JP2011116064A - Mask pattern forming apparatus, printer, mask pattern forming method, printing method, and program - Google Patents

Abstract

The present invention reduces unevenness of an output image even when registration fluctuations occur.
A pixel value of each pixel constituting a mask pattern is initialized to zero. A mask pattern is completed by selecting one pixel having a pixel value of 0 from the mask pattern, changing the pixel value of the selected pixel to 1 indicating no masking, and alternately updating the mask pattern a plurality of times. . At this time, for one of the mask patterns, one pixel having a pixel value of 0 is selected, and a modified mask pattern in which the pixel value of the selected selected pixel is changed to 1 is generated. The evaluation value is obtained by obtaining the number of pixel positions where the pixel value 1 overlaps when the correction mask pattern is overlaid with the other mask pattern while shifting the correction mask pattern in pixel units. An evaluation value for each pixel is obtained, a pixel having the smallest evaluation value is specified, and a mask pattern for changing the pixel value of the specified pixel to 1 is updated.
[Selection] Figure 1

Description

  The present invention relates to a technique for creating a mask pattern used for pass division for multi-pass printing, and an image processing technique using the mask pattern.

  In an image output apparatus such as an image output apparatus, multi-pass printing is often used in order to prevent deterioration in print quality due to variations in output accuracy of a printing unit such as a print head. In order to perform multi-pass printing, input image data is divided into a plurality of passes, and data for each pass is generated.

  There are various methods for pass division, but a method using a mask pattern prepared in advance is superior from the viewpoint of processing speed. In the method described in Patent Document 1, this mask pattern is generated based on the repulsive potential. This aims to increase the dispersibility of the dot arrangement.

JP 2007-306551 A

  However, in multi-pass printing, printing may be uneven due to a physical position error (registration fluctuation) of a printing unit such as a print head or a recording medium such as paper. The mask used in the method of Patent Document 3 is generated so that unevenness is most reduced when printing of each pass is performed in the exact same area. That is, when registration variation occurs, density unevenness may occur.

  An object of the present invention is to reduce unevenness of an output image even when registration fluctuation occurs.

In order to achieve the object of the present invention, for example, a mask pattern creating apparatus of the present invention comprises the following arrangement. That is,
In a printing apparatus that prints image data in two passes, a first mask pattern that is applied to the image data to generate image portion data to be printed in the first pass, and a second pass. A mask pattern creating apparatus for creating a second mask pattern to be applied to the image data to generate image portion data,
Initialization means for initializing a pixel value of each pixel constituting the first mask pattern and the second mask pattern to 0 indicating masking;
After initialization by the initialization means, one pixel of pixel value 0 is selected from the first mask pattern, and the pixel value of the selected pixel is changed to 1 indicating that the pixel value is not masked. And a process of selecting one pixel having a pixel value of 0 from the second mask pattern and changing the pixel value of the selected pixel to 1 to update the second mask pattern. Generating means for completing the first mask pattern and the second mask pattern by repeating a plurality of times,
Storage means for storing the completed first mask pattern and the second mask pattern in a memory;
The generating means includes
Selecting means for selecting one pixel having a pixel value of 0 for one of the first mask pattern and the second mask pattern;
Correction means for generating a correction mask pattern in which the pixel value of the selected pixel selected by the selection means is changed to 1,
A pixel in which pixels with a pixel value of 1 overlap when the correction mask pattern and the other mask pattern of the first mask pattern and the second mask pattern are overlapped so that the same pixel position overlaps First calculating means for obtaining the number of positions as a reference value;
Obtaining the absolute value of the difference between the reference value and the number of pixel positions where the pixel value of 1 overlaps when the correction mask pattern is shifted in units of pixels and superimposed on the other mask pattern; Two calculation means;
Third calculation means for obtaining, as an evaluation value, a value obtained by summing up the plurality of difference values obtained by shifting the correction mask pattern by the second calculation means;
Each time the selection means selects a pixel, the correction means and the first, second, and third calculation means are operated to obtain the evaluation value for each pixel selected by the selection means. Means,
Means for identifying the pixel having the smallest evaluation value among the respective pixels selected by the selection means, and updating the one mask pattern by changing the pixel value of the identified pixel to 1. It is characterized by providing.

  Even when registration fluctuations occur, the unevenness of the output image can be reduced.

The figure which shows the arrangement | positioning method of the mask pattern which concerns on 1st Embodiment. 6 is a flowchart illustrating processing performed by the image processing apparatus according to the first embodiment. FIG. 3 is a diagram showing a dot arrangement pattern according to the first embodiment. FIG. 3 is a diagram for explaining two-pass printing according to the first embodiment. 5 is a flowchart showing mask pattern creation processing according to the first embodiment. The block diagram which shows the structure of the computer which concerns on 3rd Embodiment. 1 is a block diagram showing a configuration of an image processing apparatus according to a first embodiment. FIG. 6 is a diagram illustrating a mask pattern creation method and a printing apparatus according to a second embodiment. 9 is a flowchart showing mask pattern creation processing according to the second embodiment. 1 is a block diagram showing a configuration of a mask pattern creating apparatus according to a first embodiment.

The mask pattern according to the present invention is created such that when multi-pass printing is performed using this mask pattern, the density is kept constant even if the print area on the medium in each pass is shifted. As an example, in the case of a mask pattern that gives binarized data of white and black, even if the mask patterns are overlapped with a shift of several dots, the number of overlaps of black dots is almost the same as when overlapped correctly. .
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments do not limit the present invention related to the scope of claims, and all the features described in the present embodiments are essential to the solution means of the present invention. Not exclusively.

