1 is not limited to this. For example, screen processing may be performed on an image transmitted from the user to the image forming apparatus 1 or an image stored in the HDD 120 in the image forming apparatus 1. . In those cases as well, screen processing can be performed in the same manner as when an image read by the document reading unit 20 is executed as an input image.

  Referring to FIG. 3, in step S <b> 100, CPU 101 reads a document with document reading unit (scanner) 20.

  In step S <b> 101, the CPU 101 causes the image attribute detection unit 104 to perform attribute detection on the image data (input image) read by the document reading unit 20. The image attribute detection unit 104 detects a character area and a background area in the input image.

  In step S <b> 102, the CPU 101 calculates the edge strength of the pixels in the character area by the strength calculation unit 107. At this time, the intensity calculating unit 107 may calculate the edge intensity for the pixels in the base area.

  In step S <b> 103, the CPU 101 performs edge determination for the pixels in the character area based on the edge strength calculated by the edge determination unit 108.

  In step S <b> 104, the CPU 101 determines each pixel as a pixel of interest, and determines whether the pixel is a pixel at a boundary portion between the character area and the background area.

  When the pixel is a boundary pixel in step S104, in step S105, the CPU 101 determines (evaluates) whether or not the target pixel is an edge, that is, whether or not the target pixel is edge-determined.

  When the target pixel is an edge pixel in step S105, the CPU 101 performs enhancement processing by the enhancement processing unit 110 in step S106. Edge enhancement processing is performed on a pixel of interest that is edge-determined that is in a boundary area between the character area and the background area.

  On the other hand, when the target pixel is not an edge pixel in step S105, in step S107, the CPU 101 performs a process of expanding the background region (outer edge region) adjacent to the target pixel by the extension unit 109. Expansion processing is performed on a pixel of interest that is not a edge determination and that is in a boundary area between the character area and the background area.

  In step S <b> 108, the CPU 101 uses the replacement unit 111 to perform replacement processing of the image data of the pixels in the outer edge region expanded in step S <b> 107.

  When the emphasis process is finished in step S106 or when the replacement process is finished in step S108, the CPU 101 ends the series of processes. When the target pixel is not a pixel at the boundary with the character area in step S104, the CPU 101 ends the series of processes for the target pixel.

  Note that the edge enhancement process, the expansion process, and the replacement process may be performed separately for each pixel that has been determined to be a pixel at the boundary with the character area in step S104, or for the target pixel. A replacement process may be performed by collectively performing a process or the like.

  [Explanation of emphasis processing]

  In the present embodiment, the emphasis processing unit 110 performs an emphasis process by performing a process of filling a region to be processed. When the edge strength calculated by the strength calculation unit 107 is higher than a predetermined strength (threshold value), the enhancement processing unit 110 performs a filling process on the contour pixels in the character area.

  FIG. 4 is a diagram illustrating a first example of the relationship between an input image and an output image after screen processing in the present embodiment.

  The upper part of FIG. 4 shows the input image 200 to be screen-processed, and the middle part of FIG. 4 shows a graph showing the edge strength calculated for the input image 200. In the graph, the edge strength increases with increasing distance from the center (zero). The lower part of FIG. 4 shows an output image 210 that is output when screen processing is performed on the input image 200. In FIG. 4, the input image 200, the graph, and the output image 210 are arranged in the vertical direction so that the horizontal positions correspond to each other vertically.

  Referring to FIG. 4, the input image 200 has a background area 201 and a character area 202 arranged between the background areas 201 on both sides. The boundary between the base area 201 and the character area 202 is relatively clear. Therefore, the edge strength of the input image 200 is larger than a predetermined edge detection threshold at the outer edge and the inner edge of the boundary portion between the base area 201 and the character area 202. That is, the input image 200 is edge-determined at the pixel at the boundary between the background area 201 and the character area 202.

  The output image 210 has a base area 211, a character area 212, and a fill portion 215. The background area 211 is converted into a screen image corresponding to the brightness of the background area 201, and the character area 212 is converted into a screen image corresponding to the brightness of the character area 202.

  Here, the image data of the inner edge region of the character region 212 and the image data of the contour region of the character region 212 are the calculation result of the intensity calculation unit 107, the detection result of the boundary detection unit 105, and the inner edge of the edge determination unit 108. For example, the CPU 101 determines the area based on the determination result of the area. In the input image 200, the edge strength at the boundary between the background area 201 and the character area 202 is larger than the edge detection threshold value, and edge determination is performed. Therefore, as edge enhancement processing, inner edge painting processing is performed, and an output image 210 is output. The filling process is performed in the emphasis processing unit 110, for example. By performing the filling process on the inner edge, in the output image 210, the painting unit 215 is provided on the inner edge in the vicinity of the base area 211 in the character area 212. In this way, the inner edge is filled (FEET process, solid process), so that the edge of the background area 211 and the character area 212 is emphasized in the output image 210, and the boundary between the character and the background is clearly reproduced. .

