JP2012254557A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus can improving the color reproducibility of a pattern when printing an image including a pattern with chromatic colors.SOLUTION: The image forming apparatus includes a frequency distribution obtaining part 12 obtaining the frequency distribution of colors of respective pixels of image data; a color setting part 13 obtaining pattern colors; and an image formation control part 16 having a pattern mode for forming an image including at least one chromatic color while the pixel number of the pattern is less than a size determination value. The pattern mode includes a single color pattern mode of forming an image on a sheet using a pattern color. The frequency distribution obtaining part 12 generates three-dimensional frequency distribution information that shows frequency distribution with three-dimensional coordinates. The color setting part 13 sets, as a third class, a class having the largest frequency out of remaining classes which are classes remaining after excluding, from three-dimensional frequency distribution information, classes belonging to a set area set to include an area that connects a class to which white belongs, linearly to a class to which black belongs on the three-dimensional coordinates, and obtains the color of the third class as the pattern color.

Description

  The present invention relates to an image forming apparatus capable of forming an image in color.

  Some image forming apparatuses such as a printer, a copier, and a multifunction peripheral have a color printing mode and a monochrome printing mode. As color printing modes, a full color mode and a two-color mode are known.

  In the full color mode, printing is performed using toner of all colors provided in the image forming apparatus. In the two color mode, black toner and one color (specific color) that is a chromatic color other than black are used. Printing. The chromatic color is obtained by mixing a plurality of chromatic color toners.

  The above-described image forming apparatus executes the two-color mode as follows.

  The above-described image forming apparatus includes a plurality of color component counter units to which, for example, blue, green, and red color components are assigned one by one (see, for example, Patent Document 1). Each color component counter unit counts the number of pixels of the color assigned to each color component counter unit among the plurality of pixels included in the image data.

  Then, the above-described image forming apparatus sets the color corresponding to the color component counter unit having the largest count value as a specific color (one mono color). In this image forming apparatus, the black portion of the image data is printed in black, and the color portion is printed using the set specific color.

JP 2009-198792 A

  In general, in business documents, even if black letters are the majority of documents, only logo marks, which are company marks, are often printed in chromatic colors. This is because the color of the logo is also an important element that represents the company. In many cases, only underlines and markers are printed in a chromatic color on a black text document.

  As described above, when a document in which only a pattern such as a logo mark, an underline, and a marker is printed in a chromatic color is printed in the two-color mode using the above-described image forming apparatus, the following problems occur. .

  That is, since the above-described image forming apparatus performs printing of the color part using the color corresponding to the color component counter unit having the largest count value, the colors that can be used for printing of the color part are set in advance for each color component counter unit. Is limited to one of the colors assigned to.

  Therefore, even when the original color image to be printed is an image that uses only one color other than black, it is actually printed in the color portion color and the two-color mode in the original color image. A difference in hue may occur between the colors of the color portions.

  An object of the present invention is to provide an image forming apparatus capable of improving the reproducibility of a pattern color when an image including a chromatic pattern is printed.

  An image forming apparatus according to the present invention includes an image data acquisition unit that acquires image data representing a color image, assigns the color of each pixel of the image data to a class in statistics, and statistically determines the appearance frequency of each color in the image data. A frequency distribution acquisition unit that acquires a frequency distribution as the frequency in the color, and a color that acquires a color belonging to a third class that means a class having the third highest frequency in the frequency distribution as a pattern color that is a predetermined pattern color A setting unit, and an image formation control unit having a pattern mode for forming an image including at least one chromatic color on a sheet, the number of pixels of the pattern being less than a preset size determination value, The pattern mode includes a single color pattern mode in which an image based on the image data is formed on a sheet using the pattern color, and the image data includes a color of each pixel. The frequency distribution acquisition unit assigns the density value of each element color to each coordinate axis of a three-dimensional coordinate, thereby representing the color of each pixel. A three-dimensional frequency distribution information representing the frequency distribution in three-dimensional coordinates is generated by arranging the frequency distribution on the three-dimensional coordinates as a class and associating the frequency of appearance of the color corresponding to each class as a frequency. The color setting unit determines, based on the three-dimensional frequency distribution information, a class belonging to a setting area set so as to include an area that linearly connects a class to which white belongs and a class to which black belongs on the three-dimensional coordinate. Of the remaining classes that are excluded, the class having the highest frequency is set as the third class, and the color of the third class is acquired as the pattern color.

  According to this configuration, the frequency distribution acquisition unit assigns the color of each pixel of the image data to a class in the statistics. In addition, the frequency distribution acquisition unit acquires the frequency of appearance of each color in the image data, that is, the number of pixels of each color, as the frequency in the statistics, and acquires the frequency distribution. Further, the frequency distribution acquisition unit generates the three-dimensional frequency distribution information by representing the frequency distribution in three-dimensional coordinates.

  Here, the predetermined pattern means an image different from characters, such as a logo mark, an underline, and a marker. A general document manuscript has black characters written on a white sheet. And it is not uncommon for such document manuscripts to have patterns such as chromatic logo marks and underlines. In this way, in an image that is mostly black characters and partially colored, i.e., an image in which the number of pixels of the pattern does not satisfy a preset size determination value, the sheet white is the background of the image. It becomes. Therefore, the frequency of the class to which white belongs is the largest among the classes. Then, after white, the frequency of the class to which the black character belongs is increased. Further, the color of the class having the third highest frequency among the classes, that is, the color of the pattern is considered.

  The setting area is set so as to include an area that linearly connects the class to which white belongs to the class to which black belongs on the three-dimensional coordinates. A class having a large frequency is included in the setting area. Therefore, the color setting unit sets the class having the highest frequency among the remaining classes that are the remaining classes obtained by excluding the classes belonging to the setting area from the three-dimensional frequency distribution information, and determines the color of the third class. By setting the pattern color, the pattern color can be acquired.

  Here, the pixels near the edge of the character image are mixed with the character color and the background color (the character color and the background color affect each other), so that the pixel color is different from the character color and the background color. There may be. Thus, when the number of pixels different from the original color increases and exceeds the number of pixels in the pattern, the color of the pixel different from the original color has the third highest frequency. Therefore, if the setting area is set to include an area that linearly connects the class to which white belongs to the class to which black belongs on the three-dimensional coordinates, the character color and the background color influence each other in this way. The class indicating the generated color is included in the setting area. Therefore, the color setting unit incorrectly sets the color of the class having the highest frequency among the remaining classes as the pattern color, and erroneously sets the color generated due to the influence of the character color and the background color as the pattern color. The fear is reduced. As a result, it is possible to improve the reproducibility of the pattern color when printing an image including a chromatic pattern.

  Further, the image formation control unit prohibits execution of the pattern mode when a value obtained by subtracting the total frequency of classes belonging to the setting area from the total number of pixels of the image data exceeds the size determination value. It is preferable to do.

  A value obtained by subtracting the total frequency of the classes belonging to the setting area from the total number of pixels of the image data is considered to correspond to the number of pixels of the chromatic image. The case where the number of pixels of the chromatic color image exceeds the size determination value is considered to be a case where the image area of the chromatic color included in the image data is large, such as a color photograph image. As described above, image formation in the pattern mode is prohibited for an image having a large chromatic color image area and therefore high printing cost. On the other hand, an image having a small chromatic color image area and thus low printing cost is determined by the pattern mode. By allowing image formation, it is possible to improve the convenience for the user while reducing the possibility of increasing the printing cost.

  Further, the image formation control unit sets a class having the second highest frequency among the remaining classes as a fourth class having the fourth highest appearance frequency in the entire frequency distribution, and the frequency of the fourth class is When the mode determination value set in advance is not satisfied, it is preferable to execute image formation in the single color pattern mode.

  As described above, in the frequency distribution, the class having the largest frequency and the class having the second largest frequency are included in the setting area, and therefore the second largest frequency among the remaining classes is selected. The class possessed is considered to be the fourth class having the fourth highest appearance frequency in the entire frequency distribution. When the frequency of the fourth class is less than the mode determination value, there is a high possibility that the chromatic color included in the pattern is only the pattern color. Therefore, the image formation control unit can improve pattern reproducibility by executing image formation in the single color pattern mode in such a case.

  The pattern mode includes a full-color pattern mode in which an image based on the image data is formed on a sheet using a plurality of chromatic colors, and the image formation control unit is configured such that the frequency of the fourth class is the mode determination value. In the above case, it is preferable to execute image formation in the full color pattern mode.

  When the frequency of the fourth class is equal to or higher than the mode determination value, there is a high possibility that a plurality of chromatic colors are included in the pattern. Therefore, the image formation control unit can improve pattern reproducibility by executing image formation in the full-color pattern mode in such a case.

  Further, the image formation control unit is a case where the frequency of the fourth class is less than the mode determination value, and from the total number of pixels of the image data, the total frequency of the class belonging to the setting area When the value obtained by subtracting the frequency of the third class and the frequency of the fourth class is equal to or greater than a preset mode determination determination value, it is preferable to perform image formation in the full color pattern mode.

