Patent Publication Number: US-9902179-B2

Title: Ink jet recording device and density unevenness correction method therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-077268, filed on Apr. 7, 2016. The above application is hereby expressly incorporated by reference, in its entirety, into the present application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink jet recording device and a density unevenness correction method therefor. 
     2. Description of the Related Art 
     Drum transportation is known as one of methods for transporting media in ink jet recording devices. The drum transportation is a method for winding a medium around a peripheral surface of a rotating drum to transport the medium. 
     A drum in which a supporting part for a medium is extendable and retractable is described in JP2010-149417A. In this drum, the supporting part for the medium is constituted by a pair of supports having a comb teeth structure. The comb teeth structure is a structure in which supporting pieces that support the medium are arranged at regular intervals in the shape of comb teeth. The supporting part for the medium is disposed such that the pair of supports having the comb teeth structure are engaged with each other, and is thereby configured in an extendable and retractable manner. 
     SUMMARY OF THE INVENTION 
     Meanwhile, if the supporting part for the medium is constituted by the supports having the comb teeth structure as in the drum described in JP2010-149417A, a region where the medium is supported in contact with the supports, and a region where the medium is supported without contacting the supports are generated when the medium is supported. As a result, the following problems occur. For example, in a case where the temperature of the medium and the temperature of the supports are different from each other, variation occurs in the temperature distribution of the entire medium. For example, in a case where the temperature of the medium is higher than the temperature of the supports, the temperature of portions contacting the supports becomes low, and variation occurs in the temperature distribution of the entire medium. If the variation occurs in the temperature distribution of the entire medium, even in a case where the same amount of ink droplets are dropped, the diameter of dots changes, the degree of landing interference changes, or density unevenness occurs. 
     For example, as described in JP2014-231155A, it is also considered that the density unevenness is solved by an image processing technique. 
     However, since related-art density unevenness correction is a method of outputting a test chart to obtain a correction value required for correction of the density unevenness, the following problems occur if this method is applied. That is, since the temperature distribution occurring in the medium is not uniform as a whole, if the related-art technique is applied as it is, there is a problem that the density unevenness is rather worsened. 
     The invention has been made in view of such circumstances, and an object thereof is to provide an ink jet recording device and a density unevenness correction method therefor that can appropriately correct density unevenness in the ink jet recording device in which a medium supporting part is constituted by a support having a comb teeth structure. 
     The means for solving the above problems is as follows. 
     (1) A density unevenness correction method for an image of an ink jet recording device, the ink jet recording device including transporting means having a medium supporting part configured such that a first support having a plurality of first supporting pieces arranged in the shape of comb teeth thereon and a second support having a plurality of second supporting pieces arranged in the shape of comb teeth thereon are engaged with each other and are extendable and retractable, and bringing a medium into close contact with the medium supporting part to transport the medium, and a line-type ink jet head that draws an image with a single pass on the medium transported by the transporting means, the density unevenness correction method comprising: a test chart output step of outputting a test chart including a plurality of grayscales; a test chart read step of reading an image of the output test chart; a first density unevenness correction value derivation step of deriving a first density unevenness correction value, which is a correction value of density unevenness in a first region, from a reading result of the test chart, in a case where a region where the medium is supported by only the first support is defined as the first region; a second density unevenness correction value derivation step of deriving a second density unevenness correction value, which is a correction value of density unevenness in a second region, from the reading result of the test chart, in a case where a region where the medium is supported by only the second support is defined as the second region; a third density unevenness correction value derivation step of deriving a third density unevenness correction value, which is a correction value of density unevenness in a third region, from the reading result of the test chart, in a case where a region where the medium is supported by the first support and the second support is defined as the third region; and a density unevenness correction step of correcting data of an image to be drawn on the medium for each region on the basis of the correction value of the density unevenness for each region. 
     According to this aspect, the density unevenness correction is performed in the following procedure. First, the test chart including the plurality of grayscales is output. That is, the medium is transported by the transporting means, and the test chart is drawn on the medium by the ink jet head. Next, the image of the output test chart is read by the image reading means. The reading can be performed either inline or offline. The inline is an aspect in which the reading of the image is performed within the ink jet recording device. The offline is an aspect of which the reading of the image is performed out of the ink jet recording device. Next, the first density unevenness correction value, the second density unevenness correction value, and the third density unevenness correction value are obtained on the basis of the reading result of the test chart. Here, the first density unevenness correction value is the correction value of the density unevenness in the first region of the medium. The first region is the region where the medium is supported by only the first support. Both of a region where the paper is supported in close contact with the first supporting pieces, a region where the paper is supported without being in close contact with the first supporting pieces, that is, a region where the paper is supported in the state of floating between the first supporting pieces adjacent to each other are included in this first region. Additionally, the second density unevenness correction value is the correction value of the density unevenness in the second region of the medium. The second region is the region where the medium is supported by only the second support. Both of a region where the paper is supported in close contact with the second supporting pieces, a region where the paper is supported without being in close contact with the second supporting pieces, that is, a region where the paper is supported in the state of floating between the second supporting pieces adjacent to each other are included in this second region. Additionally, the third density unevenness correction value is the correction value of the density unevenness in the third region of the medium. The third region is the region where the medium is supported by the first support and the second support, and is a region where the second supporting pieces of the second support are engaged with the first supporting pieces of the first support. Additionally, the first density unevenness correction value, the second density unevenness correction value, and the third density unevenness correction value are obtained from the reading result of the test chart. Then, density data of the image to be drawn on the medium are corrected for each region on the basis of the obtained correction value of the density unevenness for each region. That is, data of the first region are corrected on the basis of the first density unevenness correction value, data of the second region are corrected on the basis of the second density unevenness correction value, and data of the third region are corrected on the basis of the third density unevenness correction value. Accordingly, in the ink jet recording device in which the medium supporting part is supported by the supports having the comb teeth structure, the density unevenness can be corrected appropriately, and a high-quality image can be drawn. 
     (2) The density unevenness correction method for an ink jet recording device according to the above (1) in which the test chart includes a first chart that is a chart including a plurality of grayscales and is drawn in the first region, a second chart that is a chart including a plurality of grayscales and is drawn in the second region, and a third chart that is a chart including a plurality of grayscales and is drawn in the third region, in which the first density unevenness correction value derivation step derives the first density unevenness correction value from a reading result of the first chart, in which the second density unevenness correction value derivation step derives the second density unevenness correction value from a reading result of the second chart, and in which the third density unevenness correction value derivation step derives the third density unevenness correction value from a reading result of the third chart. 
     According to this aspect, the test chart has a configuration including the first chart, the second chart, and the third chart. The first chart is a chart to be drawn in the first region, and is constituted by a chart including a plurality of grayscales. The first density unevenness correction value is obtained on the basis of the reading result of the first chart. The second chart is a chart to be drawn in the second region, and is constituted by a chart including a plurality of grayscales. The second density unevenness correction value is obtained on the basis of the reading result of the second chart. The third chart is a chart to be drawn in the third region, and is constituted by a chart including a plurality of grayscales. The third density unevenness correction value is obtained on the basis of the reading result of the third chart. 
     (3) The density unevenness correction method for an ink jet recording device according to the above (1), in which the test chart includes a first chart that is a chart including a plurality of grayscales and is drawn in the first region, and a second chart that is a chart including a plurality of grayscales and is drawn in the second region, in which the density unevenness correction method further comprises: a main density unevenness component derivation step of calculating an average of a reading result of the first chart and a reading result of the second chart, to derive a main density unevenness component that is a density unevenness component resulting from the ink jet head, a first density unevenness component derivation step of calculating a difference between the reading result of the first chart and the main density unevenness component, to derive a first density unevenness component that is a density unevenness component resulting from the first support, and a second density unevenness component derivation step of calculating a difference between the reading result of the second chart and the main density unevenness component, to derive a second density unevenness component that is a density unevenness component resulting from the second support, in which the first density unevenness correction value derivation step derives the first density unevenness correction value on the basis of the main density unevenness component and the first density unevenness component, in which the second density unevenness correction value derivation step derives the second density unevenness correction value on the basis of the main density unevenness component and the second density unevenness component, and in which the third density unevenness correction value derivation step derives the third density unevenness correction value on the basis of the main density unevenness component. 
     According to this aspect, the test chart has a configuration including the first chart and the second chart. The first chart is a chart to be drawn in the first region, and is constituted by a chart including a plurality of grayscales. The second chart is a chart to be drawn in the second region, and is constituted by a chart including a plurality of grayscales. The correction value of the density unevenness of each region is obtained as follows on the basis of the reading result of the test chart including the first chart and the second chart. First, the main density unevenness component is obtained by calculating the average of the reading result of the first chart and the reading result of the second chart. The main density unevenness component is the density unevenness component resulting from the ink jet head, and is a component of density unevenness from which the influence of the medium supporting part is excluded. The component of the density unevenness from which the influence of the medium supporting part is excluded can be obtained by calculating the average of the reading result of the first chart and the reading result of the second chart. Next, the first density unevenness component is obtained by calculating the difference between the reading result of the first chart and the main density unevenness component. The first density unevenness component is the density unevenness component resulting from the first support. That is, the first density unevenness component is a pattern of density unevenness that appears according to arrangement intervals of the first supporting pieces. Similarly, the second density unevenness component is obtained by calculating the difference between the reading result of the second chart and the main density unevenness component. The second density unevenness component is the density unevenness component resulting from the second support. That is, the second density unevenness component is a pattern of density unevenness that appears according to arrangement intervals of the second supporting pieces. On the basis of the main density unevenness component, the first density unevenness component, and the second density unevenness component that are obtained in this way, the correction value of the density unevenness is obtained for each region. That is, the first density unevenness correction value is obtained on the basis of the main density unevenness component and the first density unevenness component, and the second density unevenness correction value is obtained on the basis of the main density unevenness component and the second density unevenness component. Additionally, the third density unevenness correction value is obtained on the basis of the main density unevenness component. 
     (4) The density unevenness correction method for an ink jet recording device according to the above (3), in which the test chart further includes a third chart that is a chart including a plurality of grayscales and is drawn in the third region, and in which the main density unevenness component derivation step calculates an average of the reading result of the first chart, the reading result of the second chart, and the reading result of the third chart, to derive the main density unevenness component. 
     According to this aspect, the third chart is further included in the test chart. The third chart is a chart to be drawn in the third region, and is constituted by a chart including a plurality of grayscales. The main density unevenness component is obtained by calculating the average of the reading result of the first chart, the reading result of the second chart, and the reading result of the third chart. 
     (5) The density unevenness correction method for an ink jet recording device according to the above (1), further comprising: a density unevenness component derivation step of deriving a main density unevenness component, which is a density unevenness component originating from the ink jet head, from the reading result of the test chart, a first density unevenness component that is a density unevenness component resulting from the first support, and a second density unevenness component that is a density unevenness component resulting from the second support, in which the first density unevenness correction value derivation step derives the first density unevenness correction value on the basis of the main density unevenness component and the first density unevenness component, in which the second density unevenness correction value derivation step derives the second density unevenness correction value on the basis of the main density unevenness component and the second density unevenness component, and in which the third density unevenness correction value derivation step derives the third density unevenness correction value on the basis of the main density unevenness component. 
