JP5333197B2 - Control device and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique in which an image of a high image quality can be formed using processed image data compensated for the variability of discharging amounts. <P>SOLUTION: In order to compensate for the variability of the discharging amounts of ink droplets discharged from a specific set of nozzle groups for chromatic color among three sets of nozzle groups for chromatic color, a control unit of a PC calculates an error value using target correction data for a target nozzle for chromatic color which belongs to the specific set of nozzle groups for chromatic color that forms a dot at a position on a print medium corresponding to a target pixel (S34). The target correction data is data obtained using target characteristic data for chromatic color corresponding to the target nozzle for chromatic color among three sets of characteristic data groups for chromatic color corresponding to the three sets of nozzle groups for chromatic color, and reference characteristic data for chromatic color that is characteristic data for chromatic color showing a minimum discharging amount of ink droplets discharged among the three sets of characteristic data groups for chromatic color. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present specification discloses a technique for causing a print execution unit including a print head unit in which a plurality of sets of chromatic color nozzle groups for ejecting a plurality of types of chromatic color ink droplets to execute printing. .

  Many ink jet printers perform binary (no dots, with dots) or ternary by performing image processing (for example, halftone processing) on CMYK image data including a plurality of pixels described in the CMYK format. Processed image data including a plurality of pixels described above (no dots, small dots, medium dots, large dots, etc.) is generated. The ink jet printer forms dots for each of a plurality of pixels in the processed image data at positions on the print medium corresponding to the pixels according to the values of the pixels. As a result, an image represented by the processed image data is formed on the print medium.

  The ink jet printer of Patent Document 1 includes a print head in which four sets of nozzle groups for ejecting four types of CMYK ink droplets are formed. This inkjet printer stores a plurality of characteristic data related to the ejection amount of ink droplets ejected from a plurality of nozzles included in the nozzle group for each of a plurality of nozzle groups formed on the print head. ing. Specifically, the characteristic data is data indicating what percentage of increase / decrease is relative to a target discharge amount that is predetermined for each of CMYK. This ink jet printer corrects CMYK image data using the characteristic data of each nozzle before executing image processing. For example, when the K value of a specific pixel in the CMYK image data is K and the characteristic data of the nozzle that forms a dot at a position on the print medium corresponding to the specific pixel is X%, K The K value of the specific pixel is corrected by a calculation formula of × (100% −X%). The above correction is executed for each pixel in the CMYK image data. The ink jet printer performs image processing on the corrected CMYK image data. As a result, processed image data is generated in which variations in the ejection amount of ink droplets ejected from a plurality of nozzles (hereinafter sometimes simply referred to as “variations in ejection amount”) are compensated.

JP 2000-25212 A JP-A-11-58704 JP 2001-38892 A JP 2005-225199 A

  There is a need to improve the quality of images printed on print media. The present specification provides a technique capable of printing a high-quality image.

  The technology disclosed in this specification is a control device for causing a print execution unit including a print head unit in which a plurality of nozzle groups for ejecting a plurality of types of chromatic ink droplets to be formed to execute printing. is there. Each set of nozzle groups includes a plurality of nozzles. The control device includes an image processing unit and a supply unit. The image processing unit generates processed image data by performing image processing on specific image data. The supply unit supplies the processed image data to the print execution unit. In order to compensate for variations in the ejection amount of ink droplets ejected from a specific set of nozzle groups among the plurality of sets of nozzle groups, the image processing unit performs the following processing on the target pixel in the target image data: A specific process using the correction data for chromatic color for the target nozzle that forms a dot at a position on the print medium corresponding to the target pixel and belongs to the specific set of nozzle groups. Execute. The chromatic color correction data includes reference characteristic data among a plurality of sets of characteristic data groups corresponding to a plurality of sets of nozzle groups, attention characteristic data corresponding to a target nozzle of a plurality of sets of characteristic data groups, and It is the data obtained by using. Each set of characteristic data groups includes a plurality of characteristic data corresponding to the plurality of nozzles included in the corresponding set of nozzle groups. The characteristic data is data related to the ejection amount of the ink droplet ejected from the corresponding nozzle. The reference characteristic data is characteristic data indicating a minimum ejection amount of the ejected ink droplets among the plurality of sets of characteristic data groups.

  For each group of nozzle groups, a high-quality image is printed even if a process for compensating for variations in the discharge amount of a plurality of nozzles included in the group of nozzle groups (hereinafter referred to as “compensation process”) is executed. May not be. A first nozzle group including a plurality of first nozzles for discharging a first type of chromatic ink droplets; and a plurality of second nozzles for discharging a second type of chromatic ink droplets. Consider a case where a print execution unit including a print head unit on which the second nozzle group is formed executes printing. For example, if correction data for each first nozzle is used based only on the discharge amount of each first nozzle included in the first nozzle group, variations in the discharge amount for the first nozzle group can be compensated. it can. Further, for example, if correction data for each second nozzle is used based on only the discharge amount of each second nozzle included in the second nozzle group, variations in the discharge amount for the second nozzle group are compensated. be able to. However, in this method, the difference in the discharge amount between the first nozzle group and the second nozzle group is not taken into consideration. For this reason, for example, when the average discharge amount of the first nozzle group is larger than the average discharge amount of the second nozzle group, the printed image is compared with the second chromatic color in comparison with the second chromatic color. One kind of chromatic color becomes stronger. That is, an image with a poor color balance is printed.

  On the other hand, in the control device disclosed in the present specification, the above-described compensation is performed for each of the plurality of nozzle groups by using the reference characteristic data indicating the minimum discharge amount among the plurality of sets of characteristic data groups. Processing is executed. In the above example, for example, when the nozzle having the smallest discharge amount in the first nozzle group and the second nozzle group is the first nozzle (hereinafter referred to as “specific first nozzle”), the first When compensating for the variation in the discharge amount of the nozzle group, not only the correction data considering the discharge amount of the specific first nozzle is used, but also when the variation in the discharge amount of the second nozzle group is compensated. Also, the correction data in consideration of the discharge amount of the specific first nozzle is used. In other words, the same reference discharge amount (the discharge amount of the specific first nozzle) is taken into account when compensating for variations in the discharge amount of either the first nozzle group or the second nozzle group. As a result, the difference in discharge amount between the first nozzle group and the second nozzle group can also be compensated. According to the above control device, processed image data capable of printing an image having an appropriate color balance, that is, a high-quality image can be generated.

  When the target nozzle belongs to the first set of nozzle groups that discharge the first type of ink droplets, the chromatic color correction data belongs to the first set of nozzle groups that discharge the first type of ink droplets. Data obtained using reference characteristic data corresponding to a specific nozzle and target characteristic data corresponding to a target nozzle belonging to the first set of nozzle groups may be used. Further, when the target nozzle belongs to the second set of nozzle groups that discharge the second type of ink droplets, the correction data for chromatic color includes the first set of nozzle groups that discharge the first type of ink droplets. Data obtained using reference characteristic data corresponding to a specific nozzle belonging to the nozzle and attention characteristic data corresponding to a nozzle of interest belonging to the second set of nozzle groups may be used.

  The print head unit may further include a black nozzle group for discharging black ink droplets. The black nozzle group may include a plurality of black nozzles. The image processing unit is arranged at a position on the print medium corresponding to the target pixel with respect to the target pixel in the target image data in order to compensate for variations in the ejection amount of the ink droplets discharged from the black nozzle group. The specific processing described above may be executed using black correction data for the black target nozzle for forming dots. The black correction data does not use the reference characteristic data described above, and the black corresponding to the black target nozzle among the plurality of black characteristic data corresponding to the plurality of black nozzles. It may be data obtained using the attention characteristic data. The characteristic data for black may be data related to the ejection amount of ink droplets ejected from the corresponding black nozzle.

  If the variation in the discharge amount of the black nozzle group is compensated using the reference characteristic data, the black density of the printed image may be lowered. In the above control device, in order to compensate for the variation in the discharge amount of the black nozzle group, the compensation process is performed using the correction data obtained using the black characteristic data without using the reference characteristic data. Run. According to this configuration, it is possible to suppress the decrease in the black density of the printed image and generate processed image data that can print a high-quality image in which variations in the discharge amount of the nozzle group for black are compensated. be able to.

  The target image data may be the specific image data. The image processing unit may include a color conversion processing unit and a halftone processing unit. The color conversion processing unit executes the specific process including the color conversion process and the correction process on the target image data expressed in the first type color space, thereby executing the second type Color-converted image data expressed in a color space may be generated. The halftone processing unit may generate processed image data by performing halftone processing on the color-converted image data. The color conversion processing unit generates a color-converted pixel expressed in the second type color space by performing color conversion processing on the target pixel in the target image data. A corrected pixel may be generated by executing a correction process on the color-converted pixel using the correction data for chromatic color in the kind of color space.

