JP2010208336A - Data processing method, data processing apparatus, and dither pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dither pattern which can limit the occurrence of grains and reduce image quality deterioration resulting from beading when a plurality of different color inks are used for recording. <P>SOLUTION: When, for example, a threshold dot Do gives the largest total of repulsive potentials among respective threshold dots for calculating a total of repulsive potentials, a change in repulsive potential before and after its moving is determined, and the threshold dot Do is moved to a pixel at which a total of repulsive potentials is smallest before and after the moving. Such processes, when repeated many times, can lower a total energy of the entire three planes, and a threshold dot distribution is so arranged in terms of overlapped three-plane dither patterns as to distribute a few low-frequency components favorably. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a data processing method, a data processing apparatus, and a dither pattern, and more particularly to a dither process for quantizing image data or a dither pattern used therefor.

  In order to generate dot recording data for forming a plurality of ink dots constituting a recording image in a printer such as an ink jet printer, generally, for example, 8-bit image data is quantized into 1-bit binary image data. Perform by processing. Dither processing is known as one of these quantization methods. By using the methods described in Patent Document 1, Patent Document 2, and the like, patterns with good dispersibility can be generated, and binary image data quantized with these patterns is also a pattern with good dispersibility with little noise. Become. The dither method has a higher calculation speed than the error diffusion method and is suitable for processing a high-speed printer that requires speed, a multicolor printer with a large number of data, and the like.

Japanese Patent No. 2622429 US Pat. No. 5,553,020

  By the way, in recent inkjet recording systems, with the increase in speed and density, and the diversification of ink types, the amount of ink applied per unit time and the amount of ink applied per unit area of the recording medium are increased. The amount tends to increase. For this reason, the problem of beading is given as a more important issue than ever. In the beading, ink that cannot be absorbed by the recording medium comes in contact with each other on the medium, which causes unevenness in the recorded image.

  In order to reduce beading, it is important to dispose the ink applied within a short time at different positions as much as possible. For this reason, it is effective to use dither patterns that are as different as possible for each color ink. By doing so, it is possible to reduce the probability that different color inks are driven into the same place.

  However, simply reducing the dither pattern for each color does not reduce the beading sufficiently.

  FIGS. 32A to 32C are diagrams for explaining this problem. This figure shows a process in which each ink is driven into a recording medium in the order of cyan, magenta, and yellow. As shown in FIG. 32A, cyan ink is first ejected onto a recording medium on which nothing has been printed yet. At this time, it goes without saying that the positions where the respective cyan inks are applied follow the arrangement of the dots of the dither pattern used. Before the ink is completely absorbed by the recording medium, the cyan ink droplet 10C exists on the recording medium in an arrangement according to the mask. Next, as shown in FIG. 32B, magenta ink is similarly ejected to a position according to the corresponding dither pattern, and similarly forms an ink droplet 10M before absorption. Here, depending on the dot arrangement relationship of the dither used for each of the cyan ink and magenta ink, the ink droplet 10B in which the cyan ink droplet 10C and the magenta ink droplet 10M are in contact with each other (the one marked with an X in the drawing) is connected. May form. Further, as shown in FIG. 32 (c), the yellow ink is similarly ejected to a position according to the corresponding dither pattern and forms an ink droplet 10Y before absorption. In this case as well, connected ink droplets 10B (those marked with x in the figure) are formed according to the relationship of the dot arrangement of the mask used for each ink. When the scanning is further repeated and the ratio of the ink droplets to the pixels becomes high, the ink droplets may be ejected in the same pixel, and the same connected ink droplets are formed.

  In this way, when ink droplets that are sequentially ejected are applied to adjacent or adjacent pixels or the same pixel, they contact each other and attract each other by the surface tension of two or three (or more) A large droplet 10B (grain) in which the ink droplets are combined is formed. Once such a grain is formed, the ink droplet applied to the next or adjacent position is likely to be attracted to the grain. That is, the first generated grain gradually grows as a nucleus and eventually produces large grains. In particular, in a uniform image area, the grains fixed on the recording medium are scattered in an irregular manner and are visually recognized as beading.

  The proximity or adjacency of dots that cause grains that occur during recording depends on the arrangement pattern of quantized data inherent in the quantized image data. That is, according to the threshold arrangement pattern in the dither pattern, the arrangement of the quantized data in the image data plane is determined.

  The dither processing or dither pattern described in Patent Document 1 cannot solve the grain problem as described with reference to FIG. That is, the dither pattern described in Patent Document 1 can also apply different dither patterns to different colors. In this case, the dither patterns are determined independently between different colors. For this reason, the arrangement of the recording dots of different colors has poor dispersion, and it may be impossible to avoid dot adjacency or even dot overlap in an image (intermediate image) in the middle of divided recording.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to suppress the occurrence of grains when recording using a plurality of different color inks and to deteriorate image quality due to beading. Is to provide a data processing method, a data processing device and a dither pattern.

  Therefore, in the present invention, in the data processing method for performing quantization for generating print data of a plurality of types of dots using a plurality of dither patterns, the plurality of dither patterns are obtained by overlapping two or more of them. Further, the threshold value average value pattern of the corresponding threshold pixel has fewer low frequency components than the threshold value average value pattern of the corresponding threshold pixel when the overlapping position is shifted for the two or more dither patterns. And

  According to the above configuration, it is possible to reduce image quality degradation due to beading caused by grains in the middle of recording.

