JP2003125219A - Threshold value matrix, and method and apparatus for gradation reproduction using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a threshold value matrix not producing an eyesore virtual image and a sense of granurality even with combinations of a plurality of color components and to provide a method and apparatus for gradation reproduction. SOLUTION: Applying one-to-one correspondence between each element of the threshold value matrix and each pixel of an original image by each color component of at least two kinds of color components expresses the density of each pixel of a output image in a binary or multi-value expression. When a dot pattern of a size corresponding to the threshold value matrix is divided into small regions, number of dots in all the regions is equal to each other for all gradations and the dot pattern in a plurality of the regions is equal to each other. A different threshold value matrix is used for at least two kinds of the color components. Then in the dot pattern generated by the threshold value matrix applied to each color component, positions of the regions in which the dot patterns are equal to each other are not entirely overlapped between the color components or only partly overlapped.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a threshold matrix,
And a color gradation reproducing method and apparatus using the same, and particularly a threshold value for gradation processing of multi-gradation image data of each color component of input color image data composed of a plurality of color components into binary or multi-valued data. The present invention relates to a matrix, a gradation reproduction method using the same, and an apparatus thereof.

[0002]

2. Description of the Related Art In a recording apparatus such as a color ink jet printer, each color component of multi-gradation color image data composed of a plurality of color components is represented by a binary value indicating whether droplets such as ink are recorded on a recording medium. A method in which multi-gradation is represented in a pseudo manner and a color image is reproduced by a combination of those binary representations has become the mainstream.

In such a digital recording apparatus, it is necessary to convert multi-tone data of each color component of an input color image into binary image data. In order to obtain a high-definition image referred to as photographic image quality, conversion into multi-valued image data of about three values may be used instead of conversion into binary data.

Conventionally known methods for reproducing gray scales in which multi-gradation data are represented in pseudo by binary data are roughly classified into "error diffusion method" and "dither method".

In the error diffusion method, the error between the multi-tone image data and the binary image data, which is generated when the multi-tone image data is converted into binary data, is weighted to a predetermined peripheral pixel before conversion. It is converted into binary image data while being diffused. With this method, the error between the multi-tone input image and the binary output image can be reduced on average, and a high-quality output image can be obtained. However, there is a problem that the processing speed is slow because arithmetic processing is required to diffuse the error. There is also a drawback that a pattern peculiar to error diffusion is likely to occur. Originally, these patterns that were not present in the input image are collectively referred to as a virtual image (artifact).

On the other hand, in the dither method, when converting multi-tone image data to binary image data, each pixel of the original image and the element of the threshold matrix are compared one-to-one to determine the output value. It is said that it is possible to perform high speed processing which is 3 to 5 times faster than the error diffusion method. The dither method is roughly classified into a random dither method and a systematic dither method.

The random dither method is a method of changing the threshold value for each pixel by a random number. Since the dot pattern generated for an input image of constant density has a white noise characteristic, the dot density varies depending on the location on the output screen. The difference is large.
Therefore, when the resolution of the output device is low, the graininess is remarkable, and even when the resolution is high, the graininess is sensed at low gradation and the distribution of shades at high gradation is impractical.

The systematic dither method is a method of using a threshold matrix (also called a dither matrix, a mask, etc.) in which thresholds are regularly arranged. Depending on how the thresholds are arranged, there are two types of dot concentration type and dot dispersion type. It can be divided into types.

In the dot-concentrated type, as the number of gradations increases,
The dots come into contact with each other to form a cluster of secondary dots, and only their size increases. Therefore, the total number of secondary dots does not depend on the gradation. Further, in the simplest case, each secondary dot has perfect periodicity because it is arranged on the lattice points of a two-dimensional square lattice. Therefore, the resolution of the output device is 2500d.
It is mainly used in the printing field because an output resolution of photographic quality can be obtained if it is as high as about pi or more (more than eye resolution at the distance of clear vision). However, the resolution is 100
Even if it is about 0 dpi, the size of the dot becomes larger as the gradation becomes higher, so that individual secondary dots can be separated and identified, resulting in an output image with outstanding graininess.
Further, when the input image includes a periodic pattern such as a striped pattern, moire may occur. However, unlike irregular graininess, high resolution can be obtained despite its low resolution, so it is still used in the printing field and in newspaper photographs where cost is important.

On the other hand, in the Bayer type systematic dither method, each dot is subjected to a predetermined rule so that the one-dimensional spatial frequency spectrum of the dot distribution in each gradation has less low frequency components below the cutoff frequency. It is a method of arranging. Therefore, although the irregular graininess that is characteristic of the random dither method is not inherently present, it has strong regularity and periodicity, and therefore the input image depends on its resolution, the number of gradations, and whether or not it contains a periodic pattern. Also, regarding the output device, the image quality of the output image greatly depends on the resolution thereof. For example, when the resolution of the output device is low, an unpleasant texture (dither pattern) having a two-dimensional cycle of 16 × 16 pixels corresponding to the size of the mask (16 × 16 elements in the case of 256 gradations) is detected. . Also, regardless of the resolution of the output device, if the input image contains a periodic pattern, there is an essential problem that moire may occur. Therefore, it is not suitable for the purpose of obtaining a high quality output image.

Nearly 10 years ago, when the average printer resolution was 300 to 500 dpi, a dither method was proposed for the purpose of obtaining a high-quality output image at a higher speed than the error diffusion method. There is a blue noise mask method as one of the above (Patent Publication No. 2622429, USP 5,111,
310, USP 5,477,305, T.I. Mitsaa
nd K. J. Parker, J .; Opt. Soc. A
m vol9, No. 11, pp. 1920-1929
(1992); Yao and K. J. Park
er, J.I. Electronic Imaging, v
ol. 3, pp. 92-97, (1994)). According to the blue noise mask mask method, a dot pattern having a blue noise characteristic can be obtained irrespective of gradation, the graininess is small, and there is no possibility of generating moire. Before this, a perturbation error diffusion method has been proposed by Urichney for the purpose of obtaining a dot pattern having a blue noise characteristic in all gradations (R. Uli).
chney, Digital Halftoning (M
IT Press, Cambridge, Massac
husetts, (1987)).

The dot pattern created by the blue noise mask method has poor dot distribution compared to, for example, the Bayer type systematic dither method due to the method of creating the dot pattern. There is a large sense of noise near the tones and near the highest tones. Also, the unit area (for example,
Since the number of dots included in each 16 × 16 pixel is not uniform, when the size of the mask is small, for example, 128 ×
With a size of 128 elements, using an output device of 600 dpi, a dither pattern in which irregular irregularity is repeated in a two-dimensional cycle is detected in many gradations. Digital cameras with 3 million pixel image sensors, 12
Now that inkjet printers having a resolution of about 00 dpi are becoming widespread, the development of a dither method with better image quality is desired.

In order to achieve the above object, as a dither method in which a weak irregularity is introduced to the Bayer type systematic dither method to the extent that the uniformity of the dot distribution obtained by the same method is maintained, The method disclosed in Kai 2000-59626 has been proposed. The dot pattern obtained by this method has a strong periodicity similar to that of the Bayer systematic dither method, and exhibits non-blue noise characteristics at all gray levels. Nevertheless, it is possible to prevent generation of moire having an unpleasant contrast even for an input image having a normal periodic pattern.

For the sake of convenience, the method disclosed in Japanese Patent Laid-Open No. 2000-59626 will be referred to as a Bayer type perturbed systematic dither method, or a perturbed systematic dither method for short. In this method, since the mask itself has a two-dimensional periodic structure in all gradations, depending on the gradation, a dither pattern appears slightly, mainly in the direction in which the same structures are periodically arranged (usually the vertical and horizontal directions on the screen). , There was room for improvement.

The cause of the occurrence of the dither pattern will be described below. The main feature of the perturbed systematic dither method is that the threshold matrix is composed of an integer number of small matrices of the same shape (when the number of gradations to be reproduced is 256, it has 16 × 16 elements) To have multiple small matrices with arrays. As the dot pattern for obtaining the threshold matrix, a dot pattern having weak irregularity is used in the 1st or 2nd gradation in the 1st or 2nd gradation dot pattern of the Bayer systematic dither method.
In this way, a repulsive potential is applied to each dot of the dot pattern one gradation below the gradation containing irregularity,
For each small section corresponding to the small matrix, a new dot is formed on the pixel where the potential of the sum is minimal. However, in the vicinity of the boundary of the small sections corresponding to the small matrix having the same threshold value array, the uniformity of the dot distribution is relatively poor compared to the other areas, which is
Depending on the gradation, it will be perceived as a weak dither pattern.

[0016]

In order to eliminate the above-mentioned drawbacks of the perturbed systematic dither method, Japanese Patent Application No. 2000-11214.
The method shown in No. 3 was proposed. The uniformity of dot distribution near the boundaries of small sections with the same dot pattern is improved by using two methods. One is that, for small sections having the same dot pattern, the repulsive force potential sums of all the sections are once averaged, and the averaged potential sum is again used as the potential sum of each section. The other one is to regulate the order in which dots are increased between a small section having the same dot pattern and other sections. Usually, the small sections having the same dot pattern are prioritized. It was confirmed by evaluation of an output image using a 600 dpi printer that these improvements can produce a non-blue noise mask in which a dither pattern does not occur.

As an improved technique of the perturbed systematic dither method, in addition to this, by increasing the regularity of the dot pattern in a local region of the above-mentioned subdivision or less and suppressing local aperiodicity in that region, the dot group is formed. Japanese Patent Application No. 2001-203384 proposes a method of improving the uniformity of the local density by the method of improving the uniformity of the dot pattern. When the perturbed systematic dither method improved by these techniques is used, the dot distribution is uniform in all gradations, and an output image without an unpleasant dither pattern or graininess can be obtained.

Generally, in a color image recording apparatus,
The gradation process is performed for each color component by using the gradation reproduction method in which each color component of the input color image data is represented by the above binary data in a pseudo manner to represent multi-gradation data.

In gradation reproduction of a color image using the error diffusion method, gradation processing is performed by the error diffusion method independently for each color component. Therefore, even if a uniform dot pattern is generated for each color component, a plurality of dot patterns are generated. When the color components are combined, the dot distribution may be biased, which may cause a graininess or a virtual image. When determining the dot pattern of each color component, it is possible to consider the dot positions of other color components and improve the uniformity of the dot distribution of multiple color components.
In addition to the calculation process for diffusing the error between the input multi-tone image and the binary image, the calculation process for correlating with the dots of other color components is required, and the processing speed is significantly reduced.

In gradation reproduction of a color image using the dither method, gradation processing is performed on each color component using a threshold matrix. The binarization process using the same threshold matrix for all color components is "dot on.
This is known as the "dot" process, but in this process, the dots of a plurality of color components overlap to increase the visibility of the dots, and a graininess is likely to occur. It is rarely used due to problems such as being greatly affected by alignment errors.
Due to such a problem, in gradation reproduction of a color image using the dither method, a method of processing using different threshold matrices for each color component has become the mainstream. However, when different threshold matrices are applied to the respective color components, image quality deterioration such as occurrence of color moire due to interference of dot patterns of a plurality of color components and occurrence of graininess due to uneven dot distribution is likely to occur.