  Even if the frequency of the fourth class is less than the mode determination value, the total frequency of the class belonging to the setting area, the frequency of the third class, and the frequency of the fourth class are calculated from the total number of pixels of the image data. If the value obtained by subtracting is equal to or greater than a preset mode determination determination value, it is considered that the pattern includes many colors little by little. When such a pattern is printed in the single-color pattern mode, only one chromatic color is used, so that the reproducibility of the pattern is lowered. Therefore, in such a case, the image formation control unit can improve pattern reproducibility by executing image formation in the full-color pattern mode.

  In addition, the image formation control unit combines the third class and the class in a range in which the distance on the three-dimensional coordinate from the third class is less than a predetermined determination distance. The class is an expanded third class, and the total frequency of each class included in the expanded third class is defined as the frequency of the expanded third class, and the next highest frequency after the expanded third class among the remaining classes. It is preferable that the class to be included is the fourth class having the fourth highest appearance frequency in the frequency distribution.

  Here, the color near the edge of the pattern may be a pixel of a color different from the original color because the color of the pattern and the surrounding color are mixed (interacted with each other). When the number of pixels different from the original color increases as described above, there is a possibility that such a color different from the original color is erroneously set to the fourth class. Therefore, the image forming control unit combines the class in the range where the distance on the three-dimensional coordinates from the third class is less than the determination distance and the third class into the expanded third class as described above. Include a different color from the original color in the expanded third class. Then, the image formation control unit sets the class having the second highest frequency after the expanded third class among the remaining classes as the fourth class, thereby improving the determination accuracy of the fourth class.

  And a charging unit that charges the image forming fee to the user. The charging unit increases a difference value obtained by subtracting the total number of classes belonging to the setting area from the total number of pixels of the image data. Accordingly, it is preferable to perform the charging by increasing the fee.

  The difference value obtained by subtracting the total frequency of the class belonging to the setting area from the total number of pixels of the image data is considered to correspond to the number of chromatic pixels included in the image data. As the number of chromatic pixels increases, the printing cost increases. Therefore, the billing unit can charge according to the printing cost by increasing the fee and charging as the difference value increases.

  In addition, an identification information receiving unit that receives input of user identification information, a monochrome mode that forms an image based on the image data with only one color, and a full color mode that forms an image based on the image data using a plurality of colors A management unit that stores identification information of a monochrome limited user who is a user permitted only to form an image in the monochrome mode, a permission instruction reception unit that receives a permission instruction that is an instruction to permit the execution of the pattern mode, The image formation control unit includes the identification information received by the identification information receiving unit when the identification information of the monochrome limited user is received and the permission instruction is received by the permission instruction receiving unit. The image formation in the pattern mode is allowed, and the identification information received by the identification information receiving unit is accepted. Information is identification information of the monochrome limited user, and when the permission instruction by the authorization instruction reception unit is not accepted, it is preferable to prohibit the image formation by the pattern mode.

  Image formation in the monochrome mode is less expensive than image formation in the full-color mode, and the monochrome-limited user is a user who is permitted only to form an image in the low-cost monochrome mode. However, the image formation in the pattern mode uses a small amount of chromatic colors and increases the cost. Therefore, when the permission instruction is received by the permission instruction receiving unit, the image formation control unit allows the monochrome limited user to form an image in the pattern mode. Thereby, the administrator of the image forming apparatus can switch whether or not to allow image formation in the pattern mode for the monochrome limited user depending on the presence or absence of the permission instruction.

  In addition, an identification information receiving unit that receives input of user identification information, a monochrome mode that forms an image based on the image data with only one color, and a full color mode that forms an image based on the image data using a plurality of colors A management unit that stores identification information of a monochrome limited user who is a user who is permitted only to perform image formation in the monochrome mode, and the image formation control unit receives the identification received by the identification information receiving unit. When the information is the monochrome limited user identification information, and the difference value obtained by subtracting the total frequency of the class belonging to the setting area from the total number of pixels of the image data is less than the size determination value, the pattern mode And the identification information received by the identification information receiving unit is limited to the monochrome limit. A user's identity, and when the difference value is equal to or greater than the size determination value, it is preferable to prohibit the image formation by the pattern mode.

  According to this configuration, even for monochrome limited users, by allowing image formation in the pattern mode for images that have a small chromatic image area and therefore low printing costs, the risk of increasing printing costs is reduced. On the other hand, it is possible to improve the convenience for monochrome limited users.

  The image forming apparatus having such a configuration can improve the reproducibility of the pattern color when an image including a chromatic pattern is printed.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an example of an electrical configuration of the image forming apparatus illustrated in FIG. 1. It is explanatory drawing which shows an example of the three-dimensional frequency distribution information produced | generated by the frequency distribution acquisition part shown in FIG. FIG. 3 is an explanatory diagram for explaining an operation of a color setting unit illustrated in FIG. 2. It is explanatory drawing which shows an example of the color group contained in a setting area | region. 3 is a diagram conceptually illustrating an example of an image of a document original represented by image data. FIG. It is explanatory drawing which shows an example of the histogram showing the appearance frequency of the color of each pixel of the image data containing a multicolor logo mark. It is explanatory drawing which shows an example of the histogram showing the appearance frequency of the color of each pixel of the image data containing a single color logo mark. It is explanatory drawing which shows an example of the histogram showing the appearance frequency of the color of each pixel of the image data containing a multicolor logo mark. 3 is a flowchart showing an example of the operation of the image forming apparatus shown in FIG. 3 is a flowchart showing an example of the operation of the image forming apparatus shown in FIG. It is explanatory drawing for demonstrating the determination operation | movement of the pattern color by the color setting part shown in FIG. It is explanatory drawing for demonstrating a group aggregate | assembly in case the determination distance is 2 in the Euclidean distance. It is explanatory drawing for demonstrating a group aggregate | assembly in case the determination distance is 2 in the Euclidean distance.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted. In this embodiment, a color image forming apparatus that performs full color printing using cyan (C), magenta (M), yellow (Y), and black (K) toners is exemplified as the image forming apparatus. Yes.

  Note that the image forming apparatus 1 may perform full-color printing using red, green, blue, and black toners.

  FIG. 1 is a schematic sectional view of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 includes an image reading unit 200 and an image forming main body unit 22. The image reading unit 200 includes a document feeding unit 210, a scanner unit 220, a CIS 231, a user interface unit I disposed so as to be exposed on the front surface of the image forming main body unit 22, and a reversing mechanism described later. Has been.

  The document feeder 210 includes an ADF (Automatic Document Feeder), and includes a document tray 211, a pickup roller 212, a platen 213, a paper discharge roller 214, and a paper discharge tray 215. A document to be read is placed on the document tray 211. Documents placed on the document tray 211 are picked up one by one by the pickup roller 212 and sequentially conveyed to the platen 213 through the gap. Documents that have passed through the platen 213 are sequentially discharged to the discharge tray 215 by the discharge rollers 214.

  Of the positions facing the peripheral surface of the platen 213, a timing sensor (not shown) for detecting the paper is installed at a predetermined position before the reading position P in the document transport direction. Based on the output request, the conveyance timing of the document to the reading position P is achieved. The timing sensor is configured by, for example, a photo interrupter.

  The scanner unit 220 optically reads an image of a document and generates image data. The scanner unit 220 includes a glass 221, a light source 222, a first mirror 223, a second mirror 224, a third mirror 225, a first carriage 226, a second carriage 227, an imaging lens 228, and a CCD (Charged Coupled Device) 229. .

  In the scanner unit 220, a white fluorescent lamp such as a cold cathode fluorescent tube is used as the light source 222, and the first mirror 223, the second mirror 224, the third mirror 225, the first carriage 226, the second carriage 227, and the imaging lens. By 228, the light from the original is guided to the CCD 229. Since the scanner unit 220 is configured using a white fluorescent lamp such as a cold cathode fluorescent tube as the light source 222, the scanner unit 220 is superior in color reproducibility to a CIS 231 described later in which a three-color LED or the like is used as the light source.

  A document is manually placed on the glass 221 by a user's manual operation when reading the document without using the document feeder 210. The light source 222 and the first mirror 223 are supported by the first carriage 226, and the second mirror 224 and the third mirror 225 are supported by the second carriage 227.

  As a document reading method of the image reading unit 200, the scanner unit 220 reads a document placed on the glass 221 and the document is read by the document feeding unit 210 (ADF). There is an ADF reading mode for reading.

  In the flatbed reading mode, the light source 222 irradiates a document placed on the glass 221, and reflected light for one line in the main scanning direction is reflected in the order of the first mirror 223, the second mirror 224, and the third mirror 225. Then, the light enters the imaging lens 228. The light incident on the imaging lens 228 is imaged on the light receiving surface of the CCD 229.

  The CCD 229 is a one-dimensional image sensor and processes the image data of one line of the document in an overlapping manner. The first carriage 226 and the second carriage 227 are configured to be movable in a direction orthogonal to the main scanning direction (sub-scanning direction, arrow Y direction). When reading for one line is completed, the first carriage 226 and the second carriage 227 are moved in the sub-scanning direction. The first carriage 226 and the second carriage 227 move, and the next line is read.

