JP2014049925A - Control device and computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new technique in which concentration unevenness in a print image can be reduced.SOLUTION: The control device has a generation section for performing image processing including error diffusion processing to image data to generate print data. The generation section has: a correction data acquisition section for acquiring correction data corresponding to a target position of a target pixel; and a compensation section for performing compensation processing using the compensation data which compensates variations in print concentration of an image to be printed on print media. The correction data corresponding to the target position can be obtained by using difference between a target value and a first neighboring value. The target value can be obtained by using a concentration characteristic value in the target position. The first neighboring value can be obtained by using the concentration characteristic value in a first neighboring position corresponding to a first neighboring pixel which is positioned in the vicinity of the target pixel.

Description

  The present invention relates to a technique for controlling printing, and more particularly to a technique for controlling printing so as to suppress uneven density in printing.

  A phenomenon is known in which the image quality of a print image formed on a print medium (for example, paper) by a printing apparatus such as a laser printer or an ink jet printer deteriorates due to density unevenness. The density unevenness occurs due to, for example, a printing medium conveyance error by the printing apparatus.

  There is a need for a technique for reducing such density unevenness. For example, a technique is known in which a print result of a test image is optically read, and correction data for correcting image data representing the print image is generated using the read result (for example, Patent Document 1).

JP 2011-25574 A

  According to this technique, the image data can be corrected so as to eliminate the density unevenness appearing in the reading result, so that the density unevenness can be reduced.

  However, in the above technique, there is a possibility that density unevenness cannot be sufficiently reduced, for example, when the print density fluctuates rapidly. Abrupt fluctuations in print density can occur, for example, due to a sudden charge transfer from the photoreceptor to the print medium that occurs when the leading edge of the print medium first contacts the photoreceptor of the laser printer.

  The main advantage of the present invention is to provide a new technique that can reduce density unevenness of a printed image.

Application Example 1 A control device that controls a print execution unit that prints a print image on a print medium,
A generation unit that performs image processing including error diffusion processing on target image data representing the target image, and generates print data for causing the print execution unit to print the print image representing the target image; A supply unit that supplies the print data to the print execution unit, and the generation unit outputs correction data corresponding to a target position that is a position on the medium corresponding to a target pixel that is a processing target of the image processing. A correction data acquisition unit to be acquired, wherein the position on the medium is a position in the sub-scanning direction on the print medium, and the print density of the image printed on the print medium A compensation unit that performs the compensation process for compensating the variation of the target pixel, wherein the compensation process is performed using the correction data corresponding to the target position; The correction data corresponding to the target position is data obtained using a first difference that is a difference between the target value and a first neighborhood value, and the target value is the target value The first neighborhood value is a value obtained using a density characteristic value at a position, and the first neighborhood value is a first neighborhood position that is a position on the medium corresponding to a first neighborhood pixel located in the neighborhood of the target pixel. It is a value obtained using the density characteristic value, and the first neighboring pixel is a pixel whose position in the sub-scanning direction is different from the target pixel, and is subject to the error diffusion process before the target pixel. And the density characteristic value is a characteristic value related to a print density of an image printed on the print medium.

  According to said structure, a compensation process is performed using the data for a correction | amendment obtained using the 1st difference which is a difference of an attention value and a 1st neighborhood value. As a result, it is possible to reduce variations in the print density (density unevenness) of an image printed on the print medium, compared to a configuration in which correction data that does not consider the first difference is used.

  The present invention can be realized in various forms. For example, a printing apparatus, a printing system, a control method for the printing apparatus, a computer program for realizing the functions of these apparatuses and the system, and the computer program therefor Can be realized in the form of a recording medium on which is recorded.

It is a block diagram which shows schematic structure of the printing system 2 of a present Example. 1 is a diagram illustrating a schematic configuration of a printing apparatus 100. FIG. It is a figure explaining surface potential Vs in transfer position SP of photosensitive drum 54K at the time of transfer. It is a graph which shows an example of the density nonuniformity with respect to the position on a medium. It is a figure which shows an example of the characteristic value table. It is a flowchart of a printing process. It is a figure which shows notionally RGB image data 300 after the resolution conversion process. 3 is a diagram conceptually showing CMYK image data 310. FIG. It is a flowchart of an error diffusion process. FIG. 3 is a schematic diagram of a print image IM to be formed on a print medium P according to print data generated by the print process. It is a figure explaining calculation of correction pixel value PV 'using an error diffusion matrix. It is a figure explaining calculation of error value deltaE. It is a graph which shows the printing density of the printing result using the printing process of a present Example. FIG. 14 is a diagram illustrating correction data HD (A) and print image density (B) for a range RA in the vicinity of the on-medium position Pa in FIG. 13. It is explanatory drawing of the data for attention correction HD in 2nd Example. It is explanatory drawing of the data for attention correction HD in 3rd Example. It is a flowchart of the error diffusion process of 4th Example. It is explanatory drawing explaining 5th Example. 14 is a flowchart of printer driver processing according to a sixth embodiment. It is a figure which shows an example of the correction data table 134A. It is a figure explaining density characteristic value CP used in the 8th example.

A. First embodiment:
A-2: Configuration of the printing system:
Next, embodiments of the present invention will be described based on examples. FIG. 1 is a block diagram illustrating a schematic configuration of a printing system 2 according to the present embodiment. The printing system 2 includes a printing apparatus 100 and a computer 200 that is communicably connected to the printing apparatus 100.

  The computer 200 is, for example, a personal computer, and communicates with a CPU 210, a memory 230 such as a ROM or a RAM, a display unit 240 such as a liquid crystal display, an operation unit 250 such as a keyboard, and an external device such as the printing apparatus 100. And a communication unit 260 that is an interface for the communication.

  The memory 230 includes a work area 234. The work area 234 is used, for example, for storing image data or the like in print processing described later. The memory 230 stores a driver program 232. The CPU 210 functions as the printer driver 500 by executing the driver program 232. The printer driver 500 generates print data for printing an image designated by the user in accordance with an instruction from the user, and supplies the generated print data to the printing apparatus 100. As a result, the printer driver 500 can cause the printing apparatus 100 to execute printing. The printer driver 500 includes an image data acquisition unit 510 that acquires target image data to be processed, and a print data generation unit that generates print data by performing image processing including halftone processing (in this embodiment, error diffusion processing). 520, and a print data supply unit 530 that supplies print data to the printing apparatus 100. The print data generation unit 520 includes a color conversion unit 521 and a halftone processing unit 522. The halftone processing unit 522 includes a correction data acquisition unit 525, an error use correction unit 526, a determination unit 527, and a calculation unit 528. The processing executed by each of these functional units will be described later. The compensation correction unit 529 shown by the broken line in FIG. 1 is a functional unit included in the halftone processing unit 522 of the second embodiment, and will be described in the second embodiment.

  The printing apparatus 100 is a printing apparatus (a so-called laser printer) that forms an image using printing materials (in this embodiment, four-color (CMYK) toner). The printing apparatus 100 includes a CPU 110, a volatile memory 120 such as a DRAM, a non-volatile memory 130 such as an EEPROM, a display unit 140 such as a liquid crystal display, an operation unit 150 such as a touch panel, and an external device (for example, a computer 200). ), And a print execution unit 50.

  The non-volatile memory 130 stores a program 132 and a characteristic value table 134 used in print processing described later. The characteristic value table 134 may be integrated into the program 132. The CPU 110 functions as the print control unit 115 by executing the program 132. For example, the print control unit 115 executes printing by controlling the print execution unit 50 according to a print job transmitted from the computer 200 to the printing apparatus 100.

  The configuration of the printing apparatus 100 will be further described with reference to FIG. 2 in addition to FIG. FIG. 2 is a diagram illustrating a schematic configuration of the printing apparatus 100. In FIG. 2, three directions Dx, Dy, Dz are shown. The two directions Dx and Dy are horizontal directions, respectively, and the Dz direction is a vertically upward direction. The Dy direction and the Dx direction are orthogonal to each other. Hereinafter, the Dx direction is also referred to as “+ Dx direction”, and the opposite direction of the Dx direction is also referred to as “−Dx direction”. The same applies to the + Dy direction, the -Dy direction, the + Dz direction, and the -Dz direction.

  The printing apparatus 100 includes a substantially rectangular parallelepiped housing 10 that houses the above-described print execution unit 50, and a paper feed tray 30 that is housed in a vertical lower end portion of the housing 10. On the upper surface of the housing 10, an inclined surface that functions as the paper discharge tray 20 and an opening OP for discharging the print medium P after printing to the paper discharge tray 20 are formed. The print execution unit 50 includes a transport mechanism, an exposure unit 51, process units 59C, 59M, 59Y, and 59K for CMYK toners, transfer rollers 55C, 55M, 55Y, and 55K for CMYK toners, and fixing. Part 56.

  The transport mechanism includes a driving roller 57A, a driven roller 57B, a transport belt 58, a motor (not shown) and other rollers, and a transport path SR (FIG. 2: one point) from the paper feed tray 30 to the paper discharge tray 20. The print medium P is conveyed along the broken line. The driving roller 57A and the driven roller 57B have a cylindrical shape whose axial direction is the Dy direction. The conveying belt 58 is provided between the driving roller 57A and the driven roller 57B. The width of the conveyance belt 58 in the Dy direction is wider than the width of the print medium P in the corresponding direction. The conveyance belt 58 rotates in synchronization with the drive roller 57A, and conveys the print medium P in a state where the print medium P is placed on the upper surface 58A (vertical upper surface).

  The process units 59C, 59M, 59Y, 59K are arranged along the upper surface 58A of the conveyor belt 58. Therefore, when the print medium P is transported in the transport direction (−Dx direction) on the upper surface 58A of the transport belt 58, the process units 59C, 59M, 59Y, and 59K are opposite to the print medium P in the transport direction (+ Dx). Direction). Hereinafter, the conveyance direction is also referred to as a sub-scanning direction. Further, the upstream end in the transport direction (sub-scanning direction) of the print medium P is called the upstream end of the print medium P, and the downstream end in the transport direction of the print medium P is the downstream end of the print medium P. Also called.

