Printing device and printing method

Abstract

To solve the problem that excess media and time are consumed by trial printing for adjusting a color.SOLUTION: A printer includes a printing head for discharging ink to a medium on the basis of printing data, a carriage which is mounted with the printing head and reciprocates in a main scanning direction, a control part which controls the carriage and the printing head, and executes a pass as ink discharge by the printing head accompanied by movement of the carriage, and a colorimetry part enabling colorimetry of concentration in the medium at the time of completion of the pass, wherein in a state where printing is executed on a predetermined region of the medium in the N-th pass, when n is a natural number smaller than N, the control part acquires n-th concentration that is a colorimetry result by the colorimetry part for the medium at the time of completion of the n-th pass for the predetermined region, corrects the printing data used in a pass after the n-th pass for the predetermined region according to the n-th concentration, and executes a pass after the n-th pass on the basis of the printing data after correction.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a printing device and a printing method. [Background technology]

[0002] An image forming apparatus is disclosed in which a carriage on which a recording head is mounted is equipped with a colorimetric camera (see Patent Document 1). According to Patent Document 1, the colorimetric camera moves over a recording medium on which a test pattern is recorded by conveying the recording medium and moving the carriage, captures an image of each patch of the test pattern, and calculates the colorimetric value of the patch using the image data. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-114507 Summary of the Invention [Problem to be solved by the invention]

[0004] In a configuration in which an image printed on a medium is captured with a camera to acquire colorimetric values ​​for color adjustment, etc., as in Reference 1, the corrections made using the colorimetric values ​​are reflected in subsequent printing. Therefore, the captured image is merely a test image printed solely for color adjustment, and is wasted as a printed product. Improvements are needed to reduce the costs associated with such media consumption and the lengthened time required to produce printed products. [Means for solving the problem]

[0005] The printing device comprises a print head that ejects ink onto a medium based on print data, a carriage that carries the print head and moves back and forth along the main scanning direction, a control unit that controls the carriage and the print head to execute passes in which the print head ejects ink as the carriage moves, and a colorimetric unit that can measure the density on the medium at the completion of the passes, wherein when printing is performed on a specified area of ​​the medium in N passes, where n is a natural number smaller than N, the control unit obtains an nth density that is the colorimetric result of the colorimetric unit on the medium at the completion of the nth pass on the specified area, corrects the print data to be used for passes after the nth to the specified area according to the nth density, and executes the passes after the nth based on the corrected print data.

[0006] A printing method that controls a print head that ejects ink onto a medium based on print data and a carriage that carries the print head and moves back and forth in the main scanning direction to execute passes in which the print head ejects ink as the carriage moves, when printing is executed in N passes onto a specified area of ​​the medium, where n is a natural number smaller than N, obtains an nth density that is the colorimetric result of the density of the medium measured by a colorimetric unit at the completion of the nth pass onto the specified area, corrects the print data to be used for passes after the nth pass onto the specified area according to the nth density, and executes the passes after the nth pass based on the corrected print data. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram showing a simplified configuration of an apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a simplified view from above of the relationship between the medium, the print head, etc.; [Figure 3] FIG. 4 is a diagram showing an example of print data for printing a predetermined area. [Figure 4] 4 is a flowchart showing a print control process according to the first embodiment. [Figure 5]6A and 6B are diagrams for explaining a specific example of a method for correcting print data. [Figure 6] 10 is a flowchart showing a print control process according to a second embodiment. [Figure 7] 10 is a flowchart showing a print control process according to a third embodiment. [Figure 8] 10 is a flowchart showing a print control process when printing continuously on a plurality of sheets of media. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the drawings are merely examples for explaining the present embodiment. Because the drawings are examples, the proportions and shapes may not be accurate, the drawings may not match each other, and some parts may be omitted.

[0009] 1. Brief description of the device configuration: 1 shows a simplified configuration of a printing device 10 according to this embodiment. The printing device 10 executes the printing method of this embodiment.

[0010] The printing device 10 includes a control unit 11, a display unit 13, an operation reception unit 14, a memory unit 15, a communication IF 16, a transport unit 17, a printing unit 18, and a colorimetric unit 19. IF stands for interface. The control unit 11 includes one or more ICs having a CPU 11a as a processor, a ROM 11b, a RAM 11c, and other non-volatile memories.

[0011] In the control unit 11, a processor, i.e., CPU 11a, executes arithmetic processing in accordance with a program 12 stored in ROM 11b or other memory, using RAM 11c or the like as a work area, thereby realizing various functions such as a print data generation unit 12a, a colorimetry result acquisition unit 12b, a print data correction unit 12c, and a print control unit 12d. The processor is not limited to a single CPU, and may be configured to perform processing using multiple CPUs or hardware circuits such as ASICs, or may be configured to perform processing in cooperation with a CPU and a hardware circuit.

[0012] The display unit 13 is a means for displaying visual information and is configured, for example, by a liquid crystal display, an organic electroluminescence (EL) display, or the like. The display unit 13 may be configured to include a display and a drive circuit for driving the display. The operation reception unit 14 is a means for receiving input from a user and is realized, for example, by physical buttons, a touch panel, a mouse, a keyboard, or the like. Of course, the touch panel may be realized as one function of the display unit 13. The display unit 13 and the operation reception unit 14 may be collectively referred to as the operation panel of the printing device 10. The display unit 13 and the operation reception unit 14 may be part of the configuration of the printing device 10, or may be peripheral devices external to the printing device 10.

[0013] The storage unit 15 is, for example, a hard disk drive, a solid state drive, or other memory storage means. Part of the memory of the control unit 11 may be regarded as the storage unit 15. The storage unit 15 may also be regarded as part of the control unit 11. The communication IF 16 is a general term for one or more IFs that allow the printing device 10 to communicate with external devices via wired or wireless connections in accordance with a predetermined communication protocol, including known communication standards. Examples of external devices include communication devices such as personal computers, servers, smartphones, and tablet terminals.

[0014] The conveying unit 17 is a means for conveying the medium 30 in a predetermined conveying direction under the control of the control unit 11. The conveying unit 17 includes, for example, rollers that rotate to convey the medium 30, and a motor as a power source for the rotation. The conveying unit 17 may also be a mechanism that conveys the medium 30 by placing the medium 30 on a belt or pallet that is driven by a motor. The medium 30 is, for example, paper, but may also be any medium that can be printed on, and may be a material other than paper, such as film or fabric.

[0015] The printing unit 18 is a means for ejecting liquid such as ink from multiple nozzles using an inkjet system under the control of the control unit 11 to print on a medium 30 transported by the transport unit 17, and includes a print head 20 and a carriage 21, which will be described later. The droplets ejected from the nozzles of the print head 20 are called dots. The print head 20 is capable of ejecting various inks, such as cyan (C), magenta (M), yellow (Y), and black (K). Of course, the liquid ejected by the print head 20 is not limited to CMYK inks. The print head 20 may also be called a liquid ejection head, a recording head, a print head, an inkjet head, etc.

