JP2007013566A - Image processor and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate a monochrome image approximate to an impression of characters in a color image. <P>SOLUTION: A CPU 710 of a control unit 700 of a copying machine 1 is provided with: an area division part 711 for dividing the color image into a character area to be an area indicating characters and a background area excluding the character area; a data conversion part 712 for converting a pixel value of the color image into a luminance component to be a component indicating luminance and a color difference component to be a component indicating the color difference; a luminance decision part 713 for deciding whether or not a luminance difference to be a difference between the luminance component in the character area and the luminance component in the background area is equal to a first preset threshold value or smaller; and an outline emphasis part 714 for changing the luminance component of the specified number of pixels corresponding to an edge part of the character area just for the first specified value in the direction that a difference from the luminance component in the background area becomes larger. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing apparatus and an image forming apparatus that convert pixel values of each color of a color image into pixel values of a monochrome image so that a color image including characters is a monochrome image.

  In an image forming apparatus such as a copying machine, it is often used to output a color image as a monochrome (black and white) image on a recording sheet from the viewpoint of cost. At this time, if the luminance of the character area and the background area, which is the background area, is the same (or approximate), the character area cannot be read because it is converted to a monochrome image with the same blackness ( Or, it becomes difficult to read).

To solve this problem, a luminance difference that is the difference between the luminance of the character area and the luminance of the background area is obtained, and when the luminance difference is equal to or less than a predetermined luminance difference determination value, the luminance difference of the character area is increased. It has been proposed to change so as to be (see Patent Document 1).
JP 2003-283848 A

  According to the above method, even when the brightness of the character area and the background area are close to each other, it can be read and the above problem can be solved. However, with regard to the sharpness of characters, there is a case where the impression in a color image and the impression in a monochrome image are greatly different.

  For example, when the character area and the background area are opposite colors, such as when the background area is magenta and the character area is cyan, the characters are clearly visible in the color image. When the character region and the background region are similar colors, such as when the background region and the character region are magenta with slightly different hues, the characters in the color image appear unclear.

  The present invention has been made in view of the above problems, and provides an image processing apparatus and an image forming apparatus capable of generating a monochrome image that approximates the impression of characters in a color image.

  The image processing device according to claim 1 is an image processing device that converts pixel values of each color of the color image into pixel values of a monochrome image so that a color image including characters becomes a monochrome image. A region dividing means that divides a character region that represents a character and a background region that excludes the character region; a luminance value that is a component that represents luminance; and a component that represents a color difference. A data conversion means for converting to a color difference component, and whether or not a luminance difference that is a difference between the luminance component of the character region and the luminance component of the background region is equal to or less than a first preset threshold value The luminance component of the predetermined number of pixels corresponding to the outer edge portion of the character region is greatly different from the luminance component of the background region when it is determined that the luminance determination means is equal to or less than the first threshold value. In the direction It is characterized by comprising a contour enhancement means for changing the predetermined value of 1.

  According to the above configuration, the color image including the character is divided into the character region which is a region representing the character and the background region which is a region excluding the character region by the region dividing means. Further, the pixel value of the color image is converted into a luminance component which is a component representing luminance and a color difference component which is a component representing color difference by the data conversion means. Then, the luminance determination means determines whether or not a luminance difference, which is a difference between the luminance component of the character area and the luminance component of the background area, is equal to or smaller than a preset first threshold value. Further, the direction in which the brightness enhancement of the predetermined number of pixels corresponding to the outer edge portion of the character area is greatly different from the brightness component of the background area by the outline emphasizing unit when it is determined that it is equal to or less than the first threshold. Is changed by the first predetermined value.

  Accordingly, when it is determined that the luminance difference that is the difference between the luminance component of the character area and the luminance component of the background area is equal to or less than the first threshold, the luminance of a predetermined number of pixels corresponding to the outer edge of the character area Since the component is changed by the first predetermined value in a direction in which the difference from the luminance component of the background area increases, the boundary between the character area and the background area can be identified by the outer edge of the character area, and the character area Since the luminance components of the pixels other than the outer edge of the image are not changed, a monochrome image that approximates the impression of characters in a color image is generated.

  The image processing apparatus according to claim 2, wherein the contour emphasizing unit includes a contour width setting unit that sets the predetermined number according to at least one of the color difference component of the character region and the color difference component of the background region. It is said.

  According to the above configuration, the predetermined number, which is the number of pixels whose luminance component is changed, is set by the contour width setting unit according to at least one of the color difference component of the character area and the color difference component of the background area. The luminance component of a predetermined number of pixels set in accordance with at least one of the color difference component and the background region color difference component is changed.