  The process units 59C, 59M, 59Y, and 59K respectively include toner cartridges 52C, 52M, 52Y, and 52K that store toners of corresponding colors, developing rollers 53C, 53M, 53Y, and 53K, and photosensitive drums as photosensitive members. 54C, 54M, 54Y, and 54K. In the following, when the four process units 59C, 59M, 59Y, 59K and their constituent parts are not distinguished for each toner color, the alphabetic character at the end of the reference numerals is omitted, and for example, the process unit 59, the photosensitive drum 54, and the like. Also called. The developing roller 53 and the photosensitive drum 54 have a cylindrical shape whose axial direction is the Dy direction. The length in the axial direction of the developing roller 53 and the photosensitive drum 54 is longer than the width in the corresponding direction of the print medium P. The developing roller 53 and the photosensitive drum 54 are in contact with each other for toner delivery (development) described later.

  The transfer rollers 55C, 55M, 55Y, and 55K have a cylindrical shape whose axial direction is the Dy direction. The axial lengths of the transfer rollers 55C, 55M, 55Y, and 55K are approximately the same as the axial length of the photosensitive drum 54. The transfer rollers 55C, 55M, 55Y, and 55K are arranged at positions that sandwich the conveyance belt 58 in pairs with the corresponding photosensitive drums 54C, 54M, 54Y, and 54K. When the four transfer rollers 55C, 55M, 55Y, and 55K are not distinguished, the letter at the end of the code is omitted as in the process unit 59.

  The exposure unit 51 is disposed above the process unit 59. Although not shown, the exposure unit 51 includes a laser light source such as a laser diode and an optical system including a polygon mirror, a lens, and a reflecting mirror that are rotationally driven. The exposure unit 51 irradiates the surfaces of the four photosensitive drums 54 with a laser LZ generated using a laser light source via an optical system. The exposure unit 51 performs main scanning in which the laser beam irradiation position on the surface of the photosensitive drum 54 is moved in the Dy direction by a polygon mirror. Instead of this, the exposure unit 51 may include a line light source in which a number of LEDs corresponding to pixels are arranged in the Dy direction. Regardless of the configuration, the exposure unit 51 can irradiate a laser at an arbitrary position in the Dy direction on the surface of the photosensitive drum 54. Hereinafter, the Dy direction is also referred to as a main scanning direction.

  The fixing unit 56 is disposed on the downstream side of the transport belt 58 in the transport path SR of the print medium P. The fixing unit 56 fixes the toner to the print medium P by pressurizing and heating the toner on the print medium P using a pair of rollers.

A-2. Printing Process Using Print Execution Unit 50 and Density Unevenness A printing process executed by the print control unit 115 by controlling the print execution unit 50 having the above-described configuration will be briefly described. The surface of the rotating photosensitive drum 54 is uniformly charged by a charger (not shown) and then exposed to each line (main scanning line) along the main scanning direction by a laser irradiated from the exposure unit 51. The Since the applied charges are removed from the exposed portions, an electrostatic latent image corresponding to the image to be printed is formed on the surface of the photosensitive drum 54 by the exposure.

  The toner accommodated in the toner cartridge 52 is uniformly carried on the surface of the rotating developing roller 53. A developing bias is applied between the developing roller 53 and the photosensitive drum 54. With the developing bias, toner is supplied from the developing roller 53 to the electrostatic latent image formed on the photosensitive drum 54 at a contact portion between the rotating developing roller 53 and the rotating photosensitive drum 54. As a result, a toner image is formed on the surface of the photosensitive drum 54 (development). A contact portion between the developing roller 53 and the photosensitive drum 54 is an area along the main scanning line.

  A transfer bias is applied to the transfer roller 55. The toner image formed on the surface of the photosensitive drum 54 by the transfer bias is transferred to the printing medium P at a contact portion between the rotating photosensitive drum 54 and the printing medium P conveyed by the conveying belt 58. A contact portion between the photosensitive drum 54 and the print medium P is an area along the main scanning line.

  The toner image transferred to the printing medium P is fixed by a pair of rollers of the fixing unit 56, and the image formation is completed.

  As can be understood from the above description, each step (exposure, development, transfer, and fixing) in printing is performed for each region along the main scanning line. For this reason, variations in print density due to manufacturing errors of the rotating body and components for driving the rotating body (motor, gear, etc.) involved in each process are caused by a plurality of main scans having different positions in the sub-scanning direction. It is likely to occur between areas along the line. As a result, variations in print density are likely to occur depending on the position in the sub-scanning direction on the print medium P. As a result, density unevenness such as a phenomenon (banding) in which strip-like streaks extending along the main scanning line appear in the image is likely to occur as a defect that causes a reduction in image quality. Hereinafter, the position in the sub-scanning direction on the print medium P is also simply referred to as a medium position.

  Specifically, the rotating shafts of the rotating body related to the conveyance of the printing medium P, for example, the driving roller 57A, the driven roller 57B, and other rollers (not shown) may be eccentric due to manufacturing errors. In this case, even if the print control unit 115 controls the transport mechanism so that the print medium P is transported at a constant transport speed, the actual transport speed of the print medium P varies. In this case, the density of the image transferred to the print medium P when the transport speed is relatively high tends to be lower than the density of the image to which the print medium P is transferred when the transport speed is relatively slow.

  Similarly, the rotating shaft of the photosensitive drum 54 may be decentered due to manufacturing errors. In this case, density unevenness may occur due to fluctuations in the rotational speed of the photosensitive drum 54.

  Main rotating bodies (for example, the photosensitive drum 54 and the driving roller 57A) that cause density unevenness are provided with sensors (for example, a rotary encoder: not shown) that detect the rotational phase of these rotating bodies. . The rotation phase is represented by a rotation angle from the reference position, for example. The print controller 115 can acquire the rotational phase of the rotating body using these sensors. In the transport control of the print medium P, the print control unit 115 executes transport synchronization control that synchronizes the rotational phase of these rotating bodies and the position (transport position) of the print medium P on the transport path SR. When this conveyance synchronization control is executed, the density unevenness caused by the eccentricity of the main rotating body constantly occurs in the same tendency with respect to the position on the medium of the print image. Density unevenness due to the eccentricity of the main rotating body has a periodicity corresponding to the rotating period of the rotating body that causes it.

  Further, on the transport path SR, there is a mechanism for sandwiching the transported print medium P, such as the pair of rollers (FIG. 2) of the fixing unit 56 described above and the transfer roller 55 corresponding to the photosensitive drum 54. . At the timing when the downstream end of the printing medium P enters these clamping mechanisms or when the upstream edge of the printing medium P is released from these clamping mechanisms, there is a case where a rapid fluctuation in the conveyance speed of the printing medium P occurs. is there. Density unevenness caused by these clamping mechanisms constantly occurs in the same tendency with respect to the position of the printed image on the medium.

  A laser printer using positively charged toner will be described. FIG. 3 is a diagram illustrating the surface potential Vs at the transfer position SP of the photosensitive drum 54K during transfer. Even when the surface potential Vs varies during transfer as described with reference to FIG. 3, steady density unevenness occurs. 3A and 3B show a structure in the vicinity of one photosensitive drum 54K. FIGS. 3A and 3B show states at times T1 and T2 during which the print execution unit 50 is executing the printing process. FIG. 3C is a graph showing the variation of the surface potential Vs with respect to time at the transfer position SP (FIG. 3A). The transfer position SP is a position where the toner image is transferred onto the print medium P by the photosensitive drum 54K and the corresponding transfer roller 55K.

  As shown in FIG. 3, a transfer bias Vt is applied to the transfer roller 55K. In this embodiment, the transfer bias Vt is applied so as to be a negative potential by predetermined control (for example, constant current control). The stable potential (target value) of the surface potential Vs when the transfer bias Vt is applied is defined as V1.

  At time T1, the downstream end of the printing medium P being conveyed has not reached the transfer position SP. At this time, the surface potential Vs is the stable potential V1. At time T2, the downstream end of the print medium P reaches the transfer position SP. At this time, it is difficult for the electric charge to flow from the photosensitive drum 54K to the transfer roller 55, and the voltage drop of the photosensitive drum 54 is rapidly reduced. As a result, the potential of the photosensitive drum 54 rapidly increases (FIG. 3C). In the example of FIG. 3C, the surface potential Vs rises from the stable potential V1 to the rising potential V2 higher than the stable potential V1. The rapid potential change occurs for a very short time, and thereafter, the surface potential Vs changes relatively slowly. For example, the surface potential Vs becomes an intermediate potential V3 that is higher than the stable potential V1 and lower than the rising potential V2 (FIG. 3C).

  Thereafter, the surface potential Vs gradually changes toward the stable potential V1. In the example of FIG. 3C, the surface potential Vs decreases from the intermediate potential V3 toward the stable potential V1 from time T3. However, at time T4 during which it gradually decreases toward the stable potential V1, the surface potential Vs temporarily rises to a value close to the rising potential V2 temporarily (FIG. 3C).

  Here, the reason why the surface potential Vs rapidly increases at time T4 will be described. When the surface potential Vs suddenly increases at the transfer position SP at time T2, the potential of the portion located at the transfer position SP on the surface of the rotating photosensitive drum 54K is not recovered immediately, It remains elevated at T4. The potential rising portion of the photosensitive drum 54K returns to the transfer position SP again when the photosensitive drum 54K rotates once. Time T4 is the time when the potential rising portion of the photosensitive drum 54K returns to the transfer position SP. As can be seen from the above description, the period required for one rotation of the photosensitive drum 54K, that is, the rotation cycle is (T4-T1). Similar fluctuations in the surface potential Vs occur in all the photosensitive drums 54C, 54M, 54Y, and 54K.

  The lower the surface potential Vs, the more the development of the toner image from the developing roller 53 to the photosensitive drum 54 is promoted, and the print density increases. Therefore, density unevenness occurs due to fluctuations in the surface potential Vs. As described with reference to FIG. 3, the fluctuation of the surface potential Vs occurs when the downstream end of the print medium P reaches the transfer position SP. Therefore, the density unevenness due to the fluctuation of the surface potential Vs constantly occurs in the same tendency with respect to the position on the medium of the print image.

