JP2010064371A - Method of correction and liquid ejection device - Google Patents

Abstract

A density unevenness correction value is easily corrected.
A nozzle row in which nozzles for ejecting liquid are arranged in a predetermined direction, a moving mechanism for moving the nozzle row and the medium in a direction crossing the predetermined direction, and the crossing direction on print data. A correction unit for correcting the correction value of the liquid ejecting apparatus, the control unit correcting a gradation value indicated by a pixel belonging to each pixel row based on a correction value for each pixel row arranged in the direction, Forming a correction pattern by a column; causing the measurement pattern to be read by a measuring device to obtain a reading gradation value smaller than the number of correction values; and based on the reading gradation value And correcting the correction value.
[Selection] Figure 11A

Description

  The present invention relates to a correction method and a liquid ejecting apparatus.

  As a liquid ejecting apparatus, an ink jet printer (hereinafter referred to as a printer) that ejects ink from nozzles is known. In such a printer, due to problems such as nozzle processing accuracy, ink droplets do not land at the correct position on the medium, and density unevenness may occur. Therefore, the gradation value indicated by the pixel is corrected so that an image piece that is visually recognized lightly is printed darkly, and an image piece that is visually recognized darkly is printed lightly.

  However, even if the nozzles associated with a certain image piece are the same, if the nozzles associated with the image piece adjacent to the image piece are different, the density of the image piece also differs. Therefore, a method of correcting density unevenness based on the correction value for each image piece has been proposed (see Patent Document 1).

JP 2005-206991 A

Ink ejection characteristics and the like change according to changes in the printer over time and environmental changes. For this reason, density unevenness is hardly suppressed with the same correction value. However, it is a difficult task to recalculate and correct the correction value for each image piece from the beginning in accordance with aging and environmental changes.
Therefore, an object of the present invention is to easily correct the density unevenness correction value.

  A main invention for solving the problems includes a nozzle row in which nozzles for ejecting liquid are arranged in a predetermined direction, a moving mechanism for moving the nozzle row and the medium in a direction crossing the predetermined direction, and the print data on the print data A correction unit for correcting the correction value of the liquid ejecting apparatus, the control unit correcting the gradation value indicated by the pixel belonging to each pixel column based on the correction value for each pixel column arranged in the direction corresponding to the intersecting direction. Forming a correction pattern by the nozzle row, causing the measurement pattern to be read by a measuring device, and obtaining a read gradation value that is smaller than the number of correction values, Correcting the correction value based on a read gradation value.

  Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

=== Summary of disclosure ===
At least the following will become apparent from the description of the present specification and the accompanying drawings.

That is, a nozzle row in which nozzles for ejecting liquid are arranged in a predetermined direction, a moving mechanism for moving the nozzle row and the medium in a direction crossing the predetermined direction, and a direction corresponding to the crossing direction on the print data A correction unit for correcting the correction value of the liquid ejecting apparatus, the control unit correcting the gradation value indicated by the pixel belonging to each pixel column based on the correction value for each pixel column arranged, Forming a correction pattern; causing the measurement pattern to be read by a measurement device; obtaining a reading gradation value less than the number of correction values; and based on the reading gradation value, A correction method is provided that includes correcting the correction value.
According to such a correction method, the correction value can be corrected more easily than re-calculating the correction value in order to suppress uneven density due to secular change or environmental change.

In this correction method, the correction value is divided into a plurality of groups, and a correction value for correcting the correction value is calculated for each group based on the read gradation value.
According to such a correction method, density unevenness due to secular change or environmental change is likely to occur for each group, and thus density unevenness can be suppressed by the correction value for each group. Also, calculating the correction value for each group can easily correct the correction value, rather than recalculating the correction value.

In this correction method, the liquid ejecting apparatus includes a plurality of heads having the nozzle row, and calculates a correction value for correcting the correction value based on the read gradation value for each head. To do.
According to such a correction method, density unevenness due to secular change or environmental change is likely to occur for each head, and thus density unevenness can be suppressed by a correction value for each head. Further, the correction value can be corrected more easily by calculating the correction value for each head than by recalculating the correction value.

In this correction method, the correction pattern is formed based on a plurality of the pixel columns, and a part of the column regions of the plurality of column regions on the correction pattern corresponding to the plurality of pixel columns The read gradation value corresponding to each of the column regions is acquired, and the correction value of the pixel column corresponding to each column region is corrected based on data obtained by interpolating the read gradation values corresponding to some of the column regions. To do.
According to such a correction method, the correction value can be corrected more easily than re-calculating the correction value in order to suppress uneven density due to secular change or environmental change.

In this correction method, the control unit corrects the gradation value indicated by the pixel based on the correction value for each of the pixel columns with respect to a plurality of instruction gradation values, and is less than the plurality of instruction gradation values. Forming the correction pattern based on a plurality of command gradation values, and correcting the correction values for the plurality of command gradation values based on the read gradation values of the correction pattern.
According to such a correction method, the correction value can be corrected more easily than re-calculating the correction value in order to suppress uneven density due to secular change or environmental change.

In this correction method, the liquid ejecting apparatus includes a head having a plurality of the nozzle rows, the correction pattern is formed by the nozzle row of the plurality of nozzle rows, and the correction is performed. Correcting the correction value of the pixel row allocated to each of the plurality of nozzle rows of the head based on the read gradation value of the pattern.
According to such a correction method, the correction value can be corrected more easily than re-calculating the correction value in order to suppress uneven density due to secular change or environmental change.

Further, (1) a nozzle row in which nozzles for ejecting liquid are arranged in a predetermined direction, (2) a moving mechanism for moving the nozzle row and the medium in a direction intersecting the predetermined direction, and (3) on the print data A control unit that corrects a gradation value indicated by a pixel belonging to each pixel row based on a correction value for each pixel row arranged in a direction corresponding to the intersecting direction, and a correction pattern is formed by the nozzle row Then, the control unit that causes the measuring device to read the correction pattern, obtains a reading gradation value that is smaller than the number of correction values, and corrects the correction value based on the reading gradation value. When,
A liquid ejecting apparatus having
According to such a liquid ejecting apparatus, the correction value can be corrected more easily than recalculating the correction value in order to suppress uneven density due to secular change or environmental change.

=== About Inkjet Printers ===
Hereinafter, an embodiment will be described by taking a line head printer (printer 1) in an inkjet printer as an example.

  FIG. 1 is a block diagram showing the overall configuration of the printer 1 according to this embodiment. FIG. 2A is a cross-sectional view of the printer 1. FIG. 2B is a diagram illustrating a state in which the printer 1 transports the paper S (medium). The printer 1 that has received print data from the computer 50, which is an external device, controls each unit (conveyance unit 20, head unit 30) by the controller 10, and forms an image on the paper S. Further, the detector group 40 monitors the situation in the printer 1, and the controller 10 controls each unit based on the detection result.

  The controller 10 is a control unit for controlling the printer 1. The interface unit 11 is for transmitting and receiving data between the computer 50 as an external device and the printer 1. The CPU 12 is an arithmetic processing unit for controlling the entire printer 1. The memory 13 is for securing an area for storing the program of the CPU 12 and a work area. The CPU 12 controls each unit by a unit control circuit 14 according to a program stored in the memory 13.

  The transport unit 20 (corresponding to a moving mechanism) has transport rollers 21A and 21B and a transport belt 22, and feeds the paper S to a printable position, and at the time of printing, a predetermined transport speed in the transport direction (corresponding to the intersecting direction). The sheet S is transported by. The paper feed roller 23 is a roller for automatically feeding the paper S inserted into the paper insertion opening onto the transport belt 22 in the printer 1. The sheet S on the transport belt 22 is transported by the rotation of the annular transport belt 22 by the transport rollers 21A and 21B. Further, the sheet on the conveyor belt 22 is electrostatically attracted or vacuum attracted from below.

  The head unit 30 is for ejecting ink onto the paper S, and has a plurality of heads 31. A plurality of nozzles that are ink ejecting portions are provided on the lower surface of the head 31. Each nozzle is provided with a pressure chamber containing ink and a driving element (piezo element) for ejecting ink by changing the capacity of the pressure chamber.

