JP4375050B2 - An image output system for outputting an image based on information on the number of dots formed in a predetermined area - Google Patents

Description

  The present invention relates to a technique for outputting an image based on image data, and more particularly to a technique for outputting an image by performing predetermined image processing on the image data to generate dots with an appropriate density.

  Image output devices that output images by forming dots on various output media such as print media and liquid crystal screens are widely used as output devices for various image devices. In these image output devices, images are handled in a state of being subdivided into small areas called pixels, and dots are formed in these pixels. When dots are formed in the pixels, of course, only one state of whether or not the dots are formed can be taken from the viewpoint of each pixel. However, when viewed in an area with a certain size, it is possible to create a density in the way dots are formed, and it is possible to output a multi-tone image by changing the dot formation density. is there. For example, when forming black ink dots on a printing paper, a region where dots are densely formed looks dark, and conversely, a region where dots are sparsely formed appears bright. In addition, when bright dots are formed on a liquid crystal screen, a region where dots are densely formed looks bright and a region where sparsely formed dots appear dark. Accordingly, if the dot formation density is appropriately controlled, a multi-tone image can be output. As described above, data for controlling dot formation so as to obtain an appropriate formation density is generated by performing predetermined image processing on an image to be output.

  In recent years, these image output apparatuses have been required to have high output image quality and large images. It is effective to divide an image into finer pixels for the demand for higher image quality. If the pixels are made smaller, the dots formed on the pixels become inconspicuous and the image quality can be improved. Also, the demand for larger images is handled by increasing the number of pixels. Of course, it is possible to enlarge the output image by increasing the size of each pixel, but this leads to a decrease in image quality. Therefore, it is effective to increase the number of pixels in response to a request for enlargement. is there.

  However, when the number of pixels constituting the image increases, it takes time for image processing, and it becomes difficult to output the image quickly. Therefore, a technique that enables image processing to be executed quickly has been proposed (Patent Document 1).

JP 2002-185789 A

  However, even if the image processing is performed quickly, if the image data transfer or the processing of the transferred data takes a long time, the effect of quickly outputting the image is naturally limited.

  The present invention has been made to solve the above-mentioned problems in the prior art, and aims to provide a technique capable of transferring image data and processing transferred data at high speed while maintaining sufficient output image quality. To do.

In order to solve at least a part of the problems described above, the image output system of the present invention employs the following configuration. That is,
An image output system comprising: an image processing device that performs predetermined image processing on image data; and an image output device that outputs an image on an output medium by forming dots based on the result of the image processing,
The image processing apparatus includes:
A predetermined number of adjacent pixels are grouped into a pixel group to divide the image into a plurality of pixel groups, and number data representing the number of dots formed in each pixel group is generated based on the image data Number data generation means to perform,
Number data supply means for supplying the number data generated for each pixel group to the image output device, and
The image output device includes:
Order value acquisition means for acquiring an order value indicating the order in which dots are formed in the pixel group for each pixel in the pixel group;
Correspondence storage means for storing the correspondence between the combination of the order value and the number data, and the presence or absence of dot formation in the pixel having the order value;
When the number data for the pixel group is received, the presence / absence of dot formation for each pixel in the pixel group is determined by referring to the correspondence for each combination of the number data and each order value. Dot formation presence / absence determining means;
And a dot forming unit that forms dots on the output medium in accordance with the determined dot formation.

The image output method of the present invention corresponding to the image output system described above,
An image output method for outputting an image on an output medium by performing predetermined image processing on image data and forming dots based on the obtained result,
A predetermined number of adjacent pixels are grouped into a pixel group to divide the image into a plurality of pixel groups, and number data representing the number of dots formed in each pixel group is generated based on the image data A first step of:
A second step of obtaining, for each pixel in the pixel group, an order value indicating an order in which dots are formed in the pixel group;
A third step of storing a correspondence relationship between the combination of the order value and the number data and the presence or absence of dot formation in the pixel having the order value;
A fourth step of determining the presence or absence of dot formation by referring to the correspondence for each combination of the number data and the order value for each pixel in the pixel group that generated the number data;
And a fifth step of forming dots on the output medium according to the determined presence / absence of dot formation.

  In such an image output system and image output method of the present invention, an image is divided into a plurality of pixel groups, number data is generated for each pixel group, and supplied to the image output apparatus. In the image output apparatus, an order value indicating the order in which dots are formed for each pixel in the pixel group is acquired. When acquiring the order value of each pixel, for example, a continuous integer value starting from “1” may be set in advance for each pixel in the pixel group, and the integer value may be read and read as the order value. Alternatively, a real value having a different value may be set in advance for each pixel, and the order value of each pixel may be determined according to the order of the size of the real value. Further, a context may be set between the pixels, and the order value of each pixel may be determined based on the context. The image output apparatus also stores a correspondence relationship between the combination of the order value and the number data, and the presence / absence of dot formation in the pixel having the order value. Then, when the number data for the pixel group is received, dot formation for each pixel in the pixel group is performed by referring to the correspondence from the combination of the number data and the order value for each pixel in the pixel group. Determine whether or not. An image is output by forming dots on the output medium according to the determined dot formation.

  As will be described in detail later, the data representing the number of dots for each pixel group can be much smaller than the data representing the presence or absence of dot formation for all the pixels of the image. For this reason, if the number data for each pixel group is supplied to the image output device, the data can be supplied quickly, and the image can be output quickly.

  Further, when the image output device receives the number data output for each pixel group, the image output device refers to the correspondence relationship from the combination of the number data and the order value for each pixel in the pixel group, whereby each pixel in the pixel group is referred to. Whether or not dots are formed is determined. If the presence or absence of dot formation is determined with reference to the correspondence in this way, the presence or absence of dot formation for each pixel in the pixel group can be immediately determined from the number data, so it is determined very quickly and easily. Therefore, it is possible to output an image quickly.

  Furthermore, if the presence / absence of dot formation can be determined by such an extremely simple process, even if the image output device does not have a high processing capacity like the image processing device, the number data can be used for each pixel. It is possible to quickly determine whether or not dots are formed.

  In such an image output system, the order value of each pixel may be acquired as follows to determine the presence or absence of dot formation. First, a plurality of sets of the order of pixels in which dots are formed in the pixel group are stored, and one order is selected for each pixel group from the plurality of sets of order. Then, based on the selected order, an order value for each pixel in the pixel group may be acquired, and the presence or absence of dot formation for each pixel may be determined based on the obtained order value.

  The presence or absence of dot formation for each pixel in the pixel group is determined based on the number data and the order value. Therefore, if one order is selected from a plurality of sets and the presence / absence of dot formation is determined using the order value obtained based on the order, even if the same number of data continues, Dots are not formed at the same pixel position across a plurality of pixel groups. For this reason, it is possible to reliably avoid the deterioration of the image quality due to the conspicuous area where dots are formed in the same pattern.

  Further, in such an image output system, the number data is generated based on a dither matrix in which a threshold is associated with each of the two-dimensionally arranged pixels, and an order value acquired based on the same dither matrix is used. Thus, the presence or absence of dot formation for each pixel may be determined. That is, the dither matrix is divided into a plurality of pixel groups, and the number data is generated by obtaining the number of dots formed in the pixel group. When the number data is generated, data on the number of dots formed in the pixel group may be generated by determining the presence or absence of dot formation for each pixel in the pixel group using the divided dither matrix. Alternatively, in order to generate the number data, since it is not necessary to know the pixel position where the dot is formed, it can be simply as follows. First, only threshold values set in the divided dither matrix are stored for each pixel group. Next, a gradation value (representative gradation value) representing the pixel group is determined. As the representative gradation value, an average value of the image data of each pixel can be used, or the image data has an approximate value between adjacent pixels, so that an image of a pixel at a predetermined position in the pixel group is obtained. It is also possible to use data as representative gradation values. The number of threshold values smaller than the representative gradation value can be obtained for each pixel group, and the obtained value can be used as the number of dots in the pixel group.

  When the number data generated in this way is received, the presence / absence of dot formation for each pixel in the pixel group is determined as follows. In advance, the dither matrix used to generate the number data is divided into a plurality of pixel groups, and a plurality of sets of pixel sequences determined based on threshold values associated with the respective pixels in the pixel group are stored. Alternatively, the order value of each pixel is determined for each pixel group based on the magnitude relation of the threshold value associated with each pixel in the pixel group, and a plurality of sets of the obtained order values are stored as an order of pixels. When the pixel group count data is received, one order corresponding to the position of the pixel group on the image is selected, and the order value of each pixel is obtained based on the order, and whether or not dots are formed. May be determined.

  As will be described in detail later, in this way, the number data of the pixel group is generated based on the dither matrix, and the presence or absence of dot formation for each pixel in the pixel group is determined based on the same dither matrix. Thus, it is possible to output an image with the same image quality as when the presence or absence of dot formation is determined for each pixel using the dither method. In particular, when the image data of the pixels grouped together as a pixel group has the same gradation value, the case where the presence or absence of dot formation is determined for each pixel using the dither method, and the pixel that forms dots from the number data When the position is determined, dots are formed at exactly the same pixel position.

In order to solve at least a part of the above-described problems of the conventional technology, the first image output apparatus of the present invention employs the following configuration. That is,
An image output device that receives image data that has undergone predetermined image processing and outputs an image by forming dots on an output medium based on the image data.
A number data receiving means for receiving, as the image data, number data representing the number of dots to be formed in the pixel group in a state where a predetermined number of adjacent pixels are grouped as a pixel group;
Order value acquisition means for acquiring an order value indicating the order in which dots are formed in the pixel group for each pixel in the pixel group;
Correspondence storage means for storing the correspondence between the combination of the order value and the number data, and the presence or absence of dot formation in the pixel having the order value;
For each pixel in the pixel group that has received the number data, by referring to the correspondence for each combination of the number data and the order value, dot formation presence / absence determination means for determining the presence / absence of dot formation;
And a dot forming unit that forms dots on the output medium in accordance with the determined dot formation.

Further, the image output method of the present invention corresponding to the first image output apparatus is as follows.
An image output method for receiving image data that has undergone predetermined image processing and outputting an image by forming dots on an output medium based on the image data,
A step (A) of receiving, as the image data, number data representing the number of dots to be formed in the pixel group in a state where a predetermined number of pixels adjacent to each other are grouped as a pixel group;
Obtaining an order value indicating the order in which dots are formed in the pixel group for each pixel in the pixel group (B);
Storing a correspondence relationship between the combination of the order value and the number data and the presence or absence of dot formation in a pixel having the order value; and
For each pixel in the pixel group that has received the number data, a step (D) of determining the presence or absence of dot formation by referring to the correspondence for each combination of the number data and the order value;
And a step (E) of forming dots on the output medium in accordance with the determined presence / absence of dot formation.

  In such an image output apparatus and image output method, when the number data of the pixel group is received, the pixel value is referred to by referring to the correspondence between the combination of the order value and the number data and the presence or absence of dot formation in the pixel having the order value. Whether to form dots for each pixel in the group is determined. An image is output by forming dots on the output medium according to the determined dot formation.

  As will be described later, since the number of pixel group data can be received quickly, it is possible to output an image quickly. In addition, since the presence or absence of dot formation for each pixel can be determined by referring to the correspondence set for each combination of the number data and the order value, it can be determined easily and quickly. For this reason, it is possible to output an image quickly, and it is possible to output an image at a sufficiently practical speed even in an image output apparatus that does not have a high level of processing capability.

  In such an image output device, a plurality of sets of pixels in which dots are formed in a pixel group are stored, and the order value for each pixel is stored for each pixel order, and the number data is stored. Upon receipt, one order may be selected for each pixel group from among the plurality of orders, and the presence or absence of dot formation for each pixel may be determined using the order value acquired based on the order.

  In this way, even when the same number of data is continuous, dots are not formed at the same pixel position across a plurality of pixel groups, so that the area where dots are formed with the same pattern becomes conspicuous, and the image quality is high. It becomes possible to avoid getting worse.

  In such an image output apparatus, a plurality of types of dots having different gradation values to be expressed can be output, and the number of various dots formed in the pixel group may be received as number data. Here, the plurality of types of dots having different gradation values to be expressed may be, for example, a plurality of types of dots having different dot sizes, or a plurality of types of dots having different dot densities. You can also. Furthermore, when one dot is formed in a pseudo manner by forming fine dots at a predetermined density, a plurality of types of dots having different fine dot densities can be used. When these various dots can be formed, a combination of the numbers of various dots is received as number data. Then, the correspondence relationship between the combination of the order value and the number data and the dot type formed on the pixel having the order value is stored, and when the number data is received, each correspondence is referred to by referring to the correspondence relationship. The type of dot formed on the pixel may be determined, and various dots may be formed on the output medium in accordance with the determined dot formation.

  When determining whether or not to form dots for each pixel in the pixel group with reference to the correspondence relationship, even if the number data is data indicating a combination of the number of dots for multiple types of dots, dot formation for each pixel The presence or absence of can be determined very easily, just as in the case of data representing the number of dots. For this reason, it is preferable because it is possible to quickly determine the presence or absence of dot formation and to output an image quickly.

  In such an image output apparatus, the number data may be received for a pixel group in which 8 to 16 pixels each having a predetermined positional relationship are grouped.