  As described above, due to various factors, density unevenness constantly occurs in the same tendency with respect to the position on the medium of the print image. Although the laser printer using the positively charged toner has been described, the surface potential is also reversed in the laser printer using the negatively charged toner, but the density unevenness constantly occurs on the same principle.

  FIG. 4 is a graph showing an example of density unevenness with respect to the position on the medium. Such density unevenness can be investigated as follows. First, the investigator causes the printing apparatus 100 to print a test image representing a single color uniform image on the entire print medium P. The test image data representing the test image includes one type of CMYK value (for example, CMYK = (255, 0, 0) representing a color (for example, cyan) corresponding to one type of toner (for example, C (cyan) toner). , 0)). Therefore, ideally, the test image is an image that should have a uniform density throughout the image. The investigator measures the density of the print result of the test image, and acquires the density characteristic value CP representing the density for each medium position.

  The horizontal axis of the graph of FIG. 4 is the medium position (coordinate in the sub-scanning direction on the print medium P), and the vertical axis is the cyan density characteristic value CP. The position on the medium represents the downstream end of the print medium P as 0 and the upstream end as Pn (0 <Pn). In FIG. 4, the density characteristic values CP of a partial range (0 to Pm) starting from the downstream end among the entire range from the downstream end 0 to the upstream end Pn are plotted. In this embodiment, the density characteristic value CP is expressed as a relative value with respect to the reference value, with the lowest density of the measured densities on the medium as the reference value (0). Specifically, for the density characteristic value CP, a value obtained by subtracting 255 from the value when the minimum density is 255 is used. For example, when the density at a specific medium position is represented by 261 when the minimum density is 255, the density characteristic value CP at the specific medium position is 6.

  FIG. 4 shows the variation in the density of the printed image corresponding to the above-described variation in the surface potential Vs (FIG. 3C). For example, in FIG. 4, the density characteristic value CP at the position 0 on the medium (downstream end) decreases corresponding to the surface potential Vs at time T2 (FIG. 3C). Further, the density characteristic value CP at the position Pa on the medium decreases corresponding to the surface potential Vs at time T4 (FIG. 3C). In other words, the amount of change in the density characteristic value CP is rapidly increased near the medium position 0 and the medium position Pa as compared with other positions. A distance RD between the medium upper position 0 and the medium upper position Pa corresponds to the outer peripheral length of the photosensitive drum 54. The outer circumferential length is the circumferential length of a circular cut surface obtained by cutting the photosensitive drum 54 along a plane perpendicular to the rotation axis. Here, the medium position 0 is an example of “a first position that is a specific medium position”, and the medium position Pa is an example of “a second position that is a specific medium position”. The distance RD is an example of “a distance corresponding to a rotation cycle of a specific rotating body included in the print execution unit”.

  The medium position Ps corresponds to time T3. It can be seen that the density characteristic value CP is increased upstream of the on-medium position Ps corresponding to the increase in the surface potential Vs after the time Ts. As a result, it can be seen that the average value of the density characteristic value CP on the downstream side from the medium position Ps is equal to or lower than the average value of the density characteristic value CP on the upstream side of the medium position Ps. Here, the on-medium position Ps is an example of “a specific position on the print medium”, and the density characteristic value CP corresponding to the on-medium position on the downstream side of the on-medium position Ps is “the first type of characteristic value”. The density characteristic value CP corresponding to the medium position upstream from the medium position Ps is an example of “second type characteristic value”.

A-3: Print processing of the printer driver 500:
The printer driver 500 of the printing apparatus 100 executes a printing process that can suppress the density unevenness that occurs regularly with respect to the above-described position on the medium. First, the characteristic value table 134 used in this printing process will be described.

  FIG. 5 is a diagram illustrating an example of the characteristic value table 134. The characteristic value table 134 is a table in which density characteristic values CP (FIG. 4) investigated for each of the four types of toners (CMYK) used in the printing apparatus 100 are recorded. FIG. 5 shows four tables in which density characteristic values CP of cyan (C), magenta (M), yellow (Y), and black (K) are recorded. Each table stores Pn density characteristic values CP corresponding to Pn medium positions from the downstream end (0) to the upstream end (Pn) (Pn is a natural number of, for example, 1000 to 10000). Yes. The characteristic value table 134 is created by the manufacturer of the printing apparatus 100, for example, and is stored in the nonvolatile memory 130 of the printing apparatus 100 at the shipping stage (FIG. 1).

  FIG. 6 is a flowchart of the printing process. This printing process is a process for generating print data using image data selected by the user and supplying the generated print data to the printing apparatus 100. For example, the printer driver 500 starts print processing in response to a print instruction from the user. Here, the contents of the printing process will be described assuming that the RGB image data is selected by the user. The RGB image data is image data in a bitmap format composed of RGB values of each pixel. When data in another format is selected, the printer driver 500 converts the data into RGB image data using a known method.

  In step S <b> 10, the image data acquisition unit 510 acquires RGB image data as target image data representing a target image to be printed, and stores the RGB image data in the work area 234.

  In step S20, the print data generation unit 520 acquires the characteristic value table 134. For example, the print data generation unit 520 transmits an acquisition command to the printing apparatus 100 and acquires the characteristic value table 134 from the printing apparatus 100 as a response to the acquisition command. The acquired characteristic value table 134 is stored in the work area 234.

  In step S30, the print data generation unit 520 performs resolution conversion processing on the RGB image data, and converts the RGB image data into image data having the number of pixels corresponding to the print resolution.

  FIG. 7 is a diagram conceptually showing the RGB image data 300 after the resolution conversion processing. FIG. 7 shows RGB values, that is, R values (for example, R (i, j)) and G values (for example, G (i, j)) of each pixel (307, 308, etc.) in the RGB image data 300. , B values (for example, B (i, j)) are shown. The R value, the G value, and the B value are, for example, 256 gradation values (0 to 255). Note that the x coordinate of the coordinates (x, y) shown in each pixel indicates the column number of each pixel, and the y coordinate indicates the row number of each pixel (the same applies to FIGS. 8 and 11 described later).

  In step S <b> 40, the color conversion unit 521 (FIG. 1) of the print data generation unit 520 executes color conversion processing that converts the RGB image data 300 into CMYK image data 310. The CMYK image data 310 is bitmap format image data composed of CMYK values for each pixel. Since the CMYK image data 310 is image data after color conversion processing, it is also called converted image data. The color conversion process is executed, for example, by converting RGB values in the RGB image data 300 into CMYK values using a lookup table.

  FIG. 8 is a diagram conceptually showing the CMYK image data 310. FIG. 8 shows CMYK values, that is, C values (for example, C (i, j)) and M values (for example, M (i, j)) of each pixel (317, 318, etc.) in the CMYK image data 310. , Y value (for example, Y (i, j)) and K value (for example, K (i, j)) are shown. The C value, M value, Y value, and K value are, for example, 256 gradation values (0 to 255).

  In step S50, the halftone processing unit 522 (FIG. 1) of the print data generation unit 520 executes error diffusion processing as halftone processing on the CMYK image data 310 to represent the dot formation state of each pixel. Generate dot data.

  FIG. 9 is a flowchart of error diffusion processing. The error diffusion processing of FIG. 9 shows processing for one component value of CMYK. The error diffusion process of FIG. 9 is executed for each of the four types of component values (C value, M value, Y value, K value), and dot data is generated for each component of CMYK.

  In step S505, the halftone processing unit 522 selects a target row. The image represented by the CMYK image data 310 includes a row having k pixels in the vertical direction in FIG. 8 (k is a natural number). From these k rows, one row is selected as the target row. The target row is selected one by one from the top in FIG.

  FIG. 10 is a schematic diagram of a print image IM to be formed on the print medium P according to the print data generated by the print processing. The upper direction in FIG. 10 is the transport direction (sub-scanning direction), and the left-right direction in FIG. 10 is the main scanning direction. That is, the upper end of the print medium P in FIG. 10 is the downstream end of the print medium P, and the lower end is the upstream end of the print medium P. Numerical values 0 to Pn attached to the left end of the print medium P represent the above-described position on the medium. The print image IM includes k print rows Rn (n is a row number and a natural number of 1 to k) corresponding to k rows of the image represented by the CMYK image data (FIG. 10). This line number n is also used as the line number of k lines of the image represented by the CMYK image data. The attention line (line number 1) selected in the first step S505 is a line corresponding to the uppermost print line R1 in FIG. 10, and the attention line (line number 2) selected in the second step S505. Is a line corresponding to the second print line R2 from the top.

  In step S515, the correction data acquisition unit 525 acquires, from the characteristic value table 134, a plurality of density characteristic values CP respectively corresponding to the target row and the neighboring row. In the first embodiment, density characteristic values CP respectively corresponding to the target row and the first neighboring row are acquired. The first neighboring row is a row of the row number (N-1) of the image represented by the CMYK image data 310, where N is the row number of the target row. That is, the first neighboring row is a row adjacent to the target row on the downstream side in the transport direction (sub-scanning direction). The first neighboring line is the attention line in the processing of steps S505 to S565 one time before the current attention line. As can be seen from the above description, the pixels constituting the first neighboring row (first neighboring pixels) are pixels whose positions in the sub-scanning direction are different from those of the pixel of interest constituting the row of interest. These are pixels that are subject to error diffusion processing.

  When the row number N of the target row is 1, there is no row having a row number of 0 or less, so there is no neighboring row. In this case, only the density characteristic value CP corresponding to the target row is acquired.

  FIG. 10 shows a case where the line number of the attention line is 4, for example, a print line corresponding to the attention line (referred to as the attention print line), and a print line corresponding to the neighboring line (referred to as the vicinity printing line). , Are shown. When the line number of the target line is 4, the target print line is the print line R4, and the first neighboring print line corresponding to the first neighboring line is the print line R3.

