JP2004200746A - Image processing apparatus and image recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus and an image recording apparatus capable of obtaining high-definition copying result. <P>SOLUTION: Input image data obtained by reading an image from an original by an image input section 12 are subjected to color conversion from RGB to YMCK by an image processing section 14, the color-converted data are dithered and formed into dots for each color to be supplied to a printing section 16. In this case, a dot recognizing section 24 obtains the number of lines of dots and angles of an image represented by the input image data i.e. an input image, thereby obtaining the feature of dot periodic patterns on the input image. A halftone generating section 26 generates a halftone screen having a pattern being the same as the number of lines and the angles which are obtained i.e. the dot pattern, and the generated halftone screen is used for dithering of the input image in a halftone processing section 22. As described above, by matching the pattern of the halftone screen with the dot pattern, interference between the both can be eliminated, and the generation of moire at the time of performing printing processing in the printing section 16 can be eliminated. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing apparatus and an image recording apparatus, and in particular, arranges multi-gradation image data indicating a reading result of a document on which an image including a halftone image is recorded according to a pattern of a halftone screen. Image processing apparatus for converting into binary data representing gradation by halftone dots, which is an aggregate of a plurality of binary dots, and image input for inputting multi-gradation image data representing an image read from a document The present invention relates to an image recording apparatus comprising: a recording unit that records an image on an image recording medium.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in the field of printing, the gradation of an image is represented by a halftone dot which is an aggregate of a plurality of binary dots. When an original having such a halftone image is copied at a high resolution, the periodicity of halftone dots on the original, that is, the periodicity of halftone dots of an input image, and the It is known that moire (shaded pattern) occurs on a printed image obtained by copying due to interference with the periodicity of the halftone screen used in the above.
[0003]
In order to remove the moiré, a technique of averaging the density of an input image in a region to be halftoned (that is, in an area corresponding to a halftone cell) and then halftoning is generally used. Since the actual resolution is reduced by averaging the images, the copy result is blurred.
[0004]
For this reason, conventionally, a technique for removing moiré without performing correction such as averaging on an input image has been proposed (for example, see Patent Document 1). Specifically, when the input image is halftoned, the halftone screen is arranged while being shifted according to a predetermined regularity, so that the periodicity of the halftone screen is changed, and the periodic interference with the halftone screen of the input image is performed. Is to prevent.
[0005]
[Patent Document 1]
JP-A-6-54175
[0006]
[Problems to be solved by the invention]
However, in the prior art, since the shift of the halftone screen has regularity, the halftoning result of the input image has a periodicity according to this regularity, and the moire due to the interference with the halftone of the input image is prevented. Even if it is possible, another type of pattern may be generated, and it is not enough to guarantee a high-quality copy result.
[0007]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide an image processing apparatus and an image recording apparatus capable of obtaining a high-quality copy result.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 arranges multi-gradation image data representing a reading result of a document on which an image including a halftone image is recorded according to a pattern of a halftone screen. An image processing apparatus for converting into a binary data representing a halftone by an aggregate of a plurality of binary dots thus obtained, wherein a periodic image on the halftone image is formed based on the multi-tone image data. Extracting means for extracting a feature of the halftone pattern; generating means for generating a halftone screen having a pattern matching the halftone pattern based on an extraction result by the extracting means; Conversion means for converting the image data into the binary data according to the pattern of the halftone screen.
[0009]
According to the first aspect of the present invention, the multi-gradation image data representing the reading result obtained by reading the image from the document on which the image including the halftone image is recorded by the extracting means is provided. The feature of the periodic halftone dot pattern on the halftone image included in the image indicated by is extracted. In the generating means, a halftone screen is generated based on the extracted features so that the halftone dot pattern matches the pattern. Multi-tone image data is converted by the converting means using the generated half screen. The image data is converted to binary data in which the gradation is represented by a set of a plurality of binary dots.
