JP5810789B2 - Image forming apparatus and program - Google Patents

Description

  The present invention relates to an image forming apparatus that forms a color image using a plurality of colorants including black.

  In an electrophotographic printer or the like, C (cyan), M (magenta), Y (yellow), and K (black) toners (colorants) are used to form images of four color plates of CMYK. Generally, a color image is obtained by superimposing.

  In addition to the four color plates of CMYK, a printer in which one color plate is added for the purpose of performing special printing using special color toner such as transparent toner is known (for example, see Patent Document 1). ).

  The object of the present invention is to make use of a printer having an additional version in addition to the four color plates of CMYK described above, and to achieve both high-quality reproduction of sharp characters and line drawings and smooth image reproduction. It is to realize image formation with high image quality.

In order to achieve the above object, an image forming apparatus according to the present invention includes:
Image forming means for forming a color image using a plurality of colorants including black,
And halftone processing data of the color component data for creating a character / line drawing area of color component data of a color image corresponding to a predetermined color of the plurality of colors, and a picture area of the color component data Halftone processing data of the color component data is generated as first and second color plane data of the predetermined color, respectively, and color component data of the color image corresponding to each color other than the predetermined color in the plurality of colors Image processing means for generating each halftone processing data as color plate data of each color,
In the image forming means, image formation of two color plates using the colorant of the predetermined color is performed according to the first and second color plate data of the predetermined color, and according to the color plate data of each color other than the predetermined color It is configured to perform image formation of one color plate using the colorant of each color ,
The halftone process applied to the first color plane data of the predetermined color is a binary halftone process, and the halftone process applied to the second color plane data of the predetermined color is ternary or quaternary or higher. Multi-value halftone processing .

  Since the color plate data of a predetermined color is multiplexed with the first color plate data for forming the character / line drawing area and the second color plate data for forming the picture area, each color plate data The halftone processing method and resolution can be individually optimized for the data. Specifically, a halftone process with good reproducibility of characters and line drawings is applied to the first color plane data, and a halftone process with good pattern reproducibility is applied to the second color plane data. And so on. Therefore, for a color plate of a predetermined color, it is possible to easily achieve both sharp character / line drawing reproduction and smooth picture reproduction, and to form a high-quality image.

1 is a block diagram for explaining an overall configuration of an image forming apparatus according to an embodiment of the present invention. It is a block diagram for demonstrating 1st Example of a halftone processing part. It is a schematic diagram for demonstrating the image formation of the multiplexed K plate in the said 1st Example. It is a block diagram for demonstrating 2nd Example of a halftone process part. It is a block diagram for demonstrating 3rd Example of a halftone process part. It is a schematic diagram for demonstrating the image formation of the multiplexed K plate in the said 3rd Example. It is a schematic diagram which shows an example of an image formation part.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an explanatory diagram of the overall configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus includes an image forming unit 100 capable of forming five color plates, an image data input unit 102 for inputting color image data from a scanner or a personal computer (not shown), and input color image data. And an image processing unit 104 that generates halftone processing data of a plurality of color plates recorded by the image forming unit 100.

  Here, the image forming unit 100 can use C (cyan), M (magenta), Y (yellow), and K (black) toners (colorants), as well as special color toners such as transparent and fluorescent colors. It shall be. Usually, among the five color plates that can be imaged by the image forming unit 100, the first color plate is the C plate, the second color plate is the M plate, the third color plate is the Y plate, The K version is assigned to each of the color versions. A special color plate can be assigned to the fifth color plate, but one of C, M, Y, and K color plates can be assigned in duplicate. A specific example of such an image forming unit will be described later.

  The main feature of the image forming apparatus according to the present invention is that any one of the color plates of C, M, Y, and K is assigned to the fifth color plate and multiplexed, thereby reproducing a smooth picture. The aim is to achieve both the reproduction of sharp characters and line drawings. For color images, it is usually effective to multiplex K plates. Therefore, the mode of multiplexing the K version is shown in FIG. However, the present invention naturally includes a mode in which any color plate of C, M, and Y is multiplexed instead of the K plate. Hereinafter, an aspect of multiplexing the K version will be described in detail, but the same applies to the case of multiplexing other than the K version.