     In this aspect, the main density unevenness component, the first density unevenness component, and the second density unevenness component are obtained from the reading result of the test chart. Then, the first density unevenness correction value is obtained on the basis of the main density unevenness component and the first density unevenness component. Additionally, the second density unevenness correction value is obtained on the basis of the main density unevenness component and the second density unevenness component. Additionally, the third density unevenness correction value is obtained on the basis of the obtained main density unevenness component. 
     (6) The density unevenness correction method for an ink jet recording device according to the above (5), in which the density unevenness component derivation step includes a main density unevenness component derivation step of deriving the main density unevenness component from the reading result of the test chart, a first density unevenness component derivation step of calculating a difference between the reading result of the test chart and the main density unevenness component, to derive the first density unevenness component, and a second density unevenness component derivation step of calculating a difference between the reading result of the test chart and the main density unevenness component, to derive the second density unevenness component. 
     In this aspect, when the main density unevenness component, the first density unevenness component, and the second density unevenness component are obtained from the reading result of the test chart, first, the main density unevenness component is obtained. Then, the first density unevenness component is obtained from the difference between the obtained main density unevenness component and the reading result of the test chart. Additionally, the second density unevenness component is obtained from the difference between the obtained main density unevenness component and the reading result of the test chart. 
     (7) The density unevenness correction method for an ink jet recording device according to the above (6), in which the main density unevenness component derivation step includes a step of Fourier-transforming the reading result of the test chart to decompose the transformed reading result into a plurality of frequency components, a step of removing a fundamental frequency and a frequency component of an integral multiple of the fundamental frequency from the reading result of the test chart after the Fourier transform, in a ease where a frequency matching arrangement intervals of the first supporting pieces and the second supporting pieces is defined as the fundamental frequency, and a step of inverse-Fourier-transforming the reading result of the test chart after the removal, to derive the main density unevenness component. 
     In this aspect, the main density unevenness component is obtained as follows. First, the reading result of the test chart is Fourier-transformed and is decomposed into the plurality of frequency components. Next, the fundamental frequency and the frequency component of the integral multiple of the fundamental frequency are removed from the reading result of the test chart after the Fourier transform. Here, the fundamental frequency is the frequency matching the arrangement intervals of the first supporting pieces and the second supporting pieces that constitute the first support and the second support. The influence of the medium supporting part can be excluded by removing the fundamental frequency and the frequency component of the integral multiple of the fundamental frequency. Next, the reading result of the test chart after the removal is inverse-Fourier-transformed. Accordingly, the main density unevenness component can be extracted from the reading result of the test chart. 
     (8) An ink jet recording device comprising: transporting means including a medium supporting part configured such that a first support having a plurality of first supporting pieces arranged in the shape of comb teeth thereon and a second support having a plurality of second supporting pieces arranged in the shape of comb teeth thereon are engaged with each other and are extendable and retractable, and bringing a medium into close contact with the medium supporting part to transport the medium; a line-type ink jet head that draws an image with a single pass on the medium transported by the transporting means; image reading means for reading the image drawn on the medium; a test chart output control unit that outputs a test chart including a plurality of grayscales; a test chart reading control unit that makes the image reading means read an image of the output test chart; a first density unevenness correction value derivation unit that derives a first density unevenness correction value, which is a correction value of density unevenness in a first region, from a reading result of the test chart, in a case where a region where the medium is supported by only the first support is defined as the first region; a second density unevenness correction value derivation unit that derives a second density unevenness correction value, which is a correction value of density unevenness in a second region, from the reading result of the test chart, in a case where a region where the medium is supported by only the second support is defined as the second region; a third density unevenness correction value derivation unit that derives a third density unevenness correction value, which is a correction value of density unevenness in a third region, from the reading result of the test chart, in a case where a region where the medium is supported by the first support and the second support is defined as the third region; and a density unevenness correction unit that corrects data of an image to be drawn on the medium for each region on the basis of the correction value of the density unevenness for each region. 
     According to this aspect, the density unevenness correction is performed in the following procedure. First, the test chart including the plurality of grayscales is output. The output of the test chart is performed under the control using the test chart output control unit. Next, the image of the output test chart is read by the image reading means. The reading is performed under the control using the test chart reading control unit. Next, the first density unevenness correction value, the second density unevenness correction value, and the third density unevenness correction value are obtained on the basis of the reading result of the test chart. The first density unevenness correction value is obtained by the first density unevenness correction value derivation unit. The second density unevenness correction value is obtained by the second density unevenness correction value derivation unit. The third density unevenness correction value is obtained by the third density unevenness correction value derivation unit. Density data of the image to be drawn on the medium are corrected for each region on the basis of the obtained correction value of the density unevenness for each region. The correction is performed by the density unevenness correction unit. The density unevenness correction unit corrects data of the first region on the basis of the first density unevenness correction value, corrects data of the second region on the basis of the second density unevenness correction value, and corrects data of the third region on the basis of the third density unevenness correction value. Accordingly, in the ink jet recording device in which the medium supporting part is constituted by the supports having the comb teeth structure, the density unevenness can be corrected appropriately, and a high-quality image can be drawn. 
     (9) The ink jet recording device according to the above (8), in which the test chart includes a first chart that is a chart including a plurality of grayscales and is drawn in the first region, a second chart that is a chart including a plurality of grayscales and is drawn in the second region, and a third chart that is a chart including a plurality of grayscales and is drawn in the third region, in which the first density unevenness correction value derivation unit derives the first density unevenness correction value from a reading result of the first chart, in which the second density unevenness correction value derivation unit derives the second density unevenness correction value from a reading result of the second chart, and in which the third density unevenness correction value derivation unit derives the third density unevenness correction value from a reading result of the third chart. 
     According to this aspect, the test chart has a configuration including the first chart, the second chart, and the third chart. The first chart is a chart to be drawn in the first region, and is constituted by a chart including a plurality of grayscales. The first density unevenness correction value derivation unit derives the first density unevenness correction value from the reading result of the first chart. The second chart is a chart to be drawn in the second region, and is constituted by a chart including a plurality of grayscales. The second density unevenness correction value derivation unit derives the second density unevenness correction value from the reading result of the second chart. The third chart is a chart to be drawn in the third region, and is constituted by a chart including a plurality of grayscales. The third density unevenness correction value derivation unit derives the third density unevenness correction value from the reading result of the third chart. 
     (10) The ink jet recording device according to the above (8), in which the test chart includes a first chart that is a chart including a plurality of grayscales and is drawn in the first region, and a second chart that is a chart including a plurality of grayscales and is drawn in the second region, in which the ink jet recording device further comprises: a main density unevenness component derivation unit that calculates an average of a reading result of the first chart and a reading result of the second chart, to derive a main density unevenness component that is a density unevenness component resulting from the ink jet head, a first density unevenness component derivation unit that calculates a difference between the reading result of the first chart and the main density unevenness component, to derive a first density unevenness component that is a density unevenness component resulting from the first support, and a second density unevenness component derivation unit that calculates a difference between the reading result of the second chart and the main density unevenness component, to derive a second density unevenness component that is a density unevenness component resulting from the second support, in which the first density unevenness correction value derivation unit derives the first density unevenness correction value on the basis of the main density unevenness component and the first density unevenness component, in which the second density unevenness correction value derivation unit derives the second density unevenness correction value on the basis of the main density unevenness component and the second density unevenness component, and in which the third density unevenness correction value derivation unit derives the third density unevenness correction value on the basis of the main density unevenness component. 
     According to this aspect, the test chart has a configuration including the first chart and the second chart. The first chart is a chart to be drawn in the first region, and is constituted by a chart including a plurality of grayscales. The second chart is a chart to be drawn in the second region, and is constituted by a chart including a plurality of grayscales. The correction value of the density unevenness of each region is obtained as follows on the basis of the reading result of the test chart including the first chart and the second chart. First, the main density unevenness component is obtained by calculating the average of the reading result of the first chart and the reading result of the second chart. The main density unevenness component is obtained by the main density unevenness component derivation unit. Next, the first density unevenness component is obtained by calculating the difference between the reading result of the first chart and the main density unevenness component. The first density unevenness component is obtained by the first density unevenness component derivation unit. Similarly, the second density unevenness component is obtained by calculating the difference between the reading result of the second chart and the main density unevenness component. The second density unevenness component is obtained by the second density unevenness component derivation unit. On the basis of the main density unevenness component, the first density unevenness component, and the second density unevenness component that are obtained in this way, the correction value of the density unevenness is obtained for each region. That is, the first density unevenness correction value derivation unit obtains the first density unevenness correction value on the basis of the main density unevenness component and the first density unevenness component. The second density unevenness correction value derivation unit obtains the second density unevenness correction value on the basis of the main density unevenness component and the second density unevenness component. The third density unevenness correction value derivation unit obtains the third density unevenness correction value on the basis of the main density unevenness component. 
     (11) The ink jet recording device according to the above (10), in which the test chart further includes a third chart that is a chart including a plurality of grayscales and is drawn in the third region, and in which the main density unevenness component derivation unit calculates an average of the reading result of the first chart, the reading result of the second chart, and the reading result of the third chart, to derive the main density unevenness component. 
     According to this aspect, the third chart is further included in the test chart. The third chart is a chart to be drawn in the third region, and is constituted by a chart including a plurality of grayscales. The main density unevenness component derivation unit obtains the main density unevenness component by calculating the average of the reading result of the first chart, the reading result of the second chart, and the reading result of the third chart. 
     (12) The ink jet recording device according to the above (8), further comprising: a density unevenness component derivation unit that derives a main density unevenness component, which is a density unevenness component originating from the ink jet head, from the reading result of the test chart, a first density unevenness component that is a density unevenness component resulting from the first support, and a second density unevenness component that is a density unevenness component resulting from the second support, in which the first density unevenness correction value derivation unit derives the first density unevenness correction value on the basis of the main density unevenness component and the first density unevenness component, in which the second density unevenness correction value derivation unit derives the second density unevenness correction value on the basis of the main density unevenness component and the second density unevenness component, and in which the third density unevenness correction value derivation unit derives the third density unevenness correction value on the basis of the main density unevenness component. 
     In this aspect, the main density unevenness component, the first density unevenness component, and the second density unevenness component are obtained from the reading result of the test chart by the density unevenness component derivation unit. The first density unevenness correction value derivation unit obtains the first density unevenness correction value on the basis of the main density unevenness component and the first density unevenness component that are obtained. The second density unevenness correction value derivation unit obtains the second density unevenness correction value on the basis of the main density unevenness component and the second density unevenness component that are obtained. The third density unevenness correction value derivation unit obtains the third density unevenness correction value on the basis of the obtained main density unevenness component. 
     (13) The ink jet recording device according to the above (12), in which the density unevenness component derivation unit includes a main density unevenness component derivation unit that derives the main density unevenness component from the reading result of the test chart, a first density unevenness component derivation unit that calculates a difference between the reading result of the test chart and the main density unevenness component, to derive the first density unevenness component, and a second density unevenness component derivation unit that calculates a difference between the reading result of the test chart and the main density unevenness component, to derive the second density unevenness component. 
     In this aspect, the main density unevenness component is obtained from the reading result of the test chart by the main density unevenness component derivation unit. Then, the first density unevenness component is obtained from the difference between the obtained main density unevenness component and the reading result of the test chart by the first density unevenness component derivation unit. Additionally, the second density unevenness component is obtained from the difference between the obtained main density unevenness component and the reading result of the test chart by the second density unevenness component derivation unit. 