The color conversion processing unit may include a determination unit that determines whether the value of the pixel of interest in the color-converted image data is a value indicating a color within a predetermined range including an achromatic color. When the value of the target pixel is a value indicating a color within the predetermined range, the color conversion processing unit executes the specific process using the correction data for chromatic color, and the value of the target pixel May not be a value indicating a color within the predetermined range , the color conversion process may be executed without executing the specific process using the chromatic color correction data. When printing an image of a color within a predetermined range including an achromatic color on a print medium, a plurality of sets of chromatic color nozzle groups are compared to printing an image of a color within the other range on a print medium. The deterioration of image quality (deterioration of color balance) due to the difference in the discharge amount between the two is easily noticeable. In the above control device, when the value indicates a color within a predetermined range including an achromatic color, by executing the above specific processing using the correction data, a plurality of sets of chromatic color nozzle groups Compensation processing is performed in consideration of the difference in discharge amount. On the other hand, when the deterioration in image quality due to the difference in the discharge amount between the plurality of chromatic color nozzle groups is relatively inconspicuous, the above specific processing using the correction data is not performed. The color conversion process is executed . Thereby, the process for calculating the correction data can be omitted. As a result, the image processing time can be shortened.

  The image processing unit may include a color conversion processing unit and a halftone processing unit. The color conversion processing unit performs color conversion processing on each pixel in the specific image data expressed in the first type color space, thereby expressing the second color space. The target image data may be generated. The halftone processing unit may generate processed image data by performing halftone processing on the target image data. The halftone processing unit may include a correction unit, a determination unit, and an error value calculation unit. The correction unit generates a corrected value by correcting the value of the target pixel in the target image data using a plurality of error values corresponding to a plurality of neighboring pixels in the vicinity of the target pixel. May be. The determination unit may determine whether or not to form a dot at a position on the print medium corresponding to the target pixel, based on the corrected value and the threshold value corresponding to the target pixel. The error value calculation unit may calculate the error value of the target pixel according to the determination regarding whether or not to form a dot for the target pixel. When it is determined to form a dot for the target pixel, the error value calculation unit calculates an error value corresponding to the target pixel using the corrected value and the correction data for chromatic color. You may perform said specific process to calculate.

  A control method and a computer program for realizing the above printer are also new and useful.

The structure of a network system is shown. The top view of the nozzle surface of a print head is shown. A characteristic data table is shown. 2 shows a raster group formed by a print execution unit. The flowchart of the binary data generation process which PC performs is shown. Each pixel in the converted RGB image data is shown. Each pixel in CMYK image data is shown. The error value of each pixel in CMYK image data is shown. An equation for calculating an error value of each pixel in CMYK image data is shown. The flowchart of the binary data generation process which PC of 2nd Example performs is shown. Each pixel in the corrected image data produced | generated in 2nd Example is shown.

(First embodiment)
(System configuration)
A first embodiment will be described with reference to the drawings. FIG. 1 shows a schematic diagram of a network system 2 of the present embodiment. The network system 2 includes a LAN 4, a PC 10, and a printer 50. The PC 10 and the printer 50 are connected to the LAN 4. The PC 10 and the printer 50 can communicate with each other via the LAN 4.

(Configuration of PC10)
The PC 10 includes an operation unit 12, a display unit 14, a network interface 16, a storage unit 20, and a control unit 30. The operation unit 12 includes a mouse and a keyboard. The user can input various instructions to the PC 10 by operating the operation unit 12. The display unit 14 is a display for displaying various information. The network interface 16 is connected to the LAN 4.

  The storage unit 20 includes a work area 22. For example, the work area 22 stores data to be printed. The data to be printed may be, for example, data generated by an application in the PC 10 or data acquired from an external device. Examples of applications in the PC 10 include word processing software and spreadsheet software. Examples of the external device include a server on the Internet, a device connected to the LAN 4, and a portable storage medium. The storage unit 20 further stores a printer driver 24 for the printer 50. The printer driver 24 is software for transmitting various instructions (for example, print instructions) to the printer 50. For example, the printer driver 24 may be installed in the PC 10 from a computer-readable medium storing the printer driver 24, or may be installed in the PC 10 from a server on the Internet.

  The control unit 30 executes various processes according to a program (for example, the printer driver 24) stored in the storage unit 20. When the control unit 30 executes processing according to the printer driver 24, the functions of the image processing unit 32 and the supply unit 48 are realized. The image processing unit 32 includes a color conversion processing unit 34, a data acquisition unit 36, a correction data calculation unit 38, and a halftone processing unit 40. The halftone processing unit 40 includes a correction unit 42, a determination unit 44, and an error value calculation unit 46. In FIG. 1, a determination unit 47 shown in the color conversion processing unit 34 is a necessary configuration in a second embodiment to be described later. In the present embodiment, the color conversion processing unit 34 may not include the determination unit 47.

(Configuration of printer 50)
The printer 50 includes a network interface 52, a display unit 54, a storage unit 56, and a print execution unit 70. The network interface 52 is connected to the LAN 4. The display unit 54 is a display for displaying various information. The print execution unit 70 prints an image represented by binary data supplied from the PC 10 on a print medium according to the program 64 stored in the storage unit 56. The print execution unit 70 includes a print head 80. In addition to the above, the print execution unit 70 includes a drive mechanism for the print head 80, a print medium transport mechanism, and the like (these are not shown).

  The drive mechanism of the print head 80 includes a carriage and a motor that moves the carriage. The print head 80 is detachably mounted on the carriage. The carriage reciprocates in a predetermined direction within the housing of the printer 50. When the carriage moves, the print head 80 also moves. The reciprocating direction of the carriage, that is, the reciprocating direction of the print head 80 is referred to as “main scanning direction”. In this embodiment, the printing head 80 reciprocating once is referred to as “one main scanning”. The drive mechanism of the print head 80 further includes a circuit that supplies a drive signal to the print head 80. When a drive signal is supplied to the print head 80, ink droplets are ejected from the nozzle group 84k and the like (see FIG. 2) formed on the print head 80. In the present embodiment, a drive signal is supplied to the print head 80 so that ink droplets are ejected from the nozzle group 84k and the like during one outward main scanning path. Note that ink droplets are not ejected from the nozzle group 84k or the like during a single main scanning return pass. The print medium transport mechanism transports the print medium in a direction perpendicular to the main scanning direction. The direction in which the print medium is conveyed is referred to as “sub-scanning direction”. In another embodiment, a drive signal is supplied to the print head 80 such that ink droplets are ejected from the nozzle group 84k or the like during both the forward and backward passes of the print head 80 once. May be. In this case, out of one reciprocation of the print head 80, each of the forward path and the return path can be referred to as “one main scan”.

  As shown in FIG. 2, the print head 80 includes three sets of nozzle groups 84c, 84m, and 84y for ejecting ink droplets of three kinds of chromatic colors (cyan, magenta, and yellow), and black ink droplets. A nozzle surface 82 on which a set of nozzle groups 84k for discharging is formed is provided. The K nozzle group 84k includes n (n is an integer of 2 or more) K nozzles. The K nozzle group 84k forms six nozzle rows Lk1 to Lk6 extending in the sub-scanning direction. The n K nozzles in the K nozzle group 84k belong to one of the six nozzle rows Lk1 and the like. For example, the K nozzles Nk1, Nk7, etc. belong to the nozzle row Lk1, the K nozzle Nk4, etc. belong to the nozzle row Lk2, and the K nozzle Nk2, etc. belong to the nozzle row Lk3. Between two adjacent K nozzles belonging to one nozzle row (for example, the K nozzle Nk1 and the K nozzle Nk7 belonging to the nozzle row Lk1), the other five nozzle rows are arranged in the sub-scanning direction. Five nozzles for K (for example, NK2 to NK6) are located. In the present specification, “Nk1” is used as the reference number of the K nozzle existing in the most downstream side (upper side in FIG. 2) in the sub-scanning direction in the K-nozzle group 84k. The reference number of the nozzle for K increases (for example, Nk2, Nk3,...) Toward the upstream side (lower side in FIG. 2).

  The nozzle groups 84c corresponding to other colors have the same configuration as the K nozzle group 84k. Accordingly, a total of 4n nozzles are formed on the nozzle surface 82. Hereinafter, all the nozzles that eject ink droplets of four colors of CMYK are referred to as “4n nozzles”. Reference numbers are set for the nozzle groups 84c and the like of the other colors as in the case of the K nozzle group 84k. Since the four nozzle groups 84k and the like have the same configuration, the four nozzles corresponding to the four colors CMYK are arranged at the same position in the sub-scanning direction. For example, in the sub scanning direction, four nozzles Nk1, Nc1, Nm1, and Ny1 are arranged at the same position, and four nozzles Nk2, Nc2, Nm2, and Ny2 are arranged at the same position. In another embodiment, the printer 50 includes one K print head in which the K nozzle group 84k is formed and three kinds of chromatic color nozzle groups 84c, 84m, and 84y. And three chromatic color print heads.

  The storage unit 56 stores a characteristic data table 60 and a program 64. In FIG. 1, the color determination table 62 shown in the storage unit 56 is a necessary configuration in a second embodiment to be described later. In the present embodiment, the storage unit 56 may not store the color determination table 62. The program 64 includes a program for printing executed by the print execution unit 70. As shown in FIG. 3, in the characteristic data table 60, for each of the 4n nozzles formed in the print head 80, the nozzle number of the nozzle and the ejection amount of the ink droplet ejected from the nozzle are related. And the characteristic data to be registered are registered in association with each other. In the characteristic data table 60 of FIG. 3, the reference number of the nozzle (Nk1 in FIG. 2, etc.) is adopted as the nozzle number of the nozzle. For example, the characteristic data “Dk1” corresponding to the nozzle number Nk1 indicates characteristic data of the K nozzle Nk1 (see FIG. 2) for discharging a black ink droplet. Each characteristic data registered in the characteristic data table 60 is examined in advance by the vendor of the printer 50. Specifically, it is investigated by the following method.

