JP7239876B2 - Method for generating dither matrix and device for generating dither matrix - Google Patents

Description

The present specification relates to a technique for generating a dither matrix used for generating dot data for causing a print execution unit to execute printing.

The image processing apparatus disclosed in Patent Document 1 executes calibration processing. Specifically, the image processing apparatus prints a correction pattern indicating a color chart for correcting the gamma correction table, and reads the correction pattern with a reading device to generate correction image data. The image processing device uses the correction image data to correct the gamma correction table. The image processing apparatus uses a table showing the correspondence relationship between the gamma correction table before correction and the logical gradation dither pattern and the gamma correction table after correction to generate the gamma correction table and the logical gradation dither pattern after correction. Create a table showing the correspondence between The image processing apparatus generates a dither pattern to be used using a table showing the correspondence relationship between the corrected gamma correction table and the logical gradation dither pattern and the logical gradation dither pattern. A dither pattern is generated so as to maintain the number of gradations before calibration.

Japanese Unexamined Patent Application Publication No. 2010-141608

However, in the above technique, it cannot be said that a specific method for selecting the dither pattern to be used from among the logical gradation dither patterns is sufficiently devised. To this end, for example, the dither pattern could be chosen such that, for increasing input values, the density represented by the dither pattern decreases, in part. As a result, using the generated dither pattern, there is a possibility that dot data that expresses an appropriate density according to the input value cannot be generated.

This specification discloses a technique for creating a dither matrix that can generate dot data that appropriately represents an input value.

The technology disclosed in this specification can be implemented as the following application examples.

[Application Example 1] A method for generating a dither matrix used for generating dot data, wherein the dot data is used for causing a print execution unit that forms dots on a print medium using a printing material to execute printing. a printing step of causing the print execution unit to print M patch images using M (M is an integer of 3 or more) dot patterns having density order determined by the print execution unit, Each of the dot patterns is a pattern of arrangement of the dots within a specific region within the corresponding patch image , and is a pattern expressing different densities due to mutually different numbers of dots arranged in the specific region. the printing step, wherein the density order is an order in which the greater the number of the dots arranged in the specific area, the later the density order; and N (N is an integer satisfying M>N≧2) input values. wherein the input value is a value of a color component corresponding to the printing material, and the target density is obtained according to the input value. The M a colorimetric step of obtaining M measured values indicating the densities of dot patterns ; a selecting step of selecting N corresponding dot patterns, wherein the N corresponding dot patterns are the dot patterns different from each other, based on the selecting step and the N corresponding dot patterns to be selected; , and a creating step of creating a dither matrix, wherein the selecting step is a first step of selecting the input values of interest one by one from the N input values in a predetermined selection order. the first step, wherein the selection order is either a first order in which the lower the corresponding target density is selected earlier, or a second order in which the higher the target density is selected earlier; a second step of acquiring the target density corresponding to the noted input value; and selecting the corresponding dot pattern to be associated with the noted input value from a pair of dot patterns having consecutive density orders among the M dot patterns. In the third step of selecting , the measured value of one of the dot patterns of the pair of dot patterns is equal to or less than the target density corresponding to the noted input value, and the third step, wherein the measured value of the other of the dot patterns is greater than the target density corresponding to the noted input value, and when there are two or more pairs of dot patterns; wherein, in the third step, the corresponding dot pattern to be associated with the target input value is selected from a specific pair of dot patterns corresponding to the predetermined selection order among the two or more pairs of dot patterns; When the predetermined selection order is the first order, the specific pair of dot patterns selected is the pair whose density order is the first among two or more sets of the pair of dot patterns. and when the predetermined selection order is the second order, the pair of dot patterns whose density order is the last among the pair of dot patterns of two or more sets, Method.

Ideally, the measured values of the M dot patterns increase or decrease sequentially according to the order of density based on the number and size of dots. In practice, such a magnitude relationship may be reversed due to unevenness, banding, or the like. If a size reversal occurs, there may be multiple pairs of dot patterns. According to the above configuration, when there are a plurality of pairs of dot patterns, the corresponding dot pattern to be associated with the target input value is selected from specific pairs of dot patterns according to a predetermined selection order. As a result, an appropriate corresponding dot pattern is selected so that the density represented by the corresponding dot pattern increases as the input value increases, even if the magnitude relationship is reversed as described above. can do. In addition, since N corresponding dot patterns are selected from M dot patterns, which is larger than the number N of input values, it is possible to prevent two or more of the same dot patterns from being included in the N corresponding dot patterns. can. As a result, it is possible to create a dither matrix capable of generating dot data that appropriately express input values.
be.

The technology disclosed in this specification can be implemented in various forms, for example, an image processing apparatus, a multifunction machine, a dither matrix creation apparatus, and a computer program for realizing the functions of these apparatuses and methods. , a recording medium on which the computer program is recorded, or the like.

2 is a block diagram showing the configuration of a multi-function device 200; FIG. 4 is a flowchart of image processing; 9 is a flowchart of dither matrix generation processing; 4 is a diagram showing an example of a test image TI printed on paper P; FIG. 4 is a conceptual diagram showing an example of dot pattern DP; FIG. FIG. 10 is a diagram showing an example of a measured value table MT in which measured values V are recorded; FIG. 4 is an explanatory diagram of setting a target density; 3 shows an example of a correspondence table CT. FIG. 4 is a diagram showing an example of a dither matrix DM for one color component; 9 is a flowchart of corresponding pattern selection processing; FIG. 10 is an explanatory diagram of corresponding pattern selection processing;

A. Example:
A-1: Configuration of MFP 200 Next, embodiments will be described based on examples. FIG. 1 is a block diagram showing the configuration of a multifunction device 200, which is an example of a generation device. The MFP 200 includes a CPU 210 as a processor that controls the MFP 200, a volatile storage device 220 such as a DRAM, a nonvolatile storage device 230 such as a flash memory or a hard disk drive, a display unit 240 such as a liquid crystal display, An operation unit 250 including a touch panel and buttons superimposed on a liquid crystal display, an interface (communication IF) 270 for communicating with an external device such as the user's terminal device 100, a print execution unit 280, and a read execution unit 290. , is equipped with