     (14) the ink jet recording device according to the above (13), in which the main density unevenness component derivation unit Fourier-transforms the reading result of the test chart to decompose the transformed reading result into a plurality of frequency components, removes a fundamental frequency and a frequency component of an integral multiple of the fundamental frequency from the reading result of the test chart after the Fourier transform, in a case where a frequency matching arrangement intervals of the first supporting pieces and the second supporting pieces is defined as the fundamental frequency, and inverse-Fourier-transforms the reading result of the test chart after the removal, to derive the main density unevenness component. 
     In this aspect, the main density unevenness component is obtained as follows. First, the reading result of the test chart is Fourier-transformed and is decomposed into the plurality of frequency components. Next, the fundamental frequency and the frequency component of the integral multiple of the fundamental frequency are removed from the reading result of the test chart after the Fourier transform. Next, the reading result of the test chart after the removal is inverse-Fourier-transformed. Accordingly, the main density unevenness component can be extracted from the reading result of the test chart. 
     (15) The ink jet recording device according to any one of the above (8) to (14), in which the transporting means is a drum including the medium supporting part on an outer peripheral part thereof, and transports the medium by the rotation of the drum. 
     According to this aspect, the transporting means is constituted by the drum. The drum includes the medium supporting part at the outer peripheral part thereof, and rotates to transport the medium. 
     (16) The ink jet recording device according to any one of the above (8) to (15), in which the transporting means transports the medium with the medium being brought in close contact with the medium supporting part with a negative pressure. 
     According to this aspect, the transporting means transports the medium with the medium being brought into close contact with the medium supporting part with a negative pressure. 
     (17) The ink jet recording device according to any one of the above (8) to (16), further comprising means for heating or cooling the transporting means. 
     According to this aspect, the means for heating or cooling the transporting means is provided. Accordingly, the medium can be heated or cooled if necessary. 
     According to the invention, in the ink jet recording device in which the medium supporting part is supported by the supports having the comb teeth structure, the density unevenness can be corrected appropriately, and a high-quality image can be drawn. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall configuration view illustrating an embodiment of an ink jet recording device related to the invention. 
         FIG. 2  is a schematic configuration diagram of a drawing unit. 
         FIG. 3  is a plan view of a nozzle surface of an ink jet head. 
         FIG. 4  is a perspective view illustrating a schematic configuration of a drawing drum. 
         FIG. 5  is a cross-sectional view illustrating a schematic configuration of the drawing drum. 
         FIG. 6  is a plan developed view of a paper supporting part. 
         FIG. 7  is a block diagram illustrating a system configuration of a control system of the ink jet recording device. 
         FIG. 8  is a block diagram of mainly functions concerning drawing extracted among various functions realized by a computer. 
         FIG. 9  is a block diagram illustrating a schematic configuration of a drawing control unit. 
         FIG. 10  is a plan view illustrating an example of a test chart used for general density unevenness correction. 
         FIG. 11  is a conceptual diagram of derivation of a correction value of density unevenness. 
         FIG. 12  is a plan developed view illustrating a supported state of paper by the paper supporting part. 
         FIG. 13  is a view illustrating an example output of a test chart for the density unevenness correction in a case where the density unevenness correction is performed by a general method. 
         FIG. 14  is an explanatory view in a case where the density unevenness is corrected by the general method. 
         FIG. 15  is a plan view illustrating an example of a test chart to be used for the density unevenness correction. 
         FIG. 16  is a block diagram illustrating the configuration of a density unevenness correction value derivation unit. 
         FIG. 17  is a flowchart illustrating a procedure of a series of processing from the input of an image to the output thereof. 
         FIG. 18  is a flowchart illustrating a processing sequence of density unevenness correction value derivation processing. 
         FIG. 19  is a flowchart illustrating a processing sequence of the density unevenness correction. 
         FIGS. 20A to 20C  are enlarged views of some of a reading result of a certain grayscale of a chart. 
         FIG. 21  is a block diagram illustrating the configuration of a main density unevenness component derivation unit. 
         FIGS. 22A to 22C  are views illustrating examples of calculation results of a main density unevenness component, a first density unevenness component, and a second density unevenness component in a certain grayscale. 
         FIG. 23  is a block diagram illustrating the configuration of a first density unevenness component derivation unit. 
         FIG. 24  is a block diagram illustrating the configuration of a second density unevenness component derivation unit. 
         FIG. 25  is a block diagram illustrating the configuration of the density unevenness correction value derivation unit. 
         FIG. 26  is a view illustrating an example of a test chart constituted by a first chart and a second chart. 
         FIG. 27  is a plan view illustrating an example of a test chart to be used for the density unevenness correction. 
         FIG. 28  is a block diagram illustrating the configuration of a density unevenness component derivation unit. 
         FIGS. 29A to 29D  are views illustrating a processing process of a reading result of a test chart. 
         FIGS. 30A to 30F  are views illustrating a method of complementing data. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. 
     &lt;&lt;Device Configuration of Ink Jet Recording Device&gt;&gt; 
       FIG. 1  is an overall configuration view illustrating an embodiment of an ink jet recording device related to the invention. 
     An ink jet recording device  1  illustrated in  FIG. 1  is a sheet type color ink jet recording device that records a desired image on paper, which is a sheet of paper, with a single pass by using ink of four colors of cyan (C), magenta (M), yellow (Y), and black (K). Particularly, the ink jet recording device  1  of the present embodiment is an ink jet recording device that records an image on general-purpose printing paper by using aqueous ink. 
     Here, the single pass means a method of completing single recording of an image on paper, which is being transported, with an ink jet head being fixed at a fixed position. The single pass is also referred to as one pass. 
     Additionally, the general-purpose printing paper means not paper only for so-called ink jet, but paper formed mainly of cellulose, such as coated paper, which is generally used for an offset printer or the like. The general-purpose printing paper means, for example, art paper, coated paper, lightweight coated paper, cast paper, fine coated paper, or the like. 
     Additionally, the aqueous ink means water and ink in which the color materials, such as a dye and a pigment, are dissolved and dispersed in a solvent that is solvable in water. 
     As illustrated in  FIG. 1 , the ink jet recording device  1  is configured to mainly include a paper feed unit  10  that feeds paper P, a processing liquid coating unit  20  that coats a processing liquid on the paper P fed from the paper feed unit  10 , a processing liquid drying unit  30  that performs drying processing of the paper P on which the processing liquid is coated, a drawing unit  40  that drops ink droplets in respective colors of cyan, magenta, yellow, and black on the paper P subjected to the drying processing to draw a color image, an ink drying unit  50  that performs drying processing of the paper P on which the ink droplets are dropped, and an accumulation unit  60  that accumulates the paper P subjected to the drying processing. 
     &lt;Paper Feed Unit&gt; 
     The paper feed unit  10  feeds the paper P that is a medium. The paper P is a sheet of paper. As illustrated in  FIG. 1 , the paper feed unit  10  is configured to mainly include a paper feeder  12 , a feeder board  14 , and a paper feed drum  16 . 
     The paper feeder  12  takes out the paper P set on a tray in a bundle state sheet by sheet sequentially from the top, to supply the taken-out paper to the feeder board  14 . 
     The paper feeder  12  is provided with a blower (not illustrated) in order to realize stable paper feed. The blower blows air against a paper bundle, and separates the paper P. The volume of the air that is blown off from the blower is adjustable, and is adjusted if necessary. 
     The feeder board  14  receives the paper P supplied from the paper feeder  12 , and feeds the received paper to the paper feed drum  16 . 
     The paper feed drum  16  receives the paper P from the feeder board  14 , and transports the received paper to the processing liquid coating unit  20 . The paper feed drum  16  winds the paper P around a peripheral surface thereof and transports the paper by gripping and rotating a leading end of the paper P with a gripper provided on the peripheral surface. 
     The paper feed unit  10  is configured as described above. The paper P is fed sheet by sheet from the paper feeder  12  to the feeder board  14 , and is fed to the paper feed drum  16  by the feeder board  14 . Then, the paper is transported to the processing liquid coating unit  20  by the paper feed drum  16 . 
     &lt;Processing Liquid Coating Unit&gt; 
     The processing liquid coating unit  20  coats a processing liquid on the paper P. This processing liquid consists of liquids including the function of aggregating, insolubilizing, or viscosity-improving the color material component in ink. By coating such a processing liquid on the paper P, a high-definition image can be drawn even in a case where an image is recorded on general-purpose printing paper using aqueous ink. 
     The processing liquid coating unit  20  is configured to mainly include a processing liquid coating drum  22  that transports the paper P, and a processing liquid coating device  24  that coats a processing liquid on a recording surface of the paper P transported by the processing liquid coating drum  22 . 
     The processing liquid coating drum  22  receives the paper P from the paper feed drum  16 , and transports the received paper to the processing liquid drying unit  30 . The processing liquid coating drum  22  winds the paper P around a peripheral surface thereof and transports the paper by gripping and rotating the leading end of the paper P with a gripper provided on the peripheral surface. 
     The processing liquid coating device  24  coats the processing liquid on the paper P transported by the processing liquid coating drum  22 . In the present embodiment, the processing liquid is coated by a roller. That is, a roller having the processing liquid applied to a peripheral surface thereof is pressed against the paper P transported by the processing liquid coating drum  22 , to coat the processing liquid. A method of coating the processing liquid is not limited to this, and a method of performing coating using an ink jet head, a method of performing coating using a spray, or the like can be used. 
     The processing liquid coating unit  20  is configured as described above. The paper P is coated with the processing liquid by the processing liquid coating device  24  in the process of being transported by the processing liquid coating drum  22 . 
     &lt;Processing Liquid Drying Unit&gt; 
     The processing liquid drying unit  30  performs drying processing of the paper P on which the processing liquid is coated. The processing liquid drying unit  30  is configured to mainly include a processing liquid drying drum  32  that transports the paper P, and a processing liquid drying device  34  that blows warm air against the paper P transported by the processing liquid drying drum  32  to dry the paper P. 
     The processing liquid drying drum  32  receives the paper P from the processing liquid coating drum  22  of the processing liquid coating unit  20 , and transports the received paper to the drawing unit  40 . The processing liquid drying drum  32  is constituted by a frame body assembled in a cylindrical shape, and winds the paper P around a peripheral surface thereof and transports the paper by gripping and rotating the leading end of the paper P with a gripper provided on the peripheral surface. 
     The processing liquid drying device  34  is installed inside the processing liquid drying drum  32 , and blows warm air toward the paper P transported by the processing liquid drying drum  32 . 
     The processing liquid drying unit  30  is configured as described above. The paper P is blown with warm air blown from the processing liquid drying device  34  and is subjected to the drying processing, in the process of being transported by the processing liquid drying drum  32 . 
     &lt;Drawing Unit&gt; 
     The drawing unit  40  records a color image on the recording surface of the paper P by using ink of four colors of cyan (C), magenta (M), yellow (Y), and black (K). 
       FIG. 2  is a schematic configuration diagram of the drawing unit. As illustrated in  FIG. 2 , the drawing unit  40  is configured to mainly include a drawing drum  100  that transports the paper P along a given transporting path, a paper presser roller  42  that presses the paper P transported by the drawing drum  100  against the drawing drum  100 , a drawing unit  44  that drops ink droplets in respective colors of cyan, magenta, yellow, and black on the paper P transported by the drawing drum  100  to draw a color image, and an image reader  48  that reads the image drawn on the paper P. 
     The drawing drum  100  is an example of transporting means. The drawing drum  100  includes a paper supporting part on an outer peripheral part thereof, and transports the paper P along the given transporting path by supporting and rotating the paper P with the paper supporting part. The paper supporting part is configured such that a first support having a plurality of first supporting pieces arranged in the shape of comb teeth thereon and a second support having a plurality of second supporting pieces arranged in the shape of comb teeth thereon are engaged with each other and are extendable and retractable. The details of the drawing drum  100  will be described below. 
     The paper presser roller  42  is disposed on a transporting path for the paper P by the drawing drum  100 . The paper presser roller  42  presses the paper P transported by the drawing drum  100  against the drawing drum  100 , and is brought into close contact with a peripheral surface of the drawing drum  100 . 
     The drawing unit  44  is disposed on the transporting path for the paper P by the drawing drum  100 . The drawing unit  44  is configured to include an ink jet head  46 C that discharges ink droplets in cyan, an ink jet head  46 M that discharges ink droplets in magenta, an ink jet head  46 Y that discharges ink droplets in yellow, and an ink jet head  46 K that discharges ink droplets in black. The respective ink jet heads  46 C,  46 M,  46 Y, and  46 K are loaded on and integrated on a carriage (not illustrated) to constitute the drawing unit  44 . 
     The respective ink jet heads  46 C,  46 M,  46 Y, and  46 K consist of line-type ink jet heads, and draw an image with a single pass on the paper P transported by the drawing drum  100 . 
     Each of the ink jet heads  46 C,  46 M,  46 Y, and  46 K includes a nozzle surface at a tip thereof; and discharges ink droplets toward the paper P transported by the drawing drum  100  from nozzles disposed in this nozzle surface. 
       FIG. 3  is a plan view of the nozzle surface of each ink jet head. As illustrated in this drawing, nozzles Nz are disposed at a constant pitch on a nozzle surface NF of each of the ink jet heads  46 C,  46 M,  46 Y, and  46 K. The nozzles Nz are arranged in an X direction if a transporting direction of the paper P is a Y direction and if a direction orthogonal to the Y direction is the X direction. 
     The respective ink jet heads  46 C,  46 M,  46 Y, and  46 K are disposed at regular intervals in the transporting direction of the paper P by being loaded on the carriage. The carriage is provided with a forward-and-backward movement mechanism that individually moves each of the ink jet heads  46 C,  46 M,  46 Y, and  46 K forward and backward toward the drawing drum  100 . The forward-and-backward movement mechanism is an example of forward-and-backward movement means. By using this forward-and-backward movement mechanism, the distance from the nozzle surface of each of the ink jet heads  46 C,  46 M,  46 Y, and  46 K to the peripheral surface of the drawing drum  100  can be adjusted. 