[First Embodiment]
In this embodiment, printing is performed by a so-called serial method in which a recording head that ejects ink is scanned with respect to a recording medium, and ink is ejected during that time to perform recording. The recording head is prepared corresponding to each ink of C, M, Y, and K, and when these are mounted on the carriage, printing can be performed on a recording medium such as recording paper. Each recording head has, for example, an ejection port arrangement density of 1200 dpi, and ejects 2 picoliter (pl) of ink droplets from each ejection port. Further, the number of ejection ports of each recording head is arbitrary, but in this embodiment, it is 512.

  FIG. 2 is a block diagram illustrating processing performed by the image processing apparatus according to the present embodiment. In this embodiment, for the sake of explanation, it is assumed that one image processing apparatus performs from acquisition of print image data to printing. That is, the image processing apparatus of the present embodiment is a printing apparatus. However, as generally performed by those skilled in the art, for example, steps S201 to S205 may be performed by an image processing apparatus (printer driver) such as a computer, and steps S206 to S209 may be performed by the image output apparatus. In this case, a print instruction data generation unit (not shown) adds print control information to the data generated in step S205 to obtain print instruction data. Then, the dot arrangement patterning processing unit 706 of the image output apparatus may receive the print instruction data and perform subsequent processing. Also, the division of roles between the image processing apparatus and the image output apparatus can be changed according to the purpose.

  First, the pre-processing unit 702 receives print image data generated by a computer application or the like (S201), and performs pre-processing, that is, color gamut mapping (S202). This process performs data conversion for mapping the color gamut reproduced by the image data R, G, B of the sRGB standard into the color gamut reproduced by the image processing apparatus. Specifically, by using a three-dimensional LUT (look-up table), data of 256 gradations in which each of R, G, and B is represented by 8 bits is used, so that each of R, G, Convert to B data.

  The post-stage processing unit 703 is based on the R, G, and B data on which the color gamut is mapped, and color separation data C, M, Y, and K (8 bits each) that are combinations of inks that reproduce the color represented by this data. ) Is obtained (S203). Here, as in the previous process, conversion is performed using a three-dimensional LUT together with an interpolation operation. The γ correction unit 704 performs density value (gradation value) conversion for each color component of the color separation data obtained by the post-processing unit 703 (S204). Specifically, conversion is performed such that the color separation data is linearly associated with the gradation characteristics of the image output using a one-dimensional LUT.

  The halftoning unit 705 performs a quantization process on each of the 8-bit color separation data C, M, Y, and K, and quantizes the data into 4-bit data (S205). In the present embodiment, 256-bit 8-bit data is converted into index data representing 5 gradations using a multilevel error diffusion method. This index data is tone value information that serves as an index for the dot arrangement patterning process (S206), which is a binarization process.

  Next, the dot arrangement patterning processing unit 706 performs binarization processing by outputting a dot arrangement pattern based on the index data (S206). As a result, it is possible to obtain binary information used to output an image and whether or not to eject ink. FIG. 3 is a diagram showing a dot arrangement pattern according to the present embodiment corresponding to five-value index data. The dot arrangement pattern is determined for each of the five values of gradation level 0 to gradation level 4 indicated by the index data of C, M, Y, and K.

  The 2 × 2 output pixel composed of two vertical pixels and two horizontal pixels shown in the figure corresponds to one input pixel output by halftone processing, and this input pixel is 600 dpi (dots in both vertical and horizontal directions). / Inch) is a size corresponding to the pixel density. Each of the plurality of pixels constituting one input pixel is an area where dot recording / non-recording (ink ejection / non-ejection) is defined. An area filled with “black” indicates a pixel in which dot recording is allowed (recording allowable pixel), and a “white” area indicates a pixel in which dot recording is not allowed (non-recording allowable pixel). Then, the number of print permitting pixels in which dot printing is defined is determined according to any value of level 0 to level 4 indicated by the index data.

  One pixel of these dot arrangement patterns corresponds to a recording density of 1200 dpi in the vertical direction and 1200 dpi in the horizontal direction in the image output according to the present embodiment. That is, the image output performed by the image processing apparatus according to the present embodiment is performed by ejecting 2 pl ink droplets one by one from the recording head of each color to one pixel of about 20 μm in length and about 20 μm in width. It is a specification to form dots. The dot arrangement patterning processing unit 706 performs a process of binarizing the quinary data using the above dot arrangement pattern, and sets “1” or “0” for the ejection port corresponding to each area and the printing column. 1-bit ejection data is generated. In the present embodiment, the pixel size of the print image data 701 is set to a size corresponding to a pixel density of 600 dpi (dots / inch), but may be a different size. In this case, a different dot arrangement pattern may be used depending on the size of the pixel, and enlargement / reduction may be performed as appropriate during the image processing according to the present embodiment.

  Next, the mask data conversion processing unit 707 performs mask processing on the dot arrangement pattern of each color determined by the dot arrangement patterning processing unit 706 using a mask pattern composed of “1” or “0” data. (S207). The mask process is a process for calculating a logical product of the dot arrangement pattern and the mask pattern. Thereby, the ejection data of the image part to be printed in each pass is generated for each color of C, M, Y and K. Note that the mask pattern used in this process is created by a mask pattern creation apparatus described later, and is held by the holding means of the image processing apparatus according to the present embodiment. As will be described in detail later, this mask pattern is created so that density unevenness is not noticeable even if the registration of each scan varies. In the following description, a pixel having data “1” is referred to as a recording-allowed pixel, and a pixel having data “0” is referred to as a recording-prohibited pixel. When performing two-pass division using the first mask pattern and the second mask pattern, the first mask data is used to generate the first ejection data (first print data) and the second mask. Second ejection data (print data) is generated using the pattern.