  FIG. 3A shows the nozzle arrangement on the lower surface of the head unit 30. The head unit 30 has a plurality (n) of heads 31. A head 31 (1), a second head 31 (2),..., An nth head 31 (n) are sequentially arranged from the head 31 located on the right side in the paper width direction (corresponding to a predetermined direction). The plurality of heads 31 are arranged in a staggered manner in the paper width direction intersecting the transport direction. A yellow ink nozzle row Y, a magenta ink nozzle row M, a cyan ink nozzle row C, and a black ink nozzle row K are formed on the lower surface of the head 31, and each nozzle row includes 180 nozzles. The nozzles of each nozzle row are aligned at a constant interval of 360 dpi in the paper width direction. In addition, the rightmost nozzle (eg, # 1 of 31 (2)) of the left head of the two heads 31 arranged in the paper width direction and the leftmost nozzle (eg, 31 (1) of the right head. Each head 31 is arranged so that the distance from # 180) is a constant distance 360 dpi. That is, in the head unit 30, the four color nozzles (YMCK) are arranged in the paper width direction at a constant interval of 360 dpi.

  FIG. 3B is a diagram illustrating members around the nozzle. The head 31 has a flow path unit 312 and a piezo element PZT. The flow path unit 312 includes a flow path forming plate 312a, an elastic plate 312b, and a nozzle plate 312c. The flow path forming plate 312a is formed with a groove that becomes the pressure chamber 312d, a through hole that becomes the nozzle communication port 312e, a through hole that becomes the common ink chamber 312f, and a groove that becomes the ink supply path 312g. The elastic plate 312b has a support frame 312h and an island portion 312j to which the tip of the piezo element PZT is joined. An elastic region is formed by the elastic film 312i around the island portion 312j. The nozzle plate 312c is a plate on which nozzles Nz as shown in FIG. 3 are formed.

  The ink stored in the ink cartridge is first supplied from the ink supply pipe 313 to the common ink chamber 312f, and then supplied to the pressure chamber 312d corresponding to each nozzle through the common ink chamber 312f. Ink is ejected from the nozzle Nz by changing the pressure in the pressure chamber 312d filled with ink using the piezo element PZT. The piezo element PZT expands and contracts in the longitudinal direction according to the potential of the drive signal. When the piezo element PZT expands and contracts, the island portion 312j is pushed toward the pressure chamber 312d or pulled in the opposite direction. At this time, the elastic film 312i around the island portion 312j is deformed, and the pressure in the pressure chamber 312d rises and falls, thereby ejecting ink droplets from the nozzle Nz.

  In such a line head printer 1, when the controller 10 receives print data, the controller 10 first rotates the paper feed roller 23 to send the paper S to be printed onto the conveyor belt 22. The sheet S is conveyed on the conveyor belt 22 without stopping at a constant speed, and passes under the head unit 30. While the paper S passes under the head unit 30, ink is intermittently ejected from each nozzle. As a result, a dot row composed of a plurality of dots along the transport direction is formed on the paper S, and an image is printed.

=== About density unevenness ===
For the following description, “pixel region” and “column region (image piece)” are set. The pixel area refers to a rectangular area virtually defined on the paper, and the size and shape are determined according to the print resolution. One “pixel” constituting the image data corresponds to one pixel area. Further, the “row area” is an area on the paper (row of pixel areas) constituted by a plurality of pixel areas arranged in the transport direction. One column region corresponds to a “pixel column” in which pixels are arranged in a direction corresponding to the transport direction (crossing direction) on the data.

  FIG. 4A is an explanatory diagram of a state when dots are ideally formed. The ideal formation of a dot means that an ink droplet has landed at the center position of the pixel region, the ink droplet spread on the paper, and a dot is formed in the pixel region. When each dot is accurately formed in each pixel region, a raster line (a dot row in which dots are arranged in the transport direction) is accurately formed in the row region.

  FIG. 4B is an explanatory diagram when density unevenness occurs. The raster line formed in the second row region is formed closer to the third row region due to variations in the flight direction of the ink droplets ejected from the nozzles. As a result, the second row region is light and the third row region is dark. In addition, the ink amount of the ink droplets ejected to the fifth row region is smaller than the prescribed ink amount, and the dots formed in the fifth row region are small. As a result, the fifth row region becomes lighter.

  When a printed image composed of raster lines having different shades is viewed macroscopically, striped density unevenness along the transport direction is visually recognized. This uneven density causes a reduction in image quality of the printed image.

  FIG. 4C is a diagram illustrating a state when dots are formed by the printing method of the present embodiment. In the present embodiment, the gradation value of the pixel data of the pixel corresponding to the row region is corrected so that a dark image piece is formed in the row region that is dark and easily visible. Further, the gradation value of the pixel data of the pixel corresponding to the row region is corrected so that a dark image piece is formed in a row region that is easily viewed.

  For example, in FIG. 4C, the dot generation rate of the second and fifth row regions that are visually recognized lightly increases, and the dot generation rate of the third row region that is visually recognized darkly decreases. The gradation value of the pixel data of the corresponding pixel is corrected. As a result, the dot generation rate of the raster line in each row area is changed, the density of the image pieces in the row area is corrected, and the density unevenness of the entire print image is suppressed.

  By the way, in FIG. 4B, the reason why the density of the image piece formed in the third row region is high is not due to the influence of the nozzles forming the raster line in the third row region, but the adjacent second row. This is due to the influence of nozzles that form raster lines in the region. For this reason, when a nozzle that forms a raster line in the third row region forms a raster line in another row region, the image piece formed in that row region is not always dark. That is, even if the image pieces are formed by the same nozzle, the density may be different if the nozzles that form adjacent image pieces are different. In such a case, the density unevenness cannot be suppressed by simply using the correction value associated with the nozzle. Therefore, in the present embodiment, the gradation value of the pixel data is corrected based on the correction value H set for each row region.

=== Calculation of Density Unevenness Correction Value H ===
FIG. 5 is a flowchart of the correction value H calculation process performed in the inspection process after manufacturing the printer. For inspection, a printer 1 and a scanner (not shown) that are to be inspected for density unevenness are connected to a computer 50. The correction value calculation program installed in the computer 50 first causes the printer 1 to actually print a test pattern in order to calculate the correction value H for each row region (S001). Then, when the correction value calculation program acquires the read gradation value that is the result of reading the test pattern with the scanner (S002), the correction value calculation program calculates the correction value H based on the read gradation value (S003). . For example, when the density of a certain row area is printed darker than the target density (gradation value), a correction value H is calculated so that the row area is printed lightly. Is printed lighter than the target density (tone value), a correction value H is calculated so that the row area is printed dark. Finally, the calculated correction value H is stored in the memory 13 of the printer 1 (S004).

<S001: Print test pattern>
FIG. 6A is a diagram showing a test pattern to be printed by the printer 1, and FIG. 6B is a diagram showing a correction pattern. The test pattern includes four correction patterns formed for each nozzle row YMCK that ejects four colors of ink. Each correction pattern is composed of three patterns (30% to 70%) of belt-like patterns. Each belt-like pattern is generated from image data having a constant gradation value (hereinafter referred to as a command gradation value). Sa (76) is the command gradation value of the belt-like pattern with the density of 30%, Sb (128) is the command gradation value of the belt-like pattern with the density of 50%, and Sc (178) is the command gradation value of the belt-like pattern with the density of 70%. . In this embodiment, the higher the gradation value, the darker the gradation value, and the lower the gradation value, the lighter the gradation value.

  In the line head printer 1 of this embodiment, the image is printed on the paper S as the paper S is conveyed under the head unit 30 without the head unit 30 moving. Further, in a printer that does not have a plurality of head units 30 (FIG. 3), such as the printer 1 of the present embodiment, one nozzle is associated with one row region (one pixel row). Therefore, the number of correction values H to be calculated (180 × n) is equal to the number of nozzles of the printer 1, and the correction pattern is composed of 180 × n raster lines. It is assumed that the nozzle on the right side in the paper width direction, that is, the first row region in order from the row region associated with the nozzle # 1 of the first head 31 (1).