     The image reader  48  is an example of image reading means, and reads an image for each line from the paper P at a third position set on the transporting path for the paper P. As illustrated in  FIG. 2 , the image reader  48  is configured to include a line sensor  48 A, an imaging lens  48 B, and an illumination unit  48 C. The line sensor  48 A reads an image drawn on the paper P for each line. The line sensor  48 A is constituted by, for example, one-dimensional charged coupled device (CCD) image sensor, and one-dimensional complementary metal oxide semiconductor (CMOS) image sensor. The imaging lens  48 B reduces an optical image on a reading surface of the paper P to form the reduced optical image on a light-receiving surface of the line sensor  48 A. The illumination unit  48 C irradiates a region read by the line sensor  48 A with illumination light. 
     The drawing unit  40  is configured as described above. In the process in which the paper P is transported by the drawing drum  100 , ink droplets in respective colors of C, M, Y, and K are dropped on the recording surface from the respective ink jet heads  46 C,  46 M,  46 Y, and  46 K that constitute the drawing unit  44 , and a color image is drawn on the recording surface. 
     &lt;Ink Drying Unit&gt; 
     The ink drying unit  50  performs the drying processing of the paper P after the recording. As illustrated in  FIG. 1 , the ink drying unit  50  is configured to mainly include a chain gripper  52  that transports the paper P, a paper guide  54  that guides traveling of the paper P transported by the chain gripper  52 , and a heating and drying device  56  that heats and dries the recording surface of the paper P transported by the chain gripper  52 . 
     The chain gripper  52  receives the paper P from the drawing drum  100 , and transports the received paper to the accumulation unit  60 . The chain gripper  52  includes an endless chain  52 A that travels along a given traveling path, and grips the leading end of the paper P with a gripper  52 B provided in the chain  52 A to transport the paper P. When being transported by the chain gripper  52 , the paper P passes through a heating region and a non-heating region, which are set in the ink drying unit  50 , and is transported to the accumulation unit  60 . In addition, the heating region is set as a region where the paper P transported from the drawing unit  40  is horizontally transported first, and a non-heating region is set as a region where the paper P is transported in an inclined manner. 
     The paper guide  54  guides the transportation of the paper P in the heating region and the non-heating region. The paper guide  54  includes a first guide board  54 A that guides the transportation of the paper P in the heating region, and a second guide board  54 B that guides the transportation of the paper P in the non-heating region. The first guide board  54 A and the second guide board  54 B have guide surfaces, respectively, and make the paper slide on the guide surfaces to guide the transportation of the paper P. In this case, the first guide board  54 A and the second guide board  54 B suction the paper P. Accordingly, a tension can be applied to the paper P transported. A negative pressure is used for the suction. The first guide board  54 A and the second guide board  54 B include a number of suction holes in the guide surfaces, and attract the paper P from the suction holes to suction the paper P thereon. 
     The heating and drying device  56  is installed in the heating region, and heats the paper P transported through the heating region, to dry the ink applied to the paper P. The heating and drying device  56  is configured to include a plurality of infrared lamps  56 A as heat sources, and is disposed inside the chain gripper  52 . The infrared lamps  56 A are disposed at regular intervals along the transporting path for the paper P in the heating region. 
     The ink drying unit  50  is configured as described above. The paper P is heated by the heating and drying device  56  and subjected to the drying processing, in the process of being transported by the chain gripper  52 . 
     &lt;Accumulation Unit&gt; 
     The accumulation unit  60  accumulates the paper P. As illustrated in  FIG. 1 , the accumulation unit  60  includes an accumulating device  62 . The accumulating device  62  receives the paper P from the chain gripper  52 , and accumulates the received papery on a tray. 
     &lt;&lt;Flow of Entire Processing by Ink Jet Recording Device&gt;&gt; 
     In the ink jet recording device  1  of the present embodiment, the paper P is processed in order of (a) paper feed, (b) coating of processing liquid, (c) drying of processing liquid, (d) recording of image, (e) drying of ink, and (f) accumulation. 
     First, the paper P is fed from the paper feed unit  10 . The paper P fed from the paper feed unit  10  is transported to the processing liquid coating unit  20 . Then, the processing liquid is coated on the recording surface in the process of being transported by the processing liquid coating drum  22  of the processing liquid coating unit  20 . 
     Next, the paper P on which the processing liquid is coated is transported to the processing liquid drying unit  30 . Then, the paper is subjected to the drying processing in the process of being transported by the processing liquid drying drum  32  of the processing liquid drying unit  30 . 
     Next, the paper P subjected to the drying processing is transported to the drawing unit  40 . Then, in the process of being transported by the drawing drum  100  of the drawing unit  40 , ink droplets in respective colors of cyan, magenta, yellow, and black are dropped and a color image is recorded. 
     Next, the paper P on which the image is recorded is transported to the ink drying unit  50 . Then, the paper is subjected to the drying processing in the process of being transported by the chain gripper  52  of the ink drying unit  50 . 
     The paper P subjected to the drying processing is transported as it is to the accumulation unit  60  by the chain gripper  52 , and is recovered by the accumulating device  62 . 
     &lt;Drawing Drum&gt; 
     &lt;Configuration of Drawing Drum&gt; 
       FIG. 4  is a perspective view illustrating a schematic configuration of the drawing drum. Additionally,  FIG. 5  is a cross-sectional view illustrating a schematic configuration of the drawing drum. 
     The drawing drum  100  transports the paper P along the given transporting path by supporting and rotating the paper P with the paper supporting part  110  provided in the outer peripheral part thereof. The drawing drum  100  of the present embodiment includes paper supporting parts  110  in two places of the outer peripheral part. 
       FIG. 6  is a plan developed view of a paper supporting part. 
     The paper supporting part  110  is constituted by a first support  112  and a second support  114  that have a comb teeth structure, and is configured such that the first support  112  and the second support  114  are engaged with each other and are thereby extendable and retractable. 
     The first support  112  has a structure in which a plurality of first supporting pieces  116  are arranged in the shape of comb teeth. Each first supporting piece  116  has a plate shape, and has a circular-arc first supporting surface  116 A. The first supporting surface  116 A functions as a surface that supports the paper P. The first supporting pieces  116  are attached to a first base  120  provided in a rotating shaft  118  of the drawing drum  100  at regular intervals, and are arranged in the shape of comb teeth. The first base  120  is fixed and attached to the rotating shaft  118  of the drawing drum  100 . Hence, the first support  112  is fixed and attached to the rotating shaft  118  of the drawing drum  100 . 
     The second support  114  has a structure in which a plurality of second supporting pieces  122  are arranged in the shape of comb teeth. Each second supporting piece  122  has a plate shape, and has a circular-arc second supporting surface  122 A. The second supporting surface  122 A functions as a surface that supports the paper P. The second supporting pieces  122  are attached to a second base  124  provided in the rotating shaft  118  of the drawing drum  100  at regular intervals, and are arranged in the shape of comb teeth. The second base  124  is attached to be movable with respect to the rotating shaft  118  of the drawing drum  100 . Hence, the second support  114  is supported to be movable with the rotating shaft  118  of the drawing drum  100  as a center. 
     The paper supporting part  110  is increased or reduced in its total length by moving the second support  114 . The direction of the increase or reduction is a direction in the transporting direction (Y direction) of the paper P. The drawing drum  100  includes a second support driving mechanism (not illustrated) for moving the second support  114 . The paper supporting part  110  is variable in its total length by moving the second support  114  with the second support driving mechanism to change the position of the second support  114 . 
     The paper supporting part  110  includes a gripper  126  that grips the leading end of the paper P, and a suctioning and holding part  128  that suctions and holds a trailing end of the paper P. 
     The gripper  126  is provided in the first support  112 . The gripper  126  has a plurality of grip claws  126 A, and grips the leading end of the paper P with the respective grip claws  126 A. Each grip claw  126 A is provided in each first supporting piece  116 . 
     The suctioning and holding part  128  is provided in the second support  114 . The suctioning and holding part  128  suctions and holds the trailing end of the paper P with a negative pressure. A suction hole  128 A is provided at rear end part of the second supporting surface  122 A of each second supporting piece  122 . The suctioning and holding part  128  attracts the paper P from the suction holes  128 A, to suction and hold the trailing end of the paper P. 
     &lt;Working of Drawing Drum&gt; 
     The drawing drum  100  configured as described above transports the paper P along the given transporting path by supporting and rotating the paper P with the paper supporting part  110 . Rotational driving of the drawing drum  100  is performed by a motor (not illustrated). 
     The paper supporting part  110  grips the leading end of the paper P with the gripper  126  provided in the first supporting pieces  116 , and suctions the trailing end of the paper P with the suctioning and holding part  128  provided in the second support  114  to support the paper P. The paper P supported by the paper supporting part  110  has a back surface brought into close contact with the first supporting surface  116 A and the second supporting surface  122 A. 
     The paper supporting part  110  is increased or reduced in its total length by moving the second support  114 . The total length of the paper supporting part  110  is adjusted according to the size of the paper P to be supported. 
     &lt;&lt;Configuration of Control System&gt;&gt; 
       FIG. 7  is a block diagram illustrating a system configuration of a control system of the ink jet recording device. 
     As illustrated in this drawing, the overall operation of the ink jet recording device  1  is controlled in an integrated manner by a computer  200 . That is, all respective processings, such as the feed of the paper by the paper feed unit  10 , the coating of the processing liquid by the processing liquid coating unit  20 , the drying of the processing liquid by the processing liquid drying unit  30 , the drawing performed by the drawing unit  40 , the drying of the ink by the ink drying unit  50 , and the accumulation performed by the accumulation unit  60 , are controlled by the computer  200 . 
     A communication unit  202  for communicating with an external instrument, an operating unit  204  for operating the ink jet recording device  1 , a display unit  206  for displaying various kinds of formation, and a storage unit  208  for storing various kinds of information are connected to the computer  200 . Image data of an image recorded on the paper P are input to the computer  200  via the communication unit  202 . Additionally, various programs that the computer  200  executes, and various data required for control are stored in the storage unit  208 . 
       FIG. 8  is a block diagram of mainly functions concerning drawing extracted among various functions realized by the computer. 
     As illustrated in  FIG. 8 , the computer  200  functions as a drawing control unit  210 , a test chart output control unit  230 , a test chart reading control unit  240 , and a density unevenness correction value derivation unit  250 , by executing predetermined programs. 
     &lt;Drawing Control Unit&gt; 
       FIG. 9  is a block diagram illustrating a schematic configuration of the drawing control unit. 
     The drawing control unit  210  is configured to include a density data generation unit  212  that generates density data from the image data, a density unevenness correction unit  214  that performs density unevenness correction on the density data, a dot arrangement data generation unit  216  that generates dot arrangement data from density data, a driving signal generation unit  218  that generates driving signals for the respective ink jet heads  46 C,  46 M,  46 Y, and  46 K from the dot arrangement data, and a head driving control unit  220  that controls driving of the respective ink jet heads  46 C,  46 M,  46 Y, and  46 K. 
     The density data generation unit  212  generates initial density data for each ink color from the image data of the image recorded on the paper P. The density data generation unit  212  fetches the image data of the image recorded on the paper P, and performs predetermined density conversion processing on the fetched image data, to generate the initial density data for each ink color. 
     The density unevenness correction unit  214  performs density unevenness correction on the density data generated by the density data generation unit  212 . The density unevenness correction is the processing performed in order to correct the density unevenness caused when the image is drawn on the paper P, and is performed on the density data for each ink color. The density unevenness correction unit  214  fetches the density data generated by the density data generation unit  212 , and performs predetermined density unevenness correction processing on the fetched density data, to correct the density unevenness of the density data. The details of density unevenness correction will be described below. 
     The dot arrangement data generation unit  216  generates the dot arrangement data from the density data. The dot arrangement data generation unit  216  fetches the density data after the density unevenness correction, and performs predetermined half-toning processing on the fetched density data, to generate the dot arrangement data. 
     The driving signal generation unit  218  generates the driving signals for the respective ink jet heads  46 C,  46 M,  46 Y, and  46 K on the basis of the dot arrangement data generated by the dot arrangement data generation unit  216 . 
     The head driving control unit  220  controls the driving of the respective ink jet heads  46 C,  46 M,  46 Y, and  46 K on the basis of the driving signals generated by the driving signal generation unit  218 . 
     &lt;Test Chart Output Control Unit&gt; 
     The test chart output control unit  230  controls the output of a test chart. The test chart is a test chart for obtaining a correction value of the density unevenness. The details of the test chart will be described below. 
     The test chart output control unit  230  makes the ink jet heads  46 C,  46 M,  46 Y, and  46 K draw the test chart according to output commands for the test chart. Data of the test chart to be output are stored in the storage unit  208 . The test chart output control unit  230  reads the data of the test chart from the storage unit  208 , to make the ink jet heads  46 C,  46 M,  46 Y, and  46 K draw the test chart. 
     &lt;Test Chart Reading Control Unit&gt; 
     The test chart reading control unit  240  controls the reading of the test chart. That is, the image reader  48  is made to read an image of the test chart drawn on the paper P according to the output commands for the test chart. The read image data of the test chart are stored in the storage unit  208 . 
     &lt;Density Unevenness Correction Value Derivation Unit&gt; 
     The density unevenness correction value derivation unit  250  derives the correction value of the density unevenness required for the density unevenness from a reading result of the test chart. The details of a derivation method will be described below. Information on the derived density unevenness correction value is stored in the storage unit  208 . 
     The density unevenness correction unit  214  corrects the density unevenness of the density data using the information on the density unevenness correction value derived by the density unevenness correction value derivation unit  250 . 
     &lt;&lt;Density Unevenness Correction Method&gt;&gt; 
     &lt;Outline of Density Unevenness Correction&gt; 
     First, a general density unevenness correction method will be outlined. Generally, the correction of the density unevenness is carried out in a following sequence. 
     First, a test chart TC including a plurality of grayscales is output to the paper P.  FIG. 10  is a plan view illustrating an example of a test chart used for general density unevenness correction. As illustrated in this drawing, a chart in which density varies at multiple levels is used as the test chart TC used for the general density unevenness correction. In addition, in this drawing, the symbol Y represents the transporting direction of the paper P. Additionally, the symbol X represents an arrangement direction of the nozzles. 