One method for improving such image quality deterioration is a screen angle method. This is a method that has been widely used in the field of printing from the past, and in the dithering method, the threshold value array of the threshold value matrix applied to each color component has an angle characteristic. By using this method, it is possible to increase the frequency of color moire caused by the interference of a plurality of color components, and reduce the occurrence of annoying moire. Typical CMYK color printing (4 color printing) with 4 colors of cyan, magenta, yellow and black has a typical screen angle of cyan: 1
5 °, magenta: 75 °, yellow: 0 °, black:
It is 45 °. This method is used especially for a dither method that generates a periodic dot pattern such as a systematic dither method. However, it is not possible to completely remove annoying moire.

Various gradation reproduction techniques for color images using a blue noise mask method for generating a random dot pattern having blue noise characteristics have been proposed (Patent Publication No. 26).
22429, USP 5,477,305). As one of them, there is a method of binarizing each color component with a mask in which several pixels are vertically or horizontally shifted when applying a blue noise mask to a plurality of color components, and in a low resolution system of 300 dpi, It has been found that when the mask is shifted by one pixel and gradation processing of each color component is performed, a visually preferable output can be obtained. Using this method, the problems that occur in the "dot-on-dot" process can be avoided. As another method, a method of applying a reference blue noise mask and an inversion body of the reference mask whose threshold is a value obtained by subtracting the threshold array of each element from the maximum value of the threshold of the mask is proposed. . By using this method, the dispersibility of a dot pattern in which a plurality of color components are combined can be improved. However, even if these methods are used, it is not possible to completely remove the graininess due to the uneven distribution of dots and the unpleasant pattern that is caused by the dots of multiple color components. There is still room for improvement in.

In gradation reproduction of a color image using the perturbative systematic dither method, a dot pattern generated by a mask created by the perturbative systematic dither method includes a plurality of sections having the same dot pattern. There is a feature unique to other dither methods such as the existence of strong periodicity due to, and thus there are problems unique to the perturbed systematic dither method. Even if a different threshold matrix is applied to each of the color components to perform the processing, there is a problem in that sections having the same dot pattern between the color components may interfere with each other to cause an unpleasant virtual image. For example, if a threshold matrix in which the arrangement of the sections having the same dot pattern is the same for all color components is applied and a virtual image such as color moire occurs in the section, the virtual image has the same dot pattern. It will occur in all the compartments and the layout of the compartments will appear as a virtual image. Even if the image does not clearly appear as a virtual image, image quality deterioration such as deterioration of graininess may occur.

As described above, in the perturbed systematic dither method, there are a plurality of small matrices having the same threshold array in the threshold matrix, and the dot patterns of the respective color components generated using these threshold matrices have the same dot pattern. Multiple partitions are included. Therefore, when the dot patterns of the respective color components are overlapped with each other, there is a possibility that a virtual image or a graininess which is not present in the original image may occur depending on the combination of the color components of the sections having the same dot pattern.

The object of the present invention is to solve the problems described in JP-A-2000-5962.
6, Japanese Patent Application No. 2000-112143, Japanese Patent Application 200
When the method shown in No. 1-203384 is used for tone reproduction of a color image, the positions of the sections where the dot patterns are equal in the dot pattern generated by the threshold matrix applied to each color component are mutually set between the color components. By not overlapping at all or only partially overlapping each other, a threshold matrix and a gradation reproduction method that do not cause annoying virtual images and graininess even in a combination of a plurality of color components To provide a device.

[0026]

The gradation reproducing method of the present invention for achieving the above-mentioned object decomposes a color image into a plurality of color components, and at least two kinds of color components are obtained for each color component. 1 for each pixel of the original image and each element of the threshold matrix
When the density in each pixel of the output image is expressed in binary or multi-valued in correspondence to 1 and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, all the gradations are all The number of dots in each section is equal, the dot patterns in a plurality of sections are equal to each other in all gradations, and gradation reproduction is performed using different threshold matrices for the at least two types of color components. The method is characterized by using threshold matrices in which the positions of the sections having the same dot pattern are different from each other.

Further, according to the gradation reproduction method of the present invention, the color image is separated into a plurality of color components, and for each color component, each pixel of the original image and each element of the threshold matrix are separated for each color component. When the density in each pixel of the output image is expressed in binary or multi-valued in a one-to-one correspondence and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, all gradations are The number of dots in all the sections is equal, the dot patterns in the plurality of sections are equal to each other in all the gradations, and gradations using different threshold matrices for the at least two types of color components The reproducing method is characterized in that a threshold matrix in which the positions of the sections having the same dot pattern partially overlap each other is used.

Further, the gradation reproduction method of the present invention decomposes a color image into a plurality of color components, and for each color component, for each color component, each pixel of the original image and each element of the threshold matrix are separated. When the density in each pixel of the output image is expressed in binary or multi-valued in a one-to-one correspondence and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, all gradations are The number of dots in all the sections is equal, the dot patterns in the plurality of sections are equal to each other in all the gradations, and gradations using different threshold matrices for the at least two types of color components In the reproduction method, the threshold value matrix used for each of the color components does not match the dot patterns at the boundaries of the sections where the dot patterns are equal to each other. At least one of the method of creating so that the dots increase from each other, and the method of restricting the order of increasing dots between the sections where the dot patterns are equal to each other and the sections other than that And a method of creating a shape based on a dot pattern formed by using a repulsive force potential that is adjusted as a non-rotation target in a plurality of gradations.

Further, the gradation reproducing apparatus of the present invention separates a color image into a plurality of color components, and for each of the at least two types of color components, each pixel of the original image and each element of the threshold matrix are separated. When the density in each pixel of the output image is expressed in binary or multi-valued in a one-to-one correspondence and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, all gradations are A gradation reproducing apparatus in which the numbers of dots in all the sections are equal and the dot patterns in the plurality of sections are equal to each other in all the gradations, and the threshold matrix for the at least two types of color components is stored. A storage unit, a comparison unit that compares the density of each pixel of the original image of each color component with each pixel by using the value of the threshold matrix as a threshold, and two values of each color component according to the comparison result of the comparison unit. Alternatively, it has an output means for outputting a multi-valued dot pattern, and the comparison means uses different threshold matrices for the at least two types of color components, and positions of sections where the dot patterns are equal to each other. It is characterized in that different threshold matrices are used.

Further, the gradation reproducing apparatus of the present invention separates a color image into a plurality of color components, and for each color component, for each color component, each pixel of the original image and each element of the threshold matrix are separated. When the density in each pixel of the output image is expressed in binary or multi-valued in a one-to-one correspondence and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, all gradations are A gradation reproducing apparatus in which the numbers of dots in all the sections are equal and the dot patterns in the plurality of sections are equal to each other in all the gradations, and the threshold value matrix for at least two types of color components is stored. A storage unit, a comparison unit that compares the density of each pixel of the original image of each color component with each other by using the value of the threshold matrix as a threshold, and a binary value of each color component according to the comparison result of the comparison unit. Or output means for outputting a multi-valued dot pattern, wherein the comparing means has different threshold matrices for the at least two types of color components, and the position of the section where the dot patterns are equal. Is characterized by using a threshold matrix that partially overlaps each other.

Further, the gradation reproducing apparatus of the present invention separates a color image into a plurality of color components, and for each of the at least two types of color components, each pixel of the original image and each element of the threshold matrix are separated. When the density in each pixel of the output image is expressed in binary or multi-valued in a one-to-one correspondence and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, all gradations are A gradation reproduction device in which the number of dots in all sections is equal, and the dot patterns in a plurality of sections are equal in all gradations,
Comparing the storage means for storing a threshold value matrix relating to the at least two types of color components, the comparison means for comparing the density of each pixel of the original image of each color component with each pixel by using the value of the threshold value matrix as a threshold value, and the comparison means Output means for outputting a binary or multi-valued dot pattern of each color component according to the result, and the comparison means applies different threshold matrices to the at least two types of color components. At the same time, the threshold value matrix used for each of the color components is created so that the dots increase while maintaining the consistency of the dot patterns at the boundary of the sections where the dot patterns are equal to each other, and the dot patterns are equal to each other. Of the method of creating by controlling the order of increasing dots between the other section and the other sections, At least one method and a method of creating a shape based on a dot pattern formed by using a repulsive force potential that is adjusted for a non-rotation target in a plurality of gradations are used. To do.

Further, the threshold matrix of the present invention separates a color image into a plurality of color components, and for at least two types of color components, each pixel of the original image and each element of the threshold matrix are paired for each color component. When the density in each pixel of the output image is expressed in binary or multi-valued corresponding to 1, and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, all the gradations and all In the threshold matrix, the number of dots in the section becomes equal, the dot patterns in the sections become equal to each other in all gradations, and different dot patterns are generated for the at least two types of color components. The positions of the sections having the same dot pattern are different from each other.

Further, the threshold matrix of the present invention decomposes a color image into a plurality of color components, and for at least two types of color components, each pixel of the original image and each element of the threshold matrix are paired for each color component. When the density in each pixel of the output image is expressed in binary or multi-valued corresponding to 1, and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, all the gradations and all In the threshold matrix, the number of dots in the section becomes equal, the dot patterns in the sections become equal to each other in all gradations, and different dot patterns are generated for the at least two types of color components. The positions of the sections having the same dot pattern partially overlap each other.

Further, the threshold matrix of the present invention decomposes a color image into a plurality of color components, and for at least two types of color components, each pixel of the original image and each element of the threshold matrix are paired for each color component. When the density in each pixel of the output image is expressed in binary or multi-valued corresponding to 1, and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, all the gradations and all In the threshold matrix, the number of dots in the section becomes equal, the dot patterns in the sections become equal to each other in all gradations, and different dot patterns are generated for the at least two types of color components. Therefore, the threshold value matrix used for each of the color components has the consistency of the dot pattern at the boundary of the sections where the dot patterns are equal to each other. At least one of the method of creating so that the dots increase while increasing the number of dots, and the method of restricting the order of increasing dots between the areas where the dot patterns are equal to each other and the areas other than that area One of the methods and a method of creating a shape based on a dot pattern formed by using a repulsive force potential that is adjusted as a non-rotation target in a plurality of gradations are used.

Further, the storage medium of the present invention separates a color image into a plurality of color components, and for at least two types of color components, each pixel of the original image and each element of the threshold matrix are paired for each color component. When the density in each pixel of the output image is expressed in binary or multi-valued corresponding to 1, and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, all the gradations and all The number of dots in a section becomes equal, the dot patterns in a plurality of sections become equal to each other at all gradations, and the at least 2
A storage medium that stores a control program for controlling gradation reproduction processing of a color image that uses different threshold matrices for different types of color components in a computer-readable manner, and the positions of sections where the dot patterns are equal are different from each other. Using a threshold value matrix, for each color component, using the threshold value of the threshold value matrix as a threshold value, the density of each pixel of the original image is compared with each pixel, and depending on the result of the comparison, each binary or multi-valued color It is characterized by including a module for controlling so as to output a dot pattern of the component.

The storage medium of the present invention separates a color image into a plurality of color components, and for each color component, at least two types of color components are paired with each pixel of the original image and each element of the threshold matrix. When the density in each pixel of the output image is expressed in binary or multi-valued corresponding to 1, and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, all the gradations and all The number of dots in a section becomes equal, the dot patterns in a plurality of sections become equal to each other at all gradations, and the at least 2
A computer-readable storage medium for storing a computer-readable control program for controlling gradation reproduction processing of a color image using different threshold matrices for different types of color components. Using a threshold matrix that overlaps each other, using the threshold value of the threshold matrix for each color component as a threshold value, and comparing the density of each pixel of the original image with each pixel, and binarizing or multivalued according to the comparison result. It is characterized by including a module for controlling so as to output the dot pattern of each color component that has been generated.