  As the enhancement process, various processing methods can be employed in addition to the above-described filling process.

  [Explanation of extended processing and replacement processing]

  In the present embodiment, for example, the extension unit 109 determines an extension size according to the edge strength calculated by the strength calculation unit 107, and extends the outer edge region according to the determined extension size.

  FIG. 5 is a diagram illustrating a second example of the relationship between the input image and the output image after screen processing in the present embodiment.

  Also in FIG. 5, as in FIG. 4, an output image is output when screen processing is performed on the input image 220 and a graph showing edge strength calculated for the input image 220 and the input image 200 in the order of the upper, middle, and lower stages. An output image 230 is shown. In the graph, the edge strength increases with increasing distance from the center (zero). Also in FIG. 5, the input image 220, the graph, and the output image 230 are arranged in the vertical direction so that the horizontal positions correspond to each other vertically.

  Referring to FIG. 5, the input image 220 includes a background area 221 and character areas 222 arranged between the background areas 221 on both sides. The boundary between the base area 221 and the character area 222 is not clear compared to that of the input image 200 shown in FIG. The edge strength of the input image 220 is less than the predetermined edge detection threshold even at the boundary portion between the base region 221 and the character region 222. That is, the input image 220 is not subjected to edge determination at pixels at the boundary portion between the base area 221 and the character area 222.

  The output image 230 has a base area 231, a character area 232, and replacement areas 235 a and 235 b (sometimes collectively referred to as replacement areas 235). The background area 231 is converted into a screen image corresponding to the brightness of the background area 221, and the character area 232 is converted into a screen image corresponding to the brightness of the character area 222.

  Here, the image data of the inner edge region of the character region 232 and the image data of the contour region of the character region 232 are the calculation result of the intensity calculation unit 107, the detection result of the boundary detection unit 105, and the inner edge of the edge determination unit 108. It is determined by the CPU 101 based on the determination result of the area. Referring to the graph of FIG. 5, in the input image 220, the edge strength at the boundary between the base area 221 and the character area 222 is smaller than the edge detection threshold value, and no edge determination is performed. Therefore, in the present embodiment, the expansion process is performed on the input image 200 by the expansion unit 109 and the replacement process is performed by the replacement unit 111. The input image 200 is not subjected to the filling process as described above.

  That is, the outer edge area on the background area side is expanded by the expansion process at the boundary between the character area and the background area. In the present embodiment, the area expanded by the expansion process is replaced with white data by the replacement process. Thereby, a replacement area 235 is provided in the output image 230. In other words, the replacement region 235 is provided by expanding the outer edge region to the base region side by the expansion processing and replacing the expanded outer edge region by the replacement processing. Thus, the replacement area 235 replaced with white data is provided at the boundary between the character area 232 and the background area 231, and the character area 232 and the background area 231 are separated from each other. The boundary of the ground is reproduced clearly. Since the portion close to the character region 232 in the base region 231 is the replacement region 235, the character region 202 is hardly affected, and the output image 230 with high reproducibility of the input image 220 is obtained.

  As described above, in the first embodiment, the edge processing is performed on the contour pixel of the character region of the input image when the edge is detected, and when the edge is not detected, the background adjacent to the target pixel is detected. The pixel area is expanded and replaced with white data. Therefore, regardless of the presence or absence of edge detection, the boundary between the background area and the character area is clearly reproduced, and screen processing can be executed so as to improve readability while retaining more information of the input image.

  [Modification Example of First Embodiment]

  FIG. 6 is a diagram illustrating an example of the relationship between the input image and the edge strength of the input image.

  In the following description of the modified example, as an example, the same image as the input image 220 shown in FIG. 5 is used as an input image, screen processing is performed, and the same image as the output image 230 shown in FIG. 5 is output as an output image. Assuming that As shown in FIG. 6, the input image 220 has a relatively small brightness difference between the base area 221 and the character area 222. Therefore, as shown in the graph of FIG. 6, the edge strength of the input image 220 does not become larger than the edge detection threshold value. In the example shown in FIG. 6, when the range of edge strength from “0” to the edge detection threshold is 0 percent to 100 percent, the maximum value of edge strength is α percent between 0 percent and 100 percent. It is.

