JP5838087B2 - Image processing apparatus, image processing method, and image processing program - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing method, and an image processing program.

  Conventionally, there has been proposed an image processing apparatus that performs systematic dithering processing on color image data and converts the image data into monochrome image data (see, for example, Patent Document 1).

JP-A-10-126630

  In the conventional systematic dithering method, when the printing rate per dot line of the printer head increases, an abnormality such as a power supply voltage drop may occur on the printer side. If a power supply voltage drop occurs, it may lead to a decrease in the quality of printed matter or a printer failure.

  Therefore, an image processing apparatus, an image processing method, and an image processing program that make it difficult for an abnormality such as a power supply voltage drop to occur on the printer side are provided.

  In order to achieve the above-described object, the dot line dots of the dithering means for performing systematic dithering on image data using a predetermined matrix pattern and the matrix patterns of all gradations in the systematic dithering A setting means for setting each shift matrix pattern that is cyclically shifted by one dot line in a direction orthogonal to the arrangement direction of the image, and for each dot line of the image data systematically dithered by the dithering means, Calculating means for calculating a ratio of dots to the total number of dots; determining means for determining whether or not there is a dot line having the ratio equal to or greater than a predetermined threshold; and said dot lines determined to be present The dot line determined to exist so that the ratio is less than the threshold. At least one matrix pattern among the one or more matrix pattern including, to provide an image processing apparatus characterized by having a replacement means for replacing either a shift matrix pattern set by the setting means.

  With the image processing apparatus, the image processing method, and the image processing program of the present invention, an abnormality such as a power supply voltage drop can hardly occur on the printer side.

The image processing system of this embodiment. The figure which showed all the gradations of the matrix pattern. Diagram for explaining organizational dithering. The figure for demonstrating a printing rate. The figure for demonstrating cyclic shift. The figure for demonstrating a shift matrix pattern. The figure which shows an example of the matrix pattern which continues 4 pieces. FIG. 4 is a diagram showing that four consecutive matrix patterns are replaced with shift matrix patterns. 1 is a diagram illustrating an example of a functional configuration of an image processing apparatus according to an embodiment. The figure which shows the processing flow of the image processing apparatus of a present Example. The figure which shows an example of the image data after a dithering process. The figure which shows 1 dot line. The figure which shows an example of the processing flow of a replacement process. The figure which has replaced the continuous matrix pattern with the shift matrix pattern. The figure which shows specifically having replaced the continuous matrix pattern with the shift matrix pattern.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In addition, the same number is attached | subjected to the process which performs the same part and the process which has the same function, and duplication description is abbreviate | omitted.
[Embodiment 1]
<Image processing system>
FIG. 1 shows a functional configuration example of the image processing system of the present embodiment. In the example of FIG. 1, the information processing apparatus 50 and the printer 20 are roughly configured. The information processing device 20 is a device that performs information processing such as a PC (Personal computer), a smartphone, and a tablet.

  An application 1 and an image processing program 100 are installed in the information processing apparatus 50 shown in FIG. The image processing program 100 may be a printer driver. Based on the setting information of the image processing program, the creating unit 2 creates a drawing area (device context) in the memory 6. Here, the setting information includes information set by the user and information set in advance. For example, the device mode (for example, paper size and resolution), the conversion method of the image data format, the control command setting of the printer 20, the execution timing of the control command, and the like.

  Next, the drawing means 4 draws the image data in the created drawing area of the memory 6. Here, the image data is, for example, characters, figures, images, and the like. When the drawing process of the drawing unit 4 ends, the calling unit 8 calls the image processing program 100.

  The image processing program 100 converts the color image data created by the application 1 into monochrome bit image data by performing image processing. The details of the image processing of the image processing program 100 will be described later.

  The image processing apparatus program 100 adds a printer control command for the bit image data as necessary, and converts the bit image data into a data format that can be processed by the printer 20. The image processing program 100 transmits the converted printer control command to the printer 20 via the interface 10 in a wired or wireless manner.

  In the printer 20, the transport unit 24 transports the paper for a predetermined distance, and after transporting the predetermined distance, the printing unit 22 performs printing. A printed matter is created while repeating the paper conveyance process and the printing process.

  In addition, the conveyance direction of the sheet by the conveyance unit 24 is a sub-scanning direction, and a direction orthogonal to the sub-scanning direction is a main scanning direction. The printing unit 22 performs printing in dot line units (for example, one dot line). Here, the dot line refers to a line of dots in the main scanning direction.