Further, the storage medium of the present invention decomposes a color image into a plurality of color components, and for at least two types of color components, each pixel of the original image and each element of the threshold matrix are paired for each color component. When the density in each pixel of the output image is expressed in binary or multi-valued corresponding to 1, and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, all the gradations and all The number of dots in a section becomes equal, the dot patterns in a plurality of sections become equal to each other in all gradations, and gradation reproduction of a color image using different threshold matrices for the at least two types of color components A storage medium storing a computer-readable control program for controlling processing, wherein a threshold matrix used for each of the color components,
At the boundary of the sections where the dot patterns are equal to each other, a method of increasing the number of dots while maintaining the consistency of the dot patterns, and a dot between the sections where the dot patterns are equal to each other and the other sections Created based on at least one of the methods of controlling the increasing order and the dot pattern formed by using the repulsive force potential adjusted for the non-rotation target in the multiple gradations. The value of the threshold matrix is used as a threshold for each color component, and the density of each pixel of the original image is compared with each pixel, and binary or multi-valued is performed according to the comparison result. It is characterized by including a module for controlling so as to output a dot pattern of each color component.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION In the simplest case of the present invention, such as a conventional ink jet printer or bubble jet (BJ) printer, ink droplets of each color component are supplied to each pixel of an output image. It can be applied to express halftone in a device that determines whether or not to strike, and similarly in a liquid crystal display device of the kind that displays an image in bright or dark for each color component of each pixel. It is preferably used for expressing a halftone.

More generally, an ink jet printer or the like for converting a monochrome or color image having continuous gradation or multi-gradation (usually 256 gradations) into multi-values of binary or ternary density and outputting the same. In addition, it is preferably used in devices such as laser beam printers, facsimiles and printing machines in order to preferably express halftones.

<Example of Configuration of Processing Apparatus According to this Embodiment> FIG.
Shows a basic system for processing an image in the present embodiment. In the figure, 1 is an image input device such as a scanner for scanning an input image 2. In this apparatus, the pre-processing unit 3 that digitizes the number of gradations in each color component, for example, into 256 gradations, performs γ correction, various color conversions, etc. on the input image 2 having continuous gradations for each color component. Is provided.

Reference numeral 4 denotes a gradation processing device, which is a memory 6 for storing a plurality of masks applied to each color component, the number of gradations of each pixel of each color component of the input image, and the corresponding mask value (threshold value). Comparator 7 for comparing the output values and determining the output value accordingly
including. Reference numeral 8 is a device for outputting a color output image 9 formed based on the output value of each color component from the comparator 7 in a format such as display or printing.

<Outline of Threshold Matrix Creating Method in this Embodiment> A mask creating method applied to each color component in this embodiment will be described. In the present embodiment, the mask applied to each color component is created by the following method, or the mask created by the following method is subjected to operations such as parallel movement, vertical / horizontal inversion, and rotation. , Create multiple masks applied to each color component.

The dot pattern corresponding to the size of one mask produced by the method of making a mask in this embodiment has the following regularity when divided into smaller sections of the same shape. Is characterized by.

(1) The dot pattern of any one of the low gradations after the first gradation is periodic or pseudo periodic.

(2) The dot patterns in the plurality of sections are equal to each other in all gradations.

(3) The number of dots in all sections is the same for all gradations. Further, in some cases, each section may be further divided into four small sections to have the following regularity.

(4) In 4n gradation (n is an integer), the number of dots in all the small sections is the same.

The above-described dot pattern regularity utilizes the dot pattern regularity of the Bayer systematic dither method, and a similar one is disclosed in Japanese Patent Laid-Open No. 2000-59626 and Japanese Patent Application No. 2000-112143 as an improved technique. Japanese Patent Application No. 2000-203384 has been proposed, and a dot pattern with high uniformity can be generated by providing such regularity in all gradation (density) regions. It should be noted that the effect based on the characteristics of the mask created in this embodiment is more remarkable as the resolution of the output device is higher. Therefore, the resolution of the output device needs to be at least about 600 dpi, and if it is about 1200 dpi, an extremely excellent output image can be obtained.

The basic mask making method according to this embodiment will be described below with reference to the flow chart shown in FIG. In step S1, the basic structure of the mask is determined.
That is, the size and shape of the mask are matched to the characteristics of the output device, for example, a 128 × 128 element square, 256 × 2
56 element square, 512 × 512 element square,
It can be determined as a cross shape in which five (64 × 64) squares are combined.

Further, when the input image is larger than the screen size corresponding to the mask size, the masks are two-dimensionally arranged and used. The manner of arrangement of the masks is also determined. For the mask arrangement, an arrangement method different from the arrangement method in which the masks are aligned vertically and horizontally can be used according to the characteristics of the output device. For example, if you use a vertically offset array,
When the output device is a printer, the main scanning direction of the head that ejects ink is not parallel to the mask array, so
It is possible to reduce the problem that mechanical streaks occur in the scanning direction on a printer or the like.

The method of forming a mask in this embodiment is 2
An explanation will be given taking as an example a mask for 256 gradations having a square shape of 56 × 256 elements. Further, in general, since the input image is larger than the screen size corresponding to the mask size, in such a case, the mask is repeatedly used in a tiled manner with regular vertical and horizontal directions.

Next, the structure in the mask, that is, the sizes and shapes of the above-mentioned sections and small sections are determined, and a plurality of sections having the same dot patterns are selected.

Here, the creation of a mask having all of the above rules (1) to (4) will be described. However, rule (4) may be disqualified if necessary. The partition used in regularity (3) is a square of 16 × 16 pixels shown by a solid line in FIG. 3, and the small partition used in regularity (4) is 8 × 8 pixels obtained by further dividing the square into four equal parts by a broken line. Of squares. In addition, the section group patched in gray in FIG. 3 is a section group in which the dot patterns are equal to each other, which is determined when the regularity (2) is realized.

In the present embodiment, since a plurality of sections having the same dot pattern are arranged inside the dot pattern corresponding to one mask, the mask itself has a strong periodicity. FIG. 3 shows an example in which the periodicity appears most typically. Since periodically arranging the sections in this way also contributes to improving the uniformity of the dot pattern, when a mask is repeatedly used in a tiled manner regularly in the vertical and horizontal directions, the occurrence of a virtual image in the repeating cycle of the mask is suppressed. Act as you do. However, since the dot patterns of a plurality of color components are combined in the gradation reproduction of a color image, the periodic array of the sections may interfere with each other depending on the combination of masks corresponding to the respective color components, so that color moire may occur. Virtual images may occur.
Therefore, when a mask of the perturbed systematic dither method is used to reproduce the gradation of a color image, it should be noted that the positional relationship between the masks of the sections in addition to the section array may greatly affect the image quality. I have to pay.

In the mask making method according to the present embodiment, the dot pattern representing each gradation is sequentially determined from the low gradation, but S2 for artificially determining the dot pattern up to a certain gradation of the low gradation, The process is largely divided into step S3 and subsequent steps for determining dot patterns of higher gradations using the repulsive potential.

The dot pattern at the lowest gradation determined in step S2, or a gradation in the vicinity thereof is periodic or
It is assumed to be pseudo-periodic with randomness. By forming a periodic or pseudo-periodic dot pattern with good uniformity, it is possible to solve the problem of the blue noise mask method, that is, the unevenness in low gradation. In general, a periodic dot pattern may cause an unpleasant pattern or the generation of moire, but it does not cause a problem when the image density is low and the gradation is very low.

Further, not only the dot pattern in the lowest gradation or the gradation in the vicinity thereof, but also the dot pattern in the highest gradation or the gradation in the vicinity thereof can be determined in step S2. That is, by making these high-gradation dot patterns periodic like the dot patterns in the vicinity of the lowest gradation determined in S2 or pseudo-periodic with randomness added thereto, the vicinity of the highest gradation is obtained. It is possible to guarantee the uniformity of the dot pattern in the gradation of. To give a concrete example, all the pixels diagonally below and to the right of each dot of the first gradation dot pattern are set to 25 pixels.
It suffices to prevent dots from being printed until the dot pattern of 5 gradations is created.

In the description of the mask making method according to the present embodiment, step S up to the dot pattern of the second gradation is performed.
It will be decided in 2. FIG. 4 shows a part of the dot pattern of the first gradation determined in the step S2. Here, a periodic dot pattern is used for the first gradation. This dot pattern is the same as that generated by the Bayer systematic dither method.

FIG. 5 shows a part of the dot pattern of the second gradation determined in step S2. The second gradation dot pattern is created by adding a pseudo-periodic dot pattern as shown by 10 to 14 to the first gradation dot pattern.

The dots shown in 10 to 14 are 19 to 23.
Randomly selected under the uniform probability distribution from the box shown in. Here, the size of this frame is 7 × 7. Also, 15-18 added to the section patched in gray
The dots shown in are not given randomness.

Randomness can be controlled by changing the size of the frame shown in 19 to 23 and the probability distribution inside the frame within a range that does not break the regularity.

It can be seen that the dot patterns up to the second gradation created as described above satisfy the conditions required for the regularities (1) to (4).

In step S3, the shape of the repulsive potential used when creating the dot pattern is determined. Step S3 is a step S for determining a basic potential shape.
3-1 and step S3-2 for locally adjusting the potential shape determined in step S3-1.

The basic shape P (r) of the potential determined in step S3-1 is shown, for example, in FIG. 6, but in step S3-2, as shown in FIG. The shape of the repulsive potential relating to a pixel in which a coefficient different from 1 is set is locally adjusted by multiplying by a coefficient that is a function of position coordinates with the origin being. r represents the distance from the dot to which the repulsive potential is applied, and when r> r _max , P (r) = 0.

The repulsive potential has such an effect that a dot having a larger value is less likely to be hit with a dot, and a smaller value is more likely to be hit with a dot. The basic potential shape has the effect of striking the dots as far apart as possible, and the local shape adjustment is performed in order to have the effect of controlling the position of the dots in the local area. The basic shape of the potential has a great influence on the tendency of the dot arrangement, but the specific shape will be described later.

The above-described local adjustment of the potential shape is intended to make it easier for the existing dot to be struck at a pixel at a specific position within a local area centered on the dot. . FIG. 7A shows the coefficients for performing the local adjustment, and when the position of the existing dot to which the repulsive force potential is applied is (x, y) = (0, 0), the surrounding of that dot is shown. It represents the coefficient in a pixel. By multiplying the basic potential shape by such a coefficient, it is possible to control the ease of hitting a dot. If the value of the coefficient is less than 1, the dot is easily hit, and if it is greater than 1, the dot is hit. It gets harder. Figure 7
In FIG. 7B, when the shape of the potential is adjusted using the coefficient of FIG. 7A, a pixel in which dots are easily hit is indicated by ◯, and a pixel in which dots are hard to be hit is indicated by X. By using the potential adjusted in this way, a large number of dots in a local area having a similar regular dot pattern are formed uniformly in the screen corresponding to the size of the mask, so that the density uniformity can be improved. Can be improved. The dot pattern created using this potential is highly uniform,
Virtually unpleasant virtual images are rarely generated when output with a 600 dpi printer.

By locally adjusting the potential shape, it is possible to arbitrarily set the position at which dots are easily hit with respect to existing dots. Vertical as seen from existing dots,
Makes it easy to hit dots at specific positions in the horizontal and diagonal directions, or at the positions of polygon vertices centering on existing dots, and forms a grid pattern or checkered dot pattern in the local area that includes existing dots. It is also possible to make it easier.
Since the positional relationship of the dots in the optimum local area differs depending on the output device, it is necessary to set the dot position in the local area according to the characteristics of the output device.