Reading executing unit 290 generates scan data by optically reading a document (for example, paper P on which test image TI is printed) using an image sensor under the control of CPU 210 . The image sensor is, for example, a contact image sensor (CIS) type one-dimensional image sensor in which a plurality of photoelectric conversion elements such as CCD and CMOS are arranged in a row. The reading execution unit 290 generates scan data representing the document based on the electrical signal output by the image sensor. The scan data is RGB image data that includes RGB values of a plurality of pixels and indicates the color of each pixel with the RGB values. The RGB value is a color value in the RGB color space, and includes three component values of red (R), green (G), and blue (B) (R value, G value, and B value).

Under the control of the CPU 210, the print execution unit 280 uses a plurality of types of toner, specifically, cyan (C), magenta (M), yellow (Y), and black (K) toners, as printing materials. An image is printed by forming dots on a printing medium such as paper using an electrophotographic method. In a modified example, the print execution unit 280 may be an inkjet print execution unit that forms an image by ejecting ink as a printing material and forming dots on paper.

Volatile storage device 220 provides a buffer area for temporarily storing various intermediate data generated when CPU 210 performs processing. The nonvolatile memory device 230 stores a computer program PG, test image data TID, dither matrix data DMD, and dot pattern data DPD. The computer program PG is a control program that causes the CPU 210 to control the MFP 200 . The test image data TID is image data representing a test image TI, which will be described later. The dither matrix data DMD is data that defines a dither matrix DM (described later) for each color component of CMYK. The dither matrix data DMD is used in dither-type halftone processing. The dither matrix data DMD is generated by dither matrix generation processing, which will be described later. The dot pattern data DPD is used in dither matrix generation processing, which will be described later. In this embodiment, the computer program PG, the test image data TID, and the dot pattern data DPD are provided in a form that is pre-stored in the non-volatile storage device 230 when the MFP 200 is manufactured. Alternatively, the computer program PG, the test image data TID, and the dot pattern data DPD may be provided in the form of being downloaded from a server, or may be provided in the form of being stored in a DVD-ROM or the like. By executing the computer program PG, the CPU 210 can execute print processing and dither matrix generation processing, as will be described later.

A-2. Print Processing FIG. 2 is a flowchart of image processing. This print processing is executed by the CPU 210 of the multifunction device 200 when a print instruction is received from the user. In the print process, the CPU 210 generates dot data using image data, and executes printing by controlling the print execution unit 280 based on the generated dot data.

At S10, the CPU 210 acquires image data representing an image to be printed. This image data is obtained, for example, by receiving image data from the terminal device 100 via the communication IF 270 . In S20, the CPU 210 performs rasterization processing on the acquired image data to generate RGB image data.

In S30, the CPU 210 performs color conversion processing on the RGB image data to generate CMYK image data. The CMYK image data is image data that expresses the color of each pixel with the gradation values of the four CMYK color components (hereinafter also referred to as CMYK values). The CMYK value is a color value in the CMYK color space, and includes four component values (C value, M value, Y value, K value) of cyan (C), magenta (M), yellow (Y), and black (K). ). The four component values of the CMYK values correspond to the four types of toner used by the print execution unit 280. FIG. Color conversion processing is performed using, for example, a lookup table that defines the correspondence between RGB values and CMYK values.

In S40, the CPU 210 performs halftone processing on the CMYK image data to generate dot data representing the dot formation state for each pixel and for each ink color. The value of each pixel included in the dot data indicates the formation state of four types of dots. The dot formation states are, for example, two states of "dots present" and "dots absent". The halftone processing of this embodiment is dither-type processing that is executed using the dither matrix data DMD (FIG. 1).

In S<b>50 , the CPU 210 supplies the generated dot data to the print executing section 280 . As a result, print execution unit 280 prints an image based on the dot data.

A-3. Dither Matrix Generation Processing FIG. 3 is a flowchart of the dither matrix generation processing. The dither matrix generation process is a process of generating the dither matrix data DMD used in the halftone process of S40 in FIG. The dither matrix generation process is executed to generate dither matrix data DMD according to the characteristics of the print execution unit 280, for example, when manufacturing the MFP 200. FIG. Further, the dither matrix generation process is periodically executed, for example, based on a user's instruction, in order to update the dither matrix data DMD in accordance with changes in the characteristics of the print execution unit 280 over time.

In S110, the CPU 210 selects a target color component from the four CMYK color components. In S120, the CPU 210 causes the print execution unit 280 to print the test image TI of the target color component using the test image data TID. The test image data TID is dot data representing the test image TI, and is dot data for one layer corresponding to one color component. The print executing unit 280 prints the test image TI on the paper P using only the toner corresponding to the target color component.

FIG. 4 is a diagram showing an example of the test image TI printed on the paper P. As shown in FIG. The test image TI includes M (M is an integer equal to or greater than 3) patch images PI. Each of the M patch images PI is an image containing a corresponding dot pattern DP out of the M dot patterns DP. For example, in the example of FIG. 4, one patch image PI has 4 vertical×4 horizontal dot patterns DP arranged in a matrix. Actually, the number of dot patterns DP included in one patch image PI is more than 4 vertical×4 horizontal, for example, 32 vertical×32 horizontal.

FIG. 5 is a conceptual diagram showing an example of the dot pattern DP defined by the dot pattern data DPD. The dot pattern DP is a dot arrangement pattern in a specific area including {(M−1)×k} pixels PX (where k is an integer equal to or greater than 1). FIG. 5 shows some pixels PX included in the dot pattern DP. Each pixel PX in FIG. 5 is assigned a number defined by the dot pattern data DPD. The dot pattern data DPD defines numbers from 1 to (M-1) assigned to {(M-1).times.k} pixels included in the dot pattern DP. The number of pixels assigned one type of number (for example, 1) is k.

