JP2007195108A - Method and device for eliminating reduced moire, and printed matter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for eliminating reduced moire by which the reduced moire is sufficiently eliminated, and a printed matter. <P>SOLUTION: An image is acquired as binary data with first resolution with respect to image data of an image including periodic patterns such as halftone dots and line pattern, the binary data is converted into continuous tone data (primary gray data), continuous tone data with second resolution is acquired by reducing size of pixels of the continuous tone data, continuous tone data (secondary gray data) with third resolution is acquired by reducing the number of pixels of the continuous tone data with the second resolution and the continuous tone data with the third resolution is converted into binary data with fourth resolution by FM screening. Thus, since a contour part of the halftone dots or the line pattern corresponding to the secondary gray data becomes fine irregular points, the reduced moire is eliminated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a reduced moire removal method, a reduced moire removal apparatus, and a printed matter.

  For example, when a comic is converted into a comic (printing a comic book), the image data of the magazine (for example, an original image of B5 size) is read by a scanner, and the read image data is reduced to a comic size (for example, B6 size) by software. In many cases, the reduced data is used and printed on a sheet by an output device (for example, a printing device). This is to avoid rescanning each time the original image is reused.

  To create this kind of comic book, a cartoonist first draws an original image (line diagram) that includes characters and backgrounds on a Kent paper with a pen. 9 and a portion of the background that has a different color from the background, cut off a commercially available screen tone consisting of many halftone dots as shown in Fig. 9 with a cutter, etc., and paste it directly on the original image. Has been done. The original image created in this way is sent to the printing process. When such an original picture is printed in black and white, the screen tone portion appears gray to human eyes, so that a realistic picture or a powerful picture can be obtained compared to a picture in which the character's shadow and background are only line drawings.

FIG. 9 is an enlarged view showing an example of a screen tone, and FIG. 10 is an enlarged view including a moire generated when the screen tone shown in FIG. 9 is reduced.
When the original image on which this screen tone is cut and pasted is read out by a scanner and then reduced, the problem is distortion such as horizontal and vertical grids as shown by lines 1001-1001 to 1011-1011 in FIG. That is, a reduction moire (an unexpectedly generated geometric pattern) is generated.

A regular periodic pattern (distortion) generated when image data including a periodic pattern is reduced is recognized as moiré by human eyes.
When a comic document is scanned for a magazine by a scanner, binary image data is created in accordance with the resolution (primary resolution) of the output machine (printing machine). For this reason, the pixel of the image data and the pixel of the output device match and are output (printed) without any problem.

On the other hand, when a comic is created by diverting data of the magazine (magazine), it is necessary to reduce the comic size (generally, it is reduced to 80 to 50%).
As described above, when the image data (eg, 1200 dpi, 2 gradation data) is reduced to 70.8%, the resolution of the image data (in this case, 1694.9 dpi, 2 gradation data) and the resolution of the output device ( In this case, 2400 dpi) does not match. As described above, if the resolution of the image data and the resolution of the output device do not match, printing cannot be performed. Therefore, it is necessary to change the number of pixels of the image data to match the resolution. Since the image data of comics is data of two gradations of black or white, if the number of pixels is changed, in the pixel matrix where black and white are adjacent, black or white may be placed on the boundary of the changed pixel matrix. Not a density level (gray) may occur. This is forcibly expressed in two gradations of black or white with a predetermined threshold. At this time, moire may occur, and there is no method for reliably predicting and confirming this moire before output (the cause of moire is that halftone dots are arranged at a constant pitch, This may or may not occur depending on the dot arrangement angle, the dot pitch, and the dot size (the same moiré occurs because the spacing is constant in the case of lines).