Generally, the repulsive force potential can be made to have gradation dependence, and when the dot pattern of the third gradation is created, the repulsive potential for the third gradation is used.

In step S4, the dot patterns of the third and subsequent gradations are sequentially determined. As the step of determining the dot position, step S4-2 of determining the dot pattern of the section patched in gray and other steps are determined. The process is divided into step S4-3 for determining the dot pattern of the section.

The method of forming the third gradation dot pattern will be described below.

First, S4-1 will be described. As shown in FIG. 5, a repulsive potential whose shape is adjusted around each pixel in which dots are formed up to the second gradation is applied.

When the repulsive force potential is applied to the dots, the portion protruding from the boundary of the mask is processed by using the periodic boundary condition in consideration of the two-dimensional arrangement of the mask determined in step S1. .

This periodic boundary condition will be described with reference to FIG. Here, with respect to the portion where the repulsive force potential applied to the dot 24 protrudes from the boundary of the section corresponding to the mask to the other three sections, it is as if the repulsive potential was applied to the pixels in 25 to 27. Considering, it is given like 28-30. When this method is used, when the masks are arranged and used, an unpleasant dot arrangement cannot be formed near the joints between the masks.

In the following, this periodic boundary condition is used when applying a potential to a dot. (S4-
1) Next, S4-2 for determining the dot arrangement of the section patched in gray in FIG. 3 will be described. First, the sum of the repulsive potentials in each of the 64 patched areas in gray is averaged, and the averaged sum is used as the new potential sum in the patched areas in gray. That is,
The distributions of the repulsive potentials, that is, the sums of the potentials of the sections patched in all gray are equal.

Next, in the section patched in gray,
When there are two or more pixels having the lowest potential sum within the range where the regularity (4) is not broken, one pixel is randomly selected from the pixels.

When the dot pattern of the third gradation is determined by the mask making method according to the present embodiment, the dot pattern of the second gradation, as shown in FIG. The number of dots contained in each of the upper left and lower right sub-parts is 1 and the number of dots in the upper right sub-part and the lower left sub-part are 0, so in order not to break the regularity (4), From the upper right and lower left subdivisions, you must choose the lowest potential sum.

In the case of the mask making method according to the present embodiment, there are 64 sections patched in gray, and the potential sums of all the sections are equal. Therefore, the lowest point of the potential sum is 64 pixels in total in each section. There are pixels. Dots are newly added to the 64 points in a regular array. In other words, the patches patched in gray are printed with dots before the other patches. in this way,
By striking an extremely regular and uniform dot pattern first, an effect of improving the uniformity of the dot pattern that is subsequently stamped can be obtained.

Next, a potential is applied to each of these 64 dots and the potential sum is recalculated. (Above S4-2) Next, S4-3 will be described. First, regularity (3), (4)
By searching for a pixel having the lowest potential sum within a range that does not break, the pixel to be hit by one dot and the section including it are determined.

That is, in the sections other than the section patched in gray, the pixel with the lowest potential sum is searched for from the upper right and lower left subsections of each section, and dots are added. Further, a potential is applied around this pixel and the potential sum is recalculated.

The position of the pixel where the next dot is to be printed and the section containing it are determined in the same way. First, regularity (3),
A pixel with the lowest potential sum is searched for within a range not breaking (4). In other words, the next dot position is searched for in the sub-sections that do not include the newly added dot, and in the sub-sections in the upper right and lower left of each section.

A dot is applied to this pixel, a potential is applied around this pixel, and the potential sum is recalculated.

The above process is repeated to form a dot pattern of the third gradation when the number of dots required to represent the third gradation is reached. The third generated in this way
In the gradation dot pattern, three dots are printed in all 16 × 16 sections, which satisfies the regularity (3).
(Above S4-3) Dot patterns for the fourth and subsequent gradations are also from S4-1 to S4-3
Repeat the same process as above, and decide sequentially. However,
When the repulsive potential has gradation dependency, the repulsive potential for that gradation must be used when creating the dot pattern.

For example, the dot patterns for the fourth and subsequent gradations are determined by the third gradation applied to the dot pattern of the third gradation when the potential sum is calculated in step S4-1.
The repulsive potential for gradation is once canceled, the repulsive potential for the fourth gradation is determined in step S3, and the potential sum is recalculated using the repulsive potential. The potential for the fourth gradation is used also in steps S4-2 and S4-3.

The dot pattern of the fourth gradation thus created includes one dot in each small section and satisfies the regularity (4).

When all the dot patterns up to the highest gradation (255 gradations) are determined, by accumulating them, when an input image having an arbitrary constant gradation on the entire screen is subjected to halftone processing. A mask that outputs a dot pattern corresponding to each of these gradations can be created.

That is, using (x, y) as coordinates representing the pixel position, the dot pattern d (g; x,
y)

[Outer 1]

Then, the mask m (x, y) is

[Outside 2]

Can be represented (step S
5).

Further, by determining the basic structure of the mask in step S1, determining the dot pattern with a low gradation in step S2, determining the basic shape of the repulsive force potential in step S3, and performing local shape adjustment, It is possible to control the array tendency freely and in a wide range, and it is possible to realize a dot pattern that matches the characteristics of the output device.

As described above, when the mask of the perturbed systematic dither method having excellent characteristics is applied to each color component of the color image, there is a problem peculiar to the present dither method that must be noted as already described. That is, when the mask of the present method is viewed in the pixel space, a plurality of sections in which the dot patterns are equal to each other are periodically arranged in all gradations. Basically, when the same dot pattern having periodicity is shifted and overlapped, moire occurs. Therefore, when the present mask is applied for each color component, it is necessary to pay attention to the positional relationship between the masks of the sections having at least the same dot pattern. Hereinafter, two embodiments having different positional relationships will be described.

<First Embodiment> In the present embodiment, an input color image is separated into four color components of cyan (C), magenta (M), yellow (Y), and black (K), and each color image is separated. Gradation reproduction is performed for each component using different masks.

A procedure for creating a mask for each color component having the features of this embodiment will be described with reference to the flowchart of FIG. All masks for each color component are created according to the flowchart of FIG.

First, in step S1, the basic structure of the mask is determined. The masks for each color component in this embodiment are all 128 × 128 element squares for 256 gradations. FIG. 9 shows a mask arranging method when the input image is larger than the mask size, and is the same for all color components.

In the figure, 128 × 128 pixels painted in gray are the size of the section corresponding to one mask. When the output device is a printer, the arrow direction indicated by is the direction in which the ink ejection head or the like is scanned, that is, the main scanning direction,
The arrow direction indicated by is a sub-scanning direction such as paper feeding.

The dot pattern of each color component of 128 × 128 pixels generated by one mask of this embodiment is 16 × 1 as shown by the solid lines in FIGS.
When divided into 6 pixel sections, the following three regularities are assumed.

(1) The dot pattern of the first gradation is a pseudo periodic dot pattern.

(2) The dot patterns in a plurality of sections are equal to each other in all gradations.

(3) The number of dots in all sections is the same for all gradations. However, the division groups of the regularity (2) in which the dot patterns are equal are patched to gray in FIG. 10 for the mask for C, FIG. 11 for the mask for M, FIG. 12 for the mask for Y, and FIG. 13 for the mask for K. , 16 16 × 16 pixel sections in which each color component is described.

FIG. 14 shows a diagram in which masks for the four color components of CMYK are superimposed. The sections in which the dot patterns of the color components CMYK are the same are shown in FIGS.
If the dot patterns generated by the respective masks are combined, the color components C
The sections in which any one of the MYK dot patterns is equal to each other are arranged in the entire area of the image, and the uniformity of the image is improved. Further, since a section group in which the dot patterns in any one of the color components CMYK are equal to each other overlaps a section in which the dot patterns of the other color components are not equal to each other, a dot pattern in which the color components CMYK are combined will be examined. That is, a section in which the dot patterns are equal to each other does not occur in most of the combinations of the gradation numbers of four types of color components CMYK. This is to suppress moire caused by overlapping of sections where the dot patterns of the color components are the same, and when there is a virtual image due to the arrangement of the sections where the dot patterns of the color components are the same. It has the effect of lowering the sex.

Next, in step S2, a dot pattern near the lowest gradation is determined. In this embodiment, up to the second gradation dot pattern is determined in step S2 of FIG.

A method of forming a dot pattern up to the second gradation of each color component will be described below. First, a method of creating a dot pattern up to the second gradation of the color component C will be described with reference to FIG. However, for convenience of drawing, only a part of the dot pattern is displayed. From the pixel in the upper left corner of the mask, the horizontal x pixel, vertical y
The position of a pixel will be represented by coordinates (x, y).
The position of the pixel in the upper left corner is (0,0).

The dot pattern of the first gradation of the color component C is 3
A periodic dot pattern such as 1-42 is used. This dot pattern is the same as that generated by the Bayer systematic dither method. The dot position is (16i +
1,16j + 1) (where i = 0, 1, ..., 7, j =
0, 1, ..., 7).

Next, a method of forming the second gradation dot pattern of the color component C will be described. Dots striking the sections where the dot patterns are equal do not give randomness like 43 to 46, and the dot position is (32m + 9, 32n + 9)
(However, m = 0,1,2,3, n = 0,1,2,3),
And Forty-eight dots that are printed in areas other than the areas where the dot patterns are equal to each other give randomness. In the present embodiment, each of the four corners of the section of 4 × 4 pixels indicated by the thick lines 47 to 51 is randomly selected with a probability of ¼.

As described above, the dot pattern of the periodic first gradation and the dot pattern of the pseudo periodic second gradation of the color component C are completed. This pattern is regularity (1) ~
Note that the condition (3) is satisfied.

Next, a method of forming a dot pattern up to the second gradation of the color component M will be described with reference to FIG. The preparation method is almost the same as the preparation method of the color component C. The dot pattern of the first gradation of the color component M uses a periodic dot pattern such as 52-60. This dot pattern is the same as that generated by the Bayer type systematic dithering method, like the color component C. The dot position is (16i + 9,16j + 9)
(However, i = 0,1, ..., 7, j = 0,1, ..., 7)
And The dot pattern of the first gradation of the color component M is at the same position as the dot pattern newly formed on the second gradation by the Bayer systematic dither method when viewed from the dot pattern of the first gradation of the color component C, When the dot patterns of the first gradation of the color component C and the color component M are overlapped, the same dot pattern as the second gradation of the Bayer systematic dither method is obtained. The spatial frequency of this dot pattern is high, an unpleasant virtual image does not occur due to the periodicity of the dot distribution, and the dot distribution is highly uniform.
By setting the first gradation dot pattern of the color component C and the color component M with high visibility of dots as described above, good image quality can be obtained in the low gradation region of the color image.

Next, a method of forming the second gradation dot pattern of the color component M will be described.

Dots applied to the sections where the dot patterns are equal to each other do not give randomness like 61 to 64,
The dot positions are (32m + 17, 32n + 17) (where m = 0, 1, 2, 3 and n = 0, 1, 2, 3). Forty-eight dots that are printed in areas other than the areas where the dot patterns are equal to each other give randomness. In this embodiment, 65
Each of the four corners of the 4 × 4 pixel section as indicated by the thick line of ˜76 is randomly selected with a probability of ¼.

