JP2010234613A - Print control apparatus and print control program - Google Patents

Abstract

A printing control apparatus and a printing control program capable of suppressing banding of an image are provided.
According to the printing process of the present embodiment, one of three types of dots is determined for K dots constituting a grayscale image. On the other hand, C, M, and Y dots that are chromatic colors are easily formed as large dots, and are difficult to be formed as medium dots and small dots. In other words, C, M, and Y dots representing a gray scale image can be represented by relatively large dots. By expressing a grayscale image using C, M, and Y dots, the landing position varies more than in the case where an image is composed of only K-colored dots, a banding suppression effect is obtained, and it is relatively easy to blur. By using a large number of size dots, a further banding suppression effect can be obtained.
[Selection] Figure 5

Description

  The present invention relates to a print control apparatus and a print control program.

  2. Related Art Inkjet printers that print images by ejecting ink droplets from nozzles formed on a head to form dots on recording paper are known. In such an ink jet printer, when a chromatic ink of cyan, magenta, and yellow and an achromatic black ink are used, a full color image can be printed. The gray color can be expressed by black ink, but can also be expressed by a combination of cyan, magenta, and yellow. Therefore, in Patent Document 1, when the input luminance data is gray data, A color image printing apparatus that prints an image using inks of all colors such as cyan, magenta, yellow, and black is disclosed.

JP-A-6-2025203

  However, in the above-described ink jet printer, if the ink droplet landing position deviates from the target point due to an ink head mounting error during manufacture, a defect called banding occurs in the image recorded on the recording paper. There was a problem that the image quality was lowered. Banding is a streak (a white portion of the recording paper) that occurs in a portion where the distance between adjacent dots is large because the distance between adjacent dots is non-uniform.

  SUMMARY An advantage of some aspects of the invention is to provide a print control apparatus and a print control program that can suppress banding of an image.

  In order to achieve this object, the printing control apparatus according to claim 1 causes an inkjet printer capable of forming k types of dots having different sizes to perform printing, and causes the inkjet printer to perform printing. Print type determination means for determining whether an image is grayscale, and if it is determined that the image is grayscale, obtain image data representing a gray color using a combination of chromatic colors that can be used in the inkjet printer. By performing halftone processing for each color, the image data acquisition means, the achromatic color component value representing the achromatic color component of each pixel, and the chromatic color component value representing the chromatic color component included in the image data, Halftone processing means for determining the type of each dot constituting the grayscale image, Achromatic color processing means for determining any one of the k types of dots for each achromatic color dot constituting the gray scale image by converting the achromatic color component value into n values (however, n = K + 1), by converting the chromatic color component value to m-value, for each chromatic color dot constituting the grayscale image, predetermined (m-1) types out of the k types of dots Chromatic color processing means for determining any one of the dots (where k> m−1), and the (m−1) types of dots include the dots of the maximum size among the k types of dots, Does not include minimum size dots.

  According to a second aspect of the present invention, in the print control apparatus according to the first aspect, the chromatic color processing means further includes the chromatic color component value of each pixel not less than a predetermined threshold value for the chromatic color. A chromatic color component value determining means for determining whether there is a chromatic color component value that is less than the threshold value is converted into an n value by the halftone process, and a value indicating that the dot is not formed, or the k types of dots A light color processing means for converting to a value corresponding to the above, a chromatic color component value that is equal to or greater than the threshold value is converted to m value by the halftone process, and a value indicating that the dot is not formed, or the (m−1) types Dark color processing means for converting to a value corresponding to any one of the dots.

  According to a third aspect of the present invention, there is provided the print control apparatus according to the second aspect, wherein the shades prepared in advance as gray scale patch data expressing a gray color using the combination of the chromatic color component values are mutually different. A first type patch based on a result obtained by converting n-values of different types of patch data into n values by the halftone process, and a second type patch based on a result obtained by converting the m value by the halftone process into the ink jet printer. And patch setting means for setting each chromatic color component value of the patch data corresponding to the patch selected by the user among the plurality of types of patches as a threshold value for each chromatic color.

  The printing control program according to claim 4 is a program for causing an inkjet printer capable of forming k types of dots having different sizes to execute printing, and an image to be printed by the inkjet printer is in gray scale. A print type determining unit that determines whether or not, and an image data acquiring unit that acquires image data representing a gray color using a combination of chromatic colors that can be used in the ink jet printer when it is determined to be grayscale The grayscale image is obtained by halftoning the achromatic color component value representing the achromatic color component of each pixel and the chromatic color component value representing the chromatic color component included in the image data for each color. Causing the computer to function as a halftone processing means for determining the type of each dot to constitute, And an achromatic color processing means for determining any one of the k types of dots for each achromatic color dot constituting the gray scale image by converting the achromatic color component value into n values. (Where n = k + 1), by converting the chromatic color component value to m-value, for each chromatic color dot constituting the grayscale image, a predetermined (m -1) chromatic color processing means for determining one of the types of dots (where k> m−1), and the (m−1) types of dots are the largest of the k types of dots. Includes dots, not the smallest size dots.

