JP2008177882A - Image processing device - Google Patents

Abstract

Image processing is appropriately performed according to an object.
A command analysis unit 202 that determines raster data from print data described in a page description language, a color space determination unit 203 that determines whether raster data is configured in an RGB color space, and an RGB color space Are determined, a color space conversion unit 204 that converts raster data into a YCbCr color space, and an attribute determination unit 205 that determines image data attributes from each pixel of raster data configured in the YCbCr color space. An intermediate data generation unit 206 and a rendering unit 207 that process raster data configured in an RGB color space based on the attribute.
[Selection] Figure 5

Description

  The present invention relates to an image processing apparatus such as a copying machine, a printer, or a printing machine that performs image formation with a plurality of colors.

  Currently, many printers have a technique for obtaining an optimal print result by switching color conversion processing, halftone pattern, and the like according to the type of object (text, graphics, raster, etc.) to be printed. For example, in a vector object such as a character or a graphic, the number of lines on the screen is set to a high resolution so that the edge of the character becomes clear or the gradation pattern becomes inconspicuous. In addition, raster data such as photographs emphasizes the gradation that makes the change in color smooth by setting the number of screen lines to be low. In addition, for color conversion processing, text and graphics use a color table that emphasizes saturation, and for photos, a color table that emphasizes gradation so that natural colors can be expressed, Color conversion is performed.

  However, although it is drawn as text or graphics on the screen of a personal computer, it may be generated as raster data depending on the type of PDL (Page Description Language). The raster data included in the PDL command data transmitted to the printer is not only photographic data (natural image). Even if image processing is performed according to the type of object, the print result may not be optimal.

  For example, as shown in FIGS. 3 and 4, even when the same red rectangle is drawn by an application, when PDL command data is generated by vector graphics (graphics), a print image as shown in FIG. 3 is obtained. When PDL command data is generated with raster data (raster image), a print image as shown in FIG. 4 is obtained. In this way, since different color tables and halftones are used in the image processing apparatus that has received the PDL command data, objects that look the same on the screen of the personal computer will be different in the print result.

Here, the technique disclosed in Patent Document 1 discloses a method of determining raster data of interest from the type of image and the number of pixels, and performing optimal image processing according to the determination result.
JP 2005-335372 A

  In the technique disclosed in Patent Document 1, brightness, saturation, and number of colors are counted from the type and number of pixels included in raster data, and the type of raster image is determined from the results. However, in order to reliably determine the type of image, it is necessary to finely classify and count the types of pixels constituting the bitmap. Therefore, the process for determination becomes complicated.

  In view of the above, an object of the present invention is to provide an image processing apparatus that can easily and appropriately perform image processing according to an object.

  The present invention relates to a type determination unit that determines the type of an object from print data described in a page description language, and a color space conversion unit that converts image data of an object from a first color space to a second color space. And an attribute determination unit that determines the attribute of the image data subjected to color space conversion, and an image processing unit that performs image processing on the print data based on the type and attribute of the object to generate image data for printing. Is.

  As a result, the type and attribute of the object can be determined, and the optimum image processing can be selected. That is, the type determination unit determines whether the type of the object is a raster image or a vector image. If it is determined as a vector image, the attribute determination unit determines the attribute of the object as character / graphics.

  If the image data of the object uses the first color space when it is determined as a raster image, the color space conversion unit converts the image data to the second color space. The attribute determination unit determines the color attribute of the image data.

  Specifically, a color space determination unit that determines whether or not the raster data is configured in the first color space when the type determination unit determines that the image is a raster image. When the color space determination unit determines that the color space is the first color space, the color space conversion unit converts the raster data into the second color space. The attribute determining unit determines the attribute of the image data from each pixel of the raster data configured in the second color space. The image processing unit processes the raster data configured in the first color space based on the determined attribute. Here, the first color space is composed of an RGB color space, and the second color space is composed of a YCbCr color space. When the color space determination unit determines that the color space is not the first color space, color space conversion is not performed, and the attribute determination unit determines the attribute of the image data from each pixel of the raster data.

