JP2010136232A - Printing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing apparatus having an improved printing quality with dither pattern selection in accordance with to image characteristics such as sharply changing portions and/or same color areas or the like within single image data. <P>SOLUTION: The printing apparatus has a filtering means to perform differential processing on gradation information on one-page print data to detect portions with large gradation changes and portions with small gradation changes within the one-page print data, a storage means to store a dither pattern corresponding to number of gradations and a dither pattern corresponding to resolutions, a selection means to select the dither pattern corresponding to number of gradations or the dither pattern corresponding to resolutions according to detection outputs from the filtering means, and a video data creation means to compare the dither pattern selected by the selection means with the corresponding print data to create video data for print processing onto a recording media. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a printing apparatus that improves image quality by using a plurality of dither patterns.

  Today, in color printing, a pattern dither method for performing multicolor expression by repeatedly using a pattern having a size of several pixels square is widely used. The dither pattern used by this method must be matched to the characteristics of the hardware in order to use it, and there are various modes. In the printing process, the print data to be printed is properly used depending on whether it is a character (text), a graphic (graphic), or a photographic image.

Japanese Patent Application Laid-Open No. 2003-228867 determines whether a character (text) or a graphic (graphic) is determined for each image according to print data, selects a corresponding dither pattern, and uses the same dither pattern for all images. An invention for performing a printing process is disclosed.
JP 2004-202944 A

However, in the invention according to Patent Document 1, a dither pattern is selected for each image, and the same dither pattern is used for all the images. Accordingly, it is not possible to perform a printing process corresponding to image features such as a sharply changing portion or the same color area in one piece of image data.
Accordingly, the present invention provides a printing apparatus in which the print quality is improved by selecting a dither pattern that matches the features of the image, such as a sharply changing portion or the same color area, in one piece of image data.

  According to the first aspect of the present invention, there is provided a filter means for differentiating gradation information of print data for one page and detecting portions having large and small gradation changes in the print data in one page. Storage means for storing a dither pattern corresponding to the number of gradations and a dither pattern corresponding to the resolution, and a dither pattern corresponding to the number of gradations or a dither pattern corresponding to the resolution according to the detection output from the filter means A printing apparatus comprising: selection means for performing selection; and video data creation means for creating video data for performing print processing on a recording medium by comparing print data corresponding to the dither pattern selected by the selection means. Can be achieved by providing.

  According to a second aspect of the present invention, the storage means further stores a dither pattern corresponding to a standard number of gradations, and the selection means selects a dither pattern corresponding to the standard number of gradations. Can also be achieved by providing a possible printing device.

  According to a third aspect of the present invention, the print data can be achieved by providing a printing apparatus in which the print data is CMYK data.

  According to the fourth aspect of the present invention, the gradation information of the print data for one page is differentiated to detect a portion with a large gradation change and a portion with a small gradation change in the print data within the one page. Filtering processing to be performed, selection processing to select a corresponding dither pattern from a storage unit that stores a dither pattern corresponding to the number of gradations and a dither pattern corresponding to the resolution according to the detection output, and the dither selected by the selection processing This can be achieved by providing a computer-executable program that compares the print data corresponding to the pattern and performs the creation process of the video data to be printed on the recording medium.

  According to a fifth aspect of the present invention, the storage means further stores a dither pattern corresponding to a standard number of gradations, and the dither pattern corresponding to the standard number of gradations in the selection process. This can be achieved by providing a computer-executable program that can also perform selection.

  According to the present invention, a resolution-prioritized dither pattern is selected for a portion where the gradation changes drastically, and the contour portion can be expressed sharply and sharply. In a portion where streak is conspicuous, such as a portion where is slowly changing, streak can be reduced by selecting a dither pattern giving priority to gradation.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 is a system configuration diagram of a printing apparatus for explaining the present embodiment. In FIG. 1, a printing apparatus 1 includes an interface controller (hereinafter referred to as an I / F controller) 2 and an engine control unit 3. The I / F controller 2 includes a reception control unit 4, a ROM 5, a flash ROM 6, and a display control unit 7. , A video I / F control unit 8, a memory (SDRAM) 9, an ASIC (DMA control unit) 10, and a CPU 11. In addition, an operation panel 24 is connected to the display control unit 7, and a display described later is performed.