  In order to acquire the density characteristic value CP corresponding to the target line, the correction data acquisition unit 525 first specifies the position on the medium (coordinate in the transport direction) of the target print line. The correction data acquisition unit 525 includes, for example, the print resolution, the line number of the target print line, and the margin width (width in the transport direction) provided at the downstream end (the upper end in FIG. 10) of the print medium P. , The position on the medium of the target print line can be specified. The correction data acquisition unit 525 has an associated on-medium position (represented by 0 to Pn: FIG. 5) among the Pn density characteristic values CP recorded in the characteristic value table 134 of FIG. Then, the density characteristic value CP closest to the position on the medium of the target print line is acquired. The acquired density characteristic value CP is the density characteristic value CP for the color component to be processed (any one of CMYK). Similarly, the correction data acquisition unit 525 acquires, from the characteristic value table 134, the density characteristic value CP corresponding to the on-medium position of the neighboring print line. The acquired density characteristic value CP is the density characteristic value CP of the neighboring row.

  In this embodiment, it is assumed that the density characteristic value CP is recorded in the characteristic value table 134 at an interval corresponding to the distance between two adjacent print lines in the print image (pitch between lines). . For this reason, one print line corresponds to one density characteristic value CP recorded in the characteristic value table 134 on a one-to-one basis. However, the density characteristic value CP recorded in the characteristic value table 134 does not have to correspond one-to-one with the print line. For example, the density characteristic value CP may be recorded in the characteristic value table 134 at an interval wider than the pitch between rows. In this case, for example, the density characteristic value CP corresponding to the print line may be calculated by interpolation calculation using a plurality of density characteristic values CP recorded in the characteristic value table 134. For the interpolation calculation, for example, linear interpolation according to the distance between the position on the medium of the print line and the position on the medium associated with the density characteristic value CP used for the complementary calculation may be employed.

  In step S520, the correction data acquisition unit 525 calculates attention correction data HD for the target row (also referred to as target correction data HD for a plurality of pixels included in the target row). The attention correction data HD can be expressed as 255 + Dtarget + x · (Dtarget−Dpre1). Here, “255” is the maximum value of 256 gradations, “x” is a predetermined coefficient, “Dtarget” is the density characteristic value CP corresponding to the target row, and “Dpre1” is the first value. This is the density characteristic value CP corresponding to one neighboring row. For example, when the characteristic data “2.0” corresponding to the target row and the characteristic data “1.5” corresponding to the first neighboring row are acquired in step S515, the correction data acquisition unit 525 calculates the attention correction data HD by calculating 255 + 2.0 + x · (2.0−1.5). The coefficient x is a coefficient corresponding to an error diffusion matrix used by error diffusion processing.

  FIG. 11 is a diagram illustrating calculation of the corrected pixel value PV ′ using the error diffusion matrix. FIG. 11 shows an error diffusion matrix MT1 used in the first embodiment. In the error diffusion matrix, M1 peripheral pixels located around the target pixel and M1 error diffusion coefficients corresponding to the M1 peripheral pixels are defined. The coefficient x uses the sum of M1 error diffusion coefficients corresponding to the M1 peripheral pixels defined in the error diffusion matrix as a denominator, and the pixel of interest among the M1 peripheral pixels defined in the error diffusion matrix. A numerical value obtained by multiplying a numerical value having the numerator of the sum of M2 error diffusion coefficients corresponding to M2 (M2 ≦ M1) peripheral pixels belonging to a row other than a row to which the design value r belongs. For example, in the error diffusion matrix MT1 in FIG. 11, when the pixel 317 is the target pixel, the two pixels 313 and 316 are M1 (M1 = 2) peripheral pixels, and the one pixel 313 is M2 These are (M2 = 1) peripheral pixels. Accordingly, the sum of M1 error diffusion coefficients is “2 (= 1 + 1)”, and the sum of M2 error diffusion coefficients corresponding to M2 peripheral pixels is “1”. For this reason, the coefficient x is “½ × r”. The coefficient x may be determined by the calculation by the correction data acquisition unit 525 or may be determined in advance by the manufacturer of the printing apparatus 100 and recorded in advance in the printer driver 500 (driver program 232). May be.

  The design value r is a value determined in advance by the manufacturer of the printing apparatus 100. The design value r may be any value that satisfies 0 <r ≦ 3. Generally speaking, the coefficient x may be determined based on the ratio between the sum of M1 error diffusion coefficients and the sum of M2 error diffusion coefficients. In the modification, the coefficient x may be determined based only on the sum of M1 error diffusion coefficients (for example, x = 1 / M1 sum of error diffusion coefficients). More generally speaking, the coefficient x may be determined based on M1 error diffusion coefficients.

  Note that the attention correction data HD calculated in this step is a value (relative density value) representing the density of the dot when the dot is formed on the target pixel in 256 gradations, considering density unevenness. It can be said that it is a calculated value. The relative density value used in the conventional error diffusion processing that does not consider density unevenness is, for example, 255.

  When the attention correction data HD is calculated, in step S525, the halftone processing unit 522 selects one target pixel as a pixel to be processed. The target pixel is selected one by one from the left side in order from the plurality of pixels included in the target row.

  In step S530, the error use correction unit 526 corrects a component value to be processed (referred to as a target pixel value PV) among the CMYK values of the target pixel and calculates a corrected pixel value PV ′ (corrected value). To do.

  Specifically, the error use correction unit 526 corrects the target pixel value PV using a plurality of error values ΔE calculated for a plurality of peripheral pixels. The peripheral pixels are pixels located in the vicinity of the target pixel in the processed pixel group in which the processes of S530 to S565 have been completed before the target pixel. As will be described later, since the error is calculated in step S550 or S555, the error value ΔE has been calculated for the pixels in the processed pixel group. The plurality of peripheral pixels are specified by the error diffusion matrix MT1 shown in FIG. If the pixel of interest is the pixel 317 of FIG. 11, the pixel 316 located to the left of the pixel of interest 317 and the pixel 313 located above the pixel 317 are adopted as peripheral pixels by the error diffusion matrix MT1.

  The error use correction unit 526 corrects the target pixel value PV of the target pixel 317 by correcting the target pixel value PV of the target pixel 317 according to the mathematical formula shown in the pixel 317 of FIG. The value PV ′ is calculated. Specifically, the error use correction unit 526 multiplies the error value ΔE (i, j−1)) of the peripheral pixel 313 by the coefficient ½ corresponding to the peripheral pixel 313 to obtain a multiplication value. Is calculated. Similarly, the error use correction unit 526 calculates a multiplication value by multiplying the error value ΔEk (i−1, j)) of the peripheral pixel 316 by the coefficient ½ corresponding to the peripheral pixel 316. To do. Next, the error use correction unit 526 calculates the corrected pixel value PV ′ by adding the two multiplied values calculated for the two peripheral pixels 213 and 216 to the target pixel value PV. The coefficient corresponding to each peripheral pixel is defined in the error diffusion matrix MT1 (FIG. 11). Even when another error diffusion matrix MT2 is employed, the corrected pixel value PV ′ is calculated by the same method.

  In step S535, the determination unit 527 determines whether or not the corrected pixel value PV ′ is larger than a threshold value TH (for example, 128). When the corrected pixel value PV ′ is larger than the threshold value TH (S535: YES), the determination unit 527 determines the dot value of the component to be processed (any one of CMYK) of the target pixel as “1” (S540). ). A dot value “1” represents forming a dot.

  In step S550, the calculation unit 528 calculates the error value ΔE of the target pixel. The calculation unit 528 calculates the error value ΔE by subtracting the target correction data HD (255 + Dtarget + x · (Dtarget−Dpre1)) calculated for each target row in step S520 from the target pixel value PV ′. That is, the difference between the corrected pixel value PV ′ of the target pixel to be actually expressed and the dot relative density value “255 + Dtarget + x · (Dtarget−Dpre1)” calculated using the density characteristic value CP is an error value. It can be said that it is calculated as ΔE. The calculation of the error value ΔE using the target correction data HD in this step is a compensation process in this embodiment. As will be described later, the compensation processing is processing for compensating for variations in print density that occur according to the position on the medium.

  FIG. 12 is a diagram for explaining calculation of the error value ΔE. In step S550, a mathematical formula for calculating the error value ΔE is shown in the pixel 317 of FIG. That is, in FIG. 12, in the process using the pixel 317 as the target pixel, the dot value is determined to be “1” in step S540 described above, and the error value ΔE is set to (PV′−HD) in step S550. It is shown that it is determined.

  On the other hand, when the corrected pixel value PV ′ is equal to or less than the threshold value TH (S535: NO), the determination unit 527 determines the dot value of the processing target component of the target pixel to “0” (S545). A dot value “0” indicates that no dot is formed.

  In step S555, the calculation unit 528 sets the corrected pixel value PV ′ as an error value ΔE (ΔE = PV ′). That is, in step S555, the error value is calculated without using the attention correction data HD. In step S555, a formula for calculating the error value ΔE is shown in the pixel 318 of FIG. That is, in FIG. 12, in the process using the pixel 318 as the target pixel, the dot value is determined to be “0” in step S545 described above, and the error value ΔE is determined to be the corrected pixel value PV ′ in step S555. Is shown.

  In step S560, the halftone processing unit 522 stores the error value ΔE calculated in step S550 or S555 in the work area 234 as the error value of the target pixel. This error value ΔE is used in the calculation of the corrected pixel value PV ′ (S530) in the process that uses other pixels to be executed later as the target pixel.

  In step S565, the halftone processing unit 522 determines whether all the pixels included in the target row have been selected as the target pixel. If there is an unselected pixel in the target row (S565: NO), the halftone processing unit 522 returns to step S525, selects an unselected pixel, and repeats the processing from step S530 to S560 described above. . If all the pixels in the target row have been selected (S656: YES), the halftone processing unit 522 proceeds to step S570.