  In FIG. 1, an image processing unit 104 performs filter processing on color image data (here, RGB data) input via the image input unit 102, and forms RGB data after this filter processing into image formation. A color correction processing unit 112 that converts color image data (CMYK data) composed of color component data corresponding to C, M, Y, and K toners used in the unit 100, and performs γ correction (density conversion) on the CMYK data The γ correction processing unit 114 performs halftone processing of the CMYK data after γ correction to generate halftone processing data for image formation of each color plane, that is, C plane data, M plane data, Y plane data, and K (1 ) A halftone processing unit 116 for generating plate data and K (2) plate data, and a pattern / character / line drawing determination unit 118.

  Of the multiplexed K plate data, the K (1) plate data is halftone processing data for creating a character / line drawing region of K data, and the K (2) plate data is a pattern region of K data. This is halftone processing data for image formation. The halftone processing method applied to the K (1) plate data is selected with emphasis on the reproducibility of characters and line drawings, while the halftone processing method applied to the K (2) plate data is reproduced. Selected with emphasis on sex.

  Typical halftone processing includes dither processing and error diffusion processing, but dither processing is suitable for K (2) version data because of excellent gradation and good picture reproducibility, and error diffusion processing has excellent resolution. Suitable for K (1) version data because of good reproducibility of characters and line drawings. In addition, there are multi-value halftone processing (multi-value dither processing, multi-value error diffusion processing) and binary half-tone processing (binary dither processing, binary error diffusion processing) of ternary or quaternary or higher. Binary halftone processing is suitable for halftone processing of K (1) version data that wants to reproduce simple characters and line drawings, and multilevel halftone processing as halftone processing for K (2) version data that wants to reproduce smooth patterns Is suitable.

  Further, the K (1) plane data and the K (2) plane data can be data having different resolutions. High resolution is desired for K (1) version data that emphasizes sharp reproduction of characters and line drawings, but K (2) version data that emphasizes smooth gradation reproduction of a picture has lower resolution than K (1) version data. In general, there is no problem. Rather, lowering the resolution and increasing the dot shape stability can be expected to produce smoother gradation reproduction. From this point of view, in one embodiment described later, the K (2) plane data has a lower resolution than the K (1) plane data.

  The pattern / character / line drawing determination unit 118 is a means for determining the pattern area and the character / line drawing area of the input color image in units of pixels and outputting the pattern / character / line drawing determination result information X. When processing color image data input from a scanner, the pattern / character / line drawing determination unit 118 uses a well-known image area separation technique that uses an image feature amount such as an edge amount extracted from color image data to determine the pattern region and character.・ Determine line drawing area. When object information is input together with color image data such as print data input from an external personal computer, the pattern / character / line drawing determination unit 118 determines the pattern area and the character / line drawing area based on the object information. Judgment can be made. In the halftone processing unit 116, the pattern / character / line drawing determination result information X is used to generate K (1) data and K (2) data. The filter processing unit 110 may perform control to adaptively switch the filter between the pattern area and the character / line drawing area based on the pattern / character / line drawing determination result information X, and this aspect is also included in the present invention. .

  Next, the halftone processing unit 116 will be specifically described with some examples.

  FIG. 2 is a block diagram for explaining the first embodiment of the halftone processing unit 116. The halftone processing unit 116 according to this embodiment performs multi-value dither processing units 200 and 201 that respectively perform well-known ternary or quaternary multi-value dither processing on C data, M data, and Y data after γ correction. , 202, and the output data of these multi-value dither processing units 200, 201, 202 are output as C plate data, M plate data, and Y plate data as they are.