  Since the number of pixel groups decreases as the number of pixels collected as a pixel group increases, the number data can be received quickly. On the other hand, if the number of pixels grouped into a pixel group becomes too large, the image quality may be deteriorated. In view of these points, from experience, the best results can be obtained when pixels of 8 to 16 pixels are grouped into a pixel group. That is, as will be described in detail later, if the number of pixels grouped into a pixel group is changed from 8 to 16, the amount of data of the number data is reduced to less than half of the data representing the presence or absence of dot formation for each pixel. Can receive data quickly. In addition, the positional relationship of a plurality of pixels grouped into a pixel group can be experienced as long as they are in a rectangular shape, for example, four pixels in the main scanning direction and two pixels in the sub-scanning direction. In addition, good image quality can be obtained.

Further, in order to solve at least a part of the above-described problems of the prior art, the second image output apparatus of the present invention employs the following configuration. That is,
An image output device that outputs an image corresponding to image data by forming dots on an output medium according to the image data,
A predetermined number of adjacent pixels are grouped into a pixel group to divide the image into a plurality of pixel groups, and number data representing the number of dots formed in each pixel group is generated based on the image data Number data generation means to perform,
Order value acquisition means for acquiring an order value indicating the order in which dots are formed in the pixel group for each pixel in the pixel group;
Correspondence storage means for storing the correspondence between the combination of the order value and the number data, and the presence or absence of dot formation in the pixel having the order value;
For each pixel in the pixel group that has generated the number data, by referring to the correspondence for each combination of the number data and the order value, dot formation presence / absence determination means that determines the presence / absence of dot formation;
And a dot forming unit that forms dots on the output medium in accordance with the determined dot formation.

  Also in the image output apparatus of the present invention, the image is divided into a plurality of pixel groups, and number data representing the number of dots formed in the pixel groups is generated. Next, the presence / absence of dot formation for each pixel in the pixel group is determined with reference to the correspondence between the combination of the order value and the number data and the presence / absence of dot formation in the pixel having the order value. An image is output by forming dots on the output medium according to the determined dot formation.

  If the presence or absence of dot formation for each pixel is determined with reference to the correspondence set for each combination of the number data and the order value, it can be determined easily and quickly. For this reason, it is possible to output an image quickly, and it is possible to output an image at a sufficiently practical speed even in an image output apparatus that does not have a high level of processing capability.

Furthermore, the present invention can also be realized using a computer by causing a computer to read a program for realizing the above-described image output method. Therefore, the present invention includes the following program or a mode as a recording medium on which the program is recorded. That is, the first program of the present invention corresponding to the image output method described above is
A program for implementing a method of outputting an image on an output medium by performing predetermined image processing on image data and forming dots based on the obtained result using a computer,
A predetermined number of adjacent pixels are grouped into a pixel group to divide the image into a plurality of pixel groups, and number data representing the number of dots formed in each pixel group is generated based on the image data A first function to
A second function for obtaining an order value indicating an order in which dots are formed in the pixel group for each pixel in the pixel group;
A third function for storing a correspondence relationship between the combination of the order value and the number data and the presence or absence of dot formation in a pixel having the order value;
For each pixel in the pixel group that has generated the number data, a fourth function that determines the presence or absence of dot formation by referring to the correspondence for each combination of the number data and the order value;
The gist of the present invention is to realize a fifth function of forming dots on the output medium in accordance with the determined dot formation.

The first recording medium of the present invention corresponding to the above program is
A recording medium recorded with a computer-readable program for outputting an image by performing predetermined image processing on image data and forming dots on the output medium based on the obtained result,
A predetermined number of adjacent pixels are grouped into a pixel group to divide the image into a plurality of pixel groups, and number data representing the number of dots formed in each pixel group is generated based on the image data A first function to
A second function for obtaining an order value indicating an order in which dots are formed in the pixel group for each pixel in the pixel group;
A third function for storing a correspondence relationship between the combination of the order value and the number data and the presence or absence of dot formation in a pixel having the order value;
For each pixel in the pixel group that has generated the number data, a fourth function that determines the presence or absence of dot formation by referring to the correspondence for each combination of the number data and the order value;
The gist of the invention is that a program that uses a computer to record the fifth function of forming dots on the output medium according to the determined dot formation is recorded.

Furthermore, the second program of the present invention corresponding to the image output method described above is
A program for realizing, using a computer, a method of receiving image data subjected to predetermined image processing and outputting an image by forming dots on an output medium based on the image data,
A function (A) for receiving, as the image data, number data representing the number of dots to be formed in the pixel group in a state where a predetermined number of adjacent pixels are grouped as a pixel group;
For each pixel in the pixel group, a function (B) for acquiring an order value indicating the order in which dots are formed in the pixel group;
A function (C) for storing a correspondence relationship between the combination of the order value and the number data and the presence or absence of dot formation in a pixel having the order value;
For each pixel in the pixel group that has received the number data, a function (D) for determining the presence or absence of dot formation by referring to the correspondence for each combination of the number data and the order value;
The gist is to realize a function (E) for forming dots on the output medium in accordance with the determined dot formation.

The second recording medium of the present invention corresponding to the above program is
A recording medium on which a program for receiving image data subjected to predetermined image processing and outputting an image by forming dots on the output medium based on the image data is recorded so as to be readable by a computer,
A function (A) for receiving, as the image data, number data representing the number of dots to be formed in the pixel group in a state where a predetermined number of adjacent pixels are grouped as a pixel group;
For each pixel in the pixel group, a function (B) for acquiring an order value indicating the order in which dots are formed in the pixel group;
A function (C) for storing a correspondence relationship between the combination of the order value and the number data and the presence or absence of dot formation in a pixel having the order value;
For each pixel in the pixel group that has received the number data, a function (D) for determining the presence or absence of dot formation by referring to the correspondence for each combination of the number data and the order value;
The gist of the invention is that a program for realizing a function (E) for forming dots on the output medium according to the determined presence / absence of dot formation is recorded using a computer.

  If such a program or a program recorded on a recording medium is read into a computer and the above-described various functions are realized using the computer, an image can be output simply and quickly.

Below, in order to demonstrate the effect | action and effect of this invention more clearly, embodiment of this invention is described in the following orders.
A. Summary of the invention:
B. First embodiment:
B-1. Device configuration:
B-2. Overview of the image printing process of the first embodiment:
B-3. Principle that can determine whether or not dots are formed for each pixel based on the number data:
B-4. Number data generation processing of the first embodiment:
B-5. Dot formation presence / absence determination process of the first embodiment:
B-6. Modification of the first embodiment:
C. Second embodiment:
C-1. Image printing process of the second embodiment:
C-2. Number data generation processing of the second embodiment:
C-3. Dot formation presence / absence determination process of the second embodiment:
C-3-1. A method for determining whether or not dots are formed without referring to the conversion table:
C-3-2. Dot formation presence / absence determination processing referring to the conversion table:

A. Summary of the invention:
Prior to detailed description of the embodiment, the outline of the present invention will be described with reference to FIG. FIG. 1 is an explanatory diagram for explaining the outline of the present invention, taking a printing system as an example. The printing system includes a computer 10 as an image processing apparatus, a printer 20 as an image output apparatus, and the like. When a predetermined program is loaded and executed on the computer 10, the computer 10 and the printer 20 and the like are executed. As a whole, it functions as an integrated image output system. The printer 20 prints an image by forming dots on a print medium. The computer 10 performs predetermined image processing on image data of an image to be printed, so that the printer 20 generates data for controlling dot formation for each pixel and supplies the data to the printer 20.

  In a general printing system, an image is printed as follows. First, image data is converted into data representing the presence or absence of dot formation for each pixel by performing predetermined image processing with a computer. Next, the obtained data is supplied to a printer, and the printer prints an image by forming dots according to the supplied data. Here, as the number of pixels of the image to be printed increases, the amount of image data increases accordingly, increasing the time required for image processing and data handling, and printing the image quickly. Difficult to do.

  In view of these points, the printing system illustrated in FIG. 1 prints an image as follows. First, the computer 10 divides the image into a plurality of pixel groups by collecting a predetermined number of pixels constituting the image as a pixel group. Then, for each pixel group, number data representing the number of dots formed in the pixel group is generated. A number data generation module provided in the computer 10 divides an image into a plurality of pixel groups and generates number data for each pixel group. The number data generated in this way is supplied from the number data supply module provided in the computer 10 to the printer 20.

  When the dot formation presence / absence determination module provided in the printer 20 receives the number data supplied from the number data supply module, it determines the presence / absence of dot formation for each pixel in the pixel group. The dot formation module then prints the image by forming dots on the print medium according to the presence or absence of dot formation determined for each pixel.

  Here, the number data for each pixel group can be much smaller than the data representing the presence or absence of dot formation for each pixel. Therefore, if the number data for each pixel is supplied from the computer 10 to the printer 20 instead of supplying data indicating the presence or absence of dot formation for each pixel, the printer 20 can receive the data very quickly.

  When the printer 20 receives the number data, the printer 20 determines whether or not to form dots for each pixel included in the pixel group as follows. First, for each pixel in the pixel group, an order value indicating the order in which dots are formed in the pixel group is stored in the order value storage module. Further, the correspondence relationship between the combination of the order value and the number data and the presence or absence of dot formation for the pixel having the order value is stored in advance in the correspondence relationship storage module. Then, when the number data for the pixel group is received, the order value for each pixel in the pixel group is acquired, and the dot for each pixel is obtained by referring to the correspondence for each combination of the number data and the order value. Determine the presence or absence of formation. If the presence or absence of dot formation is determined while referring to the correspondence as described above, the number data can be converted quickly. Therefore, coupled with being able to receive the number data from the computer 10 quickly, it is possible to print an image quickly. In the following, various embodiments of the present invention will be described in detail by taking such a printing system as an example.

B. First Example:
B-1. Device configuration :
FIG. 2 is an explanatory diagram illustrating a configuration of a computer 100 as the image processing apparatus according to the present exemplary embodiment. The computer 100 is a well-known computer configured by connecting a ROM 104, a RAM 106, and the like with a bus 116 around a CPU 102.

  The computer 100 includes a disk controller DDC 109 for reading data such as the flexible disk 124 and the compact disk 126, a peripheral device interface PIF 108 for exchanging data with peripheral devices, a video interface VIF 112 for driving a CRT 114, and the like. It is connected. A color printer 200, a hard disk 118, and the like, which will be described later, are connected to the PIF 108. Further, if the digital camera 120, the color scanner 122, and the like are connected to the PIF 108, it is possible to print an image captured by the digital camera 120 or the color scanner 122. If the network interface card NIC 110 is attached, the computer 100 can be connected to the communication line 300 to acquire data stored in the storage device 310 connected to the communication line.

  FIG. 3 is an explanatory diagram showing a schematic configuration of the color printer 200 of the present embodiment. The color printer 200 is an ink jet printer capable of forming dots of four color inks of cyan, magenta, yellow, and black. Of course, in addition to these four colors of ink, a total of six ink dots can be formed including cyan (light cyan) ink with low dye or pigment concentration and magenta (light magenta) ink with low dye or pigment concentration. An ink jet printer can also be used. In the following, cyan ink, magenta ink, yellow ink, black ink, light cyan ink, and light magenta ink are abbreviated as C ink, M ink, Y ink, K ink, LC ink, and LM ink, respectively. There shall be.

  As shown in the figure, the color printer 200 drives a print head 241 mounted on a carriage 240 to eject ink and form dots, and the carriage 240 is reciprocated in the axial direction of a platen 236 by a carriage motor 230. A mechanism for transporting the printing paper P by the paper feed motor 235, a control circuit 260 for controlling dot formation, carriage 240 movement, and printing paper transportation.

  An ink cartridge 242 that stores K ink and an ink cartridge 243 that stores various inks of C ink, M ink, and Y ink are mounted on the carriage 240. When the ink cartridges 242 and 243 are mounted on the carriage 240, each ink in the cartridge is supplied to ink discharge heads 244 to 247 for each color provided on the lower surface of the print head 241 through an introduction pipe (not shown).

  FIG. 4 is an explanatory diagram showing the arrangement of the ink jet nozzles Nz in the ink ejection heads 244 to 247. As shown in the figure, on the bottom surface of the ink ejection head, four sets of nozzle rows for ejecting ink of each color of C, M, Y, and K are formed, and 48 nozzles Nz per set of nozzle rows. Are arranged at a constant nozzle pitch k.

  The control circuit 260 is configured by connecting a CPU, a ROM, a RAM, a PIF (peripheral device interface), and the like via a bus. The control circuit 260 controls the main scanning operation and the sub-scanning operation of the carriage 240 by controlling the operations of the carriage motor 230 and the paper feed motor 235, and appropriately controls each nozzle based on the data supplied from the computer 100. Control to eject ink droplets at a proper timing. Thus, the color printer 200 can print a color image by forming ink dots of respective colors at appropriate positions on the print medium under the control of the control circuit 260.

  Further, if the drive signal waveform supplied to the nozzles for ejecting ink droplets is controlled, the size of the ejected ink droplets can be changed to form ink dots having different sizes. By controlling the size of the ink dots in this way, it is possible to print higher quality images by forming different ink dots depending on the area of the image to be printed. Become.

  Various methods can be applied to the method of ejecting ink droplets from the ink ejection heads of the respective colors. That is, a method of ejecting ink using a piezoelectric element, a method of ejecting ink droplets by generating bubbles in the ink passage with a heater arranged in the ink passage, and the like can be used. Also, instead of ejecting ink, use a method that uses ink transfer to form ink dots on printing paper using a phenomenon such as thermal transfer, or a method that uses static electricity to attach toner powder of each color onto the print medium. It is also possible to do.