  In step S570, the halftone processing unit 522 determines whether all k rows of the image represented by the CMYK image data 310 have been selected as the target row. If there is an unselected row (S570: NO), the halftone processing unit 522 returns to step S505, selects an unselected row, and repeats the processing from steps S515 to S565 described above. If all the rows have been selected (S670: YES), the halftone processing unit 522 ends the error diffusion processing for the color component to be processed.

  When the error diffusion process of FIG. 9 is executed for all four color components of CMYK, dot data (binary data) representing the dot formation state for each pixel is generated for each of the four color components of CMYK. Is done.

  When error diffusion processing is completed for all four color components of CMYK, in step S60 of FIG. 6, the print data supply unit 530 of the printer driver 500 generates print data using the generated dot data, and the print data is printed. Data is transmitted to the printing apparatus 100. The printing process ends. For example, the print data is generated by adding various printer control codes and data identification codes to the generated dot data. When the printer driver 500 transmits the print data, the print process ends.

  Upon receiving print data from the printer driver 500, the print control unit 115 of the printing apparatus 100 prints the print image IM on the print medium P using the print data.

  The effect of the present embodiment will be described with reference to FIGS. FIG. 13 is a graph showing the print density of the print result using the print processing of this embodiment. In this graph, the print density of the print result of the print data generated by executing the error diffusion process (FIG. 9) of the present embodiment on the test image data is plotted against the position on the medium. The test image data is composed of the test image data used when measuring the density characteristic value CP shown in the graph of FIG. 4, that is, one type of CMYK value (for example, CMYK = (255, 0, 0, 0)). This is image data representing a uniform image. The print density plotted in FIG. 13 is a value calculated using a simulation simulating the print execution unit 50 having the density characteristics shown in the graph of FIG. Further, the print density plotted in FIG. 13 is represented by a value having the minimum density as the reference value (0), like the density characteristic value CP, so that it can be compared with the density characteristic value CP plotted in FIG. ing. When the print density plotted in FIG. 13 is compared with the print density of FIG. 4, it can be seen that the uniformity of the print density is improved. For example, the rapid decrease in the density characteristic value CP (FIG. 4: position on the medium 0 and Pa) appearing in FIG. 4 does not appear in FIG. Further, the phenomenon that the density characteristic value CP on the downstream side from the medium position Ps shown in FIG. 4 is lower than the average value of the density characteristic value CP on the upstream side from the medium position Ps does not appear in FIG. . Accordingly, it can be understood that the density unevenness caused by the fluctuation of the surface potential Vs of the photosensitive drum 54 described with reference to FIG. 3 and the like can be suppressed by using the printing process of this embodiment. Further, the phenomenon that the density characteristic value CP appearing in FIG. 4 undulates with respect to the change in the position on the medium does not appear in FIG. Such a undulation phenomenon is considered to be density unevenness due to the eccentricity of the rotating body described above, and is a periodic density unevenness corresponding to the rotation cycle of the rotating body that is the cause. It can be seen that density unevenness due to such eccentricity of the rotating body can also be suppressed by using the printing process of this embodiment.

  That is, according to the printing process of the present embodiment, the compensation process for the target pixel (FIG. 9: S550) is executed using the target correction data HD corresponding to the position on the medium. On the other hand, it is possible to suppress variations in printing density (density unevenness) that occur constantly. As a result, it is possible to reduce the density unevenness of the printed image.

  Further, in this embodiment, by devising a calculation method for calculating the attention correction data HD using the density characteristic value CP, density unevenness is appropriately suppressed when the density characteristic value CP fluctuates rapidly. . FIG. 14 is a diagram showing the correction data HD (A) and the density (B) of the print image for the range RA in the vicinity of the medium upper position Pa in FIG. As shown in FIG. 4, the medium upper position Pa is a position where the density characteristic value CP is abruptly changed. In the graph corresponding to the first comparative example in FIG. 14A, attention correction data HD = “255 + Dtarget” in the first comparative example is plotted. The horizontal axis represents the position on the medium of the target line corresponding to the target correction data HD. Since Dtarget is the density characteristic value CP corresponding to the target row, it can be said that the variation of the density characteristic value CP itself is plotted in the graph of the first comparative example in FIG. On the other hand, the graph corresponding to the first example of FIG. 14A plots the above-described attention correction data HD = “255 + Dtarget + x · (Dtarget−Dpre1)” in the first example. The graph corresponding to the first comparative example in FIG. 14B is simulated based on the print data generated by adopting “255 + Dtarget” as the attention correction data HD in the error diffusion processing of FIG. The print density is shown. The graph corresponding to the first example of FIG. 14B is based on print data generated by adopting the above-mentioned “255 + Dtarget + x · (Dtarget−Dpre1)” (FIG. 12) as the attention correction data HD. The printing density when the simulation is executed is shown.

  Here, when the error diffusion method is used, the error value calculated for the target pixel is diffused to the pixel to be processed after the target pixel. For this reason, the result of the compensation process in step S550 (that is, the error value ΔE calculated for the target pixel) is reflected in the pixel processed after the target pixel, and as a result, the delay of the compensation process Will occur. The influence of the delay of the compensation process is noticeable when the density characteristic value CP varies greatly. Therefore, as in the first comparative example, even if the compensation process is executed using only the density characteristic value CP at the target pixel (target row) (that is, using the target correction data HD = 255 + Dtarget), In some cases, the variation when the density characteristic value CP fluctuates greatly cannot be sufficiently compensated.

  For example, the density characteristic value CP (= Dtarget) is greatly reduced at the position on the medium indicated by the arrow PT1 in FIG. In this case, as shown by the arrow PT1 in FIG. 14B, in the case of the first comparative example, it can be seen that the density of the printing result is greatly reduced. As described above, in the first comparative example, the variation in the print density according to the position on the medium cannot be appropriately compensated, and there is a possibility that a high-quality print result cannot be obtained.

  On the other hand, in the first embodiment, Dtarget is corrected using the difference between Dtarget and Dpre1. Therefore, at a position where the density characteristic value CP decreases toward the upstream side in the sub-scanning direction (for example, FIG. 14: PT1), that is, at a position where Dtarget-Dpre1 becomes a negative value, The corrected value “Dtarget + x · (Dtarget−Dpre1)” is smaller than the density characteristic value CP of the target pixel. As a result, the attention correction data HD is smaller than that in the first comparative example. Accordingly, the error value ΔE (= PV′−target correction data HD) calculated in S550 of FIG. 9 is larger than that in the first comparative example. As the error value ΔE increases, the corrected pixel value PV ′ of the peripheral pixels increases, and as a result, the print density of the peripheral pixels increases. For this reason, as shown by the arrow PT1 in FIG. 14B, the printing density is higher than that of the first comparative example. As a result, the density difference between adjacent rows is reduced, and a high-quality printing result in which density unevenness is suppressed can be obtained.

  On the contrary, at the position where the density characteristic value CP increases toward the upstream side in the sub-scanning direction, that is, at the position where Dtarget-Dpre1 becomes a positive value, the value “Dtarget + x · after correction is compared with the Dtarget before correction. (Dtarget-Dpre1) "is increased. As a result, the attention correction data HD is larger than that in the first comparative example. Therefore, the error value ΔE (= PV′−target correction data HD) calculated in S550 in FIG. 9 is smaller than that in the first comparative example. When the error value ΔE becomes small, the correction pixel value PV ′ of the peripheral pixels becomes small, and as a result, the print density of the peripheral pixels becomes smaller than that of the first comparative example. As a result, the density difference between adjacent rows is reduced, and a high-quality printing result in which density unevenness is suppressed can be obtained.

  Thus, in the compensation processing of the present embodiment, the attention correction data HD obtained using the difference between Dtarget and Dpre1 is used. Thus, when the difference between Dtarget and Dpre1 is taken into account, the delay in compensation processing can be suppressed. As a result, a high-quality printing result can be provided to the user.

  Further, in the compensation processing of the present embodiment, a coefficient “x = (1/2 × design value r)” determined based on a plurality of error diffusion coefficients (FIG. 11) included in the error diffusion matrix MT1 is The attention correction data HD is calculated using the value “x · (Dtarget-Dpre1)” multiplied by (Dtarget-Dpre1). As a result, the attention correction data HD appropriately corresponding to the delay of the compensation process can be calculated according to the error diffusion matrix MT1, so that the density unevenness of the printed image can be appropriately suppressed. More specifically, the coefficient “x” is determined based on the ratio of the sum of M1 error diffusion coefficients and the sum of M2 error diffusion coefficients as described above. As a result, it is possible to appropriately suppress the density unevenness of the print image using an appropriate coefficient “x”.

  Dtarget, Dpre1, and (Dtarget-Dpre1) are examples of “attention value”, “first neighborhood value”, and “first difference”, respectively. Further, the error diffusion matrix MT1 and the coefficient “x = (1/2 × design value r)” are examples of the “first error diffusion matrix” and the “first coefficient”, respectively.

  As can be understood from the above description, the calculation unit 528 of the present embodiment is an example of a compensation unit.

B. Second embodiment:
FIG. 15 is an explanatory diagram of attention correction data HD in the second embodiment.
In this embodiment, the halftone processing unit 522 executes error diffusion processing using the error diffusion matrix MT2 (FIG. 11) instead of the error diffusion matrix MT1. Specifically, in S530 of FIG. 9, if the target pixel is the pixel 317 of FIG. 11, the error use correction unit 526 specifies six pixels 311 to 316 as M1 peripheral pixels. Next, the error addition correction unit 526 specifies six calculated error values ΔE for each of the six peripheral pixels 311 to 316. The error use correction unit 526 multiplies the specified six error values ΔE by the corresponding error diffusion coefficient (FIG. 11: “1/8” or “2/8” defined in the error diffusion matrix MT2), respectively. Then, the sum of the error values after the six multiplications is calculated. The error use correction unit 526 calculates the corrected pixel value PV ′ by adding the total value of the error values to the target pixel value PV.

