Image forming apparatus, correction data derivation method and program

Abstract

To enable correction using a correction chart to be executed in such a state that the influence of flare is reduced.SOLUTION: An image formation apparatus comprises: an image formation unit which has a head provided with a plurality of nozzles and forms an image on a sheet conveyed in the first direction with ink droplets discharged by the nozzles; a reading unit which reads the image formed on the sheet; a generation unit which generates a correction chart including a plurality of patches indicating mutually-different densities arranged in the first direction and two marks arranged at different positions in the second direction orthogonal to the first direction; and a derivation unit which derives correction data on the basis of a reading result obtained by reading the correction chart formed on the sheet by the reading unit. The generation unit arranges both ends in the second direction of the plurality of patches on the outer side in the second direction with respect to each of the two marks. The derivation unit derives the correction data on the basis of the reading result of the plurality of patches existing on the inner side with respect to the two marks in the second direction among the reading results of the reading unit.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, a correction data derivation method, and a program. [Background technology]

[0002] Conventionally, in inkjet image forming apparatuses, a correction chart having a plurality of density patterns is printed on paper, and the paper is read by a reading device such as a CCD (Charge Coupled Device) to detect and correct density unevenness.

[0003] For example, a technique has been disclosed in which a correction chart generated using a dither matrix is ​​printed on paper, and the dither matrix or the like is corrected based on the density of the correction chart read by a reading device. Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a paper is read by a reading device, a phenomenon called flare may occur at the boundary of the density pattern where the density changes due to scattering or reflection of the incident light. When flare occurs, an error occurs in the read density, which causes a problem of a decrease in detection accuracy and a decrease in correction accuracy.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an image forming apparatus, a correction data derivation method, and a program that are capable of performing correction using a correction chart while reducing the effects of flare. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the present invention provides an image forming unit having a head provided with a plurality of nozzles, and forming an image on paper transported in a first direction by ink droplets ejected from the nozzles, a reading unit reading the image formed on the paper, a generation unit generating a correction chart including a plurality of patches arranged in the first direction and expressing different densities, and two marks arranged at different positions in a second direction perpendicular to the first direction, and a derivation unit deriving correction data based on a reading result obtained by reading the correction chart formed on the paper by the reading unit, and the generation ... and, based on a characteristic of a density difference between a reference density value of the patch and a density value of the patch read by the reading unit when the reading unit reads the patch from the second direction, at both ends of the patch in the second direction, a distance from the both ends at which the density difference is equal to or smaller than a threshold is specified as a range of influence of flare in the second direction, and the mark is disposed at a position corresponding to the range of influence. The derivation unit is characterized in that it derives the correction data based on the reading results of a plurality of the patches that are located inside the two marks in the second direction, among the reading results of the reading unit, and does not use the reading results of the plurality of the patches that are located outside the two marks in the second direction to derive the correction data. Effect of the Invention

[0007] According to the present invention, it is possible to perform correction using a correction chart while reducing the influence of flare. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of an image forming system according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of the configuration of an engine unit of the image forming apparatus according to the embodiment. [Diagram 3] FIG. 3 is a diagram showing an example of the configuration of a head according to the embodiment. [Figure 4] FIG. 4 is a diagram illustrating another example of the configuration of the image forming unit according to the embodiment. [Diagram 5] FIG. 5 is a diagram illustrating an example of a hardware configuration of the processing device according to the embodiment. [Figure 6] FIG. 6 is a diagram illustrating an example of information stored in the storage unit of the embodiment. [Figure 7] FIG. 7 is a diagram for explaining the flare characteristics in the main scanning direction. [Figure 8] FIG. 8 is a diagram for explaining the flare characteristics in the sub-scanning direction. [Figure 9] FIG. 9 is a diagram illustrating an example of a functional configuration of the processing device according to the embodiment. [Figure 10] FIG. 10 is a diagram illustrating an example of a correction chart generated by the generating unit according to the embodiment. [Figure 11] FIG. 11 is an enlarged view of a portion of the patch shown in FIG. [Figure 12] FIG. 12 is a diagram showing an example of a correction chart printed on paper P. As shown in FIG. [Figure 13] FIG. 13 is a diagram for explaining the division process of the correction chart. [Figure 14] FIG. 14 is a flowchart showing an example of the operation of the image forming apparatus (processing apparatus) according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of an image forming apparatus, a correction data derivation method, and a program will be described with reference to the accompanying drawings.

[0010] 1 is a diagram showing an example of an image forming system according to the present embodiment, which includes an image forming apparatus 1 and a digital front-end (hereinafter, DFE) apparatus 2.

[0011] The image forming apparatus 1 is an inkjet type image forming apparatus and includes an engine unit 10, an operation unit 20, and a processing device 30.

[0012] The engine unit 10 is a mechanical part that performs image formation, and has an image forming unit 12 and a reading unit 133, which will be described later, etc. (see FIG. 2). The operation unit 20 is a user interface for receiving operations for the image forming apparatus 1. The operation unit 20 has input devices such as operation keys and a touch panel, and an output device such as a display device (neither of which are shown). The display device displays, for example, a screen related to the operation of the image forming apparatus 1, an operating status, etc.

[0013] The processing device 30 is a controller that controls the operation of the image forming apparatus 1. The processing device 30 is connected to the engine unit 10, the operation unit 20, and the DFE device 2. The processing device 30 can be a computer device capable of executing applications under various operating systems.

[0014] The DFE device 2 is a device that processes data to be input to the image forming device 1. For example, the DFE device 2 renders and expands print data generated in a format such as PDL (Page Description Language), converts it into raster data, and outputs it to the image forming device 1 (processing device 30). In addition, the processing device 30 causes the engine unit 10 to execute image formation (printing) based on the raster data generated by the DFE device 2.