  Although not shown, the print head 80 includes an actuator unit for ejecting ink droplets from 4n nozzles. The actuator unit includes 4n individual electrodes corresponding to 4n nozzles. When the drive signal is supplied to the individual electrode, one ink droplet is ejected from the nozzle corresponding to the individual electrode. The vendor of the printer 50 supplies one drive signal to each of the n individual electrodes corresponding to the n K nozzles belonging to the K nozzle group 84k. Note that the n drive signals supplied here are the same signal. When the n driving signals are supplied, n black ink droplets are ejected from the n K nozzles toward a predetermined medium. As a result, n black dots corresponding to n K nozzles are formed on the predetermined medium.

  The vendor measures the area of each of the n black dots. The vendor determines the area of the specific dot having the smallest area as “255” which is the maximum value of 256 gradations. Next, the vendor specifies the area of dots formed by other K nozzles based on the area of the specific dot having the smallest area. That is, another K nozzle is formed by multiplying the actual value of the area of the dots formed by the other K nozzles by the value obtained by dividing the actual value of the area of the specific dot having the smallest area by 255. Specify the area of dots to be printed. For this reason, the area of dots formed by other K nozzles is specified by a value of 255 or more. In this embodiment, the area of the dots formed by each K nozzle is determined as the characteristic data of the K nozzle (Dkz (where z is an integer from 1 to n)). As in the case of black, the vendor determines the characteristic data of each nozzle for each of the three chromatic colors (that is, cyan, magenta, and yellow). That is, the area of a specific chromatic color dot having the smallest area among the 3n chromatic color dots is determined to be “255”. Next, the vendor specifies the area of the dots formed by the other chromatic color nozzles based on the area of the specific dot having the smallest area. The 3n drive signals supplied to the 3n individual electrodes corresponding to the three groups of chromatic color nozzle groups 84c, 84m, and 84y are the same signal. As a result, 3n pieces of characteristic data corresponding to chromatic colors are obtained. Hereinafter, the three types of chromatic colors may be referred to as “CH (Chromatic color)” without being distinguished. For example, the characteristic data corresponding to one of the three chromatic colors is called “Dchz”, and the minimum characteristic data (minimum area) of the 3n characteristic data corresponding to the chromatic color is “Dchmin”. May be called. The vendor generates the characteristic data table 60 based on the above method, and stores the characteristic data table 60 in the storage unit 56. The printer 50 has already stored the characteristic data table 60 at the shipping stage.

(About printing executed by the print execution unit)
Next, an operation when the print execution unit 70 of the printer 50 executes printing will be described. The image processing unit 32 (see FIG. 1) of the PC 10 generates binary data by executing binary data generation processing (see FIG. 5) described later. The supply unit 48 (see FIG. 1) of the PC 10 transmits the binary data generated by the image processing unit 32 to the printer 50. When the binary data is supplied, the print execution unit 70 of the printer 50 executes printing according to the binary data.

  Pk1, Pk2, etc. shown in FIG. 4 project the K nozzles Nk1, Nk2, etc. constituting the K nozzle group 84k in the main scanning direction when the projection line PL extending along the sub-scanning direction is set. The projection point obtained by this is shown. The print execution unit 70 ejects ink droplets from the K nozzles Nk1 and the like based on the binary data during one main scan of the print head 80. As a result, for example, a plurality of black dots arranged along the main scanning direction are formed on the print medium by the plurality of black ink droplets ejected from the K nozzle Nk1. Similarly, a plurality of black dots arranged in the main scanning direction are formed on the print medium by the plurality of black ink droplets ejected from the K nozzle Nk2. In the case of monochrome printing, the arrangement of a plurality of black dots formed by one K nozzle in one main scan of the print head 80 is referred to as “one raster”. . Therefore, each raster extends along the main scanning direction. In the case of monochrome printing, in one main scan of the print head 80, for example, seven K nozzles Nk1 to Nk7 form seven rasters R1 to R7.

  As described above, for example, the nozzle Nk1, the nozzle Nc1, the nozzle Nm1, and the nozzle Ny1 are arranged at the same position in the sub-scanning direction (see FIG. 2). Therefore, in the case of color printing, in one main scan of the print head 80, the four nozzles Nk1, Nc1, Nm1, and Ny1 form dots at the same position in the sub-scanning direction. Therefore, in the case of color printing, in one main scan of the print head 80, the arrangement of a plurality of CMYK dots formed by the four nozzles Nk1, Nc1, Nm1, and Ny1 is referred to as “one line”. This is called “raster”. In the first main scan of the print head 80, n rasters arranged in the sub-scanning direction are formed. When the first main scan of the print head 80 is completed, the print execution unit 70 executes conveyance of the print medium. A specific distance is adopted as the transport distance here. The specific distance is a distance corresponding to n nozzle pitches. One nozzle pitch is a distance between two adjacent nozzles (for example, Nk1 and Nk2) in the sub-scanning direction. That is, one nozzle pitch is a distance between two adjacent projection points (for example, Pk1 and Pk2). Next, the print execution unit 70 executes the second main scan of the print head 80. As a result, n rasters are newly formed. The print execution unit 70 repeatedly executes a combination of conveyance of a specific distance of the print medium and main scanning of the print head 80. As a result, the image represented by the binary data is printed on the print medium.

(Binary data generation processing of PC10)
Next, processing executed by the control unit 30 of the PC 10 will be described. The user can select desired data and apply an operation for printing an image represented by the data to the operation unit 12. In the present embodiment, processing contents will be described on the assumption that image data in RGB bitmap format (hereinafter referred to as “RGB image data”) is selected by the user. When data in another format (for example, text data, image data in a bitmap format other than RGB, composite data of text and bitmap, etc.) is selected, the control unit 30 selects the data selected by the user. Is converted into RGB image data using a known method. When the above operation is executed, the control unit 30 executes the binary data generation process of FIG. 5 according to the printer driver 24.

  The image processing unit 32 acquires RGB image data and stores the RGB image data in the work area 22 (S10). Next, the control unit 30 transmits a predetermined command for acquiring the characteristic data table 60 stored in the printer 50 to the printer 50. The printer 50 transmits the characteristic data table 60 stored in the storage unit 56 to the PC 10 in accordance with the predetermined command. As a result, the control unit 30 acquires the characteristic data table 60 (S12). The control unit 30 stores the characteristic data table 60 in the work area 22.

  Next, the image processing unit 32 generates converted RGB image data by executing resolution conversion processing on the RGB image data using a known method (S14). The converted RGB image data 200 shown in FIG. 6 is obtained by the resolution conversion process. Each pixel 201, 202, 206, 207, etc. in the converted RGB image data 200 has an R value (for example, R (i, j)), a G value (for example, G (i, j)), and a B value (for example, B (i, j)). Each of the R value, the G value, and the B value is multi-value data of 256 gradations (0 to 255). In addition, the x coordinate of the coordinates shown in each pixel in the converted RGB image data 200 indicates the column number of each pixel, and the y coordinate indicates the row number of each pixel.

  Next, the color conversion processing unit 34 (see FIG. 1) executes color conversion processing using a known method (S16). In S16, the color conversion processing unit 34 converts the converted RGB image data 200 into CMYK bitmap image data (hereinafter referred to as “CMYK image data”). By the color conversion process, CMYK image data 210 shown in FIG. 7 is obtained. One pixel (for example, the pixel 211) described in the CMYK format is obtained from one pixel (for example, the pixel 201) in the converted RGB image data 200. Therefore, the number of pixels of the CMYK image data 210 is equal to the number of pixels of the converted RGB image data 200. Each pixel 211, 212, 216, 217, etc. in the CMYK image data 210 has a C value (for example, C (i, j)), an M value (for example, M (i, j)), and a Y value (for example, Y ( i, j)) and a K value (for example, K (i, j)). The C value, M value, Y value, and K value are multi-value data of 256 gradations (0 to 255), respectively. Further, the x coordinate of the coordinates shown in each pixel in the CMYK image data 210 indicates the column number of each pixel, and the y coordinate indicates the row number of each pixel.

  Subsequently, the halftone processing unit 40 and the like (see FIG. 1) execute halftone processing using the CMYK image data 210. The halftone process includes the processes of S18 to S40. First, the correction unit 42 (see FIG. 1) specifies one pixel in the CMYK image data 210 (S18). The specific order of the pixels in S18 is determined in advance. More specifically, in the first process of S18, the correction unit 42 includes one pixel belonging to the leftmost column among the plurality of pixels belonging to the uppermost row in FIG. Identify the pixels. In the process of S18 after the second time, the correction unit 42 is one pixel belonging to the same row as the pixel specified last time (hereinafter referred to as “previous specific pixel”), and is adjacent to the right of the previous specific pixel. One pixel belonging to this column is specified. When the previous specific pixel belongs to the rightmost column, the correction unit 42 selects one pixel belonging to the leftmost column among a plurality of pixels belonging to the row immediately below the row to which the previous specific pixel belongs. Identify the pixels.