  On the other hand, the engine control unit 3 includes a print head control unit (hereinafter simply referred to as a head control unit) 12, a motor control unit 13, an MPU 14, a fixing control unit 15, a high voltage control unit 16, a print head 17, a main motor 18, and various loads. 19, various sensors 20, a fixing thermistor 21, a fixing heater 22, and a high voltage unit 23.

  The printing apparatus 1 having the above configuration is supplied with print data from a host device 25 such as a personal computer (PC) or a printer server via a Centronics interface and a LAN (local area network). The print data supplied from the host device 25 is transferred to the reception control unit 4, and when a predetermined amount of print data is transferred to the reception control unit 4, the print data is transferred to the memory (SDRAM) 9. The print data transferred to the memory (SDRAM) 9 is thereafter analyzed under the control of the CPU 11, compressed and decompressed by the ASIC (DMA controller) 10, and then from the video I / F controller 8. It is output to the engine control unit 3 (head control unit 12).

  The video data output to the head control unit 12 is subjected to processing described later and output to the print head 17. The motor control unit 13 controls the driving of the main motor 18, and the MPU 14 controls the head control unit 12 and the motor control unit 13 and also controls the fixing control unit 15 and the high voltage control unit 16.

FIG. 3 is a diagram for explaining the outline of the processing of this example in the printing apparatus 1 having the above configuration.
First, print data (RGB data) created by the application of the host device 25 is transmitted from the host device 25 to the reception control unit 4 via the LAN or USB as described above, and further transferred to the memory (SDRAM) 9. It is stored in a ring buffer in the memory (SDRAM) 9 (process a shown in FIG. 3).

  Next, the print data (RGB data) stored in the memory (SDRAM) 9 is subjected to color matching processing based on an LUT (Look Up Table) 6a registered in the flash ROM 6 and converted to subtractive color mixed CMYK data. (Processing b shown in FIG. 3). Specifically, this process converts 24-bit 256-gradation RGB data into 32-bit 256-gradation CMYK data. The converted CMYK data is written in the memory (SDRAM) 9.

  Next, the dither pattern 6b registered in the flash ROM 6 is read and written in the dither pattern area in the memory (SDRAM) 9 (process c shown in FIG. 3). At this time, the dither pattern read from the flash ROM 6 is a dither pattern selected by a filter processing unit described later, and a plurality of dither patterns described later are registered in the flash ROM 6.

Next, the CPU 11 performs a comparison operation on the CMYK data according to the threshold value of each pixel having the shape of the selected dither pattern, and converts the CMYK data into 16-gradation video data (processing d shown in FIG. 3). ).
Next, the CMYK data is expanded in the page memory in the memory (SDRAM) 9 under the control of the CPU 11 (processing e shown in FIG. 3), and the video data expanded in the page memory is used efficiently. Therefore, it is converted into compressed data by the ASIC 10 described above (processing f shown in FIG. 3).

Thereafter, the compressed CMYK data is transferred to the ASIC 10 for decompression processing, transferred to the engine control unit 3 (head control unit 12) under the control of the video I / F control unit 8, and printed on a recording medium. Perform (Process g shown in FIG. 3).
In the above processing, the conversion processing of this example will be further described in detail. FIG. 1 is a block diagram for explaining this processing, and includes an RGB / CMYK data conversion unit 28 and a dither processing unit 29. The RGB / CMYK data conversion unit 28 includes the above-described LUT (lookup table) 6a and the conversion unit 28a, reads RGB data from the above-described memory (SDRAM) 9, and based on the LUT (lookup table) 6a. A color matching process is performed to convert RGB data into CMYK data. By this processing, as described above, RGB data of 24 bit 256 gradation is converted to CMYK data of 32 bit 256 gradation.

  On the other hand, the dither processing unit 29 includes threshold tables 31 to 33 for storing the above-described dither pattern, a filter processing unit 34, a table selection unit 35, and a comparator 36. The dither processing unit 29 extracts image features from the CMYK data sent from the RGB / CMYK data conversion unit 28 by filter processing, which will be described later, and selects a dither pattern, and the comparator 36 responds based on the selected dither pattern. The CMYK data to be converted is converted into video data.

  FIG. 4 is a diagram showing the configuration of the threshold value tables 31-33. First, the threshold value table 31 stores a dither pattern I having, for example, 300 lines and 61 gradations, and is configured with a dither pattern corresponding to a high-resolution image. Further, the threshold table 32 stores, for example, a dither pattern II of 200 lines and 136 gradations, and is constituted by a dither pattern corresponding to a standard image. The threshold table 33 further includes, for example, 150 lines and 241 gradations of dither. Pattern III is stored and is composed of a dither pattern corresponding to a high gradation image.