Further, FIG. 1 shows an example in which the image processing program 100 is installed in the information processing apparatus 50. As another example, an image processing apparatus that executes the functions of the image processing program 100 may be incorporated in the information processing apparatus 50 and implemented.
<About organized dithering>
Next, systematic dithering will be briefly described. For the systematic dithering, a matrix pattern (also referred to as a dither matrix) of N × N (N is an integer of 2 or more) is used. The matrix pattern includes various types such as a Bayer type, a spiral type, and a halftone type. By performing systematic dithering, by replacing with a matrix pattern having different dot densities, it is possible to express a large number of gradations, and as a result, it is possible to express the shading of an image clearly.

  In the following, it is assumed that a 4 × 4 Bayer matrix pattern is used as the matrix pattern. By using a 4 × 4 matrix pattern, 17 gradations can be expressed while being a binary image.

  FIG. 2 shows a pattern of 17 gradations (0 to 16 gradations) when a Bayer matrix pattern is used. Thus, by using a Bayer matrix pattern, 17 gradations can be expressed while being binary image data (white dots and black dots).

  FIG. 3 schematically shows an example of color image data (original image data before the dithering process is performed). In FIG. 3, one grid is one dot. When dithering processing is performed using a 4 × 4 matrix pattern, the dithering means 204 (see FIG. 9) divides all the dots of the image data into 4 × 4 blocks. In FIG. 3, the blocks are indicated by bold lines.

Then, the dithering means 204 replaces each block with a matrix pattern of 0 to 16 gradations (see FIG. 2) corresponding to the gradation of the one block. By replacing in this way, it is possible to convert color image data as original image data into monochrome image data of 17 gradations.
<About printing rate>
Next, the printing rate will be described. 4A, 4B, and 4C show blocks with gradations of 9, 11, and 13, respectively. The printing rate is the ratio of the number of black dots to the total number of dots in each dot line.

For example, for the uppermost dot line a of gradation 9 shown in FIG. 4A, since the total number of dots is “4” and the number of black dots is “3”, the printing rate is 75% ( Or 0.75). 4A to 4C show the printing rates for other dot lines. The “printing rate” is also referred to as “ratio”.
<About cyclic shift processing>
In the image processing apparatus of the present embodiment, a matrix pattern (hereinafter referred to as a “shift matrix pattern”) that is cyclically shifted by one dot line is used for all gradation matrix patterns.

  FIG. 5 illustrates an example in which the matrix pattern of gradation 9 is cyclically shifted. FIG. 5A shows a matrix pattern before cyclic shift. Then, as shown in FIG. 5B, the matrix pattern is shifted in a direction β perpendicular to the dot arrangement direction α of one dot line. In FIG. 5B, it is shifted downward. As another example, one dot line may be shifted upward.

  Then, as shown in FIG. 5B, the one dot line b surrounded by the broken line overflows. In the cyclic shift process, as shown in FIG. 5C, the overflowed dot line b is moved to a position opposite to the position c where the dot line b existed (see FIG. 5A). In this way, the cyclic shift process can be appropriately performed.

  FIG. 6 shows a shift matrix pattern in which all the gradations (gradation 0 to gradation 16) are cyclically shifted by one dot line. FIG. 6A shows a shift matrix pattern that is cyclically shifted by 0 dot lines (that is, the same as the original matrix pattern). FIG. 6B shows a shift matrix pattern that is cyclically shifted by one dot line. FIG. 6C is a shift matrix pattern that is cyclically shifted by 2 dot lines, and FIG. 6D is a shift matrix pattern that is cyclically shifted by 3 dot lines.

Hereinafter, the matrix pattern of tone k (k = integer satisfying ^{0~N 2), s (s =} N-1) dot lines, a shift matrix pattern obtained by cyclically shifting a _P s (k). For example, the shift matrix pattern indicated by E in FIG. 6 has gradation 6 and is shifted by 2 dot lines, and is represented as P ₂ (6). Further, when s = 0, since no cyclic shift is performed, it is also referred to as a matrix pattern P ₀ (k).

In this embodiment, as shown in FIG. 6, shift matrix patterns P _s (k) each shifted by 0 to N−1 dot lines are used in an N × N matrix pattern of all gradations. However, s is an integer and a variable satisfying 0 or more and N−1 or less.
<Relationship between printing rate and shift matrix pattern>
Next, the relationship between the printing rate and the shift matrix pattern will be described. FIG. 7 shows a matrix pattern P ₀ (11) of gradation 11 that is four consecutive. In FIG. 7, the printing rate for the first dot line is 100%, the printing rate for the second dot line is 50%, the printing rate for the third dot line is 75%, and the printing rate for the fourth dot line is 50%. It becomes.