The 0th dot pattern DP(0) is a dot pattern in which dots are not formed in all pixels. The first dot pattern DP(1) is a dot pattern in which dots are formed in k pixels numbered 1 and dots are not formed in pixels numbered 2 or higher. The second dot pattern DP(2) is a dot pattern in which dots are formed in (2×k) pixels numbered 2 or less and dots numbered 3 or more are not formed. The M-th dot pattern DP(M) is a pattern in which dots are formed in all {(M−1)×k} pixels. Generally speaking, the m-th dot pattern DP(m) has dots formed on (m×k) pixels numbered below m and pixels numbered above (m+1). DP is a dot pattern DP in which dots are not formed in . m indicates the dot ON number of each of the M dot patterns DP and takes an integer value of 0≤m≤(M-1). Thus, the M dot patterns DP differ from each other in the number of dots arranged in the specific area.

It can be said that the dot pattern DP(m) is a pattern that expresses the density according to the dot ON number m. The dot pattern DP(m) expresses a higher density as the dot ON number m increases. A patch image PI including the m-th dot pattern DP(m) is assumed to be a patch image PI(m). The M patch images PI included in the test image TI are patch images PI(0) to PI(M−1) including dot patterns DP(0) to DP(M−1) having different dot ON numbers m. is.

The number M of patch images PI, that is, the number M (number of types) of dot patterns DP(m) is greater than the number N of gradations of the value of the target color component (also called an input value) (M>N). In this embodiment, the input values for each color component of the CMYK values are 256 gradation values from 0 to 255 (N=256). On the other hand, the number M of types of dot patterns DP(m) is 1001 in this embodiment. Therefore, the test image TI of this embodiment includes 1001 patch images PI(0) to PI(1000) representing 1001 levels of density. The test image TI may be printed over a plurality of sheets P depending on the number of patch images. Note that the patch image PI(0) is an image of a pattern in which dots are not formed, so the patch image PI(0) is an image of only the ground color of the paper P.

Note that, in this embodiment, the test image data TID representing the test image TI is generated in advance using the dot pattern data DPD and stored in the nonvolatile storage device 230 . Alternatively, the test image data TID may be generated using the dot pattern data DPD each time the test image TI is printed.

In S130, the CPU 210 reads the paper P on which the test image TI is printed using the reading execution unit 290 to generate scan data representing the test image TI. The process of S<b>130 is executed, for example, when the manufacturer or user of the multi-function device 200 inputs a reading instruction while the paper P is placed on the platen of the reading execution unit 290 .

The drawing showing the paper P on which the test image TI is printed in FIG. 4 can also be said to be a drawing showing the scan image SI indicated by the generated scan data. Hereinafter, simply referring to the test image TI and the patch image PI means the test image TI and the patch image PI in the scan image SI.

In S140, the CPU 210 uses the reading execution unit 290 to obtain the measured value V of the density of each patch image PI. For example, the CPU 210 calculates the average value of RGB values of a plurality of pixels in the center of each patch image PI. The CPU 210 converts the average value of the RGB values into a value indicating density according to a predetermined conversion formula, and acquires the value indicating the density as the measured value V. FIG. The measured values V(0) to V(1000) of the patch images PI(0) to PI(1000) are the measured values V(0) of the dot patterns DP(0) to DP(1000) with the ON number of dots 0 to 1000. ˜V(1000). The CPU 210 creates a measured value table MT in which measured values V(0) to V(1000) are recorded.

FIG. 6 is a diagram showing an example of a measurement value table MT in which measurement values V are recorded. In this measurement value table MT, measurement values V(0) to V(1000) of patch images PI(0) to PI(1000) are recorded in association with dot ON numbers 0 to 1000. FIG.

In S142 to S150, target densities Vt(0) to Vt(255) for each input value n (0≦n≦255) of the target color component are set.

In S142, the CPU 210 converts the measured value V(0) of the dot pattern DP(0) with the minimum dot ON number m to the target density Vt(0) of the minimum input value (0 in this embodiment) of the target color component. set to In S145, the CPU 210 converts the measured value V (1000) of the dot pattern DP (1000) having the maximum dot ON number m to the target density Vt (255) of the maximum input value (255 in this embodiment) of the target color component. set to

In S150, the CPU 210 sets target densities Vt(1) to Vt(254) of input values 1 to 254 of the target color component, excluding the minimum input value 0 and the maximum input value 255, respectively.

FIG. 7 is an explanatory diagram of setting the target density. The CPU 210 creates a target table TT in which the target densities Vt(0) to Vt(255) are recorded in association with the input values 0 to 255, as shown in FIG. 7(A). FIG. 7B shows a graph conceptually showing the correspondence relationship between the input value n and the target density Vt. As described above, the target density Vt(0) corresponding to the input value 0 is the measured value V(0) of the dot pattern DP(0), and the target density Vt(255) corresponding to the input value 255 is the dot pattern DP The measured value of (1000) is taken as V(1000). Therefore, the target densities Vt(1) to Vt(254) are set so as to increase linearly as the input value increases. That is, the target densities Vt(1) to Vt(254) are set so as to lie on the straight line VL in the graph of FIG. 7B. Specifically, the CPU 210 divides the difference between the measured value V(1000) and the measured value V(0) by the number of gradations N−1 (255 in this embodiment) to determine the step amount ΔVt ( ΔVt={V(1000)−V(0)}/255). The CPU 210 sets the target value Vt(n) of each input value n to a value obtained by multiplying the step amount ΔVt by the input value n (Vt(n)=ΔVt×n). As a result, an appropriate target density Vt can be determined so that the generated dither matrix DM can appropriately express changes in input values as changes in density.

