JP6172257B2 - Printing device - Google Patents

Description

  The present invention relates to an apparatus for generating data for printing.

  The ink jet printer preferably performs flushing during printing. Flushing is ink ejection for preventing clogging of ink nozzles separately from ink ejection for printing. By the way, unlike a serial printer, a printer including a line head (line printer) cannot perform flushing using head scanning. The line head is a print head in which nozzles are arranged over the entire width direction so that printing can be performed without scanning in the width direction of the paper (hereinafter referred to as “width direction”). In view of this, a method of performing flushing at a timing from when one sheet is printed to when the next sheet is printed can be considered. The problem with this method is that the printing speed is slow.

  On the other hand, a method of performing flushing on paper (hereinafter referred to as “paper flushing”) is also conceivable. The problem of paper flushing is to cause deterioration of image quality because ink ejection is not performed for image formation. As a technique for reducing such image quality deterioration, a method for determining whether flushing is necessary from the ink ejection timing of each nozzle, performing flushing on the paper only at the necessary timing (for example, Patent Documents 1 and 2), A technique (for example, Patent Document 3) is known in which flushing is performed by selecting a region that has a small influence on image quality even if it is performed.

JP 2001-026123 A JP2007-001118A JP 2006-272571 A

  The problem with the prior art is that there is insufficient reduction in image quality degradation.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1: A printing data generation device that generates dot data indicating the presence or absence of dot formation for each pixel by an error diffusion method in order to perform printing by ink ejection by a line head,
When flushing is required for the selected pixel, a setting unit that sets dot formation in the pixel to be present, and
The gist of the present invention is to provide an error diffusion unit that diffuses a density error of a pixel that is set to have dot formation by the setting unit.

  If printing is performed using the dot data generated by this application example, image quality deterioration can be suppressed while realizing paper flushing. In this application example, since the dot formation is set for the pixel that needs to be flushed, the flushing can be realized. Further, since the density error of the pixels set with dot formation in this way is diffused, image quality deterioration is suppressed.

Application Example 2: The printing data generation apparatus described in Application Example 1,
The setting unit includes a changing unit that changes a threshold value used in the error diffusion method to a value less than a minimum value that can be taken by a gradation value taking diffusion error into consideration when flushing is necessary for a selected pixel. And

  According to this application example, the application example 1 can be realized with a slight modification to the conventional error diffusion method.

Application Example 3: A printing data generation device that generates dot data indicating the presence or absence of dot formation of each pixel using a dither mask in order to perform printing by ink ejection by a line head,
At least one of the threshold values stored in the dither mask is a special value for setting the corresponding pixel to have dot formation,
In the dither mask, the arrangement of each threshold value including the special value is determined so that dispersibility is good,
In the dot data for printing one print medium, the pixel set with dot formation by the special value is included in at least one pixel row arranged in the print medium feeding direction. The gist is to arrange the dither mask and generate the dot data.

  If printing is performed using the dot data generated by this application example, image quality deterioration can be suppressed while realizing paper flushing. In this application example, since the special value is arranged so that the dispersibility is good, deterioration of the image quality can be suppressed. In addition, since each nozzle can eject ink at least once while printing one print medium, paper flushing can be realized.

1 is a configuration diagram of a printing system 10. FIG. 2 is a configuration diagram of a host computer 200 and a printer 300. FIG. 6 is a flowchart illustrating printing processing. The figure which shows the mode of arrangement | positioning of a dither mask. The flowchart which shows the halftone process in the case of an error diffusion method.

1. Printing system (Figs. 1 and 2):
FIG. 1 is a diagram illustrating the configuration of the printing system 10. The printing system 10 includes a host computer 200 and a printer 300. The host computer 200 and the printer 300 are connected by a USB cable 120. The host computer 200 transfers data for printing (hereinafter referred to as “print image data”) to the printer 300. The printer 300 prints an image on a print medium based on the print image data transferred from the host computer 200. The print image data is data obtained by converting display image data by a printer driver. The display image data is for displaying an image on a display device 215 (described later with FIG. 2) provided in the host computer 200. The display image data is 8-bit (0 to 255) RGB format data.

  FIG. 2 is a diagram schematically showing the configuration of the host computer 200 and the printer 300. The host computer 200 includes a CPU 201, a RAM 203, a ROM 205, a display device controller 207, a keyboard controller 209, a memory controller 211, a hard disk drive (HDD) 213, and a communication interface (I / F) 220. These components are connected to each other via a bus 230. A display device 215 is connected to the display device controller 207. A keyboard 217 is connected to the keyboard controller 209, and an external memory 219 is connected to the memory controller 211. A USB cable 120 is connected to the communication I / F 220. In the present embodiment, the standard of the communication I / F 220 and a communication I / F 320 described later is USB 2.0. The USB cable 120 is a cable compatible with USB 2.0. The CPU 201 reads out the program stored in the HDD 213 to the RAM 203 and executes it in order to control the operation of the entire host computer 200.