FIG. 2 is a block diagram mainly illustrating hardware and software configurations of a PC as an image processing apparatus according to an embodiment of the present invention. It is a block diagram for demonstrating the flow of the image data conversion process in the inkjet recording system of one Embodiment of this invention. 1 is a perspective view showing an ink jet recording apparatus applicable to an embodiment of the present invention. It is a figure explaining the dither pattern manufacturing method concerning a first embodiment of the present invention. It is a flowchart which shows the procedure of the dither pattern manufacturing method which concerns on 1st embodiment of this invention. It is a figure which shows typically the function of the basic repulsive potential E (r) which concerns on embodiment of this invention. (A)-(d) is a figure which illustrates typically the provision of the repulsive potential and attenuation | damping process of total energy concerning 1st embodiment of this invention. It is a flowchart which shows the creation process of the dither pattern of this embodiment. It is a figure which shows arrangement | positioning of the threshold value of the dither pattern which concerns on 1st embodiment of this invention. It is a figure which shows arrangement | positioning of the threshold value of the dither pattern which concerns on 1st embodiment of this invention. It is a figure which shows arrangement | positioning of the threshold value of the dither pattern which concerns on 1st embodiment of this invention. It is a figure which shows arrangement | positioning of the threshold value average of two dither pattern patterns which concern on 1st embodiment of this invention. It is a figure which shows arrangement | positioning of the threshold value average of three dither pattern patterns which concern on 1st embodiment of this invention. It is a figure which shows arrangement | positioning of the threshold value average of two dither pattern patterns when the dither pattern of 1st embodiment of this invention is shifted. It is a figure which shows arrangement | positioning of the threshold value average of three dither pattern patterns when the dither pattern of 1st embodiment of this invention is shifted. It is a figure which shows the power spectrum of the threshold value average of two dither patterns of the dither pattern of 1st embodiment of this invention, and the dither pattern which shifted it, respectively. It is a figure which shows the power spectrum of the threshold value average of three dither patterns of the dither pattern of 1st embodiment of this invention, and the dither pattern which shifted it, respectively. It is a figure which shows the difference of the low frequency component of each threshold value average of the dither pattern of 1st embodiment of this invention, and the dither pattern which shifted it. It is a figure which shows arrangement | positioning of the threshold value of the dither pattern which concerns on a prior art example. It is a figure which shows arrangement | positioning of the threshold value average of two dither pattern patterns concerning a prior art example. It is a figure which shows arrangement | positioning of the threshold value average of the three dither pattern patterns concerning a prior art example. It is a figure which shows the power spectrum of the threshold value average of three dither patterns of each of the dither pattern of 1st embodiment of this invention, and the dither pattern of a prior art example. It is a figure which shows the difference of the low frequency component of the threshold value average of the dither pattern of 1st embodiment of this invention, and the dither pattern of a prior art example. It is a figure which shows the logical product pattern of the dot pattern obtained by binarizing a uniform image using the lamination | stacking dither pattern C and M of this embodiment. It is a figure which shows the logical product pattern of the dot pattern obtained by binarizing a uniform image using the dither patterns C and M of a prior art example. It is a figure which shows the logical product pattern of the dot pattern obtained by binarizing a uniform image using the dither patterns C and M of another conventional example. It is a figure which shows the logical product pattern of the dot pattern obtained by binarizing a uniform image using the lamination | stacking dither pattern C, M, and Y of this embodiment. It is a figure which shows the [superposition] pattern of the dot pattern obtained by binarizing a uniform image using the lamination | stacking dither pattern C, M, and Y of this embodiment. It is a figure which shows the power spectrum of the [superposition] of the dot pattern obtained by binarizing a uniform image using the two dither pattern patterns of the dither pattern of the first embodiment of the present invention and the dither pattern of the conventional example. is there. FIG. 4 is a diagram showing a power spectrum of [superposition] of dot patterns obtained by binarizing a uniform image using three dither pattern patterns, each of the dither pattern of the first embodiment of the present invention and the dither pattern of the conventional example. is there. The difference of the low frequency component of the dot pattern [superimposition] obtained by binarizing a uniform image using the dither pattern of each of the dither pattern of the first embodiment of the present invention and the dither pattern of the conventional example is shown. FIG. It is a figure explaining the problem of a prior art.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  Embodiments of the present invention relate to the manufacture of a dither pattern for generating binary image data used in multi-pass printing or the dither pattern.

  FIG. 1 is a block diagram mainly showing hardware and software configurations of a personal computer (hereinafter also simply referred to as a PC) functioning as a host device according to an embodiment of the present invention. This host device generates image data to be recorded by the printer 104.

  In FIG. 1, a PC 100 as a host computer operates application software 101, a printer driver 103, and a monitor driver 105 by an operating system (OS) 102. The application software 101 performs processing related to a word processor, spreadsheet, internet browser, and the like. The monitor driver 105 executes processing such as creating image data to be displayed on the monitor 106.

  The printer driver 103 draws various drawing command groups (image drawing command, text drawing command, graphics drawing command, etc.) issued from the application software 101 to the OS 102, and finally outputs binary image data used by the printer 104. Generate. Specifically, binary image data for each of a plurality of ink colors used in the printer 104 is generated by executing image processing described later with reference to FIG.

  The host computer 100 includes a CPU 108, a hard disk (HD) 107, a RAM 109, a ROM 110, and the like as various hardware for operating the above software. That is, the CPU 108 executes the process according to the software program stored in the hard disk 107 or the ROM 110, and the RAM 109 is used as a work area when the process is executed.

  The printer 104 according to the present embodiment is a so-called serial printer that performs recording by scanning a recording medium that ejects ink with respect to a recording medium and ejecting ink during that time. The recording head is prepared corresponding to each of the C, M, Y, and K inks, and can be scanned with respect to a recording medium such as a recording sheet by being mounted on the carriage. Each recording head has an ejection port array density of 1200 dpi, and ejects 3.0 picoliter of ink droplets from each ejection port. Further, the number of ejection ports of each recording head is 512.

  FIG. 2 is a block diagram for explaining main data processing steps in the PC 100 and the printer 104 when recording is performed by the printer 104 in the configuration shown in FIG. As described above, the ink jet printer 104 according to the present embodiment performs recording with ink of four colors of cyan, magenta, yellow, and black, and includes a recording head J0010 that ejects ink of these four colors.

  A user can create image data to be recorded by the printer 104 via the application 101 of the host PC 100. When recording, the image data created by the application 101 is transferred to the printer driver 103.

  As the processing, the printer driver 103 executes a pre-stage process J0002, a post-stage process J0003, a γ correction J0004, a binarization process J0005, and a print data creation J0006. In the pre-stage process J0002, color gamut conversion is performed to convert the color gamut of the display device that displays the screen by the application into the color gamut of the printer 104. Specifically, image data R, G, and B in which R, G, and B are each expressed by 8 bits are converted into 8-bit data R, G, and B in the printer color gamut by a three-dimensional LUT. Next, in post-processing J0003, the color that reproduces the converted color gamut is separated into ink colors. Specifically, a process for obtaining 8-bit data C, M, Y, and K corresponding to the combination of inks for reproducing the colors represented by the 8-bit data R, G, and B obtained in the preceding process J0002 is performed. . In γ correction J0004, γ correction is performed on each of the CMYK data obtained by color separation. Specifically, conversion is performed so that each of the 8-bit data CMYK obtained by color separation is linearly associated with the gradation characteristics of the printer.

  Next, in the binarization process J0005, a quantization process is performed to convert the 8-bit data C, M, Y, and K subjected to the γ correction into 1-bit data C, M, Y, and K, respectively. In this process, a binarization process using a dither pattern described in each embodiment described later is performed. The dither pattern data used here is stored in advance in a predetermined memory. When the dither pattern data is not stored in a predetermined memory in advance and the PC 100 functions as a data processing device for dither pattern manufacturing, the dither pattern manufacturing process described in each embodiment described later is executed. To do. The manufactured dither pattern data is stored in a predetermined memory of the PC 100.

  Finally, in the print data creation process J0006, print data is created by attaching print control data or the like to binary image data containing binarized 1-bit data C, M, K, and Y. Here, the binary image data includes dot recording data indicating dot recording and dot non-recording data indicating non-recording of dots. The print control data includes “recording medium information”, “recording quality information”, and “other control information” such as a paper feed method. The print data generated as described above is supplied to the printer 104.

