JP2006197239A - Image processor and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate an image where characters are clarified, and gradation is expressed inside the characters. <P>SOLUTION: This image processor is provided with first to third screen processing parts 125A, 125B and 125C for inputting image data and attribute data for discriminating pixels, configuring characters and outline pixels configuring the outline section of the characters from the other pixels, and for executing screen processing on the image data, based on the attribute data. The first screen processing part 125A executes first screen processing to the outline pixels of the image data, and the second screen processing part 125B executes second screen processing to pixels included in the character region of the image data, excluding the outline pixels, and the third screen processing part 125C executes third screen processing to pixels which are not included in the character region of the image data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus and an image processing program, and more particularly to an image processing apparatus and an image processing program for executing screen processing on image data.

  Japanese Patent Application Laid-Open No. 07-333822 (Patent Document 1) is a method for creating a printing plate image from an image signal representing an original image, and (A) the original image is divided into a plurality of regions, Assigning each one of a plurality of types of dots having different shapes or / and the number of lines to each of the regions, and (B) gradation characteristics of the image signal and the plurality of types of dots. A step of correcting at least one of the gradation characteristics of a plurality of types of dot pattern signals representing threshold values for forming according to the respective dot gain characteristics of the plurality of types of dots; and (C) correction By comparing the completed image signal and the dot pattern signal, an image recording signal representing a printing plate image in which the plurality of areas are respectively reproduced by the plurality of types of dots is generated. Create a binary halftone image, characterized in that it comprises a step, is described.

However, in Japanese Patent Application Laid-Open No. 07-333822, since any one of a plurality of types of dots having a shape and / or the number of lines is assigned, screen processing is executed on characters. For this reason, there is a problem that the character edge cannot be clearly displayed. Although it is conceivable to perform edge enhancement processing on the character portion of the image data, in this case, there is a problem that a character with gradation cannot be expressed.
Japanese Patent Laid-Open No. 07-333822

  The present invention has been made to solve the above-described problems, and one of the objects of the present invention is an image processing apparatus capable of generating an image in which a character is sharpened and a gradation is expressed inside the character. And providing an image processing program.

  In order to achieve the above-described object, according to one aspect of the present invention, an image processing apparatus forms image data input means for inputting image data, a character region including pixels constituting a character, and a character outline portion. Attribute data acquisition means for acquiring attribute data for distinguishing contour pixels from other pixels, and screen processing means for executing screen processing on image data based on the attribute data. The screen processing means includes contours of image data. The first screen processing is performed on the pixel, the second screen processing is performed on the pixel that is included in the character region of the image data and is not the contour pixel, and the third pixel is not included in the character region of the image data. Perform screen processing.

  According to the present invention, the first screen processing is performed on the contour pixels of the image data, the second screen processing is performed on the pixels that are included in the character region but are not the contour pixels, and the pixels that are not included in the character region are processed. 3 screen processing is executed. For this reason, for example, the outline of a character can be emphasized to give gradation to the inside of the character and the background of the character. As a result, it is possible to provide an image processing apparatus that can sharpen characters and generate an image expressing gradation inside the characters.

  Preferably, the first screen processing is edge enhancement processing, the second screen processing is screen processing giving priority to resolution, and the third screen processing is screen processing giving priority to gradation.

  Preferably, the attribute data acquisition unit includes a character region extraction unit that extracts a character region from the input image data, and a contour pixel extraction unit that extracts a contour pixel constituting a contour portion of the character based on the extracted character region. Including.

  Preferably, the character area extraction means includes edge pixel extraction means for extracting edge pixels from the input image data, and character area determination means for extracting a character area including the edge pixels and pixels surrounded by the edge pixels. including.

  Preferably, the contour pixel extracting means includes an expanding means for expanding the character area extracted by the character area extracting means, a contracting means for contracting the character area extracted by the character pixel extracting means, and after being expanded by the expanding means. And a contour pixel determining unit that uses a pixel that is included in the character region and not included in the character region after being contracted by the contracting unit as a contour pixel.

  Preferably, the attribute data acquisition means extracts edge pixel from the input image data as edge pixels, and character attribute area that extracts a rectangular character attribute area including the extracted edge pixels as a character area Extraction means.

  Preferably, the image data further includes a gamma correction unit that corrects the gradation of the image data, and the gamma correction unit includes a contour pixel of the image data, a pixel that is included in the character region of the image data and is not a contour pixel, and the image data Gamma correction is performed on the pixels not included in the character area in accordance with a characteristic curve prepared in advance for each pixel.

  According to another aspect of the present invention, an image processing program has an attribute for distinguishing a step of inputting image data and a character region including pixels constituting a character and a contour pixel constituting a contour portion of the character from other pixels. A step of acquiring data; a step of executing a first screen process on a contour pixel of image data; and a step of executing a second screen process on a pixel that is included in a character region of image data and is not a contour pixel; And causing the computer to execute a third screen process on pixels not included in the character area of the image data.

  According to the present invention, it is possible to provide an image processing program capable of generating an image that sharpens characters and expresses gradation inside the characters.

  According to still another aspect of the present invention, an image processing apparatus includes image data input means for inputting image data, edge pixel extraction means for extracting edge pixels from the input image data, and screen processing for the image data. And a screen processing unit that executes edge enhancement processing on the edge pixels of the image data, and performs screen processing that prioritizes resolution for pixels that are not extracted as edge pixels of the image data.

  According to the present invention, the edge emphasis process is executed on the edge pixels of the image data, and the screen process giving priority to the resolution is executed on the pixels that are not extracted as the edge pixels of the image data. For this reason, for example, the outline of a character can be emphasized to give gradation to the inside of the character and the background of the character. As a result, it is possible to provide an image processing apparatus that can sharpen characters and generate an image expressing gradation inside the characters.

