JP2007044971A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the amount of pixel data for the output of an image, while enhancing the quality of the output image by making the resolution of a printing part higher. <P>SOLUTION: This image forming apparatus, which generates imaging data to be printed by a printing means with a predetermined level of resolution, comprises: a first conversion means (301-1) for rasterizing a vector image into binary data according to the resolution; a second conversion means (301-2) for rasterizing the vector image into data with a predetermined number of gradations, the resolution of which is lower than the resolution of the printing means; a switching means (301) for switching between the first and second conversion means on the basis of the attribute of the vector image; and generation means (302-309) for generating the imaging data 106 on the basis of the rasterized data. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method for generating drawing data.

  2. Description of the Related Art Conventionally, an image printing system that prints out image data created by a personal computer (PC) or the like by a printing apparatus such as an electrophotographic printer is known. FIG. 1 is a diagram illustrating an example of an image printing system. The outline of the image printing system will be described with reference to FIG. Reference numeral 101 denotes a PC, and 102 denotes a printing apparatus.

  In FIG. 1, image data created on the PC 101 is converted into a printer description language (PDL) and transmitted to the printing apparatus 102 (105).

  The image forming unit 103 in the printing apparatus 102 that has received the PDL 105 performs raster image process (RIP) processing for analyzing the PDL (105) and developing it into pixel data (raster data). Further, the image forming unit 103 performs halftone processing for quantizing the pixel data into the number of gradations that can be output by the printing unit 204.

  The pixel data 106 subjected to such processing is sent to the printing unit 104 as drawing data, and is printed out on the paper surface by the printing unit 104.

Depending on the image printing system, the RIP processing may be performed on the PC 101 side, and the image forming unit 103 may be configured to perform only halftone processing.
Japanese Patent Laid-Open No. 10-044526

  However, in the case of the image printing system, the drawing data output from the image forming unit 103 is data for each pixel corresponding to the resolution of the printing unit 104. For this reason, when the resolution of the printing unit 104 is increased, the amount of pixel data increases, and there is a problem that the amount of memory and calculation required in the image forming unit 103, the bandwidth of data transfer, and the like increase.

  On the other hand, if the data amount of pixel data is excessively suppressed, high-quality print output cannot be expected even though the resolution of the printing unit 104 is increased.

  The present invention has been made in view of the above problems, and has an object to suppress the data amount of pixel data for image output while ensuring the improvement of the image quality of the output image by increasing the resolution of the printing unit. To do.

  More specifically, the object is to achieve both the suppression of the amount of pixel data and the improvement of the sharpness of output characters and the gradation of photographs.

In order to achieve the above object, an image forming apparatus according to the present invention has the following configuration. That is,
An image forming apparatus that generates drawing data to be printed by a printing unit having a predetermined resolution,
First conversion means for rasterizing a vector image into binary data according to the resolution;
Second conversion means for rasterizing a vector image into data having a resolution lower than that of the printing means and having a predetermined number of gradations;
Switching means for switching between the first conversion means and the second conversion means based on the attribute of the vector image;
Generating means for generating drawing data based on the rasterized data.

  It becomes possible to suppress the data amount of the pixel data while ensuring the improvement of the image quality of the output image by increasing the resolution of the printing unit.

  More specifically, it is possible to achieve both suppression of the data amount of pixel data and improvement of the sharpness of characters to be output and the gradation of photographs.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings as necessary.

[First Embodiment]
<Image printing system configuration>
Since the configuration of the image printing system to which the printing apparatus including the image forming apparatus (image forming unit) according to the first embodiment of the present invention is connected is the same as that in FIG. 1, the description thereof is omitted here. In the present embodiment, the printing unit 104 is assumed to have a resolution of horizontal 3600 DPI and vertical 1200 DPI.

<Configuration of Image Forming Unit 103>
FIG. 3 is a block diagram showing the configuration of the image forming unit 103 according to the first embodiment of the present invention. In the figure, 301 is a raster image processor (RIP) unit, 302 is an image signal selector unit, and 303 is a quantizer. Also, 304 is a photographic threshold matrix, 305 is a PWM controller, 306 is a photographic phase matrix, 307 is a PWM width corrector, 308 is a PWM pattern generator, and 309 is a PWM signal synthesizer.

