JP5929385B2 - Image processing device - Google Patents

Description

  The present invention relates to an apparatus for processing an image.

  In order for the printing apparatus to print an image, the original image is usually processed. This processing is, for example, processing for converting RGB format data into dot data indicating the presence or absence of dot formation of each color such as CMYK for each pixel. Such processing is called halftone processing (for example, Patent Document 1).

  In Patent Document 1, a line printer which is a printer provided with a line head is employed. The line head is a print head in which ink ejection nozzles are arranged over the entire recording width. With this configuration, it is not necessary to scan the print head in a direction (for example, an orthogonal direction) different from the conveyance direction of the print medium, and the printing speed is improved.

JP 2011-761 A

  The problem of the prior art is that the halftone processing method is not appropriately selected according to the printing conditions. There are various methods of halftone processing, for example, an error diffusion method and a dither method are known. Each of these methods is characterized by processing speed, image quality, and the like. In particular, when a line printer is employed as in Patent Document 1, if a halftone processing method is not appropriately selected, the halftone processing may become a rate-limiting (bottleneck) for printing. That the halftone process becomes rate-limiting means that the printing apparatus cannot print at the original printing speed, and the effective printing speed is reduced. The above-mentioned problem is not limited to a line printer, but is also a problem that applies to other types of printers, for example, serial printers.

  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: An image processing apparatus that generates dot data used by a line printer for printing,
A first conversion unit that converts image data into dot data by a first technique;
A second conversion unit that performs the conversion by a second method having a higher conversion speed than the first method;
When the expected data amount of dot data for printing for a predetermined area is the first data amount, the first conversion unit is caused to perform the conversion, while the second data amount is larger than the first data amount. A control unit that causes the second conversion unit to perform the conversion.
According to this application example, it is possible to appropriately select a halftone processing method according to printing conditions, specifically the expected data amount of dot data.

Application Example 2: The image processing apparatus according to Application Example 1,
A transfer unit for transferring the generated dot data to the line printer;
The control unit causes the second conversion unit to perform the conversion when the expected data amount is the second data amount and the transfer rate of the dot data is the first transfer rate, while the transfer is performed. When the speed is a second transfer speed that is slower than the first transfer speed, the first converter is caused to perform the conversion.

  According to this application example, the halftone processing method can be appropriately selected according to the data transfer speed. That is, since the high-speed conversion by the first conversion unit is not utilized at the second transfer rate, it is preferable to use the second conversion unit. According to this application example, such an appropriate selection can be made.

Application Example 3: The image processing apparatus according to Application Example 1 or Application Example 2,
A processor for realizing the first and second conversion units by executing a program;
The control unit causes the first conversion unit to perform the conversion when the predicted data amount is the first data amount and the processing load of the processor is the first load, while the processing load of the processor When the second load is larger than the first load, the second conversion unit performs the conversion.
According to this application example, the halftone processing method can be appropriately selected according to the processing load of the processor.

Application Example 4: An image processing apparatus that transfers dot data to a line printer,
A first conversion unit that converts image data into dot data by a first technique;
A second conversion unit that performs the conversion by a second method having a higher conversion speed than the first method;
When the transfer rate of dot data to the line printer is the first transfer rate, the second conversion unit performs the conversion, while the transfer rate is lower than the first transfer rate. In some cases, a control unit that causes the first conversion unit to perform the conversion is provided.
According to this application example, the halftone processing method can be appropriately selected according to the transfer speed.

Application Example 5: An image processing apparatus that generates dot data used by a line printer for printing,
A first conversion unit that converts image data into dot data by a first technique;
A second conversion unit that performs the conversion by a second method having a higher conversion speed than the first method;
A processor for realizing the first and second conversion units by executing a program;
When the processing load of the processor is a first load, the first conversion unit performs the conversion. On the other hand, when the processing load of the processor is a second load larger than the first load, the second conversion is performed. A control unit that causes the conversion unit to perform the conversion.
According to this application example, the halftone processing method can be appropriately selected according to the processing load of the processor.

Application Example 6: The image processing apparatus according to any one of Application Examples 1 to 5,
The first method is an error diffusion method,
The second method is a dither method.
In general, the error diffusion method realizes a good print image quality while the conversion speed is lower than that of the dither method. Therefore, according to this application example, it is possible to appropriately select which of the printing speed and the image quality is given priority.

  The forms described in each application example can be regarded as other forms that are substantially the same. Examples of other forms include a dot data generation method, an image processing program, a non-temporary storage medium storing the program, a printing apparatus or a printed material production method that performs printing based on the generated dot data.

1 is a configuration diagram of a printing system 10. 5 is a flowchart showing print data generation processing. The flowchart which shows a halftone selection process. The graph which shows the relationship between the processing time for one sheet, and unit data amount VU.