  In the first embodiment, the extension unit 109 determines an extension size for extending the outer edge region according to the edge strength calculated by the strength calculation unit 107, and determines the outer size according to the determined extension size. The edge region may be expanded (first modified example).

  FIG. 7 is a graph showing the relationship between the edge strength and the outer edge extension amount in the first modification.

  Referring to FIG. 7, in the first modified example, the amount by which the outer edge region is expanded by the expansion processing (outer edge expansion amount H (dot); an example of the expansion size) It is set to be proportional to the value divided by. The outer edge extension amount H gradually decreases as the value obtained by dividing the edge strength by the edge detection threshold value approaches “1” from “0”. That is, the outer edge extension amount H decreases as the edge strength increases and approaches the edge detection threshold. The extension unit 109 calculates the outer edge extension amount H corresponding to the maximum value (α percent) obtained by dividing the edge strength calculated by the strength calculation unit 107 by the edge detection threshold value.

  FIG. 8 is a diagram illustrating an output image in the first modification.

  Referring to FIG. 8, in the output image 230, the expansion process is performed by extending the outer edge region with a size corresponding to the outer edge expansion amount H. The extended outer edge region becomes the replacement region 235. In the first variation, the extension process and the replacement process are performed so that the width of the replacement area 235, that is, the extended outer edge area (the interval between the base area 231 and the character area 232) becomes the outer edge extension amount H (dot). Is done.

  In this way, the expansion amount and the replacement process are performed by setting the expansion amount of the outer edge region according to the edge strength, so that even if the edge strength is small, the replacement region 235 becomes wide and the character region 232 and the base region 231 Are clearly separated. On the other hand, when the edge strength is large and the character region 232 and the base region 231 are relatively easy to distinguish, the replacement region 235 is narrowed. Therefore, it is possible to improve readability while retaining as much information of the input image as possible.

  In the first embodiment, the replacement data of the outer edge region expanded by the expansion process is not limited to white data. For example, even if it is not white, it may be a color having a higher brightness than the background area, or another color. For example, the replacement unit 111 may generate replacement data according to the edge strength calculated by the strength calculation unit 107, and replace the image data of the replacement target pixel with the generated replacement data (second modification example). ).

  FIG. 9 is a graph showing the relationship between the edge strength and the gradation of the replacement data in the second modification.

  Referring to FIG. 9, in the second modification, the gradation (for example, brightness) C of the replacement data replaced by the replacement process is proportional to the value obtained by dividing the edge strength by the edge detection threshold value. Is set to The gradation C gradually decreases as the value obtained by dividing the edge strength by the edge detection threshold value approaches “1” from “0”. That is, the greater the edge strength and the closer to the edge detection threshold, the lower the gradation C of the replacement data (for example, the lower the brightness). The replacement unit 111 calculates the gradation C corresponding to the maximum value (α percent) of the value obtained by dividing the edge strength calculated by the strength calculation unit 107 by the edge detection threshold value.

  FIG. 10 is a diagram illustrating an output image in the second modification.

  Referring to FIG. 10, in the output image 230, the replacement process is performed by replacing the image data of the extended outer edge region, that is, the replacement region 235, with replacement data of gradation C. Note that the gradation C (lightness or the like) of the replacement data may have at least the same lightness as the lightness of the background region 221 of the input image, for example.

  As described above, in the second modification, the gradation C of the replacement data in the replacement area 235 is set according to the edge strength. Therefore, the smaller the edge strength, the more the gradation of the image data in the replacement area 235. The character region 232 and the base region 231 are clearly separated from each other with high (for example, high brightness and close to white). On the other hand, when the edge strength is large and the character region 232 and the background region 231 are relatively easy to distinguish, the image data in the replacement region 235 has low gradation (for example, low brightness), and the input image in the output image Is relatively retained. Therefore, it is possible to improve readability while retaining as much information of the input image as possible.

  Note that the first modification example and the second modification example may be combined. In other words, both the replacement amount of the replacement area 235, that is, the outer edge area, and the replacement data may be determined according to the edge strength.

  [Second Embodiment]

  Since the basic configuration of the image forming apparatus in the second embodiment is the same as that in the first embodiment, description thereof will not be repeated here. In the second embodiment, a predetermined condition for performing the extension process or the like is different from the condition in the first embodiment.

  In the second embodiment, the extension unit 109 calculates the brightness difference calculated by the brightness calculation unit 106 for the pixels in the inner edge region and the pixels in the outer edge region detected by the image attribute detection unit 104 and the boundary detection unit 105. The expansion process is performed according to

  FIG. 11 is a diagram illustrating a first example of a relationship between an input image and an output image after screen processing according to the second embodiment.