  The color printer 200 having the hardware configuration as described above drives the carriage motor 230 to move the ink ejection heads 244 to 247 for each color in the main scanning direction with respect to the printing paper P, and the paper feed motor. By driving 235, the printing paper P is moved in the sub-scanning direction. The control circuit 260 drives the nozzles at appropriate timing to eject ink droplets in synchronization with the main scanning and sub-scanning movements of the carriage 240, so that the color printer 200 prints a color image on the printing paper. ing.

B-2. Overview of image printing process of first embodiment:
Hereinafter, image processing (image printing processing) performed inside the computer 100 and the color printer 200 in order to print an image will be described. Here, for convenience of understanding, the overall image printing process will be briefly described first, and then the principle that such image printing process is possible will be described. Finally, the details of each process will be described.

  In the following description, it is assumed that the first half of the image printing process is performed by the computer 100 and the second half is performed by the color printer 200. However, the processing performed by the computer 100 is performed inside the color printer 200. Or it is good also as implementing inside the apparatus which produces | generates image data, such as the digital camera 120. FIG.

  FIG. 5 is a flowchart showing the overall flow of the image printing process of the first embodiment. Hereinafter, the overall image of the image printing process will be briefly described with reference to FIG. When the image printing process of the first embodiment is started, first, the computer 100 starts reading image data (step S100). Here, the image data is assumed to be RGB color image data, but the present invention is not limited to color image data, and can be similarly applied to monochrome image data. Further, not only a color printer but also a single color printer can be similarly applied.

  Following the reading of the color image data, a color conversion process is performed (step S102). Color conversion processing refers to RGB color image data expressed by a combination of R, G, and B gradation values, and image data expressed by a combination of gradation values for each color of ink used for printing. It is processing to convert to. As described above, the color printer 200 prints an image using four color inks of C, M, Y, and K. Therefore, in the color conversion processing of the first embodiment, image data expressed by RGB colors is converted to data expressed by gradation values of C, M, Y, and K colors. The color conversion process is performed by referring to a three-dimensional numerical table called a color conversion table (LUT). In the LUT, gradation values of C, M, Y, and K colors obtained by color conversion are stored in advance for RGB color image data. In the process of step S102, RGB color image data can be quickly color-converted into C, M, Y, and K image data by referring to this LUT.

  When the color conversion process is finished, the resolution conversion process is started (step S104). The resolution conversion process is a process of converting the resolution of image data to a resolution (printing resolution) at which the printer 200 prints an image. When the resolution of the image data is lower than the print resolution, an interpolation operation is performed to generate new image data between the pixels. Conversely, when the resolution of the image data is higher than the print resolution, the data is at a certain rate. Is performed to match the resolution of the image data with the print resolution.

  When the resolution is converted into the print resolution as described above, the computer 100 starts the number data generation process (step S106). The detailed contents of the number data generation processing will be described in detail later, and only the outline will be described here. In the number data generation process, a predetermined number of adjacent pixels are grouped into a pixel group, thereby dividing one image into a plurality of pixel groups. Data representing the number of dots to be formed in each pixel group, that is, number data is determined for each pixel group. In general, whether or not a dot is formed in a pixel is determined depending on the image data of the pixel. Therefore, the number data indicating the number of dots formed in the pixel group is also the image data for the pixel group. Can be determined based on Next, the number data determined for each pixel group is output to the color printer 200. In the number data generation process, after the number data is generated for each pixel group based on the image data for each pixel in this way, a process for supplying the number data to the color printer 200 is performed.

  When the CPU incorporated in the control circuit 260 of the color printer 200 receives the number data supplied from the computer 100, it starts the dot formation presence / absence determination process (step S108). Although detailed processing will be described later, in the dot formation presence / absence determination processing, the following processing is roughly performed. As described above, the number data supplied from the computer 100 is data representing the number of dots to be formed in the pixel group, and it is undecided which pixel in the pixel group the number of dots is to be formed in. It is in a state. Therefore, prior to printing an image, it is necessary to determine whether or not to form dots for each pixel in the pixel group. In the dot formation presence / absence determination process, an order value indicating the order in which dots are formed in the pixel group is stored for each pixel in the pixel group, and the presence / absence of dot formation is determined based on the order value and the number data. By deciding, it is possible to decide quickly. Details of the process for determining whether or not to form dots will also be described later.

  After determining whether or not to form dots for each pixel in the pixel group as described above, processing for forming dots on the output medium is performed according to the determined presence or absence of dot formation (step S110). That is, as described with reference to FIG. 3, ink dots are formed on the printing paper by driving ink discharge heads and discharging ink droplets while repeating main scanning and sub-scanning of the carriage 240. By forming dots in this way, an image corresponding to the image data is printed.

  As described above, in the image printing process of the first embodiment, only the data of the number of dots to be formed in the pixel group is supplied from the computer 100 to the color printer 200, and each pixel included in the pixel group is supplied. It does not supply data on the presence or absence of dot formation. Compared with data representing the presence or absence of dot formation for each pixel, the number of dots formed in a pixel group can be expressed with a much smaller amount of data. Data can be supplied to the color printer 200 very quickly.

  For example, it is assumed that eight pixels are grouped in one pixel group, and one type of dot can be formed. In this case, since each pixel can only take one of the states of whether or not dots are formed, it can be expressed if there is a data length of 1 bit per pixel. Since the pixel group includes eight pixels, an 8-bit data length is required to express the presence or absence of dot formation for all the pixels in the pixel group. On the other hand, the number of dots formed in the pixel group can be only nine from 0 to 8. If there are nine patterns, four bits can be used for expression, so the number of dots formed in the pixel group can be expressed using a 4-bit data length. In this way, the number of dots formed in a pixel group can be expressed with a much smaller amount of data than data representing the presence / absence of dot formation for each pixel.

  In this way, the number of dots formed in a pixel group can be expressed with a much smaller amount of data compared to data representing the presence or absence of dot formation for each pixel. In the image printing process of the first embodiment, data is supplied very quickly from the computer 100 to the color printer 200 by supplying only data of the number of dots to be formed in the pixel group from the computer 100 to the color printer 200. Can be supplied.

  Further, when the color printer 200 receives the number data for each pixel group from the computer 100, the color printer 200 determines the presence or absence of dot formation for each pixel in the pixel group by using a method described later, thereby determining extremely rapidly. It is possible. In addition, as will be described in detail later, if the presence or absence of dot formation for each pixel is appropriately determined, the image quality will not deteriorate even when only the data for the number of dots is supplied. In particular, under the predetermined conditions described later, it is possible to obtain exactly the same result as when data representing the presence / absence of dot formation is supplied for each pixel.

B-3. Principle that can determine whether or not dots are formed for each pixel based on the number data:
In the following, when the above-described method is adopted, that is, the computer 100 supplies the data of the number of dots formed in the pixel group, and based on the data of the number of dots, the presence or absence of dot formation for each pixel is determined by the color printer. The principle of printing an image without deteriorating the image quality even when determined on the 200 side will be described.

  For the convenience of explanation, the dither method will be described first. The dither method is a typical method used for converting image data into data representing the presence or absence of dot formation for each pixel. In this method, threshold values are set in a matrix called a dither matrix, and the tone values of the image data are compared with the threshold values set in the dither matrix for each pixel. It is determined that a dot is formed for a large pixel, and a dot is not formed for a pixel that is not so. If such a determination is made for all the pixels in the image, the image data can be converted into data representing the presence or absence of dot formation for each pixel.

  FIG. 6 is an explanatory diagram conceptually illustrating a part of the dither matrix. In the illustrated matrix, 128 pixels in the horizontal direction (main scanning direction), 64 pixels in the vertical direction (sub-scanning direction), a total of 8192 pixels, were selected uniformly from the range of gradation values 1 to 255. The threshold value is stored randomly. Here, the threshold gradation value is selected from the range of 1 to 255 in addition to the fact that in this embodiment, the image data is 1-byte data that can take a gradation value of 0 to 255. If the gradation value of the image data is equal to the threshold value, it is determined that a dot is formed for that pixel.

  In other words, if the dots are formed only in pixels where the gradation value of the image data is larger than the threshold value (that is, dots are not formed in pixels where the gradation value is equal to the threshold value), the maximum possible image data can be obtained A dot is never formed on a pixel having a threshold value equal to the gradation value. In order to avoid such a situation, the range that can be taken by the threshold is a range obtained by removing the maximum gradation value from the range that can be taken by the image data. On the other hand, when dots are also formed on pixels having the same threshold value as the gradation value of the image data, dots are always formed on pixels having the same threshold value as the minimum gradation value that the image data can take. It will be. In order to avoid such a situation, the range that can be taken by the threshold is a range obtained by excluding the minimum gradation value from the range that can be taken by the image data. In this embodiment, the gradation values that the image data can take are 0 to 255, and dots are formed in pixels that have the same threshold as the image data. Therefore, the range that the threshold can take is set to 1 to 255. is there. Note that the size of the dither matrix is not limited to the size illustrated in FIG. 6, and can be various sizes including a matrix having the same number of vertical and horizontal pixels.

  FIG. 7 is an explanatory diagram conceptually showing a state in which the presence or absence of dot formation for each pixel is determined with reference to the dither matrix. When determining the presence or absence of dot formation, first, the pixel to be determined is selected, and the gradation value of the image data for this pixel is compared with the threshold value stored at the corresponding position in the dither matrix. The thin broken arrow shown in FIG. 7 schematically shows that the gradation value of the image data is compared with the threshold value stored in the dither matrix for each pixel. For example, for the pixel in the upper left corner of the image data, the gradation value of the image data is 97 and the threshold value of the dither matrix is 1, so it is determined that a dot is formed on this pixel. An arrow indicated by a solid line in FIG. 7 conceptually represents a state in which it is determined that a dot is formed in this pixel and the determination result is written in the memory. On the other hand, for the pixel on the right side of this pixel, the gradation value of the image data is 97, and the threshold value of the dither matrix is 177. Since the threshold value is larger, it is determined that no dot is formed for this pixel. In the dither method, by referring to the dither matrix and determining whether or not to form dots for each pixel, the image data is converted into data representing the presence or absence of dot formation for each pixel.

  FIG. 8 is an explanatory diagram showing a state in which image data is converted into data representing the presence or absence of dot formation using the dither method. FIG. 8A shows an enlarged part of the image data. The small rectangles in the drawing represent pixels, and the numerical values displayed in the respective rectangles represent the gradation values of the image data. Represents. As shown in the figure, the image data tends to be assigned an approximate (or the same) gradation value between adjacent pixels. These tendencies tend to increase the resolution of image data due to the demand for higher image quality. However, the tendency to assign approximate or identical gradation values between adjacent pixels becomes more prominent as the resolution of image data increases. ing.

  FIG. 8B shows how threshold values are set at corresponding positions in the dither matrix. The gradation value of the image data shown in FIG. 8A and the threshold value of the dither matrix shown in FIG. 8B are compared for each pixel to determine whether or not dots are formed. FIG. 8C shows the result of determining the presence or absence of dot formation for each pixel in this way, and the hatched pixels in the figure are pixels that are determined to form dots.

  Here, it is considered that a predetermined number of adjacent pixels are grouped into a pixel group, and the number of pixels determined to form dots within the pixel group is counted. As an example, a total of 8 pixels, which are 4 pixels in the main scanning direction (horizontal direction in FIG. 8) and 2 pixels in the sub-scanning direction (vertical direction in FIG. 8), are grouped as a pixel group. FIG. 8D shows the number of dots obtained by counting the pixels that are determined to form dots for each group of pixels grouped in this way. In the image printing process of the first embodiment, the number of data for each pixel group is supplied from the computer 100 to the color printer 200. The number data does not include information on the pixel position where dots are formed, but if the following is performed, information on the pixel positions where dots are formed is restored from the number data, and whether or not dots are formed for each pixel. Can be generated.

  FIG. 9 is an explanatory diagram showing a state in which data representing the presence / absence of dot formation for each pixel is generated from the number of data. FIG. 9A shows values obtained by counting the number of dots formed for each pixel group in FIG. FIG. 9B shows a dither matrix that is referred to in FIG. 8 to determine the presence or absence of dot formation for each pixel. As described above, in the dither method, the gradation value of the image data is compared with the threshold value set at the corresponding pixel position of the dither matrix. It is determined that dots are to be formed, and the smaller the threshold of the dither matrix, the easier it is to form dots. From this, it can be considered that the dither matrix represents an order of pixels in which dots are formed.

  Paying attention to these properties of the dither matrix, the pixel position where the dots are formed can be determined from the number of dots formed in the pixel group. For example, the pixel group at the upper left corner shown in FIG. 9A will be described. The number of dots formed in this pixel group is three. Further, referring to the dither matrix shown in FIG. 9B, in this pixel group, the pixel position at the upper left corner, that is, the pixel position where the threshold value “1” is set is the pixel in which the dot is most easily formed. It can be said that there is. Therefore, it can be considered that one of the three dots formed in this pixel group is formed in the pixel in the upper left corner. Similarly, the remaining two dots are a pixel in which a dot is most likely to be formed in this pixel group (that is, a pixel for which the threshold value “42” is set in the dither matrix in FIG. 9B), and 3 It can be considered that the dots are formed on the pixels where dots are easily formed (that is, pixels on which the threshold value “58” is set).

  Of course, the presence or absence of dot formation is influenced not only by the threshold value set in the dither matrix but also by the gradation value of the image data. Therefore, if the gradation value of the image data is extremely large, a smaller threshold value is set. It is also possible that dots are formed before the pixels that are present. However, as described above, image data tends to be assigned an approximate (or the same) gradation value to adjacent pixels, and in most cases, pixels in which dots are easily formed (that is, set in a dither matrix). It can be considered that a dot is formed from a pixel having a small threshold value.