  According to still another aspect of the present invention, an image processing program executes a step of inputting image data, a step of extracting edge pixels from the input image data, and an edge enhancement process on the edge pixels of the image data. Causing the computer to execute a step and a step of executing a screen process giving priority to the resolution of the pixels that are not extracted as edge pixels of the image data.

  According to the present invention, it is possible to provide an image processing program capable of generating an image that sharpens characters and expresses gradation inside the characters.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

<First Embodiment>
FIG. 1 is a perspective view of an MFP (Multi Function Peripheral) according to the first embodiment of the present invention. Referring to FIG. 1, the MFP includes an image reading device 10 for reading a document image and an image forming device 20 provided at a lower portion of the image reading device 10. The MFP forms an image read by the image reading device 10 on a recording medium such as paper. The MFP also includes a communication interface for connecting to a network such as a facsimile device, a local area network (LAN), or a public line.

  A flash ROM 30 can be attached to the MFP. The image processing program stored in the flash ROM 30 is executed by a central processing unit (CPU) provided in the MFP. The program may be stored in an EEPROM (electrically erasable / programmable read only memory) instead of being read from the flash ROM 30. The MFP executes a program stored in the EEPROM by the CPU. In addition, this EEPROM can be rewritten or additionally written, so that another computer connected to the network can rewrite the program stored in the EEPROM of the MFP or add a new program. You may make it write. Further, the MFP may download a program from a computer connected to the network and store the program in the EEPROM.

  The program executed by the MFP is shown as an example of being stored in the flash ROM 30 and distributed, but other recording media such as a flexible disk, a cassette tape, a CD-ROM (Compact Disc-Read Only Memory), a hard disk, Optical disks (MO (Magnetic Optical Disc) / MD (Mini Disc) / DVD (Digital Versatile Disc)), IC cards (including memory cards), optical cards, semiconductor memories such as mask ROM, EPROM, EEPROM, etc. It may be a medium carrying a program.

  The program referred to here includes not only a program that can be directly executed by the CPU but also a source program type program, a compressed program, an encrypted program, and the like.

  FIG. 2 is a block diagram showing the configuration of the MFP in the present embodiment. Referring to FIG. 2, the MFP reads a document line by line and outputs an R (red), G (green), and B (blue) analog signal, and a CCD (Charge Coupled Device) 101, and the CCD 101 inputs it. An image synthesis unit 102 that synthesizes even-numbered signals Reven, Geven, and Beven and odd-numbered signals Rodd, Godd, and Bodd, and an analog-to-digital conversion unit (A / D conversion unit) 103 that converts an analog signal into a digital signal. A shading correction unit 104 for correcting illumination unevenness of the light source, an interline correction unit 105 for synchronizing the R signal, the G signal, and the B signal to be the same line of the document, and main scanning by the lens A chromatic aberration corrector 106 for correcting directional distortion, and a magnification / movement processor 10 for changing the magnification and moving the position in the image data. When, and a color conversion unit 108 for converting the image data (CMYK data) represented the image data represented in the RGB color space by the CMY color space.

  The MFP further receives an R signal, a G signal, and a B signal to determine the attribute of each pixel of the image data, and prints that perform screen processing or the like according to the attribute determination result by the attribute determination unit 109 A data generation unit 110 and a printer I / F 111 for outputting the generated print data to the image forming apparatus 20 are provided.

  Although an example in which image data obtained by reading an original with the image reading apparatus 10 is output from the image forming apparatus 20 is shown here, an image transmitted from another computer connected to the MFP via a network is shown. Data may be output from the image forming apparatus 20. In this case, image data is received by the communication interface provided in the MFP, and the image data is input to the color conversion unit 108 and the attribute determination unit 109. Further, the image data read from the hard disk included in the MFP may be output from the image forming apparatus 20. In this case, image data read from the hard disk included in the MFP is input to the color conversion unit 108 and the attribute determination unit 109.

  Next, the attribute determination unit 109 will be described with reference to FIGS. 3 and 4. FIG. 3 is a block diagram illustrating a configuration of the attribute determination unit 109. FIG. 4 is a diagram illustrating an example of edge data generated by the attribute determination unit.

  The attribute discrimination unit 109 receives R, G, and B image data line by line. The attribute discriminating unit 109 converts the three image data of R, G, and B into lightness data, and processes the lightness data. The attribute determination unit 109 has a line buffer (FIFO) and can process brightness data for a plurality of lines.

  The attribute discriminating unit 109 is shrunk by an edge extracting unit 131 that extracts edge pixels from lightness data, a first dilation processing unit 132 that expands edge pixels, and a first erosion processing unit 133 that contracts expanded edges. A second erosion processing unit 134 for extending the edge, a second erosion processing unit 135 for further reducing the shrunken edge, and an output of the second erosion processing unit 135 from the output of the second dilation processing unit 134. A difference extracting unit 136 that extracts a difference area having a difference and outputs an attribute signal.

  The edge extraction unit 131 receives brightness data. The edge extraction unit 131 includes a first-order differential filter and a second-order differential filter, and executes filter processing using a first-order differential filter for lightness data and filter processing using a second-order differential filter for lightness data. Then, the pixel determined to be an edge (edge pixel) by the filter processing using the primary differential filter and the pixel (edge pixel) determined to be the edge by the filter processing using the secondary differential filter are set to “1”. The edge data with other pixels set to “0” is output to the first dilation processing unit 132. FIG. 4A is a diagram illustrating an example of edge data output by the edge extraction unit 131. In the figure, edge data corresponding to the character “L” is shown. An outline portion of a line constituting a character is set as an edge pixel. In the figure, it is shown by a solid line. The inside of the outline of the line constituting the character “L” is not an edge pixel.