[0015] 1, the processing device 30 is configured as an integral part of the image forming apparatus 1, but the present invention is not limited to this and may be separate from the image forming apparatus 1. In this case, the processing device 30 is realized by an information processing device such as a PC (Personal Computer) and is communicatively connected to the image forming apparatus 1. Also, the DFE device 2 is configured as a separate device from the image forming apparatus 1, but the present invention is not limited to this and may be provided as an integral part of the image forming apparatus 1 or may be provided in the same device (e.g., information processing device) as the processing device 30.

[0016] Next, the configuration of the engine unit 10 will be described with reference to Fig. 2. Fig. 2 is a diagram showing an example of the configuration of the engine unit 10 of the image forming apparatus 1.

[0017] As shown in FIG. 2, the engine unit 10 includes a paper feed unit 11, an image forming unit 12, a drying unit 13, and a paper discharge unit 14.

[0018] The paper feed section 11 has a paper feed tray 111 on which a plurality of papers P are stacked, a feed device 112 that separates and sends out the papers P one by one from the paper feed tray 111, and a pair of registration rollers 113 that send out the papers P to the image forming section 12.

[0019] The feeding device 112 may be any of various feeding devices, such as a device using rollers or a device using air suction. When the leading edge of the paper P sent out from the paper feed tray 111 by the feeding device 112 reaches the registration rollers 113, the registration rollers 113 are driven at a predetermined timing, and the paper P is fed to the image forming unit 12. Note that any type of paper feed unit 11 may be used as long as it is configured to send out the paper P to the image forming unit 12.

[0020] The image forming unit 12 has a receiving drum 121 that transports the fed paper P to a paper carrying drum 122, and a paper carrying drum 122 that supports the paper P transported by the receiving drum 121 on its outer circumferential surface and transports it to the position of an ink ejection unit 123. The image forming unit 12 also has an ink ejection unit 123 that ejects ink droplets toward the paper P carried on the paper carrying drum 122, and a transfer drum 124 that transports the paper P onto which the ink droplets have been ejected from the paper carrying drum 122 to the drying unit 13.

[0021] The paper P transported from the paper supply unit 11 to the image forming unit 12 has its leading edge gripped by a paper gripper provided on the surface of the receiving cylinder 121, and is transported as the surface of the receiving cylinder 121 moves. The paper P transported by the receiving cylinder 121 is delivered to the paper carrying drum 122 at a position opposite the paper carrying drum 122.

[0022] A paper gripper is also provided on the surface of the paper carrying drum 122, and the leading edge of the paper P is gripped by the paper gripper. In addition, a plurality of suction holes are formed and dispersed on the surface of the paper carrying drum 122. The suction device 125 generates a suction air current toward the inside of the paper carrying drum 122 for each suction hole. The leading edge of the paper P transferred from the receiving cylinder 121 to the paper carrying drum 122 is gripped by the paper gripper, and is adsorbed to the surface of the paper carrying drum 122 by the suction air current, and is transported as the surface of the paper carrying drum 122 moves.

[0023] The ink ejection unit 123 ejects ink droplets of four colors, C (cyan), M (magenta), Y (yellow), and K (black), to form an image on the paper P. The ink ejection unit 123 is equipped with ink ejection heads 126C, 126M, 126Y, and 126K for each color.

[0024] Here, the heads 126C, 126M, 126Y, and 126K have different colors of recording liquid, but otherwise have substantially the same configuration. Specifically, each of the heads 126C, 126M, 126Y, and 126K has a plurality of nozzles 126a (see FIG. 3) that eject ink droplets, and are arranged in a main scanning direction perpendicular to the sub-scanning direction so that an overlap occurs in the sub-scanning direction at the end between adjacent heads. Hereinafter, when there is no need to distinguish between the heads 126C, 126M, 126Y, and 126K, they are also simply referred to as "heads 126". The sub-scanning direction is an example of the first direction. The main scanning direction is an example of the second direction.

[0025] Fig. 3 is a diagram showing an example of the configuration of the head 126. As shown in Fig. 3, the head 126 has a nozzle array 126b in which a large number of nozzles 126a are arranged in a line along the main scanning direction (X direction in the figure) to form a nozzle row.

[0026] The head 126 has such nozzle arrays 126b arranged in a plurality of rows, such as two rows, along the sub-scanning direction (Y direction in the figure) that is a direction two-dimensionally perpendicular to the main scanning direction. The nozzle arrays 126b of the two rows are arranged in parallel such that the nozzle array 126b in the front row (upper in the figure) and the nozzle array 126b in the rear row (lower in the figure) are staggered. That is, the nozzle arrays 126b are arranged in parallel in the main scanning direction such that the ends of adjacent nozzle arrays 126b overlap in the sub-scanning direction. In other words, the heads 126C, 126M, 126Y, and 126K shown in FIG. 1 are full-line type inkjet heads.

[0027] The ejection operation of each of the heads 126 is controlled by a drive signal corresponding to image data. Specifically, each nozzle 126a of the head 126 is provided with an actuator (not shown) for ejecting liquid, and the actuator operates in response to the drive signal to control the ejection operation of ink droplets.

[0028] The processing device 30 controls the supply of drive signals to the actuators of the heads 126 (nozzles 126a). Specifically, the processing device 30 drives the actuators of the nozzles so that any image is formed on the paper P by ink droplets ejected from the nozzles 126a. As a result, when the paper P held on the paper carrying drum 122 passes through an area facing the ink ejection unit 123, ink droplets of each color are ejected from the heads 126C, 126M, 126Y, and 126K, and an image corresponding to the image data to be formed is formed on the paper P.

[0029] The actuator of the head 126 may be a shape-deforming element type such as a piezoelectric type, or may be a movable actuator of another type. The actuator may be a heating type such as a thermal type that uses a heater to boil the recording liquid and eject it from the nozzle 126a, or may be a type that ejects the recording liquid by electrostatic attraction when a voltage is applied.