[0016] The colorimetric unit 19 is a means for optically measuring the color and brightness of the medium 30 printed by the printing unit 18. Color and brightness can be expressed in various color systems, but below, the color and brightness measured from the printed medium 30 will simply be referred to as density. High density means dark, and low density means bright. The colorimetric unit 19 is specifically a colorimeter, camera, scanner, etc. Color measurement can also be referred to as measurement or reading. The colorimetric unit 19 transfers the colorimetric results to the control unit 11.

[0017] Printing device 10 may be realized by a single printer, or may be realized by a system having multiple devices connected to each other so that they can communicate with each other. For example, printing device 10 may be a system including an information processing device that functions as control unit 11, a printer that includes transport unit 17 and printing unit 18 and performs printing under the control of the information processing device, and a device that corresponds to colorimetric unit 19. In this case, the information processing device can be understood as a print control device, an image processing device, or the like.

[0018] FIG. 2 shows a simplified top-down view of the relationship between the medium 30, print head 20, and other components. As shown in FIG. 2, the print head 20 is mounted on a carriage 21. The carriage 21 is capable of reciprocating along a predetermined main scanning direction D1 using the power of a carriage motor (not shown) under the control of the control unit 11. For example, the positive direction of the main scanning direction D1 is the direction of forward movement of the carriage 21, and the negative direction of the main scanning direction D1 is the direction of backward movement of the carriage 21. Therefore, the print head 20 moves forward and backward along the main scanning direction D1 together with the carriage 21.

[0019] The print head 20 has a nozzle row for each ink color. Figure 2 shows two nozzle rows 20a and 20b in a simplified manner. Each of the white circles in Figure 2 represents an individual nozzle 22. A nozzle row corresponding to one ink color is made up of multiple nozzles 22 with a constant or nearly constant nozzle pitch, which is the distance between the nozzles 22 in a direction intersecting the main scanning direction D1. For example, nozzle row 20a is a nozzle row made up of multiple nozzles 22 that eject K ink, and nozzle row 20b is a nozzle row made up of multiple nozzles 22 that eject C ink. Although not shown in the figure, the print head 20 naturally also has nozzle rows corresponding to colors other than K ink and C ink, such as M ink and Y ink.

[0020] The control unit 11 causes the print head 20 to eject ink onto the medium 30 based on the print data. As is known, the print head 20 is provided with a drive element for each nozzle 22, and by controlling the application of a drive signal to the drive element of each nozzle 22 in accordance with the print data, each nozzle 22 ejects or does not eject a dot, thereby printing an image represented by the print data onto the medium 30. The print data is data that specifies the presence or absence of a dot of each color ink for each pixel, as well as the size of the dot. Hereinafter, the presence of a dot, i.e., ejecting a dot, is also referred to as "dot on," and the absence of a dot, i.e., not ejecting a dot, is also referred to as "dot off."

[0021] The size of the dots ejected by the nozzles 22 can be varied by varying the amplitude, shape, etc. of the drive signal applied to the drive element of the nozzles 22. For example, the nozzles 22 can eject dots of three different sizes: large dots, medium dots, and small dots. The relationship between the sizes of each dot is small dots < medium dots < large dots. Therefore, the dot-on data for each pixel specified by the print data is divided into large dots, medium dots, and small dots. Note that the number of dot sizes that the nozzles 22 can eject may be two, four, or more.

[0022] The ink ejection by the print head 20 as the carriage 21 moves is called a "pass" or a "scan." A pass made by the outward movement of the carriage 21 is called an outward pass, and a pass made by the backward movement of the carriage 21 is called a backward pass. Printing performed using both the outward and backward passes is called bidirectional printing, while printing performed using only one of the outward or backward passes is called unidirectional printing. In this embodiment, either bidirectional printing or unidirectional printing may be used.

[0023] The symbol D2 indicates the transport direction D2 of the medium 30 by the transport unit 17. The transport unit 17 transports the medium 30 from upstream to downstream in the transport direction D2. The upstream and downstream of the transport direction D2 are simply referred to as upstream and downstream. The transport direction D2 intersects with the main scanning direction D1. The intersection of the main scanning direction D1 and the transport direction D2 is perpendicular or nearly perpendicular. The multiple nozzle rows, such as the nozzle rows 20a and 20b, of the print head 20 are aligned along the main scanning direction D1 and are at the same position in the transport direction D2.

[0024] In the example of FIG. 2, colorimeters 19a and 19b are provided as the colorimetric unit 19 at both ends of the print head 20 in the main scanning direction D1. Specifically, colorimeter 19a is attached to the end of the carriage 21 facing the positive side in the main scanning direction D1, and colorimeter 19b is attached to the end of the carriage 21 facing the negative side in the main scanning direction D1. Colorimeters 19a and 19b and print head 20 move back and forth together with the carriage 21. With this configuration, the density of ink ejected from the print head 20 onto the medium 30 during a forward pass can be measured by colorimeter 19b during the same forward movement. Similarly, the density of ink ejected from the print head 20 onto the medium 30 during a return pass can be measured by colorimeter 19a during the same return movement. Colorimeters 19a and 19b are specific examples of the colorimetric unit 19 that can measure the density of the medium 30 at the completion of a pass. Completion of a pass is not limited to the state where one forward pass or one return pass has been completed; for example, even if the forward pass is in progress, the pass is completed for the range of medium 30 where ink ejection has already been completed during the forward pass.

[0025] 2. Printing a specified area by path decomposition: In FIG. 2, one area A within the medium 30, enclosed by a two-dot chain line, is an example of a "predetermined area" that is printed in N passes. N is a natural number greater than or equal to 2. For example, if N=4, printing of the predetermined area A is completed in a total of four passes. If bidirectional printing is used, printing of one predetermined area A is completed by making the carriage 21 go back and forth twice. If unidirectional printing is used, printing of one predetermined area A is completed by making the carriage 21 go back and forth four times.

[0026] The length of the predetermined area A in the transport direction D2 is referred to as the area length H. The length of the predetermined area A in the main scanning direction D1 can be understood as the length of the medium 30 in the main scanning direction D1. Of course, if the medium 30 is set to have a margin on the edge, the length of the predetermined area A in the main scanning direction D1 is the length excluding the margin on that edge.