  The attribute determining unit determines an attribute of the raster data depending on whether or not the luminance value of each pixel is constant among the raster data configured in the second color space. This determines whether the image is a solid image.

  The attribute determination unit determines an attribute of the raster data depending on whether or not the color difference value of each pixel is constant among the raster data configured in the second color space. As a result, the color attribute is determined to be color or gray.

  According to the present invention, it is possible to easily and optimally perform image processing on each object by determining whether the raster data is a natural image or a solid image from the characteristics of the raster data as well as the object attributes. It becomes.

  An image processing apparatus of this embodiment is shown in FIG. This image processing apparatus is a digital multi-function peripheral, and outputs a paper Pb on which a full color or monochrome image is formed on a paper Pa based on image data given from the outside of the apparatus. The image processing apparatus includes an exposure unit 19, photosensitive drums 12a to 12d, developing devices 13a to 13d, toner cartridges 23a to 23d, an intermediate transfer belt 11 for forming an image, a secondary transfer roller 14, and A fixing unit 21 including a primary transfer roller, a heating roller (also referred to as a fixing roller) and a pressure roller, a paper separating roller 16, and a paper discharge tray 18 are provided. In FIG. 1, the sheet conveyance path is indicated by a one-dot chain line, and the sheet is guided along the conveyance path by a predetermined roller including a conveyance roller. However, detailed description thereof is omitted.

  This image processing apparatus forms an image based on image data corresponding to each hue of four colors including black (K) and three subtractive primary colors, cyan (C), magenta (M), and yellow (Y). I do. For example, the image processing apparatus includes a photosensitive drum 12a, a developing device 13a, a charging roller, and a cleaning unit for forming a black image, and a similar configuration (photosensitive) for performing image formation for the other three colors. Body drums 12b to 12d and developing devices 13b to 13d). These components are arranged in a line as shown in FIG. 1 along the moving direction of the intermediate transfer belt 11.

  The charging roller is a contact-type charger that uniformly charges the surfaces of the photosensitive drums 12a to 12d, which are image carriers, to a predetermined potential. In this embodiment, the charging roller is used as a charging device. However, the charging device to be used is not limited to the charging roller. For example, a fur brush, a magnetic brush, or a corona wire is used. As long as it has a sawtooth shape or an ion generator, it can be used as long as it imparts a desired charging potential to the photoreceptor.

  The exposure unit 19 that is a laser beam scanning device includes a semiconductor laser, a polygon mirror 15, a plurality of reflection mirrors, and the like. Each of the four laser beams modulated based on the image data corresponding to the hues of black, cyan, magenta, and yellow is irradiated onto the surfaces of the corresponding photosensitive drums 12a to 12d. As a result, electrostatic latent images based on image data corresponding to the hues of black, cyan, magenta, and yellow are formed on the surfaces of the photosensitive drums 12a to 12d. Instead of the semiconductor laser, for example, a well-known write head in which EL or LED is arranged in an array may be used.

  The toner cartridges 23a to 23d are detachably attached near the upper portions of the developing devices 13a to 12d, and store toner that is a developer corresponding to a hue of black, cyan, magenta, or yellow.

  The developing devices 13a to 13d supply toner to the surfaces of the photosensitive drums 12a to 12d on which the electrostatic latent images are formed, and visualize the electrostatic latent images into toner images that are developer images. Specifically, the developing devices 13a to 13d receive toner corresponding to the hue from a supply port (not shown) of the toner cartridges 23a to 23d mounted on the upper portion, and the hue formed on the photosensitive drums 12a to 12d by the toner. The electrostatic latent image corresponding to 1 is visualized as a toner image corresponding to the hue of black, cyan, magenta, or yellow. The cleaning unit 17 removes and collects toner remaining on the surfaces of the photosensitive drums 12a to 12d after development and image transfer.