  Edge data is input to the first dilation processing unit 132. The first dilation processing unit 132 expands the edge pixel by setting pixels around the edge pixel as edge pixels. The peripheral pixels include pixels that are separated from the edge pixels by a predetermined number. When the character has a certain thickness, the edge pixel is extracted as the outline of the character. The process by the first dilation processing unit 132 is a process of extending the edge pixels extracted as the outline of the character to the lines constituting the character. For this reason, the range of surrounding pixels may be a range that is ½ of the line width constituting the character. Alternatively, the peripheral pixels may be enlarged gradually, and the range of the peripheral pixels may be determined at the time when the two regions obtained by expanding the two edge pixels overlap. The first dilation processing unit 132 outputs edge data obtained by extending the edge pixels to the first erosion processing unit 133.

  FIG. 4B is a diagram illustrating an example of edge data output from the first dilation processing unit 132. The hatched portion in the figure indicates an edge pixel. The edge pixel shown in FIG. 4A is extended to surrounding pixels, the inside of the line constituting the character “L” is an edge pixel, and the line width is extended.

  The first erosion processing unit 133 reduces the line width of the character by making the edge pixel a pixel that is not an edge. Since the line width of the character is expanded by the first dilation processing unit 132, it is reduced to the original line width. The number of pixels to be reduced may be the same as the number of pixels expanded by the first dilation processing unit 132. As a result, the first erosion processing unit 133 sets the edge pixels inside the line forming the character as edge pixels as they are, and sets the edge pixels outside the line forming the character as pixels that are not edges. The first erosion processing unit 133 outputs the edge data obtained by shrinking the edge pixels to the second dilation processing unit 134 and the second erosion processing unit 135. The edge data output from the first erosion processing unit 133 is data in which the pixels constituting the character line are edge pixels and the other pixels are not edge pixels.

  FIG. 4C is a diagram illustrating an example of edge data output from the first erosion processing unit 133. The hatched portion in the figure indicates an edge pixel. A region including the edge pixel is a character region. The area formed by the edge pixels shown in FIG. 4B is reduced, and the line width of the character is reduced. The character size indicated by the edge pixel shown in FIG. 4C is the same as the character size indicated by the edge pixel shown in FIG. 4A.

  In this manner, the edge extraction unit 131, the first dilation processing unit 132, and the first erosion processing unit 133 extract character regions including characters from the image data.

  The second dilation processing unit 134 expands the edge pixel by using pixels around the edge pixel as edge pixels. Thereby, the line width of the character is expanded. Here, the peripheral pixels of the edge pixel are pixels separated from the edge pixel by one pixel. The second dilation processing unit 134 outputs edge data obtained by extending the line width of the character to the difference extraction unit 136.

  FIG. 4D is a diagram illustrating an example of edge data output from the second dilation processing unit 134. The hatched portion in the figure indicates an edge pixel. The area formed by the edge pixels shown in FIG. 4C is expanded, and the line width of the character is expanded.

  The second erosion processing unit 135 reduces the line width of the character by making the edge pixel a pixel that is not an edge. A predetermined number of pixels at both ends of a continuous edge pixel are pixels that are not edges. Here, one pixel at both ends of a continuous edge pixel is a pixel that is not an edge. The second erosion processing unit 135 outputs edge data obtained by reducing the line width of the character to the difference extraction unit 136.

  FIG. 4E is a diagram illustrating an example of edge data output from the second erosion processing unit 135. The hatched portion in the figure indicates an edge pixel. The area formed by the edge pixels shown in FIG. 4C is reduced, and the line width of the character is reduced.

  The difference extraction unit 136 subtracts the edge data output from the second erosion processing unit 135 from the edge data output from the second dilation processing unit 134 to extract a difference region. This difference area corresponds to the outline portion of the character.

  FIG. 4F is a diagram illustrating an example of edge data generated by the difference extraction unit 136. A hatched portion in the figure indicates a difference region (outline portion).

  As described above, the second dilation processing unit 134, the second erosion processing unit 135, and the difference extraction unit 136 extract the contour portion from the character region.

  The difference extraction unit 136 sets the pixels included in the difference region among the edge pixels that are edges in the edge data output from the second dilation processing unit 134 as the attribute of the contour portion (attribute value “00”), and the difference Pixels not included in the region are set as attributes in the character (attribute value “01”), and pixels not edged in the edge data output from the second dilation processing unit 134 are set as attributes other than characters (attribute value “11”). ]). This attribute value is assigned to each pixel and is output to the print data generation unit 110 as an attribute signal.

  FIG. 5 is a diagram illustrating the relationship between pixel attributes and attribute signals. Referring to FIG. 5, an attribute signal “00” is assigned to the attribute of the contour portion of the pixel, an attribute signal “01” is assigned to the attribute of the pixel in the character, and the pixel attribute The attribute signal “11” is assigned to the attribute other than the character.

  In the present embodiment, the attribute determination unit 109 includes an edge extraction unit 131, a first dilation processing unit 132, a first erosion processing unit 133, a second dilation processing unit 134, and a second erosion. Although the example comprised by the process part 135 and the difference extraction part 136 was shown, the attribute discrimination | determination part 109 is not restricted to this. The attribute discriminating unit 109 in this embodiment may discriminate the attribute by using another method for discriminating the outline portion of the character, the inner portion of the character, and the portion other than the character.

  FIG. 6 is a block diagram illustrating a configuration of the print data generation unit 110. Referring to FIG. 6, the print data generation unit 110 receives image data from C (cyan), M (magenta), Y (yellow), and K (black) from the color conversion unit 108, and from the attribute determination unit 109. An attribute signal is input. Here, the four image data of C, M, Y, and K are all subjected to the same processing, and therefore are collectively referred to as image data.

  Image data is input line by line to the print data generation unit 110. In addition, a buffer (FIFO) for storing a plurality of lines is provided, and processing can be executed in units of a plurality of lines. A buffer capable of storing all of the image data may be provided.