  In this embodiment, a predetermined threshold Th is used for the printing rate of each dot line. For dot lines with a printing rate equal to or greater than the threshold Th, there is a possibility that a power supply voltage drop will occur on the printer 20 side. In the following, the threshold value Th = 75%.

  In this case, in the example of FIG. 7, the printing rate of the first dot line and the third dot line of gradation 9 is equal to or higher than the threshold value, which may cause a power supply voltage drop on the printer 20 side. Therefore, the matrix pattern is replaced with a shift matrix pattern as shown in FIG.

In the example of FIG. 8, the first matrix pattern P ₀ (11) is not replaced. Replace with the second matrix pattern P ₀ (11) → P ₁ (11). Replace with the third matrix pattern P ₀ (11) → P ₂ (11). Replace with the fourth matrix pattern P ₀ (11) → P ₃ (11).

By replacing in this way, the printing rate for all the dot lines becomes 68.75%, and for all the dot lines, it can be made less than the threshold value.
<Overall processing flow>
Next, the overall processing flow will be described. FIG. 9 is a block diagram illustrating a functional configuration example of the image processing program 100 of the present embodiment, and FIG. 10 illustrates a main processing flow of the image processing program 100.

When color image data, which is original image data, is input to the input unit 202 from the application 1 (see FIG. 1), the processing in FIG. 10 is started. First, in step S2, setting means 206, the matrix pattern of all gradations of systematic dithering, 1 each dot line, the direction beta (Fig. 5 (A) refer) shift matrix was cyclically shifted pattern P _s (K) Set each. However, s = 0,. . . , N−1 and k = 1,. . . , N ² .

Here, the shift matrix patterns set by the setting means 206 are 64 (= N ³ ) matrix patterns shown in FIG. In consideration of the matrix pattern of gradation 0, the number of matrix patterns is 65.

In the present embodiment, there are two methods as setting methods of the setting means 206. As a first method, the creating unit 216 uses P ₀ (k) to cyclically shift the P ₀ (k) 1 dot line in the direction β to create a shift matrix pattern. Then, the setting unit 206 sets all the shift matrix patterns P _s (k) created by the creating unit 216.

As a second method, all shift matrix patterns P _s (k) are stored in the storage unit 218 in advance. Then, the setting unit 206 calls and sets all the shift matrix patterns P _s (k) stored in the storage unit 218.

  In the example of FIG. 9, the creation unit 216 and the storage unit 218 are described, but either one of the creation unit 216 and the storage unit 218 may be provided.

  Next, the dithering means 204 performs an organized dithering process. The systematic dithering is as described in FIG. FIG. 11 schematically shows image data that has undergone systematic dithering by the dithering means 204.

  In FIG. 11, one matrix pattern is surrounded by a thick line, and one dot is surrounded by a thin line. As shown in FIG. 11, the number of matrix patterns arranged in the row direction (dot arrangement direction of the dot lines) is J (J is an integer of 2 or more). The total number of dots in the row direction is A. That is, A = 4J.

  Further, the number of matrix patterns arranged in the column direction (direction orthogonal to the row direction) is I (I is an integer of 2 or more). The total number of dots in the row direction is B. That is, B = 4I. In the following description, “row” and “column” refer to one matrix pattern.

  Next, the control means 220 sets the pattern determination line i (an integer and variable such that i = 1,..., I) to “1”. Here, the numbers for the pattern determination row and the pattern column are measured from the matrix pattern at the origin. In the example of FIG. 11, the matrix pattern of the origin is a matrix pattern F located at the upper left.

  Next, in step S8, the control means 220 sets the pattern string j = 1. Next, in step S10, the control means 220 determines whether the pattern determination line i = I, that is, whether the pattern determination line i has reached the final line I. Here, since I = i has not yet been reached, No is determined in step S10, and the process proceeds to step S12.

  Next, in step S12, the control means 220 determines whether the pattern string j = J, that is, whether the pattern string j has reached the final string J. Here, since j = J has not yet been reached, No is determined in step S12.

  Next, in step S14, the calculation means 208 calculates the number of black dots for each of 1 to N (here, 1 to 4) dot lines. Here, black dots are calculated for each of the 1 to 4 dot lines of the matrix pattern in which i = 1 and j = 1.