  On the other hand, the printer 300 is a line printer that performs printing by ejecting ink of four colors of cyan (C), magenta (M), yellow (Y), and black (K) from nozzles provided in the line head. The line head is a print head in which nozzles are arranged in the entire width direction so that printing can be performed without scanning in the width direction. The printer 300 includes a CPU 301, a RAM 303, a ROM 305, a printing unit interface (I / F) 307, a memory controller 309, an operation panel 313, and a communication interface (I / F) 320. These components are connected to each other by a bus 330. A printing unit 311 is connected to the printing unit I / F 307, and an external memory 315 is connected to the memory controller 309.

  The CPU 301 reads a program stored in the ROM 305 to the RAM 303 and executes it in order to control the operation of the entire printer 300. The printing unit 311 is hardware for performing printing by ejecting ink onto a print medium, such as an ink cartridge, a print head, or a platen that stores ink.

  The operation panel 313 is a user interface for the user to make settings and instructions related to printing. This setting is a setting such as the type and size of the print medium. This instruction is an instruction to start or stop printing.

2. Printing process (Figure 3):
FIG. 3 is a flowchart showing the printing process. The execution subject of the printing process is a CPU 201 provided in the host computer 200. The trigger for starting the process is that a printing instruction is input via the operation panel 313.

  First, display image data is converted from RGB format to CMYK format (step S410). CMYK conversion is executed by referring to the conversion LUT stored in the ROM 205.

  Next, halftone processing is performed (step S420). Dot data is generated by halftone processing. The dot data is data indicating ON / OFF of the dot of each pixel for each color of CMYK. Details of the halftone process will be described later.

  Subsequently, the dot data generated by the halftone process is transferred to the printer 300 (step S430), and the printing process is finished. The printer 300 executes printing according to the transferred dot data.

3. Halftone processing using a dither mask (Figure 4):
FIG. 4 shows how the dither mask is arranged. When the halftone process (step S420) of the printing process is performed using a dither mask, the dither mask shown in FIG. 4 is used. The dither mask shown in FIG. 4 is for cyan ink and has a size of 4 × 4. Actually, it is preferable to use a larger one such as 64 × 64 in terms of image quality, but here, a 4 × 4 one is illustrated for the sake of simplicity.

  In FIG. 4, a square surrounded by a thick line indicates one dither mask. Each of the 16 squares in the bold line represents a mask pixel. As shown in FIG. 4, each dither mask includes one mask pixel shown in black (hereinafter referred to as “special value mask pixel”). The special value mask pixel stores −1 as a threshold value. When the threshold is -1, the dot data of the corresponding pixel is always set to ON. On the other hand, a blank mask pixel stores a threshold value of 0 or more.

  Each threshold value including the threshold value of the special value mask pixel is arranged to have a blue noise characteristic. By having the blue noise characteristic, the dispersibility of dots is improved and high-quality printing can be realized.

  As shown in FIG. 4, the dither mask is arranged so as to be shifted by one pixel in the width direction as it advances in the paper feed direction. With this arrangement, the special value mask pixels are also shifted by one pixel in the width direction as the paper feed direction proceeds.

  With the arrangement of the special value mask pixels described above, each time the sheet is fed a distance corresponding to four dither masks, each nozzle for cyan ink ejects ink at least once. The distance for four dither masks is set shorter than the length of the paper in the paper feed direction. Therefore, by this ejection, flushing is realized for all nozzles that eject cyan while printing one sheet of paper.

  For magenta, yellow, and black, a dida mask in which special value mask pixels are similarly arranged is used. In other words, a dither mask is used in which the special value mask pixels are shifted by one pixel in the width direction as they advance in the paper feed direction. This realizes flushing for all nozzles of each color.

  In the dither mask for each color, different arrangements are used for the special value mask pixels. In other words, since the cyan special value mask pixels are arranged second from the top / second from the left as described above, for example, the third from magenta / second from the left, and yellow from the top / second Third from the left, black is third from the top / third from the left. With this arrangement, it is possible to prevent dots ejected for flushing from being formed on the same pixel, and to suppress deterioration in image quality.

4). Error diffusion method (Figure 5):
FIG. 5 is a flowchart showing halftone processing. This process is executed when the halftone process (step S420) of the printing process is performed by the error diffusion method.

  First, one pixel is selected as in the normal error diffusion method (step S421). Next, it is determined whether the selected pixel needs to set the dot to ON for flushing (step S422). As this determination method, a conventional method can be used. For example, for each nozzle, if the ink is not ejected again until a predetermined time has elapsed from the previous ink ejection, it is determined that flushing is necessary.

