JP2019147271A - Ink-jet printer and ink-jet printing method - Google Patents

Abstract

To provide a printer which saves the costs etc., needed to print a test chart.SOLUTION: Based upon difference between measured luminance values and ideal luminance values at respective multi-stage densities of a test chart, combinations of input pixel values input to a recording head and ideal pixel values for ideal densities in actual printing on a recording medium are held, head by head, for the respective multi-stage densities, and an approximate curve generated from those combinations is calculated as an interpolation function. Further, an approximate curve generated by tentatively excluding one arbitrary combination of interpolation functions from a plurality of combinations of interpolation functions is calculated, head by head, as a tentative interpolation function. When the tentative interpolation function does not deviate from the interpolation functions with respect to all the nozzles, it is determined that thinning-out is possible, and a thinned-out test chart image is generated by thinning out from the test chart a density region corresponding to the combination excluded tentatively when calculating the tentative interpolation function.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an inkjet printing apparatus and an inkjet printing method.

  2. Description of the Related Art Conventionally, an inkjet printing apparatus that records an image on a recording medium by discharging ink from a recording head while conveying the recording medium is known. The head of the ink jet printing apparatus has a plurality of nozzles arranged along the main scanning direction orthogonal to the conveyance direction of the recording medium. Each nozzle ejects an amount of ink corresponding to the density specified by the input image data. However, due to individual differences among nozzles, the amount of ink actually ejected from each nozzle may not be the ideal amount as specified. In that case, density unevenness may occur in the printed matter.

  In this type of inkjet printing apparatus, density correction is performed in order to suppress density unevenness of printed matter due to individual differences of nozzles and the like. When performing density correction, first, a predetermined test chart image is printed on a recording medium. The predetermined test chart image typically has a density that changes stepwise along the conveyance direction of the recording medium. Thereafter, the printed test chart is photographed with a camera or the like. Then, based on the obtained captured image, the density instructed to each nozzle is adjusted. Thereby, the density unevenness of printed matter is suppressed.

  For example, Patent Document 1 discloses a technique for correcting the ejection characteristics of each recording element (nozzle) in an inkjet printing apparatus.

JP 2006-210050 A

  However, when the density correction is performed by the above-described method, a large amount of ink and printing paper are consumed to print the test chart. In addition, for example, when an inkjet printing apparatus has a plurality of recording heads corresponding to different colors of ink, it is necessary to individually print a test chart corresponding to each recording head, and much labor is required for printing the test chart. And takes time. Printing the test chart is a necessary step for performing the above-described density correction satisfactorily. However, since the test chart is not an object to be finally obtained as a printed material, it is desirable that the cost and time required for printing the test chart can be reduced if possible.

  The present invention has been made in view of the above circumstances, and a potential object thereof is to reduce the cost and time required for printing the test chart in the density correction performed using the test chart.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

  Based on the first aspect of the present application, an ink jet printing apparatus that prints an image on a recording medium by a one-pass method is provided. The inkjet printing apparatus includes a recording head, a transport mechanism, a chart image storage unit, a chart print instruction unit, a chart reading unit, an interpolation function calculation unit, a provisional interpolation function calculation unit, a determination unit, and a thinning chart. An image generation unit. In the recording head, a plurality of nozzles that eject ink onto a recording medium are arranged in the main scanning direction. The transport mechanism moves the recording medium relative to the recording head in a sub-scanning direction orthogonal to the main scanning direction. The chart image storage unit stores a test chart image having a uniform density along the main scanning direction and a plurality of density areas arranged along the sub-scanning direction. The chart printing instruction unit causes the test chart image to be printed on a recording medium. The chart reading unit optically reads a test chart printed on a recording medium according to an instruction from the chart printing instruction unit, and acquires an actually measured luminance value of a printing region corresponding to each nozzle. The interpolation function calculation unit, for each of the plurality of nozzles, based on a difference between the measured luminance value at each of the plurality of levels of density and an ideal luminance value that is an ideal luminance value. A combination of a density as an input pixel value input to the image and an ideal pixel value that is an ideal density when actually printed on a recording medium is held for each of the plurality of levels of density. An approximate curve or an approximate line generated from the combination is calculated as an interpolation function. The interpolation function calculation unit calculates, as a provisional interpolation function, an approximate curve or an approximate line generated by provisionally excluding any one combination from the plurality of combinations for each of the plurality of nozzles. The determination unit, when the temporary interpolation function does not deviate from the interpolation function beyond a predetermined amount in all of the plurality of nozzles, the combination temporarily excluded by the interpolation function calculation unit It is determined that thinning is possible. The thinning chart image generation unit thins out the density region corresponding to the combination temporarily excluded when calculating the temporary interpolation function from the test chart when the determination unit determines that thinning is possible. A thinned test chart image is generated. The chart image storage unit can store the thinning test chart image. The chart print instructing unit can cause the thinning test chart image to be printed on a recording medium.

  In a second aspect of the present application, in the inkjet printing apparatus according to the first aspect, the chart image storage unit can store the thinned chart image in association with the type of recording medium.

  In a third aspect of the present application, in the inkjet printing apparatus according to the first aspect or the second aspect, the determination unit includes an ideal pixel value corresponding to an arbitrary input pixel value in the interpolation function, and the provisional interpolation. In the function, the difference from the provisional ideal pixel value corresponding to the input pixel value is obtained for all the input pixel values, and the difference is a threshold value in any of the input pixel values and in any of the nozzles. If it is less than that, it is determined that thinning is possible.

  In a fourth aspect of the present application, in the ink jet printing apparatus according to the third aspect, a different value is applied to the threshold value according to the input pixel value.

  In a fifth aspect of the present application, in the inkjet printing apparatus according to the third aspect or the fourth aspect, the determination unit includes a differential value of an ideal pixel value corresponding to an arbitrary input pixel value in the interpolation function, In the provisional interpolation function, a difference value between the differential value of the provisional ideal pixel value corresponding to the input pixel value is obtained for all the input pixel values, and at any of the input pixel values and any of the nozzles Also, when the difference value is less than the second threshold value, it is determined that thinning is possible.

  In a sixth aspect of the present application, in the ink jet printing apparatus according to any one of the first aspect to the fifth aspect, the provisional interpolation function calculation unit includes 2 of the plurality of combinations of the interpolation functions. An approximate curve or approximate line generated from the remaining combinations when one or more combinations are provisionally excluded is calculated as the provisional interpolation function.

  In the 7th viewpoint of this application, it is set as the following structures in the inkjet printing apparatus which concerns on any one from a 1st viewpoint to a 6th viewpoint. That is, the recording head has a plurality of small heads arranged side by side in the main scanning direction. The interpolation function calculation unit and the provisional interpolation function calculation unit calculate a function having a different shape for each of the small heads as the interpolation function and the provisional interpolation function.