By the way, in order to express halftone in black or white, it is necessary to generate two gradation data from continuous gradation data. Screening is an indispensable technique for generating two gradation data from continuous gradation data.
Examples of this type of screening include AM screening and FM screening.
AM screening is an abbreviation for Amplitude Modulation Screening, and is a method of expressing the shade of an image with the size of halftone dots. The advantage of AM screening is that it can reproduce a uniform and beautiful flat net without any graininess, resulting in a natural finish. In addition, AM screening makes it easy to predict the color tone when printed, but the disadvantage is that screen angles exist, so moire occurs as interference, avoiding the Rosetta pattern seen in four-color printing. I can't. This rosette pattern becomes smaller as the number of lines is increased. From around 200 lines, the size is invisible to the naked eye.
However, if the number of lines is increased too much, the highlight dots will fly out and the shadow will be completely black. This is because the halftone dots are too small to be suitable for printing.

  On the other hand, FM screening is an abbreviation for Frequency Modulatin Screening, and is a method of expressing shades of color by changing the density of halftone dots. The FM screening is characterized in that each halftone dot is all the same size and very small. The halftone dots are arranged at irregular positions, and the gradation is expressed by the density. In the case of FM screening, since there is no screen angle, there is no generation of moire or rosette.

  However, a “gritty graininess” is inevitably generated in the flat net, particularly in the intermediate net. This is because, as a result of irregularly arranging small halftone dots, there are simultaneously “contact points” and “non-contact points” between adjacent halftone dots, which are visible as “roughness”. . By devising the algorithm for calculating the dot arrangement, the “roughness” can be reduced to some extent, but it cannot be completely eliminated. Another disadvantage of FM screening is that it is difficult to predict the color tone of the final printed product. This is because each halftone dot is very small and is susceptible to slight environmental changes during plate creation and printing.

On the other hand, as a method for removing moire, a binary image signal having a first resolution is received, and then received using a model (function) resembling the actual shape of a print spot generated by a printer. Electronically simulating the printing process for a binary image signal, generating a high resolution gray image signal from the binary image signal, filtering the high resolution gray image signal, and applying the filtered gray image signal to a certain frequency There is known a method of generating a gray image signal having a second resolution by re-sampling and converting the gray image signal into a binary image signal by an error diffusion method. (For example, see Patent Document 1)
Japanese Patent Laid-Open No. 7-193703

However, the above-described conventional technique has a problem that electronic simulation is required, the system becomes complicated, and it takes time and cost.
SUMMARY OF THE INVENTION An object of the present invention is to provide a simple reduced moire removal method, reduced moire removal device, and printed matter that can sufficiently remove reduced moire.

  In order to solve the above-mentioned problem, the invention according to claim 1 is a reduced moire removal method for removing reduced moire generated when an image including a periodic pattern is reduced. And acquiring the second resolution continuous tone data by converting the two tone data into continuous tone data and reducing the pixel size of the continuous tone data. The third resolution continuous tone data is acquired by reducing the number of pixels of the continuous tone data, and the third resolution continuous tone data is converted to the second resolution two tone data by FM screening. Features.

  According to a second aspect of the present invention, in the reduced moire removal method for removing reduced moire generated when an image including a periodic pattern is reduced, the image is acquired as two-gradation data at a first resolution, and the 2 The second resolution two-gradation data is acquired by reducing the pixel size of the gradation data, the two-gradation data is converted into continuous gradation data, and the second resolution continuous gradation data pixels The third resolution continuous tone data is obtained by decreasing the number, and the third resolution continuous tone data is converted into the second resolution two tone data by FM screening.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the third resolution is 1 / 2n (n is a natural number) of the fourth resolution.

  According to a fourth aspect of the present invention, there is provided a reduced moire removal apparatus for removing reduced moire generated when an image including a periodic pattern is reduced. Image data acquisition for acquiring the image as two-gradation data at a first resolution. Means, conversion means for converting the two-gradation data into continuous gradation data, reduction means for reducing the pixel size of the continuous gradation data to obtain continuous gradation data of the second resolution, and third Reduction means for reducing the number of pixels of the second resolution continuous tone data in order to obtain resolution continuous tone data, and converting the third resolution continuous tone data into second resolution two tone data And FM screening means.