<S002: Acquisition of reading gradation value>
Next, the correction value calculation program causes the scanner to read the test pattern printed on the paper S. When the image of the correction pattern is tilted on the test pattern read data, the tilt θ of the image is detected, and the image data is rotated according to the tilt θ. Hereinafter, in the read data, an area corresponding to the “pixel area” of the correction pattern is referred to as a “pixel”, and an area corresponding to the “column area” is referred to as a “pixel column (a column of pixels arranged in a direction corresponding to the moving direction). ) ".

  When the test pattern is read at a resolution higher than the resolution in the paper width direction at the time of printing the test pattern, the number of pixel rows on the read data is the number of raster lines (number of row areas) of the correction pattern. And the same number. Thus, the pixel rows on the data and the row areas defined on the paper S are made to correspond one-to-one.

  FIG. 7 is a graph showing the reading result (reading gradation value) of the cyan correction pattern. After associating the pixel columns with the column regions, the density of each column region is calculated for each strip pattern. That is, the average value of the read gradation values of each pixel belonging to the pixel column corresponding to a certain row region of a certain belt-like pattern is set as the “read gradation value” of that row region of the belt-like pattern. In the graph in the figure, the horizontal axis is the row area number, and the vertical axis is the read gradation value. As shown in the graph, although each band pattern is uniformly formed with each command gradation value (Sa, Sb, Sc), the reading gradation value varies for each row region. Yes. For example, in the graph in the figure, it can be seen that the i-row region is visually recognized as lighter than the other row regions, and the j-row region is visually recognized as darker than the other row regions. This variation in density for each row area causes uneven density in the printed image.

<S003: Calculation of Correction Value H>
Next, the correction value calculation program calculates the correction value H based on the read gradation value for each row region for each belt-like pattern. For this purpose, it is only necessary to reduce the variation in the read gradation value for each row area at the same gradation value as shown in FIG. 7, and the density of image pieces (raster lines) formed in each row area is set to a constant value. It is good to approach. Therefore, the average value Cbt of the read gradation values of all the row regions is set as the “target value Cbt” for the same command gradation value (for example, Sb). Then, the gradation value of the pixel (data) corresponding to each column region is corrected so that the read gradation value of each column region at the command gradation value Sb approaches the target value Cbt. That is, when the pixel column data corresponding to a certain column region indicates the gradation value Sb, the gradation value Sb is actually set to the correction value so that the read gradation value of the column region becomes the target value Cbt. Printing is performed with the “target gradation value Sbt” corrected by H.

FIG. 8A is a diagram illustrating a method of calculating the target gradation value Sbt of the i-row region whose reading result is lower than the target gradation value Cbt. The horizontal axis indicates the command gradation value, and the vertical axis indicates the read gradation value. On the graph, cyan reading results (Cai, Cbi, Cci) in the i-th row area are plotted against the command gradation values (Sa, Sb, Sc). The target command tone value Sbt for representing the i-th row region with the target value Cbt with respect to the command tone value Sb is calculated by the following equation (linear interpolation based on the straight line BC).
Sbt = Sb + (Sc−Sb) × {(Cbt−Cbi) / (Cci−Cbi)}

FIG. 8B is a diagram illustrating a method of calculating the target gradation value Sbt of the j-th row area where the reading result is higher than the target gradation value Cbt. On the graph, the reading result of cyan in the j column region is plotted. The target command tone value Sbt for representing the j-th row region with the target value Cbt with respect to the command tone value Sb is calculated by the following equation (linear interpolation based on the straight line AB).
Sbt = Sa + (Sb−Sa) × {(Cbt−Caj) / (Cbj−Caj)}

Thus, after calculating the target command gradation value Sbt for expressing the density of each column region with the target value Cbt with respect to the command gradation value Sb, the command gradation value of each column region is calculated by the following equation. A correction value H for Sb is calculated.
Hb = (Sbt−Sb) / Sb

  Similarly, three correction values (Ha, Hb, Hc) for the three command gradation values (Sa, Sb, Sc) are calculated for each row region. Further, not only the cyan nozzle row C but also the correction value H of other nozzle rows YMK is calculated.

<S004: Storage of Correction Value H>
FIG. 9 is a correction value table relating to the cyan nozzle row. After calculating the correction value H, the correction value calculation program stores the correction value H in the memory 13 of the printer 1. In the correction value table, three correction values (Ha_x, Hb_x, Hc_x) corresponding to the three command gradation values are associated with each column region x. In the present embodiment, the correction value H is calculated for the number of nozzles N (= 180 × n) of the printer 1. Further, such a correction value table is stored in the memory 13 for each nozzle row YMCK.

<Use under the user>
In the manufacturing process of the printer 1, the correction value H for correcting the density unevenness is calculated, and after the correction value H is stored in the memory 13 of the printer, the printer 1 is shipped. When the user installs the printer driver when using the printer 1, the printer driver requests the printer 1 to transmit the correction value H stored in the memory 13 to the computer 50. The printer driver stores the correction value H sent from the printer 1 in a memory in the computer 50.

  When the printer driver receives a print command from the user, the printer driver converts the image data output from the application program into a resolution for printing on the paper S by resolution conversion processing. Next, the RGB data is converted into CMYK data represented by a CMYK color space corresponding to the ink of the printer 1 by color conversion processing.

  Thereafter, the gradation value of high gradation (for example, 256 gradations) indicated by the pixel data is corrected by the correction value H. The printer driver (corresponding to the control unit) corrects the gradation value of each pixel data (hereinafter referred to as gradation value S_in before correction) based on the correction value H of the column region corresponding to the pixel data ( The corrected tone value S_out).

If the gradation value S_in before correction is the same as one of the command gradation values Sa, Sb, Sc, the correction values Ha, Hb, Hc stored in the memory of the computer 50 can be used as they are. For example, if the gradation value S_in before correction is S_in = Sc, the gradation value S_out after correction (that is, the target gradation value Sbt) is obtained by the following equation.
S_out = Sc × (1 + Hc)

FIG. 10 is a diagram illustrating a correction method when the gradation value S_in before correction of the x-th row region of cyan is different from the command gradation value. The horizontal axis is the gradation value S_in before correction, and the vertical axis is the gradation value S_out after correction. For example, when the gradation value S_in before correction is between the command gradation values Sa and Sb, the following equation is obtained by linear interpolation based on the correction value Ha of the command gradation value Sa and the correction value Hb of the command gradation value Sb. To calculate a corrected gradation value S_out.
S_out = Sa + (Sbt−Sat) × {(S_in−Sa) / (Sb−Sa)}

  When the gradation value S_in before correction is smaller than the command gradation value Sa, the gradation value S_out after correction is obtained by linear interpolation between the gradation value 0 (minimum gradation value) and the command gradation value Sa. Is calculated. When the gradation value S_in before correction is larger than the command gradation value Sc, the gradation value S_out after correction is calculated by linear interpolation between the gradation value 255 (maximum gradation value) and the instruction gradation value Sc. To do. The present invention is not limited to this, and a correction value H_out corresponding to a gradation value S_in before correction different from the command gradation value may be calculated to calculate a corrected gradation value S_out (S_out = S_in × ( 1 + H_out)).

  In this way, after the density correction processing for each row region is performed, the corrected gradation value S_out is subjected to halftone processing, and converted to data of the number of gradations that can be formed by the printer 1. Finally, the rasterized processing rearranges the matrix image data for each pixel data in the order of data to be transferred to the printer 1. The print data generated through these processes is transmitted to the printer 1 by the printer driver together with command data (such as the conveyance amount) corresponding to the printing method, and printing is performed.