Next, a method of forming a dot pattern up to the second gradation of the color component Y will be described with reference to FIG. The dot pattern of the first gradation of the color component Y uses a periodic dot pattern such as 77 to 88. The dot position is (16i + 9,
16j + 1) (where i = 0, 1, ..., 7, j = 0,
1, ..., 7).

Next, a method of forming a second gradation dot pattern will be described. The dot positions are (32m + 17, 32n + 9) (where m =
0, 1, 2, 3, n = 0, 1, 2, 3). Forty-eight dots that are printed in areas other than the areas where the dot patterns are equal to each other give randomness. In this embodiment, 93 to 1
From the four corners of the 4 × 4 pixel section as shown by the thick line of 00,
We will randomly choose each with a probability of 1/4.

Next, a method of forming a dot pattern up to the second gradation of the color component K will be described with reference to FIG. The dot pattern of the first gradation of the color component K is 101 to 101 like the other color components.
A periodic dot pattern such as 112 is used. The dot position is (16i + 1, 16j + 9) (where i = 0,
1, ..., 7, j = 0, 1, ..., 7).

Next, a method of forming the second gradation dot pattern will be described. Dots striking sections where the dot patterns are equal do not give randomness like 113 to 116, and the dot positions are (32m + 9, 32n + 17) (where i = 0, 1, 2, 3, j = 0, 1, 2). , 3).
Strike in areas other than the areas where the dot patterns are the same 48
The dots give randomness. In this embodiment, 1
Each of the four corners of the section of 4 × 4 pixels indicated by the thick lines 17 to 124 is randomly selected with a probability of ¼.

As described above, the dot pattern of the periodic first gradation and the dot pattern of the pseudo periodic second gradation are completed for each color component. It can be seen that these patterns satisfy the conditions required for regularity (1) to (3).

When the dot patterns of the first gradation of all color components of CMYK are overlapped, the dot position becomes the same as the fourth gradation of the Bayer systematic dither method. Since the spatial frequency of this dot pattern is high and the dots are uniformly distributed periodically, unevenness and an unpleasant virtual image hardly occur. By setting the first gradation dot pattern of each color component as described above, it is possible to obtain an output image in which unevenness and an unpleasant virtual image do not occur even at extremely low gradations.

When the second gradations of all CMYK color components are overlapped, the dots of C and M and the dots of Y and K are overlapped or arranged close to each other, which is similar to the second gradation of the Bayer systematic dither method. The dot pattern is pseudo-periodic, and unevenness and an unpleasant virtual image are not generated.

In the present embodiment, the sections where the dot patterns are the same for each color component are set as shown in FIG. 17, but in FIG. 17, the settings of C and M are exchanged, or C
And Y or K, M and K or Y, Y and C or M, K and M or C, the above effects can be obtained.
Further, in the present embodiment, the sections where the dot patterns are the same in each color component are not completely overlapped between the color components, but even if the section arrangements are partially overlapped, an annoying virtual image is generated. It is possible to avoid image quality deterioration due to.

In the setting of the dot pattern with a low gradation in the present embodiment, when the dot patterns of each color component are combined, a dot of each color component and a secondary color dot in which two types of color components overlap is generated. However, in order to improve the decrease in brightness due to the occurrence of secondary colors, the first of each color component,
It is also possible to set the dot position of 2 gradations by shifting several pixels.
It is effective in improving image quality.

Next, in step S3, the repulsive potential shape used when creating the dot pattern is determined. First, in step S3-1, the basic shape of the repulsive force potential is determined. The basic shape P (g, r) of the repulsive potential in the present embodiment is

[Outside 3]

[0118]

[Outside 4]

That is, the same applies to the creation of dot patterns for all color components. Here _{r m ax} is 128, a is set to 0.64. Further, r represents the distance from the center of the pixel to which the repulsive potential is applied,

[Outside 5]

It is The basic shape of the repulsive potential described above has a gradation dependency that attenuation is slow at low gradations and high gradations and that attenuation is fast at intermediate gradations.

Next, in step S3-2, the local shape of the repulsive potential is adjusted. The local area here refers to an area corresponding to a section of 16 × 16 pixels. In this embodiment, C (g, y), which is a function of the number of gradations g represented by the following equation and the distance r from the center of the potential to the center of the pixel to be finely adjusted, is defined as the basic shape P (g) of the repulsive potential. ，
Local shape adjustment of the repulsive potential is performed by multiplying r). Similar to the determination of the basic potential shape, the same local shape adjustment is performed in creating dot patterns of all color components.

Of the coefficients C (g, r) shown below, the meanings of the first three coefficients will be described. The number of gradations

[Outside 6]

Or

[Outside 7]

In the gradation range represented by r = 4, that is, (x, y) = (0, 4), (0, -4), (4, 0),
The coefficient of the pixel of (−4,0) is 0.985,

[Outside 8]

That is, (x, y) = (1, 1), (1,
The coefficients of the pixels of −1), (−1, 1), and (−1, −1) are 1.050, and the coefficients of the other pixels are 1.000. The same applies to each coefficient shown after the above-mentioned coefficient. C (g, r)

[Outside 9]

[0126]

[Outside 10]

[0127]

[Outside 11]

[0128]

[Outside 12]

[0129]

[Outside 13]

By using the repulsive force potential whose shape is adjusted by the coefficient C (g, r) in the above equation, it becomes easy to arrange dots regularly or periodically in the vertical and horizontal directions in the local region. In this embodiment, an output device having a definition of 600 dpi is assumed, and the visual sensitivity to contrast is almost 0.
The regularity or periodicity of the dot pattern is increased within the distance between two dots, that is, within a local area of 4 pixels or less. The coefficient C (g, r) can be appropriately changed according to the number of gradations so as not to impair the uniformity of the dot pattern corresponding to the entire mask.

Using the repulsive potential whose shape is adjusted in the local region determined in step S3 of this embodiment,
First

[Outside 14]

In the gradation of, a dot group having a distance relationship of 4 pixels in the vertical and horizontal directions is uniformly formed on the entire mask.
The number of gradations becomes high

[Outside 15]

At the gradation of, a large number of dot groups having a distance relationship of two pixels in the vertical and horizontal directions are formed. This means that a dot is struck at the midpoint between two dots having a distance relationship of 4 pixels formed in low gradation, so that a locally periodic dot arrangement occurs.

[Outside 16]

At the gradation of, the shape of the repulsive potential is adjusted so that the dots are adjacent to each other in the vertical and horizontal directions. The purpose of this is to give priority to a dot adjacent to one of the dots having a distance relationship of two pixels, and to print the dot. In the present embodiment, the tone dependency of the coefficient C (g, r) is set to be centered on 128 tones.

By locally adjusting the shape of the repulsive potential as described above, it is possible to uniformly generate a large number of dot groups having a relationship in which the distances between dots are equal to each other.
The density unevenness due to the dot group can be significantly reduced. By using such potential, 60
When an output device having a resolution of about 0 dpi or more is used, the regularity or periodicity of the dot pattern in the local area shows that the visual sensitivity to the periodicity and the dot arrangement having regularity is almost zero. The non-uniformity of the virtual image and the density of the dot group is not perceived because the inter-dot distance is set and the irregularity is moderate. As described above, according to the present embodiment, moire with high contrast, which is a problem in the systematic dither method, does not occur at all, and the generation of other various virtual images is also suppressed.

In the present embodiment, the shape and gradation dependency of the repulsive potential used in the dot pattern creation are the same in the dot pattern creation for all color components. However, in consideration of dot visibility, etc. It is possible to improve the image quality by using different repulsive potentials.

Hereinafter, a method of forming a dot pattern of the third gradation and after will be described. The dot patterns for the third and subsequent gradations for each color component are created in the same manner as described below.

In step S4, first, the repulsive force potential determined in step S3 is applied to all the dots already hit. When the repulsive potential is applied to the dot, the portion protruding from the boundary of the mask is processed using the periodic boundary condition as described above. This periodic boundary condition is also used in the following process as needed. (Above S4-1)

Next, the averaging operation of the potential sum is performed in the sections having the same dot pattern. By this operation, the potential sums of the 16 sections where the dot patterns are equal to each other are equal.

Next, the lowest point of the potential sum is searched for within the range where the regularity (3) is not broken, and one dot is added (16 in total) to the sections where the dot patterns are equal to each other. A potential is given to each of these 16 dots, and the potential sum is recalculated. (Above S4-2)

Next, in the 48 sections other than the section having the same dot pattern, the pixel having the lowest potential sum is searched for within the range not breaking the regularity (3), and the dot is added to the pixel. A potential is given around the pixel and the potential sum is recalculated. Repeat this operation and repeat
A dot pattern of the third gradation is obtained at the time when dots have been ejected one by one in all eight sections. (End of S4-
3)

Even after the fourth gradation, it is determined in the same process as S3 and S4. When the dot patterns up to the highest gradation can be determined, the mask is completed by accumulating those dot patterns. (Step S5)

By using the mask for each color component created according to this embodiment, a uniform and even dot pattern can be obtained in low gradation. Further, by arranging the sections having the same dot pattern differently for each mask, it is possible to suppress the image quality deterioration due to the interference of the periodic structures of the masks, and obtain an output image with high image quality at all gradations. be able to.

<Second Embodiment> In the present embodiment, the input color image is dark cyan (C), light cyan (pC), dark magenta (M), light magenta (pM), yellow (Y), black. (K) is decomposed into a total of 6 color components,
Gradation reproduction is performed using a plurality of masks.

As for the mask for each color component, one mask is prepared in accordance with the flowchart of FIG. 1, and the parallel movement, rotation, and vertical / horizontal inversion operations are performed to create masks for other color components. Also, C and pC, M and pM
Respectively use the same mask.

The method of making different masks by performing parallel movement, rotation, vertical / horizontal inversion operations on one mask as in this embodiment can greatly reduce the amount of calculation at the time of making masks.

A procedure for creating one of the masks having the features of this embodiment will be described with reference to the flowchart of FIG. The mask created in this way is used for the color components C and pC.

First, in step S1, the basic structure of the mask is determined. The mask in this embodiment has a size of 256 × 256.
It is a square matrix of elements and reproduces 256 gradations. The arrangement of masks when the input image is larger than the mask size is the same as that in the first embodiment.

The dot pattern of 256 × 256 pixels generated by one mask of this embodiment has the following three regularities when divided into 16 × 16 pixel sections as shown by the solid line in FIG. And

(1) The dot patterns up to the second gradation are pseudo-periodic dot patterns.

(2) The dot patterns in a plurality of sections are equal to each other in all gradations.

(3) Dots in all sections are equal in all gradations.

In the present embodiment, the group of sections having the same dot pattern according to the regularity (2) is 64 sections patched in gray in FIG.

Next, in step S2, a dot pattern near the lowest gradation is determined. In the present embodiment, the dot pattern up to the second gradation is determined in step S2 of FIG. It should be noted that in this embodiment, in this step, 25 gradations should be applied at 25 gradations.
Six pixels (dot pattern up to 254 gradations) are determined. Then, those pixels are regulated so that no dots are printed until the gradation reaches 255.

The method of forming dot patterns up to the second gradation will be described below with reference to FIG. However, for convenience of drawing, only a part of the dot pattern is displayed. The position of horizontal x pixel and vertical y pixel from the pixel at the upper left corner of the mask is (x,
It will be represented by the coordinate y). The position of the pixel in the upper left corner is (0,0).