  In the 8th viewpoint of this application, it is set as the following structures in the inkjet printing apparatus which concerns on a 7th viewpoint. That is, the interpolation function calculation unit and the provisional interpolation function calculation unit are configured such that a difference between the actually measured luminance value and the ideal luminance value is relative to the nozzle of the small head among the plurality of small heads. A function having a higher dimensional variable is adopted as the interpolation function and the provisional interpolation function for smaller heads.

  In a ninth aspect of the present application, in the inkjet printing apparatus according to any one of the first to eighth aspects, the chart printing instruction unit performs the test chart image and the thinning-out according to a user's selection operation. Printing of the selected image on the recording medium is executed among the test chart images.

  According to a tenth aspect of the present application, in the inkjet printing apparatus according to any one of the first to ninth aspects, a post-conversion pixel value calculation unit and an input image print processing unit are provided. For each of the plurality of nozzles, the post-conversion pixel value calculation unit refers to a pixel value at a position corresponding to the nozzle in the input image input and the interpolation function corresponding to the nozzle. The pixel value given to the nozzle is calculated as a post-conversion pixel value. The input image print processing unit controls the recording head to operate the transport mechanism while giving the converted pixel values calculated by the converted pixel value calculating unit to the plurality of recording heads.

  In an eleventh aspect of the present application, the inkjet printing apparatus according to any one of the first to ninth aspects includes a pixel value correction amount calculating unit and an input image print processing unit. For each of the plurality of nozzles, the pixel value correction amount calculation unit refers to a pixel value at a position corresponding to the nozzle in the input image input and the interpolation function corresponding to the nozzle. The pixel value correction amount for correcting the pixel value of each pixel is calculated. The input image printing unit controls the recording head and supplies the plurality of recording heads with the pixel values after correction using the pixel value correction amount as the converted pixel values. Make it work.

  In a twelfth aspect of the present application, in the inkjet printing apparatus according to the eleventh aspect, a converted image holding unit that holds a converted image based on the converted pixel value calculated by the pixel value correction amount calculating unit, Further prepare. The input image print processing unit operates the transport mechanism while giving each pixel value of the converted image held in the converted image holding unit to the plurality of recording heads.

  Based on the thirteenth aspect of the present application, an ink jet printing apparatus that prints an image on a recording medium by a one-pass method is provided. The inkjet printing apparatus includes a recording head, a transport mechanism, a chart image storage unit, and a chart printing instruction unit. In the recording head, a plurality of nozzles that eject ink onto a recording medium are arranged in the main scanning direction. The transport mechanism moves the recording medium relative to the recording head in a sub-scanning direction orthogonal to the main scanning direction. The chart image printing unit stores a test chart image having a uniform density along the main scanning direction and a plurality of density areas arranged along the sub-scanning direction. The chart printing instruction unit causes the test chart image to be printed on a recording medium. The chart image storage unit can store the test chart image and a thinned test chart image obtained by thinning a part of the density region from the test chart image. The chart printing instructing unit causes the selected image of the test chart image and the thinned-out test chart image to be printed on a recording medium according to a user's selection operation.

  According to a fourteenth aspect of the present application, there is provided an ink jet printing method for printing an image on a recording medium by a one-pass method using an ink jet printer provided with a recording head, a transport mechanism, and a chart image storage unit. . In the recording head, a plurality of nozzles that eject ink onto the surface of the recording medium are arranged in the main scanning direction. The transport mechanism moves the recording medium relative to the recording head in a sub-scanning direction orthogonal to the main scanning direction. The chart image storage unit stores a test chart image having a uniform density along the main scanning direction and a plurality of density areas arranged along the sub-scanning direction. The inkjet printing method includes the following steps a) to f). In a), the test chart image is printed on a recording medium. In b), the test chart printed on the recording medium is optically read, and the actually measured luminance value of the print area corresponding to each nozzle is acquired. In c), for each of the plurality of nozzles, an input to the recording head is performed based on a difference between the measured luminance value at each of the plurality of levels of density and an ideal luminance value that is an ideal luminance value. A combination of a density as an input pixel value to be obtained and an ideal pixel value that is an ideal density when actually printed on a recording medium is held for each of the plurality of levels of density. An approximate curve or approximate line generated from the combination is calculated as an interpolation function. In d), for each of the plurality of nozzles, an approximate curve or approximate line generated by provisionally excluding any one combination from the plurality of combinations is calculated as a provisional interpolation function. In the above e), when the provisional interpolation function does not deviate from the interpolation function by a predetermined amount in all of the plurality of nozzles, the combination that is temporarily excluded by the interpolation function calculation unit is used. It is determined that thinning is possible. In step f), when it is determined that thinning is possible, a thinning test chart image is generated by thinning out the density region corresponding to the combination that is temporarily excluded when calculating the temporary interpolation function from the test chart. .

  In a fifteenth aspect of the present application, the inkjet printing method according to the fourteenth aspect includes the following steps g) to h) after the step f). That is, in the step g), the thinning test chart image is stored in the chart image storage unit. In the step h), the selected test chart image of the test chart image and the thinned-out test chart image is printed on the recording medium.

  According to the first to fifteenth aspects of the present application, the cost and time required for printing a test chart can be reduced in the density correction performed using the test chart.

  In particular, according to the first aspect or the fourteenth aspect of the present application, even when printing is performed while omitting an arbitrary density region among the plurality of density regions at the time of printing the next test chart, the printed result When the influence on the interpolation function calculated on the basis is small, the density region can be thinned out. Thereby, the cost and time required for printing the test chart can be reduced in the density correction performed using the interpolation function when printing the input image.

  Here, in general, how ink droplets spread on a recording medium differs depending on the type of the recording medium. Therefore, it is considered that an appropriate thinning test chart differs depending on the type of recording medium. In this regard, according to the second aspect of the present application, an interpolation function can be calculated by applying an appropriate thinning test chart according to the type of recording medium.

  According to the third aspect of the present application, it is possible to more specifically realize the process of determining which one of the plurality of density regions of the test chart is to be thinned out in a range where the influence on the density correction is small.

  Here, generally, the width of the variation of the ideal pixel value that is allowed varies depending on the density (input pixel value) that is intended for printing. In this regard, according to the fourth aspect of the present application, since it is determined whether thinning is possible by applying a different threshold value for each concentration, it is possible to determine whether thinning is possible in accordance with reality.

  According to the fifth aspect of the present application, when the slope of the provisional interpolation function is significantly different from the slope of the interpolation function, it becomes darker than the ideal density at a specific density (overcorrection) or is ideal. The thinning test chart is not printed because there is a high possibility that it will become thinner (undercorrection) than the typical density. Thereby, the thinning test chart can be determined efficiently by suppressing the number of thinning trials by the provisional correction function.

  According to the sixth aspect of the present application, at the time of printing the next test chart, it is possible to omit two or more density areas of the plurality of density areas and perform printing. Therefore, the cost and time required for printing the test chart can be further reduced.