  According to a fifth aspect of the present invention, there is provided a reduction moire removal apparatus for removing reduction moire generated when an image including a periodic pattern is reduced. Image data acquisition for acquiring the image as two-gradation data at a first resolution. Means, reduction means for reducing the pixel size of the two gradation data to obtain two gradation data of the second resolution, conversion means for converting the two gradation data into continuous gradation data, Reduction means for reducing the number of pixels of the second resolution continuous tone data to obtain three resolution continuous tone data, and conversion of the third resolution continuous tone data into fourth resolution two tone data And FM screening means.

  The invention according to claim 6 is the invention according to claim 4 or 5, characterized in that the third resolution is 1 / 2n of the fourth resolution (n is a natural number).

  According to a seventh aspect of the present invention, in a printed matter printed by removing moire generated when an image including a periodic pattern is reduced, the image is acquired as two-gradation data at a first resolution, and the second floor is obtained. The tone data is converted to continuous tone data, and the continuous resolution data of the second resolution is obtained by reducing the size of the pixels of the continuous tone data, and the number of pixels of the continuous tone data of the second resolution is obtained. The third resolution continuous tone data is acquired by decreasing the number, and an image obtained by converting the third resolution continuous tone data into the second resolution two tone data by FM screening is printed.

  According to an eighth aspect of the present invention, in a printed matter printed by removing reduction moire generated when an image including a periodic pattern is reduced, the image is acquired as two-gradation data at a first resolution. The second resolution two-gradation data is acquired by reducing the pixel size of the gradation data, the two-gradation data is converted into continuous gradation data, and the second resolution continuous gradation data pixels The third resolution continuous tone data is obtained by reducing the number, and the image obtained by converting the third resolution continuous tone data into the second resolution two tone data by FM screening is printed. To do.

  The invention according to claim 9 is the invention according to claim 7 or 8, wherein the third resolution is 1 / n (n is a natural number) of the fourth resolution.

  According to the present invention, an image is acquired as two-gradation data at the first resolution with respect to image data of an image including a periodic pattern such as a halftone dot or a line, and the two-gradation data is converted into continuous gradation data ( Primary gray data), the continuous resolution data of the second resolution is obtained by reducing the pixel size of the continuous gradation data, and the number of pixels of the continuous gradation data of the second resolution is reduced. The third resolution continuous tone data (secondary gray data) is acquired, and the third resolution continuous tone data is converted to the fourth resolution two tone data by FM screening. As a result, the halftone dots corresponding to the secondary gray data or the contours of the lines become minute irregular points, so that the reduction moire can be removed.

  One embodiment of the reduced moiré removal method according to the present invention (Claim 1) is a reduced moiré removal method for removing reduced moiré generated when an image including a periodic pattern is reduced. 2 gradation data is obtained, 2 gradation data is converted into continuous gradation data (primary gray data), and the continuous resolution data of the second resolution is reduced by reducing the pixel size of the continuous gradation data. The third resolution continuous tone data (secondary gray data) is acquired by reducing the number of pixels of the second resolution continuous tone data, and the third resolution continuous tone data is obtained by FM screening. It is characterized by being converted into four-resolution two-gradation data.

  According to the above configuration, the second resolution is obtained by acquiring an image as two gradation data at the first resolution, converting the two gradation data into continuous gradation data, and reducing the pixel size of the continuous gradation data. Continuous tone data is obtained, the second resolution continuous tone data is reduced to obtain the third resolution continuous tone data, and the third resolution continuous tone data is obtained by FM screening. By converting to four-resolution two-gradation data, the halftone dots or line contours corresponding to the secondary gray data become minute irregular points, so that reduced moire can be removed.

  Another embodiment (Claim 2) of the reduced moire removal method according to the present invention is a reduced moire removal method for removing reduced moire generated when an image including a periodic pattern is reduced. Is obtained as two gradation data, the two gradation data of the second resolution is obtained by reducing the pixel size of the two gradation data, the two gradation data is converted into continuous gradation data, The third resolution continuous tone data is obtained by reducing the number of pixels of the resolution continuous tone data, and the third resolution continuous tone data is converted into the second resolution two tone data by FM screening. It is characterized by.