The dot pattern of the first gradation is 125 to 13
A periodic dot pattern such as 6 is used. This dot pattern is the same as that generated by the Bayer systematic dither method. These dot positions are (16i +
1,16j + 1) (where i = 0, 1, ..., 15,
j = 0, 1, ..., 15).

Next, a method of forming the second gradation dot pattern will be described.

The dots hitting the sections having the same dot pattern do not give randomness like 137 to 140, and the dot position is (32m + 9, 32n + 9) (where m = 0, 1, ..., 7, j = 0, 1, ..., 7).

Randomness is given to dots that are individually printed in 192 sections other than the sections where the dot patterns are equal to each other. In the present embodiment, each of the four corners of the 4 × 4 pixel section indicated by the thick lines 141 to 145 is randomly selected with a probability of ¼.

As described above, the pseudo periodic second gradation dot pattern is completed.

Next, the method of determining the potential shape in step S3 will be described.

First, in step S3-1, the basic shape P (g, r) of the repulsive force potential is determined. The basic shape P (g, r) of the potential in the present embodiment is

[0163]

[Outside 17]

[0164]

[Outside 18]

It is Where r _max is 256,
a so that the potential value becomes almost 0 at r _max
Is 0.46. This is to prevent the potential applied to the dot from returning to the dot itself due to the periodic boundary condition. Alternatively, it represents the distance from the pixel to which the repulsive potential is applied.

Then, in step S3-2, the repulsive potential shape is adjusted. To adjust the shape, the coefficient C (g, r) C is added to the basic shape P (g, r) of the repulsive force potential.
(G, r) =

[Outside 19]

[0167]

[Outside 20]

[0168]

[Outside 21]

[0169]

[Outside 22]

This is done by multiplying by. The meaning of the coefficient as a function of the number of gradations g and the distance r is the same as that described for the coefficient in the first embodiment.
When the repulsive potential shape of this embodiment is used, first, a plurality of dot groups having a positional relationship of a distance of 6 pixels are formed in both vertical and horizontal directions. In this embodiment, the dot group is set so that the distance between dots is 6 pixels in a very low gradation so that the uniformity of the dot distribution in the low gradation is not deteriorated. In the next gradation range, a large number of dot groups having a positional relationship of 3 pixels, which is the middle of 6 pixels, are formed. By doing so, it becomes easier for a dot to be printed in the middle of a dot group having a positional relationship of 6 pixels in the vertical and horizontal directions, and a large number of dot groups having a positional relationship of 3 pixels in the vertical and horizontal directions can be uniformly formed. . Further, in the next gradation range, a large number of dot groups having a positional relationship of two pixels in the vertical and horizontal directions are formed. This is to prevent a locally regular dot group from being regularly formed in a wide area to form a large regular dot pattern by forming two types of dot groups having similar dot patterns in the local area. Is. (Above S3-2)

As described above, increasing the types of similar dot groups as a local dot pattern may impair the uniformity of density. However, as a preventive measure, in this embodiment, even if the directions in which dots are easily hit are the same,
The potential shape is adjusted so that dots are easily hit at positions with minute distances different from each other, and two similar but different dot groups are formed as a local dot pattern. Similarly, for example, even if it is easy to form a plurality of types of dot groups having local dot patterns in which the distances are substantially equal and the directions are slightly different, the same effect can be obtained.

Next, the method of forming the dot patterns for the third gradation and after in step S4 will be described. The dot patterns for the third gradation and thereafter are created using the repulsive potential as described above.

First, the repulsive potential whose shape is adjusted is applied to the pixels of all the dots which have already been hit. As described above, when the repulsive potential is applied to the pixel with dots, the portion of the potential protruding from the boundary of the mask is processed using the periodic boundary condition as in the first embodiment. (Above S4-1)

Next, the averaged potentials are obtained in the group of sections where the dot patterns are equal to each other, and the averaged potentials are used as a new potential sum. Next, search for the lowest point of the potential sum and hit 64 dots. Further, a potential is applied to each of these 64 dots and the potential sum is recalculated. (Above S4-2)

Next, a pixel having the lowest potential sum is searched from the remaining 192 partitions within a range not breaking the regularity (3), and a dot is added to the pixel. A potential is given around the pixel and the potential sum is recalculated. Repeat the above operation to add dots one by one and
When 92 dots have been hit, the dot pattern of the third gradation is obtained. (Above S4-3)

Even after the third gradation, S3 and S4-1 to S
Dot pattern is created in the same process as 4-3, and 254
When the gradation is created, dots are set at the positions where the dots set in S2 are not formed to form a dot pattern of 255 gradations. Finally, the mask is completed by accumulating those dot patterns (step S5).

As described above, the mask for the color components C and pC is completed. In this embodiment, the mask is translated and rotated to create a mask for other color components.

First, a method of creating a mask for the color components M and pM will be described.

First, the masks for the color components C and pC are horizontally inverted, and then vertically inverted. Further, the first gradation dot pattern of this mask is overlapped with the first gradation dot pattern of the color components C and pC by 35 in the x direction.
Translates the element by 3 elements in the y direction. In order to show what the basic structure of the mask and the dot pattern will be when these operations are performed, the basic structure of the mask and a part of the dot patterns of the first gradation and the second gradation are shown. It shows in FIG. The coordinates in the figure are relative coordinate values when the upper left corner of the color components C and pC is (0,0). In order to store this threshold in a square matrix of 256 × 256 elements with the coordinate (0,0) in the upper left corner, as shown in FIG.
As shown by the broken line in the figure, the masks are arranged in the x direction and the y direction, and a square matrix of 256 × 256 elements with the coordinates (0, 0) patched in gray in the figure as the upper left corner is formed. It is cut out and used as a mask for the color components M and pM.

The mask for the color components M and pM is completed as described above.

FIG. 23 shows the positional relationship between the masks for the color components C or pC and the masks for the color components M or pM in which the dot patterns are the same.
The section patched with a diagonal line descending to the right such as 146 to 149 is the section of the color component C or pC, and
The section patched with a diagonal line to the right such as 155 is the section of the color component M or pM. The region where the above-mentioned sections overlap between color components is a portion where the diagonal line to the right of the color component C or pC and the diagonal line to the right of the color component M or pM intersect. As shown in FIG. 23, the color component C or pC
Of the color component M or pM partially overlaps. If the sections overlap with each other between the color components, the periodic structure of the mask is emphasized, and an unpleasant virtual image is likely to be visually recognized. However, in the present embodiment, the overlap is small and the image quality is hardly affected. Further, since the mask created by the perturbed systematic dither method as shown in the flowchart of FIG. 1 hardly causes an unpleasant virtual image, the arrangement of the sections having the same dot pattern partially overlaps between the color components. Even in such a case, high image quality can be achieved.

Next, a method of creating a mask for the color component Y will be described.

First, the masks for the color components C and pC are inverted upside down. 16 elements in the x direction and 5 in the y direction so that the dot pattern of the first gradation of this mask overlaps the dot pattern of the first gradation of the color components C, pC, M and pM.
Move one element. In order to show what the basic structure of the mask and the dot pattern will be when these operations are performed, the basic structure of the mask and a part of the dot patterns of the first gradation and the second gradation are shown. It shows in FIG. The coordinates in the figure are relative coordinate values when the upper left corner of the color components C and pC is (0,0). Similar to the color component M or pM, the coordinates (0,0) are selected from the tiles arranged in this mask.
A square matrix of 256 × 256 elements having the upper left corner is cut out and used as a mask for the color component Y.

Next, a method of creating a mask for the color component K will be described.

First, the mask for the color components C and pC is rotated by 90 °. The dot pattern of the first gradation of this mask, when viewed from the dot pattern of the first gradation of the color components C, pC, M, pM and Y, was newly printed at the second gradation of the Bayer systematic dither method. 72 elements in the x direction and 91 elements in the y direction so that they are the same as the dot pattern. To show what the basic structure of the mask and the dot pattern would be if these operations were performed,
FIG. 25 shows the basic structure of this mask and a part of the dot patterns of the first gradation and the second gradation. The coordinates in the figure are relative coordinate values when the upper left corner of the color components C and pC is (0,0). Similar to the color component M or pM and Y, a 256 × 256 element square matrix with the coordinate (0,0) at the upper left corner is cut out from this mask arranged in a tile, and is used as a mask for the color component K.

In this embodiment, the color components C, pC, M,
The dot pattern of the first gradation of pM and Y is the same as the dot pattern of the first gradation of the Bayer systematic dither method,
When the dot pattern of the first gradation of the color component K is viewed from those dot patterns, it is the same as the dot pattern newly formed at the second gradation by the Bayer systematic dither method.
This is the color component C (or pC), M (or pM), Y
In order to make the combination of the composite black dot pattern and the real black dot pattern of the color component K due to the overlapping of the dots of the same color as the second gradation dot pattern of the Bayer systematic dither method, By setting the dot pattern of the first gradation of the component as described above, good image quality can be obtained with a very low gradation.

The dot pattern of the first gradation of the color component M, pM or Y is made the same as the first gradation of the color component C or pC, or the dot pattern of the first gradation of the color component K is changed to C or The moving amount of the mask when the same dot pattern is newly formed in the second gradation of the Bayer systematic dither method in terms of the first gradation of pC includes the above-described moving amount,
16 × 16 = 256 types are possible.

In the present embodiment, when a virtual image is generated on the basic mask, the position of the virtual image is made different for each color component and the visibility of the virtual image is made low, so that different movement amounts are made for each color component as described above. I am using. The same effect can be obtained by using a translation amount other than the above, and the amount needs to be optimized depending on the characteristics of the basic mask.

In this embodiment, a mask obtained by horizontally and vertically reversing the masks for the color components C and pC is used as a mask for the color components M and pM, and a mask for the color components C and pC is vertically inverted as a mask for the color component Y. As the mask for the color component K, a mask obtained by rotating the masks for the color components C and pC by 90 ° is used. This is to reduce the visibility of the virtual image by changing the position and direction of the virtual image between the color components when the virtual image is generated in the dot pattern generated by the basic mask. Further, it has an effect of weakening the correlation of the dot patterns between the color components and suppressing the generation of a virtual image. The operation of parallel movement, up / down / left / right inversion, and rotation in creating the mask of each color component is not limited to this embodiment, and other operations or other combinations of parallel movement, up / down / left / right inversion / rotation may be performed. An operation may be used, and an optimal operation may be selected as appropriate according to the structure of the mask.

Further, the present invention can be applied to a system composed of a plurality of devices such as a host computer, an interface device, a reader and a printer.
Further, it can be applied to a single device such as a copying machine or a facsimile machine.

Further, according to the present invention, a storage medium recording a program code of software for implementing the functions of the above-described embodiments is supplied to a system or apparatus, and the computer (or CPU or MP of the system or apparatus is supplied.
It is also applicable that U) reads and executes the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.

The storage medium also stores the threshold matrix created in the above-described embodiment. As a storage medium for supplying the program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a non-volatile memory card, a ROM or the like can be used. .

Further, not only the functions of the above-described embodiments are realized by executing the program code read by the computer, but also the OS (operating system) running on the computer based on the instructions of the program code. It goes without saying that this also includes the case where the above) performs a part or all of the actual processing and the processing realizes the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written in the memory provided in the function expansion board inserted into the computer or the function expansion unit connected to the computer, based on the instruction of the program code, , The CPU provided in the function expansion board or the function expansion unit performs some or all of the actual processing,
It goes without saying that the processing includes the case where the functions of the above-described embodiments are realized.