  The print data generation unit 110 includes pixel values output from the edge enhancement processing unit 121, the first and second smoothing processing units 122A and 122B, the edge enhancement processing unit 121, and the first and second smoothing processing units 122A and 122B. A first selection unit 123 that selects one of them, a gamma correction unit 124 that gamma-corrects the pixel value selected by the first selection unit 123, and first to third screen processes in which the gamma-corrected pixel value is input. Sections 125A, 125B, and 125C, and a second selection section 126 that selects one of the pixel values output from the first to third screen processing sections 125A, 125B, and 125C.

  The edge enhancement processing unit 121 receives image data. The edge enhancement processing unit 121 converts the value of the image data so as to enhance the edge of the image data. Specifically, the edge enhancement processing unit 121 includes an edge enhancement filter, and corrects the pixel value of the processing target pixel using the pixel value of the processing target pixel and the pixel values of surrounding pixels. Then, the edge-enhanced pixel value is output to the first selection unit 123.

  Image data is input to the first smoothing processing unit 122A. The first smoothing processing unit 122A converts the value of the image data so that the gradation change of the image data becomes gentle without reducing the resolution as much as possible. Specifically, the first smoothing processing unit 122A includes a smoothing filter that prioritizes resolution, and corrects the pixel value of the processing target pixel using the pixel value of the processing target pixel and the pixel values of surrounding pixels. To do. Then, the pixel value smoothed with priority given to the resolution is output to the first selection unit 123.

  Image data is input to the second smoothing processing unit 122B. The second smoothing processing unit 122B converts the value of the image data so that the change in gradation of the image data is smooth. Specifically, the first smoothing processing unit 122B includes a smoothing filter that prioritizes change in gradation, and uses the pixel value of the processing target pixel and the pixel values of surrounding pixels to process the pixel of the processing target pixel. Correct the value. Then, the pixel value that has been smoothed with priority on gradation is output to the first selection unit 123.

  The first selection unit 123 outputs the pixel value output from the edge enhancement processing unit 121, the pixel value output from the first smoothing processing unit 122A, and the second smoothing processing unit 122B according to the attribute signal input from the attribute determination unit 109. One of the pixel values to be selected is selected, and the selected pixel value is output to the gamma correction unit 124. Specifically, when the input attribute signal is “00” indicating the attribute of the contour portion, the pixel value output by the edge enhancement processing unit 121 is selected, and the input attribute signal indicates the attribute in the character. In the case of “01”, the pixel value output from the first smoothing processing unit 122A is selected, and in the case where the input attribute signal is “11” indicating an attribute other than characters, the second smoothing processing unit 122B outputs. Select a pixel value.

  The gamma correction unit 124 receives a pixel value from the selection unit 123 and an attribute signal from the attribute determination unit 109. The gamma correction unit 124 has a characteristic curve corresponding to the attribute of the pixel. Then, the gradation of the input pixel value is corrected according to the characteristic curve using the characteristic curve corresponding to the input attribute signal. Thereby, the gradation is corrected according to the attribute of the pixel. Then, the gamma correction unit 124 outputs the corrected pixel values to the first to third screen processing units 125A, 125B, and 125C.

  The first screen processing unit 125 </ b> A receives the gamma corrected pixel value from the gamma correction unit 124. The first screen processing unit 125A has an edge enhancement screen. The first screen processing unit 125A selects one screen corresponding to the pixel value from among a plurality of screens, and outputs the selected screen to the second selection unit 126.

  The second screen processing unit 125B receives the gamma corrected pixel value from the gamma correction unit 124. The second screen processing unit 125B has a screen in which the gradation of the image data changes gently without reducing the resolution as much as possible. The second screen processing unit 125B selects one screen corresponding to the pixel value from among a plurality of screens, and outputs the selected screen to the second selection unit 126.

  The third screen processing unit 125C receives the gamma corrected pixel value from the gamma correction unit 124. The third screen processing unit 125C includes a screen in which the gradation change is gentle. The third screen processing unit 125C selects one screen corresponding to the pixel value from among a plurality of screens, and outputs the selected screen to the second selection unit 126. The screen of the third screen processing unit 125C has fewer lines if the second screen processing unit 125B has the same gradation as the screen. In other words, the screen processing executed by the third screen processing unit 125C is suitable for execution on an area where a photograph or the like is represented. The screen processing executed by the second screen processing unit 125B is suitable for execution on an area where characters are represented.

  The second selection unit 126 receives screens from the first to third screen processing units 125A, 125B, and 125C, and receives attribute signals from the attribute determination unit 109. The second selection unit 126 selects one of the screens input from the first to third screen processing units 125A, 125B, and 125C according to the attribute signal input from the attribute determination unit 109, and selects the selected screen. Is output as image data. Specifically, when the input attribute signal is “00” indicating the attribute of the contour portion, the screen output by the first screen processing unit 125A is selected, and the input attribute signal indicates the attribute in the character. If “01”, the screen output by the second screen processing unit 125B is selected, and if the input attribute signal is “11” indicating an attribute other than characters, the screen output by the third screen processing unit 125C. Select.

  FIG. 7 is a flowchart showing a flow of image processing executed by the MFP in the present embodiment. Referring to FIG. 7, image data is input to the MFP (step S01). The image data may be either image data output by reading a document with the image reading apparatus 10 or image data transmitted from another computer via a communication interface.

  In the next step S02, characters are extracted from the image data input in step S01. This processing is the same as the processing executed by the edge extraction unit 131, the first dilation processing unit 132, and the first erosion processing unit 133 described above. As a result, edge data having the character shown in FIG. 4C as the edge pixel is generated.

  In the next step S03, the outline portion of the character is extracted from the character extracted in step S02. This processing is the same as the processing executed by the second dilation processing unit 134, the second erosion processing unit 135, and the difference extraction unit 136. As a result, edge data having the edge portion shown in FIG. 4F as the edge pixel is generated.

  Hereinafter, pixels included in the character extracted in step S02 and not included in the contour portion extracted in step S03 are referred to as intra-character pixels, and pixels included in the character are not included in the contour portion. Non-character pixels are referred to as pixels other than characters.