  In the ADF reading mode, the document feeder 210 takes in the documents placed on the document tray 211 one by one by the pickup roller 212. At this time, the first carriage 226 and the second carriage 227 are disposed at a predetermined reading position P located below the reading window 230.

  When the document is transported by the document feeder 210, when the document passes over the reading window 230 provided in the transport path from the platen 213 to the paper discharge tray 215, the light source 222 irradiates the document, and the main scanning one line. The reflected light is reflected in the order of the first mirror 223, the second mirror 224, and the third mirror 225 and enters the imaging lens 228. The light incident on the imaging lens 228 is imaged on the light receiving surface of the CCD 229. Subsequently, the document is conveyed by the document feeder 210 and the next line is read.

  Further, the document feeder 210 has a reversing mechanism including a switching guide 216, a reversing roller 217, and a reversing conveyance path 218. This reversing mechanism reverses the front and back of the original whose surface has been read by the first ADF reading and transports it again to the reading window 230, whereby the CCD 229 reads the back side again.

  This reversing mechanism operates only when reading both sides and does not operate when reading one side. After reading the back side during single-sided reading and double-sided reading, the switching guide 216 is switched to the upper side, and the document that has passed through the platen 213 is discharged to the discharge tray 215 by the discharge roller 214.

  After the front side reading at the time of double-sided reading, the switching guide 216 is switched to the lower side, and the document that has passed through the platen 213 is transported to the reverse transport path 218 by the reverse roller 217. Thereafter, the switching guide 216 is switched upward, and the reverse roller 217 rotates in the reverse direction to re-feed the document to the platen 213. Hereinafter, a mode in which both sides of a document are read using a reversing mechanism is referred to as a double-sided reversal reading mode.

  Further, in the ADF reading mode, the image reading unit 200 reads the back side of the document by the CIS 231 substantially in parallel with the CCD 229 (scanner unit 220) reading the surface of the document while the document is being conveyed. Is possible. In this case, the surface of the document conveyed from the document tray 211 by the document feeder 210 is read by the CCD 229 when passing through the reading window 230, and the back surface is read when passing through the location where the CIS 231 is arranged. In CIS231, RGB three-color LEDs or the like are used as light sources.

  By using the CCD 229 and the CIS 231 in this way, it is possible to read both the front and back sides of a document by a single document transport operation (one pass) from the document tray 211 to the discharge tray 215 by the document feeding unit 210. Hereinafter, a mode in which both sides of a document are read using the CCD 229 and the CIS 231 in this way is referred to as a double-sided simultaneous reading mode.

  The double-sided reverse reading mode and the double-sided simultaneous reading mode are provided as reading modes when performing double-sided reading of a document using the ADF reading mode. The double-sided reverse reading mode is used when you want to match the image quality of both-side printed images, while the double-sided simultaneous reading mode gives priority to shortening the reading time even if there is a difference in the image quality of both-side printed images Used in cases. Note that the image forming apparatus 1 is initially set to the double-sided simultaneous reading mode, and when an image forming instruction is input without performing any mode setting operation in the reading mode, the original is read in the double-sided simultaneous reading mode. The image reading operation is performed.

  The image forming apparatus 1 includes an image forming main body 22 and a stack tray 6 disposed on the left side of the image forming main body 22. The image forming main body 22 includes a plurality of paper feeding cassettes 461, a paper feeding roller 462 that feeds paper from the paper feeding cassette 461 one by one and transports the paper to the image forming unit 40, and paper transported from the paper feeding cassette 461. And an image forming unit 40 for forming an image. In addition, the image forming main body 22 includes a paper feed tray 471 and a feeding roller 472 that feeds the originals placed on the paper feed tray 471 one by one toward the image forming unit 40.

  Paper is an example of a sheet. The sheet may be, for example, an OHP (OverHead Projector) film.

  The image forming unit 40 includes a charge removing device 421 that removes residual charges from the surface of the photosensitive drum 43, a charging device 422 that charges the surface of the photosensitive drum 43 after charge removal, and image data acquired by the scanner unit 220. Based on the electrostatic latent image, an exposure device 423 that outputs a laser beam to expose the surface of the photosensitive drum 43 to form an electrostatic latent image on the surface of the photosensitive drum 43. Furthermore, developing devices 44K, 44Y, 44M, and 44C that form toner images of each color of cyan (C), magenta (M), yellow (Y), and black (K), and each color formed on the photosensitive drum 43, respectively. A transfer drum 49 on which the toner image is transferred and overlaid, a transfer device 41 for transferring the toner image on the transfer drum 49 to a sheet, and a sheet on which the toner image is transferred are heated to form a toner image. And a fixing device 45 for fixing to the paper.

  The toner supply for each color of cyan, magenta, yellow, and black is performed from a toner cartridge (not shown). Further, conveyance rollers 463, 464 and the like for conveying the sheet that has passed through the image forming unit 40 to the stack tray 6 or the discharge tray 48 are provided.

  When images are formed on both sides of a sheet, the image is formed on one side of the sheet by the image forming unit 40 and then the sheet is nipped by the conveyance roller 463 on the discharge tray 48 side. In this state, the conveying roller 463 is reversed to switch back the sheet, and the sheet is sent to the sheet conveying path PL and conveyed again to the upstream area of the image forming unit 40, and the image forming unit 40 forms an image on the other surface. Thereafter, the paper is discharged to the stack tray 6 or the discharge tray 48.

  FIG. 2 is a block diagram showing an example of the electrical configuration of the image forming apparatus 1 shown in FIG. The image forming apparatus 1 includes an image processing ASIC (Application Specific Integrated Circuit) 10, a user interface unit I, a system control unit 14, an image reading control unit 15, an image reading control unit 16, a management unit 17, an operation control unit 19, and a setting. Unit 20, image forming unit 40, and image reading unit 200.

  The image processing ASIC 10, the system control unit 14, the image reading control unit 15, the image formation control unit 16, and the management unit 17 are configured to be able to transmit / receive data to / from each other via the bus B. The operation control unit 19 is connected to the user interface unit I, the image reading control unit 15 is connected to the image reading unit 200, the image forming control unit 16 is connected to the image forming unit 40, and the management unit 17 is connected to the setting unit 20. Has been.

  The image processing ASIC 10 includes an image data acquisition unit 11, a frequency distribution acquisition unit 12, a color setting unit 13, and an intermediate image processing unit 31.

  The intermediate image processing unit 31 is an image processing unit that performs intermediate image processing such as shading, show-through removal, or background color change processing on color image data read from an original by the image reading unit 200, for example.

  Note that the intermediate image processing unit 31 does not have to execute all of shading, show-through removal, and background color change processing, and may execute part of these image processing. Further, the intermediate image processing unit 31 may execute intermediate image processing such as enlargement, reduction, and gradation correction. Further, the image processing ASIC 10 may not include the intermediate image processing unit 31.

  The background color change processing is performed when, for example, the background (background) pixel of a color image that should be white is different when the background of the original of the color image is dark or when the back page of the original is seen through. In the case of a color pixel, this is a process of replacing the color of the pixel with a predetermined color, for example, white (for example, see Japanese Patent Application Laid-Open No. 11-187266).

  The image data acquisition unit 11 acquires the image data that has been subjected to the intermediate image processing by the intermediate image processing unit 31. Note that the image data acquisition unit 11 may acquire the image data by receiving, for example, the color image data read from the document by the image reading unit 200 via the image reading control unit 15.

  The image data acquisition unit 11 may acquire image data by receiving color image data from a personal computer or the like connected to the network via a network (not shown), for example. The image data acquisition unit 11 may acquire the image data by receiving color image data transmitted from the facsimile apparatus via a telephone line (not shown), for example.

  The image data acquisition unit 11 converts the color of each pixel of the color image data obtained in this way into three preset element colors, for example, cyan (C), magenta (M), and yellow (Y ). The image data acquisition unit 11 represents each density value with a predetermined basic bit number, for example, 8 bits.

  In this way, the image data acquisition unit 11 acquires image data in which the density values of cyan (C), magenta (M), and yellow (Y) are each represented by 8 bits in the pixel value of each pixel. To do.

  Note that the image data acquisition unit 11 may represent the image data by density values of red, green, and blue. Also in this case, each density value of red, green, and blue is represented by the number of basic bits, for example, 8 bits.

  The frequency distribution acquisition unit 12 assigns the color of each pixel of the image data D to a class in the statistics based on the image data D acquired by the image data acquisition unit 11, and uses the appearance frequency of each color in the image data D as the frequency. Get frequency distribution.

  FIG. 3 is an explanatory diagram illustrating an example of the three-dimensional frequency distribution information generated by the frequency distribution acquisition unit 12 illustrated in FIG.

  Here, the frequency distribution means that when a sample has a certain variable, the range of the variable is divided into a plurality of classes, and the number of samples having variables belonging to each class is counted as the frequency (frequency of appearance). is there. The frequency distribution acquisition unit 12 uses pixels as samples, pixel values representing pixel colors as variables, and classifies colors, that is, pixel values, into a plurality of ranges. The class need not be in a certain range, and the pixel value, that is, the color, and the class may correspond one-to-one.