  In FIG. 11, an input image 200 shown in the upper part and an output image 210 shown in the lower part are substantially the same as those shown in FIG. In the middle part of FIG. 11, a graph showing a lightness / luminance conversion value (hereinafter sometimes referred to as a lightness value) calculated by the lightness calculation unit 106 for the input image 200 is shown. In FIG. 11, the input image 200, the graph, and the output image 210 are arranged in the vertical direction so that the horizontal positions correspond to each other vertically.

  In the graph shown in FIG. 11, the brightness value increases upward. Since the lightness Ya of the background region 201 of the input image 200 is higher than the lightness Yb of the character region 202, the graph has a hollow shape with a lower central portion corresponding to the character region 202.

  Here, in the second embodiment, the CPU 101 determines the brightness difference of the input image 200, that is, the outline pixel (inner edge area pixel) of the character area 202 and the pixel (outer edge area) of the ground area 201 adjacent to the outline pixel. It is evaluated whether or not the brightness difference (Ya−Yb) with respect to (a pixel of FIG. When it is evaluated that the brightness difference is greater than the predetermined value, that is, when (Ya−Yb)> Ref holds, the emphasis processing unit 110 performs a fill process on the outline pixels of the character region 202. The filling process is performed, for example, in the same manner as in the first embodiment described above. In other words, the output image 210 in which the filled portion 215 is provided at the inner edge in the vicinity of the base area 211 in the character area 212 is output. As a result, the output image 210 has the edges of the background area 211 and the character area 212 emphasized, and the boundary between the character and the background is clearly reproduced.

  FIG. 12 is a diagram illustrating a second example of the relationship between an input image and an output image after screen processing according to the second embodiment.

  In FIG. 12, the input image 220 shown in the upper part and the output image 230 shown in the lower part are substantially the same as those shown in FIG. The middle part of FIG. 12 shows a graph indicating the brightness value calculated by the brightness calculation unit 106 for the input image 220. In FIG. 12, the input image 220, the graph, and the output image 230 are arranged in the vertical direction so that the horizontal positions correspond to each other vertically. Also in the graph shown in FIG. 12, the lightness value increases toward the information. Since the lightness Ya of the background region 221 of the input image 220 is higher than the lightness Yb of the character region 222, the graph has a hollow shape with a lower central portion corresponding to the character region 222.

  Here, in the second embodiment, the CPU 101 evaluates that the brightness difference (Ya−Yb) between the contour pixel of the character region 202 and the pixel of the base region 201 adjacent to the contour pixel is equal to or less than the predetermined value Ref. In other words, when (Ya−Yb) ≦ Ref holds, the expansion process and the replacement process are performed. The expansion process and the replacement process are performed by the expansion unit 109, for example, in the same manner as in the first embodiment. That is, the extension unit 109 extends the outer edge area of the input image 220 to the base area 221. Then, the replacement unit 111 replaces the image data of the extended outer edge region with replacement data. As a result, a replacement area 235 is provided between the base area 231 and the character area 232 in the output image 230. In other words, the replacement region 235 is provided by expanding the outer edge region to the base region side by the expansion processing and replacing the expanded outer edge region by the replacement processing.

  The image data in the outer edge area is replaced with, for example, white replacement data. By providing the white replacement area 235, the base area 231 and the character area 232 are separated in the output image 230. Therefore, in the output image 230, the boundary between the character and the background is clearly reproduced. Since the portion close to the character region 232 in the base region 231 is the replacement region 235, the character region 202 is hardly affected, and the output image 230 with high reproducibility of the input image 220 is obtained.

  When screen processing is performed in this way, the image data of the inner edge region of the character region 232 and the image data of the contour region of the character region 232 are, for example, the calculation result of the strength calculation unit 107 and the boundary detection unit 105. The CPU 101 may be determined based on the detection result and the determination result of the inner edge region by the edge determination unit 108.

  As described above, in the second embodiment, when the brightness difference between the contour pixel of the character region of the input image and the pixel of the background region adjacent to the contour pixel is equal to or smaller than a predetermined value, the expansion processing and replacement processing are performed. As a result, the background area and the character area are separated. Even when the brightness difference between the background area and the character area is small, the boundary between the background area and the character area is clearly reproduced, and texture noise does not occur. Therefore, it is possible to execute screen processing so that readability is improved while more information of the input image is held.

  [Third Embodiment]

  Since the basic configuration of the image forming apparatus according to the third embodiment is the same as that of the second embodiment, description thereof will not be repeated here. The third embodiment is different from the second embodiment in that the extension size in the extension process is determined based on the brightness.