  The intermediate transfer belt 11 has a structure in which a film having a thickness of about 100 to 150 μm is formed in an endless manner. The intermediate transfer belt 11 is stretched between a driving roller and a driven roller and looped as shown in FIG. Forming a pathway. The outer peripheral surface of the intermediate transfer belt 11 faces the photosensitive drum 12d, the photosensitive drum 12c, the photosensitive drum 12b, and the photosensitive drum 12a. The intermediate transfer belt 11 rotates in this order so as to face the photosensitive drums 12a to 12d. A primary transfer roller is disposed at a position facing each of the photosensitive drums 12a to 12d with the intermediate transfer belt 11 interposed therebetween. These primary transfer rollers are rollers having a shaft made of a metal (for example, made of stainless steel) having a diameter of 8 to 10 mm as a base, and the surface thereof being covered with a conductive elastic material (for example, EPDM or urethane foam). With this conductive elastic material, a high voltage can be uniformly applied to the intermediate transfer belt 11. In addition, although it shall be a roller shape here, a brush etc. may be sufficient.

  When forming a full-color image, the primary transfer roller has a reverse polarity to the toner charging polarity (-) in order to transfer the toner image carried on the surface of the photosensitive drums 12a to 12d onto the intermediate transfer belt 11. A primary transfer bias having a constant voltage of (+) is applied. Further, the primary transfer roller is pressed against the inner peripheral surface of the intermediate transfer belt 11 with a predetermined nip pressure. As a result, the toner images corresponding to the respective hues formed on the photosensitive drums 12a to 12d are transferred so as to be sequentially superimposed on the outer peripheral surface of the intermediate transfer belt 11, and a full-color toner image is formed on the outer peripheral surface of the intermediate transfer belt 11. It is formed. When a monochrome image is formed, only the primary transfer roller arranged at a position facing the black photosensitive drum 12a is charged, and the primary arranged at a position facing the other photosensitive drums 12b to 12d. The transfer roller is not charged and is separated from the intermediate transfer belt 11 by a predetermined distance by a predetermined separation / contact mechanism. As a result, only a black toner image is formed on the outer peripheral surface of the intermediate transfer belt 11.

  The toner image transferred onto the outer peripheral surface of the intermediate transfer belt 11 in this way is conveyed to a position facing the secondary transfer roller 14 by the rotation of the intermediate transfer belt 11. At the time of image formation, the secondary transfer roller 14 is pressed against the outer peripheral surface of the intermediate transfer belt 11 whose inner peripheral surface is in contact with the peripheral surface of the driving roller with a predetermined nip pressure. In the case of such pressure contact, one of the pair of rollers is made of a hard material such as metal, and the other is made of an elastic material such as an elastic rubber roller or a foamed resin roller.

  The paper Pa is fed by a paper handling roller 16 that pulls out the paper Pa one by one from the paper feed cassette. When the paper Pa passes between the secondary transfer roller 14 and the intermediate transfer belt 11, a high voltage having a polarity opposite to the charging polarity of the toner is applied by the secondary transfer roller 14. As a result, a full-color or monochrome toner image is transferred from the outer peripheral surface of the intermediate transfer belt 11 to the surface of the paper Pa. The toner remaining on the intermediate transfer belt 11 without being transferred onto the paper among the toner adhering to the intermediate transfer belt 11 includes a cleaning blade provided so as to be in sliding contact with the driven roller in order to prevent color mixing. Collected by the unit.

  The paper Pa on which the toner image, which is a full-color or monochrome image, is transferred is guided to the fixing unit 21 and passes between a heating roller and a pressure roller constituting the fixing unit 21 and is heated and pressed. The heating roller is set to have a predetermined fixing temperature by the control unit based on a signal from a temperature detector (not shown). By the operation of the fixing unit 21, the toner image is firmly fixed on the surface of the paper Pa. The paper Pb on which the toner image is fixed is discharged onto the paper discharge tray 18 (with the printing surface facing downward) by the paper discharge roller.

  The image forming operation as described above is performed by a plurality of driving units including an electric motor and gears (not shown) and a control unit that controls these driving units. The function of the control unit is realized by a microcomputer that receives information such as a sensor and an operation input unit (not shown).

  A functional configuration of the image processing apparatus including the function of the control unit will be described. As shown in FIG. 2, the image processing apparatus 10 receives print data given via a predetermined communication line from the data processing apparatus 2 or the like, which is an external computer terminal, and displays an image corresponding to the received print data in a predetermined manner. Output on paper.