  For example, when there is image data D composed of three colors of red, blue, and yellow, red, blue, and yellow are classes, and the number of red, blue, and yellow pixels included in the image data D is each class. Frequency (appearance frequency).

  A so-called histogram is known in which such a class is taken on the horizontal axis, the frequency is taken on the vertical axis, and the frequency distribution is represented in a two-dimensional coordinate system.

  Here, since the color (pixel value) of each pixel is represented by the density values of the three element colors, if the density value of cyan is c, the density value of magenta is m, and the density value of yellow is ye, The color (pixel value) of each pixel is represented as (c, m, ye).

  Therefore, as shown in FIG. 3, when the density values of cyan (C), magenta (M), and yellow (Y) are assigned to the coordinate axes of the three-dimensional coordinates, the color (class) of each pixel is shown in FIG. It is arranged on a three-dimensional coordinate like a box G shown. In this way, by associating frequencies with boxes arranged on three-dimensional coordinates, that is, classes, three-dimensional frequency distribution information in which a histogram is represented in three dimensions is generated.

  The frequency distribution acquisition unit 12 generates the three-dimensional frequency distribution information by arranging the frequency distribution on the three-dimensional coordinates in this way.

  In FIG. 3, the cyan (C) density value on the X axis extending in the left-right direction, the magenta (M) density value on the Y axis extending in the vertical direction, and the yellow (Y) density value on the Z axis extending in the depth direction on the paper surface. Are assigned to each.

  Then, the pixel value (c, m, ye) of each pixel is indicated by a class (box G) arranged at the coordinates (x, y, z).

  The density value of each element color is represented by 8 bits and is expressed as Hx00 to HxFF in hexadecimal. Hereinafter, Hx is added to the hexadecimal number. In FIG. 3, each coordinate axis represents only the upper 4 bits of the density value of each element color. That is, the density value of each element color is represented by Hx0 to HxF.

  Then, in the three-dimensional coordinates in which the value of each coordinate axis is the upper 4 bits, for example, in the class box G indicated by the coordinates (HxF, HxF, HxF), the pixel values are actually (HxF0 to HxFF, HxF0). To HxFF, HxF0 to HxFF). The range in which the lower 4 bits of each density value are Hx0 to HxF corresponds to the range of each divided class.

  The class (box) G including a plurality of colors is hereinafter referred to as a color group G. The color group G is a class including all colors included in the color group G. The total number of pixels included in the image data D for the color pixels included in the color group G is the appearance frequency (frequency) of the color group G.

  Thus, the frequency distribution acquisition unit 12 assigns the upper 4 bits of the cyan density value to the X coordinate, assigns the upper 4 bits of the magenta density value to the Y coordinate, and assigns the upper 4 bits of the yellow density value to the Z coordinate. Assign to.

  As a result, the frequency distribution acquisition unit 12 arranges, on a three-dimensional coordinate, a color having a common upper 4 bits of density values of cyan, magenta, and yellow that are element colors as a color group (class). The frequency distribution acquisition unit 12 does not necessarily need to assign the upper 4 bits to the coordinate axis, and may have a higher bit number other than 4. Further, the frequency distribution acquisition unit 12 may assign the total number of bits of each density value to each coordinate axis. In this case, one color group (class) G represents one color.

  In this way, the frequency distribution acquisition unit 12 associates the appearance frequency of each color group G with each color group G. Thereby, the frequency distribution acquisition part 12 acquires the frequency distribution of a color group as three-dimensional frequency distribution information. The frequency distribution acquisition unit 12 transmits the three-dimensional frequency distribution information to the color setting unit 13 and the image formation control unit 16.

  The color setting unit 13 sets a pattern color based on the appearance frequency of each color in the frequency distribution acquired by the frequency distribution acquisition unit 12. The pattern color is a color of a pattern when an image including a pattern composed of one chromatic color is printed. The color setting unit 13 transmits the set pattern color to the image formation control unit 16. The image processing ASIC 10 may transmit the image data acquired by the image data acquisition unit 11 as it is to the image formation control unit 16 as print image data.

  FIG. 4 is an explanatory diagram for explaining the operation of the color setting unit 13 shown in FIG. A color group G (1) shown in FIG. 4 is a class indicating white, and coordinates (pixel values) are, for example, (0, 0, 0). The color group G (2) is a class indicating black, and the coordinates (pixel value) are, for example, (HxF, HxF, HxF).

  The setting area SE is set in advance so as to include an area SL that linearly connects the color group G (1) and the color group G (2). The setting area SE is an area having a three-dimensional spread, for example, a spindle shape (rugby ball type) in the three-dimensional coordinates. The color group G (1) is a class that assumes the background color of the paper, that is, the ground color of the paper. The color group G (2) is a class that assumes black characters.

  Note that the color group G (1) and the color group G (2) are used here for setting the setting region SE, and the color of the color group G (1) is not necessarily an actual color. It does not have to be the color of the paper, and the color of the color group G (2) does not necessarily have to be the actual character color. The actual paper color may be slightly yellow, and the actual character color may be close to gray. However, the color of the color group G (1) used for setting the setting region SE may be, for example, pure white, that is, the whitest color that can be represented by a pixel value, for example, the pixel value is (0, 0, 0). Also good. Further, the color of the color group G (2) used for setting the setting area SE may be, for example, black, that is, the blackest color that can be represented by a pixel value, for example, the pixel value is (HxFF, HxFF, HxFF). Also good.

  In order to determine the color of the pattern from the image data D read from the document, the color of the part that is considered to occupy a large area in the part other than the pattern, that is, the background color of the paper (background color) and the black of the character are excluded. Want to. However, in image data read from a document by a scanner, for example, pixels at the boundary between white and black may be represented as gray.

  Further, when the image size is reduced by image processing, pixels are thinned out. However, if the image size is reduced by simply thinning out pixels to reduce the number of pixels, an unnatural color may be obtained. Therefore, when the image is reduced, a process of replacing a plurality of pixels with one pixel having an average value of the pixel values as a pixel value may be performed. In such a case, in the reduced image data, there may be pixels of a color in which the background color or the character color is mixed with the surrounding color at the edge portion of the character.

  The image data D includes pixels of a color that is derived from the background color and the character color in this way. In order to distinguish such a pixel from a pattern color, a range of colors (pixel values) that may be generated by mixing the background color and black characters is experimentally obtained in advance, for example, as in a color group G shown in FIG. An area including these color groups G is set as the setting area SE.

  For example, the setting area SE may be obtained in advance and stored in advance in a storage element such as a ROM when the image forming apparatus 1 is manufactured. Further, the image forming apparatus 1 may include, for example, an EEPROM (Electrically Erasable and Programmable Read Only Memory) or an HDD (Hard Disk Drive) as a storage device for storing the setting area SE. The image forming apparatus 1 includes an interface circuit that can input data to the image forming apparatus 1, such as a communication interface circuit such as a LAN (Local Area Network) or a USB (Universal Serial Bus), or an interface circuit that can access a memory card. You may prepare. For example, the user may use the interface circuit to store data representing the setting area SE in a storage device included in the image forming apparatus 1 so that the setting area SE can be set as appropriate.

  For example, among the areas (remaining classes) excluding the setting area SE from the image data D, the color with the highest appearance frequency (color group G (3) described later) and the color with the second highest appearance frequency (color group described later) In the case where a circuit for detecting G (4)) is provided, it may be desired to extract colors having a high appearance frequency in the third and subsequent classes of the remaining classes. In such a case, after setting the setting area SE so that the color groups G (3) and G (4) are included in the setting area SE, the color groups G (3) and G (4) are used using the above-described circuit. As a result, the color groups G (5) and G (6) can be detected.

  As described above, if the user can appropriately set the setting area SE, it is convenient in that it makes it easier to effectively use existing hardware.

  Regarding the appearance frequency of the color in the image data D of the document original, the appearance frequency of the ground color (background color) of the paper having the largest area is the highest, and secondly, the appearance frequency of black characters is considered to be the highest. The pattern color is considered to be the third most frequently occurring. Therefore, ideally, the third most frequently occurring color in the image data D may be used as the pattern color. However, in practice, the appearance frequency of the pixel derived from the background color and the character color may be higher than the pattern color. In such a case, the pattern color cannot be correctly determined.

  Therefore, the color setting unit 13 estimates that the class having the largest frequency is the color group G (3) among the remaining classes that are the remaining classes excluding the class belonging to the setting region SE from the three-dimensional frequency distribution information. Then, the color of the color group G (3) is acquired as the pattern color. The color group G (3) corresponds to an example of the third class.

  Here, the color group G (3) includes a plurality of colors. Therefore, the color setting unit 13 selects the colors included in the color group G (3), that is, among the colors (pixel values) whose density values are represented by all 8 bits including the lower 4 bits, in the color group G (3). The color with the highest appearance frequency is set as the pattern color as the color of the color group G (3).

  The user interface unit I includes an operation input unit 18 and a display unit 5 configured by an LED (Light Emitting Diode), a liquid crystal display, or the like.