[0030] The drying section 13 has a drying mechanism 131 for drying ink droplets adhered to the paper P in the image forming section 12, and a transport mechanism 132 for transporting the paper P output from the image forming section 12 to the paper discharge section 14.

[0031] The paper P on which an image has been formed in the image forming unit 12 is transported by the transport mechanism 132 so as to pass through the drying mechanism 131, and is transported to the paper discharge unit 14. When passing through the drying mechanism 131, the paper P is subjected to a drying process. As a result, liquid content such as moisture in the ink droplets on the paper P evaporates, the ink droplets are fixed on the paper P, and curling of the paper P is suppressed.

[0032] The drying unit 13 also has a reading unit 133. The reading unit 133 has an image sensor such as a CCD, and is provided along the conveying path of the conveying mechanism 132. The reading unit 133 reads the image formed on the paper P by capturing an image of the paper P conveyed along the conveying path.

[0033] The paper discharge unit 14 has a paper discharge tray 141 on which a plurality of sheets of paper P are stacked. The sheets of paper P transported from the drying unit 13 are sequentially stacked and held on the paper discharge tray 141. Note that the paper discharge unit 14 may have any configuration as long as it is configured to discharge the sheets of paper P.

[0034] 2, the engine unit 10 has the paper feed unit 11, the image forming unit 12, the drying unit 13, and the paper discharge unit 14, but other functional units may be added as appropriate. For example, a pre-processing unit that performs pre-processing of the image formation may be added between the paper feed unit 11 and the image forming unit 12. Also, a post-processing unit that performs post-processing of the image formation may be added between the drying unit 13 and the paper discharge unit 14.

[0035] As one example, the pre-processing section may be one that performs a processing liquid application process in which processing liquid that reacts with the ink to suppress bleeding is applied to the paper P. The post-processing section may be provided with a paper inversion and transport section that inverts the paper P on which an image has been formed in the image forming section 12 and transports it again to the image forming section 12 to form images on both sides of the paper P. The post-processing section may be provided with a process for binding multiple sheets of paper P on which images have been formed, a correction mechanism for correcting deformation of the paper P, a cooling mechanism for cooling the paper P, or the like.

[0036] 2, the reading unit 133 is configured to be installed after (downstream of) the drying mechanism 131, but the location where the reading unit 133 is installed is not limited to this. For example, the reading unit 133 may be installed between the image forming unit 12 and the drying unit 13, or between the drying unit 13 and the paper discharge unit 14. Also, for example, the reading unit 133 may be installed inside the image forming unit 12, as shown in FIG.

[0037] 4 is a diagram showing another example of the configuration of the image forming unit 12. Here, the reading unit 133 is provided after the ink discharge unit 123 in the transport direction of the paper P. Specifically, the reading unit 133 is provided in the periphery of the paper carrying drum 122 and after the ink discharge unit 123. In this case, the reading unit 133 reads the image formed on the paper P by capturing an image of the paper P on which the image is formed by the ink discharge unit 123 during the process of transport by the paper carrying drum 122.

[0038] Next, a description will be given of the configuration of the processing device 30. Fig. 5 is a diagram showing an example of a hardware configuration of the processing device 30. As shown in Fig. 5, the processing device 30 includes a CPU (Central Processing Unit) 31, a memory 32, an engine interface 33, an operation unit interface 34, a storage unit 35, a DFE interface 36, and an image processing unit 37.

[0039] The CPU 31 is an example of a processor, and controls the overall operation of the processing device 30 and the image forming device 1. The memory 32 is composed of, for example, a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The memory 32 stores various programs related to the operation of the processing device 30, setting information, etc.

[0040] The engine interface 33 is an interface for connecting the engine unit 10. The engine interface 33 transmits and receives various data to and from the engine unit 10 under the control of the CPU 31. For example, the engine interface 33 transmits a drive signal for controlling the operation of the image forming unit 12 to the engine unit 10, and receives the reading result of the reading unit 133 from the engine unit 10.

[0041] The operation unit interface 34 is an interface for connecting the operation unit 20. Under the control of the CPU 31, the operation unit interface 34 transmits and receives various data to and from the operation unit 20. For example, the operation unit interface 34 receives an operation signal input via the operation unit 20, and outputs a display of the processing status, etc. to the operation unit 20.

[0042] The storage unit 35 is a storage device such as a hard disk drive (HDD) or a solid state drive (SSD), etc. The storage unit 35 stores, for example, various programs and setting information related to the operation of the processing device 30 (image forming apparatus 1), a dither pattern to be described later, and the like.

[0043] 6, the storage unit 35 stores specification information 351, paper information 352, and correction parameters 353. Here, FIG. 6 is a diagram showing an example of information stored in the storage unit 35.

[0044] The specification information 351 holds information indicating the specifications of the engine unit 10. For example, the specification information 351 holds the print speed and transport speed of the paper P, the print range in the main scanning direction, the print resolution in the main scanning direction and the sub-scanning direction, the reading resolution in the main scanning direction and the sub-scanning direction of the reading unit 133, and the like.

[0045] Furthermore, the specification information 351 holds flare characteristics that indicate the characteristics of flare that occurs when the reading unit 133 reads an image (e.g., a correction chart) printed on the paper P. Here, flare refers to a phenomenon that occurs at density boundary parts where density changes when the reading unit 133 reads the paper P, and is read as a value different from the actual density due to the influence of scattering and reflection of incident light. More specifically, flare is prominent at the boundary parts between the margins of the paper P and density patches described below, and at the boundary parts between adjacent density patches. Hereinafter, the density boundary of the density patch is also referred to as an edge part.

[0046] Hereinafter, the flare characteristics of the image forming apparatus 1 (engine unit 10) will be described with reference to FIGS.