  According to the printing control apparatus of the first aspect, since the achromatic color component value is converted to n-value, any one of k types of dots is determined for each achromatic color dot constituting the gray scale image. . On the other hand, since the chromatic color component value is converted to m-value, for each chromatic color dot constituting the gray scale image, any one of the (m−1) types of predetermined dots among the k types of dots. Is decided. The (m-1) types of dots include the maximum size of the k types of dots and do not include the minimum size of dots. Therefore, a chromatic color dot for expressing a gray color is easily formed as a maximum size dot, and is difficult to be formed as a minimum size dot. In other words, a chromatic color dot representing a gray scale image can be represented by a relatively large dot. Representing a grayscale image using chromatic color dots results in more landing positions, resulting in a banding suppression effect than the case where the image is composed of only single color dots, and there are many maximum size dots that are relatively easy to blur. By being used, there is an effect that a further banding suppression effect can be obtained.

  According to the print control device of claim 2, in addition to the effect produced by the print control device of claim 1, the chromatic color component value that is less than the threshold value is converted to an n-value, and a value indicating that dots are not formed, Since it is converted into a value corresponding to one of the k types of dots, the light gray color is composed of dots of various types and has the effect of reducing the graininess of the image. On the other hand, chromatic color component values that are equal to or greater than the threshold value are converted to m-values and converted to values that indicate that dots are not formed, or values that correspond to either (m−1) types of dots. The banding suppression effect can be obtained by using many dots of the maximum size that are relatively easy to blur. Of the image, the portion constituting the light gray color is more likely to have a lower granularity than the banding, whereas the portion constituting the dark gray color is more likely to cause the banding than the graininess.

  According to the print control apparatus of the third aspect, in addition to the effect produced by the print control apparatus of the second aspect, the first type based on the result of n-leveling a plurality of types of patch data having different shades by halftone processing Each chromatic color component value of the patch data corresponding to the patch selected by the user is set as a threshold value of each chromatic color among the patch of the patch and the second type patch based on the m-value obtained by the halftone process. Therefore, there is an effect that an appropriate threshold value can be set based on the result of viewing the patch. That is, since the first type patch is composed of dots of various sizes, the graininess is suppressed, but banding tends to be a problem in a dark color patch. On the other hand, since the second type patch uses a large number of dots of the maximum size, banding is suppressed, but graininess tends to be a problem in a light color patch. Therefore, the user visually recognizes the first type patch and the second type patch, and selects a patch in which both the graininess and the banding are suppressed. In this way, it is possible to determine as a threshold value a value that does not significantly reduce the image quality even if the chromatic color component value is n-valued or m-valued.

  According to the print control program of the fourth aspect, the same operational effects as the print control apparatus according to the first aspect can be obtained.

1 is a partial cross-sectional view of a printer equipped with a control unit according to an embodiment of the present invention. (A) is a bottom view of the ink head showing the ink ejection surface, (b) is an enlarged view showing the nozzle unit, and (c) is a diagram for explaining the rules of arrangement of nozzles in the nozzle unit. is there. It is a figure which shows the relationship between the attachment angle of an ink head, and the dot row formed. FIG. 2 is a block diagram schematically illustrating an electrical configuration of a printer. 6 is a flowchart illustrating print processing executed by a control unit of a printer. It is a graph showing the relationship memorize | stored in a GCR table. 6 is a flowchart illustrating threshold determination processing executed by a control unit of a printer. It is a figure which shows an example of a threshold determination chart image.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a partial cross-sectional view of a printer 1 equipped with a control unit 10 which is an embodiment of a print control apparatus of the present invention. The printer 1 is a line head type ink jet printer, and is configured to print an image on which banding is suppressed on a recording paper P.

  As shown in FIG. 1, the printer 1 includes an ink head 2 provided for each ink color, and a transport mechanism 21 that transports the recording paper P to the ink head 2. The recording paper P stacked on the paper supply unit 30 is transported along the transport direction A indicated by the arrow in FIG. 1 inside the printer 1, and after a desired image is printed, it is discharged to the paper discharge unit 90. It is comprised so that.

  The paper feed unit 30 includes a paper feed tray 31 that can store a plurality of recording papers P and a paper feed roller 32. The paper feed roller 32 feeds the uppermost recording paper P among the plurality of recording papers P stacked and stored in the paper feed tray 31 to the transport mechanism 21 one by one.

  Two pairs of feed rollers 33a, 33b, 34a, and 34b are disposed along the transport path of the recording paper P between the paper feed unit 30 and the transport mechanism 21. The recording paper P sent out from the paper supply unit 30 is sent out to the transport mechanism 21 while being guided by the feed roller pairs 33a, 33b, 34a, 34b.

  The transport mechanism 21 includes an endless transport belt 8 and two belt rollers 6 and 7. The conveyor belt 8 is wound around belt rollers 6 and 7. A conveyor motor 22 (FIG. 4) is connected to the belt roller 7, and the belt roller 7 rotates in the direction of arrow B in FIG. At this time, the transport belt 8 travels so as to transport the recording paper P in the transport direction A, and the belt roller 6 that is a driven roller also rotates.