  Hereinafter, one pixel specified in S18 is referred to as a “target pixel”. The correction unit 42 identifies one value (for example, K value) from the four CMYK values that constitute the pixel of interest (S20). Hereinafter, one value specified in S20 is referred to as “PV (Pixel Value)”. Subsequently, the correcting unit 42 corrects the PV specified in S20 (S22). More specifically, the correcting unit 42 calculates a plurality of neighboring pixels calculated in the vicinity of the target pixel from among the processed pixel group in which the processes of S20 to S36 have been completed before the target pixel. The PV of the target pixel is corrected using the individual error values. For example, when the target pixel is the pixel 216 in FIG. 8, the processes in S20 to S36 for the pixels 211 to 215 are completed. Therefore, for each of the pixels 211 to 215, four error values corresponding to CMYK have been calculated in S34 described later. For example, for the pixel 211, an error value corresponding to C, an error value corresponding to M, an error value corresponding to Y, and an error value corresponding to K have been calculated. In FIG. 8, for convenience of illustration, four error values corresponding to four colors of CMYK are expressed by “ΔE” without being distinguished. Hereinafter, for example, an error value corresponding to K may be expressed as “ΔEk”, and an error value corresponding to C may be expressed as “ΔEc”. In this embodiment, the four pixels 211, 212, 213, and 215 located on the upper left, upper, upper right, and left of the target pixel 216 are used as the neighboring pixels of the target pixel 216. In another embodiment, as the neighboring pixel of the target pixel 216, the pixel on the left of the pixel 211, the pixel on the pixel 212, the pixel 214 on the left of the pixel 215, and the like may be employed.

  The correction unit 42 calculates four error values ΔE (i−1, j−1) that have been calculated for one neighboring pixel 211 out of the four neighboring pixels 211, 212, 213, and 215 of the target pixel 216. One error value (for example, an error value ΔEk (i−1, j−1) corresponding to K) corresponding to the current PV color (for example, K) is specified from the inside. For each of the other three neighboring pixels 212, 213, and 215, one error corresponding to the current PV color to be corrected is selected from the four error values calculated for the neighboring pixels. As a result, four error values corresponding to the current PV color to be corrected are specified, and then the correction unit 42 uses the specified four error values as shown in FIG. The PV of the pixel of interest 216 is corrected according to the formula shown in the pixel 216 of As a result, the corrected value PV ′ is calculated, and s1, s2, s3, and s4 in the formula are determined in advance according to the positional relationship between the target pixel 216 and each neighboring pixel. For example, when PV (i, j) of the pixel of interest 216 is a K value (K (i, j)), the correction unit 42 has four neighboring pixels 211, 212, 213, and 215. , An error value ΔEk of the neighboring pixel (for example, ΔEk (i−1, j−1) of the neighboring pixel 211) and a coefficient corresponding to the neighboring pixel (for example, s1 corresponding to the neighboring pixel 211). Then, the correction unit 42 calculates the multiplication value by multiplying the K value (i, j) (ie, PV (i, j)) of the pixel of interest 216 and the four neighboring pixels 211, 212, and 213. , 215 and four multiplication values calculated for 215 , The corrected value K ′ (i, j) (ie, PV ′ (i, j)) is calculated.

  Subsequently, the determination unit 44 (see FIG. 1) determines that the corrected value PV ′ (for example, K ′ (i, j)) obtained in S22 is larger than a predetermined threshold Th (for example, 128). It is determined whether or not (S24). In the case of YES here, the determination unit 44 determines to form a dot of a color corresponding to the corrected value PV ′ to be determined on the print medium. Next, the determination unit 44 stores the value of the new pixel at the same position as the target pixel in the work area 22 (S26). The value stored here is the dot output value “1” of the color corresponding to the corrected value PV ′. For example, when the corrected value PV ′ of the target pixel 216 is K ′ (i, j), in S26, the determination unit 44 sets “K = 1” as the value of the new pixel at the same position as the target pixel. Is stored in the work area 22. When binary data including such information is supplied to the printer 50, black ink droplets are ejected toward the position on the print medium corresponding to the target pixel 216. That is, black dots are formed at positions on the print medium corresponding to the target pixel 216. When S26 ends, the process proceeds to S30.

  On the other hand, in the case of NO in S24, the determination unit 44 determines not to form a dot of a color corresponding to the corrected value PV ′ to be determined on the print medium. Next, the determination unit 44 stores the value of the new pixel at the same position as the target pixel in the work area 22 (S28). The value stored here is the dot output value “0” of the color corresponding to the corrected value PV ′. For example, when the corrected value PV ′ of the target pixel 216 is K ′ (i, j), in S28, the determination unit 44 sets “K = 0 as the value of the new pixel at the same position as the target pixel. Is stored in the work area 22. When binary data including such information is supplied to the printer 50, black ink droplets are not ejected toward the position on the print medium corresponding to the target pixel 216. That is, no black dot is formed at a position on the print medium corresponding to the target pixel 216. When S28 ends, S30 to S33 are skipped and the process proceeds to S34.

  For example, when the C value is specified as PV in S20, in S26, coordinates as a value of a new pixel at the same position as the target pixel and “C = 1” are stored in association with each other. In S28, “C = 0” is stored as the value of the new pixel at the same position as the target pixel. In the former case, cyan dots are formed at positions on the print medium corresponding to the target pixel, and in the latter case, cyan dots are not formed at positions on the print medium corresponding to the target pixel. When the M value or the Y value is specified in S20, the process is executed in the same manner as when the K value or the C value is specified in S20.

  In S30, the halftone processing unit 40 forms a nozzle (for example, “target nozzle” in the following) that forms a dot (for example, K) corresponding to PV ′ at a position on the print medium corresponding to the target pixel (for example, the pixel 216). Nozzle number (hereinafter referred to as “target nozzle number”). For example, when the color corresponding to PV ′ is K, the K nozzle is specified as the target nozzle. For example, when the color corresponding to PV ′ is any one of CMY, the CH nozzle is specified as the target nozzle. In the following, when the K nozzle is to be specified as the target nozzle, it is referred to as a “target K nozzle”, and when the CH nozzle is to be specified as the target nozzle, “the target CH nozzle (for example, the target C nozzle) Nozzle, attention Y nozzle, attention M nozzle) ”. Next, a method for specifying the attention K nozzle number will be described in detail.

  As described above, the print execution unit 70 executes printing as shown in FIG. In the first main scan, the K nozzles Nk1 to Nkn form rasters corresponding to the 1st to nth rows of the CMYK image data 210. Furthermore, the conveyance distance of the print medium (the above specific distance) is a distance corresponding to n nozzle pitches. Based on these contents, it is possible to identify the target K nozzle that forms a raster corresponding to the Lth row of the CMYK image data 210. In the printer driver 24 (see FIG. 1), a K nozzle number table for specifying a noticeable K nozzle number from the row number of each pixel of the CMYK image data 210 is registered in advance. The halftone processing unit 40 identifies the target K nozzle number based on the row number of the target pixel in the CMYK image data 210 and the K nozzle number table.

  In the printer driver 24, a nozzle number table similar to the K nozzle number table is registered in advance for each of the three types of chromatic colors CMY. When the color corresponding to the PV specified in S20 is one of the three chromatic colors CMY, the halftone processing unit 40 specifies the target nozzle number as in the case of K described above. For example, when the color corresponding to the PV specified in S20 is C, the halftone processing unit 40 specifies the target C nozzle number using the C nozzle number table.

  When S30 ends, the halftone processing unit 40 determines whether or not the color corresponding to the value PV specified in S20 is black (that is, K) (S31). If YES in S31, the process proceeds to S32. If NO in S31, the process proceeds to S33. In the following, the case where the value PV specified in S20 is one of the three chromatic colors (ie, CMY) (ie, NO in S31) will be described first, and then the case where it is black (ie, YES in S31). ).

  When the value PV specified in S20 is a chromatic color (for example, C), the correction data calculation unit 38 calculates correction data for C in S33. Specifically, first, the data acquisition unit 36 obtains characteristic data corresponding to the target C nozzle number specified in S30 from the characteristic data table 60 stored in the work area 22 in S12 (hereinafter referred to as “target C use”). Characteristic data Dcz "). The data acquisition unit 36 further acquires characteristic data indicating the minimum value (hereinafter referred to as “minimum CH characteristic data Dchmin”) from the three types of chromatic color characteristic data in the characteristic data table 60. To do. Next, the correction data calculation unit 38 calculates C correction data (hereinafter referred to as “attention C correction data”). Specifically, the correction data calculation unit 38 multiplies 255 by the value obtained by dividing the acquired attention C characteristic data Dcz by the minimum CH characteristic data Dchmin, thereby correcting the attention C correction. Data is calculated. Similarly, when the value PV specified in S20 is a value corresponding to M and Y, the correction data calculation unit 38 uses the attention CH characteristic data Dchz and the minimum CH characteristic data Dchmin. The correction data for attention CH is calculated. In this embodiment, since Dchmin is 255, the target CH correction data has the same value as Dchz. As is clear from the above description, the same minimum CH characteristic data Dchmin is used when calculating any of the CMY correction data. For example, when Dchmin is characteristic data corresponding to a specific C nozzle, not only the target C correction data but also the target M correction data and the target Y correction data are used for the specific C It is calculated using Dchmin corresponding to the nozzle. In the present embodiment, for example, the attention C correction data (or attention M correction data and attention Y correction data) for each pixel in the j-th row have the same value.