1. Printing system (Figure 1):
FIG. 1 shows the configuration of the printing system 10. The printing system 10 includes a host computer 200 and a printer 300. Further, the host computer 200 transfers data for printing (hereinafter referred to as “printing data”) to the printer 300. The printer 300 prints an image on printing paper based on the printing data transferred from the host computer 200. This print data is data obtained by converting display image data by a printer driver, and is dot data indicating the presence or absence of dot formation of each color for each pixel. An image expressed by dot data generated by the host computer 200 has a blue noise characteristic. The display image data is for displaying an image on the display device 215 provided in the host computer 200.

  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 such as the display device 215 is connected to the display device controller 207. An input device such as a keyboard 217 and a mouse (not shown) is connected to the keyboard controller 209, and an external memory 219 is connected to the memory controller 211. The communication I / F 220 is a module for performing wired connection by USB 2.0 or wireless connection by Wi-Fi (registered trademark) (IEEE 802.11n) to other devices. FIG. 1 shows a state in which a USB cable 120 is connected and wired communication by USB is possible. 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 of the paper. 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 such as an ink cartridge that stores ink, a print head, a platen, and the like for ejecting ink onto printing paper to perform printing.

  The operation panel 313 is a user interface for the user to make settings and instructions related to printing. This setting includes settings such as paper size (A4 or A3), print mode (high speed mode or high image quality mode), color mode (full color or monochrome), and the like. The content of the instruction is, for example, canceling printing or starting up the printer 300.

  The high image quality mode is a mode that employs a resolution of 720 dpi and A4 paper at 60 ppm (page per minute) (= printing per second per sheet). The high-speed mode is a mode that employs a resolution of 360 dpi and A6.6 paper at 86.6 ppm (= printing at 0.7 seconds per sheet). The printing speed for A3 paper is half that of A4 paper. This is because the paper conveyance direction by the printer 300 is the short side direction for A4 paper and the long side direction for A3 paper.

2. Print data generation processing (FIGS. 2, 3, and 4):
FIG. 2 is a flowchart showing print data generation processing. The execution subject of this processing is the CPU 201 provided in the host computer 200. The trigger for starting the execution of this process is that a print instruction is input via the keyboard 217. A necessary condition for starting this processing is that the host computer 200 and the printer 300 can communicate with each other by at least one of USB and Wi-Fi.

  When the print data generation process is started, it is determined whether or not communication by USB is possible (step S410). When it is determined that the USB communication is not possible (step S410, NO), the measurement of the communication speed by Wi-Fi is started (step S420). As is well known, since the wireless communication speed can fluctuate, actual measurement is performed to grasp the current value. This measurement is performed by transmitting and receiving a speed measurement packet, and is continued until immediately before halftone processing (immediately before step S456 or step S457 described later). The reason why the measurement is started at an early stage of the print data generation process is to take a long measurement time.

  On the other hand, if it is determined that the USB communication is possible (step S410, YES), step S420 is skipped because Wi-Fi communication, which is slower than USB communication, is not used.

  Next, display image data in RGB format is acquired from the RAM 203 (step S430). Subsequently, with reference to a lookup table (not shown) stored in the ROM 205, the obtained display image data is color-converted from the RGB format to the CMYK format (step S440). Subsequently, halftone selection processing is executed (step S450).

FIG. 3 is a flowchart showing the halftone selection process. When this process is started, a data amount (hereinafter referred to as “unit data amount”) VU of dot data (hereinafter referred to as “unit dot data”) for one sheet is calculated (step S451). The unit data amount VU is calculated by “(resolution) ² × area of printing region × number of ink colors to be used”. The area of the printing area is a value obtained by removing the margin area from the area of the paper.

  Subsequently, the upper limit data amount VL is calculated (step S452). The upper limit data amount VL is a unit data amount under the condition that even if dot data is generated by halftone processing by an error diffusion method (hereinafter referred to as “error diffusion processing”), the halftone processing does not become the rate-limiting of printing. This is the upper limit value of VU. This calculation is performed by a calculation formula of “information amount per dot (bit / dot) × time for printing one sheet (s) / speed of error diffusion processing (dot / s)”. In the present embodiment, the information amount per dot is 1 bit / dot. The time for printing one sheet of paper is determined by the print mode. The speed of error diffusion processing is estimated based on the processing load of the CPU 201 (hereinafter referred to as “CPU load”). The time for printing one sheet of paper and the speed of error diffusion processing will be described below with reference to FIG.

  FIG. 4 is a graph showing the relationship between the processing time for one sheet and the unit data amount VU. The processing time for one sheet is the printing time for one sheet, the time for generating unit dot data by error diffusion processing, the time for transferring unit dot data using Wi-Fi, the USB And the time for transferring the unit dot data using.