[0010]
Moiré is generated when different patterns having a periodicity are combined with each other, thereby causing interference between the respective pattern characteristics. In this manner, the moiré is used when converting the multi-gradation image data into halftone dots. A halftone screen is generated such that the pattern matches a dot image included in the image represented by the multi-gradation image data, that is, a periodic dot pattern on a dot image (input image) read from a document. Thus, interference can be eliminated by making the pattern characteristics of the two coincide with each other. Therefore, it is possible to prevent the occurrence of moire when the printing process is performed according to the converted binary data. Further, the halftone result of the input image has only the periodicity of the halftone pattern originally included in the input image, and there is no concern that another type of pattern different from moire is generated unlike the related art. .
[0011]
According to a second aspect of the present invention, multi-gradation image data indicating a reading result of an original on which an image including a halftone image is recorded is converted into a plurality of binary dots arranged according to a pattern of a halftone screen. An image processing apparatus for converting into binary data representing a gradation by an aggregate of a plurality of halftone screens having different patterns from each other in advance, based on the multi-gradation image data Extracting means for extracting a characteristic of a periodic halftone dot pattern on the halftone image, based on an extraction result by the extracting means, from among the plurality of halftone screens stored in the storage means, Selecting means for selecting a halftone screen having a pattern having the shortest interference cycle with a halftone dot pattern, and the halftone screen selected by the selecting means According to the pattern, it is characterized by having a conversion means for converting the image data of the multi-tone on the binary data.
[0012]
According to the invention described in claim 2, a plurality of halftone screens having different patterns from each other are stored in the storage means in advance. The feature of the periodic halftone pattern on the halftone image included in the image represented by the multi-gradation image data is extracted by the extracting means in the same manner as in the first aspect of the present invention. A halftone screen having a pattern having the shortest interference period with the halftone dot pattern is selected from the plurality of halftone screens stored in the storage means, and the multi-tone image data is converted by the conversion means. Used for halftoning.
[0013]
In general, it is known that patterns with a long period can be distinguished by human vision, but it is known that the shorter the period, the more difficult it is to distinguish a pattern. Thus, a halftone screen that minimizes the interference period is used. By converting the multi-gradation image data into halftone dots and converting the binary data into binary data, the pattern cycle of moiré generated when printing processing is performed according to the converted binary data is shortened, so that it is possible for humans to visually recognize the pattern. Can be prevented. That is, even if microscopically, moiré occurs, it can be made invisible to humans, so that a high-quality image can be obtained. There is no need to worry about the occurrence of another type of pattern different from moire as in the prior art.
[0014]
In the above image processing apparatus, as a feature of the dot pattern, an angle between an arrangement direction of dots forming a halftone dot and a predetermined reference axis, and The number of lines representing the arrangement interval of the dots constituting the halftone dot may be obtained.
[0015]
In the above image processing apparatus, as described in claim 4, an edge enhancement process is performed on the multi-tone image data before the extraction unit extracts a feature of the halftone dot pattern. It is preferable to further have an edge emphasizing means for applying.
[0016]
If the multi-gradation image data represents a color image, the image processing apparatus may convert the color components into binary data after performing color separation for each color component.
[0017]
An image recording apparatus comprising: an image input unit for inputting multi-gradation image data representing an image read from a document; and a recording unit for recording an image on an image recording medium. The image processing apparatus according to any one of claims 1 to 4, further comprising: converting the multi-gradation image data acquired by the input unit into the binary data by the image processing apparatus. A halftone image is recorded on the image recording medium by the recording means based on the binary data later.
[0018]
According to a fifth aspect of the present invention, the image processing apparatus according to any one of the first to fourth aspects converts halftone image data representing an image read from a document into halftones to form a halftone image. Then, the recording means is driven based on the binary data, and a halftone image is recorded on the image recording medium. Copies can be made.
[0019]
If the multi-gradation image data represents a color image, the image processing device may convert the color components into binary data after separating the color components. Further, when the color system (for example, RGB) of the multi-tone image data input from the image input unit and the color system (for example, CMYK) corresponding to the recording unit are different, in the image processing apparatus, It goes without saying that the color conversion is performed by the recording means to the corresponding color system and then converted into binary data for each color.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an example of an embodiment according to the present invention will be described in detail with reference to the drawings.