At S160, the CPU 210 executes a corresponding pattern selection process. The corresponding pattern selection process uses the measured value table MT and the target table TT to select a corresponding dot pattern to be associated with each of the input values 0 to 255 from among the 1000 dot patterns DP(0) to DP(1000). This is the process of selecting . The selected 256 corresponding dot patterns are different dot patterns DP. Since the dot patterns DP(0) to DP(1000) can be represented by the dot ON number m, the corresponding pattern selection process selects each of the input values 0 to 255 from the dot ON number m from 1 to 1000. It can also be said that this is a process of selecting the corresponding dot ON number to be associated.

FIG. 8 is a diagram showing an example of the correspondence table CT. A correspondence table CT in FIG. 8 is generated by the correspondence pattern selection process. Corresponding dot ON numbers (corresponding dot patterns) are recorded in correspondence with input values 0 to 255 in the correspondence table CT. The corresponding pattern selection process will be described later. Below, the number of ON dots corresponding to the input value n is also described as m(n).

In S170, the CPU 210 uses the correspondence table CT and the dot pattern data DPD to generate dither matrix data DMD indicating the dither matrix DM of the target color component.

FIG. 9 is a diagram showing an example of the dither matrix DM for one color component indicated by the dither matrix data DMD. In the dither matrix DM, for the same vertical and horizontal regions as the dot pattern DP (FIG. 5), that is, a specific region containing {(M−1)×k} pixels PX, a threshold value corresponding to each pixel PX is calculated. is stipulated. The threshold takes any value from 1 to 255.

The CPU 210 converts the pixel number (1 to 1000) of each pixel of the dot pattern DP (FIG. 5) defined in the dot pattern data DPD into a threshold value based on the corresponding dot ON number m(n) recorded in the correspondence table CT. By substituting (1 to 255), dither matrix data DMD is generated. Specifically, numbers below m(1) are replaced with a threshold of one. Numbers that satisfy m(n−1)<m≦m(n) (2≦n≦255) are replaced with the threshold value n.

For example, in the correspondence table CT of FIG. 8, the corresponding dot ON numbers m(1), m(2), and m(3) for the input values 1, 2, and 3 are 3, 7, and 12, respectively. For this reason, numbers 1 to 3 in the dot pattern DP of FIG. 5 are replaced by threshold 1, numbers 4 to 7 are replaced by threshold 2, and number 8 is replaced by threshold 3 (FIG. 9). In the correspondence table CT of FIG. 8, the corresponding dot ON numbers m(15), m(16), and m(17) for input values 15, 16, and 17 are 64, 69, and 73, respectively. To this end, the number 64 in the dot pattern DP of FIG. 5 is replaced with a threshold value of 15, the numbers 65-69 are replaced with a threshold value of 16, and the numbers 70 and 71 are replaced with a threshold value of 17 (FIG. 9). In this way, dither matrix data DMD representing the dither matrix DM of FIG. 9 is generated.

In S180, the CPU 210 determines whether or not all CMYK color components have been processed as the target color component. If there is an unprocessed color component (S180: NO), the CPU 210 returns the process to S110. When all color components have been processed (S180: YES), CPU 210 terminates the dither matrix generation process. In this manner, the processes of S110 to S170 are executed for each of the plurality of types of printing materials (CMYK toners in this embodiment) used for printing, so the input values are appropriately set for each printing material used for printing. We can create a dither matrix DM that can be expressed in

A-4. Corresponding Pattern Selection Processing The corresponding pattern selection processing of S160 in FIG. 3 will be described. FIG. 10 is a flowchart of corresponding pattern selection processing. In the corresponding pattern selection process, as described above, the measured value table MT (FIG. 6) and the target table TT (FIG. 7A) are used to select 1000 dot patterns DP(0) to DP(1000). A corresponding dot pattern to be associated with each of the input values 0 to 255 is selected from among them, and a correspondence table CT (FIG. 8) is generated.

FIG. 11 is an explanatory diagram of the corresponding pattern selection process. FIG. 11 shows a graph in which the measured values V(64) to V(77) of the dot pattern DP with the dot ON number m of 64 to 77 are plotted with black circles. Here, in FIG. 11, the measured values V(64) to V(77) do not necessarily increase sequentially as the dot ON number m increases. For example, measured values V(69), V(70), and V(75) are smaller than immediately preceding measured values V(68), V(69), and V(74). For example, banding (so-called black streaks or white streaks) occurs in the patch image PI, and the measured value V indicates a higher or lower density than the density assumed when banding does not occur. It is because In the example of FIG. 11, for example, the measured value V(68) indicates a darker density than expected due to black streaks occurring in the measured patch image PI. Also, the measured values V(70) and V(75) show a lower density than expected due to white streaks occurring in the measured patch image PI.

In S200 of FIG. 10, the CPU 210 determines the dot pattern corresponding to the minimum input value 0 as the dot pattern DP(0) with the minimum dot ON number m.

In S202, the CPU 210 determines the dot pattern corresponding to the maximum input value 255 as the dot pattern DP (1000) having the maximum dot ON number m.

In S205, the CPU 210 selects one target input value n from the input values 1 to 254 in ascending order. As shown in FIG. 7B, the larger the input value is, the higher the target density Vt is. Therefore, the smaller the input value is, the lower the corresponding target density Vt is, the earlier it is selected. That is, the target input value n is selected in the order of 1, 2, 3, 4, . In S210, the CPU 210 acquires the target density Vt(n) of the noted input value n from the target densities Vt(1) to Vt(254) recorded in the target table TT.

In S215, the CPU 210 selects one measured value V(m) of interest from the measured values V(1) to V(999) recorded in the measured value table MT in ascending order of the dot ON number m. That is, the measured values of interest are selected in order of V(1), V(2), V(3), V(4), . . . , V(999).