  Similarly, for the other pixel groups shown in FIG. 9A, the pixel positions where dots are formed can be determined based on the number of dots and the threshold value of the dither matrix. For example, for the pixel group (second pixel group from the upper left) in the pixel group described above in FIG. 9A, the number of dots is 3, so refer to the dither matrix in FIG. 9B. Then, it is considered that these three dots are formed in a pixel set with the threshold “22”, a pixel set with the threshold “33”, and a pixel set with the threshold “91”, respectively. Can do.

  For the four pixel groups shown in FIG. 9A, when the pixel positions for forming dots are determined from the number data in this way, the result shown in FIG. 9C can be obtained. In FIG. 9C, pixels indicated by hatching are pixels that are determined to form dots. As is clear from a comparison between FIG. 9C and FIG. 8C, the pixel position determined from the number data coincides with the pixel position determined for each pixel. This means that the presence or absence of dot formation for each pixel is determined with reference to the dither matrix, and if only the number of dots formed in the pixel group is stored, the pixel position may not be stored, From the dither matrix and the number of dots, it is shown that the pixel position where the dots are formed can be restored. Therefore, even when the number data for each pixel group is supplied from the computer 100 and the pixel position for forming dots is determined from the number data on the color printer 200 side, the pixel position is appropriately determined to deteriorate the image quality. This makes it possible to print an image without any problem.

  In addition, in order to appropriately determine the pixel position where the dot is formed from the number data, it is sufficient that the gradation value of the image data is not significantly different within the pixel group. As described above, since the image data has a characteristic of having an approximate gradation value between adjacent pixels, such a condition is satisfied in most cases. Therefore, when only the number data is supplied to the color printer 200. However, it is possible to print an image without deteriorating the image quality.

  In particular, when the following two conditions are satisfied, the gradation value of the image data and the threshold value of the dither matrix are compared, and the result of determining the presence or absence of dot formation for each pixel is the same as the pixel position. It is guaranteed that dots can be formed. The first condition is that the gradation value of each pixel in the pixel group has the same value, and the second condition is when the computer 100 determines whether or not dots are formed for each pixel. The dither matrix referred to in the above and the dither matrix referred to determine the pixel position from the number data on the color printer 200 side are the same matrix.

  In the dither method described with reference to FIG. 7, the threshold value set in the dither matrix is compared with the gradation value of the image data, and the presence / absence of dot formation is determined depending on which value is larger. On the other hand, when the pixel position where the dot is formed in the pixel group is determined from the number data, the pixel position where the dot is formed is set in the dither matrix as described with reference to FIG. The pixels with the smallest threshold are determined in order. That is, in order to determine the pixel position, the threshold value is not necessary, and it is sufficient that the order in which dots are formed in the pixel group is known. Therefore, instead of the dither matrix shown in FIG. 9B, a value (order value) indicating the order in which dots are formed is set for each pixel in the pixel group as shown in FIG. 9D. A matrix (in this specification, such a matrix is called an order value matrix) is stored, and a pixel position is determined from the number data while referring to the order value matrix for each pixel group. Both are possible.

  In the above description, as shown in FIG. 9, when a plurality of types of order value matrices generated based on the dither matrix are stored in advance and the number data of the pixel group is received, the pixel group corresponds to the pixel group. In the above description, the order value matrix is used to determine whether or not to form dots for each pixel. However, the presence or absence of dot formation may be determined more simply as follows. That is, when a plurality of order value matrices are stored in advance and the number data is received, whether or not to form dots for each pixel can be determined using one order value matrix randomly selected for each pixel group. good. Furthermore, more simply, it is possible to store only one set of order value matrices and determine whether or not to form dots for each pixel using this matrix.

B-4. Number data generation processing of the first embodiment:
Hereinafter, a process (step S106 in FIG. 5) for generating number data from image data in the image printing process of the first embodiment shown in FIG. 5 will be described. FIG. 10 is a flowchart showing the flow of the number data generation process of the first embodiment. The number data generation process of the first embodiment will be described below according to the flowchart.

  When the number data generation processing of the first embodiment is started, first, a predetermined number of pixels adjacent to each other are collected to generate a pixel group (step S200). Here, a total of eight pixels of four pixels in the main scanning direction and two pixels in the sub-scanning direction are combined into a pixel group. It should be noted that the pixels grouped as a pixel group do not have to be pixels with vertical and horizontal positions aligned in a rectangular shape as described above, and any pixel that is adjacent to each other and has a predetermined positional relationship can be grouped as a pixel group. good.

  Next, one pixel of interest (target pixel) is set as a processing target from a plurality of pixels grouped as a pixel group (step S202). Then, by comparing the tone value of the image data assigned to the pixel of interest with the threshold value of the dither matrix, it is determined whether or not dots are formed for the pixel of interest (step S204). That is, as described above with reference to FIG. 7, it is determined that a dot is formed for a pixel having a larger image data, and conversely, a dot is determined not to be formed for a pixel having a larger dither matrix threshold. .

  Next, it is determined whether or not the above processing has been performed on all the pixels in the pixel group (step S206). If unprocessed pixels remain in the pixel group (step S206: no), step is performed. Returning to S202, the following series of processing is performed. In this way, when the determination of dot formation is completed for all the pixels in the pixel group (step S206: yes), the number data for the processed pixel group is generated (step S208). Here, the number of dots formed in the pixel group is counted, and the obtained number of dots is used as the number data. For example, assuming that the image data shown in FIG. 8 is processed, the pixel group at the upper left corner in the image has three dots formed in the pixel group. 3 ”.

  As described above, when the process for one pixel group is completed, it is determined whether or not the process has been completed for all the pixels of the image (step S210). If unprocessed pixels remain, the process proceeds to step S200. After returning to generate a new pixel group, a series of subsequent processing is performed to generate the number data of the pixel group (step S208). By repeating such processing, when the processing for all the pixels in the image is completed (step S210: yes), the number data obtained for each pixel group is output to the color printer 200 (step S212). The number data generation process shown in FIG. As a result, the number data for each pixel group as shown in FIG. 8D is supplied to the color printer 200.

B-5. Dot formation presence / absence determination process of the first embodiment:
Next, a process (step S108 in FIG. 5) for determining the presence / absence of dot formation for each pixel in the pixel group based on the number data supplied from the computer 100 will be described. FIG. 11 is a flowchart showing the flow of the dot formation presence / absence determination process of the first embodiment. Such a process is a process executed by a CPU built in the control circuit 260 of the color printer 200. FIG. 12 is an explanatory diagram conceptually showing how the presence / absence of dot formation for each pixel is determined in the dot formation presence / absence determination process of the first embodiment. Hereinafter, the contents of the dot formation presence / absence determination process of the first embodiment will be described according to the flowchart shown in FIG. 11 with reference to FIG.

  When the dot formation presence / absence determination process is started, first, one pixel group is selected (step S300), and the number data of the pixel group is acquired (step S302). Here, it is assumed that the number data as shown in FIG.

  Next, one target pixel is selected from each pixel included in the selected pixel group (step S304), and a value (order value) indicating the order in which dots are formed in the target pixel within the pixel group is selected. Obtain (step S306). The order value of the target pixel can be easily obtained by referring to a preset order value matrix as shown in FIG. In the order value matrix illustrated in FIG. 12B, order values are set in advance for the pixel positions of the pixels constituting the pixel group. For example, the order value “1” is set for the pixel at the upper left corner in the pixel group, and the order value “6” is set for the pixel to the right of the pixel. In step S306, referring to such an order value matrix, the order value set at the position of the target pixel is acquired. In order to avoid complicated explanation, only one set of order value matrixes is stored here, and description will be made assuming that order values are always obtained using the same order value matrix. May be stored, and the order value of the target pixel may be acquired while switching the order value matrix for each pixel group.

  When the order value is obtained in this way, the presence / absence of dot formation for the target pixel is determined by referring to the conversion table (step S308). FIG. 13 is an explanatory diagram conceptually showing a conversion table that is referred to in order to determine the presence or absence of dot formation for the target pixel. As shown in the figure, in the conversion table, presence / absence of dot formation is set in association with the combination of the order value and the number data. Here, since the pixel group is composed of eight pixels, the order value takes values from 1 to 8, and the number data takes values from 0 to 8. Therefore, in the conversion table, values indicating the presence / absence of dot formation are set in association with 72 combinations obtained by combining these. In the example shown in FIG. 13, “1” is set for the combination that forms dots, and “0” is set for the combination that does not form dots.

  As an example, the pixel at the upper left corner in the pixel group shown in FIG. 12 will be described. As shown in FIG. 12B, the order value is “1”, and the number data is shown in FIG. As shown, it is “3”. Referring to the conversion table of FIG. 13, the value set for the combination of the order value “1” and the number data “3” is “1”, that is, it is determined that this pixel forms a dot. Can do. In this way, in step S308 of FIG. 11, by referring to the conversion table, the presence / absence of dot formation for the target pixel is immediately determined from the number data for the pixel group and the order value of the target pixel.

  After determining whether or not dot formation is performed for one pixel selected as the target pixel in this way, it is determined whether or not dot formation is determined for all pixels in the selected pixel group (step S310). If there is still a pixel in the pixel group that has not yet been determined for dot formation (step S310: no), the process returns to step S304 to select a new pixel as the target pixel from the pixel group. Then, the following series of processing is performed.

  If it is determined that dot formation has been determined for all pixels in the pixel group by repeating such processing (step S310: yes), whether or not processing has been completed for all pixel groups to which number data has been supplied. Is determined (step S312). If an unprocessed pixel group remains (step S312: no), the process returns to step S300 to select a new pixel group, and a series of subsequent processes are performed. By repeating such processing, the number data supplied from the computer is converted into data indicating the presence or absence of dot formation for each pixel. When the process is completed for all the pixel groups (step S306: yes), the dot formation presence / absence determination process shown in FIG. 11 is ended, and the process returns to the image printing process of FIG.

  In the dot formation presence / absence determination process of the first embodiment described above, when the pixel group number data is received, the order value of the target pixel is obtained by referring to the order value matrix, and the obtained order value and number are obtained. The presence or absence of dot formation can be determined by a very simple method of referring to the conversion table using data. Therefore, data representing the presence or absence of dot formation for each pixel can be generated very quickly from the number data.

  Furthermore, since the process for determining the presence / absence of dot formation is merely referring to stored data, it can be easily executed in hardware using a chip incorporating a dedicated logic circuit. If the process of determining the presence or absence of dot formation is executed by hardware, the process can be performed at a higher speed, and an image can be printed quickly.

  In addition, in order to speed up processing in recent computers, a technique called so-called pipeline processing is used. On the other hand, for processing including conditional branching, pipeline processing technology is used. Even if it is applied, it is known that the processing speed cannot be increased so much that the processing speed may decrease. The dot formation presence / absence determination processing of the first embodiment described above is mostly processing that refers to stored data and does not include conditional branching. Therefore, from this point of view, this processing is suitable for high-speed processing. Can be said.

  As described above, since the dot formation presence / absence determination process of the first embodiment described above includes various elements that enable rapid processing, the number data can be formed for each pixel under any condition. Can be quickly converted into data representing the presence or absence of the image, and thus the image can be printed quickly.

B-6. Modification of the first embodiment:
In the dot formation presence / absence determination process of the first embodiment described above, one or a plurality of sets of order value matrices are set in advance, and the same order value matrix is always referred to or the order value matrix to be referenced is randomly selected. The description has been made on the assumption that the presence or absence of dot formation for each pixel is determined while switching. However, as described above with reference to FIGS. 8 and 9, an order value matrix is generated based on the dither matrix, and whether or not dots are formed can be determined by referring to an appropriate order value matrix according to the position of the pixel group. Thus, it is possible to determine the presence or absence of dot formation more appropriately, and thus it is possible to print a high-quality image. Hereinafter, a dot formation presence / absence determination process according to a modification of the first embodiment will be described.

  FIG. 14 is a flowchart illustrating a flow of a dot formation presence / absence determination process according to a modification. Hereinafter, it demonstrates according to a flowchart. Also in the dot formation presence / absence determination process of the modified example, first, one pixel group is selected (step S400), and the number data of the pixel group is acquired (step S402). Next, an order value matrix corresponding to the selected pixel group is read from the order value matrix stored in plural sets (step S404). Such processing will be described in detail with reference to FIGS. 15 and 16.

  FIG. 15 is an explanatory diagram showing a method of generating a plurality of order value matrices referred to in the dot formation presence / absence determination process of the modification. As described above, one pixel group is composed of a total of 8 pixels, 4 pixels each in the main scanning direction and 2 pixels each in the sub-scanning direction. As for the threshold value, a threshold value of 8 pixels in total, that is, 4 pixels in the main scanning direction and 2 pixels in the sub-scanning direction is combined into a block. FIG. 15A is an explanatory diagram conceptually showing a state in which thresholds for 8 pixels at the upper left corner of the dither matrix are grouped into blocks. Here, as shown in FIG. 6, since the dither matrix has a size of 128 pixels in the main scanning direction and 64 pixels in the sub scanning direction, the dither matrix has a size of 4 pixels in the main scanning direction. If the pixels corresponding to two pixels in the scanning direction are grouped into blocks, the dither matrix is divided into 32 blocks each in the main scanning direction and the sub-scanning direction, for a total of 1024 blocks.