[0047] Fig. 7 is a diagram for explaining the flare characteristics in the main scanning direction. Fig. 7(a) is a diagram showing a schematic diagram of an edge portion in the main scanning direction (X direction) of paper P. In Fig. 7(a), area Pa means a blank portion of paper P, and area Pb means an area where a density pattern (corresponding to a patch described later) is printed. Here, the starting position of the arrow shown by the dashed line corresponds to the edge portion in the main scanning direction.

[0048] 7(b) is a graph showing the relationship between the distance from the edge and the density difference (color difference) between the reference value of the density detected from the area Pb. Here, the horizontal axis represents the distance dX from the edge in the main scanning direction. The vertical axis represents the density difference ΔE (color difference) between the reference density value (color density) and the density value of the area Pb read by the reading unit 133. Note that the further to the right on the horizontal axis in the figure, the farther away from the edge.

[0049] On the other hand, Fig. 8 is a diagram for explaining the flare characteristics in the sub-scanning direction. Fig. 8(a) is a diagram showing a schematic diagram of an edge portion in the sub-scanning direction (Y direction) of paper P. In Fig. 8(a), area Pa means a blank portion of paper P (or a density pattern adjacent to area Pb), and area Pb means an area where a density pattern is printed. Here, the starting position of the arrow indicated by the dashed line corresponds to the edge portion in the sub-scanning direction.

[0050] 8(b) is a graph showing the relationship between the distance from the edge and the density difference (color difference) between the reference value of the density detected from the area Pb. Here, the horizontal axis represents the distance dY from the edge in the sub-scanning direction. The vertical axis represents the density difference ΔE (color difference) between the reference density value (color density) and the density value of the area Pb read by the reading unit 133. Note that the further to the right on the horizontal axis in the figure, the farther away from the edge.

[0051] 7 and 8, the density difference ΔE is large near the edge and becomes smaller as the distance from the edge increases. In other words, the effect of flare is prominent near the edge in both the main scanning direction and the sub-scanning direction, and the effect of flare decreases as the distance from the edge increases.

[0052] The specification information 351 stores, as flare characteristics, the tendency of flare in the main scanning direction and the sub-scanning direction when the reading unit 133 reads a density image, that is, the degree of influence of flare on the distance from an edge portion. For example, the specification information 351 holds, as flare characteristics, the graphs in Fig. 7(b) and Fig. 8(b) and relational expressions from which approximate curves L1 and L2 that represent the relationship between the distance from an edge portion and the density difference can be derived.

[0053] 6, paper information 352 holds information about paper P that can be used in image forming apparatus 1. For example, paper information 352 holds characteristics such as the size of paper P (main scanning direction and length in the sub-scanning direction) for each type of paper P. Furthermore, in cases where flare characteristics change depending on the paper quality of paper P (for example, plain paper, glossy paper, etc.), paper information 352 may hold flare characteristics corresponding to the paper quality of paper P for each type of paper P.

[0054] The correction parameters 353 are an example of correction data. The correction parameters 353 hold correction parameters related to the correction of uneven density of an image formed by the image forming unit 12. Specifically, the correction parameters 353 hold correction parameters for correcting uneven density of an image formed by the heads 126 (nozzles 126a) of each color. For example, the correction parameters may be parameters for correcting a dither pattern or parameters for controlling the ejection of ink droplets. Note that, when forming an image using the image forming unit 12, the processing device 30 controls the heads 126 of each color to be driven based on the correction parameters 353, so that an image is formed with an appropriate density.

[0055] 5, the DFE interface 36 is an interface for connecting the DFE device 2. Under the control of the CPU 31, the DFE interface 36 exchanges various data with the DFE device 2. For example, the DFE interface 36 transmits print data to be printed to the DFE device 2. In addition, the DFE interface 36 receives raster data generated by the DFE device 2 from the DFE device 2.

[0056] The image processing unit 37 executes various types of image processing. For example, the image processing unit 37 generates a correction chart (described later) that represents a plurality of densities under the control of the CPU 31. In addition, the image processing unit 37 derives correction parameters for correcting density unevenness of the image formed by the image forming unit 12 from the result of reading the correction chart by the reading unit 133 under the control of the CPU 31.

[0057] The image processing unit 37 may be realized by executing a program by the CPU 31. The image processing unit 37 may also be realized by a processing circuit independent of the CPU 31, such as a graphics processing unit (GPU).

[0058] Next, the functional configuration of the processing device 30 will be described. Fig. 9 is a diagram showing an example of the functional configuration of the processing device 30. As shown in Fig. 9, the processing device 30 includes a generating unit 311, a print control unit 312, and a derivation unit 313. Here, the generating unit 311 is an example of a generating means. The print control unit 312 is an example of a print control means. The derivation unit 313 is an example of a derivation means.

[0059] A part or all of the generating unit 311, the printing control unit 312, and the derivation unit 313 may be a software configuration realized by cooperation between the CPU 31 of the processing device 30 and various programs stored in the memory 32. Also, a part or all of the generating unit 311, the printing control unit 312, and the derivation unit 313 may be a hardware configuration realized by a dedicated circuit or the like. For example, the generating unit 311 and the derivation unit 313 may be realized by a program running on the CPU 31 and the image processing unit 37.

[0060] The generating unit 311 generates a correction chart for correcting operations related to image formation based on the specification information 351 and the paper information 352. Specifically, the generating unit 311 generates a correction chart in which a plurality of patches expressing different densities are arranged (arranged) in the sub-scanning direction. The correction chart generated by the generating unit 311 will be described below with reference to FIG. 10.

[0061] Fig. 10 is a diagram showing an example of a correction chart generated by the generation unit 311. As shown in Fig. 10, the correction chart has a plurality of patches A1 to A11 arranged in the sub-scanning direction (Y direction in the figure) and two marks M1 arranged at different positions in the main scanning direction (X direction in the figure).