  The print data is a file including data described in a page description language (PDL) that can be interpreted by the image processing apparatus 10. Further, the image processing apparatus 10 and the data processing apparatus 2 are connected so as to be able to communicate with each other by a LAN (Local Area Network) 5 including a predetermined cable or a hub. Instead of the LAN 5, a known mutual communication network such as a WAN (Wide Area Network) or the Internet, or a communication connection means such as a USB (Universal Serial Bus) connection or various parallel interfaces may be used.

  The image processing apparatus 10 includes an operation display including a CPU 101, a memory (semiconductor memory) 102, a printer controller 100 including various interfaces, a display device including a liquid crystal display and an input device including a touch panel and buttons. Unit 20, a hard disk storage device (hereinafter abbreviated as "hard disk" or "HDD") 30 including a disk-shaped magnetic storage medium, and image formation for forming an image on a sheet and discharging the sheet to the outside of the apparatus Part 40.

  The image forming unit 40 receives bitmap data for printing via the video controller 115 and forms a corresponding image on a predetermined sheet. The detailed configuration of the image forming mechanism in the image forming unit 40 is as described above.

  The printer controller 100 which is a control unit includes a CPU 101, a memory 102, an operation display unit interface 112 which is a connection interface with the operation display unit 20, a hard disk interface 113 which is a connection interface with the hard disk 30, and band data which will be described later. A compression / expansion circuit 114 that compresses or expands the image, a video controller 115 that is a connection interface with the image forming unit 40, and a network interface 116 that communicates with the data processing apparatus 2 via the LAN 5.

  The CPU 101, a RAM 102 that is a freely readable / writable memory and a ROM 102 that is a read-only memory, and the various interfaces are each a predetermined bus (such as a memory bus, a system bus, or a peripheral bus). Connected with. Since the connection by these buses is a well-known configuration in a general computer, detailed description thereof is omitted.

  The printer controller 100 optically reads an image of a target document, and receives an image read by a scanner unit (not shown) formed on a predetermined sheet and output from a so-called copying function or an external data processing device 2. The printer has various known functions such as a so-called printer function for forming and outputting print data (image data) on a predetermined sheet.

  These functions are typically realized by the CPU 101 executing a predetermined program built in the ROM of the memory 102 or expanded in the RAM. Here, the program is provided by a recording medium such as a CD-ROM in which the program is recorded. That is, a CD-ROM serving as a recording medium for the program is mounted on a CD-ROM driving device (not shown) built in the image processing apparatus 10 as an auxiliary storage device, and the program is read from the CD-ROM to obtain a hard disk. 30 installed. The program may be provided via a recording medium other than a CD-ROM or a communication line. When a predetermined operation for starting the image processing apparatus 10 is performed, the predetermined program installed in the hard disk 30 is transferred to the RAM, expanded there, and executed by the CPU 101. Thereby, the various functions described above are realized.

  The printer controller 100 has a PDL interprinter 200 shown in FIG. The PDL interpreter 200 includes an input interface unit 201, a command analysis unit 202, a color space determination unit 203, a color space conversion unit 204, an attribute determination unit 205, an intermediate data generation unit 206, a rendering unit 207, and a print processing unit 208. ing.

  The input interface unit 201, the command analysis unit 202, the color space determination unit 203, the color space processing unit 204, the attribute determination unit 205, the intermediate data generation unit 206, the rendering unit 207, and the print processing unit 208 are realized by software, It is stored in the memory 102 in the form of a code. All or a part of these can be realized by hardware.

  The input interface unit 201 acquires the PDL command data sent from the data processing device 2 such as a host computer and temporarily stores it. The PDL command data stored in the input interface unit 201 is transferred to the command analysis unit 202 and sequentially analyzed. If the analyzed PDL command is raster data, the color space determination unit 203 determines whether the raster data is in RGB space. When it is determined that the color space is the RGB color space (first color space), the color space conversion unit 204 converts the color space into the YCbCr color space (second color space). The attribute determination unit 205 determines the attribute of the raster data based on the information on the YCbCr color space. The intermediate data generation unit 206 generates intermediate data in which the analyzed PDL command is classified in units of objects and bands. The intermediate data describes an object to be drawn and its attributes (object type, coordinates, color information, etc.). The rendering unit 207 generates print image data based on the intermediate data for each band. The print processing unit 208 transmits the print image data generated by the rendering unit 207 to the print engine.