  If it is determined that it is necessary to set the dot to ON (step S422, YES), the threshold for determining dot ON / OFF is changed from the initial setting of 128 to -256 (step S423), and the process proceeds to step S424. On the other hand, if it is determined that it is not necessary to set the dot to ON (step S422, NO), the process proceeds to step S424 without changing the threshold value.

  In step S424, it is determined whether the threshold value is smaller than the determination value. The determination value is a value obtained by adding the diffusion error and the gradation value of the pixel. If it is determined that the threshold value is smaller than the determination value (step S424, YES), the selected pixel is set to dot ON (step S425). Subsequently, the threshold value is returned to 128 (step S426). However, if the threshold is not set to −256, nothing is done.

  On the other hand, if it is determined that the threshold value is not smaller than the determination value (step S424, NO), the selected pixel is set to dot OFF (step S427).

  After step S426 or step S427, the error is diffused to the surroundings (step S428). The error value diffused here is a value obtained by subtracting the dot value from the value obtained by adding the gradation value of the selected pixel and the diffused error. The dot value is 255 when the dot is set to ON, and 0 when the dot is set to OFF. Further, the diffusion is performed on a plurality of surrounding pixels with predetermined weighting.

  When the diffusion error is calculated in this way, when the dot is set to ON by setting the threshold to −256, the diffusion error may be smaller than usual. The small value referred to here is a negative value that has a large absolute value. When a value smaller than normal is diffused, surrounding dots are not easily set to ON. By such error diffusion, the influence of setting the dot ON for pixels that are not set to dot ON in the case of the normal error diffusion method is offset by setting the threshold value to −256, and deterioration of image quality is suppressed. Is done.

  Subsequently, it is determined whether all pixels have been selected (step S429). If it is determined that there remains a pixel that has not been selected (step S429, NO), the process returns to step S421. If it is determined that all the pixels have been selected (step S429, YES), the halftone process ends.

  According to the halftone process described above, a dot is always set to ON for a pixel that is determined to need to be set to ON for flushing. As a result, flushing is realized. Furthermore, image quality degradation is suppressed by the error diffusion method.

5. Relationship between embodiment and application example:
Steps S423, S424, and S425 correspond to software for realizing a setting unit, step S423 is a changing unit, and step S428 is an error diffusion unit.

6). Other embodiments:
The present invention is not limited to the above-described embodiments, and can be implemented in various forms within the technical scope of the invention. For example, additional components in the embodiment can be omitted from the embodiment. The additional components referred to here are elements corresponding to matters not specified in the substantially independent application example. For example, the following can be considered.

The printer 300 may execute the CMYK conversion (Step S410) and / or the halftone process (Step S420).
In the dither mask for each color, the special value mask pixels need not necessarily be arranged differently. That is, the dots of each color may be formed so as to be overlapped by the special value mask pixels.
The special value in the dither mask may be any value as long as the dot is always set to ON.
The threshold value after being changed in the error diffusion method (threshold value after being changed in step S423) may be any value as long as it is less than a possible value for the determination value.
The special value mask pixels of cyan and magenta are preferably arranged apart from each other.

DESCRIPTION OF SYMBOLS 10 ... Printing system 120 ... USB cable 200 ... Host computer 201 ... CPU
203 ... RAM
205 ... ROM
207 ... Display device controller 209 ... Keyboard controller 211 ... Memory controller 213 ... Hard disk drive 215 ... Display device 217 ... Keyboard 219 ... External memory 220 ... Communication interface 230 ... Bus 300 ... Printer 301 ... CPU
303 ... RAM
305 ... ROM
307: Printing unit interface 309 ... Memory controller 311 ... Printing unit 313 ... Operation panel 315 ... External memory 320 ... Communication interface 330 ... Bus

Claims (5)

A printing apparatus that generates dot data for printing using a line head using a dither mask,
At least one of the threshold values stored in the dither mask is a special value for setting the corresponding pixel to have dot formation,
In the dot data for printing one print medium, the pixel set with dot formation by the special value is included in at least one pixel row arranged in the print medium feeding direction. A printing apparatus that arranges a dither mask to generate the dot data. The printing apparatus according to claim 1, wherein the dither mask is arranged so as to be shifted in the feeding direction. The printing apparatus according to claim 1, wherein the special value is arranged in the dither mask so that dispersibility is good. The printing apparatus according to any one of claims 1 to 3, wherein an arrangement of each threshold value is determined so that the dither mask has good dispersibility. A printing apparatus that performs printing using a plurality of colors including magenta and black,
A position at which the magenta dots are formed by the special value;
A position where the black dot is formed by the special value;
The printing apparatus according to claim 1, wherein the dots are formed by the dither mask so as to be arranged at different positions.

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