  In S32, correction data for K is specified. In S32, the data acquisition unit 36 (see FIG. 1) obtains characteristic data corresponding to the target K nozzle number specified in S30 from the characteristic data table 60 stored in the work area 22 in S12 (hereinafter referred to as “target K”). (Referred to as “use characteristic data Dkz”). Next, the data acquisition unit 36 acquires characteristic data indicating the minimum value among the K characteristic data (hereinafter referred to as “minimum K characteristic data Dkmin”). The correction data calculation unit 38 (see FIG. 1) calculates the attention K correction data by dividing the acquired attention K characteristic data Dkz by the minimum K characteristic data Dkmin and multiplying by 255. . In this embodiment, since Dkmin is 255, the attention K correction data has the same value as Dkz. That is, the correction data calculation unit 38 calculates the attention K correction data without using the minimum CH characteristic data Dchmin. In this embodiment, for example, the correction data for attention K for each pixel in the j-th row has the same value.

  When S32 or S33 ends, the process proceeds to S34. Further, when S28 is executed, S30 to S33 are skipped and the process proceeds to S34. In S34, the error value calculation unit 46 (see FIG. 1) calculates an error value. The process of S34 changes according to the determination result of S24. First, the process of S34 when YES is determined in S24 (when S26 is executed) will be described. The error value calculation unit 46 subtracts the attention correction data (attention K correction data or attention CH correction data) obtained at S32 or S33 from the corrected value PV ′ obtained at S22. To calculate the error value ΔE. For example, a formula for calculating the error value using the attention CH correction data obtained in S33 is shown in the pixel 216 of FIG. That is, when the pixel of interest is the pixel 216 in FIG. 9 and PV ′ (i, j) obtained in S22 is larger than the threshold Th (in the case of YES in S24), the error value calculation unit 46 calculates PV ′ ( The error value ΔE (i, j) corresponding to the pixel 216 is calculated by subtracting the target CH correction data from i, j). For example, when the color corresponding to the PV specified in S20 is K, the correction data for attention K is subtracted from the corrected value PV ′ obtained in S22, so that the pixel 216 is corrected. An error value corresponding to K is calculated. Similarly, when the color corresponding to PV specified in S20 is another color, an error value corresponding to the other color of the pixels 216 is calculated.

  Next, the process of S34 when NO is determined in S24 (when S28 is executed) will be described. In the case of NO in S24, the error value calculation unit 46 specifies the corrected value PV ′ obtained in S22 as an error value. An equation for calculating the error value in this way is shown in the pixel 217 of FIG. That is, when the target pixel is the pixel 217 in FIG. 9 and PV ′ (i + 1, j) obtained in S22 is smaller than the threshold Th (NO in S24), the error value calculation unit 46 displays the error value in FIG. An error value ΔE (i + 1, j) corresponding to the pixel 217 is specified using an expression in the pixel 217. That is, the error value calculation unit 46 calculates the error value using the corrected pixel value PV ′ without using the attention correction data.

  When S34 ends, the error value calculation unit 46 stores an error value (for example, ΔE (i, j)) corresponding to the target pixel in the work area 22 (S36). The error value stored here is used in the process of S22 to be executed later. For example, when the error value ΔE (i, j) corresponding to K of the pixel 216 is stored in S36, the error value ΔE (i, j) is K ′ corresponding to the K value of the pixel 217 in S22. Used when (i, j) is calculated.

  As described above, when the dot output value = 1 and the correction data for attention K is calculated in S32, the error value ΔE is calculated by the following equation: ΔE = PV′−correction data for attention K. To do. The attention K correction data is obtained by 255 × (Dkz / Dkmin). Accordingly, when the target K nozzle is the K nozzle having the minimum discharge amount in the K nozzle group 84k, Dkz / Dkmin is “1” and the target K correction data is “255”. become. In other words, when the noticeable K nozzle is the K nozzle with the minimum discharge amount, ΔE = PV′−255. This means that the density of dots formed by the K nozzle having the minimum discharge amount is assumed to be “255”. That is, using “255 × (Dkz / Dkmin)” (that is, a value of 256 gradations with Dkmin as a reference) as correction data for attention K means that the density of dots formed by the nozzle for attention K is determined. It means that “255 × (Dkz / Dkmin)” is assumed. In S34, the difference between the target pixel value PV 'to be actually expressed and the assumed dot density “255 × (Dkz / Dkmin)” is calculated as the error value ΔE. This difference is diffused to neighboring pixels in the process of S22.

  In S34 when the dot output value = 1 and the correction data for attention CH is calculated in S33, the attention characteristic data Dchz is used to calculate ΔE = PV′−correction data for attention CH. An error value ΔE is calculated. Here, the target CH correction data is obtained by 255 × (Dchz / Dchmin). That is, the correction data for the attention CH is 3n pieces of nozzles having the smallest discharge amount among the 3n nozzles corresponding to the three kinds of chromatic colors (Dchmin = Dymin in this embodiment). The density of each dot formed by the nozzle is expressed. Here, when the noticed CH characteristic data Dchz is equal to Dchmin, the equation is ΔE = PV′−255. This means that the density of dots formed by the nozzle having the smallest discharge amount among the 3n nozzles is assumed to be “255”. That is, using the above-mentioned “255 × Dchz / Dchmin” as the correction data for the target CH means that the density of the dots formed by the target CH nozzle is assumed to be “255 × Dchz / Dchmin”. means. In S34, the difference between the target pixel value PV 'to be actually expressed and the assumed dot density is calculated as the error value ΔE. This difference is diffused to neighboring pixels in the process of S22. In S34 when the dot output value = 0, the error value ΔE is calculated by the equation ΔE = PV ′. That is, the difference between the target pixel value PV ′ to be actually expressed and the density “0” when no dot is formed is calculated as the error value ΔE. This difference is diffused to neighboring pixels in the process of S22.

  Subsequently, whether or not the halftone processing unit 40 has performed the processing of S20 to S36 for all four CMYK pixel values (C value, M value, Y value, and K value) constituting the target pixel. Is determined (S38). In the case of NO here, the halftone processing unit 40 returns to S20 and specifies a value for which the processing of S20 to S36 has not been executed from among the four values of CMYK constituting the target pixel. In the case of YES in S38, the halftone processing unit 40 determines whether or not the processing of S18 to S38 has been completed for all the pixels constituting the CMYK image data 210 (S40). In the case of NO here, the halftone processing unit 40 returns to S18 and specifies the next pixel of the current pixel of interest (basically the pixel on the right) as the new pixel of interest. If YES in S40, the binary data generation process ends.

  As is apparent from the above description, in the binary data generation process, C = 0 or 1, M = 0 or 1, Y = 0 or 1, from one pixel constituting the CMYK image data 210, A new pixel composed of K = 0 or 1 is generated. Accordingly, the number of pixels of the binary data is equal to the number of pixels of the CMYK image data 210. The supply unit 48 (see FIG. 1) transmits binary data to the printer 50. As a result, the print execution unit 70 of the printer 50 executes print processing according to the binary data. That is, the print execution unit 70 corresponds to the K nozzle that forms the dot so that the black dot is formed at the position on the print medium corresponding to the pixel indicating K = 1 included in the binary data. Drive signals are supplied to the individual electrodes. Similarly, the print execution unit 70 supplies a drive signal so that dots of other colors are formed according to the binary data. As a result, an image represented by the RGB image data acquired in S10 of FIG. 5 (ie, an image represented by the converted RGB image data 200 obtained in S14, an image represented by the CMYK image data 210 obtained in S16, two An image represented by the value data) is formed on the print medium.

  This example has been described in detail. In this embodiment, when calculating the target correction data for three types of chromatic colors (S33 in FIG. 5), the control unit 30 determines the smallest of the 3n pieces of characteristic data corresponding to the three types of chromatic colors. Using the characteristic data, attention correction data for chromatic colors is calculated. That is, in S33 of FIG. 5, the control unit 30 sets the target characteristic data based on the discharge amount of the nozzle having the smallest ink droplet discharge amount among the 3n nozzles corresponding to the three chromatic colors. To correct. Thereby, the control unit 30 uses the attention correction data based on the discharge amount of the nozzle having the smallest ink droplet discharge amount among the 3n nozzles to perform compensation processing for compensating for the variation in the discharge amount. Can be executed. As a result, binary data is generated in accordance with the discharge amount of the nozzle having the smallest ink droplet discharge amount among the 3n nozzles. Therefore, the print execution unit 70 of the printer 50 can print an image in which the balance of the three kinds of chromatic colors is appropriately maintained on the print medium.

  For example, when the minimum CH characteristic data Dchmin is smaller than the minimum K characteristic data Dkmin for the K nozzle, the black density decreases when the K attention correction data is calculated using the minimum discharge amount data Dchmin. . In the present embodiment, when the correction data for attention K is calculated (S32 in FIG. 5), the correction data calculation unit 38 does not use the minimum discharge amount data Dchmin corresponding to the three types of chromatic colors. Thereby, the possibility that the density of black may be reduced can be eliminated.

  The correspondence between each element of the present embodiment and each element of the present invention will be described. The control unit 30 of the PC 10 is an example of a “control device”. The converted RGB image data 200, the CMYK image data 210, and the binary data generated in FIG. 5 are examples of “specific image data”, “target image data”, and “processed image data”, respectively. Further, the color conversion process and the halftone process are examples of “image processing”, and the error value calculation process executed when dot output = 1 in S34 of FIG. 5 is an example of “specific process”. Dchmin (= Dymin) is an example of “reference data”.