[0021]
<First embodiment>
FIG. 1 shows a schematic configuration of an image recording apparatus according to the first embodiment of the present invention. An image recording apparatus 10 shown in FIG. 1 includes an image input unit 12 for inputting image data indicating a result of reading an image from a document, an image processing unit 14 for converting image data into halftone dots, and A print unit 16 for performing print processing based on the image data; and the image input unit 12 is connected to the print unit 16 via the image processing unit 14.
[0022]
Although FIG. 1 shows the image recording device 10 in which the image input unit 12, the image processing unit 14, and the printing unit 16 are collectively configured as one device, the image input unit 12, the image processing unit 14, Alternatively, the printing unit 16 may be configured as a physically different device, and connected via a predetermined cable or network.
[0023]
The image input unit 12 functions as an image input unit of the present invention, reads an image from a document at high resolution, acquires image data indicating a multi-tone image of color, and inputs the image data to the image processing unit 14. is there. In the present embodiment, the image input unit 12 reads an image of a document using a CCD sensor, and expresses the color of each pixel of the read image by each color component of R (red), G (green), and B (blue). Uses a scanner device that acquires image data (referred to as “RGB image data”) in which the density of each color of RGB is represented by 256 gradations of 8 bits each. The image input unit 12 reads the image data from a recording medium (eg, CD-ROM, FD, etc.) on which the RGB image data obtained by such a scanner device is electronically recorded, or via a network. , May receive the image data.
[0024]
RGB image data indicating the reading result (input image) of the original by the image input unit 12 is input to the image processing unit 14.
[0025]
The image processing unit 14 has a function as an image processing apparatus of the present invention, and performs processing on input image data, which is RGB image data, for each color of C (cyan), M (magenta), Y (yellow), K (black) by image processing. And supplies it to the printing unit 16. For this purpose, the image processing unit 14 includes a halftone storage memory 20 for storing data (hereinafter, referred to as a “halftone screen”) 18 indicating a pattern of a halftone screen, and a conversion unit for converting image data into halftone dots. RGB image data (input image data) indicating the result of reading the original by the image input unit 12 is input to the halftone processing unit 22.
[0026]
The halftone processing unit 22 expresses the RGB input image data indicating the result of reading the document by expressing the color of each pixel with each color component of CMYK. Specifically, the density of each color of CMYK is represented by 256 gradations of 8 bits each. The image data is converted into represented image data (referred to as "CMYK image data"), and the gradation of each color is converted into binary data represented by a set of a predetermined number of binary dots called halftone cells. A so-called dithering process is performed to generate binary image data (so-called halftone dot data). Note that the halftone processing unit 22 may perform the dithering process after performing the density correction according to the image output characteristics of the printing unit 16.
[0027]
The halftone processing unit 22 is also connected to the halftone storage memory 20. The halftone storage memory 20 stores a halftone screen 18 for each color of CMYK, and the halftone processing unit 22 uses the halftone screen 18 of the corresponding color for each of the CMYK image data. Dithering. In FIG. 1, the halftone screen 18 for each color of CMYK is shown with an alphabet indicating the color corresponding to the end of the code.
[0028]
The dithering processing result, which is binary image data for each color of CMYK, generated by the halftone processing unit 22 is supplied from the image processing unit 14 to the printing unit 16.
[0029]
The printing unit 16 functions as a recording unit of the present invention, and prints an image based on input image data on an image forming medium such as paper using an image forming material such as toner or ink. For example, when toner is used as an image forming material, the printing unit 16 turns ON / OFF an exposure head that exposes a uniformly charged photosensitive material based on input binary image data for each of CMYK colors. The latent image is formed by driving it OFF, and a toner of a color corresponding to the formed latent image is supplied and developed to form a single color toner image. Then, printing is performed by transferring the toner images formed for each of CMYK colors onto a sheet in a superimposed manner.
[0030]
It is to be noted that a so-called area gradation method in which gradation is controlled by a ratio occupied by dot data having a value of 1 in a halftone cell, that is, an area of a portion where an image forming material (toner or ink) is adhered per unit area However, a so-called density gradation method for controlling the application amount (exposure amount in the case of toner and ejection amount in the case of ink) may be combined. By controlling the gradation by the printing unit 16 and printing by a combination of the area gradation method and the density gradation method, it is possible to form a multi-gradation and high-quality image.