  Here, the command analysis unit 202 functions as a type determination unit that determines the type of an object from print data described in a page description language, and determines whether the type of the object is a raster image or a vector image. The color space determination unit 203 determines whether or not the raster image is configured in the RGB color space. The attribute determination unit 205 determines the attribute of the raster data depending on whether or not the luminance value of each pixel is constant among the raster data configured in the YCbCr color space, and the color difference value of each pixel of the raster data. Depending on whether or not is constant, the attribute of the raster data is determined. The intermediate data generation unit 206 and the rendering unit 207 function as an image processing unit that performs image processing on print data based on the type and attribute of the object and generates image data for printing.

Next, a method for determining what kind of image the raster data is based on the characteristics of the raster data image will be described.
When Y is luminance, Cb is color difference (blue), Cr is color difference (red), and each value is in the range of 0 to 255, conversion from RGB to YCbCr is performed by the following conversion formula.

Y = 0.2990R + 0.5870G + 0.1140B
Cb = −0.1687R−0.3313G + 0.5000B + 128
Cr = 0.5000R-0.187G-0.0813B + 128
For example, when red (R = 255, G = 0, B = 0) is converted to a YCbCr value,
Y = 0.299x255 = 76
Cb = −0.1687 × 255 + 128 = 85
Cr = 0.5 × 255 + 128 = 255
It becomes.

In the case of the bitmap of FIG. 4, since the total pixel value Y is 76, if Y is a constant value, it is determined as a solid image. For example, when 50% gray (R = 128, G = 128, B = 128) is converted into a YCbCr value,
Y = 0.299x128 + 0.5870x128 + 0.114x128 = 143
Cb = −0.1687 × 128−0.3313 × 128 + 0.5 × 128 + 128
= 128
Cr = 0.5 × 128−0.4187 × 128−0.0813 × 128 + 128
= 128
It becomes.

  In the case of gray, Cb = Cr = 128. Therefore, if Cb = Cr = 128, it is determined as a gray image. In this way, it is determined what kind of image the raster data is.

  Next, image processing of PDL command data given from the data processing device 2 via the LAN 5 will be described in detail with reference to FIGS. The PDL data sent from the data processing device 2 to the image processing device is sequentially analyzed by the PDL interpreter 200 (S101). The type of object is determined from the type of command (S102).

  If it is determined that the object of interest is not raster data, that is, a vector image, the attribute of the object is set to character / graphics (S114). If the object is determined to be raster data (bitmap), the color space used by the raster data is confirmed. The color space used in the raster data includes RGB color and black and white, and is raster data corresponding to the color space. If the color space is not RGB, it is determined that the raster data is black and white, the object attribute is set to raster (bitmap), and the color attribute is set to black and white (S113).

  If it is determined in S103 that the color space of the raster data is RGB, first, the object attribute is set to character / graphics and the color attribute is set to gray (S104). Next, one pixel of the raster data is converted from the RGB color space to the YCbCr color space using the conversion formula described above (S105). Before referring to the Y (luminance) value of the target pixel, it is checked whether or not the attribute of the object is raster (S106). If the object attribute is already set in the raster data, it is no longer necessary to refer to the Y value.

  If the attribute of the object is not raster, the Y (luminance) value is referred to and compared with the Y value of the previous pixel (S107). If the Y value is not the same as the previous pixel, it is determined that the raster data is not a solid image, and the attribute of the object is set to raster (S108). If the Y value is the same as that of the previous pixel, the object attribute is not changed and the process proceeds to S109.

  Next, referring to the values of Cb and Cr, it is confirmed whether Cb = Cr = 128 (S109). If Cb = Cr = 128, it is determined that the image is not a gray image, and the color attribute is set to color (S110). Steps S110 to S110 are repeated until there are no more pixels to be converted.