[0027] In the example of Figure 2, the area length H is approximately equal to the length of the nozzle row in the transport direction D2. In other words, the control unit 11 completes printing on one predetermined area A by controlling the carriage 21 and print head 20 to perform N passes while the medium 30 is stationary on the transport unit 17. After printing on one predetermined area A is completed, the control unit 11 causes the transport unit 17 to transport the medium 30 by the area length H, then stops the transport and starts printing on the next predetermined area A adjacent to and upstream of the predetermined area A on which printing was most recently completed. From this perspective, the predetermined area A can be said to be an area of ​​a predetermined size that is determined in advance by the size of the medium 30, the nozzle row, etc.

[0028] In the example of FIG. 2, the colorimeters 19a and 19b are each sized to measure only a range corresponding to a portion of the length of the nozzle row in the transport direction D2. However, the colorimeters 19a and 19b may also be sized to measure a range corresponding to the entire length of the nozzle row. The control unit 11 may also cause the transport unit 17 to transport the medium 30 for each pass. For example, the region length H is set to 1 / N of the length of the nozzle row in the transport direction D2. The control unit 11 then causes the transport unit 17 to transport the medium 30 by the region length H between the completion of one pass and the start of the next pass. By repeating this process N times, printing on one predetermined region A in N passes can be completed.

[0029] FIG. 3 shows a simplified representation of print data 40 for one predetermined area A. FIG. 3 also shows the orientation of print data 40 and the correspondence between directions D1 and D2. Each rectangle constituting print data 40 represents a pixel. The white circles within each pixel represent ink dots of a certain color, and the numbers 1 through 4 within the circles represent the pass numbers for printing one predetermined area A. In other words, N=4 in FIG. 3. As mentioned above, the dot-on data specified for a pixel indicates a large dot, a medium dot, or a small dot, but FIG. 3 does not represent different dot sizes. While not all pixels in actual print data are necessarily dot-on, print data 40 illustrates an example of which pixels would be printed in which pass if all pixels were dot-on.

[0030] Corresponding to the first pass for printing a certain predetermined area A, control unit 11 supplies print data consisting of pixel data at pass number 1 in print data 40 to print head 20 and executes the first pass. Similarly, control unit 11 supplies print data consisting of pixel data at pass number 2 in print data 40 to print head 20 and executes the second pass, supplies print data consisting of pixel data at pass number 3 in print data 40 to print head 20 and executes the third pass, and supplies print data consisting of pixel data at pass number 4 in print data 40 to print head 20 and executes the fourth pass. As a result, the image represented by print data 40 is printed in the predetermined area A of medium 30 in a total of four passes.

[0031] 3. Print control process with color measurement and correction: When printing is performed on a predetermined area A of the medium 30 in N passes as described above, where n is a natural number smaller than N, the control unit 11 acquires the nth density, which is the colorimetric result of the colorimetry unit 19 on the medium 30 at the completion of the nth pass on the predetermined area A. Then, according to the nth density, the control unit 11 corrects the print data to be used for passes after the nth pass on the predetermined area A, and executes the passes after the nth pass based on the corrected print data. Several examples of printing with corrections performed in the process until the completion of such N passes are described below. For convenience of explanation, it is assumed that N=4 in all of the first, second and third embodiments.

[0032] First example: 4 is a flowchart showing the print control process according to the first embodiment, which is executed by the control unit 11 in accordance with the program 12. Each flowchart represents a printing method according to this embodiment.

[0033] In step S100, the print data generation unit 12a of the control unit 11 generates print data and performs path decomposition of the print data. First, the print data generation unit 12a acquires image data from which the print data is generated. The image data represents the image to be printed. For example, the print data generation unit 12a acquires image data specified by a user through an operation of the operation reception unit 14 from an image data storage location such as the storage unit 15 or a memory inside or outside the printing device 10. Alternatively, the print data generation unit 12a receives and acquires image data sent from an external device via the communication IF 16.

[0034] The print data generation unit 12a converts the acquired image data into print data to be used for ink ejection by the print head 20. In other words, the print data generation unit 12a performs color conversion on the values ​​of each pixel that make up the image data into gradation values ​​that represent the ink amounts of each CMYK ink that the print head 20 will use for printing, and then converts the color-converted pixel values ​​into values ​​that represent dot-on or dot-off for each color ink through halftone processing. The dot-on referred to here can naturally be a large dot-on, a medium dot-on, or a small dot-on.

[0035] The print data generation unit 12a decomposes the print data generated in this manner, which corresponds to one predetermined area A, into print data to be used for each of the first to fourth passes. As shown in Fig. 3, pass decomposition of print data is a process of associating each pixel that makes up the print data corresponding to one predetermined area A with a pass number from 1 to 4 according to the position of the pixel.

[0036] When considering a situation in which one page of image is printed on one sheet of medium 30 based on print data, printing of one page is completed as a result of printing in multiple predetermined areas A in succession along the conveyance direction D2. Therefore, the flowcharts in Figure 4 and Figures 6 and 7 described below will be explained focusing on printing in one predetermined area A. Printing of one page is completed by repeating the same process.

[0037] In step S110, the print control unit 12d executes the first pass by providing the print data to be used for the first pass, obtained by the pass decomposition in step S100, from the print data corresponding to the predetermined area A, to the print head 20. In addition, in conjunction with the first pass, the control unit 11 causes the colorimeter 19 to measure the density of the medium 30 after ink is ejected in the first pass. If the first pass is an outbound pass, the control unit 11 causes the colorimeter 19b to perform color measurement.

[0038] In step S120, the colorimetry result acquisition unit 12b acquires the first density as the colorimetry result of step S110 from the colorimetry unit 19. In steps S110 and S120, n=1. In step S130, the print data correction unit 12c corrects the print data to be used for the second pass obtained by pass decomposition in step S100 from the print data corresponding to the specified area A, according to the first density obtained in step S120.

[0039] The method of correcting print data according to the density measured by the colorimeter 19 will be specifically described using an example in which print data used in the second pass is corrected according to the first density. This correction method is naturally applicable to combinations of density and print data other than the combination of the first density and print data used in the second pass. The first density is the result of color measurement performed by a colorimeter located behind the print head 20 in the movement direction during the pass of step S110, and is therefore the density of a certain area onto which ink has been ejected in the first pass. Therefore, the print data correction unit 12c calculates, for example, the average value of the first density as a statistical value that succinctly represents the first density. Hereinafter, such a statistical value of the nth density will be simply referred to as the nth density. The statistical value may also be another value, such as the median.

[0040] The print data correction unit 12c compares the first density with a first reference value to be compared with the first density. The first reference value is an ideal value for the density of the medium 30 at the end of the first pass. The nth reference value, which is an ideal value for the density at the end of the nth pass, can be calculated, for example, from the print data generated in step S100 using a predetermined formula. Alternatively, the nth reference value may be previously attached to the image data from which the print data was generated, or may be stored in the storage unit 15 or the like together with the image data.