[0031]
As described above, in the image recording apparatus 10, the input image data obtained by reading the image from the original by the image input unit 12 is transmitted to the printing unit 16 via the halftone processing unit 22, and the printing unit 16 outputs the CMYK colors. By printing an image based on the input image data on an image recording medium such as paper using the image recording material described above, the image recorded on the document can be copied in color. Note that the image recording apparatus 10 may copy the image of the original in a single color such as black and white.
[0032]
In the first embodiment, the image processing unit 14 also includes a halftone dot recognition unit 24 as an extraction unit and a halftone generation unit 26 as a generation unit. The image processing unit 14 is connected so that RGB image data (input image data) indicating the result of reading the original by the image input unit 12 can also be input to the halftone dot recognition unit 24.
[0033]
The halftone dot recognizing unit 24 determines an input image from input image data, that is, a halftone dot on an image read from a document by the image input unit 12, and extracts a feature of the halftone dot pattern. Specifically, as shown in FIG. 2, the halftone dot recognition unit 24 includes a first line buffer 30, an edge emphasis unit 32, a color conversion / color separation processing unit 34, a second line buffer 36, and a halftone frequency analysis. A portion 38 is provided.
[0034]
The edge enhancement unit 32 is connected to the first line buffer 30 so as to be accessible. The first line buffer 30 is a memory for storing image data for n lines, and in the present embodiment, the input image data (RGB) acquired by the image input unit 12 for n lines in order from the head of the image. Image data). Since increasing the number of lines (n) stored in the first line buffer 30 is disadvantageous in terms of cost, it is preferable that the number of lines sufficient for extracting the characteristic of the halftone dot pattern is about 50 lines.
[0035]
The edge emphasizing unit 32 sharpens the image data stored in the first line buffer 30 to emphasize the edges of the image. This makes it possible to clarify each halftone dot on the image represented by the image data. The edge enhancement unit 32 is also connected to a color conversion / color separation processing unit 34, and outputs the image data after edge enhancement to the color conversion / color separation processing unit 34.
[0036]
The color conversion / color separation processing unit 34 converts the input edge-enhanced image data from RGB to CMYK image data and divides the image data for each CMYK color component. The color conversion / separation processing unit 34 is connected to the second line buffer 36 so as to be accessible.
[0037]
The second line buffer 36 is provided for each color of CMYK, and the color conversion / color separation processing unit 34 stores the divided image data for each color component of CMYK in the corresponding line buffer. ing. In FIG. 2, the second line buffer 36 for each color of CMYK is shown with an alphabet indicating the color corresponding to the end of the code. The second line buffer 36 is also connected to a dot frequency analysis unit 38.
[0038]
The dot frequency analysis unit 38 reads out and analyzes the image data stored in the second line buffer 36 for each of the CMYK color components and analyzes the image data as a feature of the dot pattern on the image represented by the image data of the color component. , The number of lines and the angle of a halftone dot are extracted, and halftone dot information 40 indicating the result is generated. Here, the number of lines means the number of halftone dots arranged in a unit length (for example, 1 inch), and the angle means the direction in which the halftone dots are arranged (arrangement direction) and a predetermined reference. It indicates the angle formed by the axis (vertical axis or horizontal axis of the image). Further, in FIG. 2, the dot information 40 for each color of CMYK is indicated by adding an alphabet indicating the color corresponding to the end of the code.
[0039]
More specifically, as shown in FIG. 3, the halftone dot frequency analysis unit 38 obtains the number of lines from the arrangement interval L of each halftone dot (dot) 50 on the image represented by the image data, and determines the arrangement direction of each dot 50. And the angle θ between the axis and the reference axis X are determined. Such an arrangement interval L and an angle θ can be easily obtained, for example, by converting image data into a frequency space by FFT (Fourier transform) processing. The dot frequency analysis unit 38 generates such dot information 40 for each color of CMYK, and the dot recognition unit 24 outputs the dot information 40 for each color generated by the dot frequency analysis unit 38. It has become.