  In the next step S04, each pixel value of the RGB color system image data input in step S01 is converted into CMY color system image data. As a result, the image data to be processed in the subsequent processing becomes CMY color system image data.

  In the next step S05, one pixel is selected from the image data as a processing target pixel, and it is determined whether or not the processing target pixel is a character. If it is determined that the character is a character, the process proceeds to step S06, and if not, the process proceeds to step S13. The determination in step S05 is determined based on whether or not the pixel to be processed is included in the character extracted in step S02. Specifically, it is determined whether or not the processing target pixel is an edge pixel by using edge data having a character as an edge pixel.

  In step S06, it is determined whether or not the processing target pixel is a contour portion. If it is determined that the contour portion is determined, the process proceeds to step S07. If not, the process proceeds to step S10. The determination in step S06 is determined based on whether or not the pixel to be processed is included in the contour extracted in step S03. Specifically, it is determined whether or not the processing target pixel is an edge pixel by using edge data having an edge portion as an edge pixel.

  That is, when the process proceeds to step S07, the process target pixel is included in the contour portion, when the process proceeds to step S10, the process target pixel is a pixel in the character, and when proceeding to step S13, the process target pixel is processed. Is a pixel other than a character.

  In step S07, edge emphasis processing for emphasizing the edge of the processing target pixel is performed. Specifically, the pixel value of the processing target pixel is corrected from the pixel value of the processing target pixel and the pixel values of surrounding pixels using an edge enhancement filter.

  In the next step S08, the pixel value of the pixel to be processed corrected in step S07 is gamma-corrected using a characteristic curve prepared for edge enhancement.

  In the next step S09, one screen corresponding to the pixel value of the processing target pixel subjected to gamma correction is selected from the screens prepared in advance for edge enhancement. Then, the process proceeds to step S16.

  In step S10, a smoothing process giving priority to resolution is performed on the processing target pixel. Specifically, the pixel value of the processing target pixel is corrected based on the pixel value of the processing target pixel and the pixel values of surrounding pixels using a smoothing filter that prioritizes resolution.

  In the next step S11, the pixel value of the processing target pixel subjected to the smoothing process in step S10 is gamma-corrected using the characteristic curve prepared for the pixels in the character.

  In the next step S12, one screen corresponding to the pixel value of the processing target pixel subjected to gamma correction is selected from screens prepared in advance for the pixels in the character. Then, the process proceeds to step S16.

  In step S13, a smoothing process is performed with priority given to the gradation for the processing target pixel. Specifically, the pixel value of the processing target pixel is corrected based on the pixel value of the processing target pixel and the pixel values of surrounding pixels using a smoothing filter that prioritizes gradation.

  In the next step S14, the pixel value of the processing target pixel subjected to the smoothing process in step S13 is gamma-corrected using a characteristic curve prepared for pixels other than characters.

  In the next step S15, one screen corresponding to the pixel value of the pixel to be processed subjected to gamma correction is selected from screens prepared for pixels other than characters. Then, the process proceeds to step S16.

  In step S16, it is determined whether or not there is a pixel to be processed next. If true, the process returns to step S05, the next pixel is selected as the processing target pixel, and the above-described processing is repeatedly executed. If not, the process proceeds to step S17.

  In step S17, the screen-processed image data is output. As a result, an image is formed by the image forming apparatus 20, and an image is formed on a recording medium such as paper based on the image data.

  As described above, in the MFP according to the first embodiment, the screen processing for emphasizing the edge is performed on the outline portion of the character extracted from the image data, and the screen processing with priority on the resolution is performed on the inner portion of the character. Executes screen processing that prioritizes gradation for parts other than characters. For this reason, the outline portion of the character is edge-enhanced, and gradation can be expressed in the area inside the character in addition to the outside of the character. For this reason, it is possible to form an image in which the outline of the character is clear and the character has gradation. Furthermore, screen processing with priority given to resolution is executed inside the character, and screen processing with priority given to gradation outside the character is executed, so that the character can be expressed clearly.

<Modification of attribute discrimination unit>
The attribute determination unit 109 described above extracts characters from the image data. The deformed attribute discriminating unit 109A discriminates pixel attributes by extracting an edge and a rectangular edge region including the edge without extracting a character.

  FIG. 8 is a block diagram showing the configuration of the modified attribute discriminating unit 109A. FIG. 9 is a diagram illustrating an example of edge data generated by the modified attribute determination unit 109A. Referring to FIGS. 8 and 9, attribute determination unit 109A includes an edge extraction unit 131, a character attribute region extraction unit 137, and an attribute signal generation unit 138.

  The edge extraction unit 131 receives brightness data. The edge extraction unit 131 includes a first-order differential filter and a second-order differential filter, and executes filter processing using a first-order differential filter for lightness data and filter processing using a second-order differential filter for lightness data. Then, the pixel determined to be an edge (edge pixel) by the filter processing using the primary differential filter and the pixel (edge pixel) determined to be the edge by the filter processing using the secondary differential filter are set to “1”. Then, edge data in which other pixels are set to “0” is output to the character attribute region extraction unit 137 and the attribute signal generation unit 138. FIG. 9A is a diagram illustrating an example of edge data output by the edge extraction unit 131. In the figure, edge data corresponding to the character “L” is shown. An outline portion of a line constituting a character is set as an edge pixel. In the figure, it is shown by a solid line. The inside of the outline of the line constituting the character “L” is not an edge pixel.

  The character attribute area extraction unit 137 receives edge data from the edge extraction unit 131. Then, a rectangular area circumscribing the edge pixel is extracted from the input edge data as a character attribute area. Then, character attribute area data in which the pixel included in the extracted character attribute area is set to “1” and the other pixels are set to “0” is output to the attribute signal generation unit 138. FIG. 9B is a diagram illustrating an example of character attribute area data output by the character attribute area extraction unit 137. In the figure, the hatched portion indicates the character attribute area. The other area is an area where, for example, a photograph or the like other than characters is displayed.