[0041] The print data correction unit 12c determines the amount of correction for the print data to be used in the second pass based on the comparison result between the first density and the first reference value. Ideally, the first density would match the first reference value. However, in reality, the degree of color development varies due to the tendency of ink to bleed on the medium 30 being used and other characteristics, and the first density often does not match the first reference value. If the first density is higher than the first reference value, this means that the amount of ink ejected in the first pass was too large, so a negative correction amount is determined based on the difference between the first density and the first reference value. On the other hand, if the first density is lower than the first reference value, this means that the amount of ink ejected in the first pass was too small, so a positive correction amount is determined based on the difference between the first density and the first reference value.

[0042] The print data correction unit 12c corrects the print data used in the second pass according to the correction amount determined from the comparison result between the first density and the first reference value. Because the difference in ink volume between dots of different sizes is known by design, the print data correction unit 12c increases or decreases the size of some of the dots specified in the print data used in the second pass according to the correction amount. For example, if the correction amount is −α, the print data correction unit 12c determines how many medium dots should be changed to small dots and how many large dots should be changed to medium dots to achieve a reduction in ink volume equivalent to −α, and changes the dot size accordingly. Also, if the correction amount is +β, for example, the print data correction unit 12c determines how many medium dots should be changed to large dots and how many small dots should be changed to medium dots to achieve an increase in ink volume equivalent to +β, and changes the dot size accordingly. Although it is possible to change large dots to small dots and small dots to large dots, the print data is originally generated taking into account image quality factors such as graininess, and abrupt changes in dot size have a significant impact on image quality. Therefore, it is preferable to minimize the amount of change in dot size per pixel and ensure the necessary correction amount for the entire image. The print data correction unit 12c determines such correction amounts for each of the CMYK inks, and changes the dot size of the K ink according to the correction amount for the K ink, for example. The same applies to the other ink colors.

[0043] FIG. 5 is a diagram illustrating a specific example of the correction performed in step S130. The middle section of FIG. 5 shows a portion of print data 42 for a certain ink color, e.g., K, to be used in the second pass. In FIG. 5, as with print data 40 in FIG. 3, each rectangle represents a pixel. Furthermore, gray pixels among the pixels indicate pixels assigned to either the first, third, or fourth pass, while white pixels constitute print data 42 to be used in the second pass. Of course, the gray and white colors in the diagram are used for convenience of explanation and are unrelated to the actual pixel colors. Of the pixels that make up print data 42, pixels with white circles are pixels for which K ink dot-on is specified, and pixels without white circles are pixels for which K ink dot-off is specified. Furthermore, different sizes of white circles indicate large, medium, and small dots. Naturally, K ink dot-on and dot-off are specified for gray pixels assigned to either the first, third, or fourth pass, but these are not shown in the figure.

[0044] The upper part of Fig. 5 illustrates print data 42a resulting from negative correction, which is a correction that reduces the amount of ink in print data 42, performed in step S130. Meanwhile, the lower part of Fig. 5 illustrates print data 42b resulting from positive correction, which is a correction that increases the amount of ink in print data 42, performed in step S130. Specifically, in the negative correction from print data 42 to print data 42a, some large dots LD1 and medium dots MD2 defined in print data 42 are changed to medium dots MD1 and small dots SD2 in print data 42a. Meanwhile, in the positive correction from print data 42 to print data 42b, some medium dots MD3 and small dots SD4 defined in print data 42 are changed to large dots LD3 and medium dots MD4 in print data 42b.

[0045] 5, the print data correction unit 12c corrects the print data by changing the dot size defined in the print data before correction. That is, it increases or decreases the dot size defined in the print data generated in step S100. In other words, it does not add new dots to pixels for which the print data generated in step S100 defines dot-off. In addition, the print data correction unit 12c randomly selects dots to be resized by correction, for example, using random numbers, so that the positions of the resized dots are distributed as evenly as possible within the image.

[0046] In step S140, the print control unit 12d provides the print data used for the second pass, after being corrected in step S130, to the print head 20, and executes the second pass. Additionally, in conjunction with the second pass, the control unit 11 causes the colorimeter 19 to measure the density of the medium 30 after ink is ejected in the second pass. If the second pass is a return pass, the control unit 11 causes the colorimeter 19a to perform color measurement.

[0047] From then on, the cycle is repeated: obtaining the nth density as the color measurement result, correcting the print data to be used in the n+1th pass according to the obtained nth density, and executing the n+1th pass reflecting the correction and measuring the color. That is, in step S150, the colorimetry result acquisition unit 12b acquires the second density as the colorimetry result of step S140 from the colorimetry unit 19. The second density is, of course, the colorimetry result for the state in which the ink ejection in the second pass is added to the ink ejection in the first pass. In steps S140 and S150, n=2. In step S160, the print data correction unit 12c corrects the print data to be used in the third pass, obtained by the pass separation in step S100, from the print data corresponding to the predetermined area A, in accordance with the second density acquired in step S150. Then, in step S170, the print control unit 12d provides the print data to be used in the third pass after the correction in step S160 to the print head 20, and executes the third pass. Furthermore, in conjunction with the third pass, the control unit 11 causes the colorimetry unit 19 to measure the density of the medium 30 after the ink ejection in the third pass.

[0048] In step S180, the colorimetry result acquisition unit 12b acquires a third density as the colorimetry result of step S170 from the colorimetry unit 19. The third density is a colorimetry result for a state in which ink ejection in the first pass is added to ink ejection in the second and third passes. In step S190, the print data correction unit 12c corrects the print data to be used in the fourth pass obtained by pass separation in step S100, among the print data corresponding to the predetermined area A, in accordance with the third density acquired in step S180. Then, in step S200, the print control unit 12d provides the print data to be used in the fourth pass after correction in step S190 to the print head 20, and executes the fourth pass. Because the fourth pass is the final pass for the predetermined area A, colorimetry by the colorimetry unit 19 is not necessary. This completes printing in N passes for one predetermined area A.

[0049] As described above, in the first embodiment, the control unit 11 corrects the print data used for the (n+1)th pass on the specified area A according to the (n)th density and executes the (n+1)th pass based on the corrected print data. In other words, each pass from the second pass onward ejects ink based on the corrected print data. Therefore, compared to the difference between the first density and the first reference value, the difference between the second density and the second reference value, which is the (n)th reference value to be compared with the second density, and the difference between the third density and the third reference value, which is the (n)th reference value to be compared with the third density, are expected to gradually decrease due to the effect of repeated correction. Therefore, the print result of the specified area A after the (N)th pass reflecting the final correction is quite close to the ideal density to be reproduced by the print data corresponding to the specified area A, regardless of the type of medium 30. In other words, a printout in which the image represented by the print data is reproduced with high accuracy can be obtained without consuming the medium 30 through so-called test printing.