  A nip roller 4 is disposed at a position facing the belt roller 6 with the conveying belt 8 interposed therebetween. The nip roller 4 presses the recording paper P sent from the paper feeding unit 30 against the outer peripheral surface 8 a of the conveying belt 8 and holds the entire recording sheet P on the outer peripheral surface 8 a of the conveying belt 8. The recording paper P on the transport belt 8 is transported to the ink head 2.

  The ink head 2 is provided for each of the four ink colors C, M, Y, and K (cyan, magenta, yellow, and black), and extends along the width direction of the transport belt 8 to each frame frame. 3 is provided in the conveyance direction A of the recording paper P. Each ink head 2 is connected to the ink reservoir 60 via a tube. The ink storage unit 60 is provided with ink cartridges 61 that individually store four inks. Each ink head 2 is supplied with a corresponding color ink.

  A substantially rectangular parallelepiped platen 19 is disposed in the loop of the conveyor belt 8 facing the ink ejection surfaces 2 a of the four ink heads 2. The upper surface of the platen 19 is in contact with the inner peripheral surface of the transport belt 8 and supports the transport belt 8 from the inner peripheral side.

  An image is formed on the recording paper P as the recording paper P held on the transport belt 8 passes through the four ink heads 2 in order. When passing through each ink head 2, the ink droplets ejected from the nozzles 2 c (FIG. 2) formed on the ink ejection surface 2 a of each ink head 2 are landed on the recording paper P as dots, thereby conveying direction A One row of dots is formed with the direction orthogonal to the longitudinal direction as the longitudinal direction. Then, the conveyance of one row by the conveyance belt 8 and the formation of one dot row by each ink head 2 are repeated to form a large number of dot rows in the conveyance direction A of the recording paper P. Print the image. The recording paper P on which the image is printed is further conveyed downstream by the conveyance mechanism 21.

  A spur roller 5 is disposed above the belt roller 7. The recording paper P transported by the transport mechanism 21 is sandwiched between the spur roller 5 and the transport belt 8, so that further transport force is applied and discharged from the transport mechanism 21. The recording paper P that has been transported in the transport direction A by the transport mechanism 21 is peeled off from the outer peripheral surface 8 a by a peeling member (not shown) and then transported to the discharge mechanism 90. The discharge mechanism 90 conveys the recording paper P conveyed between the pair of guides 91a and 91b upward by two pairs of feed rollers 92a, 92b, 93a, and 93b, and discharges it.

  FIG. 2A is a bottom view of the ink head 2 showing the ink discharge surface 2a. As shown in FIG. 2A, each ink head 2 has a long configuration, and trapezoidal nozzle units 2 b are arranged in a line in the longitudinal direction of each ink head 2. In the following description, the longitudinal direction of the ink head 2 is referred to as the X direction, and the direction orthogonal to the X direction is referred to as the Y direction. Ideally, the ink head 2 is attached to the frame 3 of the frame so that the X direction is perpendicular to the conveyance direction A (FIG. 1) of the recording paper P.

  FIG. 2B is an enlarged view showing the nozzle unit 2b, and FIG. 2C is a diagram for explaining the arrangement rules of the nozzles 2c in the nozzle unit 2b. As shown in FIGS. 2B and 2C, a number of nozzles 2c are formed in the nozzle unit 2b. The ink head 2 of this embodiment is a piezo-type ink head in which the amount of ink droplets ejected from each nozzle 2c can be adjusted by voltage control of a piezoelectric actuator (not shown). In this embodiment, each nozzle 2c Therefore, it is assumed that three types of dots (large dots, medium dots, and small dots) having different sizes can be formed on the recording paper P.

  The multiple nozzles 2c are provided such that the nozzle interval in the X direction is a constant distance (x in the example shown in FIG. 2C). On the other hand, the Y direction position of each nozzle 2c is provided unevenly. Therefore, when ink is ejected from all the nozzles 2c provided in the ink head 2 at the same timing, the positions of the dots formed on the recording paper P in the transport direction A vary. In other words, a single dot row cannot be formed. Therefore, in the present embodiment, the control unit 10 controls the ink ejection timing of each nozzle 2c according to the position of each nozzle 2c in the Y direction, so that the direction perpendicular to the transport direction A on the recording paper P is elongated. A dot row 40 (FIG. 3) having a direction can be formed. That is, among the nozzles 2c, the nozzles 2c located on the upstream side in the transport direction A are ejected with ink droplets earlier to form dots, and the recording paper P on which the dots are formed is downstream of the transport direction A. After the ink is transported to the position immediately below the nozzle 2c positioned at the position, the ink droplets are ejected from the nozzle 2c, so that a single dot row 40 perpendicular to the transport direction A is formed on the recording paper P.