  The operation input unit 18 includes, for example, a start button, various setting buttons, or a touch panel. For example, the operation input unit 18 and the display unit 5 may be configured by a touch panel with a display function in which a liquid crystal display and a touch panel are integrated.

  The operation control unit 19 receives a signal indicating the operation input received by the operation input unit 18 and outputs a signal indicating the operation input to the image formation control unit 16.

  Specifically, for example, when a start button in the operation input unit 18 is pressed, the operation control unit 19 transmits a signal requesting the start of image formation to the image formation control unit 16. When the operation instruction to permit execution of the single color printing mode is received by the operation input unit 18, the operation control unit 19 sends a signal requesting setting of permission to execute the single color printing mode to the setting unit 20. Send to. When the operation input unit 18 accepts input of user identification information, the operation control unit 19 transmits the identification information to the image formation control unit 16.

  The operation input unit 18 corresponds to an example of a print instruction receiving unit, a permission instruction receiving unit, and an identification information receiving unit.

  Further, the operation control unit 19 causes the display unit 5 to display a display corresponding to the display request output from the system control unit 14 and the image formation control unit 16.

  The management unit 17 is a storage device configured using a storage element such as a RAM (Random Access Memory). The management unit 17 stores user identification information, for example, an ID code in advance. The management unit 17 stores identification information of a user who is permitted to form an image only in the monochrome mode and identification information of a user who is permitted to form an image in the monochrome mode and the full color mode.

  Hereinafter, a user who is permitted only to form an image in the monochrome mode is referred to as a monochrome limited user, and a user who is permitted to form an image in the monochrome mode and the full color mode is referred to as an unrestricted user. The monochrome limited user corresponds to the first user, and the unlimited user corresponds to the second user.

  Note that the management unit 17 does not necessarily need to store identification information of a user who is permitted to form an image in the monochrome mode and the full color mode.

  In addition, the management unit 17 stores charging information indicating a fee to be charged to the user in association with the identification information of each user.

  Thereby, for example, a contractor managing the image forming apparatus 1 can charge the user for the image formation by reading the billing information stored in the management unit 17. That is, in the image forming apparatus 1, the process for storing the charging information in the management unit 17 corresponds to the charging process.

  The system control unit 14 is configured using, for example, a microcomputer. The system control unit 14 comprehensively controls the operation of the image forming apparatus 1 by executing a predetermined control program. Further, the system control unit 14 causes the display unit 5 to display a display screen that requests the user to input identification information. Then, the system control unit 14 performs user authentication by comparing the identification information received by the operation input unit 18 with the identification information stored in the management unit 17.

  Further, the system control unit 14 causes the management unit 17 to store the charge of the print job performed by the authenticated user using the image forming apparatus 1 as the charging information in association with the identification information of the user. The system control unit 14 charges the user by storing the charging information in the management unit 17. The system control unit 14 corresponds to an example of a charging unit.

  The image reading control unit 15 is configured using, for example, a microcomputer. The image reading control unit 15 controls an image reading operation by the image reading unit 200 by executing a predetermined control program.

  The setting unit 20 is configured using, for example, a microcomputer. The setting unit 20 sets whether to allow execution of a pattern mode, which will be described later, by executing a predetermined control program. The pattern mode includes a single color pattern mode and a full color pattern mode.

  Hereinafter, the setting that allows the execution of the pattern mode is referred to as a pattern mode permission setting. That is, “with pattern mode permission setting” indicates that execution of the pattern mode is permitted, and “without pattern mode permission setting” indicates that execution of the pattern mode is not permitted.

  The setting unit 20 stores information indicating the pattern mode permission setting in, for example, the management unit 17 when a signal requesting the setting of the pattern mode execution permission is transmitted from the operation control unit 19. Thereby, the setting unit 20 performs pattern mode permission setting.

  The setting unit 20 may perform pattern mode permission setting as a setting of the entire image forming apparatus 1 regardless of the target user. For each user (identification information) stored in the management unit 17, the pattern mode is set. You may make it memorize | store the presence or absence of permission setting.

  The setting unit 20 may not be provided, and the monochrome mode limited user may be allowed to execute the pattern mode uniformly.

  Note that the setting unit 20 does not necessarily need to perform pattern mode permission setting for a user who is permitted to execute both the monochrome mode and the full color mode.

  The image formation control unit 16 is configured using, for example, a microcomputer. The image formation control unit 16 controls image formation by the image forming unit 40 by executing a predetermined control program.

  The image formation control unit 16 receives print image data from the image processing ASIC 10. The image formation control unit 16 has a monochrome mode, a full color mode, a single color pattern mode, and a full color pattern mode as image formation modes.

  The monochrome mode is a mode in which an image based on print image data is formed using only one color, for example, black. Specifically, the monochrome mode is a mode in which a monochrome image is formed on a sheet by printing an image based on printing image data using only black (K) color toner.

  The full color mode is a mode in which an image based on the printing image data is formed using a plurality of colors, that is, all colors that can be formed by the image forming unit 40. Specifically, in the full color mode, an image based on printing image data is printed by using each color toner of cyan (C), magenta (M), yellow (Y), and black (K). In this mode, an image is formed on a sheet. Hereinafter, all colors that can be formed by the image forming unit 40 are referred to as full colors.

  The full color mode may be a mode in which printing is performed using red, green, and blue color toners.

  The single color pattern mode is a mode in which an image based on print image data is formed on a sheet using two colors, a pattern color and black.

  The full color pattern mode is a pattern mode in which an image based on printing image data is formed on a sheet in full color. The full-color pattern mode is different from the full-color mode in that the full-color pattern mode is not executed when the color image has a certain size or more.

  The single color pattern mode is used when a part of a document written in black letters contains a small logo mark of one chromatic color, or in a document written in black letters, a single chromatic color underline. When marking is performed, it is assumed that the image is formed with black toner and only the pattern portion of the color such as a logo mark, underline, or marking is formed with the pattern color set by the color setting unit 13. Mode.

  Full-color pattern mode is underlined when a part of a document written in black letters contains a small logo that contains multiple chromatic colors, or a document written in black letters contains multiple chromatic colors. In this mode, it is assumed that characters are imaged with black toner and only a chromatic pattern such as a logo mark, underline, and marking is formed in full color.

  The system control unit 14 charges a higher fee when performing image formation in the full color mode than when performing image formation in the monochrome mode. The system control unit 14 charges the same amount as the monochrome mode when performing image formation in the single color pattern mode, and charges the same amount as in the full color mode when performing image formation in the full color pattern mode.

  The image formation control unit 16 determines the image formation mode based on information indicating whether the user who has performed user authentication is an unrestricted user or a monochrome-restricted user, presence / absence of a pattern mode permission setting, and three-dimensional frequency distribution information. decide. Then, the image forming control unit 16 controls the image forming unit 40 according to the determined image forming mode so that the image forming unit 40 forms an image on the sheet. Hereinafter, it is described that the image formation control unit 16 forms an image with the image formation unit 40 simply that the image formation control unit 16 forms an image.

  Note that the system control unit 14, the image reading control unit 15, the image formation control unit 16, the operation control unit 19, and the setting unit 20 may be functionally realized by, for example, a single microcomputer.

  FIG. 6 is a diagram conceptually illustrating an example of an image of a document original represented by the image data D. The image data D is, for example, data representing a document original image in which black characters (C) occupy most, the logo mark L is printed in color on the upper right of the paper, and the background (B) color, that is, the background color is white. It is.

  The logo mark L is an example of a pattern, for example, a dark green logo mark. Although the logo mark L is shown as an example of the pattern, the pattern may be a single color line, for example, a red underline, or a marker part in which some characters are painted with a single color such as a fluorescent color.

  In the background (B), there may be a case where a color different from the original background color is mixed due to show-through. However, the mixed colors are changed to the background color by the background color changing process described above. Accordingly, the colors existing in the image data D are basically only the background color, the character color, and the pattern color such as the logo mark L.

  7, 8, and 9 are explanatory diagrams illustrating an example of a histogram representing the appearance frequency of the color of each pixel of the image data D. FIG. 7 and 9 show histograms of the image data D when the logo mark L includes a plurality of colors. FIG. 8 is a histogram of the image data D when the logo mark L is a single color.

  In the histograms shown in FIGS. 7, 8, and 9, the total number of pixels of the image data D is 551 kilopixels (k pixels). The horizontal axis represents a class, and a background color, a character color, a logo color 1, a logo color 2, a logo color 3, a logo color 4, and “other colors” are assigned to each class. The vertical axis indicates the number of pixels of each class color in the image data D, that is, the appearance frequency (frequency).

  Below the horizontal axis, the appearance frequency of pixels belonging to each class and the frequency order number assigned in order of the appearance frequency are described. For “other colors”, the sum of the appearance frequencies of the fifth and subsequent colors in the order of appearance frequency is described as the appearance frequency. Moreover, the unit of the appearance frequency shown in FIG. 7, FIG. 8, and FIG. 9 is kilopixel (k Pixel).