  If the attribute of the object is set to raster in S106, it is checked whether the color attribute is set to color (S112). If the color attribute is set to color, it is determined that the image is a natural color image, the process of checking the pixels is terminated, and the process proceeds to S201. If the color attribute is not set to color, the process proceeds to S109 and the process is continued.

  When the raster data attribute is determined, as shown in FIG. 7, the object attribute is read to determine the image processing mode of the currently processed object (S201). Color conversion processing, gray processing, and halftone processing are switched depending on the type of object.

  FIG. 8 shows a drawing mode of image processing for each object. Four drawing modes are set according to the object type and color attribute.

  It is confirmed whether or not the object attribute read in S201 is a raster (S202). If it is not a raster, the drawing mode is set to mode 1 (S210), and an intermediate code of the object currently being processed is generated (S206). ). If the object attribute read in S201 is raster, the color attribute is read (S203), and it is confirmed whether the color attribute is color (S204). If it is color, the drawing mode is set to mode 4 and an intermediate code of the object currently being processed is generated (S206). If the color attribute is gray in S211, the drawing mode is set to mode 3 (S212), and an intermediate code is generated (S206). If not gray, the drawing mode is set to mode 2 (S213), and an intermediate code of the object currently being processed is generated (S206). It is confirmed whether there is a PDL command to be processed (S207). If there is a PDL command, the processes from S101 to S206 are repeated. When all the PDL commands have been processed, the generated intermediate code is converted into bitmap data for printing (S208). Thereafter, the printing process is executed (209), and the printing process is terminated.

  In addition, this invention is not limited to the said embodiment, Of course, many corrections and changes can be added to the said embodiment within the scope of the present invention. The image processing apparatus is not limited to a multifunction machine, and may be a color printer.

The figure which shows schematic structure of the image processing apparatus which concerns on this Embodiment. Control block diagram of image processing apparatus The figure which shows the detail of the PDL command when an object is described by vector graphics The figure which shows the detail of the PDL command when an object is described by raster data The figure which shows the structure of a PDL interprinter Flowchart showing image processing procedure for input print data Flowchart showing image processing procedure for input print data The figure for demonstrating the drawing mode of the image processing for every object

Explanation of symbols

2 Data processing device 10 Image processing device 20 Operation display unit 30 Hard disk 40 Image forming unit 100 Printer controller 200 PDL interprinter 201 Input interface unit 202 Command analysis unit 203 Color space determination unit 204 Color space conversion unit 205 Attribute determination unit 206 Intermediate data Generation unit 207 Rendering unit 208 Print processing unit

Claims (6)

A type determination unit that determines the type of an object from print data described in a page description language, a color space conversion unit that converts the image data of an object from a first color space to a second color space, and a color space An attribute determination unit that determines the attribute of the converted image data, and an image processing unit that performs image processing on the print data based on the type and attribute of the object to generate image data for printing An image processing apparatus. The type determining unit determines whether the type of the object is a raster image or a vector image, and when the type is determined to be a raster image, if the image data of the object uses the first color space, the color space converting unit The image processing apparatus according to claim 1, wherein the image data is converted from the first color space to the second color space, and the attribute determination unit determines a color attribute of the image data. A type determining unit that determines raster data from print data described in a page description language, a color space determining unit that determines whether or not raster data is configured in a first color space, and a first color space A color space conversion unit that converts the raster data into the second color space, and an attribute determination unit that determines the attribute of the image data from each pixel of the raster data configured in the second color space. An image processing apparatus comprising: an image processing unit that processes raster data configured in the first color space based on the attribute. 4. The image processing apparatus according to claim 1, wherein the first color space is composed of an RGB color space, and the second color space is composed of a YCbCr color space. The attribute determination unit determines an attribute of the raster data according to whether or not the luminance value of each pixel is constant among the raster data configured in the second color space. Image processing apparatus. The attribute determination unit determines an attribute of the raster data according to whether or not the color difference value of each pixel is constant among the raster data configured in the second color space. Image processing apparatus.

Images