[0062] The patches A1 to A11 are rectangular regions each expressing a different density. The density expressed by the patches A1 to A11 is generated based on a dither pattern, for example. Dithering is a technique for pseudo-expressing colors and shades that cannot be physically reproduced using fine dots, such as when expressing more gradations with a limited number of colors. The dither pattern is data that is the basis for dot formation for such pseudo-expression. Hereinafter, when there is no need to distinguish between the patches A1 to A11, they will be simply referred to as patch A.

[0063] 10 shows a pattern in which the density increases from the first patch A1 corresponding to the start direction of printing to the last patch A11 corresponding to the end direction of printing. Note that, although the correction chart in FIG. 10 is configured with 11 levels of density (gradation), the number of gradations and density patterns are not limited to this.

[0064] Here, the length of the correction chart (patch A) in the main scanning direction is determined according to the size of the paper P used. Specifically, the generation unit 311 reads out the length in the main scanning direction of the type of paper P used for printing from the paper information 352, and determines the length DX in the main scanning direction of the correction chart based on the read-out length. Note that the type of paper P used for printing may be set in advance, or may be specified via the operation unit 20.

[0065] The length DX of the correction chart in the main scanning direction is not particularly limited as long as it is equal to or less than the length of the paper P in the main scanning direction, and the length may be determined in units of the heads 126 of the image forming unit 12. For example, if the length DX of the correction chart in the main scanning direction is equal to the length of the paper P in the main scanning direction, the correction chart is printed without a so-called border. On the other hand, if the length DX of the correction chart in the main scanning direction is less than the length of the paper P in the main scanning direction, a margin of the paper P is provided outside the correction chart (patch A) in the main scanning direction. In this case, flare will occur at the boundary between the margin of the paper P (paper white) and patch A in the main scanning direction.

[0066] Therefore, the generation unit 311 sets an invalid area that is not used for density detection at the edge portion in the main scanning direction of patch A based on the flare characteristics in the main scanning direction stored in the specification information 351. Specifically, the generation unit 311 specifies a separation distance dX1 from the edge portion at which the density difference ΔE is equal to or less than a threshold value based on the flare characteristics in the main scanning direction. For example, the generation unit 311 specifies a separation distance dX1 at which the density difference ΔE is equal to or less than 1 based on the flare characteristics in the main scanning direction shown in FIG.

[0067] Next, the generation unit 311 sets an area from an edge of patch A in the main scanning direction to a position a distance dX1 away inside patch A as an invalid area B1 that is not used for density detection. Fig. 10 shows an example in which invalid areas B1 are set at both ends of patch A in the main scanning direction. Then, the generation unit 311 places a mark M1 on the correction chart based on the position of the set invalid area.

[0068] Here, the mark M1 is placed at a position where the invalid area B1 or an area obtained by excluding the invalid area B1 from the correction chart (hereinafter also referred to as a detection target area) can be specified, that is, at a position according to the range of influence of the flare when the reading unit 133 reads the patch A in the main scanning direction. In this way, the generation unit 311 places both ends in the main scanning direction of the multiple patches A outside each of the two marks M1 in the main scanning direction. The mark M1 serves as an index when cutting out the correction chart from the reading result of the reading unit 133 in the process described later.

[0069] In addition, in Fig. 10, an example is shown in which mark M1 is arranged outside patch A (patch A1) in the sub-scanning direction so as not to interfere with concentration detection, but the arrangement position of mark M1 is not limited to this. Also, in Fig. 10, the shape of mark M1 is a register mark shape indicating the cut-out position in the main scanning direction and the sub-scanning direction, that is, the corner of the detection target area, but the arrangement position is not limited to this. For example, mark M1 may indicate the cut-out position in the main scanning direction. Also, as shown in Fig. 10, a mark may be arranged at the center position in the main scanning direction, or other marks may be arranged together.

[0070] The generation unit 311 also sets the length of patch A in the sub-scanning direction (Y direction) taking into consideration the range of influence of flare when the reading unit 133 reads patch A from the sub-scanning direction. Hereinafter, a process for setting the length of patch A in the sub-scanning direction will be described with reference to FIG.

[0071] Fig. 11 is an enlarged view of a part (patch A11) of patch A shown in Fig. 10. First, the generation unit 311 specifies the length dY1 in the sub-scanning direction of the invalid area B2 to be set for each patch A, based on the flare characteristics in the sub-scanning direction stored in the specification information 351. Specifically, the generation unit 311 specifies the separation distance dY1 from the edge portion at which the density difference ΔE is equal to or less than a threshold value, based on the flare characteristics in the sub-scanning direction. For example, the generation unit 311 specifies the separation distance dY1 at which the density difference ΔE is equal to or less than 1, based on the flare characteristics in the sub-scanning direction shown in Fig. 8.

[0072] Next, the generation unit 311 determines the length of patch A in the sub-scanning direction as DY' (=DY+(dY1×2)), which is obtained by adding, for example, twice the separation distance dY1 to a predetermined length DY in the sub-scanning direction. Then, as shown in FIG. 11, the generation unit 311 sets the area from the edge of patch A in the sub-scanning direction to a position inside patch A that is a distance dY1 away, as an invalid area B2 that is not used for density detection. Note that the length DY in the sub-scanning direction is a fixed value that specifies the length necessary for density detection, but may be varied depending on the resolution, etc., as described below.

[0073] Here, the above-mentioned invalid areas B1 and B2 correspond to the parts of patch A that are significantly affected by flare. Therefore, by detecting the density from the remaining part of patch A excluding the invalid areas B1 and B2, that is, the target area for density detection, it is possible to improve the detection accuracy.

[0074] The invalid area B2 in the sub-scanning direction may be set for all patches A or for some of the patches A. For example, since the effect of flare increases as the density difference at the edge portion increases, the invalid area B2 may be set only for the patch A11 adjacent to the margin of the paper P.