  For example, the appearance frequency of the character color in FIG. 7 is 150 (k Pixel), which indicates that there are 150 × 1024 character color pixels in the image data D. Further, the appearance frequency of the logo color 3 in FIG. 7 is 0.5 (k Pixel), which indicates that 0.5 × 1024 pixels having the color of the logo color 3 exist in the image data D.

  In the following, the color with the frequency order number 1 is assigned as the first color, the color with the frequency order number 2 is indicated as the second color, and so on. To do. That is, the color with the highest appearance frequency in the image data D is referred to as the first color, the color with the second appearance frequency in the image data D is referred to as the second color, and similarly, in the order of the filing frequency of each color. Correspondingly, they are referred to as the third to sixth colors.

  In this case, the first color corresponds to the color of the color group G (1), the second color corresponds to the color of the color group G (2), and the third color corresponds to the color of the color group G (3). The fourth color corresponds to the color of the color group G (4), the fifth color corresponds to the color of the color group G (5), and the sixth color corresponds to the color of the color group G (6). .

  In FIG. 7, the appearance frequency of the first color, which is the background color, is the highest at 340 (k Pixel). Next, the appearance frequency of the second color, which is the character color, is 150 (k Pixel).

  The logo mark L shown in FIG. 7 is composed of a plurality of, for example, two chromatic colors of a logo color 1 and a logo color 2. The logo color 1 is the third color and the logo color 2 is the fourth color. Further, for example, the logo color 3 and the logo color 4 appear when the color of the pixel at the edge of the logo mark L is mixed with the color of the adjacent surrounding pixels. The logo color 3 is the fifth color and the logo color 4 is the sixth color.

  The appearance frequency of the third color (logo color 1) is 40 (k Pixel), the appearance frequency of the fourth color (logo color 2) is 20 (k Pixel), the fifth color (logo color 3), and the sixth color. The appearance frequency of (Logo Color 4) is 0.5 (k Pixel).

  In FIG. 8, the appearance frequency of the first color as the background color is the highest at 340 (k Pixel). Next, the appearance frequency of the second color, which is the character color, is 150 (k Pixel).

  In FIG. 8, the logo mark L is configured by a single color of logo color 1. The logo color 1 is the third color. Further, for example, the logo color 2 and the logo color 3 appear when the color of the pixel at the edge of the logo mark L is mixed with the color of the adjacent surrounding pixels. Logo color 2 is the fourth color and logo color 3 is the fifth color.

  In FIG. 8, the appearance frequency of the third color (logo color 1) is 60 (k Pixel), and the appearance frequency of the fourth color (logo color 2) and the fifth color (logo color 3) is 0.5 (k Pixel). ), The appearance frequency of the sixth color (logo color 4) is zero.

  In FIG. 9, the appearance frequency of the first color as the background color is the highest at 340 (k Pixel). Next, the appearance frequency of the second color, which is the character color, is 150 (k Pixel).

  The logo mark L in FIG. 9 is a multicolor logo that is full color and includes many chromatic colors. The logo mark L includes many colors in addition to the logo colors 1 to 4. The logo color 1 is the third color, the logo color 2 is the fourth color, the logo color 3 is the fifth color, and the logo color 4 is the sixth color.

  In FIG. 9, the appearance frequency of the third color (logo color 1) is 20 (k Pixel), the appearance frequency of the fourth color (logo color 2) is 0.5 (k Pixel), and the fifth color (logo color 3). ) Has an appearance frequency of 0.4 (k Pixel), and the sixth color (logo color 4) has an appearance frequency of 0.3 (k Pixel). In addition, there are many pixels with a color that appears less frequently than the sixth color, and the total appearance frequency of the pixels of the fifth color (pixels with a frequency order number of 5 or more) is 40.5 (k Pixel). Yes.

  Hereinafter, the operation of the image forming apparatus 1 shown in FIG. 2 will be described. 10 and 11 are flowcharts showing an example of the operation of the image forming apparatus 1.

  First, when the user inputs identification information using the operation input unit 18, the system control unit 14 compares the identification information received by the operation input unit 18 with the identification information stored in the management unit 17. If the comparison results of the identification information match, the system control unit 14 accepts the user's authentication and permits logon (YES in step S101).

  Then, for example, the image data of the original is read by the image reading unit 200, the intermediate image processing unit 31 performs intermediate image processing on the image data to generate image data D, and the image data acquisition unit 11 generates the image data D. Obtained (step S102).

  Next, the system control unit 14 refers to the management unit 17 and confirms whether or not the identification information received by the operation input unit 18 is for a monochrome limited user (step S103).

  If the identification information is not for a monochrome-only user, that is, if the user who has input the identification information is an unrestricted user (NO in step S103), the image formation control unit 16 causes the user to operate the operation input unit 18. In accordance with the mode setting used and input, the image forming unit 40 is caused to execute image formation in any one of the monochrome mode and the full color mode (step S104). When the image formation is completed, the system control unit 14 proceeds to step S112 so as to charge.

  On the other hand, if the identification information is for a monochrome limited user in step S103, that is, if the user who has input the identification information is a monochrome limited user (YES in step S103), the image forming control unit 16 allows the pattern mode permission. The presence or absence of setting is confirmed (step S106).

  If there is no pattern mode permission setting (NO in step S106), the image forming control unit 16 causes the image forming unit 40 to perform image formation in the monochrome mode (step S107). When the image formation is completed, the system control unit 14 proceeds to step S112 so as to charge.

  In step S112, the system control unit 14 causes the management unit 17 to store the fee according to the image formation mode executed in step S104 or step S107 in association with the identification information of the logged-on user. As a result, the user is charged.

  On the other hand, if there is a pattern mode permission setting in step S106 (YES in step S106), the image formation control unit 16 uses the frequency distribution acquisition unit 12 to perform the three-dimensional frequency distribution information as described above based on the image data D. Is generated (step S108).

  As a general rule, cost-effective color image formation is not performed for monochrome limited users. However, images that have black text in most documents and include chromatic colors such as logo marks, underlines, and markers, consume less color toner and print these patterns. There is little increase in cost by doing.

  Therefore, when there is a pattern mode permission setting (YES in step S106), the process proceeds to step S108 in order to allow image formation for an image with a small chromatic color area even for monochrome limited users.

  Note that step S106 may not be executed, and if YES in step S103, the process may move to step S108. In addition, the process of steps S101 and S103 to S107 may not be executed, and step S108 may be executed after step S102.

  Next, the image formation control unit 16 calculates the sum of the appearance frequencies (frequency) of the color group G (class) belonging to the setting area SE as a total value SUM1 (step S109).

  Then, the image formation control unit 16 calculates a value obtained by subtracting the total value SUM1 from the total number of pixels of the image data D as the number of color pixels CN (step S110).

  In the setting area SE, an area that linearly connects the color group G (1) and the color group G (2), that is, an achromatic area, a color (pixel) that may be generated by mixing the background color and the black character. Value) range. Accordingly, the number of color pixels CN corresponds to the number of pixels constituting a meaningful chromatic color (for example, a pattern or a figure) in the image data D. Then, the color pixel number CN represents the size of the area of the chromatic image.

  Next, the image formation control unit 16 compares the number of color pixels CN with a preset size determination value tf1 (step S111). The size determination value tf1 corresponds to the first reference frequency. If the number of color pixels CN is equal to or larger than the size determination value tf1 (NO in step S111), the area of the chromatic image is large. Therefore, the image formation control unit 16 is in the pattern mode for monochrome limited users. Execution is prohibited and the process proceeds to step S107. Then, image formation in the monochrome mode is executed.

  On the other hand, when the number of color pixels CN is less than the size determination value tf1 (YES in step S111), the image formation control unit 16 allows the monochrome limited user to execute the pattern mode and proceeds to step S121. As a result, the color of the logo mark L, which is important for the user, and the color of the underline, the marker, etc., in a range where the image area of the chromatic color is small and the increase in the cost due to the use of the chromatic color toner is small is used. It is possible to reproduce the above faithfully.

  Note that the size determination value tf1 is not necessarily a preset fixed value. For example, the ratio of the number of chromatic colors to the total number of pixels of the image data D may be stored in advance in a ROM, for example, as a size determination ratio. Since the total number of pixels of the image data D varies depending on the document size, the image formation control unit 16 may calculate the size determination value tf1 by multiplying the total number of pixels of the image data D by the size determination ratio. Good. A value obtained by multiplying the total number of pixels of the image data D by the size determination ratio may be set in advance as the size determination value tf1 for each document size. Alternatively, when the ratio of the number of color pixels CN to the total number of pixels of the image data D exceeds the size determination ratio, the number of color pixels CN may exceed the size determination value tf1 for each document size.

  Further, the image forming control unit 16 may move from step S110 to step S121 without executing step S111. Further, the image formation control unit 16 may move from step S109 to step S121 without executing steps S110 and S111.

  When the service provider stores the billing information in the management unit 17 so that the charge increases as the paper size on which image formation is increased, when the paper size is large and therefore the total number of pixels of the image data D is large, The fee is higher than when the paper size is small and the total number of pixels of the image data D is small. Therefore, when the paper size is large, the consumption cost of the chromatic color toner in the charged fee is small, so even if the monochrome limited user is allowed to perform color printing in the pattern mode, there is little damage to the service provider. Therefore, based on the size determination ratio, the larger the total number of pixels of the image data D, the larger the size determination value tf1 becomes. Based on the ratio of the number of color pixels CN to the total number of pixels of the image data D, monochrome Whether or not the pattern mode can be executed for a limited user may be determined.