  The head driving unit 708 supplies the ejection data generated by the mask data conversion processing unit 707 to the recording head 709 at an appropriate timing according to the scanning of each pass (S208). The head driving unit 708 converts 1-bit data of each color into a driving pulse for the recording head 709 and ejects ink from the recording head 709 for each color. As a result, ink is ejected according to the ejection data, an image is recorded on the recording medium, and an image output 710 is performed. In this embodiment, a plurality of mask data corresponding to a plurality of recording modes are stored in a memory included in the mask data conversion processing unit 707 and the like.

  Next, the two-pass multi-pass printing in the present embodiment, in which an image is completed by two scans using a single recording head having a nozzle array that discharges cyan (C) ink as a recording element, will be described below. To do. FIG. 4A is a diagram schematically showing the positional relationship among the recording head, the mask pattern, and the recording medium in order to explain the two-pass recording. The recording head 401 includes a cyan nozzle row, and the nozzle row includes 512 nozzles arranged at an interval of 1200 dpi. The nozzles are divided into a first group and a second group, each containing 256 nozzles. Each group is associated with a mask pattern 402 (two mask patterns C1 and C2). The size of each mask C1, C2 in the sub-scanning direction (conveyance direction) is 256 pixels, which is the same as the number of nozzles in each group, and the size in the main scanning direction is also 256 pixels. As shown in FIG. 4, in the first scan, recording is performed on the area A of the recording medium 403 using the mask C1, and after the recording medium is fed by 256 pixels, the mask C2 is used for the area A. To record. The image recording is completed by these two passes.

<Mask pattern creation method>
Hereinafter, a mask pattern creating method and a mask pattern creating apparatus used by the mask data conversion processing unit 707 will be described. FIG. 10 is a block diagram showing an apparatus for creating a mask pattern according to this embodiment. In the present embodiment, print permitting pixels (pixels having a pixel value of 1) indicating that masking is not performed are alternately arranged pixel by pixel in the first mask pattern C1 and the second mask pattern C2. The arrangement is repeated a plurality of times until the allowable number of recording pixels is 256 × 256 ÷ 2 pixels. By using the first mask pattern C1, the first pass data (first print data) can be generated from the image data. Further, by using the second mask pattern C2, it is possible to generate the second pass data (second print data) from the image data and thus divide the image data.

  FIG. 5 is a flowchart showing mask pattern determination processing in the present embodiment. First, the initialization unit 1002 acquires a mask pattern creation parameter 1001 based on an instruction from a user or the like, and generates an initial mask pattern (S501). The parameter 1001 includes parameters indicating the properties of the mask pattern to be created, such as the number of mask patterns to be created, the size of the mask pattern, and the number of print permitting pixels arranged in the mask pattern. The initialization unit 1002 performs initialization by generating mask patterns (C1 and C2) of the size indicated by the mask pattern creation parameter 1001, all of which are recording prohibited pixels (pixel value 0). The recording prohibition pixel is a pixel that indicates masking.

  After the initialization in step S501, each unit included in the evaluation value calculation unit 1003 calculates an evaluation value used for determining a pixel in which a print allowable pixel is arranged. First, the pixel selection unit 1010 selects a mask pattern in which print permitting pixels are arranged (S502). It is sufficient to select C1 first, C2 next, and C1 next. Subsequently, the evaluation value calculation unit 1003 calculates evaluation values for all the recording prohibited pixels of the mask pattern selected in step S502. The evaluation value is obtained by the following calculation. Here, for the sake of explanation, it is assumed that the mask pattern C1, which is one mask pattern, is selected in step S502. It can be said that the mask pattern C2 is the other mask pattern.

  First, the corrected mask pattern generation unit 1011 selects one pixel for recording prohibition of the mask pattern C1 (S503). Then, the correction mask pattern generation unit 1011 generates a correction mask pattern that is a mask pattern in which the recording prohibited pixel selected in step S503 is changed to a recording allowable pixel (S504). Next, the reference value calculation unit 1012 calculates a cross-correlation function between the corrected mask pattern and a mask pattern other than the mask pattern that is the basis of the corrected mask pattern (S505). Specifically, when the corrected mask pattern generated in step S504 and the mask pattern C2 are overlaid, the number of print permitting pixels that overlap is obtained as a reference value (first calculation means).

  The processing so far will be described with reference to FIG. In FIG. 1, the print permitting pixels are shown in black, and the print prohibition pixels are shown in white. In step S503, a lower right pixel that is a recording prohibited pixel is selected for the 3 × 3 pixel mask pattern C1 shown in FIG. In step S504, the corrected mask pattern C11 shown in FIG. 1B is generated in which the selected pixel is changed to a recording allowable pixel. In step S505, the number of print permitting pixels that overlap with the corrected mask pattern C11 and the mask pattern C2 is determined. Specifically, since the right center pixel and the lower center pixel are both print-allowable pixels, the reference value is 2.

Next, the cross-correlation calculation unit 1013 calculates the value of the cross-correlation function with a mask pattern other than the mask pattern that is the basis of the corrected mask pattern when the corrected mask pattern is translated (S506). Then, an absolute value of a difference between the obtained value and the reference value is obtained, and this value is set as a difference value for the recording prohibited pixel selected in step S503 (second calculation means). In the present embodiment, the corrected mask pattern C11 is translated in units of pixels, and then overlapped with the mask pattern C2 to obtain the number of print permitting pixels that overlap. Further, a plurality of difference values obtained while changing the parallel movement amount are summed to obtain the following evaluation value F (third calculation means). This process is specifically shown in Expression (1).