  The attribute signal generation unit 138 generates an attribute signal from the input edge data and character attribute area data, and outputs the generated attribute signal to the print data generation unit 110. The attribute signal generation unit 138 assigns the attribute signal “00” to the edge pixels included in the character attribute area, assigns the attribute signal “01” to the pixels included in the character attribute area but not the edge pixels, and is included in the character attribute area. The attribute signal “11” is assigned to the non-existing pixel.

  FIG. 10 is a diagram illustrating a relationship among pixel attributes, edges, and attribute signals. Compared with FIG. 5, the attribute signal “00” having the same attribute as that of the contour portion is assigned to the edge pixel included in the character attribute region, and the attribute signal in the character is included in the pixel included in the character attribute region but not the edge pixel. “01” is assigned, and an attribute signal “11” other than a character is assigned to a pixel not included in the character attribute area.

  Therefore, according to the modified attribute discriminating unit 109A, the print data generating unit 110 selects the pixel value screen-processed by the first screen processing unit 125A as the edge pixel in the character attribute area, and the pixels other than the edge pixel. Selects the pixel value screen-processed by the second screen processing unit 125B, and for pixels other than the character attribute area, selects the pixel value screen-processed by the third screen processing unit 125C.

  The modified attribute discriminating unit 109A uses the edge pixel as the outline portion of the character, and distinguishes the pixel of the outline portion, the pixel of the character attribute area other than the edge pixel, and the pixel other than the character attribute area. However, the attribute determination unit 109A is not limited to this. The modified attribute discriminating unit 109A discriminates the attribute by using another method for distinguishing the outline portion of the character, the inner and outer peripheral portions of the character, and the portion where the photograph is represented. May be.

  FIG. 11 is a flowchart showing a flow of image processing executed by the MFP to which the modified attribute determination unit 109A is applied. Referring to FIG. 11, image data is input to the MFP (step S21). In the next step S22, edge pixels are extracted from the image data input in step S01. This process is the same as the process executed by the edge extraction unit 131 described above. As a result, the edge data shown in FIG. 9A is generated.

  In the next step S23, a rectangular character attribute area circumscribing the edge pixel extracted in step S02 is extracted. This process is the same as the process executed by the character attribute area extraction unit 137. As a result, the character attribute area data shown in FIG. 9B is generated.

  In the next step S24, each pixel value of the RGB color system image data input in step S01 is converted into CMY color system image data. As a result, the image data to be processed in the subsequent processing becomes CMY color system image data.

  In the next step S25, one pixel is selected from the image data as a processing target pixel, and it is determined whether or not the processing target pixel is included in the character attribute area. If it is determined that it is included in the character attribute area, the process proceeds to step S26, and if not, the process proceeds to step S33.

  In step S26, it is determined whether the processing target pixel is an edge pixel. If it is determined that the pixel to be processed is an edge pixel, the process proceeds to step S27, and if not, the process proceeds to step S30.

  The processing in steps S27 to S37 is the same as the processing in steps S07 to S17 of the image processing shown in FIG. 7, and therefore description thereof will not be repeated here.

  As described above, the screen processing for emphasizing the edge is performed on the outline portion of the character extracted from the image data, the screen processing giving priority to the resolution is performed on the character inner portion and the character attribute area outside the character, and the character Screen processing that prioritizes gradation is executed for portions other than the attribute region. For this reason, the outline portion of the character is edge-enhanced, and gradation can be expressed in the area inside the character in addition to the outside of the character. For this reason, it is possible to form an image in which the outline of the character is clear and the character has gradation.

<Second Embodiment>
The MFP in the second embodiment is obtained by changing the attribute determination unit 109 and the print data generation unit 110 in the first embodiment. Since other configurations are the same as those of the MFP in the first embodiment, different points will be mainly described here.

  FIG. 12 is a block diagram illustrating a configuration of the attribute determination unit of the MFP according to the second embodiment. FIG. 13 is a diagram illustrating an example of edge data generated by the attribute determination unit.

  The attribute determination unit 109B generates an attribute signal from the inner edge pixel and the outer edge pixel, and the inner edge extraction unit 139 that extracts the inner edge pixel from the brightness data, the outer edge extraction unit 140 that extracts the outer edge pixel, and the inner edge pixel and the outer edge pixel. Part 141.

  The inner edge extraction unit 139 receives lightness data. The inner edge extraction unit 139 includes a filter for detecting the inner edge, and executes filter processing using the inner edge filter for the brightness data. Then, the inner edge data in which the pixel (inner edge pixel) determined to be the inner edge by the filter processing using the inner edge filter is set to “1” and the other pixels are set to “0” is output to the synthesis unit 141. The inner edge is a pixel that forms the inside of the outline of a character. Here, referring to FIG. 13, a region 152 having a width corresponding to one pixel inside the character outline 151 is the inner edge.

  The outer edge extraction unit 140 receives brightness data. The outer edge extraction unit 140 includes a filter for detecting an outer edge, and executes a filtering process using the outer edge filter for brightness data. Then, the outer edge data in which the pixel (outer edge pixel) determined as the outer edge by the filter processing using the outer edge filter is set to “1” and the other pixels are set to “0” is output to the synthesis unit 141. An outer edge is a pixel that forms the outside of the outline of a character. Here, referring to FIG. 13, a region 153 having a width corresponding to one pixel outside the character outline 151 is an outer edge.

  The synthesizer 141 receives the inner edge data and the outer edge data. The synthesizing unit 141 is an OR circuit, and is composed data in which the value of the pixel set to “1” in any of the inner edge data and the outer edge data is set to “1”, and the values of the other pixels are set to “0”. Is generated. Then, an attribute signal “00” is assigned to a pixel (inner edge pixel or outer edge pixel) whose pixel value is “1” in the synthesized data, and an attribute signal “00” is assigned to a pixel whose pixel value is “0” in the synthesized data. 11 "is assigned.