  According to the above configuration, the image is acquired as the two gradation data at the first resolution, the two gradation data of the second resolution is acquired by reducing the size of the pixel of the two gradation data, and the two gradation data is obtained. The third resolution continuous tone data is obtained by converting into continuous tone data and reducing the number of pixels of the second resolution continuous tone data, and the third resolution continuous tone data is obtained by FM screening. By converting to four-resolution two-gradation data, the halftone dots or line contours corresponding to the secondary gray data become minute irregular points, so that reduced moire can be removed.

  In another embodiment (Claim 3) of the reduced moire removal method according to the present invention, in addition to the above configuration, it is preferable that the third resolution is 1 / n of the fourth resolution (n is a natural number).

  According to the above configuration, the error at the time of conversion from the third resolution to the fourth resolution is reduced by setting the third resolution to 1 / n 2n (n is a natural number) of the fourth resolution, that is, an even number. Therefore, the reduction moire can be removed more effectively.

  An embodiment of a reduction moiré removal apparatus according to the present invention (Claim 4) is a reduction moiré removal apparatus for removing reduction moiré generated when an image including a periodic pattern is reduced. Image data acquisition means for acquiring image data as two gradation data, conversion means for converting the two gradation data into continuous gradation data, and pixels of the continuous gradation data to obtain continuous gradation data of the second resolution. Reduction means for reducing the size, reduction means for reducing the number of pixels of the continuous gradation data of the second resolution to obtain the continuous gradation data of the third resolution, and the continuous gradation data of the third resolution for the fourth resolution And FM screening means for converting the data into two gradation data.

  Reduction means, reduction means, conversion means, image data acquisition means, and FM screening means are built in, for example, ROM (Read Only Memory) or RAM (Random Access Memory) and executed by a microcomputer. Software.

  According to the above configuration, the image data acquisition means for acquiring the image at the first resolution as the two gradation data, the conversion means for converting the two gradation data into the continuous gradation data, and the continuous gradation data at the second resolution. Reducing means for reducing the pixel size of the continuous tone data to obtain the second resolution, reducing means for reducing the number of pixels of the continuous tone data of the second resolution to obtain the continuous tone data of the third resolution, By providing FM screening means for converting three-resolution continuous tone data into fourth-resolution two-tone data, the halftone dots corresponding to the secondary gray data or the irregular outlines of the lines are fine. Therefore, the reduction moire can be removed.

  Another embodiment (Claim 5) of the reduction moiré removal apparatus according to the present invention is an image at a first resolution in a reduction moiré removal apparatus that removes reduction moiré generated when an image including a periodic pattern is reduced. Image data acquisition means for acquiring image data as two gradation data, reduction means for reducing the pixel size of the two gradation data to obtain two gradation data of the second resolution, and continuous gradation of two gradation data. Conversion means for converting to data, reduction means for reducing the number of pixels of the continuous gradation data of the second resolution to obtain the continuous gradation data of the third resolution, and the continuous gradation data of the third resolution to the fourth resolution And FM screening means for converting the data into two gradation data.

  According to the above configuration, the image data acquisition means for acquiring the image at the first resolution as the two gradation data, and the reduction means for reducing the pixel size of the two gradation data to acquire the two gradation data at the second resolution. Conversion means for converting the two gradation data into continuous gradation data; a reduction means for reducing the number of pixels of the continuous gradation data at the second resolution to obtain the continuous gradation data at the third resolution; By providing FM screening means for converting three-resolution continuous tone data into fourth-resolution two-tone data, the halftone dots corresponding to the secondary gray data or the irregular outlines of the lines are fine. Therefore, the reduction moire can be removed.

  In another embodiment (Claim 6) of the reduced moire removing apparatus according to the present invention, in addition to the above-described configuration, the third resolution is a fraction of 2n (n is a natural number) of the fourth resolution. Features.

  According to the above configuration, the error at the time of conversion from the third resolution to the fourth resolution is reduced by setting the third resolution to 1 / n 2n (n is a natural number) of the fourth resolution, that is, an even number. Therefore, the reduction moire can be removed more effectively.