=== About Correction of Density Unevenness Correction Value H ===
In the printer 1, the ejection characteristics of ink from the nozzles change due to aging and environmental changes. For example, if the printing apparatus continues to be used, the ink components settle in the common ink chamber 312f shown in FIG. The ink ejection characteristics change with time. The ink ejection characteristics also vary depending on the environment in which the printer 1 is used and the location where the printer 1 is installed. For this reason, the correction value H (FIG. 9) calculated first in the manufacturing process cannot completely suppress density unevenness due to secular change or environmental change. However, every time the predetermined period elapses or the environment changes, recalculating a new correction value H in accordance with the flow of FIG.

  Therefore, the present embodiment aims to suppress the density unevenness without newly calculating the density unevenness correction value H in accordance with the secular change or the environmental change. That is, an object of the present embodiment is to easily correct the density unevenness correction value H calculated first in the manufacturing process in accordance with a secular change or an environmental change. For this purpose, a correction value ΔC for correcting the correction value H is calculated. The correction value H is easily corrected. In other words, the process of calculating the correction value ΔC for correcting the correction value H is easier than the process of correcting the correction value H by recalculating the new correction value H. It is to make. Hereinafter, a method for calculating the correction value ΔC will be described.

<First modification method>
The printer 1 of this embodiment has a plurality (n) of heads 31 as shown in FIG. 3A, and all the heads 31 have the same structure. However, even if they have the same structure, the way of aging and environmental change differs depending on the head 31 due to the difference in the characteristics of the materials constituting the head 31 and the minute difference in the combination of each member. In addition, the ink supply path is different for each head 31, and the sedimentation state of the ink component changes for each ink supply path with time. For this reason, the manner of secular change is different for each head 31. Therefore, in the first correction method, the correction value H for each column region (for each pixel column) calculated first is corrected by the correction value ΔC for each head 31.

  FIG. 11A is a calculation flow of the correction value ΔC. Similarly to the correction value H, the correction value ΔC is calculated by a correction value calculation program installed in the computer 50. The correction value calculation program first causes the printer 1 to print a “correction pattern” having the same shape as the correction pattern shown in FIG. 6B for each nozzle row YMCK (S101). At this time, the correction pattern is printed using the correction value H (FIG. 9) for each row area calculated first. That is, the command gradation values Sa, Sb, and Sc are corrected with the correction value H for each row region (by the corrected gradation value S_out), and a correction pattern is printed. When the printer 1 starts to be used, density correction should not occur in the correction pattern. However, if the density unevenness cannot be suppressed with the correction value H due to aging and environmental changes of the printer 1, the correction pattern is used. Density unevenness occurs in the pattern. In the first correction method, the correction value ΔC for each head 31 is calculated in order to suppress the density unevenness caused by the secular change and the environmental change.

  FIG. 11B is a diagram showing measurement points of the correction pattern. For the sake of explanation, the number of heads 31 is reduced. After the correction pattern reflecting the correction value H for each row area is printed on the printer 1, the correction value calculation program causes the scanner (corresponding to the measuring apparatus) to read the correction pattern (S102). At this time, one reading gradation value is acquired from one band-like pattern result formed on one head 31 (nozzle row). That is, the number of read gradation values acquired from the correction pattern is smaller than the number of correction values H calculated for each row region for each belt-like pattern (command gradation value). In the figure, the measurement point is indicated by “x”. For example, one reading floor is obtained from the result of the belt-like pattern formed in the black nozzle row K of the first head 31 (1) among the belt-like pattern of black density 30%. Get key value.

  FIG. 11C is a diagram illustrating a reading result (reading gradation value) of a belt-like pattern having a cyan density of 50% in the correction pattern. The horizontal axis indicates the position of the head 31, and the vertical axis indicates the read gradation value. Each of the heads 31 (1) to 31 (4) acquires one read gradation value. For the sake of explanation, the read gradation value of the band-shaped pattern of 50% cyan density formed on the first head 31 (1) is denoted as “Cb (1)”, and the other heads 31 (2) to 31 (4). The reading gradation value is also given in the same manner. It can be seen that there is a difference in the read tone values of the different heads 31 and, as described above, a characteristic difference (density unevenness) appears for each head 31 along with aging and environmental changes. For example, the read gradation value Cb (2) of the second head 31 (2) is larger than the read gradation value Cb (1) of the first head 31 (1) and is larger than that of the first head 31 (1). It can be seen that the belt-like pattern formed on the second head 31 (2) is visually recognized darker. On the other hand, the read gradation value Cb (4) of the fourth head 31 (4) is smaller than the read gradation value Cb (1) of the first head 31 (1) and is smaller than that of the first head 31 (1). It can be seen that the belt-like pattern formed on the fourth head 31 (4) is visually recognized lighter. The difference in reading gradation value for each head 31 becomes a characteristic difference for each head 31 due to secular change or environmental change, which causes density unevenness. Therefore, the correction value ΔC for each head 31 is calculated so that the difference in the read gradation value for each head 31 is reduced.

  By the way, one reading gradation value is acquired for each head 31 from one belt-like pattern of the correction pattern. The number of row regions allocated to one head 31 is “180”, which is equal to the number of nozzles belonging to one nozzle row. Therefore, acquiring one reading gradation value from one band-like pattern result formed on one head 31 means acquiring the reading results of 180 column regions of the correction pattern as one reading gradation value. I will do it. In the above-described test pattern (FIG. 6A), the reading resolution in the paper width direction is “360 dpi (nozzle pitch / line area interval)” in order to obtain the read gradation value for each line area. On the other hand, in the correction pattern, 180 column regions need only be acquired as one read gradation value, so the read resolution in the paper width direction is “2 dpi”. That is, the reading resolution of the correction pattern in the paper width direction can be lowered as compared with the test pattern. As a result, the scanner can read the correction pattern quickly. Further, the correction value ΔC can be calculated even for a user who does not have a high-resolution scanner.

  Further, assuming that the reading resolution in the paper width direction of the scanner is the same as that when reading the test pattern, the correction pattern includes 180 rows constituting one belt-like pattern formed on one head 31 (nozzle row). One row region may be selected from the regions, and the read gradation value of that one row region may be acquired. That is, since the number of data (number of read gradation values) acquired from the correction pattern is smaller than that of the test pattern, the scanner can read the correction pattern quickly.

  Further, the reading gradation value acquired from the band-shaped pattern result formed on one head 31 is not limited to one, and a plurality of reading gradation values may be acquired. For example, when three reading tone values are acquired from the band pattern result formed on one head 31, an average value of the three reading tone values is calculated. Then, the average value is, for example, the read gradation value of the belt-like pattern with 50% cyan density formed on the first head 31 (1) is “Cb (1)”. However, it is assumed that the number of read gradation values acquired from the band pattern result formed on one head 31 is smaller than the number of row regions (180). This is because density unevenness due to secular change or environmental change is likely to occur for each head 31, and it is not necessary to acquire a read gradation value for each row region. That is, by calculating at least one reading gradation value from the band pattern result formed on one head 31 and calculating the correction value ΔC, the calculation process of the correction value ΔC is easier than the calculation process of the correction value H. To.

  In this way, after acquiring the reading gradation value for each head 31, the correction value calculation program reads “new” so that the reading gradation value of each head 31 becomes a constant value as in the case of calculating the correction value H. Is set "(S103 in FIG. 11A). The new target value is an average value of the read gradation values of the heads 31 (1) to 31 (4). However, the present invention is not limited to this, and may be a target value when the density unevenness correction value H is calculated, for example. Also, a new target value is set for each nozzle pattern YMCK and for each band pattern.

  More specifically, as shown in FIG. 11C, the new target value of the band-like pattern with cyan density of 50% is “Cbt ′ (= average value of Cb (1) to Cb (4))”. When the image is printed with the gradation value (Sb_out = Sb × (1 + Hb)) obtained by correcting the command gradation value Sb with the density unevenness correction value H, all the heads 31 (1) to 31 (4) are printed. By making the reading gradation value of the printed image constant, density unevenness is suppressed.