  Further, in the ink head 2 of the present embodiment, the positions in the Y direction of the respective nozzles 2c are arranged so as to be alternately switched between the upstream side and the downstream side in the transport direction A. More specifically, the (k + 1) th nozzle 2c (k + 1) is located upstream of the kth nozzle 2c (k) in the transport direction A (the upper side in the drawing in the example shown in FIG. 2 (c)). In this case, the (k + 1) th nozzle 2c (k + 1) is located downstream of the (k + 2) th nozzle 2c (k + 2) in the transport direction A (in the example shown in FIG. 2 (c), the lower side in the drawing).

  That is, the k + 1th nozzle with respect to the kth nozzle 2c (k) using a Y-coordinate where one point in the Y direction is the origin, the upstream side in the transport direction A is positive, and the downstream side in the transport direction A is negative. When a change in the position in the Y direction of 2c (k + 1) is represented, it is assumed that the direction of the change (y (k) in the example shown in FIG. 2C) is positive. In that case, the Y direction position of each nozzle 2c is determined so that the change direction of the position of the k + 2nd nozzle 2c (k + 2) in the Y direction with respect to the (k + 1) th nozzle 2c (k + 1) is negative. ing. In other words, when all the changes in the position in the Y direction between the pair of nozzles 2c adjacent in the X direction in the ink head 2 are obtained, the nozzles 2c are provided so that the direction of the change is alternate.

  By arranging the nozzles 2c in this way, it is easy to form a flow path for supplying ink to each nozzle 2b individually. In the nozzle unit 2b, a large number of nozzles 2c are formed at a high density. However, if all the nozzles 2c are illustrated, the drawing becomes complicated, and therefore the nozzles 2c are schematically illustrated in FIG. ing.

  FIG. 3 is a diagram showing the relationship between the mounting angle of the ink head 2 and the dot rows to be formed. 3A shows an ideal mounting angle in which the X direction (longitudinal direction) of the ink head 2 is perpendicular to the transport direction A, and the ink head 2 is attached to the frame 3 (FIG. 1). FIG. 6 is a diagram showing a relationship between a state where the nozzles 2c are arranged in the ink head 2 and a dot row 40 formed by the ink head 2. For convenience of description, in the following description, the longitudinal direction of the dot row 40 is referred to as the B direction. This B direction is also a direction orthogonal to the transport direction A.

  As shown in FIG. 3A, when the ink head 2 is mounted at an ideal mounting angle, the X direction of the ink head 2 and the longitudinal direction (B direction) of the dot row 40 formed on the recording paper P Are parallel to each other, the distance between the dots in the dot row 40 is equal to the interval in the X direction of the nozzle 2c. Therefore, in the ink head 2, if the nozzles 2c are formed so that the interval in the X direction is constant, the dot interval in the dot row 40 formed on the recording paper P is the interval in the X direction of each nozzle 2c. Therefore, the problem of image banding is less likely to occur.

  On the other hand, FIG. 3B shows a state in which the ink head 2 is attached to the frame 3 in a state where the X direction of the ink head 2 is deviated from the direction perpendicular to the transport direction A due to an error in the attachment angle. FIG. 4 is a diagram showing the relationship between the arrangement of nozzles 2c in the ink head 2 and the dot rows 40 formed by the ink head 2. In this case, the X direction of the ink head 2 is inclined with respect to the longitudinal direction (B direction) of the dot row 40 formed on the recording paper P. Therefore, in the ink head 2, even if the interval between the nozzles 2 c in the X direction is constant, the distance between the dots constituting the dot row 40 becomes non-uniform, and the density of dots in the dot row 40 occurs.

  That is, since the ink head 2c is inclined with respect to the B direction, the distance between dots in the dot row 40 is the B direction component of the X direction distance (interval) of each nozzle 2c and the Y direction distance of each nozzle 2c. This corresponds to a value obtained by adding the B direction component. As described with reference to FIG. 2, the Y-direction positions of the nozzles 2 c are not uniform, and therefore the B-direction component of the Y-direction interval of each nozzle differs for each nozzle 2 c. In FIG. 3, the distance between the dots varies variously, and as shown in FIG.

  Such dot density appears in all the dot rows 40 formed by the same ink head 2. Therefore, when the distance between dots is large at a certain position of the dot row 40 and there is a gap between the dots, the gap between the dots is continuous with the conveyance direction A and becomes a streak (banding) extending in the conveyance direction A. May appear.

  Therefore, the printer 1 according to the present embodiment is configured to suppress image banding by forming an image using a large number of large dots that are relatively easy to blur when a predetermined condition is satisfied.

  FIG. 4 is a block diagram schematically showing the electrical configuration of the printer 1. As shown in FIG. 4, the printer 1 mainly includes a control unit 10, an interface 16, an ink head 2, and a carry motor 22.

  The control unit 10 includes a CPU 11, a ROM 12, a RAM 13, a flash memory 14, and an ASIC 15, which are connected to each other via a bus line. Further, the interface 16, the ink head 2, and the transport motor 22 are connected to each other via the ASIC 15.