  An embodiment of the printed matter according to the present invention (Claim 7) is a printed matter obtained by removing moire generated when an image including a periodic pattern is reduced. The second resolution continuous tone data is obtained by converting the two tone data into continuous tone data, reducing the pixel size of the continuous tone data, and obtaining the second resolution continuous tone data. The third resolution continuous tone data is acquired by reducing the number of pixels of the data, and the image obtained by converting the third resolution continuous tone data into the second resolution two tone data by FM screening is printed. Features.

  According to the above configuration, the second resolution is obtained by acquiring an image as two gradation data at the first resolution, converting the two gradation data into continuous gradation data, and reducing the pixel size of the continuous gradation data. Continuous tone data is obtained, the second resolution continuous tone data is reduced to obtain the third resolution continuous tone data, and the third resolution continuous tone data is obtained by FM screening. By printing an image converted into four-resolution two-gradation data, halftone dots or lines corresponding to the secondary gray data become fine irregular points, so that reduction moire can be removed. .

  Another embodiment of the printed matter according to the present invention (Claim 8) is a printed matter printed by removing reduced moire generated when an image including a periodic pattern is reduced. Acquired as tone data, reduced the pixel size of the 2 gradation data, acquired 2 gradation data of the second resolution, converted the 2 gradation data into continuous gradation data, The third resolution continuous tone data was acquired by reducing the number of pixels of the tone data, and the image obtained by converting the third resolution continuous tone data into the second resolution two tone data by FM screening was printed. It is characterized by that.

  According to the above configuration, the image is acquired as the two gradation data at the first resolution, the two gradation data of the second resolution is acquired by reducing the size of the pixel of the two gradation data, and the two gradation data is obtained. The third resolution continuous tone data is obtained by converting into continuous tone data and reducing the number of pixels of the second resolution continuous tone data, and the third resolution continuous tone data is obtained by FM screening. By printing an image converted into four-resolution two-gradation data, halftone dots or lines corresponding to the secondary gray data become fine irregular points, so that reduction moire can be removed. .

  Another embodiment (claim 9) of the printed matter according to the present invention is characterized in that, in addition to the above configuration, the third resolution is 1 / n of the fourth resolution (n is a natural number).

  According to the above configuration, the error at the time of conversion from the third resolution to the fourth resolution is reduced by setting the third resolution to 1 / n 2n (n is a natural number) of the fourth resolution, that is, an even number. Therefore, a printed matter in which reduced moiré is removed more effectively can be obtained.

  The above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto, and various modifications can be made without departing from the scope of the invention. is there.

Next, an embodiment of a reduced moire removing apparatus to which the reduced moire removing method of the present invention is applied will be described with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of a reduced moire removing apparatus according to the present invention.
The reduced moire removal apparatus 100 shown in FIG. 1 mainly includes a storage device 101, a holding unit 102, and a control unit 103.
The storage device 101 uses, for example, a ROM or a RAM, and includes image data acquisition means 104 made of software, conversion means 105, reduction means 106, reduction means 107, and FM screening means 108.
The image data acquisition unit 104 acquires an image with two gradation data from the external input unit 109 at the first resolution.
The conversion means 105 converts the two gradation data into continuous gradation data (primary gray data).
The reduction means 106 reduces the pixel size of the continuous tone data so as to obtain the continuous tone data of the second resolution.
The reduction means 107 reduces the number of pixels of the second resolution continuous tone data to obtain the third resolution (secondary resolution) continuous tone data (secondary gray data). That is, the reduction unit 107 converts the primary gray data into secondary gray data with a secondary resolution smaller than the primary resolution of the printing unit as an output machine.
The FM screening means 108 removes moire by converting the continuous tone data of the third resolution into the two tone data of the fourth resolution (primary resolution).
For example, a RAM (Random Access Memory) is used as the holding unit 102, and the two gradations read by the pixels corresponding to the image internal area when the image data converted into the continuous gradation mode is reduced. The primary gray data read by the pixels corresponding to the data and the image boundary area is temporarily held.
For example, a microprocessor is used as the control means 103 and performs overall control of the reduced moire removing apparatus 100.

An input unit 109 is used to input image data to the reduced moire removing apparatus. Examples of the input unit 109 include a scanner, but image data may be input from a personal computer.
The image data from the reduced moire removing apparatus is sent to a printing unit as an output machine.