  As shown in FIG. 15B, serial numbers from 1 to 1024 are assigned to these blocks. Then, one set of order value matrices is generated from each block from No. 1 to No. 1024. FIG. 15C is an explanatory diagram showing a state in which an order value matrix is generated from the block of serial number 1. In the left half of FIG. 15C, the threshold value of the dither matrix included in the block having the serial number 1 is shown. As described above with reference to FIG. 7, in the dither method, the tone value of the image data is compared with the threshold value of the dither matrix, and it is determined that dots are formed when the image data is larger. The smaller the threshold value, the easier it is for dots to be formed. Therefore, the pixel in which the first dot is formed in the first block shown in FIG. 15C can be considered as the pixel for which the threshold value “1” is set. Therefore, “1” is set as the order value for this pixel. Similarly, the pixel in which the second dot is formed can be considered as a pixel in which the threshold “42”, which is the second smallest threshold, is set. Therefore, an order value “2” is set for this pixel. In this way, if the order value “1” to the order value “8” are determined in order from the pixel having the smallest threshold set in the block, the serial number 1 shown in the right half of FIG. An order value matrix of numbers can be obtained.

  Similarly, FIG. 15D shows an order value of serial number 2 by setting the order value “1” to the order value “8” in order from the pixel in which a small threshold is set in the block. It shows how the matrix is generated. By performing the above operation for all the blocks from the serial number “1” to the serial number “1024” shown in FIG. 15B, the sequence values from the serial numbers “1” to “1024” are obtained. A matrix is generated and stored.

  In step S404 in FIG. 14, a process is performed in which a matrix corresponding to a pixel group to be determined whether or not to form a dot is selected and read from the “1” to “1024” order value matrices. FIG. 16 is an explanatory diagram showing a method for selecting an order value matrix corresponding to a pixel group. Now, as shown in FIG. 16A, the pixel group for which the presence or absence of dot formation is to be determined is the nth pixel group in the main scanning direction and m in the sub scanning direction with reference to the upper left corner of the image. It is assumed that it is at the position of the pixel group. In addition, the position of such a pixel group is represented by a coordinate value (n, m).

  Here, the size of the dither matrix is usually not as large as the image. For this reason, in the dither method, one dither matrix is repeatedly used while shifting its position little by little with respect to the image data. For the same reason, in the dot formation presence / absence determination process shown in FIG. 14, one dither matrix is repeatedly used while being moved little by little. As a method of moving the dither matrix, various methods are used in the dither method, and various moving methods can be applied even when determining the presence or absence of dot formation. In the following description, it is assumed that the dither matrix is moved in the main scanning direction. FIG. 16B conceptually shows how the dither matrix is repeatedly used while being gradually moved in the main scanning direction.

  As shown in FIG. 15 (a), the size of the block that divides the dither matrix matches the size of the pixel group that generated the number data, so that the dither matrix is changed as shown in FIG. 16 (b). As it is moved, each block of the dither matrix matches the position of the pixel group. In other words, any block that divides the dither matrix is applied to all pixel groups.

It is assumed that the Nth block in the main scanning direction and the Mth block in the subscanning direction are applied to the pixel group to be processed in the dither matrix. As shown in FIG. 15B, here, one dither matrix is assumed to include 32 blocks in each of the main scanning direction and the sub-scanning direction, and the coordinate values of the pixel group to be processed. Is (n, m), that is, the n-th position in the main scanning direction and the m-th position in the sub-scanning direction with respect to the upper left corner of the image, N and M can be obtained by the following equations, respectively. it can.
N = n−int (n / 32) × 32
M = m−int (m / 32) × 32
Here, int is an operator representing rounding down to the integer. That is, int (n / 32) represents an integer value obtained by rounding down the numerical value after the decimal point to the calculation result of n / 32. Therefore, when determining the presence or absence of dot formation for a certain pixel group, after obtaining N and M from the coordinate values (n, m) of the pixel group according to the above equation, the block at the corresponding position in the dither matrix is determined. What is necessary is just to acquire a serial number and to use the order value matrix produced | generated from the block.

  In practice, the values of M and N can be obtained very simply without executing the calculation shown in FIG. Hereinafter, this point will be described. FIG. 17 is an explanatory diagram specifically showing a method of selecting an applied order value matrix from the coordinate values (n, m) of the pixel group. FIG. 17A conceptually shows 10-bit binary data representing the numerical value n. In FIG. 17A, in order to identify each bit, serial numbers from No. 1 to No. 10 are assigned from the most significant bit to the least significant bit.

  When selecting an order value matrix, first, int (n / 32) is calculated. That is, an operation of dividing the numerical value n by 32 and truncating the value after the decimal point is performed. Division by 32 can be performed by shifting the binary data to the right by 5 bits, and if the data is handled in integer format, the value after the decimal point is automatically truncated. . Eventually, the binary data of int (n / 32) can be obtained by bit-shifting the binary data of the numerical value n shown in FIG. 17A by 5 bits to the right. FIG. 17B conceptually shows binary data of int (n / 32) obtained by bit-shifting the numerical value n.

  The int (n / 32) obtained in this way is multiplied by 32. Multiplication by 32 can be performed by bit-shifting binary data to the left by 5 bits. FIG. 17C conceptually represents int (n / 32) × 32 binary data obtained by bit-shifting the numerical value n.

  Next, the above-described numerical value N can be obtained by subtracting int (n / 32) × 32 from the numerical value n. As is clear from the comparison of binary data of numerical value n (see FIG. 17A) and binary data of int (n / 32) × 32 (see FIG. 17C), these binary data are The upper 5 bits are common, and the lower 5 bits of the numerical value on the subtraction side are all “0”. Therefore, if the lower 5 bits of the subtracted numerical value (numerical value n) are extracted as they are, the desired numerical value N can be obtained. That is, the numerical value N can be obtained very simply by simply obtaining the logical product of the binary number data shown in FIG. 17A and the mask data shown in FIG.

  In FIG. 17, the case where the numerical value N indicating the block position in the dither matrix is obtained from the numerical value n of the coordinate value (n, m) of the pixel group has been described, but the numerical value M indicating the block position is exactly the same. Can be obtained very simply from the numerical value m. Eventually, given the coordinate values (n, m) of a pixel group, by obtaining the numerical values N and M from the numerical values n and m, it is possible to determine what sequence number matrix is applied to that pixel group. You can know. In step S404 of the dot formation presence / absence determination process shown in FIG. 14, processing for selecting and reading a matrix corresponding to the pixel group is performed in this way.

  As described above, when the order value matrix corresponding to the pixel group is read, one target pixel for determining whether or not to form dots is selected from the pixel group being processed (step S406). Then, after acquiring the order value of the target pixel by referring to the read order value matrix (step S408), the presence or absence of dot formation for the target pixel is determined by referring to the conversion table (step S408). S410). In the conversion table, whether or not to form dots is set in association with the combination of the order value and the number data, as in the conversion table of the first embodiment described above with reference to FIG. Therefore, if the number data of the pixel group and the order value of the target pixel are known, the presence / absence of dot formation can be immediately determined by referring to the conversion table.

  When the presence / absence of dot formation is thus determined for one target pixel, it is determined whether or not dot formation has been determined for all pixels in the selected pixel group (step S412). If there is still a pixel for which dot formation has not been determined (step S412: no), the process returns to step S406, a new target pixel is selected, and a series of processes are performed. If it is determined that dot formation has been determined for all the pixels in the pixel group by repeating these processes (step S412: yes), whether or not the process has been completed for all the pixel groups to which the number data has been supplied. Is determined (step S414). If an unprocessed pixel group remains (step S414: no), the process returns to step S400 to select a new pixel group, and a series of subsequent processes are performed. When such processes are repeated and the process is completed for all the pixel groups (step S414: yes), the dot formation presence / absence determination process of the modification shown in FIG. 14 is terminated, and the process returns to the image printing process of FIG.

  In the dot formation presence / absence determination process of the modification described above, a plurality of order value matrices are generated based on the dither matrix. When determining the presence or absence of dot formation for a certain pixel group, when applying the dither method, a dot value is generated using the order value matrix generated from the dither matrix of the portion applied to the position of the pixel group. Determine the presence or absence of formation. In this way, it is possible to determine whether or not dots are formed so that a distribution according to the distribution of dots obtained using the dither matrix can be obtained. As is well known, the dither matrix has a threshold value set with an appropriate distribution so that the dots are formed with an appropriate distribution. It is possible to print an image with high image quality.

  Furthermore, if the dither matrix used for generating the order value matrix and the dither matrix used in the number data generation process shown in FIG. 10 are the same matrix, as described above with reference to FIGS. In most cases, the dot distribution restored from the number data is exactly the same as the dot distribution determined by the dither method for each pixel. Of course, as described above, when the gradation value of the image data changes greatly in the pixel group, the dot distribution is different, but the image data is approximated between adjacent pixels (or In many cases, the dot distribution will be the same because they tend to have the same (same) tone values. Therefore, it is possible to determine the presence or absence of dot formation so as to obtain an appropriate dot distribution, and it is possible to print a high quality image.

  However, in the dot formation presence / absence determination process of the above-described modification, it is necessary to store a plurality of (1024 in the above example) order value matrix in addition to the conversion table. Using too much memory to store these tables and matrices is not desirable for installation in actual products. However, as will be explained below, many memories are not used to store the conversion table and the order value matrix.

First, the memory capacity necessary for storing the conversion table will be described. As shown in FIG. 13, in the conversion table, presence / absence of dot formation is set for each combination of the order value and the number data. Therefore, the data size of the conversion table is the number that the order value and the number data can take. And the data length necessary to indicate the presence or absence of dot formation for one pixel. Since the order value indicates the order in which dots are formed in each pixel in the pixel group, the order value can take the same type of value as the number of pixels included in one pixel group. In addition, since the number data represents the number of dots that can be formed in the pixel group, values from 0 to the number of pixels can be taken, so that the number of pixels + 1 can be taken. Furthermore, since it is assumed here that only one state of whether or not dots are formed in one pixel, the presence or absence of dot formation for one pixel can be expressed with one bit. After all, the memory capacity for storing the conversion table is n, where n is the number of pixels included in the pixel group.
It suffices if there are n × (n + 1) bits. Since the number of pixels included in the pixel group is about 16 at most, the amount of memory required to store the conversion table is very small.

  Next, the amount of memory necessary for storing the order value matrix will be described. The amount of memory for storing the order value matrix is determined by the amount of memory required for each matrix and the number of matrices. Since the order value matrix sets the order in which dots are formed in each pixel in the pixel group, the memory amount per matrix is determined by the number of pixels included in the pixel group. Further, as described above with reference to FIG. 15, the number of the order value matrix is equal to the number of blocks obtained when the dither matrix is divided into blocks having the same size as the pixel group. Is determined by the size of Eventually, the amount of memory required to store the order value matrix is determined by the size of the dither matrix and the size of the pixel group.

  FIG. 18 is an explanatory diagram showing the result of trial calculation of the amount of memory required to store the order value matrix, assuming dither matrices of various sizes and pixel groups of various sizes. Specifically, the dither matrix has a size of 64 × 64 (that is, 64 pixels in the main scanning direction and 64 pixels in the sub scanning direction), 128 × 64 (128 pixels in the main scanning direction, 64 pixels in the sub scanning direction). ), 128 × 128 (128 pixels in the main scanning direction and 128 pixels in the sub-scanning direction) are assumed. The size of the pixel group is 2 × 2 (2 pixels in the main scanning direction, 2 pixels in the sub scanning direction), 4 × 2 (4 pixels in the main scanning direction, 2 pixels in the sub scanning direction), 4 × 4 ( Three types of sizes are assumed: 4 pixels in the main scanning direction and 4 pixels in the sub-scanning direction. The trial calculation result under the condition corresponding to the above-described embodiment, that is, the condition where the dither matrix size is 128 × 64 and the size of the pixel group is 4 × 2 is shown in FIG. . Hereinafter, a trial calculation example of the order value matrix will be described using this condition as a representative example.

  Since the number of the order value matrix is the number of blocks obtained by dividing the dither matrix with the same size as the pixel group, the number of pixels of the dither matrix (128 × 64) is the number of pixels per pixel group (4 × 2). Divide by to get 1024. In addition, since the order values set in the order value matrix take eight values from 1 to 8, one order value can be expressed by 3 bits. Since eight order values are set in the order value matrix, the amount of memory necessary for storing one order value matrix is 3 × 8 = 24 bits (3 bytes). Since there are 1024 order value matrices, the amount of memory required to store all the order value matrices can be calculated as 3 Kbytes.

  Further, when the number of pixels included in the pixel group is four, the order value takes four values from 1 to 4, and therefore, one order value can be expressed by 2 bits. Since four order values are set in the order value matrix, the amount of memory required to store one order value matrix is 2 × 4 = 8 bits (1 byte). Similarly, when the number of pixels included in the pixel group is 16, the data length required to express one sequence value is 4 bits, and since there are 16 data lengths, the amount of memory required to store the sequence value matrix Is 4 × 16 = 64 bits (8 bytes).

  FIG. 18 collectively shows the results of trial calculation of the amount of memory necessary for storing all the order value matrices under various conditions. As is apparent from the trial calculation results shown in the drawing, it is considered that the memory amount required to store the sequence value matrix is at most 10 Kbytes. For this reason, the amount of memory necessary for storing the conversion table and the order value matrix does not become so large that it becomes an obstacle to mounting on an actual product.