     One test chart TC is output for each color. That is, the test chart is output for each of the ink jet heads  46 C,  46 M, and  46 Y and  46 K. 
     Additionally, the test chart TC is output by ink droplets being discharged from all the nozzles to be used at the time of image drawing. In the case of the line-type ink jet heads, the nozzles to be used vary according to the size of paper. For example, in a case where drawing is performed on a small size of paper, only nozzles in a partial region are used. Hence, the test chart TC is output by ink droplets being discharged from nozzles in a region corresponding to the size of the paper to be used. 
     Next, the image of the test chart output to the paper P is read by the image reader. 
     Next, the read image data of the test chart are analyzed, and a correction value of density unevenness is obtained for each grayscale with respect to all the nozzles to be used such that the density data of each grayscale become uniform in the arrangement direction of the nozzles. 
       FIG. 11  is a conceptual diagram of the derivation of the correction value of the density unevenness. 
       FIG. 11(A)  is a view illustrating a reading result of a certain grayscale. In this drawing, a horizontal axis represents positions in the arrangement direction of the nozzles, and a vertical axis represents values read by the image reader. The reading values are synonymous with density values. 
       FIG. 11(B)  is a view illustrating an example of a correction value of the density unevenness obtained from the reading result of  FIG. 11(A) . In this drawing, a horizontal axis represents positions in the arrangement direction of the nozzles, and a vertical axis vertical axis represents the correction value of the density unevenness. As illustrated in this drawing, the correction value of the density unevenness is obtained such that the density value becomes uniform in the arrangement direction of the nozzles. 
     The correction value of the density unevenness is obtained for each grayscale. In a case where a reading result of a grayscale intended to obtain is not present, complementation is performed using a reading result of another grayscale. For example, in  FIG. 10 , a correction value of the density unevenness of a grayscale between a seventh level and an eighth level is obtained using a reading result at the seventh level, the eighth level, or the like that is a reading result. 
     The density data are corrected using information on the correction value of the density unevenness obtained as described above. That is, the density data are corrected by adding the correction value to the density data. Accordingly, an image with a uniform density can be output in the arrangement direction of the nozzles in each grayscale. 
       FIG. 11(C)  is a view illustrating a reading result of an output image after the correction of the density unevenness. As illustrated in this drawing, output can be performed with a substantially uniform density in the arrangement direction of the nozzles by performing the density unevenness correction. 
     &lt;Density Unevenness Correction Method in Ink Jet Recording Device of Present Embodiment&gt; 
     As described above, in the ink jet recording devices  1  of the present embodiment, the paper supporting part  110  of the drawing drum  100  is configured such that the first support  112  and the second support  114  that have the comb teeth structure are engaged with each other and are extendable and retractable. If the paper P is supported by the paper supporting part  110  having such a structure, a region supported in contact with a support and a region supported without contacting a support are generated in the paper P. 
       FIG. 12  is a plan developed view illustrating a supported state of the paper by the paper supporting part. 
     As illustrated in  FIG. 12 , a region supported only by the first support  112 , a region supported only by the second support  114 , a region supported by both of the first support  112  and the second support  114  are generated in the paper P. Also, a region supported in contact with a support and a region supported without contacting a support are generated in the region supported only by the first support  112  and the region supported only by the second support  114 . 
     In this way, if the region supported in contact with a support and the region supported without contacting a support are present in the paper P, density unevenness occurs in a case where the temperature of the paper P is different from the temperature of the supports. 
     Although the density unevenness can be corrected by performing the above-described density unevenness correction, the following problems occur if the density unevenness correction method that is generally performed is applied as it is. 
     [Problems in Case where Density Unevenness Correction is Corrected by General Method] 
       FIG. 13  is a view illustrating an example output of a test chart for the density unevenness correction in a case where the density unevenness correction is performed by the general method. 
     A test chart TC has a structure in which images of a plurality of grayscales are lined up in the transporting direction (Y direction) of the paper P. An image of each grayscale is constituted by a beltlike image that extends in the arrangement direction (X direction) of the nozzles.  FIG. 13  illustrates an example of the test chart TC including six grayscales. In this case, six beltlike images of which the grayscales vary at six levels are drawn in the transporting direction of the paper P. As for the images of the respective grayscales, a first level image has the thinnest grayscale, a sixth level image has the deepest grayscale, and the grayscales vary stepwisely from the first level image toward the sixth level image. 
     Now, in a case where the paper P is supported by the paper supporting part  110 , a region where the paper P is supported by only the first support  112  is defined as a first region Z 1 , a region where the paper P is supported by only the second support  114  is defined as a second region Z 2 , and a region where the paper P is supported by the first support  112  and the second support  114  is defined as a third region Z 3 . 
     In addition, both of a region where the paper is supported in close contact with the first supporting pieces  116 , a region where the paper is supported without being in close contact with the first supporting pieces  116 , that is, a region where the paper is supported in the state of floating between the first supporting pieces  116  adjacent to each other are included in the first region Z 1 . Similarly, both of a region where the paper is supported in close contact with the second supporting pieces  122 , and a region where the paper is supported without being in close contact with the second supporting pieces  122  are also included in the second region Z 2 . The third region Z 3  is a region where the second supporting pieces  122  of the second support  114  are engaged with the first supporting pieces  116  of the first support  112 . In this third region Z 3 , a substantially whole surface of the paper P is supported in close contact with the first supporting pieces  116  or the second supporting pieces  122 . 
     In the test chart TC, the first level image and a second level image are drawn in the first region Z 1 , a third level image and a fourth level image are drawn in the third region Z 3 , and, a fifth level image and the sixth level image are drawn in the second region Z 2 . 
       FIG. 14  is an explanatory view in a case where the density unevenness is corrected by the general method. 
       FIG. 14(A)  is a view illustrating a reading result of the second level image of the test chart. In this drawing, a horizontal axis represents positions in the arrangement direction of the nozzles, and a vertical axis represents values read by the image reader. The reading values are synonymous with density values. 
     In addition, in the present example, in order to simplify description, it is supposed that there is no density unevenness originating from the ink jet heads. Additionally, it is supposed that the temperature of the paper supporting part  110  is higher than the temperature of the paper P before being supported in the paper supporting part  110 . In this case, when the paper P is supported by the paper supporting part  110 , the temperature of the region supported in contact with a support becomes high. Additionally, it is supposed that, as the temperature is lower, the density of an image to be drawn is lower. Hence, the density of the region supported in contact with a support becomes lower than the density of the region supported without contacting a support. 
     The second level image of the test chart is drawn in the first region Z 1  of the paper P. In the first region Z 1 , the region supported in contact with the first supporting pieces  116  of the first support  112 , and the region supported without contacting the first supporting pieces  116  appear alternately. As a result, as illustrated in  FIG. 14(A) , reading values of the second level image of the test chart vary periodically. 
       FIG. 14(B)  is a view illustrating an example of a correction value of the density unevenness obtained from the reading result of the second level image of the test chart. 
     The density of the region supported without contacting a support becomes higher than the density of the region supported in contact with a support. Hence, the correction value is obtained such that the density of the region supported in contact with a support becomes high. 
     Now, a case where an image solid-coated on the whole surface of the paper P in the density of the second level image of the test chart is output is considered. 
     In this case, if the correction of the density unevenness is performed using the correction value of the density unevenness obtained from the reading result of the second level image of the test chart, an excellent output result without density unevenness is obtained in the first region Z 1 . 
     However, since the appearance way of the density unevenness in the second region Z 2  and the third region Z 3  is different from that in the first region Z 1 , the density unevenness is rather promoted. 
       FIG. 14(C)  is a view illustrating a reading result in the second region. In the second region Z 2 , the appearance way of the region where the paper P is supported in contact with a support and the region where the paper is supported without contacting support becomes reverse to the first region Z 1 . As a result, if the density unevenness is corrected with the correction value of the density unevenness obtained from the reading result of the test chart drawn in the first region Z 1 , as illustrated in  FIG. 14(C) , an image in which the density unevenness is promoted is output. 
     [Density Unevenness Correction Method in Ink Jet Recording Device of Present Embodiment] 
     Next, the density unevenness correction method in the ink jet recording device  1  of the present embodiment will be described. 
     In the ink jet recording device  1  of the present embodiment, the correction value of the density unevenness is obtained for each region, and the density unevenness correction is carried out for each region. That is, the correction value of the density unevenness in the first region Z 1 , the correction value of the density unevenness in the second region Z 2 , and the correction value of the density unevenness in the third region Z 3  are obtained individually, and the density unevenness correction is performed for each region on the basis of the obtained correction value of the density unevenness for each region. 
     The correction of the density unevenness includes respective steps of (1) a test chart output step of outputting a test chart, (2) a test chart read step of reading an image of the output test chart, (3) a density unevenness correction value derivation step of deriving a correction value of density unevenness for each region from a reading result of the test chart, and (4) a density unevenness correction step of performing density unevenness correction for each region on the basis of the obtained correction value of the density unevenness for each region. 
     (1) Test Chart Output Step 
     The test chart output step is a step of outputting a test chart. 
       FIG. 15  is a plan view illustrating an example of a test chart to be used for the density unevenness correction. 
     A test chart TC includes a first chart TC 1  to be drawn in the first region Z 1 , a second chart TC 2  to be drawn in the second region Z 2 , and a third chart TC 3  to be drawn in the third region Z 3 . The configurations of the respective charts are the same. Additionally, the configurations of the respective charts are the same as the configuration of a test chart to be used for ordinary density unevenness correction, and are configurations including a plurality of grayscales. That is, the test chart TC to be used for the density unevenness correction of the present embodiment is configured such that the test chart to be used for the ordinary density unevenness correction is drawn for each region. 
     The test chart output control unit  230  makes the ink jet heads  46 C,  46 M,  46 Y, and  46 K draw the test chart TC illustrated in  FIG. 15  according to output commands for the test chart. 
     (2) Test Chart Read Step 
     The test chart read step is a step of reading an image of the output test chart TC. 
     The test chart reading control unit  240  makes the image reader  48  read the image of the test chart TC drawn on the paper P. The read image data of the test chart TC are stored in the storage unit  208 . 
     (3) Density Unevenness Correction Value Derivation Step 
     The density unevenness correction value derivation step is a step of obtaining a correction value of density unevenness for each region from a reading result of the test chart TC. Here if a correction value of density unevenness in the first region is defined as a first density unevenness correction value, a correction value of density unevenness in the second region is defined as a second density unevenness correction value, and a correction value of density unevenness in the third region is defined as a third density unevenness correction value, the first density unevenness correction value is obtained from a reading result of the first chart, the second density unevenness correction value is obtained from a reading result of the second chart, and the third density unevenness correction value is obtained from a reading result of the third chart. 
     The density unevenness correction value derivation unit  250  derives a density unevenness correction value of each region from the reading result of the test chart. 
       FIG. 16  is a block diagram illustrating the configuration of the density unevenness correction value derivation unit. 
     The density unevenness correction value derivation unit  250  includes a first density unevenness correction value derivation unit  250 A, a second density unevenness correction value derivation unit  250 B, and a third density unevenness correction value derivation unit  250 C. 
     The first density unevenness correction value derivation unit  250 A derives the first density unevenness correction value from the reading result of the first chart TC 1  within the test chart TC. 
     The second density unevenness correction value derivation unit  250 B derives the second density unevenness correction value from the reading result of the second chart TC 2  within the test chart TC. 
     The third density unevenness correction value derivation unit  250 C derives the third density unevenness correction value from the reading result of the third chart TC 3  within the test chart TC. 
     In addition, a method of deriving the correction value of the density unevenness of each region is the same as a method of deriving correction value of density unevenness that is generally performed. That is, image data of a test chart of each region is analyzed, and a correction value of density unevenness is obtained for each grayscale with respect to all the nozzles to be used such that density data of each grayscale become uniform in the arrangement direction of the nozzles. 
     Information on the obtained correction value of the density unevenness of each region is stored in the storage unit  208 . 
     (4) Density Unevenness Correction Step 
     The density unevenness correction step is a step of performing density unevenness correction for each region on the basis of the obtained correction value of the density unevenness for each region. The density unevenness correction is carried out on the density data generated by the density data generation unit  212 . 
     The density unevenness correction unit  214  carries out the density unevenness correction of the density data generated by the density data generation unit  212  for each region. 
     That is, density unevenness correction is carried out with the first density unevenness correction value regarding a portion belonging to the first region Z 1  among the images to be drawn on the paper P, density unevenness correction is carried out with the second density unevenness correction value regarding a portion belonging to the second region Z 2 , and density unevenness correction is carried out with the third density unevenness correction value regarding a portion belonging to the third region Z 3 . 
     In this case, if the density unevenness correction value is defined as C, C can be expressed as follows.
 