  FIG. 3 is a perspective view showing the inkjet printer 104. The carriage M4000 includes a recording head and an ink tank H1900 for supplying each ink of cyan (C), magenta (M), yellow (Y), and black (K) to the X direction (main scanning direction). ), And each nozzle of the recording head ejects ink at a predetermined timing based on binary image data.

  Hereinafter, a description will be given of a dither pattern manufacturing method and a dither pattern according to some embodiments used in the binarization processing J0005 of the recording system or manufactured by the recording system.

[Embodiment 1]
(1) Outline of Embodiment The data binarized by the dither pattern according to the first embodiment of the present invention is particularly good in that the dot distribution when the planes for each color overlap has a low low frequency component. It will be distributed. The example described above with reference to FIG. 2 relates to a configuration in which a binarization process using a dither pattern is performed in a host computer. However, in the printing apparatus, binary processing is performed according to the processing load of the printing apparatus such as a printer. Of course, the conversion processing may be performed.

  In the binarization process of the present embodiment, binary data (dots) in four planes corresponding to C, M, Y, and K are generated by the four dither patterns of the present embodiment. In the following, a dither pattern for generating binary data of three planes C, M, and Y excluding K will be described for simplification of description.

  In this embodiment, a repulsive potential is basically used in creating a dither pattern corresponding to three planes. As a result, the data of the three planes obtained by using each dither pattern may be such that the dot distribution when two or three planes are superimposed is well distributed with low frequency components. it can.

(2) Dither Pattern Manufacturing Method Before describing a specific method for manufacturing a dither pattern according to this embodiment, a method of applying a repulsive potential in this manufacturing method will be described.

  In the dither pattern manufacturing method of this embodiment, first, an initial dot pattern is created for each of a plurality of planes of the dither pattern, and at that time, by using a repulsive potential, each of the planes and other planes is used. The dots are arranged with high dispersibility. Further, the initial dot pattern is set as an initial value, and then dots are sequentially thinned out, and a threshold value corresponding to the dot pattern is arranged at the position of the dot pattern after the thinning out to obtain a dither pattern. At the time of thinning, the dot arrangement having a low repulsive potential energy is selected to increase the dispersibility of the dot arrangement after the thinning.

  In the threshold value generation algorithm described below, when determining each threshold value, a dot and a repulsive potential associated therewith are defined from time to time, and a design is performed to increase dispersibility. Therefore, it is assumed that dots are distributed in relation to the threshold distribution.

  FIG. 4 is a diagram conceptually showing dot pattern generation according to the present embodiment.

  In dot pattern generation, dot patterns C, M, and Y for C, M, and Y are generated. In the generation of this dot pattern, the dot arrangement for each of the dot patterns C, M, and Y is performed as follows.

  FIG. 5 is a flowchart showing dot arrangement determination processing in a dot pattern by the arrangement movement method according to the present embodiment.

  First, in step S501, 50% density images of C, M, and Y corresponding to the sizes of the respective dot patterns C, M, and Y are acquired. In step S502, each image is binarized using a binarization method such as an error diffusion method. As a result, for each of the dot patterns C, M, and Y, it is possible to obtain an initial arrangement in which dots whose 1-bit data is “1” are arranged in 50% of all the pixels of the dot pattern. The reason why the initial arrangement of dots is obtained using this binarization method is that an arrangement with good dispersibility can be obtained to some extent in accordance with the binarization method used. This is because the calculation time or convergence time until the final placement determination can be shortened. In other words, the method of obtaining the initial arrangement is not essential in applying the present invention. For example, in the dot pattern plane, the initial arrangement is such that dots whose 1-bit data is “1” are randomly arranged. Also good. Further, for example, a 50% image of C is the first plane, an image obtained by rotating the image 90 degrees clockwise is an M second plane, and an image rotated 180 degrees in the same manner is a third Y plane. An initial arrangement such as a plane may be obtained.

Next, in step S503, the repulsive potential is calculated for all the dots on the respective planes of the dot patterns C, M, and Y obtained as described above. In particular,
(I) A repulsive force corresponding to the distance is applied between dots in the same plane.
(Ii) Furthermore, a repulsive force is also applied to dots between different planes.
(Iii) Apply different repulsive forces between the same plane and different planes.
(Iv) Recognizing the overlap of dots in different planes, the dot overlap (two dot overlaps, three dot overlaps,...) Also gives a repulsive force according to the combination.

  FIG. 6 is a diagram schematically showing a function of the basic repulsive potential E (r) according to the present embodiment.

  As shown in the figure, the repulsive force function defined in the present embodiment has a range in which the repulsive force extends up to r = 16 (pixels: pixels of a dot pattern in which dots are arranged). By using a potential that decays with such a distance, basically, when dots are placed close to each other, the energy becomes high, that is, an unstable state. As a result of convergence calculation, close placement is not selected as much as possible. Can be.

  It is more desirable to determine the shape of the repulsive force based on the ratio of dots to the entire dot pattern pixels.

In addition, when recording is performed using a plurality of colors of ink, ink dots are arranged over the position where ink dots can be arranged (in the case of resolution 1200, there are 1200 × 1200 possible positions in one inch square). Therefore, when calculating the repulsive potential for each dot, it is considered that the dot overlaps on the dot. For this reason, a function is defined so as to have a finite repulsive potential at r = 0. Thereby, dispersion in consideration of dot overlap is possible.
In this embodiment, calculation is performed by giving a repulsive potential of αE (r) for dots in the same plane, βE (r) for dots between different planes, and γs (n) E (r) for overlapping dots. In other words, the potential due to the presence of a certain dot is added to the repulsive potential of dots in the same plane, dots in different planes, and even overlapping dots in different planes within the distance r.

  In addition, although the size of the dot pattern pattern is finite (in this embodiment, it is 128 × 128 pixels), in the potential calculation, the periodic boundary condition is such that the same pattern of 128 × 128 pixels is repeated. Use. Therefore, the left end of the dot pattern is adjacent to the right end, and the bottom is adjacent to the top.

  In the above repulsive potential, the coefficients α, β, and γ are weighting coefficients, and in this embodiment, values of α = 3, β = 1, and γ = 3 are used. The dispersion of dots is affected by the values of α, β, and γ. The values of α, β, and γ can be obtained, for example, by performing an experiment in practice and optimizing with reference to a recorded image recorded using a dot pattern.

  The coefficient s (n) is a coefficient that is further integrated in addition to γ in order to disperse overlapping dots. This coefficient s (n) is set to a value corresponding to the number of overlaps so that the more overlaps, the more the dots are dispersed. According to the experiment of the present inventor, good results regarding dispersion can be obtained by using s (n) obtained by either of the following two expressions.

  That is, when n is the number of overlaps, the sum of the number of combinations is s (n). Specifically, a dot that overlaps with the target dot for calculating repulsive force (at the same position in the same plane or in a different plane) and a dot located at a distance r from the target dot are checked. In this case, let n be the number of overlaps in common between the dot of interest and the dot of another plane that overlaps at the same position as that pixel and the dot that overlaps in the same way at that pixel of each plane at the distance r. A repulsive force caused by overlapping dots between these two pixels is considered.