[0050] Second Example: In the first embodiment, the color measurement results of the density at the end of a pass are reflected in the next pass, so time is required between passes to determine the correction amount according to the density and to correct the print data. In contrast to the first embodiment, the second and third embodiments are embodiments that aim to shorten the total printing time over N passes. For the second and third embodiments, explanations common to the first embodiment will be omitted where appropriate.

[0051] 6 is a flowchart showing the print control process according to the second embodiment, which is executed by the control unit 11 in accordance with the program 12. In the second embodiment, the control unit 11 corrects the print data used for the (n+2)th pass on the predetermined area A according to the nth density, and executes the (n+2)th pass based on the corrected print data.

[0052] Steps S100, S110, and S120 are as described in Fig. 4. In the second embodiment, after step S110, the control unit 11 performs step S142 and steps S120 and S132 in parallel.

[0053] In step S142, print control unit 12d executes the second pass by providing print data to be used for the second pass, obtained by pass decomposition in step S100, from among the print data corresponding to predetermined area A, to print head 20. Additionally, control unit 11 causes colorimetry unit 19 to measure the density of medium 30 after ink is ejected in the second pass, in conjunction with the second pass. In step S140 described with reference to FIG. 4, the second pass is executed based on print data in which the print data to be used for the second pass has been corrected according to the first density, whereas in step S142, the second pass is executed using the print data to be used for the second pass as is, without correction.

[0054] In step S132 following step S120, the print data correction unit 12c corrects the print data to be used in the third pass obtained by the pass decomposition in step S100, of the print data corresponding to the predetermined area A, in accordance with the first density acquired in step S120. In other words, step S132 differs from step S130 in that the correction target is not the print data to be used in the second pass obtained by the pass decomposition in step S100, but the print data to be used in the third pass obtained by the pass decomposition in step S100.

[0055] After step S132 and step S142 are completed, the control unit 11 performs step S172 and steps S152 and S162 in parallel. In step S172, the print control unit 12d executes the third pass by providing the print data corrected in step S132 to the print head 20. The third pass is not the last pass for the predetermined area A, but when n=3, there is no (n+2)th pass for this predetermined area A, so color measurement by the colorimetric unit 19 is not necessary.

[0056] Meanwhile, in step S152, the colorimetry result acquisition unit 12b acquires the second density as the colorimetry result of step S142 from the colorimetry unit 19. In step S162 following step S152, the print data correction unit 12c corrects the print data to be used for the fourth pass obtained by the pass decomposition of step S100, of the print data corresponding to the predetermined area A, in accordance with the second density acquired in step S152. Step S162 differs from step S160 in that the correction target is not the print data to be used for the third pass obtained by the pass decomposition of step S100, but the print data to be used for the fourth pass obtained by the pass decomposition of step S100.

[0057] After steps S162 and S172 are completed, in step S202, the print control unit 12d executes the fourth pass by providing the print data corrected in step S162 to the print head 20. This completes printing in N passes on one predetermined area A.

[0058] Thus, in the second embodiment, the control unit 11 corrects the print data used in the (n+2)th pass to the specified area A according to the nth density. Therefore, after the nth pass is executed, a series of processes for correcting the print data used in the (n+2)th pass can be executed in parallel with the (n+1)th pass, and the time required to complete N passes can be shortened compared to the first embodiment.

[0059] Example 3: 7 is a flowchart showing print control processing according to a third embodiment executed by the control unit 11 in accordance with the program 12. In the third embodiment, if n+2≦N−1, the control unit 11 corrects the print data used in the n+2-th pass on the specified area A according to the n-th density, and executes the n+2-th pass based on the corrected print data. On the other hand, if n=N−1, the control unit 11 corrects the print data used in the N-th pass on the specified area A according to the n-th density, and executes the N-th pass based on the corrected print data.

[0060] Steps S100, S110, and S120 are as described in Fig. 4. In the third embodiment, after step S110, the control unit 11 performs step S144 and steps S120 and S132 in parallel. Step S132 following step S120 is as described in Fig. 6.

[0061] In step S144, the print control unit 12d executes the second pass by providing the print data to be used for the second pass, obtained by the pass decomposition in step S100, from the print data corresponding to the predetermined area A to the print head 20. As such, when n=2, n+2≦N−1 does not hold, and therefore the second pass does not require colorimetry by the colorimetry unit 19. Step S144 differs from step S142 in FIG. 6 in that it does not involve colorimetry by the colorimetry unit 19.

[0062] After steps S132 and S144 are completed, in step S174, the print control unit 12d executes the third pass by providing the print data used for the third pass, which has been corrected in step S132, to the print head 20. Furthermore, since n=N-1 holds true when n=3 in this way, the control unit 11 causes the colorimetry unit 19 to measure the density of the medium 30 after ink is ejected in the third pass during the third pass.

[0063] In the following step S182, the colorimetry result acquisition unit 12b acquires a third density as the colorimetry result of step S174 from the colorimetry unit 19. In step S192, the print data correction unit 12c corrects the print data to be used in the fourth pass obtained by the pass separation in step S100, of the print data corresponding to the predetermined area A, in accordance with the third density acquired in step S182. Then, in step S204, the print control unit 12d provides the print data to be used in the fourth pass after the correction in step S192 to the print head 20, and executes the fourth pass. Because the fourth pass is the final pass for the predetermined area A, it is not necessary to perform colorimetry by the colorimetry unit 19. This completes printing through N passes for one predetermined area A.

[0064] This third embodiment combines the features of both the first and second embodiments. Specifically, the print data used in the (n+2)th pass is corrected according to the nth density that satisfies n+2≦N−1. This allows a series of processes for correcting the print data used in the (n+2)th pass to be executed in parallel with the (n+1)th pass, resulting in a time-saving effect. Furthermore, the print data used in the Nth pass is corrected according to the nth density that satisfies n=N−1. This repeating correction effect, in which correction is performed on the print data for the Nth pass based on the colorimetric results of a pass executed based on the corrected print data, makes it easier to obtain ideal colors as the print result for the specified area A compared to the second embodiment.

[0065] A supplementary explanation will be given for the first to third embodiments. Up to now, the case where N=4 has been described as an example, but N is of course not limited to 4. For example, N=6 may also be used. In the first embodiment, even if N=6, the above cycle is repeated.

[0066] In the second embodiment, when N=6, step S172 involves measuring the density of the medium 30 after ink is ejected in the third pass, and correcting the print data to be used in the fifth pass in parallel with step S202 according to the third density obtained by the colorimetry. Similarly, step S202 involves measuring the density of the medium 30 after ink is ejected in the fourth pass, and correcting the print data to be used in the sixth pass in parallel with the fifth pass according to the fourth density obtained by the colorimetry. After step S202, a fifth pass is executed based on the print data to be used in the corrected fifth pass, and then a sixth pass is executed based on the print data to be used in the corrected sixth pass, completing printing on the predetermined area A.