  In S520 of FIG. 9, the correction data acquisition unit 525 calculates attention correction data HD according to the mathematical formula shown in FIG. The mathematical formula shown in FIG. 15 is almost the same as the mathematical formula shown in FIG. 9 of the first embodiment, but the value of the coefficient “x” is different from that of the first embodiment. In the error diffusion matrix MT2, when the pixel 317 is the target pixel, the six pixels 311 to 316 are M1 (M1 = 6) peripheral pixels, and the four pixels 311 to 314 are M2 (M2 = 4) peripheral pixels. Therefore, the sum of M1 error diffusion coefficients is “8 (= 1 + 1 + 2 + 1 + 1 + 2)”, and the sum of M2 error diffusion coefficients corresponding to M2 peripheral pixels is “5 (= 1 + 1 + 2 + 1)”. Therefore, the coefficient “x” is “5/8 × r”. Other processes are the same as those in the first embodiment.

  According to the second embodiment, since the halftone processing unit 522 uses an appropriate coefficient “x” corresponding to the error diffusion matrix MT2, the density unevenness can be appropriately suppressed according to the error diffusion matrix MT2. it can. In the second embodiment, the error diffusion matrix MT2 “x = (5/8 × design value r)” is an example of “first error diffusion matrix” and “first coefficient”, respectively. .

  In the modification, the coefficient “x” is an error diffusion corresponding to each of the peripheral pixels belonging to the row to which the pixel of interest belongs and the row immediately above that row among the M1 peripheral pixels indicated by the error diffusion matrix. A numerical value obtained by multiplying a numerical value obtained by multiplying the sum of the coefficients by the design value r with the sum of the error diffusion coefficients corresponding to each peripheral pixel belonging to the row one row above the row to which the pixel of interest belongs as a denominator. There may be. For example, when the error diffusion matrix MT2 of FIG. 11 is used, the coefficient “x” = “4/7 × r” (the denominator is “7 (= 1 + 2 + 1 + 2 + 1)” and the numerator is “4 (= 1 + 2 + 1)”. Yes). Generally speaking, the coefficient “x” may be determined based on the error diffusion coefficient of the error diffusion matrix MT2.

C. Third embodiment:
FIG. 16 is an explanatory diagram of attention correction data HD in the third embodiment.
In the third embodiment, as in the second embodiment, the halftone processing unit 522 performs error diffusion processing using the error diffusion matrix MT2. In S515 of FIG. 9, the correction data acquisition unit 525 specifies the second neighboring row in addition to the target row and the first neighboring row. If the row number of the target row is N, the second neighboring row is the row of the row number (N-2) of the image represented by the CMYK image data 310. That is, the second neighboring row is a row adjacent to the downstream side in the transport direction (sub-scanning direction) with respect to the first neighboring row (row number (N-1)). The second neighboring line is the attention line in the processing of steps S505 to S565 two times before the current attention line. As can be understood from the above description, the pixels constituting the second neighboring row (second neighboring pixels) are pixels whose positions in the sub-scanning direction are different from those of the first neighboring pixel and the target pixel. This is a pixel that is subject to error diffusion processing before the neighboring pixel and the target pixel. FIG. 10 illustrates a print row R2 (second neighborhood print row) corresponding to the second neighborhood row, taking the case where the row number of the row of interest is 4, as an example.

  Then, the correction data acquisition unit 525 acquires density characteristic values CP respectively corresponding to the target row, the first neighboring row, and the second neighboring row.

  In the third embodiment, in S520 of FIG. 9, the correction data acquisition unit 525 calculates the attention correction data HD according to the mathematical formula shown in FIG. That is, the attention correction data HD is expressed as “255 + Dtarget + x · (Dtarget−Dpre1) + y · (Dpre1−Dpre2))”. Here, each element other than “Dpre2” is the same as in the second embodiment, and “Dpre2” is the density characteristic value CP corresponding to the second neighboring row.

  The coefficient “y” is M2 error diffusion coefficients corresponding to M2 (M2 ≦ M1) peripheral pixels belonging to a row other than the row to which the pixel of interest belongs among the M1 peripheral pixels indicated by the error diffusion matrix MT2. M3 corresponding to M3 (M3 <M2) pixels included in a row other than the first neighboring row (the row to which the first neighboring pixel belongs) out of the M2 neighboring pixels while using the sum as a denominator Is a numerical value obtained by multiplying a numerical value having the numerator of the sum of the error diffusion coefficients of n by a design value r. For example, in the error diffusion matrix MT2 in FIG. 11, when the pixel 317 is the target pixel, four pixels 311 to 314 are M2 (M2 = 4) peripheral pixels, and one pixel 311 is M3. (M3 = 1) peripheral pixels. Therefore, the sum of M2 error diffusion coefficients is “5 (= 1 + 1 + 2 + 1)”, and the sum of M3 error diffusion coefficients corresponding to M3 peripheral pixels is “1”. Therefore, the coefficient “y” is “1/5 × r”. The coefficient “x” (5/8 × r) is larger than the coefficient “y” (1/5 × r). Other processes are the same as in the second embodiment.

  In the present embodiment, when executing the compensation process, the halftone processing unit 522 uses not only the difference between Dtarget and Dpre1, but also the attention correction data HD obtained using the difference between Dpre1 and Dpre2. In particular, since the coefficient “x” is larger than the coefficient “y”, the attention correction data HD greatly depends on the difference between Dtarget and Dpre1 compared to the difference between Dpre1 and Dpre2. That is, in the attention correction data HD, the difference in the density characteristic value CP between the attention row and the first neighboring row is considered greatly, and further, between the first neighboring row and the second neighboring row. The difference in density characteristic value CP is also taken into consideration. For this reason, the halftone processing unit 522 can appropriately compensate for the density variation in accordance with the error diffusion matrix MT2, and appropriately suppress the density unevenness.

  In the present embodiment, Dpre2 and Dpre1-Dpre2 are examples of “second neighborhood value” and “second difference”, respectively. Further, the error diffusion matrix MT2, “x” (5/8 × design value r), “y” (1/5 × design value r) are respectively “second error diffusion matrix” and “first coefficient”. ”And“ second coefficient ”.

D. Fourth embodiment:
The configuration of the printing system 2 of the fourth embodiment is basically the same as the configuration of the printing system 2 of the first embodiment shown in FIG. However, the halftone processing unit 522 of the fourth embodiment includes a compensation correction unit 529 indicated by a broken line in FIG. 1 in addition to the configuration of the halftone processing unit 522 of the first embodiment. In the fourth embodiment, the contents of the error diffusion process are different from those in the first embodiment. FIG. 17 is a flowchart of the error diffusion process of the fourth embodiment. In FIG. 17, steps that execute the same process as the error diffusion process of the first embodiment (FIG. 9) are given the same reference numerals, and a process different from the error diffusion process of the first embodiment (FIG. 9) is executed. In the step, “A” is added to the end of the code.

  Similar to the error diffusion processing of the first embodiment, when the processing of S505 to S525 is completed, in step S527A, the compensation correction unit 529 corrects the target pixel value PV using the target correction data HD, thereby compensating for the target pixel value PV. A pixel value PV1 is calculated. Specifically, the compensation correction unit 529 calculates the correction coefficient CD using the attention correction data HD. The correction coefficient CD is calculated by calculating (255 + minimum density characteristic value CP) / HD. Here, as described in the first embodiment, the minimum density characteristic value CP is “0”. The compensation correction unit 529 calculates the compensation pixel value PV1 by multiplying the target pixel value PV by the correction coefficient CD.

  In step S530A, as in step S530 of the first embodiment, the error use correction unit 526 calculates the corrected pixel value PV ′ using the calculated error value ΔE. However, the correction target is not the target pixel value PV but the compensation pixel value PV1.

  The subsequent processes of S535 to S545 are the same as the error diffusion process of the first embodiment. In the process of step S550A, that is, the calculation process of the error value ΔE for the pixel of interest performed after the dot value is determined to be “1”, the calculation unit 528 differs from the first embodiment in that the data for attention correction HD is obtained. Without use, an error value Δ is calculated by subtracting 255 from the corrected pixel value PV ′. The processing in steps S555 to S570 is the same as the error diffusion processing in the first embodiment.

  According to the fourth embodiment described above, the same effects as in the first embodiment can be obtained. Note that the processing for correcting the pixel value PV of interest in the CMYK image data (converted image data) using the target correction data HD and calculating the compensation pixel value PV1 is the compensation processing in this embodiment.

  In this embodiment, either of the error diffusion matrices MT1 and MT2 in FIG. 11 may be used. Further, as in the third embodiment, “255 + Dtarget + x · (Dtarget−Dpre1) + y · (Dpre1−Dpre2)” may be used as the attention correction data HD.

  As can be seen from the above description, the compensation correction unit 529 of the present embodiment is an example of a compensation unit.

E. Example 5:
FIG. 18 is an explanatory diagram for explaining the fifth embodiment.
In the fifth embodiment, in S515 of FIG. 9, the correction data acquisition unit 525 acquires the average value AVEtarget of the density characteristic value CP in the vicinity of the target line, instead of the density characteristic value CP (Dtarget) of the target line. . When the row number of the target row (target pixel) is N, AVEtarget is three density characteristic values corresponding to the positions on the medium of the three rows of row numbers (N−1), N, and (N + 1). It is the average value of CP.

  Furthermore, in S515 of FIG. 9, the correction data acquisition unit 525 uses the average value AVEpre1 of the density characteristic value CP in the vicinity of the first neighboring row, instead of the density characteristic value CP (Dpre1) in the first neighboring row. ,get. When the row number of the first neighboring row (first neighboring pixel) is (N−1), AVEtarget is the row number (N−2), (N−1) and N of the three rows. This is an average value of the three density characteristic values CP corresponding to the position on the medium. In FIG. 10, taking as an example the case where the line number of the target line is 4, the target print line corresponding to the target line and the first to third neighboring print lines corresponding to the first to third neighboring lines are shown. It is shown in the figure. When the line number of the noticed line is 4, AVEtage has three density characteristic values respectively corresponding to the first neighboring print line R3, the noticed print line R4, and the third neighboring print line R5. It is the average value of CP. AVEpre1 is an average value of three density characteristic values CP respectively corresponding to the second neighboring print line R2, the first neighboring print line R3, and the target print line R4.