  The processing procedure in the image forming unit 103 until the drawing data 106 for forming a laser ON / OFF signal for driving the printing unit 104 is output using the PDL 105 received from the PC 101 will be described below.

  The page description language (PDL) 105 generated by the PC 101 is interpreted by the RIP unit 301 and developed into pixel data (raster data). At this time, the attribute of each pixel is determined according to the type of the image drawing command, and the format of raster data to be developed is switched.

  That is, conventionally, when the resolution of the printing portion is 3600 DPI horizontal and 1200 DPI vertical, the size of each pixel of raster data to be developed corresponds to the resolution. On the other hand, the size of each pixel of raster data developed by the RIP unit 301 differs depending on the attribute of each pixel. This will be described with reference to FIG.

  FIG. 5A is a diagram illustrating an example of raster data developed by the RIP unit 301. Each rectangle represents a pixel. Pixels 501 to 504 and 508 and 509 are pixels drawn by an image copy command for drawing a rectangular bitmap image, and each pixel has a resolution of 600 DPI horizontal and 600 DPI vertical and has 12 bits (4096 gradations). Represents information. These are generated by the first conversion unit 301-1.

  That is, the pixels 501 to 504 and 508 and 509 are composed of a total of 12 dots, 6 dots horizontally and 2 dots vertically, but the RIP unit 301 handles them as one pixel.

  On the other hand, pixels 505 to 507 are pixels drawn by a text drawing command, and each pixel represents binary information of horizontal 3600 DPI and vertical 1200 DPI. These are generated by the second conversion unit 301-2. The RIP unit 301 generates attribute data in units of 600 DPI (for each predetermined area). Further, it is assumed that the raster data is generated so that the amount of information for each predetermined area is equal.

  511 to 519 in FIG. 5B are examples of attribute data, where R represents a photo attribute, T represents a character attribute, and N represents no attribute (nothing is drawn). The attribute data is generated by the attribute data generation unit 301-3.

  The image signal selector unit 302 switches the raster data processing method based on the attribute data output from the RIP unit 301. If the attribute is a photograph attribute (R) or no attribute (N), it is input to the quantizer 303. On the other hand, if the attribute is a character attribute (T), it is input to the PWM pattern generator 308.

<Raster data processing for photo attributes (R)>
FIG. 4 shows a configuration example of a processing module for processing the raster data of the photograph attribute (R). In FIG. 4, reference numeral 410 denotes raster data input to the quantizer 303, and 304-1, 304-2, and 304-3 denote specific examples of the photo threshold matrix 304, respectively. Reference numeral 401 denotes a raster data enlarger, 402, 403, and 404, comparators, 405, 406, and 407, amplifiers, 408, an output signal selector, and 411, quantized data. Reference numeral 306 denotes a photographic phase matrix, and reference numeral 305 denotes a PWM controller.

  Each pixel value of the raster data is enlarged by the enlarger 401 twice in the vertical and horizontal directions. That is, the data output from the enlarger 401 is handled as a total of 3 dots, 3 dots horizontally and 1 dot vertically.

  Raster data output from the enlarger 401 is compared with a threshold value by the comparators 402 to 404. It is assumed that the threshold value is stored in the printing apparatus 102 as a photographic threshold matrix 304 (photographic threshold matrixes 304-1 to 304-3) having a finite size.

  Here, for reference, the processing of the quantizer in the conventional image forming apparatus will be briefly described. FIG. 2 is a diagram for explaining processing in a conventional quantizer. When the raster data 201 and the threshold matrix 202 are input to the comparator 203, the comparator 203 compares the raster data with the corresponding threshold values in the threshold matrix 203. As a result of the comparison, 255 is output when the raster data is larger than the threshold value, and 0 is output when the raster data is smaller. As a result, the quantized data 204 is output from the comparator 203.

  Returning to FIG. In the present embodiment, the photo threshold matrix 304 is composed of three matrices, each having a size of 4 pixels vertically and horizontally.