  As described above, the dither pattern I registered in the threshold value table 31 is a 300-line high-resolution pattern. For example, the dither pattern I can be used in a CMYK data (image data) where the color change is large. For example, a contour portion in an image can be expressed sharply. On the other hand, the dither pattern III registered in the threshold value table 33 is a pattern having a high gradation number of 241 gradations. For example, by using it in a location where the color change is small in CMYK data (image data), For example, it can be used for an area where streaks are conspicuous in an image, and streaks can be reduced.

  FIG. 5 shows a screen arrangement of the above dither patterns I to III, and shows a screen arrangement spread in a size of 12 × 12 dots. For example, FIG. 10A shows a dither pattern I, FIG. 10B shows a dither pattern II, and FIG. 10C shows a dither pattern III. FIGS. 4D to 5F show image formation images particularly at 25% printing in the above example. Specifically, FIG. 4D shows the dither pattern I, which is 25% (15 gradations × 1 dot / 15 gradations × 4 dots) for printing one dot in 2 × 2 dots. (E) shows the dither pattern II and prints 2 dots (16 gradations) +1 dot (4 gradations) within 3 × 3 dots 25% ((15 gradations × 2 dots + 4 gradations × 1 dot)) (F) shows dither pattern III, and 25% (15 gradations × 4 dots / (15 gradations) for printing 4 dots within 4 × 4 dots. × 16 dots)).

  The CMYK data output from the RGB / CMYK data conversion unit 28 is transferred to the filter processing unit 34 of the dither processing unit 29 and processed by the filter processing unit 34. FIG. 6A shows an example of CMYK data input to the filter processing unit 34. For example, gradation characteristics for 26 dots of CMYK data are shown.

The filter processing unit 34 obtains a differential value fx in the X direction and a differential value fy in the Y direction of the pixel value f (x, y) of the target pixel (x, y), and the differential value fx in the X direction and the Y direction. | Fx | + | fy | obtained by adding the absolute values of the differential values fy is transmitted to the table selection unit 35, and the table selection unit 35 selects the dither patterns I to III. For example, when A1 shown in FIG. 6A is a target pixel (x, y), a differential value fx in the X direction is obtained by the following calculation formula:
fx = f (x−1, y) × −1 + f (x + 1, y) × 1
Further, the differential value fy in the Y direction is obtained by the following formula,
fy = f (x, y−1) × 1 + f (x, y + 1) −1
Both differential values are added (| fx | + | fy |).

  FIG. 6B is a diagram showing the calculation result. In the CMYK data, the density gradient is large at a portion where the change in gradation value is large, and the density gradient is small at a portion where the change in gradation value is small. . FIG. 4B is a diagram showing | fx |, which is influenced by the characteristics of the CMYK data, but in the description of this example, the calculation result of | fx | + | fy | It will be described as being obtained.

  Based on the calculation result for the CMYK data, the filter processing unit 34 outputs, for example, a selection signal for each pixel of interest to the table selection unit 35, and selects dither patterns I to III to be read from the threshold tables 31 to 33. That is, when the gradation change is large based on the calculation result, the threshold value table 31 (dither pattern I) is selected. When the gradation change is moderate, the threshold value table 32 (dither pattern II) is selected. When the gradation change is small, the threshold value table 33 (dither pattern III) is selected. That is, a resolution-prioritized dither pattern (dither pattern I) is selected at locations where the gradation changes drastically, and a tone-priority dither pattern (dither pattern III) is selected at locations where the gradation changes slowly.

Therefore, the table selection unit 35 selects the dither patterns I to III shown in FIG. 7 and outputs the selected dither pattern to the comparator 36. The comparator 36 compares the dither pattern selected by the table selection unit 35 with the corresponding CMYK data and stores it in the memory (SDRAM) 9 as video data.
Thereafter, the video data is compressed and expanded in the page memory in the memory (SDRAM) 9 as described above, and the video data expanded in the page memory is further transferred to the ASIC 10 for decompression processing. Under the control of the F control unit 8, the data is transferred to the engine control unit 3 (head control unit 12), and printing processing on a recording medium is performed.