  Next, in step S16, the control means 220 increments the pattern string j by “1”, that is, sets j = 2, and returns to the process of step S12. Through the process of step S12, in the process of step S14, the calculation means 208 calculates the number of black dots for each of 1 to N (here, 1 to 4) dot lines. Here, the calculation means 208 adds the number of black dots calculated this time to the number of black dots calculated in the past. That is, the calculation unit 208 performs cumulative calculation.

In this way, by repeating the processes of steps S12, S14, and S16, the total number of black dots for each of the 1 to 4 dot lines of the matrix pattern of the pattern determination line i = 1 can be calculated as shown in FIG. I can do it. In the time of step S12 to S16, since it is not substituted with the shift matrix pattern, for every matrix pattern shown in FIG. _12, the _P 0 (k). In the description of FIG. 12, “(k)” of P ₀ (k) is omitted.

  Next, in step S <b> 18, the calculation unit 208 calculates a printing rate for each of 1 to N (= 4) dot lines. Further, assuming that the number of black dots in the n (integer satisfying n = 1,..., N) dot line of the j-th matrix pattern in the row direction is D [j] [n], 1 to 4 dot lines respectively. Can be expressed by the following equation (1).

  In step S20, the determination unit 210 determines whether the printing rate is equal to or higher than a predetermined threshold (for example, 75%) for each of 1 to N (= 4) dot lines. Further, the determination unit 210 determines whether or not there is one or more dot lines that are equal to or greater than the threshold (hereinafter referred to as “dot lines greater than or equal to the threshold”). Further, a row of a matrix pattern including dot lines above the threshold is referred to as “matrix pattern row above the threshold”. A matrix pattern row above the threshold is composed of one or more matrix patterns.

  If the determination unit 210 determines that there is no dot line equal to or greater than the threshold (No in step S20), the process proceeds to step S24. The case of No in step S20 means that there is no dot line that can cause the power supply voltage drop of the printer 20 in the pattern determination line. In step S24, the pattern determination line i is incremented by “1”, and the process returns to step S8.

  On the other hand, when the determination unit 210 determines that there is a dot line equal to or greater than the threshold (Yes in step S20), the process proceeds to step S22. If there is a dot line exceeding the threshold value, there is a possibility that the power supply voltage drop of the printer 20 may occur. Therefore, in order to avoid the power supply voltage drop, the replacement unit 212 performs a replacement process in the next step S22. The process of step S22 will be described later.

Then, in step S10, the control means 220 determines that I = i (Yes in step S10), that is, when the processing of steps S10 to S22 for all rows 1 to J is completed, End.
<About replacement processing>
Next, a suitable example of the replacement process in step S22 will be described. The replacement unit 212 is a shift matrix in which at least one of the one or more matrix patterns constituting the matrix pattern row above the threshold is set by the setting unit 206 so that the printing rate of the dot line above the threshold is less than the threshold. Replace with pattern. By this replacement processing, it is possible to disperse dot lines having a high printing rate, and as a result, it is possible to reduce the printing rate of dot lines that are equal to or greater than a threshold value.

  FIG. 13 shows an example of the replacement process in step S22. In addition, it is assumed that the printing rate of at least one dot line among the 1 to 4 dot lines of the matrix pattern in the first row shown in FIG. 12 is equal to or higher than the threshold Th (Yes in step S20). In this case, a replacement process is performed on the matrix pattern of the first row (that is, a matrix pattern row of a threshold value or more). Then, when the process of FIG. 13 is performed on the matrix pattern rows above the threshold, a matrix pattern as shown in FIG. 14 is obtained.

  FIG. 15A shows a specific example of a matrix pattern row above the threshold value in FIG. In the example of FIG. 15A, it is assumed that the gradation of all matrix patterns is 11. In the example of FIG. 15A, the printing rate of 1 dot line is 100%, the printing rate of 3 dot lines is 75%, which is equal to or greater than the threshold Th (= 75%).

  Then, by performing the replacement process shown in FIG. 13, the matrix pattern shown in FIG. 15A is changed to the matrix pattern shown in FIG. 15B. As shown in FIG. 15B, the printing rate of all the dot lines is 68.75%, which can be less than the threshold Th (= 75%) for all the dot lines.

  The process of FIG. 13 will be described with reference to FIGS. 12, 14, and 15. FIG. First, in step S52, the control means 220 sets the shift number s = 0. Next, in step S54, the control means 220 sets j = 1. Next, in step S56, the control means 220 determines whether j = J.