In S220, the CPU 210 determines whether or not the noted measured value V(m) is greater than the target density Vt(n) of the noted input value n. If the measured value of interest V(m) is less than or equal to the target density Vt(n) of the input value of interest n (S220: NO), the CPU 210 returns to S215 and selects the next measured value of interest.

If the measured value of interest V(m) is greater than the target density Vt(n) of the input value of interest n (S220: YES), in S225 the CPU 210 determines the measured value V immediately before the measured value of interest V(m). The dot pattern DP(m-1) corresponding to (m-1) is selected as the corresponding dot pattern of the target input value n.

In this way, the CPU 210 selects the measured value of interest V(m) one by one in ascending order of the dot ON number m (S215), and the measured value of interest V(m) becomes the target density Vt(n) of the input value of interest n. If it is larger (S220: YES), the dot pattern DP(m-1) corresponding to the immediately preceding measured value V(m-1) is selected as the corresponding dot pattern for the target input value n (225). In other words, the CPU 210 searches for a pair of dot patterns DP(m-1), DP(m) having a pair of measured values V(m-1), V(m) straddling the target density Vt(n). . That is, in the pair of dot patterns DP(m−1) and DP(m) to be searched, the number of ON dots is continuous, and the measured value V(m− 1) is equal to or less than the target density Vt(n) of the input value of interest n, and the measured value V(m) of the other dot pattern DP(m) is greater than the target density Vt(n) of the input value of interest n. Then, the CPU 210 selects the dot pattern DP(m−1) with the smaller dot ON number m from the pair of dot patterns DP(m−1) and DP(m) as the corresponding dot pattern.

In the example of FIG. 11, when the target input value n is 15, a pair of dot patterns DP(64) and DP(65) corresponding to the measured values V(64) and V(65) are searched. (see PR1 in FIG. 11), and the dot pattern DP(64) corresponding to the measured value V(64) is selected as the corresponding dot pattern for the noted input value 15. FIG. Similarly, when the target input value n is 16, a pair of dot patterns DP(67) and DP(68) corresponding to the measured value V(67) and the measured value V(68) are searched ( 11), the dot pattern DP (67) corresponding to the measured value V (67) is selected as the corresponding dot pattern for the target input value 16. FIG. When the input value of interest n is 17, a pair of dot patterns DP(73) and DP(74) corresponding to the measured value V(73) and the measured value V(74) are searched (PR3 in FIG. 11). ), the dot pattern DP(73) corresponding to the measured value V(73) is selected as the corresponding dot pattern for the noted input value 16. FIG.

Here, when the target input value n is 16, as shown in FIG. 11, a pair of dot patterns There are DP(69), DP(70), a pair of dot patterns DP(70), DP(71), and a pair of dot patterns DP(74), DP(75) (see PRa to PRc in FIG. 11). ). Even in such a case, in this embodiment, a pair of dot patterns is searched in the order of decreasing dot ON number m. Other pairs of dot patterns are not searched. As described above, in this embodiment, even if there are a plurality of pairs of dot patterns corresponding to two measured values that straddle the target density Vt(n) of the input value of interest n, the dot ON number m is searched for a particular pair of dot patterns with the smallest .

In S230, the CPU 210 calculates the measured value V of the dot ON number m between the corresponding dot pattern of the target input value n and the corresponding dot pattern of the previous target input value (also referred to as the previous input value (n−1)). to get

In the example of FIG. 11, when the target input value n is 16, the dots between the corresponding dot pattern DP (67) for the target input value 16 and the corresponding dot pattern DP (64) for the previous input value 15 are Two measurements V(65), V(66) with ON numbers 65, 66 are obtained. When the target input value n is 17, the dot ON number 68 to 72 between the dot pattern DP (73) corresponding to the target input value 17 and the corresponding dot pattern DP (67) for the previous input value 16 is determined. Five measurements V(68)-V(72) are taken.

In S235, the CPU 210 determines whether or not there is a measured value closer to the previous target density than the measured value V of the corresponding dot pattern of the previous input value among the one or more acquired measured values V. The previous target density is the target density Vt(n-1) of the previous input value (n-1).

If there is a measured value closer to the previous target density than the measured value V of the corresponding dot pattern of the previous input value (S235: YES), in S240, the CPU 210 determines the corresponding dot pattern of the previous input value (n−1). to change Specifically, the corresponding dot pattern of the previous input value (n-1) corresponds to the measured value V closer to the previous target density than the measured value V of the corresponding dot pattern determined in S225. The dot pattern DP is changed to If there is no measured value V closer to the previous target density than the measured value V of the dot pattern corresponding to the previous input value (S235: NO), the CPU 210 skips S240.

In the example of FIG. 11, when the input value of interest n is 16, the two measured values V(65) and V(66) obtained in S230 are higher than the measured value V(64) in the previous target density. Since it is far from Vt(15), the dot pattern corresponding to the previous input value of 15 is not changed. When the input value of interest n is 17, among the five measured values V(68) to V(72) acquired in S230, the measured value V(69) is higher than the measured value V(67). Since it is close to the previous target density Vt(16), the dot pattern corresponding to the previous input value 16 is changed from dot pattern DP(67) to dot pattern DP(69).

In S245, CPU 210 determines whether or not dot patterns corresponding to all input values 1 to 244 have been selected. If there is an input value for which the corresponding dot pattern has not been selected (S245: NO), the CPU 210 returns to S205 and selects the next target input value. Note that when the target measured value V(m) is selected in S215 for the next target input value, the measured value V(1) with the dot ON number m=1 is not selected again. The measured value V next to the last selected measured value V(m) in S215 for the immediately preceding input value of interest is selected.

When the corresponding dot patterns for all input values have been selected (S245: YES), the CPU 210 terminates the corresponding pattern selection process.