 C ( d,x,k )
 
     Here, d represents a density value, x represents a position in the arrangement direction of the nozzles, and k represents a region. The region k is any of the first region Z 1 , the second region Z 2 , and the third region Z 3 . The first region Z 1  is defined as k=k 1 , the second region Z 2  is defined as k=k 2 , and the third region Z 3  is defined as k=k 3 . Hence, the first density unevenness correction value that is the correction value of the density unevenness in the first region Z 1  can be expressed as C(d, x, k 1 ), and the second density unevenness correction value that is the correction value of the density unevenness in the second region Z 2  can be expressed as C(d, x, k 2 ). Additionally, the third density unevenness correction value that is the correction value of the density unevenness in the third region Z 3  can be expressed as C(d, x, k 3 ). 
     &lt;&lt;Processing from Image Input to Drawing&gt;&gt; 
       FIG. 17  is a flowchart illustrating a procedure of a series of processing from the input of an image to the output thereof 
     First, image data of an image to be drawn on the paper P is acquired (Step S 1 ). The image data are input to the computer  200  via the communication unit  202 . 
     Next, derivation processing of density unevenness correction value is carried out (Step S 2 ). That is, the processing of deriving the first density unevenness correction value, the second density unevenness correction value, and the third density unevenness correction value required for the density unevenness correction is carried out. 
       FIG. 18  is a flowchart illustrating a processing sequence of density unevenness correction value derivation processing. 
     First, data of a test chart are acquired (Step S 11 ). The data of the test chart are stored in the storage unit  208 , and are read and acquired from the storage unit  208 . The test chart TC, as illustrated in  FIG. 15 , includes the first chart TC 1 , the second chart TC 2 , and the third chart TC 3 . 
     Next, the test chart is output (Step S 12 ). That is, the test chart is drawn on the paper P. One test chart is output for each color. 
     Next, an image of the output test chart is read (Step S 13 ). The reading is performed by the image reader  48 . The read image data of the test chart are stored in the storage unit  208 . 
     Next, a correction value of density unevenness for each region is obtained from the reading result of the test chart (Step S 14 ). That is, the first density unevenness correction value is obtained from the reading result of the first chart TC 1 , the second density unevenness correction value is obtained from the reading result of the second chart TC 2 , and the third density unevenness correction value is obtained from the reading result of the third chart TC 3 . Information on the obtained first density unevenness correction value, second density unevenness correction value, and third density unevenness correction value is stored in the storage unit  208 . 
     From the above, the density unevenness correction value derivation processing is completed through the series of steps. 
     Next, density data are generated as illustrated in  FIG. 17  (Step S 3 ). That is, predetermined density conversion processing is performed on the image data of the image to be drawn on the paper P, and initial density data for each ink color are generated. Respective density values of this initial density data are expressed by d 0 ( x, y ). Here, x represents a position in the arrangement direction of the nozzles, and y represents a position in the transporting direction of the paper P. Hence, d 0 ( x, y ) shows a density value at a position (x, y) of a pixel. In addition, x is defined as x=0, 1, 2, . . . , xe−1, and xe, and y is defined as y 0, 1, 2, . . . , ye−1, and ye. 
     Next, density unevenness correction is performed on the initial density data (Step S 4 ). 
       FIG. 19  is a flowchart illustrating a processing sequence of the density unevenness correction. 
     First, as y=0, the value of a y coordinate of a processing object pixel is set to 0 (Step S 21 ). 
     Next, the value of k of the processing object pixel is obtained (Step S 22 ). The value of k can be obtained from the value of they coordinate of the processing object pixel. k=k 1  is established in a case where the processing object pixel belongs to the first region Z 1  from the value of the y coordinate, k=k 2  is established in a case where the processing object pixel belongs to the second region Z 2  and k=k 3  is established in a case where the processing object pixel belongs to the third region Z 3 . 
     Next, as x=0, the value of an x coordinate is set to 0 (Step S 23 ). 
     Next, information on a density value d 0 ( x, y ) is acquired on the basis of the information on the coordinate position (x, y) of the processing object pixel (Step S 24 ). 
     Next, information on a density unevenness correction value C(d, x, k) of a processing object pixel is acquired on the basis of the information on the coordinate position (x, y) of the processing object pixel and information k on a region (Step S 25 ). 
     Next, the density value d 0 ( x, y ) of the processing object pixel is corrected using the information on the acquired density unevenness correction value C(d, x, k) (Step S 26 ). 
     Next, a density value obtained by the correction is acquired as a density value dl (x, y) after the correction (Step S 27 ). Information on the acquired density value dl(x, y) after the correction is stored in the storage unit  208 . 
     Next, the value of the x coordinate is updated by adding 1 to the value of the x coordinate of the processing object pixel (Step S 28 ). That is, the next pixel in the x direction of the image is set as a processing object. 
     Next, it is determined whether or not the value of the newly set x coordinate is xe (Step S 29 ). That is, it is determined whether or not all processing equivalent to one line is completed. 
     Here, in a case where the value of the x coordinate is not xe, that is, in a case where the processing equivalent to one line is not completed, the processing returns to Step S 24 , and the processing from above-described Step S 24  to Step S 29  is executed again. 
     On the other hand, in a case where the value of the x coordinate is xe, that is, in a case where all processing equivalent to one line is completed, the value of the y coordinate is updated by adding 1 to the value of the y coordinate of the processing object pixel (Step S 30 ). That is, pixels on the next line are set as processing object pixels. 
     Next, it is determined whether or not the value of the newly set y coordinate is ye (Step S 31 ). That is, it is determined whether or not the processing of all the lines is all completed. 
     Here, in a case where the value of the y coordinate is not ye, that is, in a case where the processing of all the lines is not completed, the processing returns to Step S 22  and the processing from the above-described Step S 22  to Step S 30  is executed again. 
     On the other hand, in a case where the value of the y coordinate is ye, that is, in a case where the processing of all the lines is all completed, the processing of the density unevenness correction is ended. 
     If the processing of the density unevenness correction ends, next, as illustrated in  FIG. 17 , dot arrangement data are generated from the density data after the correction, (Step S 5 ). That is, the dot arrangement data are generated by performing half-toning processing the density data after the density unevenness correction. 
     Next, driving signals for the respective ink jet heads  46 C,  46 M,  46 Y, and  46 K are generated on the basis of the generated dot arrangement data (Step S 6 ). 
     Preprocessing for drawing is completed in the above series of steps. Thereafter, paper feed is started to start drawing (Step S 7 ). 
     As described above, in the ink jet recording device  1  of the present embodiment, the required density unevenness correction is performed on an input image to draw an image on the paper P. Additionally, when the density unevenness correction is performed, the density unevenness correction value is obtained for each region, and the density unevenness correction is performed for each region. Accordingly, a high-quality image can be drawn by appropriately correcting the density unevenness even in a case where the paper supporting part  110  of the drawing drum  100  is constituted by the supports having the comb teeth structure. 
     &lt;&lt;Other Methods for Obtaining Correction Value of Density Unevenness for Each Region&gt;&gt; 
     In the following, other methods for obtaining the correction value of the density unevenness for each region will be described. 
     &lt;First Method&gt; 
     A test chart to be used in this method is the same as the test chart used at the time of the density unevenness correction of the above embodiment. That is, the test chart is the test chart TC having the configuration illustrated in  FIG. 15 . The first chart TC 1  to be drawn in the first region Z 1 , the second chart TC 2  to be drawn in the second region Z 2 , and the third chart TC 3  to be drawn in the third region Z 3  are included in the test chart TC. 
     This method includes a main density unevenness component derivation step of deriving a main density unevenness component from a reading result of the test chart, a first density unevenness component derivation step of deriving a first density unevenness component, a second density unevenness component derivation step of deriving a second density unevenness component, and a density unevenness correction value derivation step of deriving a density unevenness correction value of each region on the basis of the main density unevenness component, the first density unevenness component, and the second density unevenness component. 
     Here, the main density unevenness component is a density unevenness component originating from an ink jet head among the density unevenness components that appear in the reading result of the test chart. Additionally, the first density unevenness component is a density unevenness component originating from the first support  112  among the density unevenness components that appear in the reading result of the test chart. Additionally, the second density unevenness component is a density unevenness component originating from the second support  114  among the density unevenness components that appear in the reading result of the test chart. 
       FIGS. 20A to 20C  are enlarged views of a portion of a reading result of a certain grayscale of a chart.  FIG. 20A  illustrates a reading result of the first chart TC 1 . Additionally,  FIG. 20B  illustrates a reading result of the third chart TC 3 . Additionally,  FIG. 20C  illustrates a reading result of the second chart TC 2 . 
     As illustrated in  FIG. 20A , since the first chart TC 1  is influenced by the first support  112 , the first density unevenness component is included in the reading result, in addition to the main density unevenness component. 
     As illustrated in  FIG. 20C , since the second chart TC 2  is influenced by the second support  114 , the second density unevenness component is included in the reading result, in addition to the main density unevenness component. The appearance way of the influence by the second support  114  becomes reverse to the appearance way of the influence by the first support  112 . 
     As illustrated in  FIG. 20B , since the third chart TC 3  is supported by both of the first support  112  and the second support  114 , there is no influence of the supports, and only the main density unevenness component mainly appears as the reading result. 
     [Main Density Unevenness Component Derivation Step] 
     In the main density unevenness component derivation step, the main density unevenness component is obtained by calculating an average of reading results of the respective charts. That is, an average of the first chart TC 1 , the second chart TC 2 , and the third chart TC 3  is calculated. In this case, in the respective levels of the respective charts, reading values of corresponding positions are added, and an average thereof is obtained. That is, reading values of the same positions of the same levels are added, and an average thereof is obtained. 
     The main density unevenness component is obtained by the main density unevenness component derivation unit  260 . 
       FIG. 21  is a block diagram illustrating the configuration of the main density unevenness component derivation unit. The main density unevenness component derivation unit  260  acquires information on reading results of the first chart TC 1 , the second chart TC 2 , and the third chart TC 3 , and calculates an average thereof to calculate the main density unevenness component. 
     Here, a reading result of the first chart TC 1  is defined as S 1 ( j, x ), a reading result of the second chart TC 2  is defined as S 2 ( j, x ) and a reading result of the third chart TC 3  is defined as S 3 ( j, x ). j is the number of levels of each chart. As illustrated in  FIG. 15 , in a case where each chart is constituted of six levels, values of j=j 1 , j 2 , j 6  can be taken as j. x is a position in the arrangement direction of the nozzles. 
     The main density unevenness component is defined as Sm(j, x). Sm(j, x) is expressed as follows.
 