Here, since j = 1, it is determined No in step S56, and the process proceeds to step S58. Next, the replacement unit 212 replaces P ₀ (k) with P _s (k). Here, since it is s = 0, it means that replacing P 0 _{(k) is} the P _{0 (k),} it may not be performed a replacement process.

  Next, the control means 220 determines whether or not s <N−1 (= 3). Here, since s = 0, it is determined Yes and the process proceeds to step S60. In step S60, the determination unit 220 increments s by “1” (that is, s = 1).

  In step S64, the value of j is incremented by “1” (that is, j = 2), and the process returns to step S56. In step S56, No is determined, and the process proceeds to step S58 again.

In step S58, P ₀ (k) is replaced with P _s (k). Here, since s = 1, P ₀ (k) is replaced with P ₁ (k). Then, steps S59, S60, and S64 are performed. If the determination unit 220 determines in step S59 that s <N−1 (No in step S59), the process proceeds to step S62.

  In step S62, the determination unit 220 resets the value of s to “0”, and proceeds to step S64. If the determination unit 220 determines in step S56 that j = J (Yes in step S56), the replacement process is terminated.

  Further, the replacement process of FIG. 13 will be further described. The replacement means 212 replaces the N · d + n-th matrix pattern in the matrix pattern row that is equal to or greater than the threshold value with a shift matrix pattern that is cyclically shifted by n−1 dot lines in the β direction (see FIG. 5).

Here, d is a variable and an integer satisfying 0 or more and [A / N ² ] or less. That is, 0,. . . , D,. . . , [A / N ² ]. [·] Is a Gaussian symbol, that is, [A / N ² ] is the largest integer not exceeding A / N ² . Further, A is the total number of dots in the dot line direction of the image data as described in FIG. N is a variable and an integer satisfying 1 or more and N or less. That is, 1,. . . , N,. . . , N.

  In all four dot lines, the threshold Th may be exceeded. In this case, it is difficult to reduce the printing rate even if the replacement unit 212 performs the replacement process. However, in order to suppress unevenness with a neighboring matrix pattern, a replacement process is performed for the matrix pattern including the 4-dot line.

  In the above description, the matrix pattern in the systematic dithering has been described as being a Bayer type and a 4 × 4 type matrix pattern. As other matrix patterns, for example, spiral or halftone matrix patterns may be used. Further, as other matrix patterns, for example, 8 × 8 type or 16 × 16 type matrix patterns may be used.

  In the image processing apparatus of this embodiment, after the dithering unit 204 performs systematic dithering on the image data, the calculation unit 208 calculates the printing rate for each dot line. The setting unit 206 sets shift matrix patterns for all tone matrix patterns. The replacement unit 212 replaces at least one of the one or more matrix patterns including the dot line above the threshold with the shift matrix pattern so as to reduce the printing rate of the dot line above the threshold.

  Accordingly, the printing rate of one dot line can be reduced, and as a result, it is possible to make it difficult to cause an abnormality such as a power supply voltage drop of the printer 20.

  Further, by performing the replacement process shown in FIG. 13, the printing rate of one dot line can be more appropriately reduced.

2 creation means 4 drawing means 6 memory 8 calling means 10 interface 20 printer 22 printing means 24 transport means 100 image processing apparatus 202 input means 204 dithering means 206 setting means 208 calculation means 210 judgment means 212 replacement means 216 creation means 218 storage means 220 Control means

Claims (12)