  In the third embodiment, the extension unit 109 increases the extension size according to the brightness of the contour pixel of the character region 222 calculated by the brightness calculation unit 106 and the brightness of the pixel of the base region 221 adjacent to the contour pixel. The outer edge region is expanded according to the determined expansion size.

  FIG. 13 is a diagram illustrating an example of the relationship between the input image and the lightness / luminance conversion value of the input image according to the third embodiment.

  In the following description of the third embodiment, as an example, the same image as the input image 220 shown in FIG. 12 is used as the input image, screen processing is performed, and the same image as the output image 230 shown in FIG. Assume that the output image is output. As shown in FIG. 13, the input image 220 has a relatively small brightness difference between the base area 221 and the character area 222. As shown in the graph of FIG. 13, in the input image 220, the difference between the lightness Ya of the background area 221 and the lightness Yb of the character area 222 is smaller than a predetermined value Ref. Therefore, when screen processing is performed on the input image 220, expansion processing and replacement processing are performed.

  FIG. 14 is a graph showing the relationship between the lightness Ya of the base region 221 and the lightness Yb of the character region 222 and the outer edge extension amount in the third embodiment.

  Referring to FIG. 14, in the third embodiment, the amount of expansion of the outer edge region determined by expansion unit 109 (outer edge expansion amount H (dot)) is the lightness Ya and character of base region 221. It is set to be proportional to the lightness Yb of the region 222 (for example, the average value of the lightness Ya and the lightness Yb; hereinafter, sometimes referred to as the lightness Ya, Yb). The outer edge expansion amount H gradually increases as the lightness Ya, Yb approaches “100” from “0”. That is, the lower the brightness of the input image, the smaller the outer edge extension amount H.

  In the input image 220, as shown in the graph of FIG. 13, both the lightness Ya of the base area 221 and the lightness Yb of the character area 222 are relatively low. Therefore, during screen processing of the input image 220, the expansion amount of the outer edge area at the boundary between the base area 221 and the character area 222 can be suppressed. On the other hand, if the extension process is performed on an input image in which both the brightness Ya of the background area and the brightness Yb of the character area are relatively high, the outer edge extension amount is relatively large.

  FIG. 15 is a diagram illustrating an example of an output image 230 according to the third embodiment.

  The output image output in the third embodiment is the same as the output image 230 shown in the second embodiment described above. That is, in the output image 230, a replacement area 235 is provided between the base area 231 and the character area 232. Here, when the expansion amount is suppressed by the expansion processing, the expansion amount of the outer edge region is reduced or is not expanded. Therefore, the replacement area 235 becomes small.

  As described above, according to the third embodiment, the expansion process is more appropriately performed according to the contents of the input image 220, that is, the character area 222, the background area 221, and the brightness information. Therefore, it is possible to obtain an output image 230 that retains more information of the input image and has high readability.

  The outer edge extension amount H may be determined according to the brightness difference between the background area 221 and the character area 222 of the input image. For example, the outer edge expansion amount H may be increased as the brightness difference is smaller.

  [Fourth Embodiment]

  Since the basic configuration of the image forming apparatus in the fourth embodiment is the same as that in the second embodiment, description thereof will not be repeated here. The fourth embodiment is different from the second embodiment in that replacement data in the replacement process is determined based on lightness. Hereinafter, as an example, a case where screen processing is performed on the input image 220 shown in FIG. 13 will be described.

  In the fourth embodiment, the replacement unit 111 generates replacement data according to the lightness of the character region 222 calculated by the lightness calculation unit 106 and the lightness of the pixel of the base region 221 adjacent to the contour pixel. The image data in the outer edge area is replaced with the replaced data.

  FIG. 16 is a graph showing the relationship between the lightness Ya of the base region 221 and the lightness Yb of the character region 222 and the gradation of the replacement data in the fourth embodiment.

  Referring to FIG. 16, the gradation (for example, lightness) C of replacement data generated by replacement unit 111 is set to be proportional to lightness Ya, Yb. The gradation C of the replacement data gradually increases as the lightness Ya, Yb approaches “100” from “0”. That is, the higher the brightness of the input image, the greater the gradation C of the replacement data (for example, the higher the brightness).