Next, the operation of the reduced moire removing apparatus shown in FIG. 1 will be described with reference to FIG.
FIG. 2 is a flowchart showing the operation of the reduced moire removing apparatus shown in FIG.
An original (for example, a main magazine) is read by an external input unit 109 (for example, a scanner), and an image is acquired as two-gradation data (1200 dpi, two-gradation data) at the first resolution (step S201).
Two gradation data is converted into continuous gradation data (primary gray data). Assuming here that the continuous gradation is 8-bit gray data, this processing is performed by converting the signal of “0” logic level, the signal of “1” logic level, the signal of “0” logic level, and the logic of “255”. The signal is converted into a level signal, and two gradations “0” and “1” are converted into 256 gradations (continuous gradations) “0” to “255”. However, there is currently no signal having a logic level of “1” to “254” (step S202).
The continuous tone data of the second resolution is obtained by reducing the pixel size of the continuous tone data (primary gray data) to, for example, a comic size (in this case, 70.8%, 1694.9 dpi). That is, the converted image data is reduced on a large number of pixel matrices. When the pixel size is reduced, the resolution becomes relatively high, but here, the resolution of the output machine and the resolution of the image data are inconsistent, and printing cannot be performed as it is. (Step S203).
Therefore, it is necessary to match the resolution of the output device with the resolution of the image data. That is, the number of pixels of the image data is changed, and finally the resolutions of both are made to coincide. Since the change in the number of pixels is performed in the continuous gradation mode instead of the two gradation mode, the value between the “0” logic level and the “1” logic level that cannot be expressed in the two gradation mode, that is, the 256th floor. It is possible to hold signals of “1” to “254” logic levels in the tone (continuous tone). As a result, when the number of pixels is changed, the “0” logic level and the “255” logic level (“0” logic level and “1” logic level in two gradations) are adjacent to each other in 256 gradations (continuous gradations). When a level signal (gray) that is neither “0” logic level nor “255” logic level is generated on the boundary of the pixel matrix after the change, the level is changed from “1” to “254” logic level. Can be held as a signal. That is, the continuous resolution data (secondary gray data) of the third resolution (1200 dpi) is obtained by reducing the number of pixels of the continuous resolution data of the second resolution. The third resolution is 1 / 2n, for example, 1/2, of the fourth resolution (2400 dpi, which is a general resolution of an offset rotary press). (Step S204).
The continuous resolution data (secondary gray data) of the third resolution is converted into the two gradation data of the fourth resolution (resolution of the output device) by FM screening. Moire can be removed by outputting image data obtained by FM screening. At this time, the resolution of the image data matches the resolution of the output device (step S205).

Here, the principle that the reduced moire can be removed by the reduced moire removing apparatus will be described with reference to the drawings.
FIG. 3A is a schematic diagram illustrating an example of binary image data, and FIG. 3B is a schematic diagram illustrating an example of halftone when the binary image data is reduced. FIG. 4C is a schematic diagram illustrating an example of an error when the halftone due to reduction is forcibly made to have two gradations with a predetermined threshold, and FIG. 4A illustrates an image before the reduction moire removal processing, 4B shows an image when gradation conversion processing, reduction processing, and resolution conversion are performed, and FIG. 4C shows an image after FM screening processing.
In the pixel matrix 300 shown in FIG. 3A, each of the 25 rectangles represents a pixel. An area 301 indicates that the pixel data is “0” logic level, and an area 302 indicated by black indicates that the pixel data is “1” logic level.
In the pixel matrix 303 shown in FIG. 3B, each of the nine rectangles represents a pixel. A hatched area 304 indicates that the pixel data is halftone.
In the pixel matrix 305 shown in FIG. 3C, each of the nine rectangles represents a pixel. An area 306 represents that the pixel data is at the “0” logic level.