[0067] In the third embodiment, when N = 6, n + 2 ≦ N − 1 holds true if n = 1 to 3. Therefore, the process is the same as the second embodiment, up to the point where the print data used in the fifth pass is corrected according to the third density and the fifth pass is executed based on the corrected print data used in the fifth pass. However, when n = 4, n + 2 ≦ N − 1 does not hold. Therefore, in the third embodiment, the print data used in the sixth pass is not corrected according to the fourth density as in the second embodiment. Instead, when n = 5, n = N − 1 holds true, so the fifth density is obtained by measuring the medium 30 after ink ejection in the fifth pass, and the print data used in the sixth pass is corrected according to the fifth density. Then, the sixth pass is executed based on the corrected print data used in the sixth pass, completing printing on the specified area A.

[0068] 4. Instructions for printing on multiple sheets: Next, the process for printing continuously on multiple sheets of media 30 in this embodiment will be described. Note that even when printing is based on print data that has been similarly corrected, the colors of the printed results will naturally differ if the type of media 30 is different. Therefore, the printing on multiple sheets of media 30 described below is a process that assumes a situation in which the transport unit 17 repeatedly transports the same type of media 30 set in a tray or other source of media 30, and these multiple sheets of media 30 of the same type are used for printing.

[0069] FIG. 8 is a flowchart showing the print control process executed by the control unit 11 according to the program 12 when printing on a plurality of media 30 in succession. In step S300, control unit 11 controls transport unit 17 and printing unit 18 to print on the first sheet of medium 30 based on the print data. As described above, printing on one sheet of medium 30 based on the print data is completed by repeatedly printing on multiple consecutive predetermined areas A along transport direction D2 within one sheet of medium 30. Naturally, printing on one predetermined area A is a process that is completed in N passes as described above, and is any of the first, second, and third embodiments.

[0070] In step S310 after step S300, the control unit 11 determines whether the correction amounts applied to the print data for each pass in printing on the first sheet of medium 30 in step S300 are all equal to or less than a predetermined threshold value. The threshold value is stored in advance in, for example, the storage unit 15. The correction amount may be a negative correction amount or a positive correction amount, but the correction amount compared with the threshold value is an absolute value.

[0071] As an easy-to-understand example, assume that printing on one sheet of medium 30 is completed by 10 consecutive predetermined areas A in the transport direction D2, and that N passes are performed for each predetermined area A according to the first embodiment. Also, assume that N=4. In this case, in step S300, the printing unit 18 performs 40 passes. According to the first embodiment, of the four passes for one predetermined area A, the second through fourth passes, excluding the first, are performed using print data corrected according to the measured density. Therefore, in step S300, the process of determining the correction amount according to the measured density is performed 30 times for each ink color, and the print data for each ink color for 30 passes is corrected. Therefore, if all of the correction amounts (30 × number of ink colors) are equal to or less than the threshold, the control unit 11 determines "Yes" in step S310. On the other hand, if one or more of the correction amounts exceed the threshold, the control unit 11 determines "No" in step S310. The control unit 11 proceeds from "Yes" in step S310 to step S340, and from "No" in step S310 to step S320.

[0072] In step S340, the control unit 11 applies the most recent correction amount to the print data, repeats printing the next sheet and subsequent sheets as many times as necessary, and then ends the flowchart. Step S340 corrects the print data according to the correction amount, but does not perform colorimetry of the ink ejection results by pass using the colorimetry unit 19 or determine the correction amount according to the measured density. The "next sheet and subsequent sheets" in step S340 refers to the sheet following the first sheet printed in step S300 or the number of sheets printed in step S330 (described below). If the determination in step S310 immediately after step S300 is "Yes" and the process proceeds to step S340, the first sheet has already been printed, so in step S340, printing of the second, third, fourth, and subsequent sheets is performed. On the other hand, if the determination in step S310 is "Yes" after one or more passes of step S330 and the process proceeds to step S340, printing of at least the first two sheets has already been completed at that point.

[0073] The "most recent correction amount" refers to the correction amount applied to printing on the most recently completed sheet of medium 30. The most recent correction amount determines what correction amount should be applied to which pass of print data for which specific area A, so in step S340, the same printing as for the most recent sheet can be performed, including correction of the print data on a pass-by basis. In step S340, which is reached by determining "Yes" in step S310 immediately after step S300, the correction amount applied to printing on the first sheet of medium 30 in step S300 is the "most recent correction amount." On the other hand, in step S340, which is reached by determining "Yes" in step S310 after step S330, the correction amount applied to printing on the medium 30 in step S330 is the "most recent correction amount."

[0074] Therefore, if the amount of correction applied to the print data for each pass in printing the first medium 30 in step S300 is equal to or less than a predetermined threshold, the control unit 11 goes through step S310 ("Yes") and applies the corrections applied to the print data for each pass in printing the first medium 30 to the print data for each pass in printing the second and subsequent media 30 in step S340. Note that the content of the print data before correction is assumed to be the same for the first sheet and the second and subsequent sheets.

[0075] In step S320, the control unit 11 changes the "most recent correction amount." Here, for the most recent correction amount that was determined to exceed the threshold in step S310, a portion of that amount is allocated to correcting print data for other passes. This is because if the correction amount applied to print data used for some of the N passes is exceptionally large, it is possible that some passes will use large dots excessively, which could have an impact on image quality, such as reducing graininess, and so it is preferable to reduce the difference in the correction amount for print data for each pass.

[0076] Although various methods for distributing the correction amount are conceivable, basically, the correction amount is distributed to the pass with a relatively small correction amount. Also, as described above, the correction amount is a value determined based on the colorimetric results by the colorimetric unit 19, so the destination of the correction amount distributed in step S320 is basically a correction amount that is not determined based on the colorimetric results, that is, a correction amount for the print data used in the first pass of the N passes. Also, when the second or third embodiment is adopted, the correction amount for the print data used in the second pass of the N passes may also be a distribution destination.

[0077] For example, suppose that in printing on the first sheet of medium 30 in step S300, the correction amount applied to the print data for the second pass for a certain predetermined region A is +γ, the correction amount applied to the print data for the third pass is +γ / 4, and the correction amount applied to the print data for the fourth pass is +γ / 8. In step S300, the correction amount applied to the print data for the first pass for the certain predetermined region A is 0. If the correction amount +γ applied to the print data for the second pass exceeds a predetermined threshold, in step S320 after step S310 returns "No," the control unit 11 determines +γ', which is the difference between this correction amount +γ and the threshold, as the correction value to be applied to the print data for the first pass for the same predetermined region A. In other words, the correction amount applied to the print data used in the first pass for the certain predetermined region A is changed from 0 to +γ'.