  In the input image 220, as shown in the graph of FIG. 13, both the lightness Ya of the base area 221 and the lightness Yb of the character area 222 are relatively low. Therefore, at the time of screen processing of the input image 220, the replacement unit 111 generates replacement data with a relatively low gradation C (for example, replacement data with low brightness) and replaces the outer edge region with the replacement data. . On the other hand, if the expansion process is performed on an input image in which both the lightness Ya of the background area and the lightness Yb of the character area are relatively high, replacement data having a relatively high gradation C (for example, replacement data having a high lightness) is used. The outer edge region is replaced.

  In the fourth embodiment, replacement processing is performed with replacement data of gradations corresponding to the lightness values Ya and Yb, and an output image is output. Therefore, the gradation of the replacement data matches the gradation of the image data in the background area and the image data in the character area. For example, when replacement processing is performed for an input image with relatively low brightness Ya and Yb, dark data with low lightness is generated as replacement data, and the replacement processing is performed. Thereby, an output image with a more natural color tone can be obtained.

  [Effects of the embodiment]

  In the image forming apparatus configured as described above, the expansion process and the replacement process are performed when an edge determination is not made at the boundary portion between the character area and the background area or the brightness difference is smaller than a predetermined value. . As a result, in the predetermined case, an output image in which the character area and the background area are separated is obtained, and screen processing can be executed so as to improve readability while retaining more information of the input image. .

  FIG. 17 is a first diagram illustrating an example of an output image after screen processing.

  In FIG. 17, among the upper and lower three images, the upper part shows the input image 500, the interruption shows the output image 510 output as a result of the conventional screen processing, and the lower part shows the image of any of the above embodiments An example of an output image 550 output as a result of screen processing performed by the forming apparatus is shown. Assume that the input image 500 has a character area 502 arranged in a different color from the background area 501 on the colored background area 501. The input image 500 is the same as that shown in FIG. That is, the color of the background area 501 is brown, and the color of the character area 502 is a khaki color brighter than the background. The input image 500 has a small brightness difference between the background area 501 and the character area 502. The input image 500 is such that the edge determination by the edge determination unit 108 is not performed at the boundary between the background area 501 and the character area 502.

  When screen processing is performed on such an input image, an output image 550 including a base area 551 and a character area 552 is obtained. The background area 551 has brightness corresponding to the background area 501. The character area 552 has brightness corresponding to the character area 502.

  Conventionally, when the screen processing is performed on the input image 500 as described above, texture noise may be conspicuous in the outline portion of the character area as in the output image 510. On the other hand, in the output image 550 output by the image forming apparatus configured as described above, the background region is defined in the outline portion of the character region 552 by edge enhancement processing or outer edge region expansion processing and replacement processing. 551 and the character area 552 are reliably separated. Therefore, it is possible to prevent the occurrence of texture noise in the outline portion of the character region and improve the readability of the character.

  FIG. 18 is a second diagram illustrating another example of the output image after the screen processing.

  In FIG. 18, among the upper and lower three images, the upper part shows the input image 600, the interruption shows the output image 610 output as a result of the conventional screen processing, and the lower part shows the image of any one of the above embodiments. An example of an output image 650 output as a result of screen processing performed by the forming apparatus is shown. Referring to the figure, an input image is assumed in which a character area 602 is arranged on a colored background area 601 in a color different from that of the background area 601. The input image 600 is the same as that shown in FIG. Here, the color of the background area 601 is gray, and the color of the character area 602 is slightly lighter gray than the background area 601. The input image 600 has a relatively small brightness difference between the background area 601 and the character area 602.

  When screen processing is performed on such an input image, an output image 650 including a base area 651 and a character area 652 is obtained. The brightness of the pixel in the base area 651 is the brightness corresponding to the brightness of the pixel in the base area 601. The brightness of the pixel in the character area 652 is a brightness corresponding to the brightness of the pixel in the character area 602.

  Conventionally, when the screen processing is performed on the input image 600 as described above, there is almost no difference in brightness between the character area and the background area as in the output image 610, and it may be difficult to distinguish characters. On the other hand, in the output image 650 output by the image forming apparatus configured as described above, the edge region or the outer edge region expansion processing and replacement processing are performed, so that the background region is represented by the outline portion of the character region 652. 651 and the character area 652 are reliably separated. Therefore, the generation of texture noise can be prevented and the readability of characters can be improved.

  [Others]

  The edge detection threshold, a predetermined value that is a reference value for whether or not the brightness difference is large, and other setting values are appropriately set so that an output image with high readability is output while a large amount of information of the input image is maintained. What is necessary is just to set to an appropriate value.

  In the second embodiment, the expansion process and the replacement process may be performed in accordance with the pixel brightness information itself. For example, the outer edge region may be expanded when the brightness of the pixel in the base region is lower than a predetermined threshold value.