  FIG. 12A is a diagram illustrating the target gradation value Sbt ′ with respect to the instruction gradation value Sb (corrected instruction gradation value Sb_out) in the cyan nozzle row C of the first head 31 (1). After calculating a new target value (for example, Cbt ′), the correction value calculation program causes the read gradation value of the image printed by each of the heads 31 (1) to 31 (4) to be new with the command gradation value Sb. The “new target gradation value Sbt ′” is calculated so as to be the target value Cbt ′ (S104 in FIG. 11A). In FIG. 12A, the reading results of the three belt-like patterns formed on the first head 31 (1) are plotted. Point A is the result of reading a belt-like pattern with a density of 30%, point B is the result of reading a belt-like pattern with a density of 50%, and point C is the result of reading a belt-like pattern with a density of 70%.

  As shown in FIG. 12A, since the reading result Cb (1) of the belt-like pattern formed on the first head 31 (1) is lower than the new target value Cbt ′, a new target floor is obtained by linear interpolation of the straight line BC. The adjustment value Sbt ′ is calculated. Similarly, the correction value calculation program calculates a new target tone value for each head 31, each nozzle row, and each command tone value.

After the new target gradation value is calculated, the correction value calculation program calculates the correction value ΔC by the following equation (S105 in FIG. 11A). The following formula is a formula for calculating the correction value ΔCb with respect to the command gradation value Sb.
ΔCb = (Sbt′−Sb_out) / Sb_out
= (Sbt'-Sb * (1 + Hb)) / (Sb * (1 + Hb))

  FIG. 12B is a correction value table for the cyan nozzle row C. After calculating the correction value ΔC, the correction value calculation program stores the correction value ΔC in the memory of the computer 50 (S106 in FIG. 11A). In the correction value table, three correction values (ΔCa, ΔCb, ΔCc) corresponding to the three command gradation values Sa, Sb, Sc are associated with each head 31. As described above, the number of correction values ΔC calculated for each head 31 (FIG. 12B, the number of heads n × 3) is equal to the number of density unevenness correction values H calculated for each row region (FIG. 9, number of row regions 180 n). Significantly less than x3). In other words, since the correction value ΔC is calculated in a smaller amount than the correction value H, the calculation process is easy and the calculation process can be performed quickly. Therefore, instead of recalculating the correction value H for each row region in order to suppress density unevenness due to secular change or environmental change, the correction value ΔC of the correction value H is calculated, thereby suppressing density unevenness. , Can be processed easily.

  The correction value ΔC (FIG. 12B) calculated in this way is used together with the density unevenness correction value H for each row region when the printer driver creates print data in actual printing. After the printer driver receives image data from various application software, the image data is subjected to resolution conversion processing and color conversion processing. Next, the printer driver corrects the correction value H by adding the correction value H to the correction value H (H + ΔC), and performs density correction processing based on the corrected correction value H. The density unevenness correction value H is calculated for each row region, but the correction value ΔC is calculated for each head 31. For this reason, the pixel data corresponding to a certain row area is obtained based on a value obtained by adding the density unevenness correction value H corresponding to the row area and the correction value ΔC corresponding to the head 31 to which the row area is assigned. Correction processing is performed. That is, the correction values H of the 180 row areas assigned to a certain nozzle row of one head 31 are corrected by the common correction value ΔC. For example, the correction value ΔCa (1) of the first head 31 (1) related to the command tone value Sa of the cyan nozzle row C shown in FIG. 12B is changed from the first value related to the command tone value Sa of the cyan nozzle row shown in FIG. Correction is made by adding to the correction values (Ha_1 to Ha_180) of the 180th row region.

Specifically, the density correction process under the user is stored in the memory of the computer 50 if the gradation value S_in before the density correction process is the same as any of the command gradation values Sa, Sb, and Sc. The corrected correction value H and correction value ΔC can be used as they are. For example, if the gradation value S_in before correction indicated by the print data is S_in = Sc, the gradation value S_out after correction is obtained by the following equation.
S_out = Sc × (1 + Hc + ΔCc)

  When the gradation value S_in before correction is different from the command gradation value, the gradation value S_out after correction is calculated by linear interpolation in the same manner as in FIG. For example, when the gradation value S_in before correction is between the command gradation values Sa and Sb, the gradation value after correction for the command gradation value Sa (= Sa × (1 + Ha + ΔCa)) and the command gradation value Sb The corrected gradation value S_out is calculated by linear interpolation of the corrected gradation value (= Sb × (1 + Hb + ΔCb)).

  Incidentally, it is necessary to correct the density unevenness generated due to the characteristics of each nozzle for each row region. For example, density unevenness caused by a row region affected by a nozzle that bends in flight or a row region affected by a nozzle whose ink ejection amount is not appropriate is suppressed by the correction value H for each row region. However, the characteristics of each nozzle, such as a flight curve, do not change much due to aging and environmental changes. Therefore, it is not necessary to correct the density unevenness caused by the secular change or the environmental change with the correction value ΔC for each row region, and it is sufficient to correct with the correction value ΔC for each head 31. Therefore, as in the first correction method, density correction processing is performed by adding the correction value H for each row region and the correction value ΔC for each head 31 to perform density unevenness and secular change caused by the characteristics of each nozzle. It is possible to suppress both density unevenness caused by environmental changes.

  In summary, since the correction value ΔC is calculated for each head 31 in the first correction method, at least one read gradation value for each head 31 is acquired when the correction pattern (FIG. 11A) is read. Good. That is, the correction value ΔC is calculated based on the read gradation value that is smaller than the number of correction values H for each row region. Therefore, the calculation process of the correction value ΔC is easier than the calculation process of the correction value H that acquires the read gradation value for each row area from the test pattern (FIG. 6A). Further, since it is not necessary to acquire the read gradation value for each row region, the correction value ΔC can be calculated without using a high-resolution scanner. Further, since the correction value ΔC is calculated for each head 31 from the reading result of the correction pattern, the calculation process of the correction value ΔC is easier than the process of calculating the correction value H for each row region from the reading result of the test pattern. It becomes. That is, density unevenness can be more easily suppressed by correcting the correction value H with the correction value ΔC for each head 31 rather than recalculating the correction value H in accordance with aging and environmental changes.

  As described above, the correction value H can be easily corrected in accordance with the secular change and the environmental change, so that the correction value H is corrected, that is, the correction value ΔC is calculated every predetermined period (for example, every other day, a fixed amount). This can be done during printing or cleaning. That is, by facilitating the correction of the density unevenness correction value H for each row region, the density unevenness correction value H can be frequently corrected, and the density unevenness can be further improved. In addition, if the printer includes a scanner or the like for reading a correction pattern downstream of the head unit 30 in the transport direction, the correction value ΔC may be automatically calculated every predetermined period. By doing so, the density unevenness is reliably suppressed even for a user who is not familiar with the calculation process of the correction value ΔC.

Here, as the measurement data for calculating the correction value ΔC, the result (density / reading gradation value) obtained by reading the correction pattern with the scanner is used, but the present invention is not limited to this. That is, the measuring device that reads the correction pattern is not limited to the scanner. For example, reflectance data may be acquired from a correction pattern by a colorimeter, and brightness values, XYZ values, RGB values, L ^* a ^* b ^* values, etc. may be acquired from the correction pattern by various measuring devices. You may get it. The result read from these correction patterns corresponds to the read gradation value.

<Modification>
FIG. 13A is a diagram illustrating another method for calculating the correction value ΔC ′, and FIG. 13B is a diagram illustrating a state in which a gradation value different from the gradation value for which the correction value ΔC ′ is calculated is corrected. So far, in order to suppress density unevenness, the gradation value indicated by the pixel data (256-gradation YMCK data) has been corrected by the correction value H and the correction value ΔC, but this is not restrictive. For example, the dot occurrence rate determined by the gradation value indicated by the pixel data may be corrected by the correction value H ′ or the correction value ΔC ′ for each row region. In the graph, the horizontal axis indicates the dot occurrence rate, and the vertical axis indicates the gradation value (pixel data). Assume that the printer driver stores a dot occurrence rate table represented by such a graph in the memory of the computer 50. When the printer driver receives the image data, it performs resolution conversion processing and color conversion processing, collates 256 gradation YMCK data with the dot generation rate table, and determines the dot generation rate. Based on the dot generation rate, the printer driver converts data of 256 gradations into data that can be printed by the printer 1 (halftone process). In the modification, in order to suppress the density unevenness, the dot occurrence rate is corrected by the correction value H ′ for each row region, and the correction value H ′ is set by the correction value ΔC ′ for each head 31 according to the secular change and the environmental change. Correct it.