  The CPU 11 controls each function of the printer 1 and controls each unit connected to the ASIC 15 according to fixed values and programs stored in the ROM 12 and the flash memory 14. The ROM 12 is a non-rewritable memory that stores a control program 12a executed by the printer 1, a lookup table 12b, a GCR table 12c, and the like. The control program 12a causes the CPU 11 to execute the processes shown in the flowcharts of FIGS. The look-up table 12b is a predetermined correspondence for converting the luminance value of each color of R (red), G (green), and B (blue) into component values of each color of C, M, Y, and K. It is a table that holds the relationship. The GCR table 12c is a table used in the GCR process in which a part of the K component value is replaced with the C, M, and Y component values. Details will be described later with reference to FIGS.

  The RAM 13 is a rewritable volatile memory, and is a memory for temporarily storing various data when each operation of the printer 1 is executed. The flash memory 14 is a rewritable nonvolatile memory and includes a binary / quaternary switching threshold memory 14a. When the binary / quaternary switching threshold memory 14a performs halftone processing on C component values, M component values, and Y component values that are chromatic color component values, each component value is binarized or quaternarized. This is a memory for storing a switching threshold value determined for each color and for each paper type in order to be assigned to any of the above. This switching threshold is determined by a threshold determination process described later with reference to FIG. 7, and is set in the binary / quaternary switching threshold memory 14a.

  FIG. 5 is a flowchart illustrating a printing process executed by the control unit 10 of the printer 1. This process is executed when image data to be printed is input from an external device such as a personal computer. Prior to the start of this processing, for example, in a personal computer, the user performs various types of operations such as grayscale printing or color printing, paper type of the recording paper P, etc. from the GUI (Graphical User Interface) of the printer driver. In the following description, it is assumed that the settings are input.

  First, the CPU 11 of the control unit 10 determines whether or not the image to be printed by the printer 1 is grayscale (S502). For example, when image data input from an external device is data that defines the brightness of each color of R, G, and B, which is the color system of the monitor, for each pixel, R brightness = G brightness = If the relationship of luminance of B is established, the determination in S502 is affirmed assuming that the image to be printed by the printer 1 is grayscale (S502: Yes). Alternatively, if the user who has instructed execution of printing sets grayscale printing, the image to be printed by the printer 1 is grayscale even if the relationship of R luminance = G luminance = B luminance is not established. As a result, the determination in S502 is affirmed (S502: Yes).

  When it is determined that the image is not grayscale (S502: No), the CPU 11 executes a normal color printing process (S505) and ends the process.

  On the other hand, if it is determined that the image is grayscale (S502: Yes), processing for converting the image data to be printed into image data for grayscale printing is performed. Specifically, first, the CPU 11 performs color conversion processing for converting the luminance values of R, G, and B colors for each pixel specified in the image data into component values of C, M, Y, and K colors. (S506) is executed. Since this process is a well-known process that is executed using a predetermined relationship in the lookup table 12b (FIG. 4), detailed description thereof is omitted.

  Next, based on the relationship stored in the GCR table 12c, the CPU 11 executes GCR processing for replacing a part of the K component values with the C, M, and Y component values (S508).

  FIG. 6 is a graph showing the relationship stored in the GCR table 12c. The graph shown in FIG. 6 shows the relationship between the input K component values (K input values) on the horizontal axis and the component values (output values of each color) output by GCR processing on the vertical axis. FIG. As shown in FIG. 6, according to the relationship stored in the GCR table 12c, the output K component value is 0 while the input K component value is between 0 and 128. That is, when the input K component value is 128 or less, a light gray color is expressed. Therefore, all K component values are replaced with chromatic component values, and K dots are not used, but only chromatic dots. It represents a gray color. As shown in FIG. 6, according to the relationship stored in the GCR table 12c, when the input K component value is 128 or less, each output chromatic color component value is the input K component value. As the gray color to be expressed becomes darker, the darker gray color can be expressed by using more chromatic dots.

  On the other hand, if the input K component value is greater than 128, the larger the input K component value, the greater the output K component value, and conversely, the C, M, Y component values are linear. Reduced to That is, when the K component value before GCR processing is greater than 128, a dark gray color is expressed. Therefore, by expressing the gray color using K dots, and expressing the gray color using K dots, The number of chromatic dots that become unnecessary is reduced.

  By using the relationship stored in the GCR table 12c, the image data after color conversion is subjected to GCR processing, so that image data expressing a gray color using a combination of C, M, and Y that are chromatic colors is used. Can be obtained.

  Returning to FIG. Next, calibration for correcting individual differences and changes with time of the printer 1 is executed (S510), and the total amount of ink to be processed so that the sum of the C, M, Y, and K component values does not exceed the specified value. A restriction process is performed (S512). Note that the calibration and the total ink amount restriction process are known processes, and thus detailed description thereof is omitted.

  In the processing after S514, each pixel included in the image data is extracted as a target pixel in order, and the C component value, the M component value, the Y component value, and the K component value of the target pixel are determined for each color. By performing halftone processing, the type of dot (large dot, medium dot, small dot) is determined for each color.