  Accordingly, since the number of pixels whose luminance component is changed is set according to at least one of the color difference component of the character area and the color difference component of the background area, a monochrome image that further approximates the impression of the character in the color image is generated. The

  The image processing apparatus according to claim 3, wherein the contour width setting unit sets the predetermined number according to a color difference component difference which is a difference between a color difference component of the character area and a color difference component of a background area. It is said.

  According to the above configuration, the predetermined number is set by the contour width setting means according to the color difference component difference which is the difference between the color difference component of the character area and the color difference component of the background area.

  Therefore, the predetermined number, which is the number of pixels whose luminance component is changed, is set according to the color difference component difference that is the difference between the color difference component of the character area and the color difference component of the background area, so that the character impression in the color image A monochrome image that more closely approximates to is generated.

  5. The image processing apparatus according to claim 4, wherein the contour emphasizing unit includes a contour density setting unit that sets the first predetermined value according to at least one of a color difference component of the character region and a color difference component of the background region. It is characterized by that.

  According to the above configuration, the first predetermined value is set by the contour density setting means according to at least one of the color difference component of the character area and the color difference component of the background area.

  Therefore, since the first predetermined value, which is the amount of change in the luminance component, is set according to at least one of the color difference component of the character area and the color difference component of the background area, the monochrome that further approximates the character impression in the color image An image is generated.

  6. The image processing apparatus according to claim 5, wherein the contour density setting unit sets the first predetermined value according to a color difference component difference that is a difference between a color difference component of the character area and a color difference component of a background area. It is characterized by that.

  According to the above configuration, the first predetermined value is set by the contour density setting means according to the color difference component difference that is the difference between the color difference component of the character area and the color difference component of the background area.

  Accordingly, since the first predetermined value that is the change amount of the luminance component is set according to the color difference component difference that is the difference between the color difference component of the character region and the color difference component of the background region, the character impression in the color image A monochrome image that more closely approximates to is generated.

  The image processing apparatus according to claim 6, wherein a color difference component difference, which is a difference between the color difference component of the character area and the color difference component of the background area, is equal to or greater than a preset second threshold value. A color difference determining unit; and a character emphasizing unit that changes a luminance component by a second predetermined value for a pixel inside the character region when it is determined to be equal to or greater than the second threshold value. Yes.

  According to the above configuration, the color difference determination unit determines whether or not the color difference component difference, which is the difference between the color difference component of the character area and the color difference component of the background area, is equal to or greater than a preset second threshold value. . And when it determines with it being more than a 2nd threshold value, a brightness | luminance component is changed only 2nd predetermined value about the pixel inside a character area by a character emphasis means.

  Therefore, when it is determined that the color difference component difference, which is the difference between the color difference component of the character area and the color difference component of the background area, is equal to or greater than the second threshold, the luminance component of the pixel inside the character area is the second luminance component. Since only the predetermined value is changed, the color difference component difference is reflected in the luminance of the pixels inside the character area, and a monochrome image that further approximates the impression of the character in the color image is generated.

  The image processing apparatus according to claim 7, wherein the character emphasis unit includes a density setting unit that sets the second predetermined value in association with the color difference component difference.

  According to the above configuration, the second predetermined value is set in association with the color difference component difference by the density setting means.

  Therefore, since the second predetermined value, which is the amount of change in the luminance component of the pixels inside the character area, is set in association with the color difference component difference, the color difference component difference more accurately matches the luminance of the pixels inside the character area. A monochrome image that is reflected and more closely approximates the impression of characters in the color image is generated.

  An image processing apparatus according to an eighth aspect is characterized in that the density setting means sets the second predetermined value in proportion to the color difference component difference.

  According to the above configuration, since the second predetermined value is set in proportion to the color difference component difference by the density setting means, the color difference component difference is more accurately reflected on the luminance of the pixels in the character area, and the color image A monochrome image that more closely approximates the impression of the character at is generated.

  The image processing apparatus according to claim 9 is characterized in that the data conversion means converts the data into a YUV format comprising a Y component as a luminance component and a U component and a V component as color difference components.

  According to the above configuration, the data conversion means converts the Y component that is the luminance component and the YUV format that includes the U component and the V component that are the color difference components. Easily converted into ingredients.

  An image forming apparatus according to claim 10 is an image processing apparatus according to any one of claims 1 to 9, an image data storage unit that stores a monochrome image generated by the image processing apparatus, and the image data storage. Printing means for reading out the pixel value of the monochrome image from the means and printing the monochrome image on the recording paper.