  Here, d (i, j) is the overlap number of the printable pixels of C11 and C2 when C11 is translated by i dots in the main scanning direction and j dots in the sub-scanning direction. d (i, j) is a cross-correlation value between C11 and C2. d (0,0) is the reference value obtained in step S505. The F value is an evaluation value obtained by the evaluation value calculation unit 1003. The F value indicates the amount of change in the number of overlapping dots of C11 and C2 when C11 is translated with respect to C2 from the state where C11 and C2 are overlapped so that the same pixel position overlaps. . Σ represents the sum from −m to m for i, and represents the sum from −n to n for j. m and n are values that define a range in which C11 is moved, and are integers of 1 or more. In this embodiment, the values of m and n are 1, but other values may be used.

  Next, the cross-correlation calculation unit 1013 determines whether or not all recording prohibited pixels are selected in step S503 for the mask pattern selected in step S502 (S507). If all are selected, the process proceeds to step S508. If there is a recording prohibited pixel that has not been selected, the process returns to step S503 to select a recording prohibited pixel that has not been selected.

  Next, the comparison unit 1004 identifies the pixel having the smallest evaluation value among the recording prohibited pixels of the mask pattern selected in step S502 (S508). If there are a plurality of pixels having the lowest evaluation value, one of them may be determined at random. Next, the arrangement unit 1005 changes the pixel specified in step S508 to a print allowable pixel, thereby arranging one dot of the print allowable pixel with respect to the mask pattern selected in step S502 (S509). Thus, the mask pattern selected in step S502 is updated.

  Next, the arrangement unit 1005 determines whether or not the number of dots arranged for the mask pattern has reached the predetermined number of dots indicated by the parameter 1001 (S510). For example, when the two-pass division is performed, it may be determined that a predetermined number of dots is obtained when the print allowable pixels, which is half the number of pixels of the mask pattern, are arranged in each mask pattern. If the predetermined number of dots is arranged, the process proceeds to step S511. If the predetermined number of dots is not arranged, the process returns to step S502 to select another mask pattern. Finally, the storage unit 1006 stores the mask pattern C1 in which the arrangement of the print permitting pixels is finished as a mask pattern 1007 in a memory of a storage device (not shown) (S511).

  When a mask pattern is created by the processing described above, the evaluation value F is approximately 0 when the evaluation value F is calculated for the dot arrangement pattern of each pass created using this mask pattern. As a result, even if the registration of each scan varies, the number of overlapping dots does not vary. For this reason, it is possible to form a high-quality image while reducing density unevenness due to variations in registration.

  The formula for obtaining the evaluation value F is not limited to the formula shown above. Any value can be used as an evaluation value as long as it can express the amount of change in the number of print-allowable pixels overlap between C11 and C2 when C11 is translated with respect to C2. In addition, the number of black pixels in the image after mask processing using the mask pattern may be evaluated instead of the number of print pattern allowable pixels in the mask pattern. For example, as shown in FIG. 1B, binary images D11 and D2 are generated by applying a correction mask pattern C11 and a mask pattern C2 to a binary image D0 in which all pixels are black pixels. Then, evaluation values may be calculated for D11 and D2. In the case of FIG. 1B, the same result as that in the case of evaluating the number of overlapping print permitting pixels of the mask pattern is obtained, but it is also possible to use an arbitrary binary image D0 as shown in FIG. In this case, a mask pattern suitable for an image to be masked can be generated.

[Second Embodiment]
In this embodiment, printing is performed by a sublimation type image output method in which an ink sheet is sublimated and diffused on a dedicated recording medium by the heat of a thermal head. FIG. 8C is a schematic diagram for explaining the basic principle of the sublimation image output method. In the sublimation type image output method, an image is output using a dye diffusion phenomenon. In the figure, reference numeral 801 denotes a plastic sheet (ink sheet) coated with a sublimable dye 805. The ink sheet 801 is sandwiched between the thermal head 803 and the platen roller 804 in a form superimposed on the dedicated recording medium 802. The ink sheet 801 is sublimated and thermally diffused on a dedicated recording medium by the heat of the thermal head 803 to obtain a color print. The thermal head 803 can record a pattern of 255 gradations for each color according to the input image data for each color. Also, multi-pass printing as shown in Embodiment 1 can be performed by conveying the ink sheet and the dedicated recording medium a plurality of times back and forth with respect to the thermal head.

  The processing performed by the image processing apparatus according to the present embodiment is the same as the processing of FIG. 2 according to the first embodiment. However, since a 255-tone pattern can be recorded for each color, the halftoning unit 705 and the dot arrangement patterning processing unit 706 are not necessary, and an image processing unit suitable for the sublimation image output method may be added instead. . In this embodiment, since the mask pattern is not binary, the mask data conversion processing unit 707 performs multiplication using the value of the mask pattern instead of taking a logical product using the mask pattern, and outputs the print data. Generate.

  Hereinafter, a method for creating a mask pattern used in the recording system according to the present embodiment will be described. In this embodiment, as in the first embodiment, two-pass multi-pass printing using only cyan (C) will be described. FIG. 4B is a view for explaining 2-pass multi-pass printing according to the present embodiment. The configuration is the same as in FIG. 4A according to the first embodiment. The recording head 411 includes a cyan recording element array, and the recording element array includes 1500 recording elements arranged at an interval of 300 dpi. Mask patterns C1 and C2 are associated with each pass, and the size of each mask C1 and C2 in the printing element array direction is 1500 pixels and the size in the transport direction is 750 pixels. As shown in FIG. 7, printing is performed on the entire area of the recording medium using the mask C1 in the first pass, and the recording medium is conveyed in the opposite direction to the first pass while the same area as the first pass is applied. Recording is performed using the mask C2. The image recording is completed by these two passes.