  Next, in step S121, the color setting unit 13 sets a residual color group from the three-dimensional frequency distribution information by excluding the color group G belonging to the setting area SE as a residual class (step S121). For example, in the three-dimensional frequency distribution information shown in FIG. 4, the color groups G (3), G (4), G (5), and G (6) correspond to the remaining classes.

  Next, the color group having the highest appearance frequency among the color groups G determined as the remaining classes by the color setting unit 13 is estimated to be the color group G (3) as the third class (step S122). ).

  Next, the image formation control unit 16 selects the color group having the second highest appearance frequency among the remaining classes, that is, the color group considered to be the fourth highest appearance frequency in the frequency distribution of the entire image data D. Let G (4) (step S123). Then, the image formation control unit 16 compares the appearance frequency of the color group G (4) with the mode determination value tf2 (step S124). The mode determination value tf2 is a determination value for determining whether the chromatic pattern included in the image data D is a single color or a plurality of colors.

  Note that the mode determination value tf2 does not necessarily have to be a fixed value set in advance. For example, the ratio of the fourth color to the total number of pixels of the image data D when the pattern has a plurality of colors may be stored in advance in the ROM as a mode determination ratio, for example. The color setting unit 13 may calculate the mode determination value tf2 by multiplying the total number of pixels of the image data D by the mode determination ratio.

  Further, for each document size, a value obtained by multiplying the total number of pixels of the image data D by the mode determination ratio may be set in advance as the mode determination value tf2 for each document size. Alternatively, when the ratio of the appearance frequency of the color group G (4) to the total number of pixels of the image data D is less than the mode determination ratio, the appearance frequency of the color group G (4) is determined as the mode determination for each document size. It may be less than the value tf2.

  Then, when the appearance frequency of the color group G (4) is equal to or higher than the mode determination value tf2 (NO in step S124), the fourth color occupies a certain area or more. In this case, the pattern is considered to include a plurality of colors including at least the third color and the fourth color. Therefore, the image formation control unit 16 determines that the image data D includes a pattern of a plurality of colors, proceeds to step S125, and causes the image formation unit 40 to perform image formation in the full color pattern mode. (Step S125).

  For example, when the mode determination value tf2 is 1 (k Pixel) and the frequency distribution shown in FIG. 7 is obtained, the appearance frequency of the fourth color corresponding to the color group G (4) is 20 (k Pixel). Therefore, the appearance frequency of the fourth color belonging to the color group G (4) exceeds the mode determination value tf2 (NO in step S124), and the logo mark L is a multicolor logo including a plurality of colors by the image formation control unit 16. Is determined, and image formation in the full-color pattern mode is executed (step S125).

  As a result, when a pattern that wants to faithfully reproduce the original color, such as a company logo, includes a plurality of colors, the pattern can be formed in full color, thereby improving the reproducibility of the pattern.

  When the image formation is completed, the system control unit 14 adds a fee according to the number of color pixels CN to the monochrome mode fee, and stores the fee in the management unit 17 in association with the identification information of the logged-on user. (Step S126), and the process ends. The fee is added as the number of color pixels CN increases, that is, as the amount of chromatic color toner consumed in the full color pattern mode in step S125 increases. As a result, the user is charged.

  Note that the system control unit 14 does not necessarily have to charge so that the amount of addition increases as the amount of chromatic color toner consumed increases. Further, the system control unit 14 may be configured not to execute steps S112, S126, and S136. Further, the image forming apparatus 1 may not include the management unit 17. Further, the image forming apparatus 1 may not include the setting unit 20.

  On the other hand, when the appearance frequency of the color group G (4) is less than the mode determination value tf2 in step S124 (YES in step S124), there is a high possibility that the image data D includes a single color pattern. . Therefore, the image formation control unit 16 proceeds to step S131 to confirm whether or not the pattern included in the image data D is a single color.

  In step S131, the image formation control unit 16 calculates the sum of the appearance frequency of the color group G (3) and the appearance frequency of the color group G (4) as a total value SUM2 (step S131).

  Then, the image formation control unit 16 subtracts the total value SUM2 from the color pixel number CN, that is, the total appearance frequency value of the color group G belonging to the setting area SE and the color group G (3) from the total pixel number. A difference value obtained by subtracting the appearance frequency value and the appearance frequency value of the color group G (4) is calculated as the auxiliary determination value SV (step S132).

  Here, the auxiliary determination value SV corresponds to the sum of the appearance frequency values of the color groups G whose appearance frequency is the fifth or later in the image data D.

  Next, the image formation control unit 16 compares the auxiliary determination value SV with the mode determination determination value tf3 (step S133). The mode determination determination value tf3 corresponds to the third reference frequency.

  If the determination auxiliary value SV is equal to or greater than the mode determination determination value tf3 (NO in step S133), the image formation control unit 16 determines that the pattern included in the image data D includes a plurality of chromatic colors, The process proceeds to step S125. Then, as a result of image formation in the full color pattern mode, the reproducibility of a pattern including a plurality of chromatic colors is improved.

  On the other hand, if the determination auxiliary value SV is less than the mode determination determination value tf3 (YES in step S133), the image formation control unit 16 determines that the pattern included in the image data D is a single color, and proceeds to step S134. . Then, the color setting unit 13 sets the color of the color group G (3) as a pattern color (step S134).

  Specifically, among the plurality of colors included in the color group G (3) (colors distinguished by the lower 4 bits of the pixel value), the color having the largest number of pixels (appearance frequency) included in the image data D (Color represented by an 8-bit pixel value) is set as the pattern color.

  FIG. 12 is an explanatory diagram for explaining the pattern color determining operation by the color setting unit 13 shown in FIG. In FIG. 12, in the color group G (3) in the three-dimensional frequency distribution GG in which the value of each coordinate axis is the upper 4 bits, a plurality of colors CO in which the upper 4 bits of the pixel value are common and the lower 4 bits are different. include. The lower 4 bits of each element color in the pixel value of the color CO are assigned to the coordinate axes of the three-dimensional coordinates, and the frequency distribution of the colors included in the color group G (3) is expressed in three dimensions. Illustrated as distribution CC.

  Thus, the three-dimensional frequency distribution CC includes a plurality of colors CO (1) to CO (5), and the frequency distribution acquisition unit 12 uses the appearance frequency of the colors CO (1) to CO (5). Get (frequency). And the color setting part 13 determines the color with the most appearance frequency as a pattern color among the colors contained in the three-dimensional frequency distribution CC.

  In addition, it is good also as a structure which does not perform step S131-S133 and transfers to step S134, when it is YES at step S124. Further, steps S123 to S133 may not be executed, that is, the image forming control unit 16 may not have the full color pattern mode.

  Then, the image forming control unit 16 causes the image forming unit 40 to perform image formation in the single color pattern mode using the pattern color set by the color setting unit 13 and black (black toner) (step S135). . When the image formation is completed, the system control unit 14 causes the management unit 17 to store, for example, a charge equal to the monochrome mode charge as a single color pattern mode charge in association with the identification information of the logged-on user (step S136). The process is terminated.

  Hereinafter, the process of confirming whether or not the pattern included in the image data D is a single color in steps S131 to S133 will be specifically described with reference to FIGS.

  For example, when the mode determination value tf2 is 1 (k Pixel), the frequency of appearance of the fourth color (logo color 2) corresponding to the color group G (4) is 0.5 in the frequency distribution of the single color logo shown in FIG. (K Pixel), which is less than the mode determination value tf2 (YES in step S124).

  However, for example, when a number of colors having appearance frequencies of the fourth and subsequent colors are used little by little as in the frequency distribution of the multicolor logo shown in FIG. 9, the mode determination value tf2 is 1 (k Pixel), and The appearance frequency of the fourth color (logo color 2) corresponding to the color group G (4) is 0.5 (k Pixel), which is less than the mode determination value tf2 (YES in step S124).

  Therefore, when it is attempted to determine whether the pattern is a single color or a plurality of colors based only on the appearance frequency of the color group G (4) in step S124, a multicolor having a frequency distribution as shown in FIG. There is a possibility that the pattern is erroneously determined as a single color.

  Therefore, by executing steps S131 to S133, the risk of determining a multicolor pattern having a frequency distribution as shown in FIG. 9 as a single color is reduced.

  For example, in the frequency distribution of the single color logo shown in FIG. 8, 0.5 (k Pixel), which is the appearance frequency of other colors (the fifth and subsequent sums), is obtained as the auxiliary determination value SV. Here, the mode determination determination value tf3 is set to 1 (k Pixel), for example. Then, in step S133, the determination auxiliary value SV is less than the mode determination determination value tf3 (YES in step S133), so that the image formation control unit 16 correctly determines that the pattern included in the image data D is a single color. Thus, image formation in the single color pattern mode is performed.