  According to the above configuration, the image processing apparatus according to any one of claims 1 to 9 performs image processing on the color image to generate a monochrome image. Then, the monochrome image generated by the image processing apparatus is stored in the image data storage means. Further, the printing unit reads out the pixel value of the monochrome image from the image data storage unit, and the monochrome image is printed on the recording paper.

  Accordingly, since the image processing apparatus according to any one of claims 1 to 9 is provided, a monochrome image that approximates the impression of characters in a color image is printed on the recording paper.

  According to the first aspect of the present invention, the boundary between the character region and the background region can be identified by the outer edge portion of the character region, and the luminance component of the pixels other than the outer edge portion of the character region is not changed. It is possible to generate a monochrome image that approximates the impression of characters in

  According to the invention described in claim 2, since the number of pixels whose luminance component is changed is set according to at least one of the color difference component of the character region and the color difference component of the background region, the character impression in the color image A monochrome image that more closely approximates can be generated.

  According to the third aspect of the present invention, the predetermined number that is the number of pixels whose luminance component is changed is set according to the color difference component difference that is the difference between the color difference component of the character area and the color difference component of the background area. Therefore, it is possible to generate a monochrome image that further approximates the impression of characters in a color image.

  According to the fourth aspect of the present invention, since the first predetermined value that is the amount of change in the luminance component is set according to at least one of the color difference component of the character area and the color difference component of the background area, It is possible to generate a monochrome image that more closely approximates the impression of the character.

  According to the fifth aspect of the present invention, the first predetermined value that is the change amount of the luminance component is set according to the color difference component difference that is the difference between the color difference component of the character area and the color difference component of the background area. Therefore, it is possible to generate a monochrome image that further approximates the impression of characters in a color image.

  According to the sixth aspect of the present invention, when it is determined that the color difference component difference that is the difference between the color difference component of the character region and the color difference component of the background region is equal to or greater than the second threshold value, Since the luminance component of the pixel is changed by the second predetermined value, the color difference component difference is reflected in the luminance of the pixel inside the character region, and a monochrome image that further approximates the impression of the character in the color image can be generated.

  According to the seventh aspect of the invention, since the second predetermined value, which is the amount of change in the luminance component of the pixels inside the character area, is set in association with the color difference component difference, the color difference component difference is It is possible to generate a monochrome image that is more accurately reflected on the brightness of the internal pixels and more closely approximates the impression of characters in a color image.

  According to the eighth aspect of the invention, since the second predetermined value is set in proportion to the color difference component difference, the color difference component difference is more accurately reflected on the luminance of the pixels in the character area, and the color image It is possible to generate a monochrome image that more closely resembles the impression of the character.

  According to the ninth aspect of the present invention, since the Y component that is the luminance component and the U component and the V component that are the color difference components are converted into the YUV format, the pixel value of the color image is converted into the luminance component and the color difference. Can be easily converted into components.

  According to the tenth aspect of the present invention, a monochrome image that approximates the impression of characters in a color image can be printed on recording paper.

  Embodiments according to the present invention will be described below with reference to the drawings. FIG. 1 is a side view of a copying machine as an example of an image forming apparatus according to the present invention. The copying machine 1 includes a main unit 200, a sheet post-processing unit 300 disposed on the left side of the main unit 200, an operation unit 400 for a user to input various operation commands and the like, and an upper part of the main unit 200. A document reading unit 500 (corresponding to a part of the document reading unit) provided and a document feeding unit 600 provided above the document reading unit 500 are provided.

  The operation unit 400 includes an operation panel 401, a start key 402, a numeric keypad 403, and the like. The operation panel 401 displays various operation screens and a liquid crystal display (LCD) 401a that displays various operation buttons and the like for the user to input various operation commands, and the LCD 401a. The touch panel 401b and the like disposed on the touch panel. The start key 402 is used for the user to input a print execution command and the like, and the ten key 403 is used for inputting the number of copies to be printed.

  The touch panel 401b is a rectangular thin layered body, which is configured by covering a pressure-sensitive material made of a linear transparent material at predetermined pitches in the vertical and horizontal directions with a transparent cover, etc. on the screen of the LCD 401a. It is affixed to. And it is comprised so that it can determine which button was instruct | indicated from the address and press position of a button which urges selection etc. which are displayed on the LCD 401a screen.