C. Second embodiment:
In the first embodiment described above, the dot that can be formed by the color printer 200 has been described as one type. However, printers that can form various types of dots such as dots having different sizes and dots having different ink densities (so-called multi-value dot printers) are widely used today for the purpose of improving printing image quality. . The invention of the present application can achieve a great effect even when applied to such a multi-value dot printer. Below, the case where this invention is applied to a multi-value dot printer is demonstrated as 2nd Example.

C-1. Outline of the image printing process of the second embodiment:
The image printing process of the second embodiment is the same as the image printing process of the first embodiment shown in FIG. Hereinafter, the outline of the image printing process of the second embodiment will be briefly described with reference to the flowchart of FIG.

  When the image printing process of the second embodiment is started, first, after the image data is read by the computer 100, the color conversion process is performed (corresponding to step S100 and step S102 in FIG. 5). Next, resolution conversion processing is performed to convert the resolution of the image data into print resolution (corresponding to step S104), and then the number data generation processing is started (corresponding to step S106).

  As described above, in the first embodiment, the number of dots that can be formed by the color printer 200 is one, and in the number data generation process, number data representing the number of dots formed in the pixel group is generated. And output to the color printer 200. On the other hand, in the second embodiment, the color printer 200 can form a plurality of types of dots. Here, it is assumed that three types of dots having different sizes, that is, large dots, medium dots, and small dots can be formed. Corresponding to this, in the number data generation process of the second embodiment, the number data is generated that represents how many large dots, medium dots, and small dots are formed in the pixel group. It will be.

  As will be described in detail later, in order to efficiently output the number data with a small data amount, the numbers of large dots, medium dots, and small dots are not output as they are, but are output in a coded state. Details of the number data generation processing of the second embodiment will be described later. Here, it is assumed that the dots that can be formed by the color printer 200 are large dots, medium dots, and small dots that are different in size, but of course, if the types of dots are different, It is not limited to when the sizes are different. For example, in the case where a plurality of types of dots having different ink densities for forming dots are formed, or a single dot is formed in a pseudo manner by forming a plurality of fine dots, a plurality of fine dots having different densities are used. It is also possible to use different types of dots.

  When the CPU built in the control circuit 260 of the color printer 200 receives the number data supplied from the computer 100, it starts the dot formation presence / absence determination process (corresponding to step S108 in FIG. 5). As will be described in detail later, in the dot formation presence / absence determination process of the second embodiment, when the coded number data is received, any one of large dots, medium dots, and small dots is received for each pixel in the pixel group. Processing for determining whether to form a dot or not to form a dot is performed.

  In this way, when the presence / absence of dot formation is determined for various large, medium, and small dots, various dots are formed according to the obtained results (corresponding to step S110 in FIG. 5). By forming large dots, medium dots, and small dots in this way, an image corresponding to the image data is printed.

C-2. Number data generation processing of the second embodiment:
Next, a process for generating the number data in which the numbers of large dots, medium dots, and small dots formed in the pixel group are encoded in the image printing process of the second embodiment described above will be described.

  FIG. 19 is a flowchart showing a flow of processing for determining the number of large dots, medium dots, and small dots formed in the pixel group and generating the number data. Details of such processing are disclosed in Japanese Patent No. 3292104. Hereinafter, it demonstrates according to a flowchart. When the processing is started, first, a predetermined number of pixels adjacent to each other are collected to form a pixel group (step S500). Here, as in the first embodiment described above, a total of eight pixels, which are four pixels in the main scanning direction and two pixels in the sub-scanning direction, are collected as a pixel group.

  Next, in order to determine the presence / absence of dot formation from the pixel group, one pixel to be processed is selected (step S502), and the formation presence / absence of large dots, medium dots, and small dots is determined for the selected processing pixel. Judgment is made (step S504). Whether large, medium, and small dots are formed is determined as follows.

  FIG. 20 is a flowchart illustrating a flow of processing for determining whether or not large dots, medium dots, and small dots are formed by performing halftone processing on one selected pixel. When the halftone process for large, medium, and small dots is started, first, image data for the pixel to be processed is converted into density data for each of the large, medium, and small dots (step S550). Here, the density data is data representing the density at which dots are formed. The density data represents that dots are formed at a higher density as the gradation value becomes larger. For example, the gradation value “255” of the density data indicates that the dot formation density is 100%, that is, dots are formed in all pixels, and the gradation value “0” of the density data indicates that the dot is formed. This indicates that the formation density is 0%, that is, no dot is formed in any pixel. Such conversion into density data can be performed by referring to a numerical table called a dot density conversion table.

  FIG. 21 is an explanatory diagram conceptually showing a dot density conversion table that is referred to when converting the gradation value of image data into density data for large, medium, and small dots. As shown in the drawing, in the dot density conversion table, density data for each dot of small dots, medium dots, and large dots is set for the gradation value of the image data obtained by color conversion. . In the area where the image data is near the gradation value “0”, the density data of medium dots and large dots are both set to the gradation value “0”. The density data of small dots increases as the gradation value of the image data increases, but when the image data reaches a certain gradation value, it starts to decrease, and instead the density data of medium dots. Begins to increase. When the gradation value of the image data further increases and reaches a certain gradation value, the density data of the small dots becomes the gradation value “0”, and the density data of the medium dots starts to decrease. Instead, the density of the large dots Data increases little by little. In step S552 in FIG. 20, the gradation value of the image data is converted into large dot density data, medium dot density data, and small dot density data while referring to the dot density conversion table.

  In this way, when density data of large, medium, and small dots is obtained for the pixel to be processed, first, it is determined whether or not large dots are formed (step S554 in FIG. 20). Such a determination is made by comparing the density data of large dots and the threshold value of the dither matrix set at the corresponding position of the pixel to be processed. If the density data is larger, it is determined that a large dot is to be formed on the pixel to be processed (step S554: yes), and the halftone process is exited to return to the number data generation process shown in FIG. .

  Conversely, when the threshold value is larger than the density data of large dots, it is determined that no large dot is formed on the pixel to be processed (step S554: no), and this time, the process of determining whether or not a medium dot is formed. To start. To determine whether or not medium dots are formed, the medium dot intermediate data is calculated by adding the large dot density data and the medium dot density data (step S556). Then, by comparing the obtained intermediate data for medium dots and the threshold value of the dither matrix, it is determined whether or not medium dots are formed (step SS558). If the intermediate data for medium dots is larger, it is determined that a medium dot is to be formed in the pixel to be processed (step S560: yes), and the halftone process is skipped and the number data generation process in FIG. 19 is performed. Return.

  On the other hand, if the threshold value is larger than the intermediate dot intermediate data, it is determined that no medium dot is formed on the pixel to be processed (step S560: no), and this time, whether or not a small dot is formed is determined. Start processing. To determine whether or not small dots are formed, intermediate data for medium dots and density data for small dots are added to calculate intermediate data for small dots (step S562). Then, by comparing the obtained intermediate data for small dots and the threshold value of the dither matrix, it is determined whether or not small dots are formed (step S564). If the intermediate data for small dots is larger, it is determined that a small dot is formed in the pixel to be processed. Conversely, if the threshold is larger than the intermediate data for small dots, It is determined that no dot is formed.

  By performing the processing as described above, it is possible to determine whether a large dot, a medium dot, or a small dot is formed for a pixel to be processed, or whether any dot is not formed. Thus, when it is determined whether or not dots are formed for the target pixel, the halftone process shown in FIG. 20 is exited and the process returns to the number data generation process shown in FIG.

  The manner of determining whether large, medium, and small dots are formed while performing the above-described processing will be supplementarily described with reference to FIG. FIG. 22 is an explanatory diagram conceptually showing a state in which the presence / absence of large / medium / small dots is determined for each pixel in the pixel group while applying the dither method. Here, in order to avoid complicated explanation, all the pixels in the pixel group have the same gradation value, and therefore the density data of the large, medium, and small dots also have the same gradation value. Shall. FIG. 22A shows the density data of large, medium, and small dots obtained for each pixel in the pixel group. For each pixel, the density data of large dots is “2” and the density data of medium dots is “ 90 ”, and the density data of small dots is“ 32 ”.

  FIG. 22B shows threshold values stored at positions corresponding to pixel groups in the dither matrix. When determining whether or not large dots are formed, the density data of large dots is compared with these threshold values. Here, since the density data of large dots is “2” for any pixel, the pixels that are determined to form large dots are only those for which the threshold value “1” is set. In FIG. 22B, the pixels for which large dots are determined to be formed are displayed with fine diagonal lines. For the other pixels, it is considered that either medium dots or small dots are formed, or no dot is formed. Therefore, it is determined whether or not medium dots are formed.

  In determining whether or not a medium dot is formed, the medium dot intermediate data is calculated by adding the large dot density data “2” and the medium dot density data “90” and obtaining the intermediate data “92”. And the dither matrix threshold. As a result, it is determined that medium dots are formed only in two pixels, the pixel for which the threshold “42” is set and the pixel for which the threshold “58” is set. In FIG. 22 (c), a pixel that is determined to have a medium dot formed is displayed with a slight diagonal line. A pixel in which neither a large dot nor a medium dot is formed is considered to be either a small dot is formed or no dot is formed. Therefore, the small dot density data “32” is added to the intermediate dot intermediate data “92” to calculate the intermediate data for small dots, and the obtained intermediate data “124” and the threshold value of the dither matrix are calculated. Compare. As a result, it is determined that a small dot is formed only on a pixel for which the threshold value “109” is set. In FIG. 22D, the pixels for which small dots are determined to be formed are displayed with rough diagonal lines.

  In steps S502 to S506 of the number data generation process shown in FIG. 19, the presence / absence of formation for large, medium, and small dots is determined while calculating intermediate data for each pixel in the pixel group as described above. When the determination is completed for all the pixels in the pixel group (step S506: yes), the number of large dots, medium dots, and small dots formed in the pixel group is acquired (step S508). The pixel group illustrated in FIG. 22 has one large dot, two medium dots, and one small dot.

  When the number of various dots formed in the pixel group is obtained as described above, a combination of the numbers of various dots (in the example shown in FIG. 22, one large dot, two medium dots, and one small dot 1). A process of encoding the combination of the individual pieces is performed (step S510). This is due to the following reason. For example, when there are three types of dots, large, medium, and small, if the number of dots formed for each dot type is output, the number of dots must be output three times for each pixel group, and the computer 100 can output the color. By quickly outputting data to the printer 200, the effect of quickly printing an image is diminished. Therefore, instead of individually outputting the number of dots, the combination of the numbers of dots is converted into individual codes set for each combination.

  The process of coding the combination of large, medium, and small dots is performed by storing the dot number combination and the coded number data in advance in a correspondence table and referring to the correspondence table. FIG. 23 is an explanatory diagram showing a correspondence table in which combinations of the numbers of large, medium, and small dots formed in a pixel group are set in association with coded number data. In the correspondence table illustrated in FIG. 23, for example, a combination in which the numbers of large dots, medium dots, and small dots are all 0 is associated with coded number data “0”. In addition, a code implied number data “1” is associated with a combination of 0 large dots, 0 medium dots, and 1 small dot. In this way, the coded number data is preset in the correspondence table for each combination of the number of dots.

Here, the number of combinations of the numbers of large, medium, and small dots is as follows. A large dot, medium dot, and small dot can be formed on each pixel in the pixel group. However, since a plurality of dots are not formed in one pixel, the total number of dots is the pixel group. The number of pixels (8 in the above-described embodiment) is not exceeded. Therefore, the combination of the number of large, medium and small dots overlaps among the four states of “form large dots”, “form medium dots”, “form small dots” and “do not form dots”. Is equal to the number of combinations when selecting 8 times with
₄ H ₈ (= _{4 + 8-1} C ₈ )
Thus, there are 165 combinations. Here, _n H _r is an operator for obtaining the number of combinations (number of overlapping combinations) obtained when r times are selected from n types of objects while allowing duplication. _N C _r is an operator that calculates the number of combinations obtained when r times are selected from n types of objects without allowing duplication.

  Since there are 165 combinations of the numbers of large, medium, and small dots in this way, there are only 165 code data “0” to “164”. If there are 165 patterns, an 8-bit data length can be expressed. In the end, instead of outputting the number of large dots, the number of medium dots, the number of small dots, and outputting three times, the 8-bit coded number data is output only once. The number can be output. Accordingly, in step S510 in FIG. 19, the combination of the numbers for the various dots obtained for each pixel group in step S508 is converted into coded number data with reference to the correspondence table as shown in FIG. I will leave it.

  Thus, when the number data obtained by encoding the combination of the number of dots for each pixel group is obtained, it is determined whether or not the above processing has been performed for all the pixels of the image (step S512). If unprocessed pixels remain, the process returns to step S500 and repeats a series of processes. When it is determined that the process has been completed for all pixels of the image, the encoded number data is output ( Step S514), the number data generation process shown in FIG. 19 is terminated.

C-3. Dot formation presence / absence determination process of the second embodiment:
Next, in the image printing process of the second embodiment described above, a process for receiving the coded state number data generated for each pixel group and determining the presence or absence of dot formation for each pixel in the pixel group will be described. To do. In the dot formation presence / absence determination process of the first embodiment described above, the presence / absence of dot formation is immediately determined from the number data and the order value by referring to the conversion table. In the dot formation presence / absence determination process of the second embodiment, Similarly, by referring to the conversion table, it is possible to immediately determine whether large / medium / small dots are formed from the coded number data and the sequence value. In order to clarify the reason why such a process is possible and to show that the process is speeded up by performing such a process, first, in the following, dot formation is performed from the number data without using the conversion table. The process for determining the presence or absence of will be described. Next, the dot formation presence / absence determination process according to the second embodiment, which can quickly determine whether large / medium / small dots are formed from the number data by referring to the conversion table, will be described.