  Here, since the small heads constituting the recording head are generally manufactured and processed, individual differences are assumed between the small heads. In view of this point, in the seventh aspect of the present application, for each small head, a function having a shape common to all nozzles in the small head is employed as an interpolation function and a provisional interpolation function. Therefore, it is possible to reduce the amount of arithmetic processing required for calculating the interpolation function and the provisional interpolation function. In addition, the capacity of the memory for storing the interpolation function and the provisional interpolation function can be reduced.

  According to the eighth aspect of the present application, the smaller the head that is inferior in processing accuracy and mounting accuracy, more specifically, for example, the greater the individual difference of the nozzles included in the small head, the higher the dimensional function becomes the interpolation function and the provisional function. Adopted as an interpolation function. Therefore, it is possible to calculate an appropriate interpolation function and provisional interpolation function while suppressing an excessive amount of calculation processing.

  According to the ninth aspect or the fifteenth aspect of the present application, when printing a test chart, selecting whether to print a normal test chart image or a thinned-out test chart image depending on the situation Is possible. Thus, for example, if you want to save on ink and recording media, print out a thinned test chart image, but if you change the recording head, change the recording medium, or if the external environment changes significantly, It is possible to perform flexible operations such as printing (full version) test chart images.

  According to the tenth aspect or the eleventh aspect of the present application, a good printed matter can be obtained by appropriately correcting the density of the input image while reducing the cost and time required for printing the test chart.

  According to the twelfth aspect of the present application, when the same input image is printed a plurality of times, it is not necessary to perform density correction for each input image, thereby reducing the cost and time required for printing the test chart. it can.

  According to the thirteenth aspect of the present application, when the influence on the density correction is small, the cost and time required for printing the test chart can be reduced by using the thinned test chart image.

It is the figure which showed the whole structure of the inkjet printing apparatus which concerns on this embodiment. It is a bottom view of the recording head. It is a block diagram which shows roughly the main structures of the control system for implement | achieving density correction. It is the figure which showed an example of the test chart image. It is a flowchart explaining the process performed when calculating an interpolation function. It is a figure which illustrates notionally the process which investigates the difference of a measured luminance value and an ideal luminance value. It is a figure which illustrates notionally a mode that the combination of an input pixel value and an ideal pixel value is hold | maintained, and the interpolation function as an approximated curve is produced | generated. It is a flowchart explaining the process which produces | generates a thinning-out test chart image. It is a figure which illustrates notionally a mode that a temporary interpolation function is produced | generated. It is a figure explaining the difference D of the ideal pixel value in an interpolation function, and the ideal pixel value in a temporary interpolation function. It is the figure which showed an example of the thinning-out test chart image. It is a flowchart explaining the process performed when printing a thinning-out test chart. It is a figure which illustrates notionally the example of the thinning chart image memorize | stored for every recording medium in a chart image memory | storage part.

  Embodiments of the present invention will be described below with reference to the drawings. Hereinafter, the direction in which the recording medium moves relative to the recording head is referred to as a “sub-scanning direction”. A direction along the surface of the recording medium and perpendicular to the sub-scanning direction is referred to as a “main scanning direction”.

<1. Configuration of Inkjet Printing Device>
FIG. 1 is a diagram showing a schematic configuration of an inkjet printing apparatus 1 according to an embodiment of the present invention. The inkjet printing apparatus 1 discharges ink from a plurality of heads 21 toward the printing paper 9 while conveying the printing paper 9 that is a long belt-like recording medium, so that the recording surface of the printing paper 9 is multicolored. A one-pass inkjet printing apparatus that prints an image. As shown in FIG. 1, the inkjet printing apparatus 1 includes a transport mechanism 10, an image recording unit 20, a control unit 30, and the like.

  The transport mechanism 10 is a mechanism that moves the printing paper 9 with respect to the plurality of recording heads 21 along the sub-scanning direction that is the longitudinal direction thereof. The transport mechanism 10 according to the present embodiment includes an unwinding unit 11, a plurality of transport rollers 12, and a winding unit 13. The printing paper 9 is fed out from the unwinding unit 11 and conveyed along a conveyance path constituted by a plurality of conveyance rollers 12. Each transport roller 12 guides the printing paper 9 to the downstream side of the transport path by rotating about the horizontal axis. Further, the printed printing paper 9 is collected to the winding unit 13.

  As shown in FIG. 1, the printing paper 9 moves substantially horizontally below the image recording unit 20 along the arrangement direction of a plurality of recording heads 21 having different ink colors to be ejected. At this time, the printing paper 9 is passed over the plurality of transport rollers 12 in a state where tension is applied. Thereby, slack and wrinkles of the printing paper 9 during conveyance are suppressed.

  The image recording unit 20 is a processing unit that ejects ink droplets (hereinafter referred to as “ink droplets”) onto the printing paper 9 moved by the transport mechanism 10. The image recording unit 20 of this embodiment includes four recording heads 21 arranged along the sub-scanning direction. These recording heads 21 apply C (Cyan), M (Magenta), Y (Yellow), and K (Black) ink droplets, which are color components of a multicolor image, to the recording surface of the printing paper 9, respectively. Discharge. Each recording head 21 is fixedly arranged with respect to a housing (not shown) of the apparatus.

  FIG. 2 is a bottom view of the recording head 21. As shown in FIG. 2, an ejection surface 210 that ejects ink droplets is provided below the recording head 21. The ejection surface 210 covers the entire area of the printing paper 9 in the main scanning direction. Further, as shown in an enlarged manner in FIG. 2, a plurality of nozzles 211 are regularly arranged on the ejection surface 210 along the main scanning direction. The plurality of nozzles 211 are arranged with their positions in the main scanning direction being shifted from each other, and one nozzle 211 is assigned to an area of 1 pixel width on the printing paper 9. During printing, ink droplets are ejected from the plurality of nozzles 211 of each recording head 21 toward the recording surface of the printing paper 9. At this time, each nozzle 211 ejects an ink droplet of an amount corresponding to the instructed density. As a result, each of the four recording heads 21 records a multi-tone single-color image on the recording surface of the printing paper 9 by the one-pass method. A multicolor image is formed on the recording surface of the printing paper 9 by superimposing the four single color images.

  As shown in FIG. 2, each recording head 21 of this embodiment has a plurality of small heads 21a, 21b, 21c, and 21d arranged side by side in the main scanning direction. In the present embodiment, for convenience of explanation, each recording head 21 has four small heads 21a, 21b, 21c, and 21d. However, the number of small heads may be five or more, or two or three. Good. Further, as shown in FIG. 2, the plurality of small heads of the present embodiment are arranged in a staggered manner with the positions in the sub-scanning direction being shifted from each other. However, the present invention is not limited to this. The small heads may be arranged in a straight line.