[0040]
As shown in FIG. 1, the halftone generation unit 26 is connected to the halftone generation unit 26, and the halftone information 40 for each color output from the halftone generation unit 24 is generated by the halftone generation unit 26. Is done. The halftone generation unit 26 generates a halftone screen with the same number of lines and the same angle as the number of lines and the angle indicated by the input halftone dot information 40 for each color of CMYK. The halftone generation unit 26 is connected to the halftone storage memory 20, and the halftone storage memory 20 stores the halftone screen for each of the CMYK colors generated by the halftone generation unit 26. That is, in the halftone processing unit 22 described above, the input image data acquired by the image input unit 12 is dithered with the same number of lines and the same angle as the image indicated by the input image data, and is converted into a halftone dot. .
[0041]
Next, the operation of the first embodiment will be described. In the image recording apparatus 10 according to the first embodiment, when a copy of a document is instructed by operating a user interface (not shown), the document is read by the image input unit 12 and RGB indicating the result of image reading from the document. Are obtained as input image data. Then, the image processing unit 14 executes the processing shown in FIG. 4 in order to convert the input image data into halftone dots for each of CMYK colors.
[0042]
That is, in the image processing unit 14, as shown in FIG. 4, first, in step 100, the halftone dot recognizing unit 24 fetches the input image data of N lines into the first line buffer 30, and in the next step 102, The input image data fetched into the first line buffer 30 is subjected to sharpness processing by the edge enhancing unit 32, and the edge of the image (input image) indicated by the input image data is enhanced. By emphasizing the edges in this manner, the dots of the halftone dots on the input image become clear, and the analysis in step 108 described later, that is, the number of lines and the angle of the halftone dots can be easily obtained.
[0043]
Subsequently, in step 104, the input image data after edge enhancement is color-converted from RGB to CMYK by the color conversion / color separation processing unit 34, and in step 106, the input image data is divided for each color of CMYK, and The data is stored in the corresponding second line buffer 36.
[0044]
In the next step 108, the halftone frequency analysis unit 38 analyzes the image data of each color of CMYK in the second line buffer 36, and for each color, the number of lines of the halftone dot on the image indicated by the image data. And an angle are obtained, and dot information 40 is generated.
[0045]
Here, for example, when the input image data for N lines taken into the first line buffer is a so-called solid image having a uniform dark color, the number of halftone dots and Sometimes the angle cannot be determined. As described above, when the number of lines and the angle of the halftone dot cannot be obtained, the analysis is failed and the process proceeds from the next step 110 to step 112, where the input image for the next N lines is stored in the first line buffer 30. The data is fetched, the process returns to step 102, and the same processing is repeated to determine the number of lines and angles of the halftone dots from the input image data for the next N lines. In other words, when the analysis fails, the halftone dot is analyzed by shifting the input image data by N lines until the number of lines and the angle of the halftone dot are obtained.
[0046]
When the halftone frequency analysis unit 38 calculates the halftone frequency and angle of each halftone dot for each color of CMYK to generate halftone dot information 40, the analysis is successful and the process proceeds from the next step 110 to step 114. In step 114, the halftone screen 18 is generated for each color of CMYK based on the dot information 40 of the color so as to have the same number of lines and the same angle as the analysis result of the dot. The halftone screen 18 is stored in a halftone storage memory 20.
[0047]
Finally, in step 116, the halftone processing unit 22 converts the input image data from RGB to CMYK, reads the halftone screen 18 of the corresponding color from the halftone storage memory 20 as appropriate, and uses A ring process is performed to generate image data of each of the CMYK halftone dots, and the process of the image processing unit 14 in FIG. 4 is ended.
[0048]
The binary image data for each color of CMYK, which indicates the dithering processing result generated by the image processing unit 14 in this manner, is supplied to the printing unit 16, and the printing unit 16 performs the processing based on the binary image data. When driven, an image based on the input image data is printed on the image recording medium. As a result, a result of copying the image recorded on the document in color can be obtained.