According to the embodiment described above, the print execution unit 280 is caused to print M patch images PI using M (M is an integer of 3 or more, M=1001 in this embodiment) dot patterns (Fig. 3 S120). By performing colorimetry on the M patch images PI using the reading execution unit 290, M measured values V indicating the densities of the M dot patterns DP are obtained (S130 and S140 in FIG. 3, 6). Using M measured values V, out of M dot patterns DP, N (N is an integer that satisfies M>N≧2, in this embodiment, N=256) should be associated with input values. N corresponding dot patterns are selected (S142-S160 in FIG. 3). A dither matrix DM is created based on the N corresponding dot patterns (S170 in FIG. 3).

The CPU 210 selects one target input value from the N input values in a predetermined selection order (S205 in FIG. 10). The predetermined selection order is an order (also referred to as first order) in which the lower the corresponding target density is, the earlier it is selected.

The CPU 210 acquires the target density Vt(n) corresponding to the noted input value (S110 in FIG. 7). The CPU 210 selects the measured values of interest V(m) one by one in ascending order of the dot ON number m, and selects two measured values (for example, PR1 to PR1 in FIG. 11) that straddle the target density Vt(n) of the input value of interest n. PR3), the dot pattern corresponding to the target input value n is selected from the pair of dot patterns corresponding to PR3) (S215 to S225 in FIG. 10).

In this embodiment, as described in FIG. 11 for the case where the input value of interest n is 16, a pair of measured values corresponding to two measured values of the input value of interest n straddling the target density Vt(n) Even if there are a plurality of dot patterns, from a specific pair of dot patterns with the smallest dot ON number m, in other words, from a specific pair of dot patterns with the dot ON number corresponding to the lowest density, A dot pattern corresponding to the input value of interest n is selected.

Ideally, the measured value V of the M dot patterns DP increases sequentially as the number of ON dots increases. However, in reality, such a magnitude relationship may be reversed due to unevenness, banding, or the like. When the size relationship is reversed, a plurality of pairs of dot patterns may exist as described above. According to the above configuration, when two or more dot pattern pairs exist, the corresponding dot pattern to be associated with the target input value is selected from the specific pair of dot patterns with the smallest ON number of dots. As a result, an appropriate corresponding dot pattern is selected so that the density represented by the corresponding dot pattern increases as the input value increases, even if the magnitude relationship is reversed as described above. can do. For example, if the input value of interest n is 16 in the example of FIG. 11, the dot pattern corresponding to the input value of interest 16 is selected from the pair of dot patterns DP(74) and DP(75) in FIG. and In this case, the number of ON dots in the dot pattern corresponding to the input value of interest 16 can be larger than the number of ON dots in the dot pattern corresponding to the input value of interest 17, so it cannot be said that an appropriate corresponding dot pattern is selected. . According to this embodiment, such inconvenience can be suppressed.

Further, in this embodiment, N corresponding dot patterns are selected from M dot patterns DP, which is larger than the number of input values (the number of gradations) N. Inclusion of the same dot pattern can be suppressed. As a result, it is possible to create a dither matrix DM capable of generating dot data that appropriately express input values.
be.

Furthermore, according to this embodiment, for example, the dot pattern DP (67) is selected as the dot pattern corresponding to the input value of interest 16, and the dot pattern DP (73) is selected as the dot pattern corresponding to the next input value of interest 17. If selected, CPU 210 may change the corresponding dot pattern of the previous input value of interest 16 as follows. That is, as described above, the CPU 210 inserts the dot pattern DP into the dot patterns DP(68) to DP(72) having dot ON numbers between the dot pattern DP(67) and the dot pattern DP(73). It is determined whether or not there is a dot pattern having a measured value V closer to the target density Vt(16) than the measured value V(67) of (67) (S230, 235 in FIG. 10). In the example of FIG. 11, since the dot pattern DP(69) exists (YES in S235 of FIG. 10), the CPU 210 changes the dot pattern corresponding to the target input value 16 to the dot pattern DP(69) ( S240 in FIG. 10). As a result, the corresponding dot pattern to be associated with the target input value 16 can be determined as a dot pattern expressing a density closer to the target density Vt(16).

Furthermore, according to the above embodiment, as shown in S230 of FIG. 10, the candidates for the dot pattern corresponding to the previous target input value 16 are the dot pattern DP(67) and the dot pattern DP( 73) and dot patterns DP(68) to DP(72). That is, a dot pattern (for example, DP(74), DP(75)) with a larger dot ON number than dot pattern DP(73) is not a candidate for the dot pattern corresponding to the previous target input value 16. FIG. In other words, the CPU 210 determines that the dot pattern whose dot ON number is larger than that of the corresponding dot pattern DP(73) of the target input value 17, that is, whose density order determined by the dot ON number comes later, has the measured value V of dot pattern DP(73). Even if the patterns DP(67) and DP(69) are closer to the target density Vt(16) than the patterns DP(67) and DP(69), they are not regarded as the dot pattern corresponding to the target input value 16. FIG. For example, in the example of FIG. 11, the measured value V(75) of the dot pattern DP(75) is closer to the target density Vt(16) than the dot patterns DP(67) and DP(69). is not adopted as the corresponding dot pattern. As a result, even if the magnitude relationship of the measured value V is reversed due to banding or the like, as the input value n increases, the density represented by the corresponding dot pattern also increases. , an appropriate corresponding dot pattern can be selected.

Furthermore, in this embodiment, the density order of the dot patterns DP, that is, the order of the dot patterns DP from which the measured values V are obtained in S215 is the order based on the dot ON number m. As a result, at S215, the measured values V are acquired in an appropriate order. As a result, the dot pattern DP that more appropriately expresses the input value is selected as the corresponding dot pattern.