  Each of the comparators (402 to 404) outputs 1 when the pixel value of each pixel of the raster data output from the enlarger 401 is larger than the threshold value of the photographic threshold value matrix (304-1 to 304-3). On the other hand, when the pixel value of each pixel of the raster data output from the enlarger 401 is equal to or less than the threshold, 0 is output. The output signal is amplified by amplifiers 405 to 407.

  The output of the comparator 405 is amplified 85 times by the amplifier 405, the output of the comparator 406 is amplified 170 times by the amplifier 406, and the output of the comparator 407 is amplified 255 times by the amplifier 407. The output signal selector 408 selects and outputs the largest signal among the amplified output signals as the pixel value of the quantized data 411.

  The PWM signal controller 305 controls the width and position of the output dot pattern based on the pixel value of the quantized data 411 and the photographic phase matrix 306. The photographic phase matrix 306 is the same size as the photographic threshold matrices 304-1 to 304-3, and determines whether the dots of each quantized data are grown from the left or right.

  In the photographic phase matrix 306, the pixel indicated as R is controlled to grow dots from the right end to the left side, and the pixel indicated as L is controlled to grow dots from the left end to the right side. Note that the phase control is not limited to either left or right, and for example, the center, both ends, and the like can be additionally used.

  6 and 7 illustrate a dot pattern for each gradation of a photograph generated by the image forming apparatus 103 according to the present embodiment. Since the dot growth direction is controlled so that halftone dots are not divided by the photographic phase matrix 306 for each pixel position, stable dot reproduction is possible at any gradation. The PWM width and phase signals generated in this way are corrected by the PWM width corrector 307 in order to correct the nonlinearity of the response between the PWM signal and the laser emission. Then, it is output as drawing data 106 for forming a laser ON / OFF signal having a resolution of horizontal 1800 DPI and vertical 1200 DPI.

<Raster data processing for character attribute (T)>
On the other hand, the raster data of the character attribute (T) is converted into 3-bit drawing data 106 forming a laser ON / OFF signal by the PWM pattern generator 308. FIG. 9 shows an example of conversion from raster data of character attributes (T) to drawing data for forming a laser ON / OFF signal.

  Reference numeral 901 denotes a three-pixel pattern of raster data of the character attribute (T). Reference numeral 902 represents drawing data corresponding to each raster data. Since the raster data of the character attribute (T) is composed of 6 horizontal pixels and 2 vertical pixels (see 505 to 507 in FIG. 5), the above conversion is performed in four steps. This conversion method is an example, and raster data of 6 pixels × 2 pixels may be converted into drawing data in a lump.

  The drawing data 106 of the photo attribute (R) and the character attribute (T) generated as described above is synthesized by the PWM signal synthesizer 309 and printed on the paper surface by the printing unit 104.

  As is clear from the above description, in the image forming apparatus according to the present embodiment, the received PDL is classified according to its attributes. Then, processing that emphasizes gradation rather than resolution is performed on PDL with a photograph attribute or no attribute, and processing that focuses on resolution rather than gradation is performed on PDL with character attributes. As a result, in a printing apparatus including the image forming apparatus, it is possible to reduce the amount of pixel data while realizing a high-quality output image using the reproducibility (high resolution) of the printing unit to the maximum. It becomes.

  More specifically, it is possible to achieve both suppression of the data amount of pixel data and improvement of the sharpness of characters to be output and the gradation of photographs.

[Second Embodiment]
In the first embodiment, the size of the photographic threshold matrix 304 and the photographic phase matrix 306 is fixed to 4 × 4 pixels, but is not particularly limited thereto. It is also possible to apply the same processing to the four primary colors of Cyan, Magenta, Yellow, and Black to apply to a color printing apparatus.

  In color printing, when the same dot pattern is used for each color, color unevenness may occur due to slight positional deviation. Therefore, the photographic threshold matrix and the photographic phase matrix may be configured to have different screen angles for each color.

  In addition, when the number of pixels constituting the halftone dot is small, sufficient gradation cannot be expressed, but the gradation can be obtained by taking a large photographic threshold matrix and configuring a plurality of halftone dots within the photographic threshold matrix. The number can be increased.