C-3-1. How to determine dot formation without referring to the conversion table:
FIG. 24 is a flowchart showing the flow of processing for determining whether large, medium, and small dots are formed without referring to a conversion table. Below, it demonstrates easily according to a flowchart. When the process is started, first, one pixel group whose pixel position is to be determined is selected (step S600), and the number data of the pixel group is acquired (step S602). The number data obtained in this way is coded data. Therefore, the number data is decoded and converted into data indicating the number of large dots, medium dots, and small dots (step S604). The process of decoding the number data is performed by referring to the decoding table. FIG. 25 is an explanatory diagram conceptually showing a decoding table referred to for decoding the encoded number data.

  As shown in the figure, combinations of the numbers of large dots, medium dots, and small dots corresponding to the coded number data are set in the decoding table. For example, when the encoded number data is “1”, the number of large dots and medium dots is 0, and the number of small dots is 1 and is decoded into a combination of dot numbers. In step S604 of FIG. 24, the coded number data is converted into data representing the number of large, medium, and small dots by referring to such a decoding table.

  Next, after reading the order value matrix corresponding to the pixel group from which the number data has been decoded (step S606), referring to the read order value matrix, large dots, medium dots, and small dots for each pixel in the pixel group. Judging whether or not it is formed. Here, the order value matrix is a matrix in which the order in which dots are formed is set for each pixel in the pixel group, as described above with reference to FIG. FIG. 26 is an explanatory diagram conceptually showing a state where the presence / absence of formation of large, medium, and small dots is determined for each pixel with reference to the order value matrix. For example, it is assumed that a combination of one large dot, two medium dots, and one small dot is obtained by decoding the number data.

  When determining the presence or absence of dot formation for each pixel, first, a pixel on which a large dot is to be formed is determined (step S608 in FIG. 24). Here, since the number of large dots is one, a large dot is formed in a pixel in which the dot is most easily formed, that is, a pixel in which the order value is set to “1” in the order value matrix. Judge. Here, when the number of large dots is N, it is determined that large dots are to be formed in pixels in which the order values are set to values “1” to “N” in the order value matrix. In FIG. 26, pixels forming large dots are displayed with fine diagonal lines.

  If the pixel which forms a large dot is determined, the pixel which forms a medium dot is determined from the pixel in which the large dot was not formed next (step S610 of FIG. 24). As shown in FIG. 26, the number of medium dots is two, and large dots are formed at the pixel positions where the order value “1” is set. Therefore, the order value “2” is set for the medium dots. And the pixels for which the order value “3” is set. In FIG. 26, pixel positions where medium dots are formed are displayed with a slightly rough diagonal line.

  When the pixels for forming the medium dots are determined in this way, the pixels for forming the small dots are determined from the pixels in which neither the large dots nor the medium dots are formed (step S612 in FIG. 24). As shown in FIG. 26, the number of small dots is one, and large dots are formed in the pixels with the order value “1”, and medium dots are formed in the pixels with the order values “2” and “3”. Therefore, the small dots are formed in the pixels for which the order value “4” is set. In FIG. 26, pixels on which small dots are formed are displayed with rough diagonal lines. Finally, it is determined that no dot is formed for a pixel in which neither a large dot, a medium dot, nor a small dot is formed (step S614 in FIG. 24).

  Thus, after decoding the coded number data for one pixel group and determining the pixels that form the large, medium, and small dots, it is determined whether or not the processing has been completed for all the pixel groups (step in FIG. 24). S616). If an unprocessed pixel group remains (step S616: no), the process returns to step S600, and a series of subsequent processes are repeated for the new pixel group. When it is determined that the process has been completed for all the pixel groups (step S616: yes), the dot formation presence / absence determination process shown in FIG. 24 is terminated.

C-3-2. Dot formation presence / absence determination processing referring to the conversion table:
In the dot formation presence / absence determination process described above, when coded number data is received, it is decoded into data indicating the number of large, medium and small dots formed in the pixel group, and then any dot is formed for each pixel. This is a two-step operation. However, with reference to the conversion table, the dots to be formed in each pixel can be determined immediately without decoding the number data. Hereinafter, the dot formation presence / absence determination process of the second embodiment for determining the presence / absence of dot formation with reference to the conversion table will be described.

  The dot formation presence / absence determination processing of the second embodiment is different from the dot formation presence / absence determination processing of the modification described with reference to FIG. The process flow is the same. Accordingly, in the following, the dot formation presence / absence determination process of the second embodiment will be described using the flowchart of FIG.

  When the dot formation presence / absence determination process of the second embodiment is started, first, one pixel group is selected (corresponding to step S400), and the number data of the pixel group is acquired (corresponding to step S402). Next, the sequence value matrix corresponding to the selected pixel group is read from the sequence value matrix stored in plural sets (corresponding to step S404). That is, as described above with reference to FIGS. 15 and 16, the lower 5 bits of n and m are extracted from the coordinate values (n, m) of the pixel group to obtain N and M, respectively. Then, an order value matrix generated from a block of N rows and M columns in the dither matrix may be selected and read.

  As described above, when the order value matrix corresponding to the pixel group is read, one target pixel for determining whether or not to form dots is selected from the pixel group being processed (corresponding to step S406). Then, after obtaining the order value of the target pixel by referring to the read order value matrix (corresponding to step S408), the presence or absence of dot formation for the target pixel is determined by referring to the conversion table ( Step S410 equivalent).

  Here, in the conversion table referred to in the dot formation presence / absence determination process of the first embodiment described above, data indicating the presence / absence of dot formation is set for each combination of the number data and the order value (see FIG. 13). ) On the other hand, in the conversion table referred to in the dot formation presence / absence determination process of the second embodiment, which of large / medium / small dots is formed for each combination of the coded number data and the sequence value, Alternatively, data indicating whether dots are not formed is set.

  FIG. 27 is an explanatory diagram conceptually showing a conversion table referred to in the dot formation presence / absence determination process of the second embodiment. As described above with reference to FIG. 23, the coded number data can take 165 values from 0 to 164. Since one pixel group is composed of eight pixels, the order value can take eight values from 1 to 8. In the conversion table of the second embodiment, for each of these 165 × 8 = 1320 combinations, a value “0” indicating that dots are not formed, a value “1” indicating that small dots are formed, and medium dots are displayed. Either a value “2” indicating formation or a value “3” indicating formation of a large dot is set. Therefore, if the number data of the pixel group and the order value of the target pixel are known, the presence / absence of dot formation can be determined immediately. In the dot formation presence / absence determination process of the second embodiment, by referring to such a conversion table, it is immediately determined whether a large / medium / small dot is formed in the target pixel or a dot is not formed ( (Corresponding to step S410 in FIG. 14).

  Here, the reason why it is possible to appropriately determine the presence / absence of dot formation for large, medium and small dots even when the presence / absence of dot formation is determined with reference to the conversion table as shown in FIG. As described above with reference to FIGS. 24 to 26, when the presence / absence of dot formation is determined without referring to the conversion table, two steps of operations are performed. That is, in the first stage, the coded number data is converted into the number of various large, medium, and small dots. In the subsequent second stage, whether or not to form dots for each pixel is determined according to the order value matrix. Here, as shown in FIG. 25, the encoded number data and the combination of the numbers of large, medium, and small dots have a one-to-one relationship. In other words, if one coded number data is given, a combination of numbers for various dots can be uniquely determined.

  On the other hand, when the number of various dots formed in the pixel group is decoded, the presence / absence of dot formation for each pixel is determined according to the order value matrix as shown in FIG. That is, if the order value matrix is determined, the combination of the numbers for various dots and the presence / absence of dot formation for each pixel have a one-to-one relationship. As described above, the combination of the numbers for various dots is uniquely determined from the encoded number data. Therefore, if the order value matrix is determined after all, the pixel group is determined from the encoded number data. Whether or not various dots are formed is uniquely determined for each of the pixels.

  Here, when the operation for determining the presence / absence of dot formation for each pixel is observed in more detail according to the number of various dots and the order value matrix, the following can be understood. That is, the combination of the number of various dots determines what dots are formed in a pixel with a certain order value, and the order value matrix has such pixels with such order value in the pixel group. The position is determined. For example, in the example shown in FIG. 26, since there are one large dot, two medium dots, and one small dot, a large dot is formed in the pixel having the order value “1”, and the order values “2” and “ It can be seen that medium dots are formed in the pixels of “3”, small dots are formed in the pixels of the order value “4”, and no dots are formed in the pixels of the order values “5” to “8”. The position of the pixels having the order values in the pixel group is determined by the order value matrix. From this, given the coded number data, it is possible to determine uniquely what kind of dots are formed in a pixel of a certain order value.

  Therefore, for all the number data, the order value and the type of dot formed on the pixel having the order value are determined in advance and set in a conversion table as shown in FIG. When determining the presence or absence of dot formation for the target pixel in the pixel group, the order value of the target pixel is obtained by referring to the order value matrix, and then formed into the order value by referring to the conversion table. If the type of dot to be obtained is acquired, it is possible to appropriately determine the presence or absence of dot formation.

  When the presence / absence of dot formation is thus determined for one target pixel, it is determined whether or not dot formation has been determined for all pixels in the selected pixel group (corresponding to step S412 in FIG. 14). If pixels that have not yet been determined for dot formation remain, the process returns to the position corresponding to step S406, a new target pixel is selected, and a series of processes are performed. If it is determined that dot formation has been determined for all the pixels in the pixel group by repeating such processing, it is determined whether or not processing has been completed for all pixel groups to which the number data is supplied (step S414). Equivalent). If an unprocessed pixel group remains, the process returns to the very beginning, selects a new pixel group, and performs a series of subsequent processes. When these processes are repeated and the process is completed for all pixel groups, the dot formation presence / absence determination process of the second embodiment is completed.

  In the dot formation presence / absence determination process of the second embodiment described above, when the coded number data is received, the order value of the target pixel is obtained by referring to the order value matrix, and then the number data and order By referring to the conversion table from the values, it is possible to determine whether or not to form various dots without decoding the number data. For this reason, it is possible to quickly execute the process of determining the presence or absence of dot formation for each pixel, and thus it is possible to output an image quickly.

  Further, the main processing content of the dot formation presence / absence determination processing of the second embodiment is simply reading data with reference to the order value matrix and the conversion table, which is a very simple processing. Accordingly, even the color printer 200 that does not have a high data processing capability like the computer 100 can be executed sufficiently quickly, and an image can be printed quickly.

  Furthermore, in the dot formation presence / absence determination processing of the second embodiment, it is possible to determine the presence / absence of dot formation for the target pixel simply by referring to the matrix or table, and no conditional branching is included in the processing. On the other hand, when determining the presence or absence of dot formation without referring to the conversion table, a large number of conditional branches occur. A slight supplementary explanation will be given on this point with reference to FIG.

  When determining whether or not various dots are formed without referring to the conversion table, first, it is determined whether or not a large dot is formed (step S608 in FIG. 24). If no large dot is formed, it is determined whether or not a medium dot is formed (step S610 in FIG. 24). If neither a large dot nor a medium dot is formed, it is determined whether or not a small dot is formed (step S612 in FIG. 24). And about the pixel judged not to form a small dot, it is judged that no dot is formed. As described above, the subsequent processing contents differ depending on whether a large dot is formed, whether a medium dot is formed, or whether a small dot is formed. The determination process includes a large number of conditional branches.

  Recent CPUs employ a technique called pipeline processing to enable high-speed processing. However, if conditional branching occurs, the effect of pipeline processing cannot be obtained. In this respect, the process of determining whether or not to form dots without referring to the conversion table includes a large number of conditional branches as described above, and thus it is difficult to perform a quick process. On the other hand, the process of determining the presence or absence of dot formation by referring to the conversion table does not include conditional branching as shown in FIG. 14, so that the effect of pipeline processing can be maximized. In this respect, it can be said that the processing is suitable for high-speed processing.

  As described above, in the dot formation presence / absence determination process of the second embodiment, the dot formation presence / absence for each pixel in the pixel group can be determined easily and quickly. It is necessary to store the matrix and the conversion table as shown in FIG. Using too much memory to store these matrices and tables is not desirable for installation in an actual product. However, also in the dot formation presence / absence determination process of the second embodiment, the memory amount necessary for storing the conversion table and the order value matrix is an obstacle to mounting on the product, as in the first embodiment. It won't be so big. This point will be briefly described below.

  First, the order value matrix is the same as that of the first embodiment described above. That is, the amount of memory for storing the order value matrix is determined by the size of the dither matrix and the size of the pixel group, and if there is a memory amount of about 10 Kbytes as shown in FIG. It is considered possible.

  Next, the memory capacity necessary for storing the conversion table will be described. As shown in FIG. 27, in the conversion table, whether or not dots are formed is set for each combination of the order value and the number data. If the number of pixels included in the pixel group is eight, the order value takes eight values. Assuming that there are three types of dots that can be formed, large dots, medium dots, and small dots, the number data can take 165 values as described above with reference to FIG. Furthermore, the determination result of dot formation presence / absence can be obtained only in four ways: forming a large dot, forming a medium dot, forming a small dot, and not forming a dot. can do. Therefore, the conversion table shown in FIG. 27 can be stored if 8 × 165 × 2 = 2640 bits (0.322 Kbytes).