(Second embodiment)
Differences from the first embodiment will be described. The storage unit 56 of the printer 50 further stores a color determination table 62. In the color determination table 62, the value range of the color is registered for three types of colors (R, G, B). The color value range is set to a predetermined range including gray. In the present embodiment, as a range of color values, a difference value range between the maximum value of the three types of color values and the minimum value of the three types of color values (for example, the difference value is a predetermined value (for example, 10 ) Or less) is set. That is, when the difference between the minimum value and the maximum value of the R value, the G value, and the B value is within the range of the color value in one pixel, the color of the pixel is in a predetermined range including gray. It can be said that this is the value shown. In a binary data generation process described later, a difference between the maximum value and the minimum value of three values (that is, R value, G value, B value) among a plurality of pixels in the converted RGB image data 200 is calculated. Compensation processing that compensates for variations in the ejection amount is performed on pixels within the color value range described above. The vendor stores the color determination table 62 in the printer 50 in advance. In the present embodiment, the contents of the binary data generation process executed by the control unit 30 of the PC 10 are different from those in the first embodiment. The contents of the binary data generation process of this embodiment will be described with reference to FIG. S10 is the same as that of the first embodiment. In S <b> 12, the data acquisition unit 36 acquires the color determination table 62 in addition to the characteristic data table 60. S14 is the same as that of the first embodiment. Next, the determination unit 47 (see FIG. 1) specifies a pixel corresponding to a value indicating a color within a predetermined range including gray from a plurality of pixels in the converted RGB image data 200 (S15). . Specifically, the determination unit 47 sequentially specifies a plurality of pixels in the converted RGB image data 200 in the same order as in S18 of FIG. Next, the determination unit 47 determines whether each of the RGB values of the specified pixel is within the range registered in the color determination table 62. When it is determined that all the RGB values are within the above range, the determination unit 47 specifies information for specifying the pixel (for example, the row number and column number of each pixel; hereinafter, “specific information”) Is stored in the work area 22. The determination unit 47 performs the above determination process for all the pixels in the converted RGB image data 200. As a result, the work area 22 stores the specific information for specifying a pixel group indicating a color within a predetermined range including gray.

  In S16, CMYK image data is generated using the same method as in S16 of FIG. When S16 ends, the color conversion processing unit 34 performs a correction process for generating corrected image data 250 (see FIG. 11) from the CMYK image data 210 (see FIG. 7). The correction process includes the processes of S50 to S68. The color conversion processing unit 34 identifies one pixel (hereinafter referred to as “target pixel”) from the CMYK image data 210 (S50). The color conversion processing unit 34 identifies the target pixel in the same order as S18 in FIG. Hereinafter, the description will be continued by taking the case where the pixel 216 is the target pixel as an example. The color conversion processing unit 34 determines whether or not the specific information for specifying the target pixel 216 specified in S50 is stored in the work area 22 (S52). If YES here, the process proceeds to S54, and if NO, the process proceeds to S68. In S <b> 54, the color conversion processing unit 34 specifies one value PV (i, j) from the four values of CMYK constituting the target pixel 216. Next, the color conversion processing unit 34 performs the process of S56 for specifying the nozzle number of interest using the same method as in S30 of FIG. Next, the color conversion processing unit 34 determines whether or not the value PV specified in S54 corresponds to K (S58). If YES in S58, the correction data calculation unit 38 calculates attention K correction data (S60). In S60, the data acquisition unit 36 obtains the target K characteristic data Dkz corresponding to the target nozzle number (ie, the target K nozzle number) specified in S56 from the characteristic data table 60 stored in the work area 22 in S12. get. Further, the data acquisition unit 36 acquires the minimum K characteristic data Dkmin from the K characteristic data group from the characteristic data table 60 stored in the work area 22 in S12. Next, the correction data calculation unit 38 calculates the attention K correction data CDk by calculating Dkmin / Dkz. In this embodiment, for example, the target K correction data CDk for each pixel in the j-th row has the same value.

  On the other hand, in S62, the correction data calculation unit 38 calculates the target CH correction data. In S62, the data acquisition unit 36 obtains the target CH characteristic data Dchz corresponding to the target nozzle number (ie, the target CH nozzle number) specified in S56 from the characteristic data table 60 stored in the work area 22 in S12. get. The data acquisition unit 36 further acquires the minimum CH characteristic data Dchmin from the characteristic data table 60 stored in the work area 22 in S12. Next, the correction data calculation unit 38 calculates the target CH correction data CDch by dividing the minimum CH characteristic data Dchmin by the target CH characteristic data Dchz. In this embodiment, for example, the target C correction data CDc, the target M correction data CDm, and the target Y correction data CDy for each pixel in the j-th row have the same value.

  When S60 or S62 ends, the process proceeds to S64. In S <b> 64, the color conversion processing unit 34 calculates the corrected value PV ″ (i, j) by multiplying PV (i, j) by the target correction data CD (j). S66 and S68 are the same as S38 and S40 of FIG. The color conversion processing unit 34 calculates a corrected value PV ″ (i, j) for each of the four values CMYK constituting the target pixel 216. As a result, based on the target pixel 216, corrected pixels having four corrected values corresponding to the four colors of CMYK are generated. Similarly, the color conversion processing unit 34 generates corrected pixels for each pixel other than the pixel 216. Thereby, the corrected image data 250 shown in FIG. 11 is obtained. In the corrected image data 250, pixels belonging to the upper row are not included in the pixel group indicating colors within a predetermined range including gray, and pixels belonging to the lower row are included within the predetermined range including gray. It is included in the pixel group indicating the color of. For this reason, the corrected value PV ″ (i, j) is not calculated for the pixels belonging to the upper row, and the corrected value PV ″ (i, j) is applied only to the pixels belonging to the lower row. ) Is calculated. As described above, the color conversion processing unit 34 generates the corrected image data 250 from the CMYK image data 210 by executing the above correction processing in the CMYK color space.

  The halftone processing unit 40 performs halftone processing on the corrected image data 250 (S70). The halftone process of this embodiment is different from the halftone process (S18 to S40) of FIG. 5 in the following points. In S18, the target pixel in the corrected image data 250 is specified, and in S20, one value (for example, the corrected value PV ″) is specified from the four values constituting the target pixel. . In S22, PV ′ is calculated by adding an error value (ie, Σs · ΔE) to the value specified in S20. The processes of S30 to S33 shown in FIG. 5 are not executed. Further, in S34, when the dot output = 1, the error value ΔE is calculated by subtracting the fixed value 255 from PV ′. Other processes are the same as those in the first embodiment.

  The second embodiment has been described in detail. In this embodiment, when the pixel value in the converted RGB image data 200 is within a specific range including gray (achromatic color), the correction process is executed using the attention correction data. When gray is printed on a print medium, a color with a large discharge amount (for example, C) becomes conspicuous if the CMY balance is not appropriate. In other words, gray is tinted (for example, C). In this embodiment, the CMY balance can be made appropriate by executing the correction process using the target correction data. Thereby, gray can be expressed correctly. The correspondence between each element of the present embodiment and each element of the present invention will be described. The converted RGB image data 200 generated in S14 of FIG. 10 is an example of “specific image data” and “target image data”. The corrected image data 250 is an example of “color converted image data”. Each pixel in the CMYK image data 210 generated in S16 in FIG. 10 is an example of “color-converted pixel”, and each pixel in the corrected image data 250 generated in the correction process in FIG. It is an example of “completed pixels”. The color conversion process, the correction process, and the halftone process are examples of “image processing”, and the color conversion process and the correction process are examples of “specific process”.

(Third embodiment)
In each of the above embodiments, the characteristic data table 60 (see FIG. 3) is stored in the storage unit 56 of the printer 50. In this embodiment, the storage unit 56 of the printer 50 stores a correction data table instead of the characteristic data table 60. In the correction data table, attention correction data to be used when each of the 4n nozzles is the target nozzle is registered. That is, the vendor of the printer 50 executes, for each of 4n nozzles in advance, the attention correction data to be used when the nozzle is the attention nozzle, for example, the calculation executed in S62 of FIG. To calculate. Thereby, a correction data table is obtained. The vendor stores the correction data table in the storage unit 56 of the printer 50.

  In the present embodiment, the control unit 30 of the PC 10 acquires a correction data table from the printer 50 in S12 of FIG. The halftone processing unit 40 does not execute S60 and S62 of FIG. That is, regardless of whether the color value PV identified in S54 corresponds to K or any of the three chromatic colors, the data acquisition unit 36 performs correction in S64 of FIG. Attention correction data corresponding to the attention nozzle number is acquired from the data table. Other processes are the same as in the second embodiment. According to this configuration, the control unit 30 of the PC 10 does not have to calculate correction data.

Modifications of the above embodiments are listed below.
(Modification)
(1) In the above-described embodiment, the control unit 30 of the PC 10 includes the image processing unit 32 and the supply unit 48. Instead, the printer 50 includes the image processing unit 32 and the supply unit 48. May be. In this case, the printer is an example of a “control device”.

(2) In the embodiment described above, the PC 10 acquires the characteristic data table 60 from the printer 50 after receiving a print instruction from the user. However, the PC 10 may acquire the characteristic data table 60 from the printer 50 at the timing when the printer driver 24 is installed in the PC 10 and hold the characteristic data table 60 and the like. The PC 10 may acquire necessary characteristic data from the printer 50 each time the processes of S32 and S33 in FIG. 5 and S15, S60, and S62 in FIG.