  Note that a drying processing unit that dries the ink ejected onto the recording surface of the printing paper 9 may be further provided on the downstream side in the transport direction of the image recording unit 20. For example, the drying processing unit blows a heated gas toward the printing paper 9 to vaporize the solvent in the ink attached to the printing paper 9 to dry the ink. However, the ink may be fixed to the recording medium by a method different from that described above, such as ultraviolet irradiation of UV ink (ultraviolet curable ink).

  The control unit 30 is means for controlling the operation of each unit in the inkjet printing apparatus 1. The control unit 30 of the present embodiment is configured by a computer having a processor 31 such as a CPU, a memory 32 such as a RAM, and a storage unit 33 such as a hard disk drive. As indicated by a broken line in FIG. 1, the control unit 30 is electrically connected to the transport mechanism 10, the four recording heads 21, and the imaging device 54 described later. The control unit 30 temporarily reads out the computer program CP stored in the storage unit 33 into the memory 32, and the processor 31 performs arithmetic processing based on the computer program CP, thereby controlling the operation of each unit described above. Thereby, the printing process in the inkjet printing apparatus 1 and the density correction process to be described later proceed in cooperation with the above hardware and software.

<2. About shading correction>
Next, the density correction performed in a timely manner in the above-described inkjet printing apparatus 1 will be described with reference to FIG. The density correction is a process (shading correction process) for adjusting the amount of ink droplets ejected from each nozzle 211 of the recording head 21 to an appropriate amount corresponding to the instructed density.

  More specifically, in an inkjet printing apparatus, due to differences in processing accuracy and mounting accuracy of each nozzle, there is a slight variation in ink ejection ease and ink ejection direction between nozzles of the same recording head. It is generally known that there is. Such individual differences between the nozzles cause density unevenness in the printed material. In order to solve this problem, density correction is performed.

  Briefly described, when the density correction is performed, a predetermined test chart T7 ′ is printed on the printing paper 9. The test chart T7 ′ typically prints a test chart image T7 having a uniform density along the main scanning direction and a plurality of levels of density areas arranged along the sub-scanning direction on the printing paper 9. (See FIG. 4). Based on this test chart T7 ′, the input pixels for each nozzle 211 are reduced so as to reduce the difference between the actually printed (output) density and the ideal density in the print area corresponding to each nozzle 211. Adjust the value. More specifically, when there is a nozzle A that ejects a predetermined amount of ink and a nozzle B that ejects less ink than a predetermined amount for a specified density, the input pixel value of the nozzle A is relatively set. The correction is performed by lowering (decreasing) the input pixel value of the nozzle B.

  FIG. 3 is a block diagram schematically showing the function of the control unit 30 for realizing the density correction. As shown in FIG. 3, the control unit 30 includes a chart image storage unit 41, a chart print instruction unit 42, a chart reading unit 43, an interpolation function calculation unit 44, a provisional interpolation function calculation unit 45, a determination unit 46, and a thinned chart image generation. Mainly includes a unit 47, a post-conversion pixel value calculation unit 48, an input image print processing unit 49, and a user selection receiving unit 53. In addition to the chart image storage unit 41 described above, the control unit 30 includes an ideal density information storage unit 51, an input image storage unit 52, and an interpolation function storage unit (not shown). The functions of these units are realized by the control unit 30 operating based on the computer program CP.

  The chart image storage unit 41 is a memory that stores a test chart image T7 having a uniform density along the main scanning direction and a plurality of density areas arranged along the sub-scanning direction. An example of the test chart image T7 is shown in FIG. The test chart image T7 is a full version test chart image before performing a thinning process described later. In the test chart image T7, a predetermined number of density regions are arranged along the sub-scanning direction. In the example of this embodiment shown in FIG. 4, seven levels of density regions are arranged in order of density. As will be described in detail later, the chart image storage unit 41 may store a thinning test chart image T6 described later together with the test chart image T7.

  The chart printing instruction unit 42 causes the test chart image T7 to be printed on the printing paper 9. The chart printing instruction unit 42 reads the test chart image T7 from the chart image storage unit 41, and acquires the pixel value at the position corresponding to each nozzle 211 in the test chart image T7. The chart print instructing unit operates the transport mechanism 10 while giving a post-conversion pixel value, which will be described later, corresponding to the acquired pixel value to each nozzle 211 of the recording head 21. Thereby, a test chart T7 ′ obtained by printing the test chart image T7 on the printing paper 9 is obtained. Note that the chart printing instruction unit 42 can also cause the thinning test chart image T6 described later to be printed on the printing paper 9.

  The chart reading unit 43 optically reads the actually measured luminance value of the printing area corresponding to each nozzle 211 from the test chart T7 ′ printed on the printing paper 9 according to the instruction from the chart printing instruction unit 42. Specifically, a photographic image I obtained by photographing the entire area of the test chart T7 ′ is acquired by the photographic device 54 such as a camera or a scanner. The chart reading unit 43 optically reads the captured image I acquired by the imaging device 54 and acquires the luminance value at the position corresponding to each nozzle 211.

  The ideal light / dark information storage unit 51 is a memory that stores, for each density, information related to an ideal brightness value that is an ideal brightness value that realizes the density. Specifically, for example, a printed matter that has been printed (output) at an ideal density in advance can be photographed by a photographing device such as a camera or a scanner, and the luminance value of the photographed image can be set as an ideal luminance value. Alternatively, the average value or the median value of all the nozzles 211 of the actually measured luminance values read by the chart reading unit 43 may be calculated as the ideal luminance value for each of the multiple levels of density.

  The interpolation function calculation unit 44 calculates the difference between the actually measured luminance value and the ideal luminance value at each of a plurality of levels (for example, seven levels) for each of the plurality of nozzles 211. Based on this difference, the interpolation function calculation unit 44 determines the correspondence (combination) between the density as the input pixel value input to each nozzle 211 and the ideal pixel value actually printed on the printing paper 9. Plotting (holding) each of the plurality of levels of concentrations, and calculating an approximate curve or an approximate line of these multiple plots as an interpolation function. In this specification, in order to conceptually explain the processing, it is assumed that an approximate curve or plot is drawn on a graph. However, it is not necessary to actually draw a plot or approximate curve or the like. What is necessary is just to obtain a combination of functions and values by processing.

  For each of the plurality of nozzles 211, the provisional interpolation function calculation unit 45 calculates an approximate curve or a straight line of the remaining combinations when an arbitrary combination is temporarily excluded from a plurality of combinations of the interpolation functions described above. Calculated as a provisional interpolation function.

  The determination unit 46 determines from the test chart image T7 whether or not the density region corresponding to the provisionally excluded combination can be thinned out. The determination unit 46 determines that thinning is possible when the provisional interpolation function does not deviate beyond a predetermined amount from the interpolation function in all of the plurality of nozzles 211 for each recording head 21.