  FIG. 28 is an explanatory diagram summarizing the results of trial calculation of the amount of memory necessary for storing the conversion table for each size of the pixel group. As shown in the figure, the conversion table can be sufficiently stored if it is about several kilobytes. Therefore, even in the dot formation presence / absence determination process of the second embodiment, a small amount of memory is sufficient to store the sequence value matrix and the conversion table, and the memory capacity does not become an obstacle to mounting on the product. .

  Although various embodiments have been described above, the present invention is not limited to all the embodiments described above, and can be implemented in various modes without departing from the scope of the invention. For example, in the above embodiments, the case where an image is printed by forming dots on printing paper has been described. However, the scope of application of the present invention is not limited to the case where an image is printed. For example, the present invention can be suitably applied to a liquid crystal display device that expresses an image whose gradation changes continuously by dispersing bright spots at an appropriate density on a liquid crystal display screen.

1 is an explanatory diagram for explaining an overview of the present invention taking a printing system as an example; FIG. And FIG. 14 is an explanatory diagram illustrating a configuration of a computer as an image processing apparatus. It is explanatory drawing which shows schematic structure of the color printer 200 of a present Example. It is explanatory drawing which shows the arrangement | sequence of the inkjet nozzle in an ink discharge head. It is a flowchart which shows the whole flow of the image printing process of 1st Example. It is explanatory drawing which illustrated a part of dither matrix conceptually. It is explanatory drawing which showed notionally the mode of determining the presence or absence of the dot formation about each pixel, referring a dither matrix. It is explanatory drawing which showed a mode that the image data was converted into the data showing the presence or absence of dot formation using the dither method. It is explanatory drawing which showed a mode that the data showing the presence or absence of dot formation for every pixel were produced | generated from number data. It is a flowchart which shows the flow of the number data generation process of 1st Example. It is a flowchart which shows the flow of the dot formation existence determination process of 1st Example. It is explanatory drawing which showed notionally the mode that the presence or absence of the dot formation about each pixel was determined in the dot formation presence or absence determination process of 1st Example. It is explanatory drawing which showed notionally the conversion table referred in order to determine the presence or absence of the dot formation about an object pixel. It is a flowchart which shows the flow of the dot formation presence / absence determination process of the modification. It is explanatory drawing shown about the method of producing | generating the several order value matrix referred in the dot formation presence / absence determination process of a modification. It is explanatory drawing which showed the method of selecting the order value matrix corresponding to a pixel group. It is explanatory drawing which showed specifically the method of selecting the order value matrix applied from the coordinate value (n, m) of a pixel group. It is explanatory drawing which shows the result of having calculated the memory amount required in order to memorize | store an order value matrix supposing the dither matrix of various sizes, and the pixel group of various sizes. It is a flowchart which shows the flow of the process which determines the number of the various large / medium / small dots formed in a pixel group, and produces | generates number data. It is a flowchart which shows the flow of a process which judges the formation presence or absence about various large / medium / small dots about the selected pixel. It is explanatory drawing which showed notionally the dot density conversion table for converting the gradation value of image data into the density data about various large, medium, and small dots. It is explanatory drawing which showed notionally the mode that the presence or absence of formation of various large, medium, and small dots was determined while applying the dither method to each pixel in the pixel group. It is explanatory drawing which shows the corresponding | compatible table in which the combination of the number of each large / medium / small dot formed in a pixel group and code data were matched and set. It is a flowchart which shows the flow of the process which determines the formation existence of various large / medium / small dots without referring to a conversion table. It is explanatory drawing which showed notionally the decoding table referred in order to decode the number data encoded. It is explanatory drawing which showed notionally the mode that the presence or absence of formation about various large and small dots was determined for every pixel, referring an order value matrix. It is explanatory drawing which showed notionally the conversion table referred by the dot formation presence determination process of 2nd Example. It is explanatory drawing which put together the result of having calculated the memory amount required in order to memorize | store a conversion table for every magnitude | size of a pixel group.

Explanation of symbols

10 ... computer, 20 ... color printer, 100 ... computer,
108: Peripheral device interface PIF,
109 ... disk controller DDC,
110: Network interface card NIC,
112 ... Video interface VIF,
116 ... Bus, 118 ... Hard disk, 120 ... Digital camera,
122 ... color scanner, 124 ... flexible disk,
126: Compact disc, 230: Carriage motor, 235 ... Motor,
236 ... Platen, 240 ... Carriage, 241 ... Print head,
242 ... Ink cartridge, 243 ... Ink cartridge,
244 ... Ink ejection head 260 ... Control circuit 200 ... Color printer
300 ... communication line, 310 ... storage device

Claims (11)

An image output system comprising: an image processing device that performs predetermined image processing on image data; and an image output device that outputs an image on an output medium by forming dots based on the result of the image processing,
The image processing apparatus includes:
Means for sequentially extracting a pixel group in which a predetermined number of adjacent pixels are collected from the image ;
By comparing the gradation values of the pixels belonging to the pixel group with a plurality of threshold values existing at positions corresponding to the position of the pixel group in the image among the threshold values constituting the dither matrix , the number data representing the number of dots to be formed and the number data generation means that generates,
Number data supply means for supplying the number data generated for each pixel group to the image output device, and
The image output device includes:
A dot is formed in each pixel constituting the pixel group based on the order of a plurality of threshold values existing at positions corresponding to the pixel group of the dither matrix used when generating the number data for each pixel group. An order value indicating an order to be processed is determined, and when the number data of the pixel group is supplied from the image processing apparatus, the order value corresponding to the pixel group in which the number data is generated is acquired. A value acquisition means;
Associate before Symbol number data and the order value, a correlation storage means for storing a correspondence relationship between the presence or absence of dot formation in the pixel of the order value and the sequence value,
Determining when supplied with count data for said pixel group, by referring to the correspondence relationship, in accordance with the order value obtained for the pixel groups, the presence or absence of dot formation for each pixel constituting the pixel group Dot forming presence / absence determining means to perform,
Dot forming means for forming dots on the output medium according to the determined presence or absence of dot formation ,
The dither matrix is an image output system in which the number of thresholds constituting the dither matrix is two digits or more larger than the number of pixels constituting the pixel group . The image output system according to claim 1 , wherein the pixel group is configured as one of 2 × 2, 4 × 2, and 4 × 4 pixels . The image output system according to claim 2, wherein the number of thresholds constituting the dither matrix is 2 ^m × 2 ⁿ (m and n are integers of 6 or more) . An image output device that receives image data that has undergone predetermined image processing and outputs an image by forming dots on an output medium based on the image data.
And Matomera is, in the state number data representing the number of dots to be formed in the pixel group number data receiving means for receiving the image data adjacent pixels from each other as the pixel group by a predetermined number in the image,
A dot is formed in each pixel constituting the pixel group based on the order of a plurality of threshold values existing at positions corresponding to the pixel group in the dither matrix used when generating the number data for each pixel group. An order value indicating the order to be performed, and when receiving the image data in the state of the number data, the order value acquisition means for acquiring the order value corresponding to the number data ;
Associate before Symbol number data and the order value, a correlation storage means for storing a correspondence relationship between the presence or absence of dot formation in the pixel of the order value and the sequence value,
Determining when supplied with count data for said pixel group, by referring to the correspondence relationship, in accordance with the order value obtained for the pixel groups, the presence or absence of dot formation for each pixel constituting the pixel group Dot forming presence / absence determining means to perform,
An image output device comprising: dot forming means for forming dots on the output medium in accordance with the determined dot formation. The image output apparatus according to claim 4 , wherein the pixel group is configured as one of 2 × 2, 4 × 2, and 4 × 4 pixels . The number of thresholds which constitute the dither matrix ^{is, 2 m × 2 n (m} , n is 6 or more integer) image output apparatus according to claim 5, wherein a. An image output device that outputs an image corresponding to image data by forming dots on an output medium according to the image data,
Means for sequentially extracting a pixel group in which a predetermined number of adjacent pixels are collected from the image ;
By comparing the gradation values of the pixels belonging to the pixel group with a plurality of threshold values existing at positions corresponding to the position of the pixel group in the image among the threshold values constituting the dither matrix , the number data representing the number of dots to be formed and the number data generation means that generates,
A dot is formed in each pixel constituting the pixel group based on the order of a plurality of threshold values existing at positions corresponding to the pixel group of the dither matrix used when generating the number data for each pixel group. Order value indicating the order to be performed, and when receiving the number data of the pixel group, the order value acquisition means for acquiring the order value corresponding to the pixel group from which the number data is generated ;
Associate before Symbol number data and the order value, a correlation storage means for storing a correspondence relationship between the presence or absence of dot formation in the pixel of the order value and the sequence value,
Determining when supplied with count data for said pixel group, by referring to the correspondence relationship, in accordance with the order value obtained for the pixel groups, the presence or absence of dot formation for each pixel constituting the pixel group Dot forming presence / absence determining means to perform,
Dot forming means for forming dots on the output medium according to the determined presence or absence of dot formation ,
The dither matrix is an image output device comprising a number of thresholds constituting the dither matrix that is two or more digits larger than the number of pixels constituting the pixel group . An image output method for outputting an image on an output medium by performing predetermined image processing on image data and forming dots based on the obtained result,
A pixel group in which a predetermined number of adjacent pixels are grouped is sequentially extracted from the image, and the gradation value of the pixel belonging to the pixel group is determined from the threshold values constituting the dither matrix in the position of the pixel group in the image. a first step of more compared to multiple thresholds to generate the number data representing the number of dots to be formed in the pixel group of the respective existing in positions corresponding to,
A dot is formed in each pixel constituting the pixel group based on the order of a plurality of threshold values existing at positions corresponding to the pixel group of the dither matrix used when generating the number data for each pixel group. A second step of obtaining an order value corresponding to the pixel group in which the number data is generated when the order value indicating the order to be performed is received and the number data of the pixel group is received ;
Associate before Symbol number data and the order value, a third step of storing the correspondence between the presence or absence of dot formation in the pixel of the order value and the sequence value,
Determining when supplied with count data for said pixel group, by referring to the correspondence relationship, in accordance with the order value obtained for the pixel groups, the presence or absence of dot formation for each pixel constituting the pixel group A fourth step of
A fifth step of forming dots on the output medium in accordance with the determined presence / absence of dot formation ,
The dither matrix is an image output method in which the number of thresholds constituting the dither matrix is two digits or more larger than the number of pixels constituting the pixel group . An image output method for receiving image data that has undergone predetermined image processing and outputting an image by forming dots on an output medium based on the image data,
The adjacent pixels in the image Matomera is as pixel groups by a predetermined number, a state number data representing the number of dots to be formed in the pixel group, and step (A) receiving said image data,
A dot is formed in each pixel constituting the pixel group based on the order of a plurality of threshold values existing at positions corresponding to the pixel group in the dither matrix used when generating the number data for each pixel group. A step (B) of determining an order value indicating an order to be performed and obtaining the order value corresponding to the number data when the image data in the number data state is received ;
Associate before Symbol number data and the order value, a step of storing the correspondence between the presence or absence of dot formation in the pixel of the order value and the sequence value (C),
Determining when supplied with count data for said pixel group, by referring to the correspondence relationship, in accordance with the order value obtained for the pixel groups, the presence or absence of dot formation for each pixel constituting the pixel group Step (D) to perform,
And (E) forming a dot on the output medium according to the determined dot formation. A program for implementing a method of outputting an image on an output medium by performing predetermined image processing on image data and forming dots based on the obtained result using a computer,
A pixel group in which a predetermined number of adjacent pixels are grouped is sequentially extracted from the image, and the gradation value of the pixel belonging to the pixel group is determined from the threshold values constituting the dither matrix in the position of the pixel group in the image. first and capabilities more, to generate the number data representing the number of dots to be formed in the pixel group of the each compared with a plurality of threshold values that exist in a position corresponding to,
A dot is formed in each pixel constituting the pixel group based on the order of a plurality of threshold values existing at positions corresponding to the pixel group of the dither matrix used when generating the number data for each pixel group. A second function for obtaining an order value corresponding to the pixel group in which the number data is generated when the order value indicating the order to be performed is determined and the number data of the pixel group is received ;
Associate before Symbol number data and the order value, a third function of storing a correspondence relationship between the presence or absence of dot formation in the pixel of the order value and the sequence value,
Determining when supplied with count data for said pixel group, by referring to the correspondence relationship, in accordance with the order value obtained for the pixel groups, the presence or absence of dot formation for each pixel constituting the pixel group A fourth function to
And a fifth function for forming dots on the output medium in accordance with the determined dot formation. A program for realizing, using a computer, a method of receiving image data subjected to predetermined image processing and outputting an image by forming dots on an output medium based on the image data,
The adjacent pixels in the image Matomera is as pixel groups by a predetermined number, a state number data representing the number of dots to be formed in the pixel group, function of receiving the image data and (A),
A dot is formed in each pixel constituting the pixel group based on the order of a plurality of threshold values existing at positions corresponding to the pixel group in the dither matrix used when generating the number data for each pixel group. A function (B) for obtaining an order value corresponding to the number data when receiving the image data in the state of the number data ;
Before Symbol number data and association with the order value, functions of storing a correspondence relationship between the presence or absence of dot formation in the pixel of the order value and the sequence value (C), and
Determining when supplied with count data for said pixel group, by referring to the correspondence relationship, in accordance with the order value obtained for the pixel groups, the presence or absence of dot formation for each pixel constituting the pixel group Function (D) to
A program for realizing a function (E) for forming dots on the output medium in accordance with the determined dot formation.

Images