B. Modification (1) In the above-described embodiment, the order of selection of the target input values in S205 of FIG. 10 is in ascending order of the input value, in other words, the lower the target density Vt, the earlier it is selected. Alternatively, the order of selection of the input values of interest may be such that the input values are selected in descending order, in other words, the higher the target density Vt, the higher the selection order. For example, the input values of interest may be selected in the order 254, 253, 252, . In this case, in S215 of FIG. 10, the measured value of interest V is selected in descending order of the dot ON number m. Then, in S220 of FIG. 10, it is determined whether or not the noted measured value V is smaller than the target density Vt(n) of the noted input value n. Further, in this case, when there are a plurality of pairs of dot patterns DP corresponding to two measured values of the target input value n straddling the target density Vt(n), the pair of dot patterns DP having the largest dot ON number m A dot pattern (that is, a pair of dot patterns with the number of ON dots corresponding to the highest density) is selected.

(2) In the corresponding pattern selection process of the above embodiment, when a pair of dot patterns DP corresponding to two measured values straddling the target density Vt(n) of the input value of interest n is searched (S220 in FIG. 10). YES), the dot pattern DP with the smaller number of ON dots is selected as the dot pattern corresponding to the target input value n (S225 in FIG. 10). Alternatively, of the pair of dot patterns DP, the dot pattern DP with the larger number of ON dots may be selected as the dot pattern corresponding to the target input value n. Also, from the pair of dot patterns DP, the dot pattern DP whose measured value V is close to the target density Vt(n) may be selected as the dot pattern corresponding to the target input value n.

(3) In the above embodiment, the dot ON number m is used as the value indicating the order of the densities of the M dot patterns DP. That is, the density order in the above embodiment is an order based on the number of dots arranged in a specific area in the dot pattern DP. Therefore, the larger the dot ON number m, the higher the density expressed by the dot pattern DP(m), and the higher the density order. Alternatively, for example, if the print execution unit 280 is an inkjet printer and three types of dots, small, medium, and large, are used, the dot pattern density order is not limited to the ON number of dots m. It is not determined, but is determined based on both the dot ON number m and the dot size. For example, when the dot ON number m is the same, the higher the proportion of large size dots, the later the density order.

(4) In the corresponding pattern selection process (FIG. 10) of the above embodiment, the process of changing the corresponding dot pattern once selected (S230 to S240) may be omitted.

(5) The target densities Vt corresponding to each of the M input values need not be set so as to increase linearly as shown in FIG. 7B. For example, the target densities Vt may be set such that the graph plotting the target densities Vt corresponding to each of the M input values is an upwardly convex graph or a downwardly convex graph.

(6) Since the print execution unit 280 of the above embodiment is a printer that uses four types of CMYK printing materials, in the above embodiment, four types of dither matrices DM corresponding to the four types of CMYK printing materials are created. be done. Instead of this, for example, when a monochrome printer using only K printing material is employed, only one type of dither matrix DM corresponding to K printing material is created. Further, when a printer using six types of printing materials in which light cyan and light magenta are added to the four types of CMYK printing materials, six types of dither matrices DM corresponding to the six types of printing materials are created. can be

(7) In the above embodiment, the test image TI is printed on the paper P using the print execution unit 280 of one multifunction device 200 (S120 in FIG. 2), and the reading execution unit 290 of the multifunction device 200 is used to Then, by reading the sheet P, the measurement value V of each patch image is acquired (S130, S140 in FIG. 3). Alternatively, the printing of the test image may be performed using one printer, and the reading of the paper P may be performed by a scanner separate from the one printer. Alternatively, instead of the scanner, a spectral colorimeter (for example, X-rite's i1iSis) is used to measure the color of each patch image PI one by one, thereby obtaining the measured value V of each patch image. Also good.

(6) A part of the dither matrix generation process in FIG. or the terminal device 100 such as a personal computer. Further, the processes of S140 to S170 may be executed by a server connected to the MFP 200, for example, a server operated by the manufacturer of the MFP 200. FIG. In these cases, for example, the terminal device 100 or the server supplies the test image data TID to the MFP 200, and the MFP 200 uses the test image data TID to print the test image TI on the paper P. You can print it. Further, the terminal device 100 and the server may acquire scan data generated by reading the paper P in the multifunction device 200 from the multifunction device 200, and use the scan data to execute the processes of S140 to S170. .

(7) Further, a plurality of computers (for example, a cloud server) that can communicate with each other via a network may partially share the processing of S140 to S170. In this case, a collection of computers is an example of a generating device.

(8) In each of the above embodiments, part of the configuration implemented by hardware may be replaced with software, or conversely, part or all of the configuration implemented by software may be replaced with hardware. You may do so.

Although the present invention has been described above based on examples and modifications, the above-described embodiments of the present invention are intended to facilitate understanding of the present invention, and are not intended to limit the present invention. The present invention may be modified and modified without departing from the spirit and scope of the claims, and the present invention includes equivalents thereof.

DESCRIPTION OF SYMBOLS 100... Terminal device, 200... MFP, 210... CPU, 220... Volatile memory device, 230... Non-volatile memory device, 240... Display part, 250... Operation part, 270... Communication IF, 280... Print execution part, 290 ... reading execution part, P ... paper, PG ... computer program, CT ... correspondence table, MT ... measurement value table, TT ... target table, TID ... test image data, DMD ... dither matrix data, DPD ... dot pattern data

Claims (6)