 Sm ( j,x )=( S 1( j,x )+ S 2( j,x )+ S 3( j,x ))/3
 
       FIGS. 22A to 22C  are views illustrating examples of calculation results of the respective density unevenness components in a certain grayscale.  FIG. 22A  illustrates a calculation result of the main density unevenness component.  FIG. 22B  illustrates a calculation result of the first density unevenness component.  FIG. 22C  illustrates a calculation result of the second density unevenness component. 
     As illustrated in  FIG. 22A , the main density unevenness component Sm(j, x) that is a density unevenness component excluding the influence of the supports can be extracted by obtaining an average of the respective charts. 
     [First Density Unevenness Component Derivation Step] 
     In the first density unevenness component derivation step, the first density unevenness component is obtained by calculating a difference between the reading result of the first chart and the main density unevenness component. 
     The first density unevenness component is obtained by the first density unevenness component derivation unit  262 .  FIG. 23  is a block diagram illustrating the configuration of the first density unevenness component derivation unit. The first density unevenness component derivation unit  262  acquires information on the reading result of the first chart and the calculation result of the main density unevenness component, and calculates the difference therebetween to obtain the first density unevenness component. 
     The first density unevenness component is defined as T 1 ( j, x ). T 1 ( j, x ) is expressed as follows.
 
 T 1( j,x )= S 1( j,x )− Sm ( j,x )
 
     As illustrated in  FIG. 22B , the first density unevenness component T 1 ( j, x ) that is a density unevenness component resulting from the first support  112  can be extracted by calculating the difference between the reading result S 1 ( j, x ) of the first chart and the main density unevenness component Sm(j, x). 
     [Second Density Unevenness Component Derivation Step] 
     In the second density unevenness component derivation step, the second density unevenness component is obtained by calculating a difference between the reading result of the second chart and the main density unevenness component. 
     The second density unevenness component is obtained by the second density unevenness component derivation unit  264 .  FIG. 24  is a block diagram illustrating the configuration of the second density unevenness component derivation unit. The second density unevenness component derivation unit  264  acquires information on the reading result of the second chart and the calculation result of the main density unevenness component, and calculates the difference therebetween to obtain the second density unevenness component. 
     The second density unevenness component is defined as T 2 ( j, x ). T 2 ( j, x ) is expressed as follows.
 
 T 2( j,x )= S 2( j,x )− Sm ( j,x )
 
     As illustrated in  FIG. 22C , the second density unevenness component T 2 ( j, x ) that is a density unevenness component resulting from the second support  114  can be extracted by calculating the difference between the reading result S 2 ( j, x ) of the second chart and the main density unevenness component Sm(j, x). 
     [Density Unevenness Correction Value Derivation Step] 
     The density unevenness correction value derivation step includes a first density unevenness correction value derivation step of deriving the first density unevenness correction value that is a density unevenness correction value of the first region Z 1  on the basis of the main density unevenness component and the first density unevenness component, a second density unevenness correction value derivation step of deriving the second density unevenness correction value that is a density unevenness correction value of the second region Z 2  on the basis of the main density unevenness component and the second density unevenness component, and a third density unevenness correction value derivation step of deriving the third density unevenness correction value that is a density unevenness correction value of the third region Z 3  on the basis of the main density unevenness component. A density unevenness correction value of each region is derived by the density unevenness correction value derivation unit  250 . 
       FIG. 25  is a block diagram illustrating the configuration of the density unevenness correction value derivation unit. 
     The density unevenness correction value derivation unit  250  includes the first density unevenness correction value derivation unit  250 A, the second density unevenness correction value derivation unit  250 B, and the third density unevenness correction value derivation unit  250 C. 
     The first density unevenness correction value derivation unit  250 A derives the first density unevenness correction value on the basis of the main density unevenness component Sm(j, x) and the first density unevenness component T 1  ( j, x ). That is, the correction value of the density unevenness is obtained for each grayscale such that the density value becomes uniform in the arrangement direction of the nozzles regarding each grayscale. In this case, in a case where data of a grayscale intended to obtain are not present, complementation is performed using data of another grayscale. 
     The second density unevenness correction value derivation unit  250 B derives the second density unevenness correction value on the basis of the main density unevenness component Sm(j, x) and the second density unevenness component T 2 ( j, x ). In this case, in a case where data of a grayscale intended to obtain are not present, complementation is performed using data of another grayscale. 
     The third density unevenness correction value derivation unit  250 C derives the third density unevenness correction value on the basis of the main density unevenness component Sin(j, x). In this case, in a case where data of a grayscale intended to obtain are not present, complementation is performed using data of another grayscale. 
     According to this method, since an average of the respective regions is taken when the main density unevenness component is obtained, noise can be reduced. Accordingly, for example, even in a case where the width of each level of a chart to be drawn in each region becomes narrow, high-precision density unevenness correction can be performed. 
     Modification Example of First Method 
     At least the first chart TC 1  and the second chart TC 2  may be included in a test chart to be used in the above method. That is, the first chart TC 1  to be drawn in the first region Z 1  and the second chart TC 2  to be drawn in the second region Z 2  may be included. 
       FIG. 26  is a view illustrating an example of a test chart constituted by the first chart and the second chart. 
     If the size of the paper P to be supported by the paper supporting part  110  becomes large, the third region Z 3  becomes small. As a result, it is impossible to secure a region where the third chart is recorded. 
     Then, in such a case, a configuration in which the third chart is not drawn is adopted. That is, as illustrated in  FIG. 26 , the test chart TC is constituted by only the first chart TC 1  and the second chart TC 2 . 
     The main density unevenness component, the first density unevenness component, and the second density unevenness component are obtained as follows. 
     As the main density unevenness component, an average of the first chart TC 1  and the second chart TC 2  is calculated. The main density unevenness component Sm(j, x) is expressed as follows.
 
 Sm ( j,x )=( S 1( j,x )+ S 2( j,x ))/2
 
     As the first density unevenness component, a difference between the reading result of the first chart and the main density unevenness component is calculated. The first density unevenness component T 1 ( j, x ) is expressed as follows.
 
 T 1( j,x )= S 1( j,x )− Sm ( j,x )
 
     As the second density unevenness component, a difference between the reading result of the second chart and the main density unevenness component is calculated. The second density unevenness component T 2 ( j, x ) is expressed as follows.
 
 T 2( j,x )= S 2( j,x )− Sm ( j,x )
 