  In this case, for example, when an example in which dots exist in common in the first plane, the second plane, and the third plane between certain two pixels, n = 3. A repulsive force resulting from the overlap of three dots is applied between these pixels. Here, when the repulsive force due to the overlap of three dots is considered, it is considered that the overlap of two dots and the repulsive force of one dot act in a multiplexed manner together with the overlap of three dots. In other words, if the third plane is not considered, it can be considered that two dots of the first plane and the second plane overlap, and if the second plane is not considered, the two of the first plane and the third plane are considered. It can also be thought of as overlapping dots. If the first plane is not considered, it is considered that the second plane and the third plane overlap. In order to calculate the multiple effect of overlapping such dots, the repulsive force due to the combination of overlaps is defined and s (n) as described above is used. According to this, it has been experimentally confirmed that a dot arrangement with good dispersibility can be obtained.

  Referring to FIG. 5 again, in step S503, the total energy obtained by summing up the repulsive potentials of all dots is obtained. And the process which attenuates this total energy is performed.

  In this process, the dots are moved to the pixel having the lowest repulsive potential among the pixels having the distance r within 4 in order for all the dots. By repeating such processing (step S504), the total energy, which is the total value of the repulsive potential of all dots, is reduced.

  In step S505, the reduction rate of the total energy in step S504 is calculated, and if it is determined that it is equal to or less than a predetermined value, the energy attenuation process is terminated. The predetermined value can be obtained as a reduction rate at which an image in which low frequency components are appropriately suppressed can be recorded based on the result of actual printing.

  Finally, in step S506, each plane in a state where the reduction rate of the total energy is equal to or less than a predetermined value as described above is set as initial dot patterns C, M, and Y of processing to be described later with reference to FIG.

  In the present embodiment, it is determined in step S505 whether or not the reduction rate of the total energy is equal to or less than a predetermined value. When the reduction rate is equal to or less than the predetermined value, the process proceeds to step S506. However, the present embodiment is not limited to this example. For example, it may be determined whether or not the total energy is equal to or less than a predetermined value in step S505, and the process may proceed to step S506 when the total energy is equal to or less than the predetermined value.

  FIGS. 7A to 7D are diagrams schematically illustrating the repulsive potential calculation and the total energy attenuation process described above. Specifically, the three planes C, M, and Y according to the present embodiment are shown in a perspective view, and in particular, the movement of dots is shown in a plan view. Here, the smallest square represents a pixel of a dot pattern, and the overlapping pixels in the overlap of the three planes correspond to the same pixel position between the planes.

  FIG. 7A is a diagram for explaining that potential is added (increased) by repulsive force between dots when dots exist in the same plane. The example shown in the figure is an example in which one dot exists in a pixel separated by a distance r in the same plane as the dot Do of the target pixel of the plane C. In this case, α = 3 is applied, and the potential of the dot Do is 1 A potential of × αE (r) is added.

  FIG. 7B is a diagram for explaining the repulsive potential applied in relation to these two dots when dots exist on a plane (planes M and Y) different from the target dot Do. Because of the relationship with dots between different planes, β = 1 is applied and a potential of 2 × βE (r) corresponding to two dots is added as the potential of the dot Do.

  FIG. 7C shows the above two cases, in addition to the case where dots are present on the same plane and the case where dots are present on different planes. It is a figure explaining the repulsive potential added in relation to those dots, when it exists. In addition to the cases of FIGS. 7A and 7B, since the dot exists in the same pixel of the plane Y different from the plane C of the target dot Do, the same pixel as the repulsive potential 1 × αE (r) of the same plane Repulsive potential 1 × βE (0) due to one dot in different planes, repulsive potential 2 × βE (r) due to two dots in different planes, and overlapping number n = 2 and γ = 3 are applied , A repulsive potential γs (2) × E (r) potential due to the overlap is added. As a result, the total repulsive potential due to the presence of the target dot Do in the dot arrangement shown in FIG. 7C is 1 × βE (0) + 1 × αE (r) + 2 × βE (r) + γs (2) × E (r).

  FIG. 7D is a diagram for explaining that in the dot arrangement shown in FIG. 7C, the total repulsive potential of the dot changes by moving the dot Do. As shown in FIG. 7D, when the dot Do (dot of the plane C1) moves to the adjacent pixel of the same plane, the total repulsive potential due to the presence of the dot Do is the distance r2, When the number n becomes 0, it changes to βE (1) + 1 × αE (r2) + 2 × βE (r2). Then, the total repulsive potential 1 × βE (0) + 2 × αE (r) + 1 × βE (r) + γs (2) × E (r) in the case of the dot arrangement shown in FIG. It is possible to know the change in the total repulsive potential before and after the movement by comparing the total repulsive force due to the movement of the dots Do in d).

  In the above description, the total repulsive potential is obtained by calculating the total energy of the dots of three pixels when two pixels or dots are moved. This is for the sake of simplicity. In fact, it is a matter of course that it is obtained as an integral of the repulsive potential based on the relationship with dots including dots of other pixels that may exist other than these dots.

  As shown in FIGS. 7A to 7C, among the dots for which the total repulsive potential is calculated, for example, when the dot Do has the largest total repulsive potential, the description has been given with reference to FIG. Thus, the change in repulsive potential before and after the movement is obtained, and the dot Do is moved to the pixel having the lowest total repulsive potential before and after the movement. By repeating such processing, the total energy of the entire three planes can be reduced. In other words, the dot distribution in the overlapping of the three-plane dot patterns has an arrangement in which the low frequency component is small and is well dispersed. By the processing described above, an initial dot pattern with high dispersibility that is a basis for generating a dither pattern can be obtained.

  FIG. 8 is a flowchart showing a dither pattern creation process according to the present embodiment.

  First, in step S301, a binary pattern having good dispersibility in a certain gradation is created as an initial dot pattern. In this embodiment, a 50% density pattern is created. Specifically, an initial dot pattern having a size of 128 × 128 and having a 50 percent density is created by the method described with reference to FIG. The dot patterns C, M, and Y of each plane created in this way are stored as initial patterns.

Next, in step S302, repulsive potential is applied to the initial dot pattern of 128 gradations obtained above to perform dot thinning, and threshold data is created for each level of 128 gradations in the low gradation direction. . Specifically, the dots are thinned out while calculating the repulsive potential for the initial dot pattern. In this process, first, the repulsive potential is calculated for all dots of the dot pattern Y in the same manner as described with reference to FIG. 5, and the dot with the highest energy is thinned out. Next, similarly for the dot pattern M, the repulsive energy is calculated for all the dots, and the largest dot is thinned out. Further, similarly, with respect to the dot pattern C, the repulsive potential of all dots is calculated, and the dots with the maximum energy are thinned out.