[0196]

As described in detail above, according to the present invention, the positions of the sections where the dot patterns are equal in the dot pattern generated by the threshold value matrix applied to each color component are different between the color components, or By making them partially overlap with each other, it is possible to provide a threshold matrix in which an unpleasant virtual image does not occur even in a combination of a plurality of color components, and a gradation reproduction method and apparatus using the same.

[Brief description of drawings]

FIG. 1 is a flowchart showing a procedure for creating a mask according to the present embodiment.

FIG. 2 is a diagram showing a configuration example of a basic system for processing an image according to the present embodiment.

FIG. 3 is a diagram illustrating a basic structure of a mask according to the present embodiment.

FIG. 4 is a diagram for explaining a method of creating a dot pattern of the first gradation according to the present embodiment.

FIG. 5 is a diagram for explaining a method of creating a second gradation dot pattern in the present embodiment.

FIG. 6 is a diagram schematically showing a basic shape of a repulsive force potential.

FIG. 7 is a diagram schematically showing coefficients used for changing the shape of the repulsive force potential in the present embodiment.

FIG. 8 is a diagram illustrating a periodic boundary condition of repulsive potential in the present embodiment.

FIG. 9 is a diagram showing a mask shape and a mask arranging method according to the first embodiment.

FIG. 10 is a diagram illustrating a basic structure of a cyan mask according to the first embodiment.

FIG. 11 is a diagram illustrating a basic structure of a magenta mask according to the first embodiment.

FIG. 12 is a diagram illustrating the basic structure of a yellow mask according to the first embodiment.

FIG. 13 is a diagram illustrating a basic structure of a black mask according to the first embodiment.

FIG. 14 is a diagram illustrating a positional relationship between sections in which the dot patterns of the cyan, magenta, yellow, and black masks are the same in the first embodiment.

FIG. 15 is a diagram for explaining a method of creating a dot pattern up to a second gradation of cyan in the first embodiment.

FIG. 16 is a second magenta image in the first embodiment.
It is a figure for explaining a method of creating a dot pattern up to gradation.

FIG. 17 is a second yellow image according to the first embodiment.
It is a figure for explaining a method of creating a dot pattern up to gradation.

FIG. 18 is a second black screen according to the first embodiment.
It is a figure for explaining a method of creating a dot pattern up to gradation.

FIG. 19 is a diagram showing a basic structure of a cyan mask according to the second embodiment.

FIG. 20 is a diagram for explaining a method of creating a dot pattern up to the second gradation of cyan in the second embodiment.

FIG. 21 is a diagram for explaining a method of creating a magenta mask according to the second embodiment.

FIG. 22 is a diagram for explaining a method of storing a threshold array of a magenta mask in the second embodiment.

FIG. 23 is a diagram for explaining the positional relationship of sections in which the dot patterns of the cyan mask and the magenta mask are the same in the second embodiment.

FIG. 24 is a diagram for explaining a method of forming a mask for yellow in the second embodiment.

FIG. 25 is a diagram for explaining a method of creating a black mask in the second embodiment.

[Explanation of symbols]

S1, S2, S3-1, S3-2, S4-1, S4-
2, S5 Step 1 of mask creation Image input device 2 Input image 3 Pre-processing 4 Gradation processing device 5 Mask 6 Memory 7 Comparator 8 Output device 9 Output image 10-18 Newly printed dots 19 in the second gradation -23 Frame 24 used to determine the dot position of the second gradation 24 Dots 25, 26, 27 that give repulsive potentials Virtual dots 28, 29, 30 Potentials 31-42 provided by periodic boundary conditions Cyan dots 43 to 46 printed with one gradation Cyan dots 47 to 51 printed with second gradation Frames 52 to 60 used to determine the dot position of the second gradation of cyan First floor Frames 77 to 88 used to determine the dot position of the second gradation of magenta. Yellow dots 89 to 92 printed with gradations Yellow dots 93 to 100 printed with second gradations Frames 101 to 112 used to determine dot positions of second gradations of yellow First gradation Black dots 113-116 hit by the black dots 117-124 Black dots hit by the second gradation 117-124 Frames 125-136 used for determining the dot positions of the second gradation of the black Folded cyan dots 137-140 Frames 146-149 used for deciding the dot positions of the second gray level of the cyan dots 141-145 that have been printed at the second gray level. The cyan dot patterns are the same. Sections 150 to 155 Sections having the same magenta dot pattern

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/405 B41J 3/00 B 1/52 A (72) Inventor Keiji Okinaka 3 Shimomaruko Ota-ku, Tokyo C-No. 30-2 F-term within Canon Co., Ltd. (reference) 2C262 AA02 AB07 AB11 BB03 BB06 EA04 EA12 5B057 AA11 CA01 CA08 CA12 CA16 CB01 CB07 CB12 CB16 CC01 CE13 CE16 CH07 CH08 5C077 LL19 MP08 NN09 PP33 P05 PQQ08P02 PQQ08P02 PQQ08Q02 HB03 LA31 LC04 LC05 LC11 MA04 MA11 NA05 NA06 PA02 PA03

Claims (48)