  In the present embodiment, each pixel of the mask patterns C1 and C2 is a real value from 0 to 1, and the image recorded in each pass is the pixel value of the mask pattern for the input image data of 255 colors for each color. Is generated by multiplying In this embodiment, the sum of the pixel values of C1 and C2 corresponding to the same position of the recording medium, that is, the same pixel position is set to 1. That is, when the pixel value of C1 is determined, the pixel value of C2 is determined by subtracting the pixel value of C1 from 1, and therefore, processing for determining the mask pattern C1 will be described below. However, the sum of the pixel values at the same pixel position of C1 and C2 is not limited to 1, and may be a predetermined value.

  Hereinafter, the process of creating the mask pattern C1 will be described with reference to FIG. In this process, the pixel value of C1 is sequentially determined for each pixel until all the pixel values of the mask pattern C1 are determined. The mask pattern creating apparatus according to this embodiment is the same apparatus as the mask pattern creating apparatus according to the first embodiment shown in FIG. The mask pattern creation process according to the present embodiment is also performed by a method similar to the process according to the first embodiment described with reference to FIG. Hereinafter, a description will be given centering on portions different from the first embodiment.

  In step S901, the initialization unit 1002 acquires a mask pattern creation parameter 1001 based on an instruction from a user or the like, and initializes the mask pattern C1. Unlike the first embodiment, the initial value of the mask pattern C1 is 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0. .9 and 1.0 are determined by a random number for each pixel. However, the values to be determined are not limited to these 11 values, and may be determined by random numbers from arbitrary values between 0 and 1. When the sum of the pixel values at the same pixel position of C1 and C2 is a predetermined value other than 1, it may be determined by a random number from an arbitrary positive value less than or equal to the predetermined value.

  After initialization in step S901, in step S902, the pixel selection unit 1010 selects one of the pixels of the mask pattern C1 (first selection means). Unlike the first embodiment, all pixels are selected in this embodiment. The order of determining the pixel values may be arbitrary, but in this embodiment, the pixel values are determined in the order of the upper line to the lower line, and the pixel values are determined in the order of the left pixel to the right pixel for the same line. decide. In step S903, the correction mask pattern generation unit 1011 generates the correction mask pattern C11 by changing the pixel value of the pixel selected in step S902 (first correction means). Pixel values include 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0. Select in order (second selection means). Ultimately, evaluation values are obtained in the following step S905 for all eleven pixel values for one pixel.

  The correction mask pattern generation unit 1011 further obtains a correction mask pattern C22 (complementary mask pattern) using the correction mask pattern C11 (second correction means). The sum of the pixel values of the correction mask pattern C11 and the correction mask pattern C22 corresponding to the same position may be set to 1. For example, when the pixel value of a pixel having C11 is 0.1, the pixel value of the corresponding pixel of C22 is 0.9. The positional relationship at this time is as shown in FIG.

  In step S904, the reference value calculation unit 1012 obtains a cross-correlation between the corrected mask pattern C11 and the corrected mask pattern C22 and sets it as a reference value. That is, the pixel value of the correction mask pattern C11 and the corresponding pixel value of the correction mask pattern C22 are multiplied to obtain the sum of the values obtained for each pixel position. According to the example in Fig. 8 (a), 0.5 * 0.5 + 0.6 * 0.4 + 0.2 * 0.8 + 1.0 * 0.0 + 0.5 * 0.5 + 0.3 * 0.7 + 0.5 * 0.5 + 0.2 * 0.8 + 0.4 * 0.6 Become.

Next, the cross-correlation calculation unit 1013 calculates the cross-correlation with the correction mask pattern C22 when the correction mask pattern C11 is translated. Then, an absolute value of a difference between the obtained value and the reference value is obtained, and this value is set as a difference value, and an evaluation value is obtained similarly to the first embodiment (S905). The parallel movement method is the same as in the first embodiment, and the evaluation value is obtained as shown in Equation (2).

  In Equation (2), the reference value is R (0,0). Also, let R (i, j) be the cross-correlation value obtained after D11 is translated by i pixels in the main scanning direction and j pixels in the sub scanning direction with respect to D22. That is, R (i, j) is obtained by multiplying the pixel value of D11 and the pixel value of D22 at the overlapping position and adding the values for all the pixels. Then, the evaluation value F is calculated as described above. In the present embodiment, the values of m and n are 1, but other values may be used. Further, the expression for obtaining the evaluation value is not limited to the expression shown above, and any expression that can express the amount of change in the cross-correlation value between D11 and D22 may be used.

  In step S906, the cross-correlation calculating unit 1013 determines whether or not the corrected mask pattern C11 has been generated for all eleven pixel values in step S903. If all the pixels have been generated, the process proceeds to step S907. If not all have been generated, the process returns to step S903 to select the next pixel value. In step S907, the comparison unit 1004 compares the evaluation values calculated in step S905, and identifies the pixel value having the smallest evaluation value among the 11 pixel values selected in step S903. If there are a plurality of pixel values having the smallest evaluation value, any one may be selected at random.

  In step S908, the arrangement unit 1005 replaces the pixel value of the pixel selected in step S902 with the pixel value specified in step S907. Thus, the mask pattern selected in step S902 is updated. In step S909, the arrangement unit 1005 determines whether all the pixels have been selected in step S902. If all the pixels have been selected, the process proceeds to step S910. If there is a pixel that has not been selected, the process returns to step S902 to select the next pixel. In step S910, similarly to the first embodiment, the mask pattern C1 obtained by the processing so far is stored as a mask pattern 1007 in a memory of a storage device (not shown). Further, as described above, the mask pattern C2 is obtained from the mask pattern C1, and the mask pattern C2 is also stored as a mask pattern 1007 in a memory of a storage device (not shown).

  When the mask pattern is created by the above-described processing, when the evaluation value F is calculated for the dot arrangement pattern of each pass created using this mask pattern, the evaluation value F is approximately 0 as in the first embodiment. It becomes. As a result, even if the registration of each scan varies, the number of overlapping dots does not vary. For this reason, it is possible to form a high-quality image while reducing density unevenness due to variations in registration.