[0075] 9, the print control unit 312 causes the correction chart generated by the generation unit 311 to be printed on the paper P. Specifically, the print control unit 312 controls the image forming unit 12 to form an image of the correction chart generated by the generation unit 311 on the paper P.

[0076] Fig. 12 is a diagram showing an example of a correction chart printed on paper P. As shown in Fig. 12, the correction chart printed on paper P includes the above-mentioned mark M1. After the paper P on which the correction chart is printed is transported from the image forming unit 12, it is read by the above-mentioned reading unit 133.

[0077] The print control unit 312 may directly print the correction chart generated by the generation unit 311, or may print a correction chart that has been generated by the generation unit 311 and then processed by the DFE device 2 or the like.

[0078] The derivation unit 313 derives correction parameters related to the correction of print density based on the reading result of the reading unit 133 of the correction chart printed (formed) on the paper P. Specifically, the derivation unit 313 acquires the reading result of the reading unit 133 in association with printing of the correction chart by the print control unit 312. From the reading result of the reading unit 133, the derivation unit 313 cuts out patch A that exists inside two marks M1 in the main scanning direction. For example, when the paper P in the state shown in FIG. 12 is read by the reading unit 133, the derivation unit 313 cuts out patch A (A11-A11) that exists within a rectangular area C divided by the corners of the mark M1 as a correction chart.

[0079] Next, the derivation unit 313 detects the density represented in each patch A constituting the extracted correction chart. When an invalid area B2 in the sub-scanning direction is set in the patch A, the derivation unit 313 detects the density of the area excluding the invalid area B2.

[0080] 11, when the length of patch A in the sub-scanning direction is DY' (=DY+(dY1×2)), the derivation unit 313 performs density detection from the remaining area (reading result) obtained by excluding invalid areas B2 of length dY1 from the upper and lower ends of patch A in the sub-scanning direction. Then, the derivation unit 313 derives correction parameters for correcting density unevenness based on the density detected from each patch A, and stores the correction parameters in the storage unit 35.

[0081] The method of deriving the correction parameters is not particularly limited, and any known method can be used. For example, the derivation unit 313 detects density unevenness in units of the head 126 or nozzle 126a by comparing the density value of each patch A of a previously prepared reference correction chart (hereinafter also referred to as a reference chart) with the detected density value or its average value, and derives correction parameters for correcting the density unevenness.

[0082] Here, when focusing on the main scanning direction of patch A printed on paper P, the derivation unit 313 removes invalid area B1 that is significantly affected by the flare area by extracting the area based on mark M1. Furthermore, based on the value of length dY1 that defines invalid area B2 identified by the generation unit 311, the derivation unit 313 sets the remaining area, excluding invalid area B2 from the edge part of patch A in the sub-scanning direction, as the target of density detection.

[0083] As a result, the derivation unit 313 detects the density from each patch in a state where the influence of the flare is reduced. Therefore, the derivation unit 313 can accurately detect the density represented in the patch A, and therefore the accuracy of the correction parameters can be improved.

[0084] In the above embodiment, the length DY of patch A in the sub-scanning direction is a fixed value, but the invention is not limited to this and the length may be adjusted according to various conditions.

[0085] For example, the generating unit 311 adjusts the length DY of the correction chart in the sub-scanning direction based on the ratio between a reference resolution in the sub-scanning direction (hereinafter also referred to as the reference resolution) and the reading resolution in the sub-scanning direction of the reading unit 133. Here, the reference resolution is not particularly important, and various conditions can be set. For example, the reference resolution may be the resolution in the sub-scanning direction when the reference chart is read by an offline reading device different from the reading unit 133.

[0086] As an example, assume that the reference resolution in the sub-scanning direction is 600 dpi (dots per inch), and the reading resolution in the sub-scanning direction of the reading unit 133 stored in the specification information 351 is 300 dpi. In this case, the generation unit 311 adjusts the length DY of the patch A in the sub-scanning direction to be doubled based on the ratio between the reference resolution of 600 dpi and the reading resolution of 300 dpi of the reading unit 133. This makes it possible to treat the reading result in the sub-scanning direction read by the reading unit 133 as equivalent to the reference resolution, making it easier to compare with the reference chart.

[0087] In this case, the generation unit 311 also adjusts the length dY1 of the invalid area B2 in the sub-scanning direction by the same magnification as the length DY. Therefore, the generation unit 311 adjusts the length DY' of the patch A2 in the sub-scanning direction including the invalid area B2 based on the reference resolution in the sub-scanning direction and the reading resolution of the reading unit 133 in the sub-scanning direction.

[0088] Depending on the addition of an invalid area B2 to patch A or the adjustment of the length DY (or DY') in the sub-scanning direction, it may not be possible to fit all of the patches A constituting the correction chart onto one sheet of paper P. In such a case, the generation unit 311 divides the patch A at the boundary portion in the sub-scanning direction into sizes according to the size of the paper P, thereby generating multiple correction charts.

[0089] Fig. 13 is a diagram for explaining the division process of the correction chart. As shown in Fig. 13(a), when all the patches A (A1 to A11) constituting the correction chart cannot fit on one sheet of paper P, the generation unit 311 divides the patches A into a plurality of groups so that they can fit on one sheet of paper P. Specifically, the generation unit 311 divides the patches A into groups by dividing them at the edges of the patches A in the sub-scanning direction, that is, at the density boundaries.

[0090] Here, it is preferable that the generation unit 311 groups the patches A by a division number that minimizes the number of sheets of paper P used. Next, the generation unit 311 generates a correction chart for each grouped patch A. The generation unit 311 adds the above-mentioned mark M1 to each correction chart generated. Then, the print control unit 312 causes each of the generated correction charts to be printed individually on paper P.