[0078] In step S330, the control unit 11 corrects the print data for the pass corresponding to the correction amount changed in step S320 using the correction amount changed in step S320, and prints the next sheet. For example, if step S330 is performed after step S300 and step S320, the control unit 11 prints the second sheet of the medium 30. Like step S300, printing in step S330 involves measuring the ink ejection results for each pass, determining a correction amount based on the measured density, and correcting the print data for each pass using the determined correction amount. According to the example described above, the print data used for the first pass for a certain predetermined area A is corrected by applying a correction amount +γ', and the first pass is executed based on the corrected print data. Each subsequent pass for the same predetermined area A involves ejecting ink based on print data corrected with a correction amount based on the colorimetric results obtained by the colorimetric unit 19. However, because the correction amount for the first pass is set to +γ', the correction amount for the second pass is unlikely to exceed the threshold.

[0079] In step S310, after step S330, the control unit 11 determines whether the correction amounts (most recent correction amounts) applied to the print data for each pass in printing on one sheet of medium 30 in step S330 are all equal to or less than a predetermined threshold, and branches the process accordingly. As shown in FIG. 8, after repeating the cycle of "No" in step S310, S320, and S330 multiple times, the process may proceed from "Yes" in step S310 to step S340. Thus, if the correction amount applied to the print data for any pass in printing on the first sheet of medium 30 in step S300 exceeds the threshold, the control unit 11 determines corrections to be applied to the print data for each pass in printing on the second or subsequent sheets of medium 30 after "No" in step S310, so that the correction amount is equal to or less than the threshold, and applies the determined corrections to the print data for each pass.

[0080] Thus, printing in step S300 and printing in step S330 require color measurement and correction amount determination based on the color measurement results, which takes a certain amount of time, but printing in step S340 does not require color measurement or correction amount determination. Therefore, most of the multiple media 30, excluding the first one or first two or three, can be printed quickly. In other words, the total time required to print on multiple media 30 of the same type is not significantly longer, and even when using media 30 with unknown color characteristics such as ink bleeding, it is possible to obtain printed material with ideal color reproduction without wasting any paper, starting from the first sheet.

[0081] 5. Summary: As described above, according to this embodiment, the printing device 10 includes a print head 20 that ejects ink onto the medium 30 based on print data, a carriage 21 that carries the print head 20 and moves back and forth along the main scanning direction D1, a control unit 11 that controls the carriage 21 and the print head 20 to execute passes in which the print head 20 ejects ink as the carriage 21 moves, and a colorimetric unit 19 that can measure the density on the medium 30 at the completion of a pass. When printing is performed on a predetermined area A of the medium 30 in N passes, where n is a natural number smaller than N, the control unit 11 obtains an nth density that is the colorimetric result of the colorimetric unit 19 on the medium 30 at the completion of the nth pass on the predetermined area A, corrects the print data to be used for passes after the nth pass on the predetermined area A according to the nth density, and executes passes after the nth pass based on the corrected print data.

[0082] According to the above configuration, in the process of completing N passes on the specified area A, the print data used for passes after the nth pass is corrected according to the nth density, and passes after the nth pass are executed based on the corrected print data, so that once N passes are completed, print results that are the same or nearly the same as the ideal density can be obtained. Therefore, even when using a medium 30 for the first time whose color characteristics are unknown, it is possible to obtain high-quality print results without wasting time or money on the medium 30 for test printing.

[0083] Furthermore, according to this embodiment, the print data is data that specifies the presence or absence of ink dots for each pixel and the size of the dots, and the control unit 11 changes the specified dot size when correcting the print data to be used for passes after the nth pass. According to this configuration, the size of dots originally specified by the print data to be corrected is changed to a larger or smaller size, thereby correcting the amount of ink ejected onto the medium 30 while minimizing changes to the image quality, such as graininess, that the print data is originally trying to reproduce. However, the correction of the print data may include a process of adding new dots to pixels where the pre-correction print data does not specify dot-on, or a process of deleting dots from pixels where the pre-correction print data specifies dot-on.

[0084] Furthermore, according to this embodiment, various examples are provided as specific examples of "correcting print data used in passes after the nth pass to the predetermined area A according to the nth density." In other words, as in the first embodiment, the control unit 11 may correct the printing data to be used for the n+1th pass to the specified area A according to the nth density, and execute the n+1th pass based on the corrected printing data.

[0085] Furthermore, as in the second embodiment, the control unit 11 may correct the printing data to be used for the n+2th pass to the specified area A according to the nth density, and execute the n+2th pass based on the corrected printing data. Furthermore, as in the third embodiment, if n+2≦N−1, the control unit 11 may correct the print data to be used for the n+2th pass to the specified area A according to the nth density, and execute the n+2th pass based on the corrected print data, and if n=N−1, may correct the print data to be used for the Nth pass to the specified area A according to the nth density, and execute the Nth pass based on the corrected print data. The effects of each of the first to third embodiments are as explained above.

[0086] Furthermore, according to this embodiment, the printing device 10 may have a color measurement unit 19 at each end of the print head 20 in the main scanning direction D1. According to the above configuration, the results of ink ejection can be measured in accordance with ink ejection on the forward pass of the print head 20, and the results of ink ejection can be measured in accordance with ink ejection on the return pass. In other words, there is essentially no time required just for color measurement.

[0087] Furthermore, according to this embodiment, if the amount of correction applied to the print data for any pass in printing the first medium 30 is equal to or less than a predetermined threshold, the control unit 11 applies the corrections applied to the print data for each pass in printing the first medium 30 to the print data for each pass in printing the second or subsequent medium 30 of the same type as the first medium 30. On the other hand, if the amount of correction applied to the print data for any pass in printing the first medium 30 exceeds the threshold, the control unit 11 determines corrections to be applied to the print data for each pass in printing the second or subsequent medium 30 of the same type as the first medium 30, such that the amount of correction is equal to or less than the threshold, and applies the determined corrections to the print data for each pass. According to the above configuration, when printing on multiple sheets of the same type of media 30 is evaluated in total, it is possible to minimize the lengthening of printing time while eliminating waste of media 30 and obtaining high-quality printing results for each sheet.

[0088] This embodiment discloses inventions in various categories, such as not only devices and systems, but also methods executed by devices and systems, and programs 12 that cause a processor to execute the methods. For example, a printing method that controls a print head 20 that ejects ink onto a medium 30 based on print data and a carriage 21 that carries the print head 20 and moves back and forth along the main scanning direction D1 to perform passes in which the print head 20 ejects ink as the carriage 21 moves involves, when printing is performed in N passes onto a predetermined area A of the medium 30, where n is a natural number smaller than N, obtaining the nth density, which is the colorimetric result of the density of the medium 30 measured by the colorimetric unit 19 at the completion of the nth pass onto the predetermined area A, correcting the print data to be used for passes after the nth pass onto the predetermined area A according to the nth density, and executing passes after the nth pass based on the corrected print data.