  FIG. 14 is a diagram illustrating the relationship between edges and attribute signals. Compared with FIG. 5, the attribute signal “00” having the same attribute as that of the contour portion is assigned to the inner edge pixel or the outer edge pixel, and the attribute signal “non-character” is assigned to the pixel of the background portion that is neither the inner edge nor the outer edge. 11 "is assigned.

  FIG. 15 is a diagram illustrating a configuration of a print data generation unit according to the second embodiment. Referring to FIG. 15, print data generation unit 110A determines one of the pixel values output from edge enhancement processing unit 121, second smoothing processing unit 122B, edge enhancement processing unit 121, and second smoothing processing unit 122B. A first selection unit 123A to select, a gamma correction unit 124A to gamma-correct the pixel value selected by the first selection unit 123A, and first and third screen processing units 125A to which the gamma-corrected pixel value is input. 125C and a second selection unit 126A that selects one of the pixel values output from the first and third screen processing units 125A and 125C.

  The first selection unit 123A selects one of the pixel value output from the edge enhancement processing unit 121 and the pixel value output from the second smoothing processing unit 122B according to the attribute signal input from the attribute determination unit 109B. The selected pixel value is output to the gamma correction unit 124A. Specifically, when the input attribute signal is “00” indicating the inner edge pixel or the outer edge pixel, the pixel value output by the edge enhancement processing unit 121 is selected, and the input attribute signal is the inner edge pixel. However, in the case of “11” indicating that the pixel is not an outer edge pixel, the pixel value output by the second smoothing processing unit 122B is selected.

  The gamma correction unit 124A receives the pixel value from the selection unit 123A and the attribute signal from the attribute determination unit 109B. The gamma correction unit 124A corrects the gradation of the input pixel value according to the characteristic curve using the characteristic curve corresponding to the input attribute signal. Thereby, the gradation is corrected according to the attribute of the pixel. Then, the gamma correction unit 124A outputs the corrected pixel value to the first and third screen processing units 125A and 125C.

  The second selection unit 126A receives screens from the first and third screen processing units 125A and 125C, and receives attribute signals from the attribute determination unit 109B. The second selection unit 126A selects one of the screens input from the first and third screen processing units 125A and 125C according to the attribute signal input from the attribute determination unit 109B, and displays the selected screen as an image. Output as data. Specifically, when the input attribute signal is “00” indicating the inner edge pixel or the outer edge pixel, the screen output by the first screen processing unit 125A is selected, and the input attribute signal is the inner edge pixel. However, in the case of “11” indicating that the pixel is not an outer edge pixel, the screen output by the third screen processing unit 125C is selected.

  Note that the attribute determination unit 109B in the second embodiment uses the inner edge pixel and the outer edge pixel as the contour portion of the character, and distinguishes the pixel of the contour portion from the pixels other than the contour portion. The attribute determination unit 109B is not limited to this. The attribute discriminating unit 109B may discriminate the attribute by using another method for distinguishing the pixel in the outline portion of the character from the other pixels. For example, an edge pixel extracted using one edge extraction filter, such as only the inner edge pixel and only the outer edge pixel, may be used as the contour portion.

  FIG. 16 is a flowchart showing the flow of image processing executed by the MFP in the second embodiment. Referring to FIG. 16, image data is input to the MFP (step S41). In the next step S42, edge pixels are extracted from the image data input in step S01. This process is the same as the process executed by the inner edge extraction unit 139 and the outer edge extraction unit 140 described above. Thereby, edge data in which the inner edge pixel and the outer edge pixel shown in FIG. 13 are “1” and the other pixels are “0” is generated.

  In the next step S43, each pixel value of the RGB color system image data input in step S01 is converted into CMY color system image data. As a result, the image data to be processed in the subsequent processing becomes CMY color system image data.

  In the next step S44, one pixel is selected from the image data as a processing target pixel, and it is determined whether the processing target pixel is an inner edge pixel or an outer edge pixel. If it is determined that the pixel is an inner edge pixel or an outer edge pixel, the process proceeds to step S45, and if not, the process proceeds to step S48.

  In step S45, an edge enhancement process for enhancing an edge on the processing target pixel is performed. Specifically, the pixel value of the processing target pixel is corrected from the pixel value of the processing target pixel and the pixel values of surrounding pixels using an edge enhancement filter. In the next step S46, the pixel value of the processing target pixel corrected in step S45 is gamma-corrected using a characteristic curve prepared for edge enhancement. In the next step S47, one screen corresponding to the pixel value of the processing target pixel subjected to gamma correction is selected from the screens prepared in advance for edge enhancement. Then, the process proceeds to step S51.

  In step S48, a smoothing process is performed with priority given to gradation for the processing target pixel. Specifically, the pixel value of the processing target pixel is corrected based on the pixel value of the processing target pixel and the pixel values of surrounding pixels using a smoothing filter that prioritizes gradation. In the next step S49, the pixel value of the processing target pixel subjected to the smoothing process in step S48 is gamma-corrected using a characteristic curve prepared for pixels other than characters. In the next step S50, one screen corresponding to the pixel value of the processing target pixel subjected to gamma correction is selected from screens prepared in advance for pixels other than characters. Then, the process proceeds to step S51.

  In step S51, it is determined whether or not there is a pixel to be processed next. If true, the process returns to step S44, the next pixel is selected as the processing target pixel, and the above-described processing is repeatedly executed. If not, the process proceeds to step S52. In step S52, the screen-processed image data is output. As a result, an image is formed by the image forming apparatus 20, and an image is formed on a recording medium such as paper based on the image data.

<Modification of attribute discrimination unit>
FIG. 17 is a diagram illustrating a configuration of a modified attribute determination unit of the MFP according to the second embodiment. Referring to FIG. 17, the modified attribute determination unit 109 </ b> C includes an inner edge extraction unit 139.