  A method of calculating the modification value ΔC ′ according to the modification will be described below. As in the above-described embodiment, the correction value calculation program first corrects the dot occurrence rate with the correction value H ′ for each row region, causes the printer 1 to print the correction pattern shown in FIG. Is read by the scanner, and the read gradation value for each head 31 is acquired. The graph in the figure shows the reading result (reading gradation value) of a band-shaped pattern having a certain density in a nozzle row having the first head 31 (1). The correction value calculation program calculates the difference “ΔY” between the average reading gradation value of each head 31 and the reading gradation value of the first head 31 (1). As shown in FIG. 13A, since the strip pattern of the first head 31 (1) is printed lighter than the strip patterns of the other heads 31, the dot generation rate is higher than the dot generation rate D1 corresponding to the average value. There is a need. That is, the first head 31 (1) performs printing based on the dot occurrence rate D2 corresponding to the target gradation value obtained by adding the difference “ΔY” between the average value and the read gradation value to the average value. An image having the same density as the other heads 31 can be printed, and density unevenness can be suppressed.

  Then, the correction value calculation program calculates “the difference ΔC ′ between the dot occurrence rate D1 corresponding to the average value and the dot occurrence rate D2 corresponding to the target gradation value” as the correction value ΔC ′ and stores it in the memory of the computer 50. Remember. In actual printing, the correction value H ′ is corrected by adding the correction value H ′ to the correction value H ′ for each row region, and the correction value H is corrected to the dot occurrence rate D3 corresponding to the gradation value X indicated by the print data. 'Is added (D4 = D3 + H' + ΔC '). In this way, the first head 31 (1) performs printing based on the corrected dot occurrence rate D4, whereby density unevenness can be suppressed. Also in this modified example, first, a correction value H ′ for the dot occurrence rate for each row region is calculated, and thereafter, a correction value ΔC ′ of the correction value H ′ is calculated for each head 31 in accordance with aging and environmental changes. . By doing so, the correction value H ′ for each row region can be easily corrected in order to suppress density unevenness due to secular change or environmental change.

<Second modification method>
FIG. 14 is a diagram showing a correction pattern printed by the second correction method. For the sake of explanation, the number of heads 31 is reduced. In the first correction method described above, correction for each head 31 is performed based on a correction pattern (FIG. 11A) having the same shape as the test pattern (FIG. 6A) printed when calculating the density unevenness correction value H for each row region. The value ΔC is calculated. That is, in the first correction method, for each nozzle row, a correction pattern composed of three belt-like patterns is formed based on the three command gradation values Sa, Sb, and Sc. On the other hand, in the second correction method, for each nozzle row, a correction pattern composed of one band pattern (for example, a band pattern having a density of 50%) based on one command gradation value (for example, Sb). A pattern, that is, a correction pattern having a uniform density is formed. That is, in the second correction method, a correction pattern is formed based on a smaller number of command gradation values than the three command gradation values on which the test pattern for calculating the correction value H is formed. A correction value ΔC is calculated. When the printer 1 prints the correction pattern, the correction value H for each row area is used for printing.

  The correction value calculation program causes the scanner to read a correction pattern (FIG. 14) having a uniform density, and acquires a read gradation value for each head 31. That is, the correction pattern is read by the scanner, and a reading gradation value smaller than the correction value H for each row region is acquired. Therefore, as compared with the case where the correction value H is calculated, the scanner can read the correction pattern faster by calculating the correction value ΔC for each head 31. Further, it is possible to obtain the read gradation value necessary for the correction value ΔC from the correction pattern without using a high-resolution scanner. Further, in this second correction method, since the number of band-like patterns is smaller than in the first correction method, the number of read gradation values acquired by the scanner from the correction pattern is reduced, and the scanner reads the correction pattern earlier. be able to. Note that the correction pattern is not limited to the correction pattern including one band pattern, and may be a correction pattern including two band patterns smaller than the three band patterns forming the test pattern.

  When the read gradation value for each head 31 is obtained from the correction pattern of uniform density, the correction value ΔC is calculated as in the first embodiment. Briefly, the correction value calculation program calculates a target value (for example, Cbt ′) as shown in FIG. 11C. Then, a target gradation value (for example, Sbt ') for a command gradation value (for example, Sb) on which a correction pattern is printed for each head 31 is calculated, and a correction value ΔC is calculated based on the target gradation value. Since the correction value ΔC is calculated for each head 31, the processing becomes easier than calculating the correction value H for each row region. In the first correction method, the correction value ΔC for three command gradation values (Sa, Sb, Sc) is calculated, whereas in the second correction method, the correction value ΔC for one command gradation value (Sb). Since the number of correction values ΔC to be calculated is small, the processing is further facilitated.

However, with only one correction value ΔC for one command gradation value, as in the first correction method, based on the three correction values ΔCa, ΔCb, ΔCc for the three command gradation values Sa, Sb, Sc, The correction value ΔC corresponding to each gradation value (0 to 255) cannot be calculated by linear interpolation. That is, in the second correction method, the correction value H changes according to the gradation value (S_in) indicated by the pixel data as shown in FIG. 10, but the correction value ΔC is changed to the gradation value (S_in) indicated by the pixel data. Therefore, the common correction value ΔC is corrected by adding it to the three correction values H for the three command gradation values. As shown in the following equation, the corrected gradation value S_out may be calculated.
S_out = S_in × (1 + H + ΔC)

If the same correction value ΔC is used for all gradation values (S_in) as in the above equation, the calculation process of the corrected gradation value S_out becomes easy, but a low gradation value (near 0) or a high value is possible. The difference disappears in the gradation value (near 255). Therefore, as shown in the following equation, the ratio between the gradation value “Sbt = Sb × (1 + H)” used when the correction pattern is printed and the new target gradation value “Sbt ′ = Sb × (1 + H + ΔC)” Thus, a corrected gradation value S_out for another gradation value S_in may be calculated.
S_out = S_in × {1 + H + (Sbt ′ / Sbt)}

  In summary, in the second correction method, one correction value ΔC for one command gradation value is calculated for each head 31 based on a correction pattern of uniform density. Therefore, the correction process of the correction value H using the correction value ΔC is easier than the process of recalculating the correction value H for the three command gradation values for each row region. Then, the density unevenness due to the characteristic difference for each nozzle can be suppressed by the correction value H for each row region, and the density unevenness due to secular change or environmental change can be suppressed by the correction value ΔC for each head 31. That is, according to the correction value ΔC calculated for each head 31 from the correction pattern of uniform density, the correction value H for suppressing density unevenness due to secular change or environmental change can be easily corrected.

<Third modification method>
FIG. 15 is a diagram showing a correction pattern in the third correction method. In the first and second correction methods described above, a correction pattern is formed for each nozzle row, and a correction value ΔC for each nozzle row is calculated. On the other hand, in the third correction method, one correction pattern is formed by one nozzle row of the four nozzle rows YMCA of the printer 1. Then, the correction value calculation program acquires the read gradation value for each head 31 from the correction pattern formed by one nozzle row, and the correction value for each head 31 regarding the nozzle row in which the correction pattern is formed. ΔC is calculated. Therefore, the number of read gradation values acquired from the correction pattern is smaller than the number of read gradation values acquired from the test pattern in order to calculate the correction value H for each row region for each nozzle row YMCK. In other words, the read gradation values smaller than the number of correction values H are acquired from the correction pattern. The calculation method of the correction value ΔC is the same as the first correction method described above.