[0049]
To summarize the above, in the first embodiment, the periodicity of the halftone screen of the input image and the periodicity of the halftone screen used when converting the input image to halftone for printing are determined by the number of lines and the angle. Paying attention to this, input image data obtained by reading an image from a document by the image input unit 12 is color-converted from RGB to YMCK by the image processing unit 14, and is dithered and halftone-dotted for each color. When supplying the data to the printing unit 16, the dot recognition unit 24 (more specifically, the dot frequency analysis unit 38) obtains the number of lines and the angle of the halftone dots of the input image, thereby obtaining the periodicity on the input image. The feature of the halftone dot pattern is extracted. Then, the halftone generation unit 26 generates a halftone screen having a pattern identical to the determined number of lines and angles, that is, a pattern that matches the halftone pattern, and uses the halftone screen for dithering the input image in the halftone processing unit 22. It has become.
[0050]
Moiré appears when patterns having different periodicities are synthesized, and their pattern characteristics interfere with each other. In this manner, the halftone screen pattern is changed to a halftone screen pattern with the same number of lines and angles. , The periodicity of the halftone screen can be made to match the periodicity of the halftone dots of the input image. That is, since the pattern characteristics of the two that have the possibility of interference are matched, the interference can be eliminated, and the occurrence of moire at the time of printing processing in the printing unit 16 can be prevented. Further, since there is no occurrence of another periodicity as in the related art, there is no fear that another type of pattern different from moire is generated. Therefore, in the first embodiment, moiré and another type of pattern different from moiré can be prevented from being generated, so that a high-quality copy result can be obtained.
[0051]
<Second embodiment>
Next, an image recording apparatus according to a second embodiment of the present invention will be described. FIG. 5 shows a schematic configuration of an image recording apparatus 10 according to the second embodiment. In FIG. 5, the same members as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0052]
As shown in FIG. 5, in the image recording apparatus 10 according to the second embodiment, a plurality of types of halftone screens 18 are stored in advance as storage means instead of the halftone storage memory 20 and the halftone generation unit 26. The first embodiment differs from the first embodiment in that the image processing unit 14 is configured to include the halftone storage memory 60 thus selected and a halftone selection unit 62 that is accessible to the halftone storage memory 60 as selection means. .
[0053]
The halftone selecting unit 62 is connected to the halftone dot recognizing unit 24, and receives the halftone dot information 40 for each color of CMYK generated by the halftone dot recognizing unit 24. The halftone selection unit 62 calculates the interference frequency between the halftone pattern indicated by the halftone dot information 40 and the halftone screen 18 stored in the halftone storage memory 60 for each color of CMYK, and stores the halftone. The halftone screen 18 having the shortest interference frequency is selected from the memory 60 and supplied to the halftone processing unit 22. The halftone processing unit 22 uses the halftone screen 18 supplied from the halftone selection unit 62 to dither the input image data of the corresponding color.
[0054]
The image processing unit 14 configured as described above performs the processing shown in FIG. In FIG. 6, the same processes as those in FIG. 4 are denoted by the same step numbers, and detailed description thereof will be omitted below.
[0055]
That is, in the second embodiment, as shown in FIG. 6, the image processing unit 14 succeeds in the analysis by the halftone frequency analysis unit 38 in step 108, and determines the number of halftone dots of each color of CMYK. When the halftone dot information 40 is generated by calculating the angle and the angle, the process proceeds from the next step 110 to step 120. In step 120, the halftone selector 62 determines, for each of the CMYK colors, the interference frequency with the halftone dot indicated by the halftone information 40 of each color for all the halftone screens 18 stored in the halftone storage memory 60. Ask for. Subsequently, in step 122, the halftone screen 18 having the shortest interference frequency is selected for each color of CMYK and supplied to the halftone processing unit 22.
[0056]
Finally, in step 124, the input image data is dithered by the halftone processing unit 22 using the halftone screen 18 supplied from the halftone selection unit 62 in this manner, and for each color of CMYK, The halftone image data is generated, and the processing of the image processing unit 14 in FIG. 6 ends.