  In FIG. 4, a time T1 that is the printing time for one sheet of paper illustrates the time corresponding to the high-speed mode, and is indicated by a horizontal line. This indicates that the printing time is determined if the printing mode is designated. If the high image quality mode is set, the time corresponding to the high image quality mode is reached.

  On the other hand, the time required for error diffusion processing has a strong positive correlation with the unit data amount VU. In FIG. 4, this relationship is indicated by a straight line, and the slope of this straight line represents the reciprocal of the speed of the error diffusion process. However, this relationship is not necessarily a straight line.

  The speed of the error diffusion process depends on the CPU load as described above. In FIG. 4, two kinds of relationships are shown. Actually, the speed of the error diffusion process is a value that continuously changes according to the CPU load. The CPU load is estimated based on the usage rate or temperature of the CPU 201.

  As shown in FIG. 4, the upper limit data amount VL corresponds to the data amount of dot data generated by error diffusion processing during the time T1.

  Subsequently, it is determined whether the unit data amount VU is larger than the upper limit data amount VL (step S453). If it is determined that the unit data amount VU is not larger (smaller or the same) than the upper limit data amount VL (step S453, NO), error diffusion processing is executed (step S456). The reason why the error diffusion process is employed in this case is that it can be estimated that the printing speed does not exceed the speed of the error diffusion process.

  Thus, when it determines with NO in step S453, in FIG. 4, it shows by the area | region (the area | region whose processing time is T1 or less) without shading, for example, point A corresponds. Point A indicates a case where the CPU load is low and the unit data amount VU is V1.

  On the other hand, if it is determined that the unit data amount VU is larger than the upper limit data amount VL (step S453, NO), it is determined whether or not USB communication is possible (step S454). If it is determined that the USB communication is possible (step S454, YES), halftone processing is executed by the dither method (step S457). In this embodiment, since the communication speed by USB is sufficiently high, transfer of print data by USB does not become the rate-limiting of printing. Therefore, when the printing speed exceeds the speed of the error diffusion processing and communication by USB is possible, it is estimated that the error diffusion processing becomes the rate limiting for printing. Therefore, a halftone process is executed by adopting a dither method that is faster than the error diffusion method. By adopting the dither method, when the halftone processing is not rate-limiting or when the halftone processing is rate-limiting, the effective degree of decrease in the printing speed can be reduced.

  Thus, when it determines with YES in step S454, in FIG. 4, it shows by the area | region where the dot pattern was given, and the area | region where the hatching was given, for example, the point B and the point C correspond. Point B shows a case where the CPU load is low and the unit data amount VU is the data amount V2 (> V1). Point C indicates a case where the CPU load is high and the unit data amount VU is the data amount V1.

  On the other hand, if it is determined that communication by USB is not possible (step S454, NO), it is determined whether the transfer rate by Wi-Fi is faster than the error diffusion processing rate (step S455). In this comparison, the transfer rate by Wi-Fi determines the communication rate by Wi-Fi, which has been measured from step S420, and is “communication speed (bit / s) / information amount per dot (bit / dot)”. The value calculated by “is used. The transfer rate by Wi-Fi corresponds to the reciprocal of the gradient of “transfer time by Wi-Fi” in FIG.

  If it is determined that the transfer rate by Wi-Fi is not faster than the speed of error diffusion processing (step S455, NO), it is estimated that the error diffusion processing will not be rate limiting, so error diffusion processing is executed (step S456). ). If NO is determined in step S455, it is indicated by a hatched area in FIG.

  On the other hand, if it is determined that the transfer rate by Wi-Fi is faster than the error diffusion processing rate (step S455, YES), halftone processing by the dither method is executed (step S457). If YES is determined in step S455, the dot C is indicated by a dot-patterned region in FIG.

  As shown in FIG. 2, after the halftone selection process, an interlace process is performed so that the printer 300 can handle the dot data (step S460). Finally, the data generated in step S460 is transferred to the printer 300 as print data (step S470). As a transfer method, USB is used if communication by USB is possible, and Wi-Fi is used otherwise. The printer 300 executes printing based on the transferred printing data.

3. Effect:
According to the printing system 10, it is possible to balance the suppression of the decrease in the effective printing speed and the image quality. The determination of whether or not the halftone processing is rate-determining is determined by comparing the speed of the halftone processing, the transfer speed of the dot data, and the printing speed. Since the printing system 10 makes this comparison after estimating these fluctuating speeds, the determination is highly accurate.

4). Correspondence between embodiment and application example:
Steps S453 to S455 correspond to the control unit, step S456 corresponds to the first conversion unit, step S457 corresponds to the second conversion unit, and step S470 corresponds to software for realizing the transfer unit.
The data amount V1 is the first data amount, the data amount V2 is the second data amount, the USB communication speed is the first transfer speed, and the Wi-Fi communication speed is the second transfer speed. The CPU load corresponds to the first load, and the higher CPU load corresponds to the second load.