  Here, in order to create an 8-bit dither pattern, a dot pattern can be obtained for each gradation level gl of 128 gradations, and a dither pattern, that is, a distribution of threshold values can be generated according to the pattern. In this embodiment, since the dither pattern has a size of 128 × 128, each plane has 128 × 128 pixels ÷ 128 gradations = 128 pixels / 1 gradation (one gradation level), and each plane has one gradation level. 128 dots are thinned out.

  That is, when thinning is performed for each plane, the thinning number parameter n is incremented (step S303), and it is determined whether n has reached 128 (step S304). The processes of steps S302 and S303 are repeated until 128 thinnings are completed (step S304). When the process is completed, in step S305, the dot pattern dot of each plane finally obtained is the value of the gradation level gl ( This is stored as a threshold arrangement pattern replaced with (gradation value). Of course, the threshold pattern of gl = 127 corresponding to the initial dot pattern is created in advance based on the initial pattern.

  The above processing (steps S302 to S304) is repeated until the gradation level gl becomes 0 (steps S302 to S307) using the dot pattern obtained at the immediately preceding level as the initial dot pattern, and each of the low gradation side is changed. A threshold value pattern of gradation values can be obtained.

  The threshold pattern on the high gradation side can be obtained in the same manner. In the case of the high gradation side, dots are added, and the energy increase is calculated by applying the repulsive potential. First, the increase in energy when dots are added to the blank points of the dot pattern C is calculated for all blank points. And a dot is added to the point with the least energy increase. This process can be performed in the same manner as the process shown in FIG. Similarly, dots are added to the dot patterns M and Y. Other processes are the same as those on the low gradation side.

  The threshold pattern of each plane for each gradation obtained as described above can be combined into a dither pattern for each of the C, M, and Y planes.

  Note that the arrangement of the dither pattern dots is not limited to dot thinning and addition using 50% density as an initial value as in the above example. For example, the initial value may be set to 0% so that dots (threshold values) are added from a state where nothing is arranged. This addition is the same as the above-described method for obtaining the threshold arrangement on the high gradation side.

(3) Dither pattern evaluation
Effect of Repulsive Potential Weighting Coefficients α, β, γs (n) in Dither Pattern First, with respect to the dither pattern manufactured by the dither pattern manufacturing method of the present embodiment described above, repulsive potential calculation (distance discussion) How the weighting coefficients α, β, and γs (n) (only the influence of the coefficients are not affected) will be described in detail. In the above-described dither pattern threshold value creation algorithm, when determining each threshold value, the dot and the repulsive potential associated therewith are defined, and the design is made so that the dispersibility is increased. Therefore, it is assumed here that dots are distributed in relation to the threshold distribution. As described above, the coefficient α affects the dispersion of dots in the same plane, the coefficient β affects the dispersion of dots between different planes, and γs (n) indicates that dots of different planes are in the same position pixels. It affects the dispersion of this overlap in the case of overlap.

  In this embodiment, the same function (FIG. 6) is used for all terms as E (r), but different potential functions can be used for each term. In this case, the difference between αE (r), βE (r) ′, and γE (r) ″, which is the product of the respective weighting coefficients α, β, and γ (n) corresponding to each function E (r). Of course, the difference in dispersion, which will be explained below, has an influence.

  If the repulsive potential is defined only between dots within the same plane and the energy distribution is attenuated to determine the dot distribution, that is, α = 1 and β = γ = 0 in αE (r), one plane Each dot distribution has good dispersibility of dot arrangement in each plane. This is due to the effect of αE (r). However, an extracted dot (logical product, logical sum) pattern obtained by superimposing two (plural) planes is uneven in dot arrangement and has a lot of low frequency components. This is because a dot that happens to overlap between two planes is generated, or because there is no relationship between the two planes, a bias occurs.

  Next, it is assumed that the same repulsive potential is applied to all the dots of the three planes, that is, α = β = 1 and γ = 0 in αE (r) and βE (r). In this case, the dot distribution of each plane has a low frequency component of a certain size and the distribution is biased. On the other hand, the dot distribution (logical sum) of the above three color planes is well distributed. Since α and β are the same value, the effect of dispersing the dots in the same plane is the same as the effect of dispersing the dots in the other planes. This is because it becomes insufficient.

  Therefore, in order to change the repulsive potential between the same plane and different planes, for example, α = 3 and β = 1. Thereby, the influence of other planes can be made relatively small, and the dispersibility within the same plane is improved. Further, the dot distribution (logical sum pattern) obtained by superimposing two planes has a good distribution with a small amount of low frequency components. Thus, both the dispersibility of dots in the same plane and different planes is improved. That is, by causing the terms αE (r) and βE (r) to act and making the values of α and β different, the dispersibility both in the same plane and in different planes is improved.

  Next, let us consider a case where the term of γs (n) E (r) is not used when there is overlap of dots. Extracting overlapping dots from the dot distribution obtained by superimposing two planes having a dot distribution that does not have low frequency components without applying the term of γs (n) E (r) (logical product) ) Has a poor distribution with many low frequency components.

  On the other hand, when the term γs (n) E (r) is added, first, a dot distribution having no low frequency component is obtained for each plane. Then, the distribution (logical product) obtained by extracting overlapping dots from the dot distribution obtained by superimposing these planes is also an arrangement of dots having no low frequency component.

  As described above, the term γs (n) E (r) basically gives the effect that the overlapping dots are well dispersed, but as explained in FIGS. 7 (a) to (d). In addition, this term is set so that the potential increases as the overlap increases. By moving or arranging dots one by one according to the potential and reducing the energy, the overlap is reduced in the process of reducing the energy. Has the effect of reducing the number. This means that for dots that are adjacent in the same plane, αE (r) gives the effect of reducing the number of adjacent dots. As described above, the term of γs (n) E (r) not only makes it possible to disperse overlapping dots as much as possible, but also has an effect of reducing the number of overlapping dots. With this effect, the number of dots in a cluster of dots due to adjacent or overlapping can be reduced as much as possible, and as a result, a dot distribution with a low frequency component can be obtained.

  From the above viewpoint, in this embodiment, the values of α = 3, β = 1, and γ = 3 are used as described above.

  Note that, for example, as α and β << γ, pay particular attention to the overlapping dots extracted in the overlapping of a plurality of planes, and the overlapping dots are particularly low in frequency due to the effect of the term of γs (n) E (r). It is also possible to achieve good dispersion with few components.

  In this embodiment, the repulsive force between the planes is all βE (r), but it is effective to make the interactions different between the planes in consideration of the magnitude of the interaction. For example, when the number of planes is large, the repulsive potential between the planes of the dither pattern used for ink that is printed as close as possible is made larger than other repulsive potentials, that is, the coefficient of βE (r) or the shape of E (r) It is also effective to change between planes. Also, for example, in the case of fixing using a reaction system, when a reaction liquid or ink having such a component is ejected by a recording head, a dither pattern plane used for the reaction liquid or the like and the reaction action of the reaction liquid or the like It is also effective to increase the repulsive potential of the dither pattern plane used for ink having a large value than usual. As a specific example of changing the repulsive potential function, an example of changing the distance r in the range where the repulsive force can be given can be given. For example, when the gradation value of the image data to be processed is 50% gradation, r = 16 as described above, and r can be increased as the gradation value is larger or smaller than 50%.