  First, the CPU 11 determines whether or not the C component value of the target pixel is greater than or equal to a predetermined switching threshold for C (S514). The switching threshold value is stored in advance in the binary / 4-value switching threshold memory 14a (FIG. 4). When the paper type is input by the user before the start of the printing process, the switching threshold corresponding to the input paper type is read from the binary / quaternary switching threshold memory 14a, and the C component value of the target pixel is read. Compare.

  When it is determined that the C component value is greater than or equal to the switching threshold (S514: Yes), the C component value is binarized by, for example, an error diffusion algorithm (S516). When the C component value before binarization processing is any value from 0 to 255, the component value is compared with, for example, a threshold value of 128, and if it is equal to or less than the threshold value, there is no dot (no dot is formed) If it is larger than the threshold value, it is converted into a large dot (a value indicating the formation of a large dot). That is, when the C component value is binarized, if dots are formed, only one type of large dot (an example of m-1 types) can be determined. The dot to be formed is not determined. When an error diffusion algorithm is employed in binarization processing, an error generated during binarization is distributed to surrounding pixels and the binarization processing of each pixel is performed after reflecting the error. Since the algorithm itself is a known algorithm, detailed description thereof is omitted.

  On the other hand, when it is determined that the C component value is less than the switching threshold value (S514: No), the C component value is quaternized by, for example, an error diffusion algorithm (S518). When the C component value before the quaternarization process is any value from 0 to 255, the component value is, for example, 64 as the first threshold, 128 as the second threshold, and the third threshold. Compared with a certain 192, if it is less than or equal to the first threshold, it is converted to no dot, and if it is greater than the first threshold and less than or equal to the second threshold, it is converted to a small dot (a value representing the formation of small dots) If it is larger than the third threshold value, it is converted into a medium dot (a value representing the formation of medium dots), and if it is larger than the third threshold value, it is converted into a large dot. That is, when the C component value is subjected to quaternarization processing, it is converted to a value corresponding to one of three types of dots (one example of k types) of no dots or large dots, medium dots, and small dots. . When the error diffusion algorithm is adopted in the quaternarization process, an error generated in the quaternization process is distributed to the peripheral pixels as in the case of the binarization process, but detailed description is omitted. .

  Next, the CPU 11 determines whether or not the M component value of the pixel of interest is greater than or equal to a predetermined switching threshold for M (S520). If it is determined that the M component value is greater than or equal to the switching threshold (S520: Yes), the M component value is binarized by, for example, an error diffusion algorithm (S522), and converted to either no dot or large dot. . Note that the specific content of the binarization processing for the M component value is the same as that for the binarization processing for the C component value (S516), and thus detailed description thereof is omitted.

  On the other hand, when it is determined that the M component value is less than the switching threshold (S520: No), the M component value is quaternized by, for example, an error diffusion algorithm (S524), and there is no dot, or there is no large dot or medium dot. , And converted into a value corresponding to one of three types of small dots (an example of k types). The specific content of the M component value quaternization process is the same as that of the C component value quaternization process (S518), and thus detailed description thereof is omitted.

  Next, the CPU 11 determines whether or not the Y component value of the target pixel is greater than or equal to a predetermined switching threshold for Y (S526). When it is determined that the Y component value is greater than or equal to the switching threshold (S526: Yes), the Y component value is binarized by, for example, an error diffusion algorithm (S528), and converted to either no dot or large dot. . Note that the specific content of the binarization processing of the Y component value is the same as that of the binarization processing of the C component value (S516), and thus detailed description thereof is omitted.

  On the other hand, when it is determined that the Y component value is less than the switching threshold (S526: No), the Y component value is quaternized by, for example, an error diffusion algorithm (S530), and there is no dot, or there is no large dot or medium dot. , And converted into a value corresponding to one of three types of small dots (an example of k types). Since the specific content of the quaternization processing of the Y component value is the same as that of the quaternization processing of the C component value (S518), detailed description is omitted.

  Next, the CPU 11 performs quaternarization processing on the K data (S532). Thereby, for each achromatic color dot constituting the gray scale image, one of three types of dots (an example of k types) of a large dot, a medium dot, and a small dot is determined.

  Next, the CPU 11 determines whether or not all the pixels have been processed as the target pixel (S533). If the determination in S533 is negative (S533: No), the process returns to S514 and repeats the process. If the determination in S533 is affirmed while the processing is repeated (S533: Yes), the ink head 2 and the transport motor 22 (FIG. 4) are driven to print a grayscale image (S534). Here, the image to be printed is composed of dots based on the values for each pixel color (no dots, large dots, medium dots, small dots) binarized or quaternarized by halftone processing.

  According to the printing process of the present embodiment, one of the three types of dots is determined for the K dots constituting the grayscale image. On the other hand, C, M, and Y dots that are chromatic colors are easily formed as large dots, and are difficult to be formed as medium dots and small dots. In other words, C, M, and Y dots representing a gray scale image can be represented by relatively large dots. By expressing a grayscale image using C, M, and Y dots, the landing position varies more than in the case where an image is composed of only K-colored dots, a banding suppression effect is obtained, and it is relatively easy to blur. By using a large number of size dots, a further banding suppression effect can be obtained.