[0057]
To summarize the above, in the second embodiment, it is possible to discriminate a pattern having a long cycle with human vision, but it is more difficult to discriminate the pattern as the cycle becomes shorter. More specifically, when the halftone frequency and the angle of the halftone dots of the input image are calculated by the halftone frequency analysis unit 38) to extract the characteristics of the halftone dot pattern, the halftone screen 18 is prepared from the plurality of halftone screens 18 prepared in advance. A halftone screen having the shortest interference frequency with the halftone pattern of the input image is selected and used for dithering the input image.
[0058]
By using the halftone screen having the shortest interference frequency as described above, the moiré pattern cycle can be shortened, and can be prevented from being visually recognized by humans. Even if microscopically, moiré is generated, if the moiré is invisible, a high-quality image is obtained for the user. Further, since there is no occurrence of another periodicity as in the related art, there is no fear that another type of pattern different from moire is generated. Therefore, in the second embodiment, it is possible to prevent the moire from being visually recognized and to prevent the occurrence of another type of pattern different from the moire, thereby obtaining a high-quality copy result.
[0059]
【The invention's effect】
As described above, the present invention has an excellent effect that a high-quality copy result can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a schematic configuration of an image recording apparatus according to a first embodiment.
FIG. 2 is a block diagram illustrating a detailed configuration of a halftone dot recognition unit used in the image recording apparatus of FIG.
FIG. 3 is a diagram for explaining the number of lines and the angle of a halftone dot;
FIG. 4 is a flowchart illustrating a process executed by an image processing unit according to the first embodiment.
FIG. 5 is a block diagram illustrating a schematic configuration of an image recording apparatus according to a second embodiment.
FIG. 6 is a flowchart illustrating processing executed by an image processing unit according to the second embodiment.
[Explanation of symbols]
10 Image recording device
12 Image input unit
14 Image processing unit
16 printing section
18 Halftone screen
20 Halftone storage memory
22 Halftone processing section
24 Halftone dot recognition unit
26 Halftone generator
32 Edge enhancement section
34 Color Conversion / Separation Processing Unit
38 Halftone frequency analysis unit
40 dot information
60 Halftone storage memory
62 Halftone selection section

Claims (5)

Multi-gradation image data indicating the reading result of a document on which an image including a halftone image is recorded is represented by a set of a plurality of binary dots arranged according to a pattern of a halftone screen. An image processing device for converting into value data,
Extracting means for extracting a characteristic of a periodic halftone dot pattern on the halftone image based on the multi-tone image data;
Generating means for generating a halftone screen having a pattern that matches the halftone dot pattern based on the extraction result by the extracting means;
Conversion means for converting the multi-tone image data into the binary data according to the halftone screen pattern generated by the halftone generation means;
An image processing apparatus comprising: Multi-gradation image data indicating the reading result of a document on which an image including a halftone image is recorded is represented by a set of a plurality of binary dots arranged according to a pattern of a halftone screen. An image processing device for converting into value data,
A storage means in which a plurality of halftone screens having different patterns from each other are stored in advance,
Extracting means for extracting a characteristic of a periodic halftone dot pattern on the halftone image based on the multi-tone image data;
Selecting means for selecting a halftone screen of a pattern having the shortest interference cycle with the halftone dot pattern from among the plurality of halftone screens stored in the storage means, based on an extraction result by the extracting means; ,
Conversion means for converting the multi-tone image data into the binary data according to the pattern of the halftone screen selected by the selection means;
An image processing apparatus comprising: The feature of the halftone dot pattern is an angle formed by the arrangement direction of the dots forming the halftone dot and a predetermined reference axis, and the number of lines representing the arrangement interval of the dots forming the halftone dot in the arrangement direction. The image processing apparatus according to claim 1, wherein: 4. The image processing apparatus according to claim 1, further comprising an edge emphasis unit that performs an edge emphasis process on the multi-tone image data before the extraction unit extracts a feature of the halftone dot pattern. The image processing device according to claim 1. An image recording apparatus comprising: image input means for inputting multi-gradation image data representing an image read from a document; and recording means for recording an image on an image recording medium.
An image processing device according to any one of claims 1 to 4 is provided,
The multi-gradation image data obtained by the input means is converted into the binary data by the image processing device, and a halftone image is recorded on the image recording medium by the recording means based on the converted binary data. Record,
An image recording apparatus, comprising:

Images