  The image forming apparatus may be configured by appropriately combining each of the above-described embodiments and variations thereof. For example, the extension unit performs an extension process according to both the evaluation result of whether or not the edge determination is performed and the evaluation result of whether or not the brightness difference is a predetermined value or more, or performs edge processing and edge strength and brightness. The expansion size at the time of expansion processing may be determined based on both of the differences. Similarly, the replacement unit may determine the gradation of the replacement data based on both the edge strength and the brightness difference. In the first embodiment, when the extension process or the replacement process is performed, the extension size (outer edge extension amount) is determined or the replacement data is generated according to the brightness calculated by the brightness calculation unit. You may be made to be.

  The image forming apparatus may be a monochrome / color copying machine, a printer, a facsimile machine, or a multifunction machine (MFP) thereof. The image forming apparatus is not limited to an apparatus that forms an image by an electrophotographic method, and may be an apparatus that forms an image by a so-called inkjet method, for example.

  The present invention is not limited to an image forming apparatus, and can be widely applied to an image processing apparatus that outputs a screen image printed on the image forming apparatus. For example, the present invention can be applied to an image processing apparatus having a function of outputting a screen image to an external image forming apparatus connected to be communicable.

  The processing in the above embodiment may be performed by software or by using a hardware circuit.

  A program for executing the processing in the above-described embodiment can be provided, or the program can be recorded on a recording medium such as a CD-ROM, a flexible disk, a hard disk, a ROM, a RAM, or a memory card and provided to the user. It may be. The program may be downloaded to the apparatus via a communication line such as the Internet. The processing described in the text in the above flowchart is executed by the CPU according to the program.

  The above embodiment should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Image forming apparatus (an example of an image processing apparatus)
10 Document reading unit (an example of reading means)
30 Image forming unit 100 Control unit (an example of an image processing apparatus)
101 CPU (an example of evaluation means)
104 pixel attribute detection unit 105 boundary detection unit (an example of boundary detection means)
106 brightness calculation unit (an example of brightness calculation means)
107 Strength calculation unit (an example of strength calculation means)
108 Edge determination unit (an example of a first edge determination unit, an example of a second edge determination unit)
109 Expansion unit (an example of expansion means)
110 Emphasis processing unit (an example of an emphasis processing means, an example of a painting means)
111 Replacement part (an example of replacement means)
120a Control program H Outer edge extension amount (example of extension size)
200, 220, 500, 600 Input image 201, 221, 501, 601 Base area (for input image) 202, 222, 502, 602 Character area (for input image) 210, 240, 550, 650 Output image 211, 231, 551, 651 (Output image) background area 212, 232, 552, 652 (Output image) character area 215 Filled portions 235, 235a, 235b Replacement area

Claims (15)