Here, a case where the image represented by the pixel matrix 300 composed of 25 pixels is reduced will be described.
When an image composed of pixels of the pixel matrix 300 is reduced to the rectangular size indicated by the wavy lines L1 and L2, a method of reducing the number of pixels without changing the size of the pixels themselves and the size of the pixels themselves (the number of pixels). Does not change). In the method of reducing the size of the pixel itself, there is no change in the number of pixels in the pixel matrix (25), and the data of each pixel is the data of both the original “0” logic level and the original “1” logic level. The data becomes “0” logic level data and “1” logic level data, and moire does not occur, but the resolution is relatively increased by reducing the pixel size.
On the other hand, in the method of reducing the number of pixels, the number of pixels in the pixel matrix 303 is reduced (9). For this reason, the pixel matrix 300 and the pixel matrix 303 do not coincide with each other, and the pixel data of the region 304 has an intermediate value (halftone) of the region on the boundary in the pixel matrix 300 corresponding to the region 304.
In this case, since the intermediate value data has been conventionally divided into two “0” logic level and “1” logic level at a predetermined threshold value (for example, 50%), moire is generated due to an error.

  Therefore, the present inventors obtain the image with two gradation data at the first resolution, convert the two gradation data into continuous gradation data, and reduce the pixel size of the continuous gradation data. The second resolution continuous tone data is acquired, the third resolution continuous tone data is acquired by reducing the number of pixels of the second resolution continuous tone data, and the third resolution continuous tone data is FM. The second resolution is obtained by converting to the second gradation data of the fourth resolution by screening, or by acquiring the image with the two gradation data at the first resolution and reducing the pixel size of the two gradation data. Obtaining tone data, converting the two tone data into continuous tone data, reducing the number of pixels of the second resolution continuous tone data, obtaining third resolution continuous tone data, Resolution continuous tone data By conversion to bi-level data of the fourth resolution by Ningu found that can remove the reduced moiré that occurs when reducing the image containing a periodic pattern consisting of halftone dot or line screen.

When gradation conversion processing, reduction processing, and resolution conversion are performed on the image 401 shown in FIG. 4A, a uniform central portion 402 as shown in FIG. 4B and a blurred peripheral portion 403 are obtained. And are formed. The central portion corresponds to the above-described “1” logic level signal (two gradation data), and the peripheral portion 403 corresponds to the intermediate value logic level signal (halftone data).
When FM screening is performed on the entire image data shown in FIG. 4B at the resolution of the printing means, an image 404 with irregularly deformed contours as shown in FIG. 4C is formed. Moire is removed by forming such a deformed image 404 on paper, that is, printing.

  Table 1 shows the relationship between the reduction ratio, which is the ratio between the secondary resolution and the primary resolution, and the occurrence of moire.

同表より、縮小率が１／１、３／８のときはモアレが発生し、縮小率が１／２、１／４のときはモアレが発生しないことが分かる。
すなわち、２次解像度は、１次解像度の２ｎ（ｎは自然数）分の１であるのが好ましいことが分かる。これは２次解像度を１次解像度の２ｎ分の１とすることで、２次解像度への変換時に、１次解像度の画像データの画素を相対的に２ｎ倍の微細点で境界上の領域を発生させずに表現することが可能になるからである。

From the table, it can be seen that moire occurs when the reduction ratio is 1/1, 3/8, and no moire occurs when the reduction ratio is 1/2, 1/4.
That is, it is understood that the secondary resolution is preferably 1 / n of the primary resolution (n is a natural number). This is because the secondary resolution is set to 1 / 2n of the primary resolution, and when converting to the secondary resolution, the pixels on the boundary are defined by the 2n times as many fine points as the pixels of the image data of the primary resolution. This is because it becomes possible to express without generating.

Next, another embodiment of a reduced moire removing apparatus to which the reduced moire removing method of the present invention is applied will be described with reference to the drawings. The configuration of the reduced moire removing apparatus itself in this embodiment is the same as that of the reduced moire removing apparatus shown in FIG. 1, and only the operation is different.
FIG. 5 is a flowchart illustrating the operation of the reduced moire removing apparatus according to the second embodiment.
The difference between the flowchart shown in FIG. 5 and the flowchart shown in FIG. 2 is that the pixels are reduced and converted to primary gray data.