  In the present specification, the more uniformly the dots or their overlap are dispersed, the more “good dispersion” or “the dispersion is better”. “Uniform dispersion” means the state where the total energy is as low as possible in the above repulsive potential example, that is, when there are dots due to overlapping or adjacent dots, the number of overlapping or adjacent points is determined. In this state, the dots are arranged as evenly as possible. Furthermore, “low frequency component is reduced (decreased)” means that when the dispersion is good as described above, a region having a high sensitivity in human visual characteristics (low frequency region) in the power spectrum described later regarding the distribution. This means that the frequency component decreases (decreases) depending on the degree of good dispersion.

The dither pattern of the present embodiment and the dither pattern of the conventional example are shown in FIG. 9 to FIG. 11, respectively. It is a figure which shows an arrangement | positioning pattern by the density | concentration according to the value of a threshold value. FIG. 19 is a diagram showing a similar pattern of the conventional dither pattern described in Patent Document 1 and Patent Document 2.

  Each of the dither pattern patterns shown in FIGS. 9 to 11 and FIG. 19 has an area of 128 × 128 pixels. In each pattern, the lower the density, the larger the threshold value.

  As shown in these figures, the conventional dither pattern shown in FIG. 19 and the dither pattern of the present embodiment (FIGS. 9 to 11) take into account the dispersibility within the same plane, particularly by the effect of the coefficient α. Since the dots are arranged, there is no bias in the dispersion of the respective densities indicated by the threshold value, and an overall smooth impression is received.

  FIG. 12 is a diagram showing a density pattern according to the average threshold value of the same pixels of the stacked dither patterns C and M of the present embodiment shown in FIGS. 9 and 10. FIG. 13 is a diagram showing a density pattern according to the average of the threshold values of the laminated dither patterns C, M, and Y of the present embodiment shown in FIGS. On the other hand, FIG. 20 is a diagram showing a density pattern according to the average of threshold values of the same pixels of the conventional dither pattern C shown in FIG. 19 and the dither pattern M obtained by shifting it. FIG. 21 is a diagram showing a pattern of density according to the average of threshold values of the same dither pattern M and Y obtained by shifting the conventional dither pattern C shown in FIG. 19 and the dither pattern M and Y respectively. is there. Since these patterns satisfy the above-described periodic boundary conditions, they can be easily set to shift the overlap.

  As shown in FIGS. 12 and 13, the average threshold arrangement in the case where two or three dither patterns according to the present embodiment are overlaid is well distributed and has no rough feeling. This is because, as described above, the dispersion of dots between the two planes is taken into consideration (coefficient β) and the dispersion of the overlap itself is taken into account (coefficient γs (n)). On the other hand, the threshold-average arrangement pattern of the conventional dither pattern shown in FIG. 20 and FIG. 21 exhibits a rough feeling due to a decrease in dispersibility.

  FIG. 22 is a diagram showing a comparison of power spectra of threshold average arrangement patterns when the laminated dither pattern of the present embodiment and the conventional laminated dither pattern are overlapped. Here, the power spectrum can be treated as a one-dimensional two-dimensional spatial frequency, “T. Mitsa and KJ Parker,“ Digital Halftoning using a Blue Noise Mask ”, Proc. SPIE 1452, pp. 47-56 (1991)”. It is described as a radially averaged power spectrum.

  As is clear from this figure, the conventional threshold average arrangement pattern that does not consider the dispersion with other planes has a larger power in the entire frequency domain, and this embodiment also in the low frequency domain. The ingredients are larger than those of

  FIG. 23 is a diagram comparing the amount of low frequency components in the power spectrum of the threshold average arrangement pattern of each of the laminated dither pattern of the present embodiment and the conventional dither pattern. As is apparent from this figure, the conventional pattern with more dither patterns has more low frequency components.

  As a performance evaluation of a dither pattern, it is a major feature of the present invention to pay attention to a “low frequency component” that is on the lower frequency side than about half of the frequency region where the power spectrum of the dither pattern exists. In the situation where the low frequency component of the dither pattern is kept low, the beading due to the grain distribution is not likely to appear and is hardly visible as described above. As a result, the recorded image does not bother visually. In particular, one dither pattern is repeatedly used in a two-dimensional manner for a recorded image. When one dither pattern is repeatedly used, the more low frequency components of the dither pattern, the more easily the pattern of the repeated pattern is recognized by human eyes. Again, the pattern greatly affects the appearance and appearance of beading. For this reason, a rough feeling related to the dither cycle occurs. Therefore, it is important to pay attention to the repetitive pattern and to suppress the low frequency component side of the dither pattern. In other words, the present invention focuses on the low frequency region where the roughness or the like is visually worrisome, and suppresses the low frequency region component to a low level. Further, the dither pattern of the present invention is characterized in that such low frequency power is kept low.

  The frequency characteristics related to the sensitivity of the human eye depend on the distance between the printed material and the human eye. For example, Dooley (“RP Dooley: Prediction Brightness Appearance at Edges Using Linear and Non-Liner Visual Describing Functions, SPES annual Meeting (1975) ”). When viewing a printed matter from various experiments, it is said that components in a frequency region lower than about 10 cycles / mm are easily recognized by human eyes. In this regard, the present inventor has also confirmed experimentally. Therefore, it can be said that it is important to pay attention to a region (low frequency region) including a frequency lower than 10 cycles / mm. Since the eyes may actually be closer to the recorded matter, the present inventor considers that it is important to pay attention to the design at a frequency lower than about 20 cycles / mm. Note that the low-frequency region of interest in the dither evaluation (for example, FIG. 16) of each embodiment to be described later substantially overlaps these ranges.

Evaluation by Shift One of the differences between the dither pattern according to the embodiment of the present invention and the dither pattern obtained by considering only one conventional plane (the dither pattern described in Patent Document 1 and Patent Document 2) is different. This is a change in dispersion characteristics when a plane dither pattern is overlapped at a normal position and when it is overlapped at a non-normal position. In the dither pattern according to the embodiment of the present invention, the dispersibility of the threshold arrangement pattern is greatly deteriorated when the dither pattern of different planes is intentionally shifted. That is, in the present embodiment, since dispersion is taken into consideration even between different planes, dispersibility is greatly reduced if a superposition method different from the normal superposition method when considering the dispersion is used. On the other hand, in the case of the dither pattern according to the conventional example, the dispersibility between different planes is not taken into consideration, and therefore the dispersibility does not change even when the overlap is different from the normal overlap.

  This deviation is evaluated as follows. Patterns C, M, and Y created by the above-described manufacturing method are randomly shifted from each other in the direction of each color raster. At this time, since the dither pattern itself is periodically arranged, it can be shifted.