  For example, the photo threshold matrix shown in FIG. 10 is an example of a case where the halftone dots in FIG. In the photographic threshold matrix, the threshold values of the photographic threshold matrix 304 in FIG. 4 are slightly changed. By using such a photographic threshold matrix, the number of reproduced gradations can be increased while maintaining stability.

  In addition, the attributes of raster data are not limited to photo attributes and text attributes, but by providing a mode for vector graphics or making only the edge part a separate mode, more detailed optimization processing is possible Become. Note that reference numerals 801 to 803 in FIG. 8 are examples of a threshold matrix used in the vector graphics mode, and 804 is an example of a phase matrix. By using the matrix, it is possible to perform the same processing as raster data of a photo attribute on raster data of a vector graphics image.

[Other Embodiments]
Note that the present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, and a printer), and a device (for example, a copying machine and a facsimile device) including a single device. You may apply to.

  Another object of the present invention is to supply a storage medium storing software program codes for implementing the functions of the above-described embodiments to a system or apparatus, and the computer (or CPU or MPU) of the system or apparatus stores the storage medium. Needless to say, this can also be achieved by reading and executing the program code stored in the.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.

  As a storage medium for supplying the program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, or the like is used. be able to.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) operating on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

1 is a diagram illustrating an example of an image printing system. It is a figure for demonstrating the process in the conventional quantizer. FIG. 2 is a block diagram illustrating a configuration of an image forming unit 103 according to the first embodiment of the present invention. It is a figure which shows the structural example of the processing module for processing the raster data of a photograph attribute (R). It is a figure which shows the structure of raster data and attribute data. The dot pattern for every gradation for photographs produced | generated by the image formation mounting part 103 concerning this embodiment is illustrated. The dot pattern for every gradation for photographs produced | generated by the image formation mounting part 103 concerning this embodiment is illustrated. It is a figure which shows an example of the threshold value and phase matrix in vector graphics mode. It is a figure which shows the example of conversion from raster data of character attribute (T) to drawing data. It is a figure which shows an example of the threshold matrix for photographs.

Claims (10)

An image forming apparatus that generates drawing data to be printed by a printing unit having a predetermined resolution,
First conversion means for rasterizing a vector image into binary data according to the resolution;
Second conversion means for rasterizing a vector image into data having a resolution lower than that of the printing means and having a predetermined number of gradations;
Switching means for switching between the first conversion means and the second conversion means based on the attribute of the vector image;
An image forming apparatus comprising: generating means for generating drawing data based on the rasterized data. 2. The image according to claim 1, wherein the data rasterized by the first conversion unit and the data rasterized by the second conversion unit have the same data amount in an area of a predetermined size. Forming equipment. The switching means is
When the attribute of the vector image is a character attribute, switching to the first conversion unit is performed, and when the attribute of the vector image is a photograph attribute, switching is performed to the second conversion unit. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1, further comprising an attribute data generation unit configured to generate attribute data defining an attribute of the rasterized data for each predetermined area. The generating means includes
First generation means for generating drawing data based on the data rasterized in the first conversion means;
Second generation means for generating drawing data based on the data rasterized by the second conversion means,
5. The image forming apparatus according to claim 4, wherein drawing data is generated using either the first or second conversion unit based on the attribute data. The first generation means includes:
The drawing data is generated by changing the area of each data position of the output data obtained by comparing a plurality of threshold values determined in advance according to the data position and each data of the rasterized data. The image forming apparatus according to claim 5, wherein: The second generation means includes
The image forming apparatus according to claim 5, wherein the drawing data is generated by changing an area of each data position of the rasterized data. An image forming method for generating drawing data to be printed by a printing means having a predetermined resolution,
A first conversion step of rasterizing a vector image into binary data according to the resolution;
A second conversion step of rasterizing the vector image into data having a resolution lower than that of the printing unit and having a predetermined number of gradations;
A switching step of switching between the first conversion step and the second conversion step based on the attribute of the vector image;
An image forming method comprising: a generation step of generating drawing data based on the rasterized data. A storage medium storing a control program for realizing the image forming method according to claim 8 by a computer. A control program for realizing the image forming method according to claim 8 by a computer.

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