  The document feeding unit 600 includes a document placement unit 601, a document discharge unit 602, a paper feed roller 603, a document transport path 604, a contact glass 605, and the like, and the document reading unit 500 includes a scanner 501 and the like.

  The paper feed roller 603 feeds out the original set on the original placement unit 601, and the original conveyance path 604 conveys the delivered original one by one on the scanner 501 one by one. The scanner 501 includes a direction imaging device (CCD; Charge Coupled Device) arranged in a line in a direction orthogonal to the document conveyance direction, and capable of receiving, for example, each color of RGB. Reading is performed in units of pixels in the transport direction (sub-scanning direction) while repeating scanning (main scanning), and the document after reading is discharged to the document discharge unit 602. In a mode in which the scanner 501 reads a document while being placed on the contact glass 605, the drive mechanism for reciprocating movement causes the scanner 501 to move in the direction indicated by the arrow A along the contact glass 605 (right direction in the drawing: sub-scanning direction). The document is read while moving.

  The main body 200 includes a plurality of (here, three) paper feed cassettes 201a to 201c, a plurality of (here, three) paper feed rollers 202a to 202c, a manual paper feed unit 201d, and a manual paper feed roller 202d. , Transfer roller 203, intermediate transfer roller 204, photosensitive drum 205, exposure device 206, developing devices 207Y and 207M for developing colors of yellow (Y), magenta (M), cyan (C), and black (K). 207C, 207K, a fixing roller 208, a discharge port 209, a discharge tray 210, a recording paper conveyance path 211, and the like.

  The photosensitive drum 205 is uniformly charged by a charging device (not shown) while rotating in the direction of the arrow. The exposure device 206 converts the modulation signal generated based on the image data of the original read by the original reading unit 500 into a laser beam and outputs it, and forms an electrostatic latent image on the photosensitive drum 205 for each color. It is. The developing devices 207Y, 207M, 207C, and 207K supply the respective color developers to the photosensitive drum 205 to form toner images for the respective development colors. The intermediate transfer roller 204 is configured to transfer a toner image of each development color from the photosensitive drum 205 and form a color toner image on the intermediate transfer roller 204.

  On the other hand, the paper feeding rollers 202a to 202c pull out the recording paper from the paper feeding cassettes 201a to 201c in which the recording paper is stored, and the recording paper conveyance path 211 conveys the drawn recording paper to the transfer roller 203. is there. The transfer roller 203 transfers the toner image on the intermediate transfer body roller 204 to the conveyed recording paper. The recording paper onto which the toner image has been transferred is conveyed to the fixing roller 208 through the recording paper conveyance path 211, and the fixing roller 208 heats the transferred toner image to fix it on the recording paper. The recording sheet on which the toner image is fixed is conveyed to the discharge port 209 via the recording sheet conveyance path 211 and is carried into the sheet post-processing unit 300. The recording paper is also discharged to the discharge tray 210 as necessary.

  The paper post-processing unit 300 includes a carry-in port 301, a recording paper conveyance path 302, a carry-out port 303, a stack tray 304, and the like. The recording paper conveyance path 302 sequentially conveys the recording paper carried into the carry-in port 301 from the discharge port 209 and finally discharges the recording paper from the carry-out port 303 to the stack tray 304. The stack tray 304 is configured to move up and down in the direction of the arrow in accordance with the number of recording sheets stacked from the carry-out port 303.

  FIG. 2 is a block diagram showing an example of a functional configuration of the control unit of the copying machine 1 shown in FIG. The copying machine 1 includes a control unit 700 that is disposed at an appropriate position of the copying machine 1 and controls the operation of the copying machine 1. Here, the control unit 700 includes a CPU (Central Processing Unit) 710, a RAM (Random Access Memory) 720 used as a work area of the CPU, and a ROM (Read Only Memory) that stores an image processing program according to the present invention. (Omitted).

  The CPU 710 functionally divides a color image stored in a color image storage unit 721, which will be described later, into a character area that is an area representing characters and a background area that is an area excluding the character area (area And a data conversion unit that converts pixel values of a color image stored in a color image storage unit 721, which will be described later, into a luminance component that is a component representing luminance and a color difference component that is a component representing color difference 712 (corresponding to data conversion means) and a luminance determination for determining whether or not a luminance difference, which is a difference between the luminance component of the character region and the luminance component of the background region, is equal to or less than a preset first threshold value A luminance component of a predetermined number of pixels corresponding to the outer edge portion of the character area and a luminance component of the background area when it is determined to be equal to or less than the first threshold value difference And a contour emphasis section 714 to change the direction of increasing by a first predetermined value (corresponding to the contour enhancement means).