  The evaluation value F is not limited to the above-described formula, and any evaluation value can be used as long as it can express the amount of change in the number of overlapping printable pixels of C11 and C2 when C11 is translated with respect to C2. Can be used as As in the first embodiment, the cross-correlation value may be evaluated for the image after the mask process is performed using the mask pattern, instead of the number of mask pattern recording allowable pixels. For example, as shown in FIG. 8A, the images D11 and D22 are generated by applying the correction mask pattern C11 and the mask pattern C22 to the image D0 in which all pixels are 255 values. Then, evaluation values may be calculated for D11 and D22. In the case of FIG. 8A, the same result as that in the case of evaluating the number of maskable pixels of the mask pattern is evaluated, but an arbitrary image D0 can be used as shown in FIG. 8B. D0 does not have to have the same value for each pixel, and a mask pattern suitable for an image to be masked can be generated.

[Third Embodiment]
In the present embodiment, at least a part of the processing according to each of the above-described embodiments is performed by the computer 101. For example, in this embodiment, the computer 101 performs steps S201 to S205, and the printer 105 performs steps S206 to S209. Of course, the division of roles between the computer 101 and the printer 105 may be changed according to the purpose of processing.

  FIG. 6 is a diagram showing a basic configuration of the computer 101. For example, when each function is executed in the computer 101, each function configuration is expressed by a program and is read by the computer. Thus, each function of the above-described embodiment can be realized by the computer 101. In this case, each of the components including FIG. 6 may be functioned by a function or a subroutine executed by the CPU 109.

  In general, the computer program is stored in a computer-readable storage medium such as a CD-ROM. This storage medium can be executed by setting it in a reading device (such as a CD-ROM drive (not shown)) of the computer and copying or installing it in the system. Therefore, it is obvious that such a computer-readable storage medium is also within the scope of the present invention.

  In FIG. 6, a computer 101 that is a host computer operates application software 102, a printer driver 104, and a monitor driver 106 by an operating system (OS) 103. The application software 102 performs data processing related to a word processor, spreadsheet, internet browser, and the like. The monitor driver 106 executes processing such as creating image data to be displayed on the monitor 107.

  The printer driver 104 performs drawing processing on various drawing command groups (image drawing commands, text drawing commands, graphics drawing commands, etc.) issued from the application software 102 to the OS 103. Finally, image data used by an image output apparatus such as the printer 105 is generated. Specifically, similarly to the above-described embodiment, data is generated for each color component of cyan (C), magenta (M), yellow (Y), and black (K) of the ink used by the printer 105.

  The computer 101 includes a CPU 109, a hard disk (HD) 108, a RAM 110, a ROM 111, and the like as various hardware for operating the above software. That is, the CPU 109 executes the process according to the software program stored in the hard disk 108 or the ROM 111, and the RAM 110 is used as a work area when the process is executed.

[Other Embodiments]
In the first and second embodiments, only the cyan (C) ink is shown. However, the present invention can be applied to a case where two or more types of ink are used. That is, the mask described in each embodiment may be used for each ink. For example, when cyan (C) ink and yellow (Y) ink are used, a mask pattern for cyan ink is created by the method shown in the first embodiment, and a mask pattern for yellow (Y) ink is shown in the first embodiment. You may create by arbitrary methods other than. In that case, the evaluation value F regarding the dot arrangement pattern of each pass of yellow ink is larger than the evaluation value F regarding cyan ink. However, since yellow ink is less conspicuous than cyan ink, there is no significant difference in image quality from the case where a mask pattern related to yellow ink is created by the method shown in the first embodiment. Of course, the present invention can also be applied to the case of using three or more colors of ink.

  In the first embodiment, in step S503, by preventing the selection of pixels at positions where print permitting pixels exist in other mask patterns, the print permitting pixels do not overlap at the same position of each mask pattern. You can also. In this way, it is possible to reduce the graininess of an image formed on a recording medium using this mask pattern, particularly when generating a mask pattern with a small number of print-allowable pixels.

  In the second embodiment, the gradation has a value of 255, but the present invention can be applied if the gradation is binary or more. Furthermore, in the second embodiment, 11 pixel value candidates are used, but the pixel value may not be 11 candidates, which is different from the 11 sets shown in the second embodiment. It doesn't matter. In the second embodiment, the sum of the pixel values at the same pixel position in the mask pattern of each pass is set to 1, but the present invention can be applied to a value other than 1. Furthermore, even if each mask pattern is independently generated by the method of the second embodiment, it is possible to generate a uniform mask pattern by fixing the average of the pixel values selected in step S504. . In this case, the pixel value selected in step S504 is preferably set so that the sum of the pixel values at the same position in each mask pattern does not exceed a certain value (for example, 1). Then, it becomes possible to reduce the graininess of the image formed on the recording medium using the generated mask pattern.

  In the first embodiment and the second embodiment, the form of a mask pattern that is divided into two passes has been described. However, the present invention can also be applied to a case of dividing into three or more passes. In the first embodiment, an evaluation value is obtained between the corrected mask pattern C11 and the mask pattern C2. Consider a case in which a print permitting pixel is arranged in the mask pattern C1 when creating a mask pattern to be divided into N passes. An evaluation value is obtained between the corrected mask pattern C11 and the mask pattern C2, and further an evaluation value is obtained between the corrected mask pattern C11 and the mask pattern C3. If a total of (N-1) evaluation values are obtained up to the Nth mask pattern, and these sums are used as the evaluation values used in the determination in step S508, the print allowable pixels between the N mask patterns. Can be evaluated.