5. Other embodiments:
The embodiment of the invention is not limited to the above-described form, and various forms within the technical scope of the invention can be adopted. 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 embodiments may be used.

  The selection criterion of the error diffusion method or the dither method may not be whether or not the halftone process is rate-limiting. For example, if importance is placed on image quality, the error diffusion method may be employed even when halftone processing is rate limiting, or when the degree of effective printing speed reduction is small.

  The printer 300 may execute halftone processing. In this case, the image processing apparatus is incorporated in the printer 300. Specifically, a multifunction machine or the like can be considered. In this case, since transfer of dot data is not executed, steps S410, S420, S454, and S455 are not necessary. If YES is determined in step S453, the dither method is employed.

  Both the upper limit data amount VL and the transfer rate of dot data may be treated as fixed values. In this way, step S452, step S454, and step S455 can be omitted. If YES is determined in step S453, the dither method is employed. When the printing speed and the CPU load are handled as fixed values, the upper limit data amount VL is inevitably handled as a fixed value as described above.

  One of the upper limit data amount VL and the transfer rate of dot data may be treated as a fixed value. Alternatively, one of the printing speed and the CPU load may be handled as a fixed value.

  On the other hand, when the printing speed can be considered sufficiently high, the error diffusion method or the dither method is determined based on the comparison between the error diffusion processing speed and the dot data transfer speed without considering the printing speed. You may do it. For example, step S453 may be omitted. Alternatively, when the unit data amount can be considered constant, the error diffusion method or the dither method may be determined based on the transfer rate of dot data and / or the CPU load.

  In the embodiment, the time required to generate the dot data of the unit data amount VU by the halftone process is calculated based on the premise that the time is proportional to the number of ink colors to be used. However, dot data for each ink color can be generated in parallel. Therefore, the halftone speed may be determined based on the generation speed in accordance with the actual situation without adopting the above assumption.

When printing continuously, the dot data used for printing the first sheet may be generated by the dither method regardless of the printing conditions. In this way, the halftone speed is increased, and the process for selecting the error diffusion method or the dither method can be omitted, so that the start of printing of the first sheet is accelerated.
The halftone method may be other than the error diffusion method and the dither method. For example, the average error minimum method can be considered.

  A dedicated hardware RIP may be used. For example, the hardware RIP performs halftone processing on display image data transferred from a computer, and transfers dot data generated thereby to a printer.

The printer may use a serial head. The serial head is a print head that is scanned in a direction (for example, an orthogonal direction) different from the conveyance direction of the print medium.
The print data generation process may be realized by hardware.

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 ... HDD
215 ... Display device 217 ... Keyboard 219 ... External memory 220 ... Communication I / F
230 ... Bus 300 ... Printer 301 ... CPU
303 ... RAM
305 ... ROM
307 ... Printing section I / F
309 ... Memory controller 311 ... Printing section 313 ... Operation panel 315 ... External memory 330 ... Bus

Claims (4)

An image processing apparatus that generates dot data used by a line printer for printing,
A first conversion unit that converts image data into dot data by a first technique;
A second conversion unit that performs the conversion by a second method having a higher conversion speed than the first method;
When the expected data amount of dot data for printing for a predetermined area is the first data amount, the first conversion unit is caused to perform the conversion, while the second data amount is larger than the first data amount. a control unit for the conversion to the second conversion unit in the case of the amount of data,
A transfer unit that transfers the generated dot data to the line printer;
With
The control unit causes the second conversion unit to perform the conversion when the expected data amount is the second data amount and the transfer rate of the dot data is the first transfer rate, while the transfer is performed. The image processing apparatus that causes the first conversion unit to perform the conversion when the speed is a second transfer speed lower than the first transfer speed . The image processing apparatus according to claim 1 ,
A processor for realizing the first and second conversion units by executing a program;
The control unit causes the first conversion unit to perform the conversion when the predicted data amount is the first data amount and the processing load of the processor is the first load, while the processing load of the processor An image processing apparatus that causes the second conversion unit to perform the conversion when the second load is greater than the first load. An image processing apparatus that generates dot data used by a line printer for printing,
A first conversion unit that converts image data into dot data by a first technique;
A second conversion unit that performs the conversion by a second method having a higher conversion speed than the first method;
A processor that realizes the first and second conversion units by executing a program;
When the processing load of the processor is a first load, the first conversion unit performs the conversion. On the other hand, when the processing load of the processor is a second load larger than the first load, the second conversion is performed. An image processing apparatus comprising: a control unit that causes the conversion unit to perform the conversion. An image processing apparatus according to any one of claims 1 to 3 , wherein
The first method is an error diffusion method,
The image processing apparatus according to the second method is a dither method.

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