  The halftone processing unit 116 performs a known binary dither processing unit 203 that performs a known binary dither process on the K data after γ correction, and a known multi-value dither process that performs a known ternary or quaternary multi-value dither process. And the output data of the binary dither processing unit 203 is selected and output for the pixels determined to be the character / line drawing area according to the pattern / character / line drawing determination result information X, and other pixels (picture The data selection unit 205 that selects and outputs “0” data (density 0) for the pixels in the region, and the output data of the multi-value dither processing unit 204 for the pixels determined to be the pattern region are selected and output. A data selection unit 206 that selects and outputs “0” data (density 0) for other pixels (pixels in the character / line drawing area).

  The output data of the data selection unit 5 is K (1) version data for creating an image of a character / line drawing area of K data, and is obtained by applying a binary dither process suitable for reproducing a sharp character / line drawing. is there. The output data of the data selection unit 206 is K (2) version data for creating an image area of K data, and is applied with a multi-value dithering process suitable for smooth picture reproduction. Here, the C, M, Y, K (1), and K (2) plate data have the same resolution (600 dpi in both the main scanning direction and the sub-scanning direction).

  FIG. 3 is a schematic diagram for explaining the state of image formation of the K plate in the image forming unit 100. As schematically shown in FIG. 3, an image 220 based on the K (1) plane data and an image 221 based on the K (2) plane data are created, and these two images are overlapped to form a final K plane image 223. It becomes. The K (1) plane image 220 is an image obtained by binary dithering the character / line drawing area of the K data, and the character / line drawing is sharply reproduced. On the other hand, the K (2) plane image 221 is an image in which the pattern area of K data is subjected to multi-value dither processing, and the gradation of the pattern is smoothly reproduced. Therefore, the smooth reproduction of the gradation of the pattern in the final K plate image 223, which is a composite image of the K (1) plate image 220 and the K (2) plate image 221, and the sharp reproduction of the characters and line drawings are compatible. Can be made.

  FIG. 4 is a block diagram for explaining the second embodiment of the halftone processing unit 116. The halftone processing unit 116 according to this embodiment is a binary error diffusion unit in which the binary dither processing unit 203 (FIG. 2) of the halftone processing unit according to the first embodiment performs a known binary error diffusion process. The configuration is replaced with the processing unit 207. The data selection unit 205 selects and outputs the output data of the binary error diffusion processing unit 207 for the pixels determined as the character / line drawing area, and selects “0” data (density 0) for the other pixels. And output. Here, the C, M, Y, K (1), and K (2) plate data have the same resolution (600 dpi in both the main scanning direction and the sub-scanning direction).

  Also in this embodiment, since the error diffusion processing is superior to the dither processing in the resolution, the K (1) plane data is imaged, so that the sharper characters / characters in the K plane image are compared with the first embodiment. Line drawings can be reproduced.

  Note that the binary error diffusion processing unit 207 can be replaced with a known multi-value error diffusion processing unit that performs multi-value error diffusion processing of three values or four or more values, and such an aspect is also included in the present invention. . Even with multi-level error diffusion processing, it is possible to reproduce characters and line drawings with good resolution due to the high resolution of the error diffusion processing.

  In the halftone processing unit 116 according to the first embodiment or the second embodiment, the binary dither processing unit 203 (FIG. 2) or the binary error diffusion processing unit 207 is used regardless of the pattern / character / line image determination result. The output data of (FIG. 4) is output as it is as K (1) version data, and the output data of the multi-value dither processing unit 204 (FIG. 2 or FIG. 4) is output as it is as K (2) version data, for each page. , K (1) plane data or K (2) plane data can be exclusively selected and image forming unit 100 can perform control. A mode in which such control is performed is also included in the present invention.