  FIG. 14 is a diagram showing a threshold arrangement pattern of average threshold values when the laminated dither patterns C and M according to the present embodiment are overlaid. FIG. 15 shows the shifted laminated dither patterns C, M, and Y according to the embodiment. It is a figure which shows the threshold value arrangement pattern of the threshold value when it overlaps. As is clear from these drawings, the threshold average pattern in which the overlapping position of the laminated dither pattern of the present embodiment is shifted has reduced dispersibility, and the feeling of roughness when the pattern is observed is increased.

  FIG. 16 and FIG. 17 are diagrams comparing the power spectra when the overlapping position is shifted and when the overlapping position is not shifted (that is, when overlapping is performed at a normal position), and each of the stacked dither patterns C of the present embodiment. , M, or laminated dither pattern C, M, Y is a diagram showing a power spectrum of an arrangement pattern of average threshold values.

  In the laminated dither pattern of the present embodiment shown in these drawings, the power increases in all frequency ranges when shifted, and the low frequency components also become larger than when there is no shift. This is because, as described above, the laminated dither pattern considers dispersion even between different planes. Therefore, when the overlap is different from the normal overlap when considering the dispersion, the dispersibility is This is because it is greatly reduced.

  FIG. 18 is a diagram showing the evaluation based on the shift in terms of the amount of the low frequency component. The shift average of the threshold dither pattern of the laminated dither pattern according to the present embodiment and the case where the shift is not shifted (normal case) are shown. A comparison of the amount of low frequency components in the spectrum is shown.

  As shown in FIG. 18, in the case of the laminated dither pattern of this embodiment, the shifted one is compared with the case where the dither patterns C and M and the dither patterns C, M, and Y are not shifted. It can be seen that the amount of low frequency components increases.

Evaluation by Image FIG. 24 is a diagram showing a logical product pattern of dot patterns obtained by actually binarizing a uniform image having a density of 64 using the laminated dither patterns C and M of this embodiment. FIG. 27 is a diagram illustrating a logical product pattern of dot patterns obtained by binarizing a uniform image having a density of 64 using the stacked dither patterns C, M, and Y according to the present embodiment. Further, FIGS. 25 and 26 respectively show two dither patterns C and M obtained by randomly shifting according to the conventional example, and two dither patterns C and M obtained by shifting only one pixel according to the conventional example, respectively. It is a figure which shows the logical product pattern of the dot pattern obtained by binarizing the uniform image of density 64.

  As shown in FIG. 24 and FIG. 27, the arrangement (logical product) of the extracted dot arrangement obtained by superimposing the two or three dither patterns according to the present embodiment is distributed. It has become a rough feeling well. This is because, as described above, the dispersion of dots between the two dither planes is taken into consideration (coefficient β) and the dispersion of the overlap itself is taken into account (coefficient γs (n)).

  On the other hand, the logical product when the dot patterns based on the dither pattern disclosed in Patent Document 1 and Patent Document 2 are overlapped is not as well dispersed as the pattern of this embodiment (FIG. 24) regardless of the way of shifting. It has become a thing. As described above, in Patent Document 1 and the like, the dispersion within the same plane is considered, but the dispersion of the dots between the planes (coefficient β) and the dispersion of the dot overlaps (coefficient γs (n)) are considered. It is because it is not.

  Here, as another evaluation method of the dither pattern, a method using an “overlapping” pattern is defined. This “overlapping” pattern uses a plurality of dither patterns, for example, when a dot (“1”) exists in each dot pattern pixel obtained by binarizing a uniform image having a density of 64. When there is data “1” indicating a dot in a pixel to be overlapped, and the dots overlap with the same pixel, there is a pattern in which data corresponding to the number exists. For example, when the overlap is 2, “2” is set, and when it is 3, “3” is set. The pattern shown in FIG. 28 below is represented by the density corresponding to the number indicated by the data. That is, this superposition pattern can show the dot arrangement of different planes as a single plane and the dot overlap arrangement along with the degree of overlap.

  FIG. 28 is a diagram showing an “overlapping” pattern when the respective dot patterns obtained by binarizing a uniform image having a density of 64 using three stacked dither patterns of the present embodiment are overlapped. The pattern shown in FIG. 28 represents a pattern close to the superimposed ink dot pattern when recording is performed using the dither pattern of the present embodiment. Therefore, it can be seen from these patterns that the superimposed ink dots and their overlap are well dispersed.

  FIGS. 29 and 30 show the “overlapping” pattern obtained as described above when the laminated dither pattern of this embodiment and the above two conventional dither patterns are overlapped, respectively. It is a figure which compares and shows a power spectrum.

  Comparing the three curves, the overlay pattern by the two conventional dither patterns has more low frequency components than the overlay pattern by the laminated dither pattern of this embodiment. That is, the dispersion becomes worse and the feeling of roughness of the pattern increases.

  FIG. 31 shows the power spectrum of the “overlapping” pattern obtained as described above when the dither pattern according to the present embodiment and the two conventional dither patterns according to the two conventional examples are overlapped, respectively. It is a figure which compares and shows the quantity of a low frequency component.

  As shown in the figure, the overlay pattern by the two conventional dither patterns has more low frequency components than the overlay pattern by the laminated dither pattern of this embodiment. That is, it is understood that the dispersion becomes worse and the feeling of roughness of the pattern increases.

[Embodiment 2]
The dither pattern may be switched according to the gradation value. That is, when the dither pattern is created as in the above-described embodiment, for example, when the coverage of all three planes is 50%, it becomes relatively clean. However, the image quality may be degraded when the coverage of each plane is 50%, 25%, or 25%. This is because, for example, a dot distribution with a threshold value of magenta 25% is created while being influenced by repulsive force when all other colors are printed with a 25% plane.

  Therefore, different dither patterns are prepared according to the duty and used by switching. Specifically, a dither pattern is created by dividing three planes into two stages. First, it is divided into four as one plane 255. At this time, there are two stages of 0 to 127 and 128 to 255. Then, as a combination, it is possible to immediately calculate whether the remaining two planes are equal to or more than half of the maximum gray value of each plane.

  Assuming that the average value of the gradation values of the image to be processed is the first plane, the second plane, and the third plane = 200, 150, 50, the dither of (1, 1, 0) is selected. Here, the dither of (1, 1, 0) is an initial binary image in which an initial dot pattern is created from the 128/255 level for the first plane, and an initial binary pattern from which the second plane is also created from the 128/255 level. A dither pattern is created from an initial binary image created from 64/255 levels of the image and the third plane. Then, after arranging dots by applying the repulsive potential, the first plane and the second plane are thinned by 2 dots, whereas the third plane is thinned by 1 dot.

[Other Embodiments]
The present invention may apply the laminated dither pattern described in the above embodiment to all of a plurality of types of ink used in the recording apparatus, or a combination of some of the plurality of types of ink used in the recording apparatus. A laminated dither pattern may be applied.