  Further, the CPU 710 functionally determines whether the color difference component difference, which is the difference between the color difference component of the character area and the color difference component of the background area, is equal to or greater than a second threshold value set in advance. 715 (corresponding to the color difference determination means) and a character emphasis unit 716 (character emphasis) that changes the luminance component by a second predetermined value for pixels inside the character area when it is determined to be equal to or greater than the second threshold. Corresponding to the means).

  Further, the contour emphasizing unit 714 sets a predetermined number, which is the number of pixels corresponding to the outer edge of the character region, in accordance with the color difference component difference that is the difference between the color difference component of the character region and the color difference component of the background region. A first predetermined value, which is a density change amount of the outline portion of the character area, and a color difference component difference which is a difference between the color difference component of the character area and the color difference component of the background area. A contour density setting unit 714b (corresponding to a contour density setting unit) that is set in accordance with this, and the character emphasizing unit 716 is a difference between the color difference component of the character region and the color difference component of the background region. A density setting unit 716a (corresponding to density setting means) that is set in proportion to the color difference component difference is provided.

  The RAM 720 stores a color image of a document including characters to be subjected to image processing for each color as a pixel value for each pixel address, and a luminance component and a color difference component generated by the data conversion unit 712. Are converted data storage unit 722, and a monochrome image storage unit 723 stores each pixel value of the generated monochrome image in association with an address.

  Here, the CPU functions as functional units such as an area dividing unit 711, a data converting unit 712, and a luminance determining unit 713 by reading and executing an image processing program according to the present invention stored in advance in a ROM or the like. It is.

  Further, among various data stored in the RAM 720 and ROM, data that can be stored in a removable recording medium is read by a driver such as a hard disk drive, an optical disk drive, a flexible disk drive, a silicon disk drive, or a cassette medium reader. In this case, the recording medium is, for example, a hard disk, an optical disk, a flexible disk, a CD, a DVD, a semiconductor memory, or the like.

  The area dividing unit 711 divides the color image stored in the color image storage unit 721 into a character area that is an area representing characters and a background area that is an area excluding the character area, and is one area, here a character area. The address in the color image storage unit 721 corresponding to is specified. The method of separating the character area and the background area is to synchronize pixel values for a predetermined line and develop them in a line memory or the like, and compare the center pixel of interest among adjacent addresses with surrounding pixel values. It is possible to adopt a known method in which the process for determining whether or not a character is performed while sequentially shifting in the line direction, and a known method described in Japanese Patent Laid-Open No. 2003-283848 and Japanese Patent Laid-Open No. 8-149298. Is used.

The data conversion unit 712 converts the pixel value at each address of the color image stored in the color image storage unit 721 into a luminance component that is a component representing luminance and a color difference component that is a component representing color difference. Specifically, when the pixel value of the color image is composed of R (red), G (green), and B (blue) color components, the following equations (1) to (3) are used to express Y (Luminance component), U, and V (color difference component) are converted into three components.
Y = 0.299 × R + 0.587 × G + 0.114 × B (1)
U = −0.169 × R−0.331 × G + 0.500 × B (2)
V = 0.500 × R−0.419 × G−0.081 × B (3)

  The luminance determination unit 713 determines whether the luminance difference ΔY (= | Y1-Y2 |), which is the difference between the luminance component Y1 of the character region and the luminance component Y2 of the background region, is equal to or smaller than a preset first threshold value ΔY0. It is to determine whether or not.

  The contour enhancement unit 714 uses the luminance determination unit 713 to determine that the luminance difference ΔY (= | Y1-Y2 |), which is the difference between the luminance component Y1 of the character region and the luminance component Y2 of the background region, is equal to or less than the first threshold value ΔY0. Is determined, the luminance component of a predetermined number of pixels corresponding to the outer edge portion of the character area is changed by a first predetermined value in a direction in which the difference from the luminance component of the background area increases.

The contour width setting unit 714a determines the difference between the color difference components U1 and V1 in the character region and the color difference components U2 and V2 in the background region as a predetermined number (hereinafter referred to as contour width) W which is the number of pixels corresponding to the outer edge of the character region. Is set in accordance with the color difference component difference ΔUV. Here, the color difference component difference ΔUV is calculated using the following equation (4), and the contour width W is obtained using the following equation (5).
ΔUV = Max (| U1-U2 |, | V1-V2 |) (4)
W = α × ΔUV (5)
Here, Max () is a function that takes the largest value among the numerical values in parentheses, and α is a preset constant. When the contour width W is set, the contour width setting unit 714a uses the upper portion of the address corresponding to the outer edge portion of the character area of the color image stored in the color image storage unit 721 to set the contour width W. An address included in the image is calculated, and an address within the contour width W is specified.