[Claims] 1. A color image is decomposed into a plurality of color components, and for at least two types of color components, each pixel of the original image and each element of the threshold matrix are made to correspond to each other in an output image. When the density of each pixel is expressed in binary or multi-valued and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, the number of dots in all the sections is In the gradation reproduction method, the dot patterns in the plurality of sections are equal to each other in all gradations, and different threshold matrices are used for the at least two types of color components. A gradation reproducing method for a color image, characterized in that a threshold matrix in which the positions of the sections having the same value are different from each other is used. 2. A method of creating each of the threshold matrices so that the dots increase while maintaining the consistency of the dot patterns at the boundaries of the sections where the dot patterns are equal to each other, and the dot patterns are equal to each other. The color according to claim 1, wherein the color is formed by using at least one of a method of creating by controlling an order of increasing dots between a partition and other partitions. Image gradation reproduction method. 3. The threshold value matrix is created based on a dot pattern formed by using a repulsive force potential whose shape is adjusted to be non-rotational at a plurality of gradations. The method for reproducing the gradation of the color image described in. 4. A repulsive force potential whose shape is adjusted to be non-rotational is adjusted so that a dot is easily struck at a pixel located at a specific position with respect to the center of the potential. The method for reproducing gradation of a color image according to item 3. 5. A repulsive force potential adjusted so that a dot is easily hit on a pixel at the specific position,
5. The gradation of a color image according to claim 4, wherein a dot is adjusted so that a pixel inside a circle whose radius is the length of one side of the section with respect to the center of the potential is easily hit. How to reproduce. 6. A color image is decomposed into a plurality of color components, and for at least two types of color components, each pixel of the original image and each element of the threshold matrix are made to correspond to each other in an output image. When the density of each pixel is expressed in binary or multi-valued and the dot pattern of the size corresponding to the threshold matrix is divided into small sections, the number of dots in all the sections is In the gradation reproduction method, the dot patterns in the plurality of sections are equal to each other in all gradations, and different threshold matrices are used for the at least two types of color components. A gradation reproducing method for a color image, characterized by using a threshold matrix in which the positions of the sections having the same value are partially overlapped with each other. 7. A method of creating each of the threshold matrices so that dots increase while maintaining consistency of dot patterns at a boundary of sections where the dot patterns are equal to each other, and the dot patterns are equal to each other. 7. The color image according to claim 6, wherein the color image is created by using at least one of a method in which the order of increasing dots is regulated between the partition and the other partition. Gradation reproduction method. 8. The threshold value matrix is created based on a dot pattern formed by using a repulsive force potential whose shape is adjusted to be non-rotational at a plurality of gradations. The method for reproducing the gradation of the color image described in. 9. The repulsive force potential whose shape is adjusted to be non-rotational is adjusted so that a dot is easily struck at a pixel located at a specific position with respect to the center of the potential. 8. The method for reproducing the gradation of a color image according to item 8. 10. A pixel in which a repulsive potential adjusted so that a dot is easily hit on the pixel at the specific position is inside a circle having a radius of one side of the partition with respect to the center of the potential. 10. The gradation reproducing method for a color image according to claim 9, wherein the dot is adjusted so as to be easily hit. 11. A color image is decomposed into a plurality of color components,
For each of the at least two types of color components, each pixel of the original image and each element of the threshold matrix are made to correspond to each other in a one-to-one manner to express the density in each pixel of the output image in a binary or multi-valued manner. When a dot pattern of a size corresponding to the threshold matrix is divided into small sections, the number of dots in all sections becomes equal at all gradations, and the dot pattern in multiple sections at all gradations. Are equal to each other, and a gradation reproduction method using different threshold matrices for the at least two types of color components, and the threshold matrix used for each of the color components is a section in which the dot patterns are equal to each other. At the boundary of, the method of creating so that the dots increase while maintaining the consistency of the dot pattern, and the dot pattern is equal to each other. The shape is adjusted to non-rotation target in at least one of the following method and the method of creating by controlling the order of increasing dots between the other section and the other sections. And a method of creating based on a dot pattern formed by using a repulsive force potential. 12. The gradation reproduction method of a color image according to claim 11, wherein threshold values matrix in which the positions of the sections where the dot patterns are equal are different from each other are used. 13. The gradation reproduction method for a color image according to claim 11, wherein a threshold matrix in which the positions of the sections having the same dot pattern partially overlap each other is used. 14. The repulsive potential whose shape is adjusted as a non-rotational object is adjusted so that a dot is easily hit on a pixel located at a specific position with respect to the center of the potential. 11. The gradation reproduction method for a color image according to item 11. 15. A repulsive potential adjusted so that a dot is easily struck at a pixel at the specific position is inside a circle having a radius of one side of the partition with respect to the center of the potential. 15. The pixel is adjusted so that dots are easily printed.
The method for reproducing the gradation of the color image described in. 16. A threshold value matrix created by performing at least one operation of parallel movement, inversion, and rotation on a threshold value matrix applied to at least one type of color component is converted to another at least one type of color component. The gradation reproduction method for a color image according to claim 1, wherein the gradation reproduction method is applied. 17. The threshold matrix applied to at least one type of color component is subjected to at least one type of operation among inversion and rotation, and further, the number of pixels is 2 pixels or more in at least one direction in two vertical and horizontal directions. The threshold matrix created by adding the corresponding translation operation to at least one other
The gradation reproduction method for a color image according to claim 16, wherein the gradation reproduction method is applied to a color component of a type. 18. The color image gradation reproduction method according to claim 1, wherein the at least two types of color components are cyan (blue) and magenta (red). . 19. A threshold matrix corresponding to cyan (blue) and magenta (red), wherein the threshold matrix is a dot pattern of the first gradation of one color component and a first gradation of the other color component. The positional relationship of the dot patterns is 1 of the Bayer type systematic dither method.
19. The positional relationship between the dot pattern at the gradation and the dot pattern newly formed at the second gradation is substantially equal to or slightly deviated from each other. The method for reproducing the gradation of the color image described in. 20. In a gradation reproduction method of a color image having three or more values including gradation, different threshold matrices for dark and light colors are applied to at least one of the at least two kinds of color components. The method according to claim 1, 6, or 11.
A method for reproducing gradation of a color image according to any one of 1. 21. In a gradation reproduction method of a color image having three or more values including shades, at least one kind of color components among at least two kinds of color components is applied to one of dark and light colors. 21. The gradation reproduction method for a color image according to claim 20, wherein the threshold matrix created is subjected to at least one operation of parallel movement, inversion, and rotation, and the created threshold matrix is applied to the other. . 22. In the gradation reproduction method of a color image having three or more values including shades, at least one kind of color components among at least two kinds of color components has the same threshold matrix for dark and light colors. It applies, The claim 1, 6, 11 characterized by the above-mentioned.
A method for reproducing gradation of a color image according to any one of 1. 23. In order to create a dot pattern of at least one type of color component, when the division is further divided into four identical subdivisions, with 4n (n is an integer) gradation, all subdivisions 12. The color image gradation reproduction method according to claim 1, wherein the number of dots is the same. 24. When the threshold matrix applied to at least one type of color component is used two-dimensionally and regularly, the direction of repetition is shifted in either the vertical or horizontal direction. Claims 1, 6, characterized in that
12. The method for reproducing gradation of a color image according to any one of 11. 25. The gradation reproducing method for a color image according to claim 1, wherein the shape of the threshold matrix applied to at least one type of color component is different from a square. 26. Decomposing a color image into a plurality of color components,
With respect to at least two types of color components, each pixel of the original image and each element of the threshold value matrix are made to correspond one-to-one for each color component, and the density in each pixel of the output image is represented by binary or multivalued, When a dot pattern of a size corresponding to the threshold matrix is divided into small sections, the number of dots in all sections becomes equal at all gradations, and the dot pattern in a plurality of sections at all gradations. Are equal to each other, and a storage unit that stores a threshold matrix for the at least two types of color components; and the density of each pixel of the original image of each color component and each pixel Comparing means for comparing with, the output means for outputting a binary or multi-valued dot pattern of each color component according to the comparison result of the comparing means, the comparing means, A gradation reproducing apparatus for a color image, wherein different threshold matrices are used for at least two types of color components, and threshold matrixes in which the positions of the sections having the same dot pattern are different from each other are used. 27. A color image is decomposed into a plurality of color components,
For each of the at least two types of color components, each pixel of the original image and each element of the threshold matrix are made to correspond to each other in a one-to-one manner to express the density in each pixel of the output image in a binary or multi-valued manner. When a dot pattern of a size corresponding to the threshold matrix is divided into small sections, the number of dots in all sections becomes equal at all gradations, and the dot pattern in a plurality of sections at all gradations. Are equal to each other, and storage means for storing a threshold matrix relating to the at least two types of color components; and a density of each pixel of the original image of each color component and each pixel Comparing means for comparing with each other, and an output means for outputting a binary or multi-valued dot pattern of each color component according to the comparison result of the comparing means, Is a different threshold matrix for the at least two types of color components, and a threshold matrix in which the positions of the sections having the same dot pattern partially overlap each other is used. . 28. A method of creating each of the threshold matrices so that dots increase while maintaining consistency of dot patterns at a boundary of sections where the dot patterns are equal to each other, and the dot patterns are equal to each other. 28. The method according to claim 26 or 27, characterized in that the method is performed by using at least one of a method in which the order of increasing dots is regulated between a section and other sections. A color image gradation reproduction device according to claim 1. 29. The threshold value matrix is created based on a dot pattern formed using a repulsive force potential whose shape is adjusted to be non-rotational at a plurality of gradations. 28. A gradation reproducing device for color images according to any one of 27. 30. Decomposing a color image into a plurality of color components,
For each of the at least two types of color components, each pixel of the original image and each element of the threshold matrix are made to correspond to each other in a one-to-one manner to express the density in each pixel of the output image in a binary or multi-valued manner. When a dot pattern of a size corresponding to the threshold matrix is divided into small sections, the number of dots in all sections becomes equal at all gradations, and the dot pattern in a plurality of sections at all gradations. Are equal to each other, and storage means for storing a threshold matrix relating to the at least two types of color components; and a density of each pixel of each pixel of the original image of each color component Comparing means for comparing with each other, and an output means for outputting a binary or multi-valued dot pattern of each color component according to the comparison result of the comparing means, The step uses different threshold matrices for the at least two types of color components, and the threshold matrix used for each of the color components ensures that the dot patterns match at the boundaries of the sections where the dot patterns are equal to each other. At least one of the method of creating so that the dots increase while taking, and the method of creating by restricting the order of increasing dots between the areas where the dot patterns are equal to each other and the other areas One of the methods and a method of creating a shape based on a dot pattern formed using a repulsive force potential that is adjusted for non-rotation target in a plurality of gradations are used to create a color image. Gradation reproduction device. 31. The gradation reproducing apparatus for a color image according to claim 30, wherein the positions of the sections where the dot patterns are equal are different from each other. 32. The gradation reproducing apparatus for a color image according to claim 30, wherein the positions of the sections having the same dot pattern partially overlap each other. 33. Decomposing a color image into a plurality of color components,
For each of the at least two types of color components, each pixel of the original image and each element of the threshold matrix are made to correspond to each other in a one-to-one manner to express the density in each pixel of the output image in a binary or multi-valued manner. When a dot pattern of a size corresponding to the threshold matrix is divided into small sections, the number of dots in all sections becomes equal at all gradations, and the dot pattern in multiple sections at all gradations. Are equal to each other and generate different dot patterns for the at least two types of color components, and the positions of the sections where the dot patterns are equal are different from each other. 34. Decomposing a color image into a plurality of color components,
With respect to at least two types of color components, each pixel of the original image and each element of the threshold value matrix are made to correspond one-to-one for each color component, and the density in each pixel of the output image is represented by binary or multivalued, When a dot pattern of a size corresponding to the threshold matrix is divided into small sections, the number of dots in all sections becomes equal at all gradations, and the dot pattern in multiple sections at all gradations. Is a threshold matrix for generating different dot patterns for the at least two types of color components, and the positions of the sections having the same dot pattern partially overlap each other. Threshold matrix. 35. A method of creating each of the threshold matrices so that dots increase while maintaining consistency of dot patterns at a boundary of sections where the dot patterns are equal to each other, and the dot patterns are equal to each other. 35. The method according to claim 33 or 34, wherein the method is performed by using at least one of a method in which the order of increasing the dots is regulated between the section and the other sections. The threshold matrix according to claim 1. 36. The plurality of threshold matrices are created based on a dot pattern formed by using a repulsive force potential whose shape is adjusted to be non-rotational in a plurality of gradations. Or 34
The threshold matrix according to any one of 1. 37. Decomposing a color image into a plurality of color components,
For each of the at least two types of color components, each pixel of the original image and each element of the threshold matrix are made to correspond to each other in a one-to-one manner to express the density in each pixel of the output image in a binary or multi-valued manner. When a dot pattern of a size corresponding to the threshold matrix is divided into small sections, the number of dots in all sections becomes equal at all gradations, and the dot pattern in multiple sections at all gradations. Are equal to each other, and are threshold matrices that generate different dot patterns for the at least two types of color components, and the threshold matrix used for each color component is At the boundary, the method of creating so that the dots increase while maintaining the consistency of the dot patterns, and the dot patterns are equal to each other. Adjusting the shape to non-rotation target in at least one of the method of creating by controlling the order of increasing dots between the areas that become And a threshold value matrix formed by using a dot pattern formed by using the generated repulsive force potential. 38. The threshold matrix according to claim 33, wherein in the threshold matrix relating to the at least two types of color components, the positions of the sections where the dot patterns are equal are different from each other. 39. The threshold value matrix according to claim 37, wherein in the threshold value matrix relating to the at least two types of color components, the positions of the sections having the same dot patterns partially overlap each other. 40. A translation, inversion, or rotation with respect to a threshold matrix applied to at least one color component,
The threshold matrix according to any one of claims 33, 34, and 37, wherein at least one type of operation is performed to create a threshold matrix for applying to at least another type of color component. 41. Decomposing a color image into a plurality of color components,
For each of the at least two types of color components, each pixel of the original image and each element of the threshold matrix are made to correspond to each other in a one-to-one manner to express the density in each pixel of the output image in a binary or multi-valued manner. When a dot pattern of a size corresponding to the threshold matrix is divided into small sections, the number of dots in all sections becomes equal at all gradations, and the dot pattern in multiple sections at all gradations. Which are equal to each other, and in which the control program for controlling the gradation reproduction processing of a color image using different threshold matrices for the at least two types of color components are stored in a computer-readable manner, A threshold matrix in which the positions of the sections with the same pattern are different from each other is used, and the value of the threshold matrix is set as the threshold value for each color component. A module for controlling the density of each pixel of the original image to be compared pixel by pixel and outputting a binary or multi-valued dot pattern of each color component according to the comparison result. Storage medium. 42. Decomposing a color image into a plurality of color components,
For each of the at least two types of color components, each pixel of the original image and each element of the threshold matrix are made to correspond to each other in a one-to-one manner to express the density in each pixel of the output image in a binary or multi-valued manner. When a dot pattern of a size corresponding to the threshold matrix is divided into small sections, the number of dots in all sections becomes equal at all gradations, and the dot pattern in multiple sections at all gradations. Which are equal to each other and which are computer-readable and store a control program for controlling a gradation reproduction process of a color image that uses different threshold matrices for the at least two types of color components. Using a threshold matrix in which the positions of the sections with the same pattern partially overlap each other, for each color component,
Control is performed so that the density of each pixel of the original image is compared with each pixel by using the value of the threshold matrix as a threshold, and a binary or multi-valued dot pattern of each color component is output according to the comparison result. A storage medium including a module for performing the operation. 43. A method of creating each of the threshold matrices so that dots increase while maintaining consistency of dot patterns at a boundary of sections where the dot patterns are equal to each other, and the dot patterns are equal to each other. 43. The method of creating by controlling at least one of the order of increasing the dots between the section and the other section, the method of creating the dot. The storage medium according to claim 1. 44. The threshold value matrix is created based on a dot pattern formed by using a repulsive force potential whose shape is adjusted to be non-rotational at a plurality of gradations. Or 42
The storage medium according to any one of 1. 45. Decomposing a color image into a plurality of color components,
For each of the at least two types of color components, each pixel of the original image and each element of the threshold matrix are made to correspond to each other in a one-to-one manner to express the density in each pixel of the output image in a binary or multi-valued manner. When a dot pattern of a size corresponding to the threshold matrix is divided into small sections, the number of dots in all sections becomes equal at all gradations, and the dot pattern in multiple sections at all gradations. Are equal to each other, and a computer-readable storage medium that stores a control program that controls the gradation reproduction processing of a color image that uses different threshold matrices for at least two types of color components. The threshold matrix used for the dot pattern consistency at the boundaries of the sections where the dot patterns are equal to each other. A method of creating so that the dots increase, and a method of creating by controlling the order of increasing the dots between the section where the dot patterns are equal to each other and the section other than that, at least one of Method and a method of creating a shape based on a dot pattern formed by using a repulsive force potential that is adjusted to a non-rotation target in a plurality of gradations, and the value of the threshold matrix for each color component. The threshold value is set as a threshold value, and the density of each pixel of the original image is compared with each pixel, and a module for controlling to output a binary or multi-valued dot pattern of each color component is included. Storage medium. 46. The storage medium according to claim 45, wherein the positions of the sections where the dot patterns are equal in the different threshold matrices are different from each other. 47. The storage medium according to claim 45, wherein the positions of the sections where the dot patterns are equal in the different threshold matrices partially overlap each other. 48. A threshold value matrix created by performing at least one operation of parallel movement, inversion, and rotation on a threshold value matrix applied to at least one color component, and using the threshold value matrix as at least one other color component. The storage medium according to any one of claims 41, 42 and 45, which is applied to the storage medium.