  For example, when six color inks of cyan (C), magenta (M), yellow (Y), black (K), light cyan (Lc), and light magenta (Lm) are used, the laminated dither is applied to all these six colors. A pattern may be applied. In this case, a laminated dither pattern for six colors is generated by the manufacturing method described in the above embodiment.

  On the other hand, a laminated dither pattern may be applied to combinations of some of these six colors (two colors, three colors, four colors, and five colors). In this case, two forms are possible. The first form is a form in which the laminated dither pattern is generated for the part of the colors and the dither pattern manufacturing method for the other colors is not limited. For example, a laminated dither pattern is generated by the manufacturing method described in the above-described embodiment for three colors (for example, CMY) among six colors, and a dither pattern is generated by a known manufacturing method for the other three colors (KLcLm). . The second form is a form in which the laminated dither pattern is generated for the part of the colors, and for the other colors, a selected one of the laminated dither patterns generated for the part of the colors is assigned. . For example, for the three colors of CMY among the six colors, a laminated dither pattern is generated by the manufacturing method described in the above embodiment, and for the other three colors (KLcLm), if they are among the laminated dither patterns generated for CMY Apply the selection.

  In the above-described embodiment, the case where the laminated dither pattern is applied to combinations of different ink colors has been described. However, the present invention is not limited to this embodiment. The present invention is also applicable to a mode in which printing is performed using dots of the same color and different diameters (same color inks having different ejection volumes). In this case, the above-described stacked dither pattern may be applied to dots (for example, large dots and small dots) having the same color and different diameters. For example, consider a case where six types of dots of large cyan, small cyan, large magenta, small magenta, yellow, and black are used. In this case, a laminated dither pattern is generated by the manufacturing method described in the above embodiment for large cyan and small cyan, or large magenta and small magenta.

  Furthermore, in the form using dots of the same color and different diameters (for example, large dots and small dots), the above-described stacked dither pattern is applied to the combination of different color dots, and the same dither pattern is applied to the combination of the same color dots having different diameters. May be applied. For example, in the case of using the above-described six types of dots, a stacked dither pattern is generated by the manufacturing method described in the above embodiment for large cyan and large magenta, and the same dither pattern as that of large cyan is applied to small cyan, For magenta, the same dither pattern as large magenta is applied.

  The number of types of dots having the same color and different diameters is not limited to two types of large and small, and may be three types of large, medium, and small, or more. Further, the present invention is not effective only when applied to dots having at least one of different colors and sizes. For example, the present invention may be applied to the same color ink ejected from different nozzle groups at different timings. Demonstrate the effect. For example, in the form in which the nozzle groups are arranged in the order of CMYMC along the main scanning direction of the head, the stack manufactured by the above manufacturing method for the same color nozzle groups (C nozzle group, M nozzle group) that are separated from each other. Apply a dither pattern.

  Further, as described above, the present invention can be applied to a form using a liquid other than ink. Examples of the liquid other than the ink include a reaction liquid that aggregates or insolubilizes the color material in the ink. In this case, for at least one kind of ink and reaction liquid, a laminated dither pattern is generated by the manufacturing method described in the above embodiment.

  In the present invention, any of a dye ink containing a dye as a color material, a pigment ink containing a pigment as a color material, and a mixed ink containing a dye and a pigment as a color material can be applied.

[Other Embodiments]
In the evaluation by shifting the dither pattern in the embodiment of the present invention, the size is horizontal: 128 pixels × vertical: 128 pixels. However, there may be dither patterns having different vertical and horizontal sizes. When obtaining frequency components for such a pattern, the frequency components are obtained after aligning the vertical and horizontal sizes of the dither pattern. For example, when the vertical size is 256 × 128 and the vertical size is short, the vertical and horizontal sizes are aligned to the size in the longitudinal direction (in this example, 256 pixels in the horizontal direction). Evaluate the ingredients.

  The same applies to other sizes, and the frequency component is evaluated for a pattern in which the vertical and horizontal sizes are aligned in the longitudinal direction. Specifically, the pattern is repeated in the short direction until the size in the short direction of the pattern is equal to or greater than the size in the long direction, the pattern is cut out from the pattern, and the cut pattern is evaluated. At that time, the vertical and horizontal sizes are preferably 2 to the nth power (n is a positive integer) so that the fast Fourier transform can be used when performing the frequency conversion. If it is not 2 to the power of n, the 2 n power closest to the size in the longitudinal direction is specified, and the pattern is repeated vertically and horizontally so that it can be cut out with the specified size of 2 n. Then, from the pattern generated by this repetition, the specified pattern of 2 n size is cut out, and the cut out pattern is evaluated. For example, consider a case where the dither pattern is horizontal: 500 pixels × vertical: 320 pixels. In this case, since the size in the longitudinal direction is “500”, the 2 n power closest to “500” is specified. The nearest 2 to the power of n is identified as “512”. Therefore, in order to cut out a pattern of 512 pixels × 512 pixels, the pattern is repeated once in the horizontal direction and the vertical direction to generate a pattern of 1000 pixels × 640 pixels. A 512 pixel × 512 pixel pattern is cut out from the 1000 pixel × 640 pixel pattern thus generated, and the cut pattern is evaluated.

100 Host computer (PC)
101, J0001 Application 102 OS
103 Printer driver 104 Printer 107 HD
108 CPU
109 RAM
110 ROM
J0005 Binary processing J0006 Print data creation J0008 Mask data conversion processing

Claims (7)

In a data processing method for performing quantization for generating recording data of a plurality of types of dots using a plurality of dither patterns,
When the two or more dither patterns are overlapped, the threshold value pixel corresponding to the average threshold value pattern of the corresponding threshold pixels is shifted when the overlapping position is shifted with respect to the two or more dither patterns. A data processing method characterized in that there are fewer low frequency components than the average value pattern of the threshold values.   The data processing method according to claim 1, wherein the plurality of types of recording dots have different types of recording dot colors.   The data processing method according to claim 1, wherein the plurality of types of recording dots have different types of recording dot sizes. In a data processing apparatus that performs quantization to generate print data of a plurality of types of dots using a plurality of dither patterns,
When the two or more dither patterns are overlapped, the threshold value pixel corresponding to the average threshold value pattern of the corresponding threshold pixels is shifted when the overlapping position is shifted with respect to the two or more dither patterns. A data processing device characterized in that there are fewer low-frequency components than the average value pattern of the thresholds.   5. The data processing apparatus according to claim 4, wherein the plurality of types of recording dots have different types of recording dot colors.   The data processing apparatus according to claim 4, wherein the plurality of types of recording dots have different types of recording dot sizes. In a plurality of dither patterns used to perform quantization to generate recording data of multiple types of dots,
When the two or more dither patterns are overlapped, the threshold value pixel corresponding to the average threshold value pattern of the corresponding threshold pixels is shifted when the overlapping position is shifted with respect to the two or more dither patterns. A dither pattern characterized in that there are fewer low-frequency components than the pattern of the average value of the threshold values.

Images