[0091] Fig. 13(b) shows an example of dividing patch A. Here, an example is shown in which the correction chart in which patches A1 to A11 shown in Fig. 13(a) are divided into two at the density boundary between patch A4 and patch A5 is printed on paper P1 and paper P2.

[0092] In addition, the derivation unit 313 performs the same processing as described above based on the reading results of each of the papers P1 and P2 read by the reading unit 133, thereby detecting the concentration from the remaining areas excluding the invalid areas B1 and B2.

[0093] As a result, in the image forming apparatus 1, even if the length of the correction chart in the sub-scanning direction is equal to or longer than the length of the paper P in the sub-scanning direction, the correction parameters can be derived using multiple sheets of paper P. Therefore, in the image forming apparatus 1, the correction chart can be formed in a size according to the flare characteristics without being limited by the size of the paper P.

[0094] Hereinafter, the operation of the image forming apparatus 1 (processing device 30) related to derivation of the correction parameters will be described with reference to Fig. 14. Fig. 14 is a flowchart showing an example of the operation of the image forming apparatus 1 (processing device 30).

[0095] First, the generation unit 311 waits until an instruction to execute density correction is given (step S11; No). Here, the instruction to execute density correction may be given manually via the operation unit 20, or may be given automatically when the image forming apparatus 1 is started or at predetermined intervals.

[0096] When the generation unit 311 receives an instruction to perform density correction (step S11; Yes), it specifies the length dX1 in the main scanning direction and the length dY1 in the sub-scanning direction that define the invalid areas B1, B2 based on the flare characteristics of the specification information 351 (step S12).

[0097] Next, the generation unit 311 calculates the size of each patch A constituting the correction chart based on the size of the paper P to be used, the processing result of step S12, the ratio to the reference resolution, etc. (step S13). Next, the generation unit 311 determines whether the size in the sub-scanning direction of the correction chart calculated in step S13 (length in the sub-scanning direction) fits on one sheet of paper P (step S14).

[0098] If it is determined that the image fits on one sheet of paper P (step S14; Yes), the generation unit 311 generates a correction chart with a mark M1 added to a position indicating the invalid area B1, that is, a cut-out position of the correction chart (step S16).

[0099] On the other hand, if it is determined that the correction chart will not fit on one sheet of paper P (step S14; No), the generation unit 311 divides the patches A constituting the correction chart into multiple groups at density boundary portions so that the correction chart will fit within the length of the paper P in the sub-scanning direction (step S15). Next, the generation unit 311 generates a correction chart with a mark M1 added to each of the divided groups of patches A (step S16).

[0100] Next, the print control unit 312 controls the image forming unit 12 to print the correction chart generated in step S15 on the paper P (step S17). In conjunction with the process of step S16, the reading unit 133 reads the paper P on which the correction chart is printed.

[0101] When the derivation unit 313 acquires the read result of the reading unit 133 (step S18), the derivation unit 313 cuts out the correction chart excluding the invalid area B1 in the main scanning direction based on the mark M1 included in the read result (step S19). Next, the derivation unit 313 detects the density of each patch A included in the cut correction chart from the remaining area (target area) excluding the invalid area B2 (step S20).

[0102] Next, the derivation unit 313 derives correction parameters for correcting density unevenness based on the detection result of step S20 (step S21). Then, the derivation unit 313 stores the derived correction parameters in the storage unit 35 as correction parameters 353 (step S22), and ends this process.

[0103] As described above, the image forming apparatus 1 (processing device 30) generates a correction chart in which both ends of the patch A in the main scanning direction are positioned outside the two marks M1 in the main scanning direction. Then, the image forming apparatus 1 (processing device 30) derives correction data based on the reading result of the patch A that exists inside the two marks M1 in the main scanning direction, from among the reading results of the correction chart formed on the paper P.

[0104] As a result, the image forming device 1 (processing device 30) can detect the concentration from each patch A while reducing the effect of flare when reading patch A from the main scanning direction, thereby improving the detection accuracy as well as the accuracy of the derived correction parameters.

[0105] Furthermore, the image forming apparatus 1 (processing device 30) generates a correction chart in which the length in the sub-scanning direction of part or all of patch A is set to a length that takes into account the range of influence of flare when reading patch A from the sub-scanning direction. Then, the image forming apparatus 1 (processing device 30) derives the correction data based on the reading results of the remaining patches excluding the range of influence in the sub-scanning direction from the reading results of the correction chart.

[0106] As a result, the image forming device 1 (processing device 30) can detect the concentration from each patch A while reducing the effect of flare when reading patch A from the sub-scanning direction, thereby improving the detection accuracy as well as the accuracy of the derived correction parameters.

[0107] The above-described embodiment can be modified as appropriate by changing a portion of the configuration or functions of the image forming apparatus 1 (processing device 30). Therefore, the following describes a modified example of the above-described embodiment as another embodiment. Note that the following mainly describes the differences from the above-described embodiment, and a detailed description of the points in common with the contents already described will be omitted. The modified examples described below may be implemented individually or in appropriate combination.

[0108] [Variation 1] In the above embodiment, a correction chart is generated in which the mark M1 is added to a position indicating the invalid area B1, but the mark M1 may not be added, as in the case of the invalid area B2. In this case, the derivation unit 313 excludes the invalid area B1 from the edge portion in the main scanning direction of the patch A based on the value of the length dX1 that defines the invalid area B1 identified by the generation unit 311, in the same manner as in the process of excluding the invalid area B2.

[0109] As a result, the image forming apparatus 1 (processing device 30) according to this modified example can achieve the same functions and effects as those of the above-described embodiment, thereby improving the accuracy of density detection and the accuracy of the derived correction parameters.