  The thinning chart image generation unit 47 thins out the density region corresponding to the combination temporarily excluded when calculating the temporary interpolation function from the test chart image T7 when the determination unit 46 determines that thinning is possible. A test chart image T6 is generated. The thinning test chart image T6 generated by the thinning chart image generation unit 47 is stored in the chart image storage unit 41.

  The input image storage unit 52 stores the input image R input to the apparatus.

  For each of the plurality of nozzles 211, the post-conversion pixel value calculation unit 48 refers to the pixel value at the position corresponding to the nozzle in the input image R and the interpolation function corresponding to the nozzle. Then, a post-conversion pixel value to be given to the nozzle is calculated.

  The input image print processing unit 49 is a processing unit for causing the input image R to be printed as a print target. The input image print processing unit 49 controls the recording head 21 to operate the transport mechanism 10 while giving the converted pixel values calculated by the converted pixel value calculating unit 48 to the plurality of nozzles 211.

  The user selection receiving unit 53 receives a selection operation by the user as to whether or not to print a thinning test chart image T6 described later on the printing paper 9.

  Next, specific processing when calculating an interpolation function used for shading correction will be described with reference to FIGS. FIG. 5 shows a control flow performed when the interpolation function is calculated.

  First, the chart printing instruction unit 42 instructs printing of the test chart image T7 on the printing paper 9 (S1). That is, the chart printing instruction unit 42 controls the transport mechanism 10 and the plurality of recording heads 21 to execute printing of the test chart image T7 on the printing paper 9. Thereby, a test chart T7 ′ obtained by actually printing the test chart image T7 on the printing paper 9 is obtained (see FIG. 4). The test chart T7 ′ reflects the ejection characteristics of each nozzle 211.

  Next, the photographing device 54 photographs the printed test chart 7 ′. Then, the chart reading unit 43 optically reads the photographed image I obtained by photographing, and acquires the actually measured luminance value at the position corresponding to each nozzle 211 (S2).

  Next, the interpolation function calculation unit 44 obtains the actually measured luminance value at each of the seven levels of density for each nozzle 211, and plots each value on the graph G1 with the horizontal axis representing density and the vertical axis representing luminance value. To do. An example of this graph G1 in this embodiment is shown in FIG. As shown in FIG. 6, in this graph G1, the values of the actually measured luminance values corresponding to the seven levels of the chart density are plotted as seven points. Then, the interpolation function calculation unit 44 generates an approximate curve L1 of the actually measured luminance value based on these seven plots (S3). For obtaining the approximate curve L1, various known methods can be adopted. For example, the approximate curve L1 may be approximated to a cubic equation obtained by a least square method. In FIG. 6, seven plots are indicated by X, and each plot is indicated by a combination of the chart density and the actually measured luminance value.

  The interpolation function calculation unit 44 plots the correspondence relationship between the input density and the ideal luminance value (target luminance value) read from the ideal grayscale information storage unit 51 on the graph G1 created in step S3. An approximate curve L2 of the plot is generated (S4). FIG. 6 shows an example in which the approximate curve L2 of the ideal luminance value generated in step S4 is drawn on the above-described graph G1.

  Subsequently, the interpolation function calculation unit 44 reads the ideal luminance value that realizes the density for each of the seven levels of density from the approximate curve L2. Then, the density corresponding to the actually measured luminance value that is the same as the ideal luminance value is read from the approximate curve L1 (S5). A state in which these values are read from the approximate curves L1 and L2 is indicated by broken lines in FIG. FIG. 6 shows that the density at which an ideal luminance value corresponding to a density of 80% can be output is 68% as an example. Thereby, in order to actually print an arbitrary density, the density to be instructed to the nozzle 211 is known. In other words, in this step, for each of the seven levels of density, a relationship as to which density should be replaced with which value to obtain an ideal target luminance value is calculated.

  Subsequently, the interpolation function calculation unit 44 plots the combination of the input pixel value read with reference to the approximate curves L1 and L2 and the ideal pixel value on the graph G2 as described above (S6). FIG. 7 shows an example of the graph G2 in the present embodiment. As shown in FIG. 7, the graph G2 has the horizontal axis as an input pixel value and the vertical axis as an ideal pixel value, and seven points P1 to P7 corresponding to seven levels of density are plotted. In FIG. 7, seven plots are indicated by X marks.

  And the interpolation function calculation part 44 produces | generates the approximated curve L3 of said seven plots P1-P7 as an interpolation function (S7). FIG. 7 shows an example in which an approximate curve L3 as an interpolation function is drawn on the graph G2 created in step S7. For obtaining the approximate curve L3, various known methods can be employed. For example, the approximate curve L3 may be approximated to a three-dimensional expression obtained by a least square method. Alternatively, it may be approximated to a function including a quartic function or a trigonometric function.

  The interpolation function L3 calculated for each nozzle 211 in this way is stored in an interpolation function storage unit (not shown) (S8). The interpolation function L3 is read by the post-conversion pixel value calculation unit 48 when the input image R is printed on the printing paper 9. Thereby, the converted pixel value to be given to each nozzle 211 is calculated in consideration of the ejection characteristics of each nozzle 211. Based on the converted pixel value, the input image print processing unit 49 performs a printing process, whereby the input image R is appropriately shade-corrected and a good printed matter is obtained.

  In order to satisfactorily perform the above-described density correction, the printing process of the test chart T7 ′ is indispensable. The printing of the test chart T7 ′ is required each time, for example, when a part or all of the recording head 21 is replaced or when the external environment such as the temperature changes greatly. This is because the ejection characteristics of each nozzle 211 may change. In general, it is known that the recording medium such as the printing paper 9 is compatible with the type of ink and the recording head 21. Therefore, it is necessary to reprint the test chart T7 ′ even when the type of the recording medium is changed to another material such as printing paper made by another company or film.

  However, since the test chart T7 ′ is not an object to be finally obtained as a printed material, it is desirable that the cost and time required for printing the test chart T7 ′ can be reduced if possible. From this point of view, in the present embodiment, the thinning test chart image T6 can be generated as a characteristic configuration. FIG. 11 shows an example of a thinning test chart image T6 in the present embodiment. This thinning test chart image T6 can be printed in place of the full version of the test chart T7 'when the next test chart is printed by the user's selection operation.

<3. About generation of thinning test chart image>
Hereinafter, specific processing when generating the thinning test chart image T6 will be described with reference to FIGS. FIG. 8 shows a control flow for generating the thinning test chart image T6.

  Note that the time when the process of generating the thinning test chart image T6 is performed is not particularly limited. For example, it may be performed immediately after the correction function L3 is calculated, or may be performed immediately before performing the next printing.