  As described above, in the MFP according to the second embodiment, screen processing for emphasizing edges is performed on edge pixels of image data, and screen processing is performed with priority given to gradation on pixels that are not edge pixels. For this reason, the outline portion of the character is edge-enhanced, and an image in which gradation is expressed in the inside and outside regions of the character is obtained. For this reason, it is possible to form an image in which the outline of the character is clear and the character has gradation.

  The embodiment disclosed this time 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 is a perspective view of an MFP according to a first embodiment of the present invention. 2 is a block diagram showing a configuration of an MFP in the present embodiment. FIG. It is a block diagram which shows the structure of an attribute discrimination | determination part. It is a figure which shows an example of the edge data produced | generated by the attribute discrimination | determination part. It is a figure which shows the relationship between the attribute of a pixel, and an attribute signal. 3 is a block diagram illustrating a configuration of a print data generation unit 110. FIG. 6 is a flowchart showing a flow of image processing executed by the MFP in the present embodiment. It is a block diagram which shows the structure of the modified attribute discrimination | determination part. It is a figure which shows an example of the edge data produced | generated by the transformed attribute discrimination | determination part. It is a figure which shows the relationship between the attribute of a pixel, an edge, and an attribute signal. 6 is a flowchart illustrating a flow of image processing executed by an MFP to which a modified attribute determination unit is applied. FIG. 10 is a block diagram illustrating a configuration of an attribute determination unit of an MFP according to a second embodiment. It is a figure which shows an example of the edge data produced | generated by the attribute discrimination | determination part. It is a figure which shows the relationship between an edge and an attribute signal. It is a figure which shows the structure of the print data generation part in 2nd Embodiment. 10 is a flowchart illustrating a flow of image processing executed by the MFP according to the second embodiment. FIG. 10 is a diagram illustrating a configuration of a modified attribute determination unit of an MFP according to a second embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Image reader, 20 Image forming apparatus, 102 Image composition part, 104 Shading correction part, 105 Interline correction part, 106 Chromatic aberration correction part, 107 Scaling / movement processing part, 108 Color conversion part, 109, 109A, 109B, 109C Attribute discrimination unit, 110, 110A Print data generation unit, 121 Edge enhancement processing unit, 122A First smoothing processing unit, 122B Second smoothing processing unit, 123, 123A First selection unit, 124, 124A Gamma correction unit, 125A first 1 screen processing unit, 125B second screen processing unit, 125C third screen processing unit, 126 second selection unit, 126A selection unit, 131 edge extraction unit, 132 first dilation processing unit, 133 first erosion processing unit, 134 Second Dilation Processing Unit 135 second erosion processing unit, 136 differential extraction module, 137 the character region extracting unit, 138 attribute signal generating section, 139 in the edge extraction unit 140 the outer edge extracting unit, 141 combining unit, 111 a printer I / F.

Claims (10)

Image data input means for inputting image data;
Attribute data acquisition means for acquiring attribute data for distinguishing a character region including a pixel constituting a character and a contour pixel constituting a contour portion of the character from other pixels;
Screen processing means for executing screen processing on the image data based on the attribute data;
The screen processing means performs a first screen process on the contour pixel of the image data, and executes a second screen process on a pixel that is included in the character area of the image data and is not the contour pixel. An image processing apparatus that performs a third screen process on pixels that are not included in the character area of the image data. The first screen processing is edge enhancement processing;
The second screen process is a screen process giving priority to resolution,
The image processing apparatus according to claim 1, wherein the third screen processing is screen processing giving priority to gradation. The attribute data acquisition means includes character area extraction means for extracting the character area from the input image data,
The image processing apparatus according to claim 1, further comprising: a contour pixel extracting unit that extracts a contour pixel that forms a contour portion of a character based on the extracted character region. The character region extraction means includes edge pixel extraction means for extracting edge pixels from the input image data;
The image processing apparatus according to claim 3, further comprising: a character area determining unit that extracts a character area including the edge pixels and pixels surrounded by the edge pixels. The contour pixel extraction means includes an expansion means for extending the character area extracted by the character area extraction means;
Contraction means for contracting the character region extracted by the character pixel extraction means;
And a contour pixel determining unit including a pixel that is included in the character region expanded by the expansion unit and not included in the character region contracted by the contraction unit as a contour pixel. The image processing apparatus described. Attribute data acquisition means, edge pixel extraction means for extracting edge pixels from the input image data as the contour pixels,
The image processing apparatus according to claim 1, further comprising: a character attribute area extracting unit that extracts a rectangular character attribute area including the extracted edge pixel as the character area. Further comprising gamma correction means for correcting the gradation of the image data;
The gamma correction means may be applied to each of the outline pixel of the image data, the pixel that is included in the character area of the image data and is not the outline pixel, and the pixel that is not included in the character area of the image data. The image processing apparatus according to claim 1, wherein gamma correction is performed according to a characteristic curve prepared in advance. Inputting image data;
Obtaining attribute data for distinguishing a character region including pixels constituting a character and a contour pixel constituting a contour portion of the character from other pixels;
Performing a first screen process on the contour pixels of the image data;
Performing a second screen process on pixels that are included in the character region of the image data and that are not the contour pixels;
The image processing program which makes a computer perform the step which performs a 3rd screen process to the pixel which is not contained in the said character area of the said image data. Image data input means for inputting image data;
Edge pixel extraction means for extracting edge pixels from the input image data;
Screen processing means for executing screen processing on the image data,
The image processing apparatus, wherein the screen processing means executes edge enhancement processing on the edge pixels of the image data, and executes screen processing giving priority to resolution to pixels not extracted as the edge pixels of the image data. Inputting image data;
Extracting edge pixels from the input image data;
Performing edge enhancement processing on the edge pixels of the image data;
An image processing program that causes a computer to execute a screen process that prioritizes resolution for pixels that are not extracted as the edge pixels of the image data.

Images