  FIG. 8 is a diagram showing the printing result. An original image (image D1 in a region where the gradation changes drastically, an image D2 in a region where the gradation changes moderately, and an image D3 in an area where the gradation changes slowly is shown. A print result of (image data) D is shown. In this case, as described above, in the region (standard region) D2 where the gradation change is moderate, the comparison process is performed by the dither pattern II read from the threshold value table 32, and the standard D2 ′ print result is obtained. Can be obtained. Further, in the region D3 where the gradation changes slowly, a comparison process is performed by the dither pattern III read from the threshold value table 33, and a print result of D3 ′ with reduced streak can be obtained. In the region D1 where the tone changes abruptly, a comparison process is performed by the dither pattern I read from the threshold value table 31, and a print result of D1 ′ that expresses an image sharply can be obtained.

  As described above, according to the present embodiment, the filter processing unit 34 performs filtering of CMYK data, extracts image features, and selects a resolution-priority and tone-priority dither pattern corresponding to the features. Since the image data is created, a resolution-prioritized dither pattern is selected in a portion where the gradation changes drastically, and for example, a contour portion or the like can be sharply expressed. In addition, streaks are reduced by selecting a tone-first (low resolution) dither pattern for areas where streaks are conspicuous, such as solid images with a constant gradation or portions where the gradation changes slowly. be able to.

FIG. 3 is a diagram illustrating an outline of processing of this example in a printing apparatus. 1 is a system configuration diagram of a printing apparatus illustrating an embodiment. It is a figure which shows the correction data memorize | stored in the light quantity correction data conversion table as a characteristic view. It is a figure which shows the structure of a threshold value table. The screen arrangement of dither patterns I to III is shown, (a) shows an example of dither pattern I, (b) shows an example of dither pattern II, (c) shows an example of dither pattern III, (D) shows an example of 25% printing for dither pattern I, (e) shows an example of 25% printing for dither pattern II, and (f) shows 25% printing for dither pattern III. Example (A) shows an example of CMYK data input to the filter processing section, and (b) is a diagram showing the differential value of (a). It is a figure which shows the example of selection of the dither pattern I-III which a table selection part performs. It is a figure which shows an example of a printing result.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Printing apparatus 2 ... I / F controller 3 ... Engine control part 4 ... Reception control part 5 ... ROM
6 ... Flash ROM
7 ... Display control unit 8 ... Video I / F control unit 9 ... Memory 10 ... DMA control unit 11 ... CPU
12. ・ Head controller 13 ・ ・ Motor controller 14 ・ ・ MPU
15. ・ Fixing control unit 16 ・ ・ High pressure control unit 17 ・ Print head 18 ・ Main motor 19 ・ Various loads 20 ・ Various sensors 21 ・ Fixing thermistors 22 ・ Fixing heaters 23 ・ High pressure unit 24 Operation panel 25. Host device 28. RGB / CMYK data conversion unit 29 Dither processing units 31 to 33 Threshold table 34 Filter processing unit 35 Table selection unit 36 Comparator

Claims (5)

Filter means for differentiating gradation information of print data for one page and detecting portions where gradation change is large and small in the print data within the one page;
Storage means for storing a dither pattern corresponding to the number of gradations and a dither pattern corresponding to the resolution;
A selection means for performing a selection process of a dither pattern corresponding to the number of gradations or a dither pattern corresponding to the resolution in accordance with a detection output from the filter means;
Video data creation means for comparing the print data corresponding to the dither pattern selected by the selection means and creating video data for printing on the recording medium;
A printing apparatus comprising:   2. The dither pattern corresponding to a standard number of gradations is further stored in the storage unit, and the selection unit is capable of selecting a dither pattern corresponding to the standard number of gradations. Printing device.   The printing apparatus according to claim 1, wherein the print data is CMYK data. A filter process for differentiating gradation information of print data for one page, and detecting a portion having a large gradation change and a portion having a small gradation change in the print data in the one page;
In accordance with the detection output, a selection process of selecting a corresponding dither pattern from a storage unit that stores a dither pattern corresponding to the number of gradations and a dither pattern corresponding to the resolution;
A process of creating video data for comparing print data corresponding to the dither pattern selected by the selection process and performing print processing on a recording medium;
A program that can be executed by a computer.   The dither pattern corresponding to the standard number of gradations is further stored in the storage means, and the dither pattern corresponding to the standard number of gradations is also selected in the selection process. A program executable by the computer described above.