  First, when the provisional interpolation function calculation unit 45 shown in FIG. 3 tentatively excludes an arbitrary plot P5 from the plurality of plots P1 to P7 that are the basis of the interpolation function L3 for each of the plurality of nozzles 211. The approximate curve L4 of the remaining plots P1 to P4 and P6 to P7 is calculated as a provisional interpolation function (S11). FIG. 9 shows an example in which the provisional interpolation function L4 is generated in the present embodiment. Here, the tentatively excluded plot P5 described above corresponds to the density common to all the nozzles 211 (in this example, the input pixel value is 60%). In this example, the fifth plot P5 whose density is from the bottom is provisionally excluded, but the present invention is not limited to this. That is, a plot having a lighter density than this may be excluded, or a plot having a higher density may be excluded. Various methods known in the art can be adopted as a method of obtaining the approximate curve L4 (provisional interpolation function). For example, the approximate curve L4 (provisional interpolation function) may be approximated to a three-dimensional expression obtained by a least square method. Alternatively, it may be approximated to a function including a quartic function or a trigonometric function.

  Subsequently, the determination unit 46 determines whether or not the provisional interpolation function L4 has deviated beyond the predetermined amount from the interpolation function L3 in all of the plurality of nozzles 211. It is determined that “thinning is possible”. More specifically, the determination unit 36 calculates a difference D between an ideal pixel value corresponding to an arbitrary input pixel value in the interpolation function L3 and a temporary ideal pixel value corresponding to the input pixel value in the temporary interpolation function L4. All input pixel values are obtained (S12), and in any input pixel value and in any nozzle 211, if the difference D is less than the threshold value (S13, Yes), it is determined that “thinning is possible”. . In other words, the maximum value of the deviation in the vertical axis direction of the approximate curve L4 generated by provisionally excluding the arbitrary plot P5 with respect to the approximate curve L3 before the exclusion is within the allowable range. In this case, it is determined that the plot P5 can be thinned out. FIG. 10 shows a specific example of the difference D.

  Note that the determination unit 46 of the present embodiment applies different threshold values depending on the numerical range of the input pixel value. Specifically, for example, the threshold value is ± 2% when the input pixel value is 0 to 40%, the threshold value is ± 3% when the input pixel value is 40 to 60%, and the threshold value when the input pixel value is 60% to 100%. Can be ± 5%. According to this configuration, it is possible to determine whether thinning is possible by applying a different threshold value for each density. For this reason, for example, in a density region where the difference in shading is conspicuous, it is possible to determine whether or not thinning can be performed in a fluid manner by making the threshold value smaller than others.

  However, the same threshold value may be applied to all the input pixel values instead of applying different threshold values depending on the numerical range of the input pixel values.

  If the determination unit 46 determines that “thinning is possible”, then, the thinning chart image generation unit 47 calculates density regions corresponding to the plot P5 provisionally excluded when calculating the temporary interpolation function L4 (S11). Then, a thinned test chart image T6 thinned out from the test chart image T7 is generated (S14). In the present embodiment, a thinning test chart image T6, which is image data from which the 60% density region corresponding to the plot P5 has been excluded, is generated (see FIG. 11). As shown in FIG. 4 and FIG. 11, in the thinning test chart T6 ′ obtained by printing the thinning test chart image T6, since some of the plurality of levels of density are thinned, the area of the printing region is larger than that of the test chart T7 ′. Is also getting smaller.

  The generated thinning test chart image T6 is stored in the chart image storage unit 41 together with the test chart image T7 before thinning (S15).

<4. About printing a thinning test chart>
Hereinafter, a specific process in the case where a thinning test chart T6 ′ obtained by printing the thinning test chart image T6 on the printing paper 9 will be described with reference to FIG. FIG. 12 shows a control flow performed when the thinning test chart T6 ′ is printed.

  First, the chart printing instruction unit 42 accesses the chart image storage unit 41 to check whether or not the thinning test chart image T6 is stored (S21). As a result, if the thinning test chart image T6 has been stored in the chart image storage unit 41 (S21, Yes), has the user selection receiving unit 53 received an operation for selecting a thinning test chart? It is determined whether or not (S22).

  When the selection operation for selecting the thinning test chart by the user has been received (S22, Yes), the chart printing instruction unit 42 reads the thinning test chart image T6 from the chart image storage unit 41. Then, the chart printing instruction unit 42 reads the pixel value at the position corresponding to each nozzle 211 from the thinning test chart image T6, and operates the transport mechanism 10 while giving the pixel value to the nozzle 211. Thereby, the thinning test chart T6 ′ is printed (S24).

  On the other hand, when the thinning test chart image T6 is not originally stored in the chart image storage unit 41 (step S21, No), or when the user has not performed an operation for selecting printing of the thinning test chart (step S21). (S22, No), the chart printing instruction unit 42 reads the full version of the test chart image T7 from the chart image storage unit 41 (S25). Then, the chart printing instruction unit 42 operates the nozzle 211 and the transport mechanism 10 by normal processing. Thereby, the test chart T7 'is printed (S26).

  Through the processing as described above, in the inkjet printing apparatus 1 of the present embodiment, at the time of printing a test chart, an arbitrary density region (60% in the present embodiment) among a plurality of density regions (seven levels in the present embodiment). Even if printing is performed with the () omitted, if the influence on the interpolation function calculated based on the printing result is small, the density (60% in this embodiment) can be thinned out. Thereby, in the density correction performed using the interpolation function at the time of printing the next input image R, it is possible to reduce the cost, labor, time, and the like of the ink cost and the printing paper cost required for printing the test chart.

  Here, in general, the manner in which ink droplets spread to the recording medium differs depending on the type of the recording medium. Therefore, it is considered that the density region that can be thinned out in the test chart differs depending on the type of the recording medium. Therefore, the chart image storage unit 41 of the inkjet printing apparatus 1 may store a plurality of thinned-out test chart images in association with the type of recording medium, as shown in FIG. According to this, an interpolation function can be calculated by applying a suitable thinning test chart according to the type of recording medium.

  Further, in the inkjet printing apparatus 1 according to the present embodiment, the thinning test chart image T6 is used only when the user selection accepting unit 53 accepts a user operation to select a thinning test chart from among a plurality of test charts. The printing on the printing paper 9 is executed. In other words, when the user has not selected to print the thinning test chart, the normal test chart image T7 is printed on the printing paper 9. As a result, the user can select whether to print a thinned test chart or a normal test chart depending on the situation. Therefore, flexible operation is possible.

<5. About modification>
As mentioned above, although embodiment of this invention was described, this invention is not limited to said embodiment.

  In the above embodiment, the determination unit 46 determines that the difference D between the ideal pixel value corresponding to an arbitrary input pixel value in the interpolation function L3 and the ideal pixel value corresponding to the input pixel value in the provisional interpolation function L4 is a threshold value. It is determined whether or not “thinning is possible” based on the criterion of whether or not it is within. However, in addition to this, the following determination may be performed in parallel. That is, the determination unit 46 obtains a differential value of an ideal pixel value corresponding to an arbitrary input pixel value in the interpolation function L3 and a differential value of an ideal pixel value corresponding to the input pixel value in the provisional interpolation function L4. Then, the determination unit 46 obtains a residual R ′ that is a difference value between these two differential values with respect to all the input pixel values, and the residual is obtained at any input pixel value and at any nozzle 211. When R ′ is less than the second threshold, it is determined that “thinning is possible”. According to this, when the slope of the temporary interpolation function L4 is significantly different from the slope of the interpolation function L3, the temporarily excluded density is not thinned out when the next test chart is printed. Therefore, it is possible to prevent the shading from changing significantly in the next printing compared to the previous printing. In addition, it is possible to suppress the occurrence of a phenomenon such as tone jump in the printed material.