  Then, the correction value ΔC of the nozzle row in which the correction pattern is formed is applied not only to the nozzle row but also to the density correction processing of print data assigned to other nozzle rows. For example, a correction pattern is formed in the black nozzle row K of the first head 31 (1), and the correction value ΔC obtained from the correction pattern is applied to the cyan nozzle row C of the first head 31 (1). This also applies to the assigned print data. As described above, a difference in ink ejection characteristics due to aging and environmental changes is likely to occur for each head 31. Therefore, if the nozzle rows belong to the same head 31, uneven density due to secular change or environmental change can be suppressed with the same correction value ΔC. By doing so, the calculation process of the correction value ΔC becomes easier than the process of calculating the correction value H for each nozzle row and each row region. That is, according to the third correction method, it is possible to facilitate the process of correcting the correction value H in order to suppress density unevenness due to secular change or environmental change.

  Further, in the third correction method, the correction value ΔC is calculated in comparison with the first correction method and the second correction method in which a correction pattern is formed for each nozzle row and the correction value ΔC is calculated for each nozzle row. Becomes even easier. However, since the ink supply path and the like differ depending on the nozzle row, density unevenness can be further suppressed by calculating the correction value ΔC for each nozzle row.

  In FIG. 15, a correction pattern having a uniform density is formed in one nozzle row and one correction value ΔC for one command gradation value is calculated. However, the present invention is not limited to this. For example, a correction pattern composed of three belt-like patterns may be printed by one nozzle row as in the first correction method.

<Fourth modification method>
FIG. 16A shows the result of reading a cyan test pattern to calculate the uneven density correction value H, and FIG. 16B shows the result of reading a cyan correction pattern to calculate the correction value ΔC. The plotted points in the figure are the reading results. The density unevenness correction value H is calculated as the correction value H for the number of row regions (180 nozzles × n heads) for each nozzle row. On the other hand, in order to easily correct the density unevenness correction value H according to the secular change and the environmental change, the correction value ΔC for each head 31 is calculated in the first to third correction methods. In the fourth correction method, not only the heads 31 but also the reading results of a plurality of row areas are acquired as one reading gradation value (corresponding to the reading gradation values corresponding to some row areas). In other words, a smaller number of read gradation values than the correction value H for each row region is acquired from the correction pattern.

  The correction value calculation program first causes the printer 1 to print a correction pattern reflecting the correction value H for each row area, as in the correction pattern (FIG. 11B) of the first correction method. Then, the correction pattern is read by the scanner at a reading resolution lower than the reading resolution in the paper width direction when the density unevenness correction value H test pattern (FIG. 6) is read by the scanner. As shown in FIG. 16A, when the test pattern is read by the scanner in order to calculate the correction value H for each row region, the read gradation value for each row region is acquired. Therefore, the reading resolution in the paper width direction is “row area interval = nozzle pitch = 360 dpi”. On the other hand, as shown in FIG. 16B, since the reading results of the four row regions are acquired as one reading gradation value, the reading resolution in the paper width direction when the correction pattern is read by the scanner is “90 dpi”. Become. Note that the number of reading gradation values to be acquired is not limited to every four row regions.

  As a result, in the test pattern reading result (FIG. 16A), one reading gradation value is obtained for each row region. On the other hand, in the reading result of the correction pattern (FIG. 16B), one reading gradation value is obtained for the four row regions. Thus, by reducing the reading resolution in the paper width direction of the scanner, the scanner can read the correction pattern quickly. Further, the density unevenness correction value H can be corrected even for a user who does not have a high-resolution scanner.

  In this way, the correction value H for each row region is corrected based on the read gradation values obtained discretely for each of the four row regions. For example, when the reading results of the first to fourth row regions are acquired as one reading gradation (a point indicated by “1-4” in FIG. 16B), each correction value H of the first to fourth row regions is acquired. May be corrected with a correction value ΔC calculated based on the same reading gradation value. The correction value ΔC calculation method and the correction value H correction method based on the correction value ΔC are the same as the first correction method. By doing so, the number of data to be calculated is smaller when the correction value ΔC of every plurality of column regions is calculated than when the correction value H for each column region is calculated. In other words, rather than recalculating the correction value H for each row region, it is better to correct the correction value for each row region with the correction value ΔC calculated based on the read gradation value of every other row region. Concentration unevenness can be easily suppressed.

  Further, the correction value ΔC calculated based on the read gradation value for each of the four row regions is not limited to being used as it is for the correction of the correction value H of the four row regions. For example, even if the ninth to twelfth row regions are acquired as one read gradation value (a point indicated as “9-12” in FIG. 16B), the ninth row region is read from the fifth to eighth row regions. The gradation value “5-8” is affected, and the twelfth row area affects the read gradation value “13-16” of the 13th to 16th row areas. Therefore, the result of the read gradation value (corresponding to the read gradation value corresponding to a part of the row areas) obtained for each of the four row areas is interpolated, and the correction value H for each row area based on the interpolated data. May be modified. As shown in FIG. 16B, the correction value calculation program may interpolate the result of the read gradation value obtained discretely for each of the four row regions with an approximate curve or the like. The points plotted on the graph in the figure are measurement results, and the dotted lines are approximate curves. By doing so, the number of read gradation values acquired by causing the scanner to read the correction pattern is smaller than the number of correction values H for each row region.

  With this approximate curve, for example, the read gradation value ΔC (9) of the ninth row region is read from the read gradation value “5-8” of the fifth to eighth row regions and the reading of the ninth to twelfth row regions. Prediction can be made based on the gradation value “9-12”. Then, the average value of discrete reading gradation values (Cbt in the figure) is set as a target value, and the reading gradation value (the reading gradation value predicted by the actual reading gradation value and the approximate curve) of each row region is obtained. A correction value ΔC corresponding to each row region is calculated so as to be constant.

  As described above, in the fourth correction method, the read gradation value corresponding to a part of the plurality of column regions constituting the correction pattern (that is, the plurality of column regions are acquired as one column region). Reading gradation value) is acquired, and the correction value of each column region (pixel column) is corrected based on the data obtained by interpolating the reading gradation values of some column regions. As a result, the number of data read by the scanner can be reduced, and it is easier to correct the correction value H with the correction value ΔC than to recalculate the density unevenness correction value H. In actual printing, when the printer driver creates print data, the tone value indicated by the pixel data is corrected based on the correction value H obtained by correcting the correction value H by adding the correction value ΔC. To do. Therefore, the density unevenness due to the characteristic difference for each nozzle is suppressed by the correction value H for each row region. Therefore, even if the correction value ΔC for suppressing the density unevenness due to the secular change or the environmental change is calculated based on the data obtained by interpolating the read gradation values of every other row region, the density unevenness can be suppressed without any problem.

  FIG. 17 is a diagram showing a graph obtained by interpolating the correction value ΔC calculated discretely with an approximate curve or the like. The horizontal axis indicates the row area number, and the vertical axis indicates the correction value ΔC. As shown in FIG. 16B described above, the correction value ΔC for each of the four row regions may be calculated based on the read gradation value that is discretely calculated for each of the four row regions. Then, the correction value ΔC calculated for each column region may be calculated by interpolating the correction value ΔC calculated discretely with an approximate curve or the like. For example, as shown in the drawing, the correction value ΔC (6) of the correction value H of the sixth row region is changed from the correction value ΔC (1-4) based on the read gradation value of the first to fourth row regions to 5−5. The correction value ΔC (5-8) based on the read gradation value of the eighth row region may be calculated based on the interpolated data. By doing so, since the number of correction values ΔC to be calculated is smaller than the number of correction values H for each row region, not only the process of acquiring the read gradation value from the correction pattern, but also the correction value ΔC is calculated. This process is also easier than the correction value H calculation process.

  Here, it is assumed that the read gradation value for each of the four row regions is acquired, and the correction value ΔC is calculated regardless of the head 31, but as described above, the density unevenness due to secular change or environmental change is as follows. It tends to occur with the head 31. Therefore, if the correction value ΔC of the row region to which the boundary of the head 31 is assigned is calculated based on the data obtained by interpolating the reading gradation value of the adjacent head 31, the effect of suppressing density unevenness may be reduced. Therefore, the density unevenness can be further suppressed by dividing the head 31 for each group (each group) and calculating the correction value ΔC based on the result of the discrete read gradation value.