[0089] Several other aspects included in this embodiment will be described below. The colorimetry unit 19 is not limited to a configuration in which the colorimetry devices 19a and 19b are mounted on the carriage 21 together with the print head 20, as in the example of FIG. 2. If the printing unit 18 is a model that performs unidirectional printing, the colorimetry unit 19 may be only one of the colorimetry devices 19a and 19b. Furthermore, the colorimetry unit 19 may be configured to measure the color of an area of ​​the medium 30 that has received ink ejection in a pass before the next pass begins. Therefore, the colorimetry unit 19 may be fixed to a location or position other than the carriage 21, or the colorimetry unit 19 itself may be configured to move as necessary for colorimetry. Furthermore, the colorimetry unit 19 may be a device separate from the printing device 10.

[0090] 2, in a configuration in which the area length H of the predetermined area A is 1 / N of the length of the nozzle row in the transport direction D2 and the medium 30 is transported by the area length H between passes, one pass of the print head 20 naturally serves as a pass for each of the different predetermined areas A. For example, when N=4, the fourth pass for the most downstream predetermined area A of four predetermined areas A lined up in the transport direction D2 also serves as the third, second, and first pass for the three predetermined areas A adjacent to this predetermined area A upstream. Therefore, it is natural that the value obtained by multiplying the number of predetermined areas A in one sheet of medium 30 by N may not match the number of passes required to print on that sheet of medium 30. [Explanation of symbols]

[0091] 10...printing device, 11...control unit, 12...program, 12a...print data generation unit, 12b...colorimetry result acquisition unit, 12c...print data correction unit, 12d...printing control unit, 13...display unit, 14...operation reception unit, 15...storage unit, 16...communication IF, 17...transport unit, 18...printing unit, 19...colorimetry unit, 19a, 19b...colorimeter, 20...print head, 20a, 20b...nozzle array, 21...carriage, 22...nozzle, 30...medium, 40, 42...print data

Claims

1. a print head that ejects ink onto a medium based on print data; a carriage that carries the print head and moves back and forth along the main scanning direction; a control unit that controls the carriage and the print head to execute a pass, which is an ink ejection by the print head in association with the movement of the carriage; a color measurement unit capable of measuring the density of the medium at the completion of the pass, The control unit When printing is performed on a predetermined area of ​​the medium in N passes, where n is a natural number smaller than N, an nth density, which is a color measurement result of the color measurement unit on the medium at the completion of the nth pass to the predetermined area; correcting the print data to be used in passes after the nth pass to the predetermined area according to the nth density; executes passes after the nth pass based on the corrected print data; When the amount of correction applied to the print data for any pass in printing the first sheet of the medium is equal to or less than a predetermined threshold value, the correction applied to each print data for each pass in printing the first sheet of the medium is applied to each print data for each pass in printing the second or subsequent sheets of the medium of the same type as the first sheet of the medium; When the amount of correction applied to the print data for any pass in printing the first sheet of the medium exceeds the threshold value, when printing the second or subsequent sheets of the medium of the same type as the first sheet of the medium, corrections to be applied to the print data for each pass are determined so that the amount of correction is equal to or less than the threshold value, and the determined corrections are applied to the print data for each pass. A printing device characterized by:

2. The print data is data that specifies the presence or absence of ink dots for each pixel and the size of the dots, The printing device according to claim 1 , wherein the control unit changes a defined dot size when correcting the print data used in passes after the nth pass.

3. The printing device according to claim 1 or claim 2, characterized in that the control unit corrects the print data used for the n+1th pass to the specified area according to the nth density, and executes the n+1th pass based on the corrected print data.

4. The printing device according to claim 1 or claim 2, characterized in that the control unit corrects the print data used for the n+2th pass to the specified area according to the nth density, and executes the n+2th pass based on the corrected print data.

5. The control unit If n+2≦N−1, correct the print data to be used in the n+2-th pass to the predetermined area according to the n density, and execute the n+2-th pass based on the corrected print data; A printing device as described in claim 1 or claim 2, characterized in that if n = N-1, the printing data to be used for the Nth pass to the specified area is corrected according to the nth density, and the Nth pass is executed based on the corrected printing data.

6. 6. The printing device according to claim 1, wherein the color measurement unit is provided at each end of the print head in the main scanning direction.

7. A printing method for controlling a print head that ejects ink onto a medium based on print data and a carriage that carries the print head and moves back and forth along a main scanning direction, and executing passes that eject ink by the print head in association with the movement of the carriage, comprises the steps of: When printing is performed on a predetermined area of ​​the medium in N passes, where n is a natural number smaller than N, an n-th density, which is a color measurement result of the density of the medium by the colorimetric unit at the completion of the n-th pass to the predetermined area; correcting the print data to be used in passes after the nth pass to the predetermined area according to the nth density; executes passes after the nth pass based on the corrected print data; When the amount of correction applied to the print data for any pass in printing the first sheet of the medium is equal to or less than a predetermined threshold value, the correction applied to each print data for each pass in printing the first sheet of the medium is applied to each print data for each pass in printing the second or subsequent sheets of the medium of the same type as the first sheet of the medium; When the amount of correction applied to the print data for any pass in printing the first sheet of the medium exceeds the threshold value, when printing the second or subsequent sheets of the medium of the same type as the first sheet of the medium, corrections to be applied to the print data for each pass are determined so that the amount of correction is equal to or less than the threshold value, and the determined corrections are applied to the print data for each pass. A printing method characterized by:

8. A print head that ejects ink onto a medium based on print data; a carriage that carries the print head and moves back and forth along the main scanning direction; a control unit that controls the carriage and the print head to execute a pass, which is an ink ejection by the print head in association with the movement of the carriage; a color measurement unit capable of measuring the density of the medium at the completion of the pass, The control unit When printing is performed on a predetermined area of ​​the medium in N passes, where n is a natural number smaller than N, an nth density, which is a color measurement result of the color measurement unit on the medium at the completion of the nth pass to the predetermined area; correcting the print data to be used in passes after the nth pass to the predetermined area according to the nth density; executes passes after the nth pass based on the corrected print data; If n+2≦N−1, correct the print data to be used in the n+2-th pass to the predetermined area according to the n density, and execute the n+2-th pass based on the corrected print data; If n=N−1, the print data used in the Nth pass to the predetermined area is corrected according to the nth density, and the Nth pass is executed based on the corrected print data. A printing device characterized by:

Images