  In the above embodiment, the provisional interpolation function L4 is generated by provisionally excluding one plot P5 from the plots P1 to P7 that are the basis of the interpolation function L3. However, it is not necessarily limited to this. For example, instead of the above, a provisional interpolation function may be generated by provisionally excluding two or more plots. According to this, the cost and time required for printing the test chart can be further reduced. However, in order to keep the amount of variation of the temporary interpolation function from the interpolation function small, two or more plots that are temporarily excluded are plots that are not adjacent to each other (for example, P3 and P5 in the above example). It is preferable.

  In addition, when two or more plots are temporarily excluded from the original plot of the interpolation function, instead of excluding them at the same time, exclude them one by one each time it is necessary to print a test chart. It is good to go.

  The process of thinning out the test chart may be performed by the manufacturer of the inkjet printing apparatus 1 or the like instead of the user who uses the inkjet printing apparatus 1. In that case, the manufacturer, for example, first prints a test chart having extremely multi-stage (for example, 3 to 5%) density areas, and omits some of the density areas by the same process as described above. The thinned test chart image is generated, the test chart based on the thinned test chart image is printed, and the operation of sequentially repeating the process of creating the optimal thinned test chart image and distributing it to the user .

  Instead of making it possible to apply functions having different shapes for each nozzle 211 as the interpolation function L3 and the provisional interpolation function L4, a function applied as an interpolation function and a provisional interpolation function for each of the small heads 21a to 21d. The shape may be common. Specifically, for example, all the interpolation functions of the nozzles 211 belonging to the small heads 21a to 21c may be cubic functions, and all the interpolation functions of the nozzles 211 belonging to the small head 21d may be quaternary functions. According to this, the interpolation function L3 and the provisional interpolation function L4 according to the tendency (individual difference) for each small head can be adopted. In addition, the amount of arithmetic processing required for calculating these functions L3 and L4 can be reduced. Furthermore, the memory capacity for storing these functions L3 and L4 can be reduced.

  Further, among the plurality of small heads 21a to 21d, the smaller the head in which the difference between the measured luminance value and the ideal luminance value is relatively large in the nozzle 211 of the small head, the higher the dimensional variable. It is good also as what employ | adopts the function which has as an interpolation function. Specifically, as a result of reading from the approximate curves L1 and L2, the small head 21d having a poor feature is approximated to a quartic function, while the small heads 21a to 21c having a relatively good feature are cubic functions. It is good also as making it approximate. As a result, an approximate curve with a small deviation from the combination value can be obtained by approximating the necessary nozzle 211 with a high-dimensional function while suppressing the amount of the entire calculation processing.

  Instead of the post-conversion pixel value calculation unit 48 and the input image print processing unit 49 provided in the inkjet printing apparatus 1 of the above embodiment, a pixel value correction amount calculation unit and an input image print processing unit different from the above are provided. It may be provided. For each of the plurality of nozzles 211, the pixel value correction amount calculation unit refers to the pixel value at the position corresponding to the nozzle 211 in the input image R and the interpolation function corresponding to the nozzle 211. Thus, a pixel value correction amount for correcting the pixel value of each pixel of the input image R is calculated. Further, the input image print processing unit controls the recording head 21 to convey each pixel value after correction using the pixel value correction amount to the plurality of recording heads 21 as converted pixel values. The mechanism 10 is operated. Even with such a configuration, similarly to the above-described embodiment, it is possible to obtain a good printed matter by appropriately correcting the density of the input image while reducing the cost required for printing the test chart. That is, the pixel value input to each nozzle 211 may be adjusted according to the ejection characteristics of each nozzle 211, or alternatively, each pixel value itself of the input image R is corrected to each nozzle 211. May be given. Further, a post-conversion image holding unit that holds the post-conversion image in which each pixel value itself of the input image R is corrected may be provided. When the same input image R is printed, the transport mechanism 10 is operated while giving each pixel of the converted image held in the converted image holding unit to the plurality of recording heads 21. According to such a configuration, when the same input image is printed a plurality of times, it is not necessary to perform density correction for each input image, so that the cost required for printing the test chart can be reduced.

  Each recording head 21 may not be divided into a plurality of small heads.

  In the above embodiment, the printing paper 9 as a recording medium moves in the sub-scanning direction with respect to the recording head 21, but the present invention is not limited to this. For example, instead of this, the recording head may move in the sub operation direction with respect to the recording medium. That is, the transport mechanism may be any mechanism that relatively moves the recording head and the recording medium in the sub-scanning direction.

  You may combine suitably each element which appeared in said embodiment and modification in the range which does not produce inconsistency.

1 Inkjet printer 9 Printing paper (recording medium)
DESCRIPTION OF SYMBOLS 10 Conveyance mechanism 21 Recording head 41 Chart image memory | storage part 42 Chart printing instruction | indication part 43 Chart reading part 44 Interpolation function calculation part 45 Temporary interpolation function calculation part 46 Judgment part 47 Thinning-out chart image generation part 211 Nozzle

Claims (15)