The contour density setting unit 714b sets the first predetermined value (hereinafter referred to as the contour density change amount) ΔY3 that is the density change amount of the contour portion to the color difference components U1 and V1 of the character region, the color difference components U2 and V2 of the background region, and the character. It is set using the following equation (6) according to the color difference component difference ΔUV which is a difference between regions.
ΔY3 = β × ΔUV (6)
Here, β is a preset constant.

  The color difference determination unit 715 determines whether or not the color difference component difference ΔUV, which is the difference between the color difference components U1 and V1 in the character area and the color difference components U2 and V2 in the background area, is greater than or equal to a preset second threshold value ΔUV0. Judgment.

  When the color difference determining unit 715 determines that the color difference component difference ΔUV is greater than or equal to a second threshold ΔUV0 set in advance, the character emphasizing unit 716 sets the luminance component for the pixels in the character area to a second predetermined value. Only the value ΔY4 is changed.

The density setting unit 716a uses a second predetermined value (hereinafter referred to as “character internal density change amount”) ΔY4, which is a change amount of the luminance component for pixels inside the character area, as the color difference components U1 and V1 of the character area and the background area. It is set using the following equation (7) in proportion to the color difference component difference ΔUV which is the difference between the color difference components U2 and V2.
ΔY4 = γ × ΔUV (7)
Here, γ is a preset constant.

  FIG. 3 is a flowchart illustrating an example of the operation of the control unit 700. Here, a case where a color image including characters to be subjected to image processing is stored in advance in the color image storage unit 721 will be described. First, the pixel value of the color image is read from the color image storage unit 721 by the region dividing unit 711 (step S101), and divided into a character region and a background region (step S103). That is, the address of the character area is extracted. Then, the pixel value (R, G, B) of the color image is converted into the YUV system by the data conversion unit 712 (step S105).

  Next, the luminance determination unit 713 obtains the luminance component Y1 of the character region and the luminance component Y2 of the background region (step S107), and the luminance difference ΔY (= | Y1-Y2 |) is less than or equal to the first threshold value ΔY0. It is determined whether or not there is (step S109). If it is determined that the luminance difference ΔY (= | Y1-Y2 |) is not less than or equal to the first threshold value ΔY0 (greater than the first threshold value ΔY0) (NO in step S109), the process proceeds to step S121. . When it is determined that the luminance difference ΔY (= | Y1-Y2 |) is equal to or smaller than the first threshold value ΔY0 (YES in step S109), the contour emphasizing unit 714 and the color difference components U1 and V1 of the character area and the background The color difference components U2 and V2 of the area are obtained (step S111).

  Then, the contour enhancement unit 714 obtains the color difference component difference ΔUV using the above-described equation (4) (step S113). Next, the contour width setting unit 714a and the contour density setting unit 714b obtain the contour width W (and corresponding address) and the contour density change amount ΔY3 using the above-described equations (5) and (6), respectively ( Step S115).

  Next, the color difference determination unit 715 determines whether or not the color difference component difference ΔUV is equal to or larger than a preset second threshold value ΔUV0 (step S117). If it is determined that it is not greater than or equal to the second threshold value ΔUV0 (less than the second threshold value ΔUV0) (NO in step S117), the process proceeds to step S121. If it is determined that the value is greater than or equal to the second threshold ΔUV0 (YES in step S117), the character emphasis unit 716 (density setting unit 716a) sets the character internal density change amount ΔY4 using the above equation (7). It is set (step S119). If NO in step S109, NO in step S117, or when the process in step S119 ends, a monochrome image is generated according to the set conditions (step S121) and stored in the monochrome image storage unit 723. Then, the process is terminated.

  FIG. 4 is an explanatory diagram showing an example of image processing according to the present invention. (A) is explanatory drawing of a color image, (b) is explanatory drawing which shows the process by the outline emphasis part 714, (c) is explanatory drawing which shows the process by the character emphasis part 716. FIG. The character region C1 and the background region B1 shown in (a) are assumed to have similar luminance (the luminance difference ΔY is equal to or smaller than the first threshold value ΔY0), and the color difference component and the background region of the character region C1. It is assumed that the color difference component difference ΔUV that is the difference from the color difference component of B1 is equal to or greater than the second threshold value ΔUV0.