  Then, in S520 of FIG. 9, the correction data acquisition unit 525 further calculates the attention correction data HD according to the equation of FIG. 18C (attention correction data HD = 255 + AVEtarget + x · (AVEtarget−AVEpre1)). .

  The effect of the present embodiment will be described with reference to FIGS. 18 (A) and 18 (B). 18 is a diagram showing correction data HD (A) and print image density (B) for the same range as the graph of FIG. 14 (range RA shown in FIG. 13). In the graph corresponding to the second comparative example in FIG. 16A, attention correction data HD = “255 + AVEtarget” in the second comparative example is plotted. On the other hand, in the graph corresponding to the fifth example of FIG. 14A, the above-described attention correction data HD = “255 + AVEtarget + x · (AVEtarget−AVEpre1)” in the fifth example is plotted. In the graph corresponding to the second comparative example in FIG. 16B, simulation is executed based on print data generated by adopting “255 + AVEtarget” as the attention correction data HD in the error diffusion processing of FIG. The print density is shown. A graph corresponding to the fifth example of FIG. 16B is a simulation executed based on print data generated by adopting the above-mentioned “255 + AVEtarget + x · (AVEtarget−AVEpre1)” as the attention correction data HD. Shows the print density in the case of printing.

  As is clear from the print density at the position on the medium indicated by the arrow PT2 in FIG. 16B, the fifth embodiment has a smaller density difference between adjacent rows and a higher quality print result than the second comparative example. Can be obtained.

  In this embodiment, AVEtarget is calculated using three density characteristic values CP corresponding to three rows of row numbers (N−1) to (N + 1). In general, AVEtarget may be calculated using L density characteristic values CP corresponding to L rows including the target row (L is an integer of 2 or more). Also, AVEpre1 may be calculated using L density characteristic values CP corresponding to L rows including the first neighboring row.

F: Sixth embodiment:
FIG. 19 is a flowchart of printer driver processing according to the sixth embodiment. This printer driver process is executed when a designation instruction for designating a print mode is received from the user prior to the printing process. In the sixth embodiment, the user can designate one mode from the high image quality mode and the low image quality mode when printing an image.

  In step S1, the printer driver 500 determines whether or not the print mode designated by the designation instruction from the user is the high image quality mode. When the designated print mode is the high image quality mode (S1: YES), the printer driver 500 performs print processing using error diffusion processing, that is, printing described in the first to fifth embodiments. Processing is executed (S5). On the other hand, when the designated print mode is not the high image quality mode (S1: NO), that is, when the designated print mode is the low image quality mode, the printer driver 500 executes the print process using the dither process. (S3). The dither process is a known halftone process executed using a dither matrix. In this process, the compensation process (see the first embodiment, etc.) for compensating for variations in print density is not executed.

  According to the sixth embodiment, an appropriate printing process (a printing process using an error diffusion process (S5) or a printing process using a dither process (S3)) is executed according to a printing mode designated by the user. be able to. For example, when the processing speed is prioritized over the image quality, a relatively high-speed but relatively low-quality printing process (S3) is executed. When the image quality is prioritized over the processing speed, the processing speed is relatively high. A print process that is image quality but relatively slow is executed. As a result, user convenience can be improved.

G. Seventh embodiment:
FIG. 20 is a diagram illustrating an example of the correction data table 134A.
In each of the above embodiments, the characteristic value table 134 (FIG. 4) is stored in the nonvolatile memory 130 of the printing apparatus 100. In the seventh embodiment, the nonvolatile memory 130 stores a correction data table 134A shown in FIG. 20 instead of the characteristic value table 134. In the correction data table 134A, correction data calculated using the density characteristic value CP instead of the density characteristic value CP is recorded. In the correction data table 134A of FIG. 20, Pn correction data are recorded in association with Pn media positions (represented by natural numbers 0 to Pn). Each correction data recorded in the correction data table 134A is a value calculated in advance for attention correction data HD (see the first embodiment) for the attention row located at the corresponding position on the medium. Similar to the characteristic value table 134, the correction data table 134A is created by the manufacturer of the printing apparatus 100 and stored in the nonvolatile memory 130, for example.

  In the printing process of the present embodiment, in step S20 of the printing process (FIG. 6) of the first embodiment, the print data generation unit 520 acquires the correction data table 134A instead of the characteristic value table 134. Further, instead of steps S515 and S520 of the error diffusion processing (FIG. 9) of the first embodiment, the correction data acquisition unit 525 obtains the attention correction data HD corresponding to the attention row from the correction data table 134A. Execute the acquisition process. Other processes are the same as those in the first embodiment. According to the present embodiment, the correction data acquisition unit 525 does not have to calculate the attention correction data HD, so that the printing process can be speeded up.

H. Example 8:
In the characteristic value table 134 in the above embodiment, the density characteristic value CP of the entire range from the downstream end to the upstream end of the print medium P is recorded, but it is not necessary to record the density characteristic value CP of the entire range. The density characteristic value CP in a partial range may be recorded. Such an example will be described as a seventh embodiment. FIG. 21 is a diagram for explaining the density characteristic value CP used in the eighth embodiment. A density characteristic value CP shown in FIG. 21 represents density fluctuations based on periodic fluctuations in the conveyance speed based on the eccentricity of the rotating body included in the conveyance mechanism. Such a density characteristic value CP may be theoretically calculated, for example, by calculation based on the amount of eccentricity.

  Here, as shown in FIG. 21, the density characteristic value CP in the present embodiment is periodically repeated with the same value. Specifically, the density characteristic value CP in the first range RG1 at the medium position 0 to P1, and the density characteristic value CP in the second range RG2 at the medium position P1 to P2 (P2 = 2 × P1), The density characteristic value CP in the third range RG3 of the medium upper positions P2 to P3 (P3 = 3 × P1) is the same value.

  Therefore, only the density characteristic value CP within the first range RG1 is recorded in the characteristic value table 134 of the eighth embodiment. In the error diffusion process (FIG. 9), the printer driver 500 uses the density characteristic value CP in the first range RG1 recorded in the characteristic value table 134 as the density characteristic value CP in the second range RG2. Similarly, the printer driver 500 uses the density characteristic value CP in the first range RG1 recorded in the characteristic value table 134 as the density characteristic value CP in the third range RG3. Other specific processing is the same as in the first embodiment. According to the present embodiment, it is possible to appropriately suppress density unevenness due to periodic fluctuations in the conveyance speed. Furthermore, only the density characteristic value CP of a part of the entire range from the downstream end to the upstream end of the print medium P is recorded in the characteristic value table 134 of the present embodiment. The amount of data can be reduced. As a result, the memory capacity for storing the characteristic value table 134 can be reduced.

I. Variations:
(1) In each embodiment described above, the functions of the printer driver 500 of the printing apparatus 100, that is, the functions of the image data acquisition unit 510, the print data generation unit 520, and the print data supply unit 530, It may be provided. That is, in each of the above embodiments, the computer 200 is an example of a “control device”, and in the present modification, the printing device 100 is an example of a “control device”.

(2) In the first embodiment, the density characteristic value CP corresponding to the first neighboring row adjacent to the downstream side in the sub-scanning direction of the target row is used for calculating the target correction data HD. . In the third embodiment, the density characteristic value CP corresponding to the second neighboring row adjacent to the downstream side in the sub-scanning direction of the first neighboring row is further used to calculate the attention correction data HD. ing. Not limited to this, the two or more density characteristic values CP used for the calculation of the attention correction data HD are the density characteristic value CP corresponding to the attention row and one or more neighborhoods where the position of the attention row is different in the sub-scanning direction. The density characteristic value CP corresponding to the row (neighboring pixel) may be included. These neighboring lines do not need to be adjacent to the target line, and may correspond to lines at positions one to several lines away. Generally speaking, the neighboring row (neighboring pixel) is a row (pixel) whose position in the sub-scanning direction is different from that of the target row (target pixel), and the error diffusion process is performed before the target row (target pixel). Any row (pixel) may be used. The second neighboring row (second neighboring pixel) is a row (pixel) whose position in the sub-scanning direction is different from that of the first neighboring row (first neighboring pixel), and the first neighboring row ( Any row (pixel) that is subject to error diffusion processing prior to (first neighboring pixels) may be used.

(3) In each of the above embodiments, the error value ΔE for the pixel of interest is stored in the work area 234 in step S560 of FIG. In step S530 of FIG. 9, the halftone processing unit calculates the corrected pixel value PV ′ by collecting the error values ΔE of the peripheral pixels stored in the work area 234. Instead of this configuration, in step S560, the halftone processing unit 522 may assign an error value ΔE to unprocessed pixels around the target pixel according to the error diffusion matrix MT1. For example, in step S560, the allocated portion of the error value ΔE is added to the pixel value of the unprocessed pixel that is the allocation destination. When the target pixel is selected in step S525, the pixel value of the target pixel is equal to the corrected pixel value PV ′ of the above embodiment, and the process of S530 in FIG. 9 is omitted.

(4) The density characteristic value CP recorded in the characteristic value table 134 of FIG. 5 is calculated with the lowest density value among the density values obtained by measuring the density of the test image representing the uniform image as the reference value “0”. Yes. However, the density value other than the lowest density value may be calculated as the reference value “0”. In this case, the density characteristic value CP recorded in the characteristic value table 134 can take a negative value.

(5) In each of the above embodiments, the numerical value “255” is used to calculate the attention correction data HD (255 + Dtarget + x · (Dtarget−Dpre1)). This is because “255 (CMYK image data) is the maximum value of the relative density value of dots formed corresponding to one dot value“ 1 ”(dot density value represented by 256 gradations) in the print image. This means that the maximum value that can be taken by the pixels within 310 is adopted. Instead of this configuration, a numerical value other than “255” may be used as a numerical value for calculating the attention correction data HD.