(3) In the above-described embodiment, the halftone processing unit 40 generates binary data indicating dot output = 1 and dot output = 0. However, the halftone processing unit 42 may generate ternary or higher data. For example, the halftone processing unit 40 has a value “3” corresponding to a large dot, a value “2” corresponding to a medium dot, a value “1” corresponding to a small dot, and “0” corresponding to no dot. Further, quaternary data indicating the above may be generated. In this case, the halftone processing unit 42 uses a threshold Th1 (for example, 191) for distinguishing large dots and medium dots as a threshold used in S24 of FIG. You may utilize threshold value Th2 (for example, 127) and threshold value Th3 (for example, 63) for classifying a small dot and no dot. In this example, the halftone processing unit 40 may change the attention correction data calculated in S32 or S33 of FIG. 5 according to the dot size to be formed. For example, when a medium dot is formed, the halftone processing unit 40 (value obtained in S32 or S33 in FIG. 5 of the first embodiment) × (density to be expressed by a medium dot) / (large When the density to be expressed by dots (for example, 255) is specified as the attention correction data and a small dot is formed, (value obtained in S32 or S33) × (density to be expressed by a small dot) ) / (Density to be expressed by large dots (for example, 255)) may be specified as the attention correction data.

(4) In the above-described embodiment, the target pixel and the error value calculated in S34 are stored in association with each other in S36 of FIG. In S <b> 22 of FIG. 5, the correction unit 43 calculates PV ′ by collecting the error values stored in S <b> 36 (error values corresponding to pixels near the target pixel). Instead of this configuration, the correction unit 43 may assign the error value calculated in S34 of FIG. 5 to each unprocessed pixel near the target pixel in S36. For example, when the error value ΔEk (i, j) corresponding to K of the pixel 216 in FIG. 8 is calculated, the correction unit 43 determines that K (i + 1, j) which is the K value of the unprocessed pixel 217 in S36. ) And a value obtained by multiplying the error value ΔEk and the coefficient s, a new K value of the pixel 217 may be calculated. When this configuration is adopted, the PV specified in S20 of FIG. 5 is equal to PV ′, and the process of S22 of FIG. 5 is not executed.

(5) In the second embodiment, the halftone processing unit 40 performs the halftone process using the error diffusion method. Instead, the halftone process is performed using the dither method. May be executed.

(6) In the first embodiment, the attention K correction data is calculated by calculating 255 × Dkz / Dkmin using the attention K characteristic data Dkz and the minimum K characteristic data Dkmin. Calculated. This means that “255 (the maximum value that can be taken by the K value of the pixel in the CMYK image data 210)” is adopted as the density value of the dot formed by the nozzle with the minimum ejection amount. Instead of this configuration, Dkz / Dkmin may be multiplied by a numerical value other than “255” in order to calculate correction data for attention K. Similarly, the target CH correction data is calculated by calculating 255 × Dchz / Dchmin using the target CH characteristic data Dchz and the minimum CH characteristic data Dchmin. This also means that “255 (the maximum value that can be taken by the CH value of the pixel in the CMYK image data 210)” is adopted as the density value of the dot formed by the CH nozzle having the minimum discharge amount. Instead of this configuration, Dchz / Dchmin may be multiplied by a numerical value other than “255” in order to calculate the correction data for the attention channel.

(7) In the above-described embodiment, the correction data calculation unit 38 calculates correction data using the target characteristic data of the target nozzle. However, the correction data calculation unit 38 may calculate the correction data using the target nozzle characteristic data and the specific nozzle characteristic data. The specific nozzle is a nozzle that forms a raster adjacent to a raster including dots formed by the nozzle of interest (hereinafter referred to as “target raster”). For example, in FIG. 4, when the target K nozzle is the nozzle Nk4 (when the target raster is R4), the specific nozzles are the nozzles Nk2, Nk3, Nk5 that form the rasters R2, R3, R5 to R7. Nk7 may be used. In this case, in S30 of FIG. 5, the halftone processing unit 40 may acquire the nozzle number of interest and the nozzle number of the specific nozzle (hereinafter referred to as “specific nozzle number”). In S32 of FIG. 5, when calculating the attention correction data, the halftone processing unit 40 determines from the characteristic data table 60 not only the attention K characteristic data corresponding to the attention K nozzle number, but also a plurality of characteristics. For each specific K nozzle number, K characteristic data corresponding to the specific K nozzle number may be acquired. Next, the correction data calculation unit 38 may calculate 255 × the K characteristic data / minimum K characteristic data Dkmin for each of the plurality of acquired K characteristic data. Next, the correction data calculation unit 38 may calculate the average value of the plurality of values calculated by the above calculation as the attention K correction data. Similarly, in S33 of FIG. 5, not only the characteristic CH characteristic data corresponding to the target CH nozzle number but also the specific CH nozzle number for each of a plurality of specific CH nozzle numbers from the characteristic data table 60. You may acquire the characteristic data for CH corresponding to. Next, the correction data calculation unit 38 may calculate 255 × the CH characteristic data / minimum CH characteristic data Dchmin for each of the plurality of acquired CH characteristic data. Next, the correction data calculation unit 38 may calculate an average value of a plurality of values calculated by the above calculation as attention correction data.

(8) In the present embodiment, the same drive signal is supplied to 3n individual electrodes corresponding to 3n nozzles for three kinds of chromatic colors. However, the drive signal may be different depending on the type of color. In this case, it is preferable that the reference density of the dots to be ejected is set for each of the three types of colors. In this case, the vendor may create the characteristic data table 60 as follows. The characteristic data of the n K nozzles may be the same value as the characteristic data registered in the characteristic data table 60. The vendor measures the density of each of the n cyan dots. The vendor calculates a C comparison value obtained by dividing the density of a specific cyan dot having the lowest density by the cyan reference density Cs. Similarly, for the magenta (or yellow), the vendor also calculates an M comparison value (or Y comparison value) obtained by dividing the density of a specific dot having the lowest density by the reference density Cm (or Cy). Next, the vendor specifies the minimum comparison value among the calculated three comparison values. Hereinafter, a case where the C comparison value is the minimum comparison value will be described.

  Subsequently, the vendor determines the density of a specific cyan dot having the lowest density to be “255”, which is the maximum value of 256 gradations. Next, the vendor determines the characteristic data of the n C nozzles by a method similar to the method for determining the characteristic data of the K nozzle in the first embodiment. Next, the vendor determines the characteristic data of the M nozzle as follows. First, the vendor multiplies the magenta reference density Ms by the C comparison value. Next, for each of the n magenta dots, the vendor sets a value obtained by multiplying the value obtained by dividing the dot density by the above (Ms × C comparison value) by 255 to form M for forming the dot. This is determined as characteristic data of the nozzle for use. The vendor determines n pieces of characteristic data corresponding to n pieces of Y nozzles by using a method similar to the method of determining the characteristic data of M nozzles. The vendor may generate the characteristic data table 60 based on the above method and store the characteristic data table 60 in the storage unit 56.

(9) Instead of the characteristic data table 60 in FIG. 3 or the modification (8), the PC 10 uses a characteristic data table in which the value obtained by subtracting 255 from each characteristic data in the characteristic data table 60 is registered as characteristic data. You may remember. That is, the characteristic data of the K nozzle that forms the black dot with the smallest area may be determined as “0”. In this case, the characteristic data of the other K nozzles includes the area of the dots formed by the other K nozzles (the area when the area of the smallest area is determined to be 255) and the smallest area of the dots. It can also be said that this is the difference in the area (255) of the nozzle for K to be performed. The 3n characteristic data for chromatic colors may be determined in the same manner.

  In the case of this modification, in S32 of FIG. 5, the correction data calculation unit 38 calculates the correction data for attention K by adding 255 to the value obtained by subtracting Dkmin (= 0) from Dkz. Also good. In S33 of FIG. 5, the correction data calculation unit 38 may calculate the correction data for the attention CH by adding 255 to the value obtained by subtracting Dchmin (= 0) from Dchz.

(10) The PC 10 may store the following discharge amount data table instead of the characteristic data table 60 of FIG. 3 or the modified example (8). The discharge amount data table of the present modification may be created as follows by a vendor. The discharge amount data of the n K nozzles may be the same value as the characteristic data registered in the characteristic data table 60. The vendor measures the area of each of the n cyan dots. The vendor determines the area of the specific cyan dot having the smallest area as “255” which is the maximum value of 256 gradations. Next, the vendor specifies the area of dots formed by other C nozzles based on the area of the specific dot having the smallest area. In the present modification, the area value is determined as the discharge amount data. That is, the discharge amount data Dcmin of the C nozzle that forms a specific dot with the smallest area is “255”. As in the case of cyan, the vendor determines the discharge amount data of each nozzle for each of the other two chromatic colors (that is, magenta and yellow). For example, the vendor determines “Dmmin” (= 255) as the discharge amount data of a specific M nozzle that forms a specific dot having the smallest characteristic data in the M nozzle group 84c. Further, the vendor specifies the discharge amount data of the other M nozzles with reference to the discharge amount data (Dmmin) of a specific magenta having the smallest discharge amount data, and sets the characteristic value to the C nozzle. Is determined as discharge amount data (Dmz). Note that the three minimum discharge amount data (ie, Dcmin, Dmmin, Dymin (= 255)) corresponding to the three types of chromatic colors (ie, CMY) are equal to Dkmin.