A method for generating a dither matrix used for generating dot data, comprising:
The dot data is data for causing a print executing unit that forms dots on a printing medium using a printing material to execute printing,
A printing step of causing the print execution unit to print M patch images using M dot patterns (M is an integer equal to or greater than 3) whose density order is determined , wherein each of the M dot patterns is an arrangement pattern of the dots in a specific area in the corresponding patch image , and is a pattern expressing different densities by different numbers of dots arranged in the specific area, and the density the printing step, wherein the order is an order that becomes later as the number of the dots arranged in the specific region increases ;
an acquisition step of acquiring a corresponding target density for each of N input values (N is an integer satisfying M>N≧2), wherein the input value is a color component corresponding to the printing material; and the target density is the density of a color to be expressed using the printing material according to the input value, and is set to increase as the input value increases. process and
a colorimetric step of obtaining M measured values indicating densities of the M dot patterns by colorimetrically measuring the M patch images;
A selection step of selecting N corresponding dot patterns to be associated with the N input values from the M dot patterns using the M measured values , wherein the N corresponding dots the selecting step, wherein the patterns are the dot patterns different from each other;
a creation step of creating a dither matrix based on the N corresponding dot patterns to be selected;
with
The selection step includes
A first step of selecting the input values of interest one by one from the N input values in a predetermined selection order, wherein the predetermined selection order is such that the lower the corresponding target density, the earlier it is selected. 1 order, or a second order in which the higher the target density is, the higher the selected order is;
a second step of obtaining the target density corresponding to the input value of interest;
A third step of selecting the corresponding dot pattern to be associated with the input value of interest from a pair of dot patterns having consecutive density orders among the M dot patterns , wherein: The measured value of one of the dot patterns is equal to or less than the target density corresponding to the input value of interest, and the measured value of the other dot pattern of the pair of dot patterns corresponds to the input value of interest. greater than the target concentration, the third step;
with
When there are two or more pairs of dot patterns, in the third step, a specific pair of dot patterns according to the predetermined selection order is selected among the two or more pairs of dot patterns. the corresponding dot pattern to be associated with the input value of interest is selected from
When the predetermined selection order is the first order, the specific pair of dot patterns is the pair of dot patterns whose density order is the first among two or more sets of the pair of dot patterns. and wherein the predetermined selection order is the second order, the pair of dot patterns having the last density order among two or more pairs of dot patterns. The method of claim 1, wherein
The input values of interest selected one by one in the first step include a first input value of interest and a second input value of interest,
In the third step,
selecting a first dot pattern out of the M dot patterns as the corresponding dot pattern to be associated with the first input value of interest ;
selecting a second dot pattern out of the M dot patterns as the corresponding dot pattern to be associated with the second input value of interest selected next to the first input value of interest;
The selecting step further comprises:
when a third dot pattern exists among the M dot patterns, the corresponding dot pattern to be associated with the first input value of interest is changed from the first dot pattern to the third dot pattern; A fourth step of changing,
The density order of the third dot pattern is between the density order of the first dot pattern and the density order of the second dot pattern, and corresponds to the third dot pattern. The method, wherein the measured value is closer to the target density of the first input value of interest than the measured value corresponding to the first dot pattern. 3. The method of claim 2, wherein
In the fourth step, even if a fourth dot pattern exists among the M dot patterns, the corresponding dot pattern to be associated with the first input value of interest is selected from the first dots. pattern or without changing from said third dot pattern to said fourth dot pattern,
The density order of the fourth dot pattern is after the density order of the second dot pattern, and the measured value corresponding to the fourth dot pattern is the density order of the first dot pattern. or closer to said target density of said first input value of interest than said measured value corresponding to said third dot pattern. The method according to any one of claims 1 to 3 ,
A method, wherein a target concentration corresponding to each of said N input values is determined to increase linearly as said input value increases. The method according to any one of claims 1 to 4 ,
The print execution unit forms the dots using a plurality of types of printing materials ,
The printing step includes printing the M patch images for each of the plurality of types of printing materials,
The colorimetric step acquires the M measured values for each of the plurality of types of printing materials,
The selecting step selects the N corresponding dot patterns to be associated with the N input values for each of the plurality of types of printing materials;
The method according to claim 1, wherein the creating step creates the dither matrix for each of the plurality of types of printing materials. A generating device for generating a dither matrix used for generating dot data for causing a print execution unit that forms dots on paper using a printing material to execute printing,
A print control unit that causes the print execution unit to print M patch images using M dot patterns (M is an integer equal to or greater than 3) whose density order is determined , wherein: Each of the patterns is an arrangement pattern of the dots in a specific region in the corresponding patch image , and is a pattern expressing different densities by different numbers of dots arranged in the specific region. the print control unit , wherein the density order is an order in which the greater the number of dots arranged in the specific area, the later ;
an acquisition unit that acquires a corresponding target density for each of N input values (N is an integer that satisfies M>N≧2), wherein the input value is a color component corresponding to the printing material; and the target density is the density of a color to be expressed using the printing material according to the input value, and is set to increase as the input value increases. Department and
a colorimetry unit that acquires M measured values indicating the density of the M dot patterns by measuring the colors of the M patch images;
A selection unit for selecting N corresponding dot patterns to be associated with the N input values from the M dot patterns using the M measured values, wherein the N corresponding dots the selection unit, wherein the patterns are the dot patterns different from each other;
a creation unit for creating a dither matrix based on the N corresponding dot patterns to be selected;
with
The selection unit
A first processing unit that selects input values of interest one by one from the N input values in a predetermined selection order, wherein the predetermined selection order is such that the lower the corresponding target density is, the earlier it is selected. the first processing unit, which is either a first order or a second order in which the higher the target density is, the earlier it is selected;
a second processing unit that acquires the target density corresponding to the input value of interest;
a third processing unit that selects the corresponding dot pattern to be associated with the input value of interest from a pair of dot patterns having consecutive densities among the M dot patterns , wherein, of the pair of dot patterns, The measured value of one of the dot patterns is equal to or less than the target density corresponding to the input value of interest, and the measured value of the other dot pattern of the pair of dot patterns corresponds to the input value of interest. the third processing unit having a density higher than the target density;
with
When there are two or more pairs of dot patterns , the third processing unit selects from among the two or more pairs of dot patterns a specific pair of dot patterns according to the predetermined selection order. , selecting the corresponding dot pattern to be associated with the input value of interest;
When the predetermined selection order is the first order, the specific pair of dot patterns is the pair of dot patterns whose density order is the first among two or more sets of the pair of dot patterns. and when the predetermined selection order is the second order, the generating device is the pair of dot patterns whose density order is the last among two or more sets of the pair of dot patterns.

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