  In this case, as shown in (b), the contour emphasizing unit 714 converts the luminance component of a predetermined number of pixels (hereinafter referred to as the contour region) C21 corresponding to the outer edge of the character region C2 to the luminance component of the background region B2. The first predetermined value is changed in the direction in which the difference increases. Further, as shown in (c), the character enhancement unit 716 changes the luminance component by the second predetermined value ΔY4 for the pixel C32 inside the character area C3.

  As described above, when it is determined that the luminance difference ΔY (= | Y1-Y2 |), which is the difference between the luminance component Y1 of the character region and the luminance component Y2 of the background region, is equal to or smaller than the first threshold value ΔY0. In addition, since the luminance component of a predetermined number of pixels corresponding to the outer edge portion of the character area is changed by the contour density change amount ΔY3 in a direction in which the difference from the luminance component of the background area becomes larger, the character edge is changed by the outer edge portion of the character area. Since the boundary between the area and the background area can be identified and the luminance component of the pixels other than the outer edge of the character area is not changed, a monochrome image that approximates the impression of the character in the color image is generated.

  Further, the number of pixels (contour width W) whose luminance component is changed by the contour width setting unit 714a is a difference between the color difference components U1 and V1 in the character region and the color difference components U2 and V2 in the background region. Since it is set according to (see the above-mentioned equation (4)), a monochrome image that further approximates the impression of characters in a color image is generated.

  Further, the outline density setting unit 714b causes the outline density change amount ΔY3 to be the difference between the color difference components U1 and V1 in the character area and the color difference components U2 and V2 in the background area (see the above-described equation (4)). Therefore, a monochrome image that further approximates the impression of characters in a color image is generated.

  In addition, it is determined that the color difference component difference ΔUV (see the above equation (4)), which is the difference between the color difference components U1 and V1 in the character area and the color difference components U2 and V2 in the background area, is greater than or equal to the second threshold value ΔUV0. In this case, since the luminance component of the pixels inside the character area is changed by the character internal density change amount ΔY4, the color difference component difference ΔUV is reflected on the luminance of the pixels inside the character area, and the character in the color image A monochrome image that more closely approximates the impression is generated.

  Further, since the character internal density change amount ΔY4, which is the amount of change in the luminance component of the pixels inside the character area, is set in proportion to the color difference component difference ΔUV, the color difference component difference ΔUV becomes the luminance of the pixels inside the character area. A monochrome image that is more accurately reflected and that more closely approximates the impression of characters in a color image is generated.

  Further, since the data conversion unit 712 converts the Y component that is the luminance component and the U component and the V component that are the color difference components into the YUV format, the pixel value of the color image is converted into the luminance component Y and the color difference component U. , V and easily converted.

  In addition, this invention can take the following aspects.

  (A) In the present embodiment, the case where the image forming apparatus is the copying machine 1 has been described. However, another type of image forming apparatus (for example, a facsimile, a printer, or the like) may be used.

  For example, when the image forming apparatus is a printer that is communicably connected to a personal computer, a color image including characters stored in the color image storage unit 721 is received from the personal computer.

(B) In the present embodiment, the case where the data conversion unit 712 converts to the YUV format has been described. However, the data conversion unit 712 may convert to another data format. For example, it may be converted into the La ^* b ^* format.

  (C) In the present embodiment, the case where the first threshold value ΔY0 is set in advance has been described. However, the first threshold value ΔY0 may be set via the operation unit 400. In this case, the user can set the first threshold value ΔY0 to a desired value, and convenience is improved.

  (D) In the present embodiment, the case where the contour width setting unit 714a sets the contour width W in proportion to the color difference component difference ΔUV has been described. However, the contour width W is set according to the color difference component difference ΔUV. But you can. For example, when the color difference component difference ΔUV is within a predetermined range, the predetermined contour width W may be set stepwise.

  Alternatively, the contour width setting unit 714a may set the contour width W according to at least one of the color difference components U1 and V1 of the character region and the color difference components U2 and V2 of the background region. For example, the contour width W may be set in proportion to the larger color difference components U1 and V1 of the character area. In this case, the process is simplified.

  (E) In the present embodiment, the contour density setting unit 714b sets the contour density change amount ΔY3 as the difference between the color difference components U1 and V1 in the character area and the color difference components U2 and V2 in the background area and the character area. However, the contour density change amount ΔY3 may be set according to the color difference component difference ΔUV. For example, when the color difference component difference ΔUV is within a predetermined range, the predetermined contour density change amount ΔY3 may be set stepwise.