  FIG. 5 is a block diagram for explaining a third embodiment of the halftone processing unit 116. The halftone processing unit 116 according to this embodiment has a resolution in the main scanning direction and the sub-scanning direction from 600 dpi by pixel thinning and line thinning after the data selection unit 206 in the halftone processing unit according to the first embodiment. A resolution converting unit 208 for converting to 300 dpi is added, and the resolution in the main scanning direction and sub-scanning direction of the K (2) plane data is set to 300 dpi, which is half of 600 dpi of the other plane data. In this embodiment, it is natural that the image forming unit 100 creates a K (2) plane image with a resolution of 300 dpi.

  FIG. 6 is a schematic diagram for explaining image formation of the K plate in the present embodiment. As schematically shown in FIG. 6, the K (1) plate image 230 is formed with a resolution of 600 dpi in both the main scanning direction and the sub scanning direction, and the K (2) plate image 231 is formed in both the main scanning direction and the sub scanning direction. An image is created with a resolution of 300 dpi. The dot size for recording the K (1) plate image 230 and the K (2) plate image 231 is the same, but in the K (2) plate image 231 recorded at 300 dpi, one pixel of the K (2) plate data. Is recorded as a 2 × 2 dot cluster, it is possible to form a smooth image with a stable dot shape similar to that recorded with a double size dot as shown in FIG. The K (2) plane data is data that has been subjected to multi-value dither processing with excellent gradation. On the other hand, the K (1) plane image data is data that has been subjected to binary dither processing with excellent resolution. Therefore, in the final K version image 232 obtained as a composite image of the images 230 and 231, details of characters and line drawings are reproduced with sharpness, and gradations are reproduced with a smooth pattern.

  In this embodiment, the binary dither processing unit 203 can be replaced with a binary error diffusion processing unit, and such an aspect is also included in the present invention. Furthermore, in this embodiment, the binary dither processing unit 203 can be replaced with a multi-level error diffusion processing unit, and such an aspect is also included in the present invention.

  In the halftone processing unit 116 according to each of the embodiments, the halftone processing suitable for the character / line drawing area and the halftone processing suitable for the picture are executed by separate processing means for all the pixels of the K data. A configuration is adopted in which K (1) plane data and K (2) plane data are generated by selecting two halftone processing result data in accordance with the character / line drawing determination result. However, K (1) version data that has been subjected to halftone processing suitable for the character / line drawing area by switching the halftone processing method executed by one processing means in units of pixels according to the pattern / character / line drawing determination result. The K (2) plane data that has been subjected to halftone processing suitable for the pattern area can be generated, and such an aspect is also included in the present invention.

  Further, the function of the halftone processing unit 116 according to each of the above embodiments can be realized by a program using a computer, and such a form is also included in the present invention. Further, the present invention includes such a computer program and various information recording (storage) media that can be read by a computer such as a storage element, a magnetic disk, an optical disk, and a magneto-optical disk in which the program is recorded. .

  FIG. 7 is a schematic diagram illustrating an example of the image forming unit 100. The example shown here is a so-called tandem type electrophotographic printer engine, which uses five image forming units 20 to form five color plate images using C, M, Y, K toners or special color toners. can do. Each image forming unit 20 includes a photosensitive drum 21, a charging unit 22, a developing unit 23, and a cleaning unit 24 arranged around the photosensitive drum 21.

  A laser optical unit 12 is provided as an optical writing unit for the photosensitive drum 21 of each image forming unit 20. The laser optical unit 12 has a laser diode 13 corresponding to each image forming unit 20, and the laser beam emitted from each laser diode 13 is exposed to the corresponding image forming unit 20 via a rotating deflector (not shown). The surface of the body drum 21 is irradiated and scanned. In the embodiment in which the K plate data is multiplexed as described here, the optical writing circuit 14 outputs the C plate data, M plate data, Y plate data, and K (1) output from the image processing unit 104. This is means for driving the corresponding laser diode 13 of the laser optical unit 12 in accordance with the plate data and the K (2) plate data.