(6) In the characteristic value table 134 of FIG. 5, the density characteristic value CP corresponding to the position on the medium where the density characteristic value CP is minimum may be set to “255”. That is, the density characteristic value CP may be a value obtained by adding “255” to the value shown in FIG. In this case, for example, the correction data acquisition unit 525 of the first embodiment may calculate the attention correction data HD according to the mathematical expression “Dtarget + x · (Dtarget−Dpre1)” in S520 of FIG. 255 ”need not be added). Generally speaking, the “density characteristic value CP” may be a characteristic value related to the print density of an image printed on a print medium.

(7) In each of the above embodiments, the print data generation unit 520 of the printer driver 500 acquires the characteristic value table 134 from the printing apparatus 100 after the printing process is started (FIG. 6: S20). However, the acquisition timing of the characteristic value table 134 is not limited to this. For example, the printer driver 500 may acquire the characteristic value table 134 from the printing apparatus 100 at the timing when the printer driver 500 is installed in the printing apparatus 100.

(8) In each of the above embodiments, the characteristic value table 134 is stored in a server managed by the manufacturer of the printing apparatus 100 in association with information (such as a manufacturing number) that identifies each printing apparatus 100. Also good. In this case, the printing apparatus 100 or the printer driver 500 may acquire the characteristic value table 134 by notifying the server of the manufacturing number or the like as necessary.

(9) In each of the above-described embodiments and modifications, a part of the configuration realized by hardware may be replaced with software. Conversely, part or all of the configuration realized by software is used. May be replaced with hardware.

  As mentioned above, although this invention was demonstrated based on the Example and the modification, Embodiment mentioned above is for making an understanding of this invention easy, and does not limit this invention. The present invention can be changed and improved without departing from the spirit and scope of the claims, and equivalents thereof are included in the present invention.

    2 ... printing system, 10 ... housing, 20 ... paper discharge tray, 30 ... paper feed tray, 50 ... print execution unit, 51 ... exposure unit, 52 ... toner Cartridge, 53 ... developing roller, 54 ... photosensitive drum, 55 ... transfer roller, 56 ... fixing unit, 57A ... driving roller, 57B ... driven roller, 58 ... conveying belt 59 ... Process unit 100 ... Printing device 110 ... CPU 115 ... Print control unit 120 ... Volatile memory 130 ... Nonvolatile memory 132 ... Program 134 ... Characteristic value table, 134A ... Correction data table, 140 ... Display unit, 150 ... Operation unit, 160 ... Communication unit, 200 ... Computer, 210 ... CPU , 230 ... Memory, 232 ... Driver program, 234 ... Work area, 240 ... Display unit, 250 ... Operation unit, 260 ... Communication unit, 500 ... Printer driver 510 ... Image data acquisition unit, 520 ... Print data generation unit, 521 ... Color conversion unit, 522 ... Halftone processing unit, 525 ... Data acquisition unit for correction, 526 ... Error Use correction unit, 527 ... determination unit, 528 ... calculation unit, 529 ... compensation correction unit, 527 ... compensation unit, 530 ... print data supply unit

Claims (10)

A control device that controls a print execution unit that prints a print image on a print medium,
A generation unit that performs image processing including error diffusion processing on target image data representing the target image, and generates print data for causing the print execution unit to print the print image representing the target image;
A supply unit for supplying the print data to the print execution unit;
With
The generator is
A correction data acquisition unit that acquires correction data corresponding to a target position that is a position on the medium corresponding to a target pixel that is a processing target of the image processing, wherein the position on the medium is a subordinate on the print medium. The correction data acquisition unit, which is a position in the scanning direction;
A compensation unit that performs the compensation process for compensating for variations in print density of an image printed on the print medium for the pixel of interest, wherein the compensation process corresponds to the correction data corresponding to the position of interest. The compensation unit is implemented using:
With
The correction data corresponding to the attention position is data obtained using a first difference that is a difference between the attention value and the first neighborhood value;
The attention value is a value obtained using a density characteristic value at the attention position,
The first neighborhood value is a value obtained using the density characteristic value at a first neighborhood position that is a position on the medium corresponding to a first neighborhood pixel located in the neighborhood of the target pixel,
The first neighboring pixel is a pixel whose position in the sub-scanning direction is different from that of the target pixel, and is a pixel to be processed by the error diffusion process before the target pixel.
The control device, wherein the density characteristic value is a characteristic value related to a print density of an image printed on the print medium. The correction data is data obtained by using a value calculated by multiplying the first difference by a first coefficient,
The generation unit executes the error diffusion process using a first error diffusion matrix,
The first error diffusion matrix includes a plurality of error diffusion coefficients corresponding to a plurality of peripheral pixels located around the target pixel;
The control device according to claim 1, wherein the first coefficient is determined based on the error diffusion coefficient. The first error diffusion matrix includes M1 error diffusion coefficients corresponding to M1 (M1 ≧ 2) peripheral pixels located around the target pixel,
The M1 error diffusion coefficients are M2 error diffusion coefficients corresponding to M2 (M2 ≦ M1) peripheral pixels located in a row other than the row including the target pixel among the M1 peripheral pixels. Including
The control device according to claim 2, wherein the first coefficient is determined based on a ratio of a sum of the M1 error diffusion coefficients and a sum of the M2 error diffusion coefficients.   4. The control device according to claim 1, wherein the row including the first neighboring pixel is a row adjacent to the row including the target pixel in a sub-scanning direction. 5. The correction data is data obtained by further using a second difference that is a difference between the first neighborhood value and the second neighborhood value,
The second neighborhood value is a value obtained by using the density characteristic value at the second neighborhood position that is the position on the medium corresponding to the second neighborhood pixel located in the neighborhood of the first neighborhood pixel. Yes,
The second neighboring pixel is a pixel whose position in the sub-scanning direction is different from that of the first neighboring pixel, and is a pixel to be processed by the error diffusion process before the first neighboring pixel. The control device according to any one of claims 1 to 4. The correction data uses a value calculated by multiplying the first difference by a first coefficient and a value calculated by multiplying the second difference by a second coefficient. Data obtained by
The generation unit executes the error diffusion process using a second error diffusion matrix,
The second error diffusion matrix includes M1 error diffusion coefficients corresponding to M1 (M1 ≧ 2) peripheral pixels located around the target pixel,
The M1 error diffusion coefficients are M2 error diffusion coefficients corresponding to M2 (M2 <M1) peripheral pixels located in a row other than the row including the target pixel among the M1 peripheral pixels. M3 error diffusion coefficients corresponding to M3 (M3 <M2) peripheral pixels included in a row other than the row including the first neighboring pixel among the M2 peripheral pixels,
The first coefficient is determined based on a ratio of a sum of the M1 error diffusion coefficients and a sum of the M2 error diffusion coefficients,
6. The control device according to claim 5, wherein the second coefficient is determined based on a ratio of a sum of the M2 error diffusion coefficients and a sum of the M3 error diffusion coefficients. The attention value is an average value of L density characteristic values at L positions on the medium corresponding to L (L ≧ 1) rows including the row including the target pixel,
2. The first neighborhood value is an average value of L density characteristic values at L positions on the medium corresponding to L rows including a row including the first neighborhood position. The control device according to claim 6. The generator is
A color conversion unit that performs color conversion processing on the target image data represented in the first type color space to generate converted image data represented in the second type color space;
A halftone processing unit that performs halftone processing on the converted image data to generate the print data;
With
The halftone processing unit
The correction data acquisition unit;
Error use for correcting a value of the target pixel in the converted image data using a plurality of error values corresponding to a plurality of peripheral pixels located around the target pixel to generate a corrected value A correction unit;
A determination unit that determines a dot formation state at the position of interest using the corrected value and a threshold;
A calculation unit as the compensation unit, wherein the calculation unit calculates an error value corresponding to the target pixel according to a formation state of the dot in the target pixel;
Including
8. The calculation unit according to claim 1, wherein the calculation unit executes the calculation process of calculating the error value using the corrected value and the correction data as the compensation process. The control device described in 1. The generator is
A color conversion unit that performs color conversion processing on the target image data represented in the first type color space to generate converted image data represented in the second type color space;
A halftone processing unit that performs halftone processing on the converted image data to generate the print data;
With
The halftone processing unit
The correction data acquisition unit;
The compensation correction unit as the compensation unit, wherein the compensation correction unit executes the compensation process for correcting the value of the target pixel in the converted image data before the halftone process using the correction data. When,
An error use correction unit that corrects the corrected value of the pixel of interest using a plurality of error values corresponding to a plurality of peripheral pixels located around the pixel of interest, and generates a corrected value; ,
A determination unit that determines a dot formation state at the position of interest using the corrected value and a threshold;
The control device according to claim 1, further comprising: a calculation unit that calculates an error value corresponding to the target pixel in accordance with a dot formation state in the target pixel. A computer program for controlling a print execution unit for printing a print image on a print medium,
A generation function for performing image processing including error diffusion processing on target image data representing the target image and generating print data for causing the print execution unit to print the print image representing the target image;
A supply function for supplying the print data to the print execution unit;
With
The generation function is
A correction data acquisition function for acquiring correction data corresponding to a target position that is a position on a medium corresponding to a target pixel that is a processing target of the image processing, wherein the position on the medium is a subordinate position on the print medium. The correction data acquisition function, which is a position in the scanning direction;
A compensation function that performs the compensation process for compensating for variations in print density of an image printed on the print medium for the pixel of interest, wherein the compensation process corresponds to the correction data corresponding to the position of interest. The compensation function performed using:
Is realized on a computer,
The correction data corresponding to the attention position is data obtained using a first difference that is a difference between the attention value and the first neighborhood value;
The attention value is a value obtained using a density characteristic value at the attention position,
The first neighborhood value is a value obtained using the density characteristic value at a first neighborhood position that is a position on the medium corresponding to a first neighborhood pixel located in the neighborhood of the target pixel,
The first neighboring pixel is a pixel whose position in the sub-scanning direction is different from that of the target pixel, and is a pixel to be processed by the error diffusion process before the target pixel.
The computer program, wherein the density characteristic value is a characteristic value related to a print density of an image printed on the print medium.

Images