  In the case of this modification, the three minimum discharge amount data (that is, Dcmin, Dmmin, Dymin) corresponding to CMY are equal. However, the dot area (minimum C area) formed by the specific C nozzle with the smallest discharge amount in the C nozzle group 84c and the specific M with the smallest discharge amount in the M nozzle group 84m. The area of the dots formed by the nozzle for nozzles (minimum area for M) is different from the area of the dots formed by a specific Y nozzle with the smallest ejection amount in the Y nozzle group 84y (minimum area for Y). obtain. When the vendor sets the value of the smallest area among the three areas corresponding to the three specific nozzles to “255” as well as the 4n discharge amount data corresponding to the 4n nozzles. These three area values (that is, three characteristic data) are registered in the discharge amount data table.

  In the above embodiment, the following processing may be executed when the discharge amount data table of the present modification is acquired in S12 of FIG. In S32, the data acquisition unit 36 acquires the discharge amount data corresponding to the attention K nozzle number specified in S30 from the discharge amount data table. The correction data calculation unit 38 calculates the attention K correction data by multiplying 255 by the value obtained by dividing the acquired discharge amount data by the minimum discharge amount data (ie, Dkmin). In S33, the data acquisition unit 36 acquires the discharge amount data corresponding to the target CH nozzle number specified in S30. Next, for example, when the target CH nozzle number is the C nozzle number, the correction data calculation unit 38 adds (minimum C area) / (minimum C area and minimum) to the acquired discharge amount data. The attention CH correction data may be calculated by multiplying the M area and the minimum Y area). Similarly, for example, when the target CH nozzle number is the M nozzle number (or Y nozzle number), the acquired discharge amount data includes (minimum M area (or minimum Y area)) / The correction data for the target CH may be calculated by multiplying (the minimum area of the minimum C area, the minimum M area, and the minimum Y area).

  In the case of this modification, the correction data for the target CH is the discharge amount data corresponding to the target CH nozzle and the minimum area among the minimum C area, the minimum M area, and the minimum Y area (“present” Example of “reference characteristic data for coloring”). The ejection amount data is generated using an area corresponding to the target CH nozzle (an example of “chromatic color target characteristic data”). Therefore, the configuration of this modification is included in the configuration in which “correction data for chromatic color is data obtained using attention characteristic data for chromatic color and reference characteristic data for chromatic color”. It is.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

2: network system, 12: operation unit, 14: display unit, 16: network interface, 20: storage unit, 22: work area, 24: printer driver, 30: control unit, 32: image processing unit, 34: color conversion Processing unit 36: Data acquisition unit 38: Correction data calculation unit 40: Halftone processing unit 42: Correction unit 44: Determination unit 46: Error value calculation unit 48: Supply unit 50: Printer 52: Network interface, 54: Display unit, 56: Storage unit, 60: Characteristic data table, 64: Program, 70: Print execution unit, 80: Print head, 84k, 84c, 84m, 84y: Nozzle group, 200: Conversion Finished RGB image data, 210: CMYK image data, 250: corrected image data

Claims (7)

A plurality of sets of nozzle groups for discharging a plurality of types of chromatic ink droplets, wherein each set of nozzle groups includes a plurality of nozzles, and a print head unit having the plurality of sets of nozzle groups formed therein. A control device for causing a print execution unit to execute printing,
An image processing unit that generates processed image data by performing image processing on specific image data;
A supply unit for supplying the processed image data to the print execution unit,
In order to compensate for variations in the ejection amount of ink droplets ejected from a specific group of nozzles of the plurality of groups of nozzles, the image processing unit performs the following processing on target pixels in target image data: A target nozzle that forms a dot at a position on the print medium corresponding to the target pixel, and using a chromatic color correction data for the target nozzle belonging to the specific group of nozzles, a specific color Execute the process,
The chromatic color correction data includes reference characteristic data among a plurality of sets of characteristic data groups corresponding to the plurality of sets of nozzle groups, and attention corresponding to the target nozzles of the plurality of sets of characteristic data groups. Data obtained using characteristic data,
Each set of characteristic data groups includes a plurality of characteristic data corresponding to the plurality of nozzles included in the corresponding set of nozzle groups,
The characteristic data is data related to the ejection amount of ink droplets ejected from the corresponding nozzle,
The control device, wherein the reference characteristic data is characteristic data indicating a minimum ejection amount of the ejected ink droplets among the plurality of sets of characteristic data groups. When the target nozzle belongs to the first set of nozzle groups that discharge the first type of ink droplets, the correction data for chromatic color includes the first set of ink that discharges the first type of ink droplets. Data obtained using the reference characteristic data corresponding to a specific nozzle belonging to a nozzle group and the attention characteristic data corresponding to the target nozzle belonging to the first set of nozzle groups;
When the target nozzle belongs to a second group of nozzles that ejects the second type of ink droplets, the correction data for chromatic color includes the first group of ink that ejects the first type of ink droplets. The data obtained by using the reference characteristic data corresponding to the specific nozzle belonging to the nozzle group and the attention characteristic data corresponding to the target nozzle belonging to the second set of nozzle groups. The control device described in 1. In the print head portion, a black nozzle group for discharging black ink droplets is further formed,
The black nozzle group includes a plurality of black nozzles,
The image processing unit corresponds to the target pixel with respect to the target pixel in the target image data in order to compensate for variations in the ejection amount of the ink droplets discharged from the black nozzle group. Using the correction data for black for the target nozzle for black that forms dots at positions on the print medium, the specific processing is executed,
The black correction data does not use the reference characteristic data, and the black corresponding to the black target nozzle among the plurality of black characteristic data corresponding to the plurality of black nozzles. Data obtained by using attention characteristic data for black and reference characteristic data for black ,
Characteristic data for the black, Ri Ah with data relating to the discharge amount of ink droplets ejected from the nozzles for the corresponding black,
Reference characteristic data for the black, among the characteristic data for the plurality of black, Ru Oh in characteristic data for black the discharge amount of ink droplets the minimum ejected, according to claim 1 or 2 Control device. The target image data is the specific image data,
The image processing unit
Color conversion expressed in the second type color space by executing the specific processing including color conversion processing and correction processing on the target image data expressed in the first type color space. A color conversion processing unit for generating finished image data;
A halftone processing unit that generates the processed image data by performing a halftone process on the color-converted image data,
The color conversion processing unit
With respect to the target pixel in the image data of the object, the color conversion processing by executing generate color-converted pixel represented by the second type of color space, the second type of color space in respect of the color converted pixel, wherein by generating a corrected pixel by performing a correction process to generate the color converted image data using the correction data for the chromatic, The control device according to any one of claims 1 to 3. The color conversion processing unit
A determination unit that determines whether a value of the target pixel in the color-converted image data is a value indicating a color within a predetermined range including an achromatic color;
The color conversion processing unit
When the value of the target pixel is a value indicating a color within the predetermined range, the specific process is executed using the correction data for the chromatic color,
The color conversion process is executed without executing the specific process using the chromatic color correction data when the value of the pixel of interest is not a value indicating a color within the predetermined range. Item 5. The control device according to Item 4. The image processing unit
The target image data expressed in the second type color space is generated by performing color conversion processing on each pixel in the specific image data expressed in the first type color space. A color conversion processing unit;
A halftone processing unit that generates the processed image data by performing halftone processing on the target image data,
The halftone processing unit
A correction unit that generates a corrected value by correcting the value of the target pixel in the target image data using a plurality of error values corresponding to a plurality of neighboring pixels in the vicinity of the target pixel. When,
A determination unit that determines whether or not to form a dot at the position on the print medium corresponding to the target pixel based on the corrected value and a threshold corresponding to the target pixel;
An error value calculation unit that calculates an error value of the pixel of interest according to the determination regarding whether or not to form a dot for the pixel of interest;
The error value calculation unit corresponds to the target pixel by using the corrected value and the correction data for the chromatic color when it is determined to form a dot for the target pixel. The control device according to claim 1, wherein the specific processing for calculating the error value is executed. A computer program,
A plurality of sets of nozzle groups for discharging a plurality of types of chromatic ink droplets, wherein each set of nozzle groups includes a plurality of nozzles, and a print head unit having the plurality of sets of nozzle groups formed therein. In the control device for causing the print execution unit to execute printing to execute the following steps:
An image processing step for generating processed image data by performing image processing on specific image data; and
Supplying the processed image data to the print execution unit, and
In the image processing step, in order to compensate for variations in the ejection amount of ink droplets ejected from a specific group of nozzle groups of the plurality of groups of nozzles, for a target pixel in target image data, A target nozzle that forms a dot at a position on the print medium corresponding to the target pixel, and using a chromatic color correction data for the target nozzle belonging to the specific group of nozzles, a specific color Execute the process,
The chromatic color correction data includes reference characteristic data among a plurality of sets of characteristic data groups corresponding to the plurality of sets of nozzle groups, and attention corresponding to the target nozzles of the plurality of sets of characteristic data groups. Data obtained using characteristic data,
Each set of characteristic data groups includes a plurality of characteristic data corresponding to the plurality of nozzles included in the corresponding set of nozzle groups,
The characteristic data is data related to the ejection amount of ink droplets ejected from the corresponding nozzle,
The computer program, wherein the reference characteristic data is characteristic data indicating a minimum ejection amount of the ejected ink droplet among the plurality of sets of characteristic data groups.

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