  In each image forming unit 20, the photosensitive drum 21 is driven to rotate in the clockwise direction in the figure, and the surface of the photosensitive drum 21 uniformly charged by the charging unit 22 is electrostatically applied to each color plate by scanning exposure with a laser beam. A latent image is formed. The electrostatic latent image is developed into a toner image by passing through the developing means 23. The C, M, Y, K (1), and K (2) color toner images developed on the photosensitive drum 21 of each image forming unit 20 are rotated in the counterclockwise direction in the figure by the primary transfer roller 25. Are sequentially transferred onto the intermediate transfer belt 26 driven by the motor. The toner remaining on the photosensitive drum 21 without being transferred is removed when passing through the cleaning means 24.

  A transfer conveyance belt 29 is disposed below the intermediate transfer belt 26. The intermediate transfer belt 26 and the transfer conveyance belt 29 are sandwiched between the transfer roller 28 and the transfer counter roller 27 around which the transfer conveyance belt 29 is stretched to form a secondary transfer portion. The recording paper fed by a paper feeding mechanism (not shown) is sent to the secondary transfer section by the registration roller pair 30 in accordance with the running and timing of the intermediate transfer belt 26, and the toner image on the surface of the intermediate transfer belt 26 is transferred. The images are transferred all at once onto the recording paper. The recording paper to which the toner image has been transferred is passed through the fixing device 31 and the toner image is melted and fixed on the recording paper by heating and pressing. The inter-recording sheet after fixing is discharged to a discharge tray (not shown).

  Although an example of a tandem printer engine has been described, an electrostatic latent image of a plurality of color plates and toner development are performed on a single photoconductor drum, and a toner image of each color plate on the photoconductor drum is obtained. A printer engine of a type that transfers to a recording sheet via an intermediate transfer medium or directly can be used as the image forming unit 100. In addition, an image forming unit using an ink jet method or a thermal transfer method other than the electrophotographic method can also be used.

  Further, it has been described so far that the image forming unit 100 uses four colorants of C, M, Y, and K. For example, in addition to the colorants of C, M, Y, and K, light cyan (LC) Even when a light colorant such as light magenta (LM) is used, the same multiplexing can be performed for the K plate. Multiple color plates other than the K plate are also possible, but in that case, light color plate multiplexing such as LC, LM would generally not be effective.

DESCRIPTION OF SYMBOLS 100 Image formation part 102 Image input part 104 Image processing part 110 Filter process part 112 Color correction process part 114 γ correction process part 116 Halftone process part 118 Picture / character line drawing determination part 200, 201, 202, 204 Multi-value dither process part 203 Binary dither processing unit 205, 206 Data selection unit 207 Binary error diffusion processing unit 208 Resolution conversion unit

JP 2009-55601 A

Claims (5)

Image forming means for forming a color image using a plurality of colorants including black,
And halftone processing data of the color component data for creating a character / line drawing area of color component data of a color image corresponding to a predetermined color of the plurality of colors, and a picture area of the color component data Halftone processing data of the color component data is generated as first and second color plane data of the predetermined color, respectively, and color component data of the color image corresponding to each color other than the predetermined color in the plurality of colors Image processing means for generating each halftone processing data as color plate data of each color,
In the image forming means, image formation of two color plates using the colorant of the predetermined color is performed according to the first and second color plate data of the predetermined color, and according to the color plate data of each color other than the predetermined color There one row image forming color plate using respective colors of the color agent,
The halftone process applied to the first color plane data of the predetermined color is a binary halftone process, and the halftone process applied to the second color plane data of the predetermined color is ternary or quaternary or higher. An image forming apparatus characterized in that it is multi-value halftone processing .   The halftone process applied to the first color plane data of the predetermined color is an error diffusion process, and the halftone process applied to the second color plane data of the predetermined color is a dither process. The image forming apparatus according to claim 1. 3. The image forming apparatus according to claim 1, wherein the second color plate data of the predetermined color has a lower resolution than the first color plate data of the predetermined color. The image forming apparatus according to any one of claims 1 to 3, wherein the predetermined color is black. A program that causes a computer as the image processing unit of the image forming apparatus according to any one of claims 1 to 4.