An inkjet printing apparatus that prints an image on a recording medium by a one-pass method,
A recording head in which a plurality of nozzles that eject ink to a recording medium are arranged in the main scanning direction;
A transport mechanism for moving the recording medium relative to the recording head in a sub-scanning direction orthogonal to the main scanning direction;
A chart image storage unit for storing a test chart image having a uniform density along the main scanning direction and a plurality of density regions arranged along the sub-scanning direction;
A chart printing instruction unit for executing printing of the test chart image on a recording medium;
A chart reading unit that optically reads a test chart printed on a recording medium according to an instruction from the chart printing instruction unit, and obtains an actually measured luminance value of a print region corresponding to each nozzle;
For each of the plurality of nozzles, an input pixel value input to the recording head based on a difference between the measured luminance value at each of the plurality of levels of density and an ideal luminance value that is an ideal luminance value. And a combination of an ideal pixel value that is an ideal density when actually printed on a recording medium is held for each of the multiple levels of density, and an approximation generated from the plurality of combinations. An interpolation function calculation unit for calculating a curve or an approximate straight line as an interpolation function;
For each of the plurality of nozzles, a provisional interpolation function calculation unit that calculates an approximate curve or an approximate line generated by provisionally excluding any one combination from the plurality of combinations, as a provisional interpolation function;
In all of the plurality of nozzles, when the provisional interpolation function does not deviate from the interpolation function beyond a predetermined amount, it is determined that the combination that has been temporarily excluded in the interpolation function calculation unit can be thinned out. A determination unit;
When the determination unit determines that thinning is possible, a thinned test chart image is generated by thinning out the density region corresponding to the combination that is temporarily excluded when calculating the temporary interpolation function from the test chart image. A decimation chart image generation unit,
With
The chart image storage unit can store the thinning test chart image,
The chart printing instruction unit is an inkjet printing apparatus capable of executing printing of the thinning test chart image on a recording medium. The inkjet printing apparatus according to claim 1,
The chart image storage unit is an inkjet printing apparatus capable of storing the thinning chart image in association with a type of recording medium. The inkjet printing apparatus according to claim 1 or 2,
The determination unit calculates a difference between the ideal pixel value corresponding to an arbitrary input pixel value in the interpolation function and a temporary ideal pixel value corresponding to the input pixel value in the temporary interpolation function for all the inputs. An ink jet printing apparatus that obtains pixel values and determines that thinning is possible when the difference is less than a threshold value for any of the input pixel values and for any of the nozzles. The inkjet printing apparatus according to claim 3,
The threshold value is an inkjet printing apparatus to which a different value is applied according to the input pixel value. The ink jet printing apparatus according to claim 3 or 4, wherein:
The determination unit includes a difference between a differential value of the ideal pixel value corresponding to an arbitrary input pixel value in the interpolation function and a differential value of a temporary ideal pixel value corresponding to the input pixel value in the temporary interpolation function. Inkjet which calculates | requires value regarding all the said input pixel values, and determines that it can be thinned out when the said difference value is less than a 2nd threshold value in any said input pixel value and in any said nozzle Printing device. An inkjet printing apparatus according to any one of claims 1 to 5, wherein
The provisional interpolation function calculation unit calculates an approximate curve or an approximation line generated from the remaining combinations when two or more combinations of the plurality of combinations of the interpolation functions are provisionally excluded. Inkjet printer that calculates as a function. The inkjet printing apparatus according to any one of claims 1 to 6,
The recording head has a plurality of small heads arranged side by side in the main scanning direction,
The ink jet printing apparatus, wherein the interpolation function calculation unit and the provisional interpolation function calculation unit calculate a function having a different shape for each of the small heads as the interpolation function and the provisional interpolation function. The inkjet printing apparatus according to claim 7,
The interpolation function calculation unit and the provisional interpolation function calculation unit have a relatively large difference between the measured luminance value and the ideal luminance value in the nozzle of the small head among the plurality of small heads. An inkjet printing apparatus that employs a function having a higher dimensional variable as the interpolation function and the provisional interpolation function as the head is smaller. The inkjet printing apparatus according to any one of claims 1 to 8,
The chart printing instruction unit is an inkjet printing apparatus that causes printing of a selected image of the test chart image and the thinning-out test chart image on a recording medium according to a user's selection operation. An inkjet printing apparatus according to any one of claims 1 to 9, wherein
For each of the plurality of nozzles, the pixel value given to the nozzle by referring to the pixel value at the position corresponding to the nozzle in the input image and the interpolation function corresponding to the nozzle. A post-conversion pixel value calculation unit that calculates post-conversion pixel values;
An input image print processing unit that controls the recording head and operates the transport mechanism while giving the converted pixel values calculated by the converted pixel value calculating unit to the plurality of recording heads;
An inkjet printing apparatus comprising: An inkjet printing apparatus according to any one of claims 1 to 9, wherein
For each of the plurality of nozzles, the pixel value of each pixel is corrected by referring to the pixel value at the position corresponding to the nozzle in the input image and the interpolation function corresponding to the nozzle. A pixel value correction amount calculation unit for calculating a pixel value correction amount for
An input image print processing unit that controls the recording head to operate the transport mechanism while giving each pixel value after correction using the pixel value correction amount as the converted pixel value to the plurality of recording heads. When,
An inkjet printing apparatus comprising: The inkjet printing apparatus according to claim 11,
A post-conversion image holding unit that holds a post-conversion image based on the post-conversion pixel value calculated by the pixel value correction amount calculation unit;
The ink jet printing apparatus, wherein the input image print processing unit operates the transport mechanism while supplying each pixel value of the converted image held in the converted image holding unit to the plurality of recording heads. An inkjet printing apparatus that prints an image on a recording medium by a one-pass method,
A recording head in which a plurality of nozzles that eject ink to a recording medium are arranged in the main scanning direction;
A transport mechanism for moving the recording medium relative to the recording head in a sub-scanning direction orthogonal to the main scanning direction;
A chart image storage unit for storing a test chart image having a uniform density along the main scanning direction and a plurality of density regions arranged along the sub-scanning direction;
A chart printing instruction unit for executing printing of the test chart image on a recording medium;
With
The chart image storage unit can store the test chart image and a thinned test chart image obtained by thinning a part of the density region from the test chart image.
The chart printing instruction unit is an inkjet printing apparatus that causes printing of a selected image of the test chart image and the thinning-out test chart image on a recording medium according to a user's selection operation. A recording head in which a plurality of nozzles that eject ink to a recording medium are arranged in the main scanning direction;
A transport mechanism for moving the recording medium relative to the recording head in a sub-scanning direction orthogonal to the main scanning direction;
A chart image storage unit for storing a test chart image having a uniform density along the main scanning direction and a plurality of density regions arranged along the sub-scanning direction;
An inkjet printing method for printing an image on a recording medium by a one-pass method using an inkjet printer comprising:
a) printing the test chart image on a recording medium;
b) Optically reading a test chart printed on a recording medium, obtaining an actually measured luminance value of a print area corresponding to each nozzle,
c) For each of the plurality of nozzles, an input that is input to the recording head based on a difference between the measured luminance value at each of the plurality of levels of density and an ideal luminance value that is an ideal luminance value. A combination of a density as a pixel value and an ideal pixel value that becomes an ideal density when actually printed on a recording medium is held for each of the multiple levels of density, and is generated from the plurality of combinations. Calculated approximate curve or approximate straight line as an interpolation function,
d) For each of the plurality of nozzles, an approximate curve or an approximate line generated by provisionally excluding any one combination from the plurality of combinations of the interpolation functions is calculated as a provisional interpolation function;
e) when the provisional interpolation function does not deviate from the interpolation function beyond a predetermined amount in all of the plurality of nozzles, it is determined that the provisionally excluded combination can be thinned;
f) Inkjet printing for generating a thinned test chart image in which density regions corresponding to the combinations temporarily excluded when calculating the provisional interpolation function are thinned out from the test chart when it is determined that thinning is possible Method. The inkjet printing method according to claim 14, comprising:
After the step f)
g) storing the thinning test chart image in the chart image storage unit;
h) An inkjet printing method for executing printing on a recording medium of a selected test chart image of the test chart image and the thinning-out test chart image.