  As another method, the number of pixel positions at which print permitting pixels exist in all mask patterns when the corrected mask pattern C11 and the 2nd to Nth mask patterns are overlaid is used in step S506. i, j). Also in the second embodiment, N mask patterns can be created by the same method. That is, a total of (N-1) evaluation values can be obtained and summed, or when the corrected mask pattern and another mask pattern are overlaid, all overlapping pixel values are integrated to obtain R (i, j). That's fine.

  In addition, low frequency components (less than about 10 cycles / mm) except for the DC component of the power spectrum of the mask pattern being created or the mask image obtained by masking the image using the mask pattern being created The sum may be added to the evaluation value F. In this way, a mask pattern that generates a dot arrangement pattern with high dot dispersibility can be created. Further, it is desirable that the density change amount when the registration of each scan fluctuates is 0.3 or less when converted by lightness. In view of this, an embodiment using the amount of change in brightness when the registration of each scan varies as the evaluation value F is also conceivable. In this case, the brightness change amount is predicted based on the dot pattern of each pass using a physical model.

  The present invention is also realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program code. Execute. In this case, the program and the storage medium storing the program constitute the present invention.

Claims (9)

In a printing apparatus that prints image data in two passes, a first mask pattern that is applied to the image data to generate image portion data to be printed in the first pass, and a second pass. A mask pattern creating apparatus for creating a second mask pattern to be applied to the image data to generate image portion data,
Initialization means for initializing a pixel value of each pixel constituting the first mask pattern and the second mask pattern to 0 indicating masking;
After initialization by the initialization means, one pixel of pixel value 0 is selected from the first mask pattern, and the pixel value of the selected pixel is changed to 1 indicating that the pixel value is not masked. And a process of selecting one pixel having a pixel value of 0 from the second mask pattern and changing the pixel value of the selected pixel to 1 to update the second mask pattern. Generating means for completing the first mask pattern and the second mask pattern by repeating a plurality of times,
Storage means for storing the completed first mask pattern and the second mask pattern in a memory;
The generating means includes
Selecting means for selecting one pixel having a pixel value of 0 for one of the first mask pattern and the second mask pattern;
Correction means for generating a correction mask pattern in which the pixel value of the selected pixel selected by the selection means is changed to 1,
A pixel in which pixels with a pixel value of 1 overlap when the correction mask pattern and the other mask pattern of the first mask pattern and the second mask pattern are overlapped so that the same pixel position overlaps First calculating means for obtaining the number of positions as a reference value;
Obtaining the absolute value of the difference between the reference value and the number of pixel positions where the pixel value of 1 overlaps when the correction mask pattern is shifted in units of pixels and superimposed on the other mask pattern; Two calculation means;
Third calculation means for obtaining, as an evaluation value, a value obtained by summing up the plurality of difference values obtained by shifting the correction mask pattern by the second calculation means;
Each time the selection means selects a pixel, the correction means and the first, second, and third calculation means are operated to obtain the evaluation value for each pixel selected by the selection means. Means,
Means for identifying the pixel having the smallest evaluation value among the respective pixels selected by the selection means, and updating the one mask pattern by changing the pixel value of the identified pixel to 1,
A mask pattern creating apparatus comprising: The evaluation value is a pixel value 1 that overlaps when the correction mask pattern is shifted by i dots in the main scanning direction and j dots in the sub scanning direction from a state where the same pixel position as that of the other mask pattern overlaps. The number of pixels is d (i, j), and m and n are one or more integers that define a range in which the correction mask pattern is shifted. The mask pattern production apparatus described.

In a printing apparatus that prints image data in two passes, a first mask pattern that is applied to the image data to generate image portion data to be printed in the first pass, and a second pass. A mask pattern creating apparatus for creating a second mask pattern to be applied to the image data to generate image portion data,
Initialization means for initializing a pixel value of each pixel constituting the first mask pattern to a random positive number equal to or less than a predetermined value;
After the initialization by the initialization means, selecting one pixel from the first mask pattern, changing the pixel value of the selected pixel and updating the first mask pattern for each pixel, Generating means for completing the first mask pattern;
Means for generating a second mask pattern in which the sum of overlapping pixel values becomes the predetermined value when overlapping the first mask pattern completed by the generating means so that the same pixel position overlaps;
Storage means for storing the first mask pattern completed by the generation means and the second mask pattern in a memory;
The generating means includes
First selection means for selecting one pixel from the first mask pattern;
Second selection means for selecting one positive value less than or equal to the predetermined value;
First correction means for generating a correction mask pattern in which the pixel value of the selected pixel is changed to a value determined by the second selection means;
Second correction means for generating a complementary mask pattern in which the sum of overlapping pixel values becomes the predetermined value when the correction mask pattern and the same pixel position are overlapped with each other;
First calculation means for obtaining, as a reference value, a sum of pixel products of overlapping pixel values when the correction mask pattern and the complementary mask pattern are overlapped so that the same pixel position overlaps When,
The absolute value of the difference between the sum of the product of the overlapping pixel values and the reference value when the correction mask pattern is shifted in units of pixels and superimposed with the complementary mask pattern is obtained as a difference value. A second calculation means;
Third calculation means for obtaining, as an evaluation value, a value obtained by summing up the plurality of difference values obtained by shifting the correction mask pattern by the second calculation means;
Each time the second selection means selects a value, the second selection means operates by operating the first and second correction means and the first, second, and third calculation means. Means for determining the evaluation value for each selected value;
By specifying the value with the smallest evaluation value among the values selected by the second selection means, and changing the pixel value of the pixel selected by the first selection means to the specified value, Means for updating the first mask pattern;
A mask pattern creating apparatus comprising: The evaluation value is the overlapped pixel value when the correction mask pattern is shifted by i dots in the main scanning direction and j dots in the sub scanning direction from the overlapped state so that the same pixel positions as the complementary mask pattern overlap. The sum of the product pixel positions is R (i, j), and m and n are integers greater than or equal to 1 that define the range in which the correction mask pattern is shifted. The mask pattern creating apparatus according to claim 3.