  Further, even if the component values of C, M, and Y are less than the switching threshold value, they are converted into quaternary values and converted into no dots, large dots, medium dots, and small dots. It is composed of dots of three sizes, large, medium and small. By comprising many types of dots, the graininess in the light gray color of the image is reduced. On the other hand, the component values of C, M, and Y that are equal to or higher than the switching threshold are binarized and converted to no dots or large dots, so that it is possible to obtain a banding suppression effect in a dark gray color of the image.

  FIG. 7 is a flowchart showing threshold determination processing executed by the control unit 10 of the printer 1. This process is executed, for example, when an operation key (not shown) of the printer 1 is pressed by the user.

  First, a threshold determination chart image is printed based on the patch data prepared in advance in the ROM 12 (S702).

  FIG. 8 is a diagram illustrating an example of the threshold determination chart image. As shown in FIG. 8, the threshold determination chart image includes eight types of gray patches 81 to 88 that gradually increase from 1 to 8, and each gray patch is a first type patch 81a shown in the upper part of each patch. To 88a and second-type patches 81b to 88b shown in the lower part of each patch. A numerical value written on the left side of each patch is referred to as a chart number.

  In the ROM 12, eight types of patch data corresponding to the eight types of gray patches 81 to 88 and having different shades are prepared in advance. The patch data further includes first type patch data corresponding to the first type patches 81a to 88a and second type patches 81b to 88b.

  The first type patch data includes eight types of K component values (16, 32, 48, 64, 80, 96, 112, 128) according to the relationship stored in the GCR table 12c (FIG. 4). This is patch data obtained as a result of quaternization by replacing with a combination of M component value and Y component value. On the other hand, the second type of patch data is obtained by binarizing the combination of the C component value, the M component value, and the Y component value obtained by replacing the K component value according to the relationship stored in the GCR table 12c. This is the patch data obtained.

  That is, the first type patches 81a to 88a are composed of three types of C, M, and Y dots, large dots, medium dots, and small dots, whereas the second type patches 81b to 88b are large dots. It is composed of C, M, and Y dots that are only dots.

  As shown in FIG. 8, the first type patches 81 a to 88 a and the second type patches 81 b to 88 b are arranged on the recording paper P as a set according to density. That is, the first type patch and the second type patch having the same density are paired, arranged in contact with one side in the longitudinal direction of the belt, and given the same chart number.

  Therefore, the user visually recognizes the first type patch and the second type patch, and in particular, visually recognizes the boundary lined up and in contact with each other according to the density, thereby suppressing both graininess and banding. Select a patch. In this way, by visually recognizing the surface where the two types of patches are in contact, a value that does not significantly reduce the image quality even if the chromatic color component value is converted to n or m can be determined as the threshold value. . Further, since the boundaries between the different densities are not in contact with each other, it is possible to prevent the user from mistakenly comparing the first type patch and the second type patch having different densities.

  Returning to FIG. Next, the CPU 11 determines whether or not a paper type has been input by the user (S704). If the determination in S704 is negative (S704: No), the process waits. On the other hand, when the paper type is input (S704: Yes), the CPU 11 next determines whether or not a chart number is input (S706). If the determination in S706 is negative (S706: No), the process waits. On the other hand, when the chart number is input (S706: Yes), the component values of each color of C, M, and Y included in the patch data corresponding to the chart number are associated with the paper type input as the switching threshold value for each color. The binary / quaternary switching threshold memory 14a (FIG. 4) is set (S708), and the process is terminated.

  That is, since the first type patches 81a to 88a are composed of three types of dots, the graininess is suppressed, but banding tends to be a problem in a dark color patch. On the other hand, since the second type patches 81b to 88b are composed only of large dots that are relatively easy to blur, the banding is suppressed, but granularity tends to be a problem in a light color patch. Therefore, the user visually recognizes the first type patches 81a to 88a and the second type patches 81b to 88b, and selects a patch in which both the graininess and the banding are suppressed. In this way, it is possible to determine a value that does not significantly reduce the image quality even if the C, M, and Y component values are binarized or quaternarized as the switching threshold for each color.

  The printer 1 described in the above embodiment corresponds to an example of an inkjet printer, the control program 12a corresponds to an example of a print control program, the CPU 11 corresponds to an example of a computer, and a large dot corresponds to an example of a maximum size dot. The small dot corresponds to an example of a minimum size dot, the K component value corresponds to an example of an achromatic color component value, the component values of each color of C, M, and Y correspond to an example of a chromatic color component value, The switching threshold corresponds to an example of a predetermined threshold. The CPU 11 that executes S502 corresponds to an example of a print type determination unit, the CPU 11 that executes S508 corresponds to an example of an image data acquisition unit, and the CPU 11 that executes S516 to S532 corresponds to an example of a halftone processing unit. The CPU 11 that executes S532 corresponds to an example of an achromatic color processing unit, and the CPU 11 that executes S514 to S530 corresponds to an example of a chromatic color processing unit. The CPU 11 that executes S514, S520, and S526 corresponds to an example of a chromatic color component value determining unit, the CPU 11 that executes S518, S524, and S530 corresponds to an example of a light color processing unit, and the CPU 11 that executes S516, S522, and S528. Corresponds to an example of dark color processing means. The CPU 11 that executes S702 corresponds to an example of a patch forming unit, and the CPU 11 that executes S708 corresponds to an example of a threshold setting unit.