  The contour density setting unit 714b may set the contour density change amount ΔY3 according to at least one of the color difference components U1 and V1 of the character area and the color difference components U2 and V2 of the background area. For example, the contour density change amount ΔY3 may be set in proportion to the larger of the color difference components U1 and V1 of the character area. In this case, the process is simplified.

  (F) In the present embodiment, the case where the second threshold value ΔUV0 is set in advance has been described. However, the second threshold value ΔUV0 may be configured to be set via the operation unit 400. In this case, the user can set the second threshold value ΔUV0 to a desired value, and convenience is improved.

  (G) In the present embodiment, the case where the density setting unit 716a sets the character internal density change amount ΔY4 in proportion to the color difference component difference ΔUV has been described, but the character internal density change amount ΔY4 is set to the color difference component difference ΔUV. A form may be set accordingly. For example, when the color difference component difference ΔUV is within a predetermined range, the predetermined character internal density change amount ΔY4 may be set stepwise.

1 is a side view of a copying machine as an example of an image forming apparatus according to the present invention. FIG. 2 is a block diagram illustrating an example of a functional configuration of a control unit of the copier illustrated in FIG. 1. It is a flowchart which shows an example of operation | movement of a control part. It is explanatory drawing which shows an example of the image processing which concerns on this invention.

Explanation of symbols

1 Copying machine (image forming device)
200 Main Body 300 Paper Post-Processing Unit 400 Operation Unit 500 Document Reading Unit 600 Document Feeding Unit 700 Control Unit 710 CPU
711 Area division unit (area division means)
712 Data converter (data converter)
713 Luminance determination unit (luminance determination means)
714 Outline enhancement unit (contour enhancement means)
714a Contour width setting unit (contour width setting means)
714b Contour density setting unit (contour density setting means)
715 Color difference determination unit (color difference determination means)
716 Character emphasis part (character emphasis means)
716a Density setting unit (density setting means)
720 RAM
721 Color image storage unit 722 Conversion data storage unit 723 Monochrome image storage unit

Claims (10)

An image processing apparatus for converting a pixel value of each color of the color image into a pixel value of a monochrome image so that a color image including characters is a monochrome image,
An area dividing means for dividing the color image into a character area which is an area representing a character and a background area which is an area excluding the character area;
Data conversion means for converting the pixel value of the color image into a luminance component which is a component representing luminance and a color difference component which is a component representing color difference;
A luminance determination means for determining whether or not a luminance difference that is a difference between the luminance component of the character region and the luminance component of the background region is equal to or less than a first preset threshold;
When it is determined that the luminance component is equal to or less than the first threshold, the luminance component of a predetermined number of pixels corresponding to the outer edge portion of the character region is changed in the direction in which the difference from the luminance component of the background region increases. An image processing apparatus comprising: an outline emphasizing unit that changes a predetermined value.   The image processing apparatus according to claim 1, wherein the contour emphasizing unit includes a contour width setting unit that sets the predetermined number according to at least one of a color difference component of the character region and a color difference component of a background region. .   The image processing apparatus according to claim 2, wherein the contour width setting unit sets the predetermined number according to a color difference component difference that is a difference between a color difference component of the character area and a color difference component of a background area. .   The contour enhancement means comprises contour density setting means for setting the first predetermined value according to at least one of the color difference component of the character area and the color difference component of the background area. The image processing apparatus according to any one of the above.   5. The contour density setting unit sets the first predetermined value according to a color difference component difference which is a difference between a color difference component of the character area and a color difference component of a background area. Image processing device. A color difference determination means for determining whether or not a color difference component difference, which is a difference between the color difference component of the character area and the color difference component of the background area, is equal to or greater than a preset second threshold value;
6. A character emphasizing unit that changes a luminance component by a second predetermined value for a pixel inside the character region when it is determined that the second threshold value or more. An image processing apparatus according to any one of the above.   The image processing apparatus according to claim 6, wherein the character emphasis unit includes a density setting unit that sets the second predetermined value in association with the color difference component difference.   The image processing apparatus according to claim 7, wherein the density setting unit sets the second predetermined value in proportion to the color difference component difference.   9. The image processing apparatus according to claim 1, wherein the data conversion unit converts the data into a YUV format including a Y component that is a luminance component and a U component and a V component that are color difference components. . An image processing device according to any one of claims 1 to 9,
Image data storage means for storing a monochrome image generated by the image processing device;
An image forming apparatus comprising: a printing unit that reads out a pixel value of a monochrome image from the image data storage unit and prints the monochrome image on a recording sheet.

Images