  In addition, the correction pattern is not limited to the three strip patterns as shown in FIG. 11A, but may be a correction pattern having a uniform density as shown in FIG. Further, the correction value ΔC calculated from the correction pattern formed by a certain nozzle row may be applied to the density correction processing of other nozzle rows without calculating the correction value ΔC for each nozzle row.

=== Other Embodiments ===
Each of the above embodiments is described mainly for a printing system having an ink jet printer, but includes disclosure of a density unevenness correction method and the like. The above-described embodiments are for facilitating understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<Calculation of correction value for each group>
In the first correction method to the third correction method described above, density unevenness occurs for each head 31 due to secular change or environmental change. Therefore, the correction value ΔC is calculated for each head 31, but the present invention is not limited to this. For example, in the head 31 in which the nozzle rows are long in the paper width direction, when the ink supply path is divided into a plurality of parts and the common ink chamber is also divided into a plurality of parts, the density is increased for each ink supply path in accordance with aging and environmental changes. Unevenness occurs. Therefore, it is preferable to correct the density unevenness correction value H with the correction value ΔC for each group, with the row region formed by the nozzles that are the common ink supply path as one group. That is, the correction value for each row region is divided into groups, and a correction value ΔC for correcting the correction value H based on the read gradation value of the correction pattern is calculated for each group. By doing so, it is possible to easily correct the density unevenness correction value H.

<About serial printers>
In the above-described embodiment, a line head printer in which heads are arranged in the paper width direction intersecting the medium conveyance direction is described as an example. For example, a serial type that alternately performs an image forming operation for forming an image while moving a head unit 30 to which one or a plurality of heads are attached in a moving direction that intersects the conveying direction of the medium, and a conveying operation that conveys the medium. In this printer, the correction value H may be corrected by the above-described correction method in order to suppress density unevenness due to secular change or environmental change.

<About liquid ejecting device>
In the above-described embodiment, the ink jet printer is exemplified as the liquid ejecting apparatus (part) for performing the liquid ejecting method, but the present invention is not limited thereto. The liquid ejecting apparatus can be applied to various industrial apparatuses, not a printer (printing apparatus). For example, a textile printing apparatus for applying a pattern to a fabric, a display manufacturing apparatus such as a color filter manufacturing apparatus or an organic EL display, a DNA chip manufacturing apparatus for manufacturing a DNA chip by applying a solution in which DNA is dissolved to a chip, and the like. Also, the present invention can be applied.

  The liquid ejection method may be a piezo method that ejects liquid by applying a voltage to the drive element (piezo element) to expand and contract the ink chamber, or generates bubbles in the nozzle using a heating element. It is also possible to use a thermal method in which liquid is ejected by the bubbles.

  In the above-described embodiment, since the printer driver installed in the computer 50 corrects the gradation value indicated by the pixel by the correction value, the printing system in which the printer 1 and the computer 50 are connected corresponds to the liquid ejecting apparatus. Further, when the controller 10 in the printer 1 corrects the gradation value indicated by the pixel with the correction value, the printer 1 corresponds to a liquid ejecting apparatus.

1 is an overall configuration block diagram of a printer. FIG. 2A is a cross-sectional view of the printer, and FIG. 2B is a diagram illustrating a state in which paper is conveyed. FIG. 3A shows the nozzle arrangement of the head unit, and FIG. 3B shows the nozzle peripheral members. FIG. 4A shows ideal dot formation, FIG. 4B shows a state when density unevenness occurs, and FIG. 4C shows a state when dots are formed by the printing method of the present embodiment. It is a flow of a correction value calculation process. FIG. 6A is a diagram showing a test pattern, and FIG. 6B is a diagram showing a correction pattern. It is a figure which shows the reading result of the pattern for cyan correction. FIG. 8A is a calculation method of a target gradation value of a reading result lower than the target gradation value, and FIG. 8B is a diagram illustrating a calculation method of a target gradation value of a reading result higher than the target gradation value. . It is a correction value table regarding a cyan nozzle row. It is a figure which shows the case where the gradation value before correction | amendment differs from a command gradation value. It is a calculation flow of a correction value. It is a figure which shows the measurement point of the pattern for correction. It is a figure which shows the reading result of the pattern for correction. FIG. 12A is a diagram showing the target gradation value with respect to the command gradation value, and FIG. 12B is a correction value table for the cyan nozzle row C. FIG. 13A is a diagram illustrating another method for calculating a correction value, and FIG. 13B is a diagram illustrating a state in which a gradation value different from the gradation value for which the correction value is calculated is corrected. It is a figure which shows the pattern for a correction printed with the 2nd correction method. It is a figure which shows the pattern for a correction | amendment in the 3rd correction method. FIG. 16A shows the result of reading the test pattern, and FIG. 16B shows the result of reading the correction pattern. It is a figure which shows the graph which interpolated the correction value calculated discretely.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer, 10 Controller, 11 interface part, 12 CPU, 13 Memory, 14 Unit control circuit, 20 Conveyance unit, 21A Conveyance roller, 21B Conveyance roller, 22 Conveyance belt, 23 Feeding roller, 30 Head unit, 31 Head, 312 Flow path unit, 312a flow path forming plate, 312b elastic plate, 312c nozzle plate, 312d pressure chamber, 312e nozzle communication port, 312f common ink chamber, 312g ink supply path, 312h support frame, 312i elastic film, 313 ink supply pipe, 40 detector groups, 50 computers

Claims (7)

A nozzle row in which nozzles for ejecting liquid are arranged in a predetermined direction;
A moving mechanism for moving the nozzle array and the medium in a direction crossing the predetermined direction;
A control unit that corrects gradation values indicated by pixels belonging to each of the pixel columns based on correction values of the pixel columns arranged in a direction corresponding to the intersecting direction on the print data;
A correction method of the correction value of the liquid ejecting apparatus having
Forming a correction pattern by the nozzle rows;
Causing the measuring device to read the correction pattern, and obtaining a reading gradation value that is smaller than the number of correction values;
Correcting the correction value based on the read gradation value;
A correction method comprising: The correction method according to claim 1,
The correction value is divided into a plurality of groups,
For each group, calculate a correction value for correcting the correction value based on the read gradation value,
How to fix. The correction method according to claim 1 or 2, wherein
The liquid ejecting apparatus has a plurality of heads having the nozzle row,
For each of the heads, a correction value for correcting the correction value based on the read gradation value is calculated.
How to fix. The correction method according to claim 1,
Forming the correction pattern based on the plurality of pixel columns;
Obtaining the read gradation value corresponding to a part of the plurality of column regions on the correction pattern corresponding to the plurality of pixel columns;
Correcting the correction values of the pixel columns corresponding to the respective column regions based on data obtained by interpolating the read gradation values corresponding to some of the column regions;
How to fix. It is the correction method as described in any one of Claims 1-4, Comprising:
The control unit corrects the gradation value indicated by the pixel based on the correction value for each of the pixel columns with respect to a plurality of instruction gradation values,
Forming the correction pattern based on a smaller number of command gradation values than the plurality of command gradation values;
Correcting the correction values for the plurality of command gradation values based on the read gradation values of the correction pattern;
How to fix. A correction method according to any one of claims 1 to 5, comprising:
The liquid ejecting apparatus includes a head having a plurality of the nozzle rows,
The correction pattern is formed by the nozzle row of the plurality of nozzle rows,
Correcting the correction values of the pixel rows respectively assigned to the plurality of nozzle rows of the head based on the read gradation values of the correction pattern;
How to fix. (1) a nozzle row in which nozzles for ejecting liquid are arranged in a predetermined direction;
(2) a moving mechanism that moves the nozzle array and the medium in a direction intersecting the predetermined direction;
(3) A control unit that corrects a gradation value indicated by a pixel belonging to each pixel column based on a correction value for each pixel column arranged in a direction corresponding to the intersecting direction on the print data,
A correction pattern is formed by the nozzle row, and the correction pattern is read by a measuring device to obtain a reading gradation value smaller than the number of correction values, and based on the reading gradation value A control unit for correcting the correction value;
A liquid ejecting apparatus.