  On the other hand, in the frequency distribution of the multicolor logo shown in FIG. 9, for example, 40.5 (k Pixel), which is the appearance frequency of the other colors (the fifth and subsequent sums), is obtained as the auxiliary determination value SV. Then, in step S133, the determination auxiliary value SV is equal to or greater than the mode determination determination value tf3 (NO in step S133), and therefore the pattern included in the image data D includes a plurality of chromatic colors by the image formation control unit 16. The image is correctly determined and image formation is performed in the full-color pattern mode.

  Note that steps S101 to S136 may be executed using the following group aggregate S (3) instead of the color group G (3).

  The image forming control unit 16 determines the color group G (class) and the color group in which the distance on the three-dimensional coordinate from the color group G (3) (third class) is less than the predetermined determination distance JD. A group obtained by combining G (3) (third class) together is defined as a group aggregate S (3) (enlarged third class).

  Further, the image formation control unit 16 sets the appearance frequency (frequency) of the color group G (class) included in the group aggregate S (3) as the appearance frequency of the group aggregate S (3), and out of the remaining classes A color group G (class) having the next highest appearance frequency (frequency) of the group aggregate S (3) is defined as a color group G (4) (fourth class). Steps S101 to S136 may be executed using the group aggregate S (3) and the color group G (4) obtained in this way.

  Further, the image formation control unit 16 also sets the color group G (4) in which the distance on the three-dimensional coordinates from the color group G (4) (fourth class) is less than the determination distance JD. G (class) and color group G (4) (fourth class) combined into one class group S (4) (extended fourth class), and the group set obtained in this way You may perform step S101-S136 using the body S (4).

  For example, 2 in the Euclidean distance is used as the determination distance JD. Here, the Euclidean distance d (a, b) between the color group G located at the coordinates a (a1, a2, a3) and the color group G located at the coordinates b (b1, b2, b3) is as follows. It is represented by the formula (1).

  13 and 14 are explanatory diagrams for explaining the group aggregate S when the determination distance JD is 2 in the Euclidean distance. FIG. 13 is a perspective view schematically showing an example of the configuration of the group assembly S. FIG. FIG. 14 is an exploded perspective view schematically showing an example of the configuration of the group assembly S. FIG.

  In FIG. 13 and FIG. 14, the group aggregate S (X) whose frequency order number is X is illustrated.

  As shown in FIGS. 13 and 14, the group aggregate S (X) includes a color group G (X), a color group G (X1) in which the surface or sides of the color group G (X) are in contact with each other, The group G (X) is composed of a color group G (X2) in which points are in contact with each other without faces and sides being in contact with each other. Hereinafter, the color group G (X1) is referred to as a first adjacent color group, and the color group G (X2) is referred to as a second adjacent color group.

  13 and 14, the group G (X) is represented by a broken line, the first adjacent color group G (X1) is represented by white, and the second adjacent color group G (X2) is represented by a shaded pattern. Yes.

  In the group aggregate S (X), the coordinates at which the first adjacent color group G (X1) and the second adjacent color group G (X2) have an Euclidean distance of less than 2 between the color group G (X) Is located.

  The color setting unit 13 is obtained by adding the appearance frequency of the color group G (X), the appearance frequency of the first adjacent color group G (X1), and the appearance frequency of the second adjacent color group G (X2). The appearance frequency is stored in the RAM, for example, as the appearance frequency of the group aggregate S (X).

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 5 Display part 6 Stack tray 11 Image data acquisition part 12 Frequency distribution acquisition part 13 Color setting part 14 System control part 15 Image reading control part 16 Image formation control part 17 Management part 18 Operation input part 19 Operation control part 20 Setting unit 22 Image forming main body 31 Intermediate image processing unit 40 Image forming unit 41 Transfer device 43 Photosensitive drums 44K, 44Y, 44M, 44C Developing device 45 Fixing device 48 Discharge tray 49 Transfer drum 200 Image reading unit 210 Document feeding unit 211 Document tray 220 Scanner unit 229 CCD
230 Reading Window 10 Image Processing ASIC
B Bus CN Number of color pixels d Euclidean distance D Image data G Color group I User interface section JD Determination distance L Logo mark S Group aggregate SE Setting area SL Area SUM1, SUM2 Total value SV Determination auxiliary value tf1 Size determination value tf2 Mode determination Value tf3 Mode decision judgment value

Claims (9)

An image data acquisition unit for acquiring image data representing a color image;
A frequency distribution acquisition unit that assigns a color of each pixel of the image data to a class in statistics, and acquires a frequency distribution in which the frequency of appearance of each color in the image data is a frequency in statistics;
A color setting unit that acquires a color belonging to a third class, which means a class having the third highest frequency in the frequency distribution, as a pattern color that is a predetermined pattern color;
An image forming control unit having a pattern mode for forming an image including at least one chromatic color on a sheet, the number of pixels of the pattern being less than a preset size determination value;
The pattern mode includes a single color pattern mode for forming an image based on the image data on a sheet using the pattern color,
The image data is data representing the color of each pixel by density values of three preset element colors,
The frequency distribution acquisition unit
By assigning the density value of each element color to each coordinate axis of a three-dimensional coordinate, the color of each pixel is arranged on each of the three-dimensional coordinates as each class, and the frequency of appearance of the color corresponding to each class is represented by a frequency. By associating with each of the classes, the three-dimensional frequency distribution information representing the frequency distribution in three-dimensional coordinates is generated,
The color setting unit
On the three-dimensional coordinates, a class that belongs to a set area that is set so as to include an area that linearly connects a class to which white belongs and a class to which black belongs is a residual class that is excluded from the three-dimensional frequency distribution information. An image forming apparatus that obtains a class having the highest frequency among the remaining classes as the third class, and acquires a color of the third class as the pattern color. The image formation control unit
2. The image forming apparatus according to claim 1, wherein execution of the pattern mode is prohibited when a value obtained by subtracting a total frequency of classes belonging to the setting area from the total number of pixels of the image data exceeds the size determination value. . The image formation control unit
The class having the second highest frequency among the remaining classes is set as the fourth class having the fourth highest occurrence frequency in the entire frequency distribution, and the frequency of the fourth class satisfies the preset mode determination value. The image forming apparatus according to claim 1, wherein when there is no image formation, the image formation in the single color pattern mode is executed. The pattern mode is
Including a full color pattern mode for forming an image based on the image data on a sheet using a plurality of chromatic colors;
The image formation control unit
The image forming apparatus according to claim 3, wherein when the frequency of the fourth class is equal to or higher than the mode determination value, image formation in the full color pattern mode is executed. The image formation control unit
The frequency of the fourth class is less than the mode determination value, and from the total number of pixels of the image data, the total frequency of the class belonging to the setting area, the frequency of the third class, and the first The image forming apparatus according to claim 4, wherein when the value obtained by subtracting the frequency of the fourth class is equal to or greater than a preset mode determination determination value, image formation in the full color pattern mode is executed. The image formation control unit
A class in which the distance from the third class on the three-dimensional coordinate is in a range that does not satisfy a predetermined determination distance and the third class and the third class are combined into an expanded third class. The frequency of each class included in the expanded third class is defined as the frequency of the expanded third class, and the class having the second highest frequency after the expanded third class among the remaining classes is 4 in the frequency distribution. The image forming apparatus according to claim 3, wherein the fourth class having the second highest appearance frequency is used. A charge unit for charging the image formation fee to the user;
The billing unit
The charging is performed by increasing the fee as the difference value obtained by subtracting the sum of the frequencies of the classes belonging to the setting area from the total number of pixels of the image data is increased. Image forming apparatus. An identification information receiving unit that receives input of user identification information;
A user who is permitted only to form an image in the monochrome mode among a monochrome mode that forms an image based on the image data using only one color and a full color mode that forms an image based on the image data using a plurality of colors. A management unit for storing identification information of a monochrome-only user;
A permission instruction receiving unit that receives a permission instruction that is an instruction for permitting execution of the pattern mode;
The image formation control unit
When the identification information received by the identification information receiving unit is identification information of the monochrome limited user and the permission instruction is received by the permission instruction receiving unit, image formation in the pattern mode is permitted, and the identification 8. The image formation in the pattern mode is prohibited when the identification information received by the information reception unit is the identification information of the monochrome limited user and the permission instruction is not received by the permission instruction reception unit. The image forming apparatus according to any one of the above. An identification information receiving unit that receives input of user identification information;
A user who is permitted only to form an image in the monochrome mode among a monochrome mode that forms an image based on the image data using only one color and a full color mode that forms an image based on the image data using a plurality of colors. A management unit for storing identification information of a certain monochrome limited user,
The image formation control unit
The identification information received by the identification information receiving unit is the monochrome limited user identification information, and a difference value obtained by subtracting the total frequency of the class belonging to the setting area from the total number of pixels of the image data is the size. When the determination value is not satisfied, image formation in the pattern mode is allowed, the identification information received by the identification information receiving unit is the identification information of the monochrome limited user, and the difference value is greater than or equal to the size determination value The image forming apparatus according to claim 1, wherein image formation in the pattern mode is prohibited.

Images