     On the basis of the main density unevenness component, the first density unevenness component, and the second density unevenness component that are obtained as described above, the correction value of the density unevenness is obtained for each region. 
     According to this method, even in a case where the third region Z 3  is small, high-precision density unevenness correction can be performed. 
     &lt;Second Method&gt; 
     This method is also in common with the above first method in that the main density unevenness component, the first density unevenness component, and the second density unevenness component are obtained from the reading result of the test chart, and the density unevenness correction values of the respective regions are obtained on the basis of the main density unevenness component, the first density unevenness component, and the second density unevenness component. 
     This method is different from the above first method in terms of a method of deriving the main density unevenness component, the first density unevenness component, and the second density unevenness component. 
     In this method, one test chart TC is drawn on one entire paper P. That is, one test chart including a plurality of grayscales on one paper P is drawn. 
       FIG. 27  is a plan view illustrating an example of a test chart. The test chart TC is an example of a test chart TC including six grayscales. In this case, an image of the six grayscales is included in the test chart TC. 
     In the test chart TC, the first level image and the second level image are drawn in the first region Z 1 , the third level image and the fourth level image are drawn in the third region Z 3 , and, the fifth level image and the sixth level image are drawn in the second region Z 2 . In this case, the first level image is drawn in a first thin grayscale, and the second level image is drawn in a fourth thin grayscale. Additionally, the third level image is drawn in a second thin grayscale, and the fourth level image is drawn in a fifth thin grayscale. Moreover, the fifth level image is drawn in a third thin grayscale, and the sixth level image is drawn in a sixth thin grayscale, that is, in a deepest grayscale. 
     This method includes a density unevenness component derivation step of deriving the main density unevenness component, the first density unevenness component, and the second density unevenness component from the reading result of the test chart, and a density unevenness correction value derivation step of deriving a density unevenness correction value of each region on the basis of the main density unevenness component, the first density unevenness component, and the second density unevenness component. 
     &lt;Density Unevenness Component Derivation Step&gt; 
     The density unevenness component derivation step includes the main density unevenness component derivation step of deriving the main density unevenness component, the first density unevenness component derivation step of deriving the first density unevenness component, and the second density unevenness component derivation step of deriving the second density unevenness component. 
     The main density unevenness component, the first density unevenness component, and the second density unevenness component are derived by the density unevenness component derivation unit  270 .  FIG. 28  is a block diagram illustrating the configuration of the density unevenness component derivation unit. The density unevenness component derivation unit  270  includes a main density unevenness component derivation unit  272 , a first density unevenness component derivation unit  274 , and a second density unevenness component derivation unit  276 . 
     [Main Density Unevenness Component Derivation Step] 
     The main density unevenness component derivation step derives the main density unevenness component from the reading result of the test chart. The main density unevenness component derivation step includes a first step of Fourier-transforming the reading result of the test chart to decompose the transformed result into a plurality of frequency components, a second step that removes a fundamental frequency, and a frequency component of an integral multiple of a fundamental frequency, from the reading result of the test chart after the Fourier transform, and a third step of inverse-Fourier-transforming the reading result of the test chart after the removal, to derive the main density unevenness component. 
       FIGS. 29A to 29D  are views illustrating a processing process of the reading result of the test chart. 
       FIG. 29A  is an extracted view of a portion of the reading result of the second level image of the test chart TC. 
     Since the second level image of the test chart TC is drawn in the first region Z 1 , the first density unevenness component other than the main density unevenness component is included in the reading result. 
     —First Step— 
     In the first step, the reading result of the test chart is Fourier-transformed and is decomposed into a plurality of frequency components. 
       FIG. 29B  is a view illustrating the reading result after the Fourier transform. The reading result of the test chart can be decomposed into the plurality of frequency components by carrying out the Fourier transform. In addition, in this drawing, a horizontal axis represents frequencies co (cycle/mm). 
     —Second Step— 
     In the second step, a fundamental frequency ω 1 , and a frequency component of an integral multiple of a fundamental frequency ω 1  are removed from the reading result of the test chart after the Fourier transform. 
     Here, the fundamental frequency ω 1  is a frequency matching arrangement intervals of the first supporting pieces  116  and the second supporting pieces  122  that constitute the first support  112  and the second support  114 . Regarding the reading result of the test chart TC to be drawn in the first region Z 1 , a frequency matching arrangement intervals of the first supporting pieces  116  becomes the fundamental frequency ω 1 . Hence, regarding the reading results of the first level image and the second level image, the frequency matching the arrangement intervals of the first supporting pieces  116  becomes the fundamental frequency ω 1 . Additionally, regarding the reading result of the test chart TC to be drawn in the second region Z 2 , a frequency matching arrangement intervals of the second supporting pieces  122  becomes the fundamental frequency ω 1 . Hence, regarding the reading results of the fifth level image and the sixth level image, the frequency matching the arrangement intervals of the second supporting pieces  122  becomes the fundamental frequency ω 1 . 
     The fundamental frequency ω 1  is uniquely determined from the arrangement intervals of the first supporting pieces  116  and the second supporting pieces  122 . Hence, the fundamental frequency can be obtained in advance. Information on the obtained fundamental frequency ω 1  is stored in the storage unit  208 . 
       FIG. 29C  is a view illustrating the reading result of the test chart after the fundamental frequency ω 1  and the frequency component of the integral multiple of the fundamental frequency ω 1  are removed. 
     The influence of the paper supporting part  110  can be removed by removing the fundamental frequency ω 1  and the frequency component of the integral multiple of the fundamental frequency ω 1 . That is, the first density unevenness component can be removed regarding the reading result in the first region Z 1 , and the second density unevenness component can be removed regarding the reading result in the second region Z 2 . 
     —Third Step— 
     In the third step, the main density unevenness component is derived by inverse-Fourier-transforming the reading result of the test chart after the fundamental frequency ω 1  and the frequency component of the integral multiple of the fundamental frequency ω 1  are removed. 
       FIG. 29D  is a view illustrating the reading result of the test chart after the inverse Fourier transform. 
     The main density unevenness component is obtained by inverse-Fourier-transforming the reading result of the test chart after the fundamental frequency ω 1  and the frequency component of the integral multiple of the fundamental frequency ω 1  are removed. 
     As described above, the main density unevenness component is obtained by Fourier-transforming the reading result of the test chart, removing the fundamental frequency and the frequency component of the integral multiple of the fundamental frequency from the data after the Fourier transform, and inverse-Fourier-transforming the data after the removal. The main density unevenness component is obtained for each grayscale. A grayscale with no reading result is complemented. 
     As illustrated in  FIG. 28 , the main density unevenness component derivation unit  272  acquires the reading result of the test chart TC, and performs the above respective processings to obtain the main density unevenness component. 
     [First Density Unevenness Component Derivation Step] 
     In the first density unevenness component derivation step, the first density unevenness component is derived by calculating a difference between the reading result of the test chart and the main density unevenness component. 
     As illustrated in  FIG. 28 , the first density unevenness component derivation unit  274  acquires information on the reading result of the test chart and information on the main density unevenness component, and calculates the difference therebetween to obtain the first density unevenness component. 
     The first density unevenness component is also obtained for each grayscale. A grayscale with no reading result is complemented. For example, regarding the first region Z 1 , only reading results of grayscales equivalent to the first level image and the second level image of the test chart TC are present. Therefore, the first density unevenness components of other grayscales can be obtained using the reading results of the first level image and the second level image. 
       FIGS. 30A to 30F  are views illustrating a method of complementing data. 
     In a case where only the reading results of the grayscales equivalent to the first level image and the second level image of the test chart TC are present, the first density unevenness correction components of the grayscales equivalent to the first level image and the second level image of the test chart TC can be calculated from the difference between the reading result of the test chart and the main density unevenness component. 
     In  FIGS. 30A to 30F , it is supposed that (A) is the first density unevenness component of a grayscale equivalent to the first level image of the test chart TC and (D) is the first density unevenness component of a grayscale equivalent to the second level of test chart TC. In a case where two grayscales are present between the first level image and the second level image of the test chart TC, the two grayscales between the first level image and the second level image can be obtained from the first density unevenness component of the grayscale of the first level image, and the first density unevenness component of the grayscale of the second level image. In this case, the first density unevenness component of each grayscale is estimated by obtaining the first density unevenness component from a change tendency of the first density unevenness component of the grayscale of the first level image and the first density unevenness component of the grayscale of the second level image. The first density unevenness components of the other grayscales can be obtained similarly. In  FIGS. 30A to 30F ,  FIGS. 30B, 30C, 30E, and 30F  illustrate the first density unevenness components obtained by complement. 
     [Second Density Unevenness Component Derivation Step] 
     In the second density unevenness component derivation step, the second density unevenness component is derived by calculating a difference between the reading result of the test chart and the main density unevenness component. 
     As illustrated in  FIG. 28 , the second density unevenness component derivation unit  276  acquires information on the reading result of the test chart and information on the main density unevenness component, and calculates the difference therebetween to obtain the second density unevenness component. 
     The second density unevenness component is also obtained for each grayscale. A grayscale with no reading result is complemented. For example, regarding the second region Z 2 , only reading results of grayscales equivalent to the fifth level image and the sixth level image of the test chart TC are present. Therefore, the second density unevenness components of other grayscales can be obtained using the reading results of the fifth level image and the sixth level image. 
     [Density Unevenness Correction Value Derivation Step] 
     The density unevenness correction value derivation step is the same as the above-described first method. That is, the density unevenness correction value derivation step includes the first density unevenness correction value derivation step of deriving the first density unevenness correction value that is the density unevenness correction value of the first region Z 1  on the basis of the main density unevenness component and the first density unevenness component, the second density unevenness correction value derivation step of deriving the second density unevenness correction value that is the density unevenness correction value of the second region Z 2  on the basis of the main density unevenness component and the second density unevenness component, and the third density unevenness correction value derivation step of deriving the third density unevenness correction value that is the density unevenness correction value of the third region Z 3  on the basis of the main density unevenness component. A density unevenness correction value of each region is derived by the density unevenness correction value derivation unit  250 . 
     As described above, also in this method, the density unevenness correction value of each region is obtained by separating the reading result of the test chart TC into the main density unevenness component, the first density unevenness component, and the second density unevenness component. In this method, since one test chart TC is drawn on one paper P, the length of each grayscale in the paper transporting direction (Y direction) can be secured to be long. Accordingly, noise of the reading result can be reduced. 
     Modification Example of Second Method 
     A density unevenness correction value of each region can also be obtained in the following procedure. 
     First, a temporary density unevenness correction value for each grayscale is obtained from the reading result of the test chart TC. This temporary density unevenness correction value includes the influence of the paper supporting part  110 . 
     Next, the temporary density unevenness correction value is Fourier-transformed, and is decomposed into a plurality of frequency components. 
     Next, the fundamental frequency ω 1  and the frequency component of the integral multiple of the fundamental frequency ω 1  are removed from the data after the Fourier transform. 
     Next, the data after the fundamental frequency ω 1  and the frequency component of the integral multiple of the fundamental frequency ω 1  are inverse-Fourier-transformed. Accordingly, the correction value of the density unevenness for correcting the main density unevenness component is obtained. This correction value is used as the main density unevenness component correction value. 
     Next, the density unevenness correction value of each region is obtained on the basis of information on the temporary density unevenness correction value and the main density unevenness component correction value. 
     Also in this method, since one test chart TC is drawn on one paper P, the length of each grayscale in the paper transporting direction (Y direction) can be secured to be long. Accordingly, noise of the reading result of each grayscale can be reduced. 
     Other Embodiments 
     &lt;&lt;Density Unevenness Correction Method&gt;&gt; 
     In the above embodiment, the density unevenness is corrected by performing predetermined grayscale conversion processing on the density data. However, the density unevenness correction method is not limited to this. For example, the density unevenness may be corrected by the dot arrangement data after half toning. Additionally, the density unevenness may be corrected by correcting a driving signal for each nozzle. Even in this case, a correction value is obtained for each region from a reading result of a test chart, and the density unevenness is corrected for each region. 
     &lt;Medium&gt; 
     In the above embodiments, a case where an image is drawn on the paper has been described as an example. However, the medium as an object to be drawn is not limited to this. The invention can be similarly applied to, for example, a case where drawing is performed on a sheet made of resin. 
     &lt;Transporting Means&gt; 
     In the above embodiments, the transporting means of the medium is constituted by the drum. However, the transporting means of the medium is not limited to this. The invention functions effectively as long as there is transporting means of a type in which the medium is transported in close contact with the medium supporting part configured such that the first support having the plurality of first supporting pieces arranged in the shape of comb teeth thereon and the second support having the plurality of second supporting pieces arranged in the shape of comb teeth thereon are engaged with each other and are extendable and retractable, and the medium is conveyed. 
     Additionally, the above embodiments have a configuration in which the medium is brought into close contact with the medium supporting part using a negative pressure. However, means for bringing the medium into contact with the medium supporting part is not limited to this. In addition to this, a configuration in which the close contact is performed using static electricity can also be adopted. 
     Additionally, the above embodiments have a configuration in which only the trailing end part of the paper is suctioned. However, a configuration in which the paper is suctioned as a whole can also be adopted. In this case, the suction holes are disposed in the supporting surface of each support. 
     Moreover, the transporting means may include means for heating or cooling a surface contacting the medium. If the means for heating or cooling the surface contacting the medium is provided, the temperature of the medium to be supported varies locally and causes the density unevenness. Even in such a case, occurrence of the density unevenness can be effectively prevented by applying the invention. As heating aspects, for example, an aspect in which a heater is built in the medium supporting part to heat the medium, an aspect in which the heat from the heater is applied to the supporting surface of the medium to heat the medium, an aspect in which a hot blast is blown against the supporting surface of the medium to heat the medium, and the like can be adopted. Additionally, as cooling aspects, for example, an aspect in which cooling means of an air cooling or water cooling type, is built in the medium supporting part to cool the medium, an aspect in which a cold blast is blown against the medium supporting surface to cooling the medium, and the like can be adopted. 
     &lt;Ink Jet Head&gt; 
     In the above embodiments, the nozzles are arranged in one row on the nozzle surface. However, the arrangement method of the nozzle is not limited to this. For example, the nozzles may be arranged in a matrix. Accordingly, the nozzles can be disposed in high density. 
     Additionally, the ink jet heads may be configured by connecting a plurality of modules. That is, one ink jet head may be connected by joining a plurality of small-sized ink jet heads including a plurality of nozzles together. 
     EXPLANATION OF REFERENCES 
     
         
         
           
               1 : ink jet recording device 
               10 : paper feed unit 
               12 : paper feeder 
               14 : feeder board 
               16 : paper feed drum 
               20 : processing liquid coating unit 
               22 : processing liquid coating drum 
               24 : processing liquid coating device 
               30 : processing liquid drying unit 
               32 : processing liquid drying drum 
               34 : processing liquid drying device 
               40 : drawing unit 
               42 : paper presser roller 
               44 : drawing unit 
               46 C: ink jet head 
               46 K: ink jet head 
               46 M: ink jet head 
               46 Y: ink jet head 
               48 : image reader 
               48 A: line sensor 
               48 B: imaging lens 
               48 C: illumination unit 
               50 : ink drying unit 
               52 : chain gripper 
               52 A: chain 
               52 B: gripper 
               54 : paper guide 
               54 A: first guide board 
               54 B: second guide board 
               56 : heating and drying device 
               56 A: infrared lamp 
               60 : accumulation unit 
               62 : accumulating device 
               100 : drawing drum 
               110 : paper supporting part 
               112 : first support 
               114 : second support 
               116 : first supporting piece 
               116 A: first supporting surface 
               118 : rotational axis 
               120 : first base 
               122 : second supporting piece 
               122 A: second supporting surface 
               124 : second base 
               126 : gripper 
               126 A: grip claw 
               128 : suction holding part 
               128 A: suction hole 
               200 : computer 
               202 : communication unit 
               204 : operating unit 
               206 : storage unit 
               208 : storage unit 
               210 : drawing control unit 
               212 : density data generation unit 
               214 : density unevenness correction unit 
               216 : dot arrangement data generation unit 
               218 : driving signal generation unit 
               220 : head driving control unit 
               230 : test chart output control unit 
               240 : test chart reading control unit 
               250 : density unevenness correction value derivation unit 
               250 A: first density unevenness correction value derivation unit 
               250 B: second density unevenness correction value derivation unit 
               250 C: third density unevenness correction value derivation unit 
               260 : main density unevenness component derivation unit 
               262 : first density unevenness component derivation unit 
               264 : second density unevenness component derivation unit 
               270 : density unevenness component derivation unit 
               272 : main density unevenness component derivation unit 
               274 : first density unevenness component derivation unit 
               276 : second density unevenness component derivation unit 
             NF: nozzle surface 
             Nz: nozzle 
             P: paper 
             S 1  to S 7 : processing procedure from input of image to output 
             S 11  to S 14 : processing sequence of density unevenness correction value derivation processing 
             S 21  to S 31 : processing sequence of density unevenness correction 
             TC: test chart 
             TC 1 : first chart 
             TC 2 : second chart 
             TC 3 : third chart 
             Z 1 : first region 
             Z 2 : second region 
             Z 3 : third region