  Although the present invention has been described based on the embodiments, the present invention is not limited to the above-described embodiments, and various improvements and modifications can be easily made without departing from the spirit of the present invention. Can be inferred.

  For example, in the above-described embodiment, the control unit 10 of the printer 1 is an example of a print control apparatus. However, an external device such as a personal computer that is communicably connected to the printer 1 is configured as the print control apparatus of the present invention. Also good. In that case, color conversion processing and halftone processing of the component values of each color may be performed by an external device that is a print control device, and the image data after the halftone processing may be output to the ink jet printer.

  In the above embodiment, the printer 1 is described as a line head type ink jet printer that has a long ink head 2 and performs printing with the ink head 2 fixed. However, the ink head intersects the transport direction. The present invention can also be applied to a serial printer that performs printing while reciprocating in the direction.

  In the above embodiment, binarization and quaternary switching are performed depending on whether the chromatic color component values of C, M, and Y are equal to or greater than the switching threshold. May be configured to be binarized uniformly without determining the magnitude relationship with the switching threshold. In this way, only large dots are used as the chromatic color dots constituting the gray scale image, and a further banding suppression effect can be obtained. In the above-described embodiment, n, m, and k described in the claims have been described as n = 4, m = 2, and k = 3, respectively. The target value is not limited to this and can be changed as appropriate.

DESCRIPTION OF SYMBOLS 1 Printer 2 Ink head 10 Control part 12a Control program

Claims (4)

A printing control apparatus for causing an inkjet printer capable of forming k types of dots having different sizes to execute printing,
Print type determination means for determining whether an image to be printed by the inkjet printer is grayscale;
If it is determined that it is a gray scale, image data acquisition means for acquiring image data expressing a gray color using a combination of chromatic colors that can be used in the inkjet printer;
The grayscale image is formed by performing halftone processing for each color of the achromatic color component value representing the achromatic color component of each pixel and the chromatic color component value representing the chromatic color component included in the image data. Halftone processing means for determining the type of each dot to be
The halftone processing means includes
An achromatic color processing means for determining any one of the k types of dots for each achromatic color dot constituting the gray scale image by converting the achromatic color component value into n values (where n = k + 1) ),
By converting the chromatic color component value to m-value, for each chromatic color dot constituting the grayscale image, any one of the (m−1) types of dots determined in advance among the k types of dots. Chromatic color processing means for determining whether (k> m-1),
The (m−1) types of dots include a maximum size dot among the k types of dots, and do not include a minimum size dot. The chromatic color processing means further includes
Chromatic color component value determining means for determining whether the chromatic color component value of each pixel is equal to or greater than a predetermined threshold for the chromatic color;
Light color processing means for converting a chromatic color component value that is less than the threshold value into n values by the halftone processing and converting the chromatic color component value into a value indicating that the dots are not formed or a value corresponding to any of the k types of dots
A chromatic color component value that is equal to or greater than the threshold value is converted to m-value by the halftone process and converted to a value that represents that the dot is not formed or a value that corresponds to one of the (m−1) types of dots. The print control apparatus according to claim 1, further comprising a color processing unit. Based on the result of n-value conversion of a plurality of types of patch data with different shades prepared in advance as gray scale patch data expressing a gray color using a combination of the chromatic color component values by the halftone process Patch forming means for causing the inkjet printer to print a first type patch and a second type patch based on the result of m-value conversion by the halftone process;
The threshold value setting means which sets each chromatic color component value of the patch data corresponding to the patch selected by the user among the plurality of types of patches as a threshold value of each chromatic color. Print control device. A print control program for causing an inkjet printer capable of forming k types of dots having different sizes to execute printing,
Print type determination means for determining whether an image to be printed by the inkjet printer is grayscale;
If it is determined that it is a gray scale, image data acquisition means for acquiring image data expressing a gray color using a combination of chromatic colors that can be used in the inkjet printer;
The grayscale image is formed by performing halftone processing for each color of the achromatic color component value representing the achromatic color component of each pixel and the chromatic color component value representing the chromatic color component included in the image data. The computer functions as a halftone processing means for determining the type of each dot to be
The halftone processing means includes
An achromatic color processing means for determining any one of the k types of dots for each achromatic color dot constituting the gray scale image by converting the achromatic color component value into n values (where n = k + 1) ),
By converting the chromatic color component value to m-value, for each chromatic color dot constituting the grayscale image, any one of the (m−1) types of dots determined in advance among the k types of dots. Chromatic color processing means for determining whether (k> m-1),
The (m-1) types of dots include a maximum size dot among the k types of dots, and do not include a minimum size dot.

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