Means for holding the first mask pattern and the second mask pattern generated by the mask pattern creating apparatus according to any one of claims 1 to 4;
Acquisition means for acquiring image data;
Means for applying a first mask pattern to the image data to perform mask processing and generating first print data to be printed in a first pass;
Means for applying the second mask pattern to the image data to perform mask processing, and generating second print data to be printed in a second pass;
Means for printing the image data acquired by the acquisition means in two passes using the first print data and the second print data;
A printing apparatus comprising: In a printing apparatus that prints image data in two passes, a first mask pattern that is applied to the image data to generate image portion data to be printed in the first pass, and a second pass. A mask pattern creating method performed by a mask pattern creating apparatus for creating a second mask pattern to be applied to the image data to generate image portion data,
An initialization step of initializing a pixel value of each pixel constituting the first mask pattern and the second mask pattern to 0 indicating masking;
After initialization in the initialization step, one pixel having a pixel value of 0 is selected from the first mask pattern, and the pixel value of the selected pixel is changed to 1 indicating that the pixel value is not masked. A process of updating the pattern, and a process of selecting one pixel having a pixel value of 0 from the second mask pattern, changing the pixel value of the selected pixel to 1, and updating the second mask pattern. A generation process of completing the first mask pattern and the second mask pattern by alternately repeating a plurality of times, and
Storing the completed first mask pattern and the second mask pattern in a memory, and
The generating step includes
A selection step of selecting one pixel with a pixel value of 0 for one of the first mask pattern and the second mask pattern;
A correction step of generating a correction mask pattern in which the pixel value of the selected pixel selected in the selection step is changed to 1,
A pixel in which pixels with a pixel value of 1 overlap when the correction mask pattern and the other mask pattern of the first mask pattern and the second mask pattern are overlapped so that the same pixel position overlaps A first calculation step for determining the number of positions as a reference value;
Obtaining the absolute value of the difference between the reference value and the number of pixel positions where the pixel value of 1 overlaps when the correction mask pattern is shifted in units of pixels and superimposed on the other mask pattern; 2 calculation steps;
A third calculation step of obtaining, as an evaluation value, a value obtained by summing the plurality of difference values obtained while shifting the correction mask pattern in the second calculation step;
A step of obtaining the evaluation value for each pixel selected in the selection step by performing the correction step and the first, second, and third calculation steps each time a pixel is selected in the selection step. When,
Identifying the pixel having the smallest evaluation value among the respective pixels selected in the selection step, and updating the one mask pattern by changing the pixel value of the identified pixel to 1,
A mask pattern creating method comprising: In a printing apparatus that prints image data in two passes, a first mask pattern that is applied to the image data to generate image portion data to be printed in the first pass, and a second pass. A mask pattern creating method performed by a mask pattern creating apparatus for creating a second mask pattern to be applied to the image data to generate image portion data,
An initialization step of initializing a pixel value of each pixel constituting the first mask pattern to a random positive number equal to or less than a predetermined value;
After initialization in the initialization step, a process of selecting one pixel from the first mask pattern, changing the pixel value of the selected pixel, and updating the first mask pattern is performed for each pixel. Generating the first mask pattern; and
Generating a second mask pattern in which the sum of overlapping pixel values becomes the predetermined value when overlapping the first mask pattern completed in the generating step so that the same pixel position overlaps;
A storage step of storing the first mask pattern completed in the generation step and the second mask pattern in a memory;
The generating step includes
A first selection step of selecting one pixel from the first mask pattern;
A second selection step of selecting one positive value less than or equal to the predetermined value;
Generating a correction mask pattern in which the pixel value of the selected pixel is changed to the value determined in the second selection step;
A second correction step of generating a complementary mask pattern in which the sum of overlapping pixel values becomes the predetermined value when the correction mask pattern and the same pixel position are overlapped with each other;
A first calculation step of obtaining, as a reference value, a sum for each pixel position of a product of overlapping pixel values when the corrected mask pattern and the complementary mask pattern are overlapped so that the same pixel position overlaps When,
The absolute value of the difference between the sum of the product of the overlapping pixel values and the reference value when the correction mask pattern is shifted in units of pixels and superimposed with the complementary mask pattern is obtained as a difference value. A second calculation step;
A third calculation step of obtaining, as an evaluation value, a value obtained by summing the plurality of difference values obtained while shifting the correction mask pattern in the second calculation step;
Each time a value is selected in the second selection step, the first selection step is performed in the second selection step by performing the first and second correction steps and the first, second, and third calculation steps. Obtaining the evaluation value for each of the obtained values;
By specifying the value with the smallest evaluation value among the respective values selected in the second selection step, and changing the pixel value of the pixel selected in the first selection step to the specified value Updating the first mask pattern;
A mask pattern creating method comprising: A printing method performed by a printing apparatus,
Holding the first mask pattern and the second mask pattern generated by the mask pattern creating method according to claim 6 or 7,
An acquisition process for acquiring image data;
Applying the first mask pattern to the image data to perform mask processing, and generating first print data to be printed in a first pass;
Applying the second mask pattern to the image data to perform mask processing, and generating second print data to be printed in a second pass;
Using the first print data and the second print data, printing the image data acquired in the acquisition step in two passes; and
A printing method comprising:   The computer program for functioning a computer as each means which the mask pattern production apparatus of any one of Claims 1 thru | or 4 or the printing apparatus of Claim 5 has.

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