Dithering means for performing systematic dithering on the image data using a predetermined matrix pattern;
Setting means for setting each shift matrix pattern that is cyclically shifted by one dot line in a direction orthogonal to the dot arrangement direction of the dot lines for all gradation matrix patterns in the systematic dithering;
Calculating means for calculating the ratio of the number of black dots to the total number of dots for each dot line of the image data systematically dithered by the dithering means;
Determination means for determining whether or not there is a dot line with the ratio equal to or greater than a predetermined threshold;
When it is determined by the determining means that there is a dot line having the ratio equal to or greater than a predetermined threshold, the dot line determined to exist is present so that the ratio of the dot line determined to be present is less than the threshold. Image processing comprising: replacement means for replacing at least one of the one or more matrix patterns including the determined dot line with any one of the shift matrix patterns set by the setting means. apparatus. The matrix pattern is N × N dots (N is an integer of 2 or more),
The replacement means includes
In one or more matrix patterns including dot lines determined to exist, the N · d + n-th matrix pattern is replaced with a shift matrix pattern that is cyclically shifted by n−1 dot lines in the orthogonal direction,
d is a variable and an integer satisfying 0 or more and [A / N ² ] or less, A is the total number of dots in the dot line direction of the image data subjected to the systematic dithering, and [α] represents α. The image processing apparatus according to claim 1 , wherein the image processing apparatus is a maximum integer not exceeding and n is a variable and an integer satisfying 1 or more and N or less. Creating means for creating each shift matrix pattern that is cyclically shifted by one dot line;
The image processing apparatus according to claim 1, wherein the setting unit sets a shift matrix pattern created in the creation unit. Storage means for storing each shift matrix pattern cyclically shifted by one dot line;
The image processing apparatus according to claim 1, wherein the setting unit sets a shift matrix pattern stored in the storage unit. A dithering process for performing systematic dithering on the image data using a predetermined matrix pattern;
A setting step of setting each of the shift matrix patterns that are cyclically shifted by one dot line in a direction orthogonal to the dot arrangement direction of the dot lines for all gradation matrix patterns in the systematic dithering;
A calculation step of calculating a ratio of the number of black dots to the total number of dots for each dot line of the image data that is systematically dithered by the dithering step;
A determination step of determining whether or not there is a dot line whose ratio is equal to or greater than a predetermined threshold;
When it is determined by the determination step that there is a dot line having the ratio equal to or higher than a predetermined threshold, the dot line determined to be present is present so that the ratio of the dot line determined to be present is less than the threshold. And a replacement step of replacing at least one of the one or more matrix patterns including the determined dot line with any of the shift matrix patterns set in the setting step. Method. The matrix pattern is N × N dots (N is an integer of 2 or more),
The replacement step includes
In one or more matrix patterns including dot lines determined to exist, the N · d + n-th matrix pattern is replaced with a shift matrix pattern that is cyclically shifted by n−1 dot lines in the orthogonal direction,
d is a variable and an integer satisfying 0 or more and [A / N ² ] or less, A is the total number of dots in the dot line direction of the image data subjected to the systematic dithering, and [α] represents α. 6. The image processing method according to claim 5, wherein the image processing method is a maximum integer not exceeding and n is a variable and an integer satisfying 1 or more and N or less. A creation step of creating each shift matrix pattern that is cyclically shifted by one dot line;
7. The image processing method according to claim 5, wherein the setting step sets the shift matrix pattern created in the creation step.   7. The image processing method according to claim 5, wherein the setting step sets a shift matrix pattern stored in a storage unit that stores each shift matrix pattern that is cyclically shifted by one dot line. Computer
Dithering means for performing systematic dithering on the image data using a predetermined matrix pattern;
Setting means for setting each shift matrix pattern that is cyclically shifted by one dot line in a direction orthogonal to the dot arrangement direction of the dot lines for all gradation matrix patterns in the systematic dithering;
Calculating means for calculating the ratio of the number of black dots to the total number of dots for each dot line of the image data systematically dithered by the dithering means;
Determination means for determining whether or not there is a dot line with the ratio equal to or greater than a predetermined threshold;
When it is determined by the determining means that there is a dot line having the ratio equal to or greater than a predetermined threshold, the dot line determined to exist is present so that the ratio of the dot line determined to be present is less than the threshold. It functions as a replacement unit that replaces at least one matrix pattern of one or more matrix patterns including the determined dot line with any of the shift matrix patterns set by the setting unit. Image processing program. The matrix pattern is N × N dots (N is an integer of 2 or more),
The replacement means includes
In one or more matrix patterns including dot lines determined to exist, the N · d + n-th matrix pattern is replaced with a shift matrix pattern that is cyclically shifted by n−1 dot lines in the orthogonal direction,
d is a variable and an integer satisfying 0 or more and [A / N ² ] or less, A is the total number of dots in the dot line direction of the image data subjected to the systematic dithering, and [α] represents α. The image processing program according to claim 9, wherein the image processing program is a maximum integer that does not exceed, and n is a variable and an integer satisfying 1 or more and N or less. Creating means for creating each shift matrix pattern that is cyclically shifted by one dot line;
The image processing program according to claim 9 or 10, wherein the setting means sets a shift matrix pattern created by the creating means.   11. The image processing program according to claim 9, wherein the setting unit sets a shift matrix pattern stored in a storage unit that stores each shift matrix pattern that is cyclically shifted by one dot line.

Images