[0110] Although the embodiments (and modifications) of the present invention have been described above, the above-mentioned embodiments are presented as examples and are not intended to limit the scope of the invention. The present invention is not limited to the above-mentioned embodiments as they are, and the components can be modified and embodied in the implementation stage without departing from the gist of the invention. Furthermore, various inventions can be formed by appropriate combinations of multiple components disclosed in the above-mentioned embodiments. For example, some components may be deleted from all the components shown in the embodiments. [Explanation of symbols]

[0111] 1. Image forming device 2 DFE device 10 Engine section 20 Control section 30 Processing equipment 126 Head 126a Nozzle 126b Nozzle Array 133 Reading unit 311 Generation part 312 Printing control unit 313 Derivation part [Prior art documents] [Patent documents]

[0112] [Patent Document 1] Patent No. 4828241

Claims

1. an image forming unit having a head with a plurality of nozzles, and forming an image on a sheet of paper transported in a first direction by ink droplets ejected from the nozzles; A reading unit that reads an image formed on the paper; a generation unit that generates a correction chart including a plurality of patches that are arranged in the first direction and that express different densities, and two marks that are arranged at different positions in a second direction that is perpendicular to the first direction; a derivation unit that derives correction data based on a reading result obtained by reading the correction chart formed on the paper by the reading unit; Equipped with the generation unit arranges both ends of the plurality of patches in the second direction outboard of each of the two marks, and at both ends of the patch in the second direction, specifies, based on characteristics of a density difference between a reference density value of the patch and a density value of the patch read by the reading unit when the reading unit reads the patch from the second direction, a distance from the both ends at which the density difference is equal to or smaller than a threshold as a range of influence of flare in the second direction, and arranges the mark at a position according to the range of influence; The image forming apparatus is characterized in that the derivation unit derives the correction data based on the reading results of a plurality of the patches that are located inside the two marks in the second direction, among the reading results of the reading unit, and does not use the reading results of the plurality of the patches that are located outside the two marks in the second direction to derive the correction data.

2. An image forming unit having a head with a plurality of nozzles, the image forming unit forming an image on a sheet of paper transported in a first direction by ink droplets ejected from the nozzles; A reading unit that reads an image formed on the paper; a generation unit that generates a correction chart including a plurality of patches that are arranged in the first direction and that express different densities, and two marks that are arranged at different positions in a second direction that is perpendicular to the first direction; a derivation unit that derives correction data based on a reading result obtained by reading the correction chart formed on the paper by the reading unit; Equipped with the generation unit disposes both ends of the plurality of patches in the second direction on the outer side of each of the two marks, and specifies, based on a characteristic of a density difference between a reference density value of the patch and a density value of the patch read by the reading unit when the reading unit reads the patch from the first direction, a distance from the both ends at which the density difference is equal to or smaller than a threshold value as an affected range of flare in the first direction, and sets a length in the first direction of some or all of the plurality of patches to a length taking into account the affected range; The image forming apparatus is characterized in that the derivation unit derives the correction data based on the reading results of the remaining patches excluding the affected range in the first direction from the reading results of the reading unit and the reading results of a plurality of the patches that exist inside the two marks in the second direction, and does not use the reading results of the plurality of the patches that exist outside the two marks in the second direction to derive the correction data.

3. 3 . The image forming apparatus according to claim 2 , wherein the generation unit sets a length in the first direction of the patch that represents the highest density to a length that takes into account the range of influence.

4. the generation unit generates a plurality of the correction charts by dividing the plurality of patches into sizes corresponding to the size of the paper at a boundary portion in the first direction when the correction chart does not fit on one sheet of paper; 4. The image forming apparatus according to claim 1, wherein the deriving unit derives the correction data based on the reading results of a plurality of the correction charts.

5. 1. A correction data deriving method executed in an image forming apparatus including: an image forming unit having a head with a plurality of nozzles, the image forming unit forming an image on paper transported in a first direction by ink droplets ejected from the nozzles; and a reading unit reading the image formed on the paper, the method comprising: a generating step of generating a correction chart including a plurality of patches representing different densities arranged in the first direction and two marks arranged at different positions in a second direction perpendicular to the first direction; a derivation step of deriving correction data based on a reading result obtained by reading the correction chart formed on the paper by the reading unit; Including, In the generating step, both ends of the plurality of patches in the second direction are disposed outside of each of the two marks in the second direction, and at both ends of the patch in the second direction, based on characteristics of a density difference between a reference density value of the patch and a density value of the patch read by the reading unit when the reading unit reads the patch from the second direction, a separation distance from the both ends at which the density difference is equal to or smaller than a threshold is specified as an affected range of flare in the second direction, and the mark is disposed at a position corresponding to the affected range. A correction data derivation method characterized in that, in the derivation process, the correction data is derived based on the reading results of a plurality of the patches that are located inside the two marks in the second direction among the reading results of the reading unit, and the reading results of a plurality of the patches that are located outside the two marks in the second direction are not used to derive the correction data.

6. A computer of an image forming apparatus including an image forming unit having a head with a plurality of nozzles and forming an image on a sheet of paper transported in a first direction by ink droplets ejected from the nozzles, and a reading unit reading the image formed on the sheet of paper, a generating means for generating a correction chart including a plurality of patches representing different densities arranged in the first direction and two marks arranged at different positions in a second direction perpendicular to the first direction; a deriving unit that derives correction data based on a reading result obtained by reading the correction chart formed on the paper by the reading unit; and make it work. the generation means arranges both ends of the plurality of patches in the second direction outboard of each of the two marks, and at both ends of the patch in the second direction, specifies, based on characteristics of a density difference between a reference density value of the patch and a density value of the patch read by the reading unit when the reading unit reads the patch from the second direction, a distance from the both ends at which the density difference is equal to or smaller than a threshold value as a range of influence of flare in the second direction, and arranges the mark at a position according to the range of influence; The derivation means derives the correction data based on the reading results of a plurality of the patches that are located inside the two marks in the second direction, among the reading results of the reading unit, and does not use the reading results of a plurality of the patches that are located outside the two marks in the second direction to derive the correction data.

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