An image processing apparatus that performs screen processing and outputs a screen image printed on the image forming apparatus,
A reading means for reading the input image;
Boundary detection means for detecting a boundary between a character area and a base area other than the character area, present in the input image read by the reading means;
Strength calculating means for calculating edge strength of the character region;
First edge determination means for determining an outer edge area on the background area side of the boundary between the character area and the background area based on the edge intensity calculated by the intensity calculation means;
Based on the detection result by the boundary detection means and the determination result of the first edge determination means, an expansion means for extending the outer edge area to the base area;
Replacement means for replacing the image data of the outer edge region extended by the extension means with replacement data;
An evaluation unit that evaluates whether or not a condition regarding a feature of a boundary portion between the character region and the background region in the input image is satisfied;
An image processing apparatus in which the expansion unit performs the expansion and the replacement unit performs the replacement based on an evaluation result by the evaluation unit. The image processing apparatus further includes second edge determination means for performing edge determination based on the edge strength calculated by the strength calculation means,
The evaluation means evaluates whether or not the edge determination is performed by the second edge determination means on the contour pixels of the character region;
The image processing apparatus according to claim 1, wherein when the evaluation unit evaluates that the edge determination has not been performed, the expansion unit performs the expansion, and the replacement unit performs the replacement. The image processing apparatus further includes enhancement processing means for performing enhancement processing for enhancing the edge determined by the second edge determination means,
The image processing apparatus according to claim 2, wherein when the evaluation unit evaluates that the edge determination has been performed, the enhancement processing unit performs the enhancement processing. The image processing apparatus further includes a filling unit that performs a filling process of a region to be processed;
The said filling means performs the said filling process with respect to the outline pixel of the said character area, when the edge intensity | strength calculated by the said intensity | strength calculation means is higher than predetermined | prescribed intensity | strength. Image processing device. The expansion means includes
Determine the extension size according to the edge strength calculated by the strength calculating means,
The image processing apparatus according to claim 1, wherein the expansion is performed according to the determined expansion size. The replacement means includes
Generating replacement data according to the edge strength calculated by the strength calculating means;
The image processing apparatus according to claim 1, wherein the replacement is performed using the generated replacement data. The image processing apparatus further includes a brightness calculation unit that calculates the brightness of each pixel of the input image read by the reading unit,
The evaluation means evaluates whether or not the brightness difference between the contour pixel of the character area calculated by the brightness calculation means and the pixel of the background area adjacent to the contour pixel is a predetermined value or less,
The image processing according to any one of claims 1 to 6, wherein when the evaluation unit evaluates that the brightness difference is equal to or less than a predetermined value, the expansion unit performs the expansion, and the replacement unit performs the replacement. apparatus. The expansion means includes
The extension size is determined according to the brightness of the contour pixel of the character area calculated by the brightness calculation means and the brightness of the pixel of the background area adjacent to the contour pixel,
The image processing apparatus according to claim 7, wherein the expansion is performed according to the determined expansion size. The replacement means includes
Generating replacement data according to the brightness of the contour pixel of the character area calculated by the brightness calculation means and the brightness of the pixel of the background area adjacent to the contour pixel;
The image processing apparatus according to claim 7, wherein the replacement is performed using the generated replacement data. The image processing apparatus further includes a brightness calculation unit that calculates the brightness of each pixel of the input image read by the reading unit,
The expansion means includes
The extension size is determined according to the brightness of the contour pixel of the character area calculated by the brightness calculation means and the brightness of the pixel of the background area adjacent to the contour pixel,
The image processing apparatus according to claim 1, wherein the expansion is performed according to the determined expansion size. The image processing apparatus further includes a brightness calculation unit that calculates the brightness of each pixel of the input image read by the reading unit,
The replacement means includes
Generating replacement data according to the brightness of the contour pixel of the character area calculated by the brightness calculation means and the brightness of the pixel of the background area adjacent to the contour pixel;
The image processing apparatus according to claim 1, wherein the replacement is performed using the generated replacement data. The first edge determination unit determines an inner edge region on the character region side of the boundary between the character region and the background region based on the edge strength calculated by the strength calculation unit;
The image processing apparatus is configured to generate image data of the inner edge region based on the calculation result of the intensity calculating unit, the detection result of the boundary detecting unit, and the determination result of the inner edge region by the first edge determining unit. The image processing apparatus according to claim 1, further comprising a boundary processing unit that performs a process of determining image data of a contour area of the character area. An image processing apparatus according to any one of claims 1 to 12,
An image forming apparatus comprising: an image forming unit that forms a screen image based on image data processed by the image processing apparatus. A control method for an image processing apparatus that performs screen processing and outputs a screen image printed on the image forming apparatus,
A reading step for reading the input image;
A boundary detection step for detecting a boundary between a character region and a base region other than the character region, which is present in the input image read by the reading step;
An intensity calculating step for calculating an edge intensity of the character region;
An edge determination step for determining an outer edge region on the base region side of the boundary between the character region and the base region based on the edge strength calculated by the strength calculation step;
Based on the detection result of the boundary detection step and the determination result of the edge determination step, an expansion step of extending the outer edge region to the base region;
A replacement step of replacing the image data of the outer edge region expanded by the expansion step with replacement data;
An evaluation step for evaluating whether or not a condition regarding a feature of a boundary portion between the character region and the background region in the input image is satisfied,
A control method for an image processing apparatus, wherein the expansion step performs the expansion and the replacement step performs the replacement based on an evaluation result of the evaluation step. A control program for an image processing apparatus that performs screen processing and outputs a screen image printed on the image forming apparatus,
A reading step for reading the input image;
A boundary detection step for detecting a boundary between a character region and a base region other than the character region, which is present in the input image read by the reading step;
An intensity calculating step for calculating an edge intensity of the character region;
An edge determination step for determining an outer edge region on the base region side of the boundary between the character region and the base region based on the edge strength calculated by the strength calculation step;
Based on the detection result of the boundary detection step and the determination result of the edge determination step, an expansion step of extending the outer edge region to the base region;
A replacement step of replacing the image data of the outer edge region expanded by the expansion step with replacement data;
Causing the computer to execute an evaluation step for evaluating whether or not a condition regarding a feature of a boundary portion between the character region and the background region in the input image is satisfied,
A control program for an image processing apparatus, wherein the expansion step performs the expansion and the replacement step performs the replacement based on an evaluation result of the evaluation step.