That is, for the image data read by the external input unit 109 (for example, a scanner), an image is acquired as two-gradation data at the first resolution (step S501).
The two-gradation data of the second resolution is acquired by reducing the pixel size of the two-gradation data (step S502).
The two gradation data is converted into continuous gradation data (step S503).
The third resolution continuous tone data is acquired by reducing the number of pixels of the second resolution continuous tone data (step S504).
The continuous tone data of the third resolution is converted into two tone data of the fourth resolution by FM screening. Moire can be removed by outputting image data obtained by FM screening (step S505).

Next, an embodiment of a printing apparatus to which the reduced moire removal method of the present invention is applied will be described with reference to the drawings.
FIG. 6 is a block diagram illustrating an embodiment of a printing apparatus. In addition, the same code | symbol was used for the member similar to the reduction | restoration moire removal apparatus shown in FIG.
The printing apparatus shown in FIG. 5 is characterized in that an input unit and a printing unit are provided in the reduced moire removing apparatus shown in FIG.

That is, the printing apparatus 600 shown in FIG. 6 mainly includes a reduced moire removing apparatus 100, an input unit 501, and a printing unit 602.
The input unit 601 may be a scanner, but image data may be input from a personal computer.
The printing unit 602 may be any device that performs printing using halftone dots or lines, such as an intaglio printing machine, a lithographic printing machine, a relief printing machine, and a stencil printing machine.

Next, the operation of the printing apparatus shown in FIG. 6 will be described with reference to FIG.
FIG. 7 is a flowchart showing the operation of the printing apparatus shown in FIG.
The flowchart shown in FIG. 7 is obtained by adding steps S701 and 706 to the flowchart shown in FIG.

That is, image data is input by the input means 601 (see FIG. 6) (step S701).
For the read image data, an image is acquired as two-gradation data at the first resolution (step S702).
The two gradation data is converted into continuous gradation data (primary gray data) (step S703).
The continuous tone data of the second resolution is acquired by reducing the pixel size of the continuous tone data (primary gray data) (step S704).
The third resolution continuous tone data (secondary gray data) is acquired by reducing the number of pixels of the second resolution continuous tone data. The third resolution is 1 / 2n of the fourth resolution (n is a natural number), for example, 1/2. (Step S705).
The continuous resolution data (secondary gray data) of the third resolution is converted into the two gradation data of the fourth resolution (resolution of the output device) by FM screening. Image data obtained by FM screening is output (step S705).
Moire can be removed by printing the obtained image data (step S706).

Next, another embodiment of a printing apparatus to which the reduced moire removal method of the present invention is applied will be described with reference to the drawings. Note that the configuration of the printing apparatus itself in this embodiment is the same as that of the printing apparatus shown in FIG.
FIG. 8 is a flowchart illustrating the operation of the printing apparatus according to the fourth embodiment.
The difference between the flowchart shown in FIG. 8 and the flowchart shown in FIG. 7 is that the pixels are reduced and then converted to primary gray data.

That is, image data is input by the input means 601 (see FIG. 6) (step S801).
By performing the two-gradation processing on the read image data, the image is acquired as the two-gradation data at the first resolution (step S802).
The two-gradation data of the second resolution is acquired by reducing the pixel size of the two-gradation data (step S803).
The two gradation data is converted into continuous gradation data (step S804).
The third resolution continuous tone data is acquired by reducing the number of pixels of the second resolution continuous tone data (step S805).
The continuous tone data of the third resolution is converted into two tone data of the fourth resolution by FM screening (step S806).
Moire can be removed by printing the obtained image data (step S807).

[Effect]
In the above, while one-source multi-use is shouted, the comic creation work has the same tendency. One of them is the creation of comics using the magazine images. The biggest concern of this comic creation work is the occurrence of reduced moire. The reduced moire can be confirmed only if the output product has the same high resolution as the final output product, which is expensive and laborious for re-output. The technique related to this reduction moire removal solves these problems.

  INDUSTRIAL APPLICABILITY The present invention can be used for a reduced moire removing apparatus, a printing apparatus, and a printed matter that can remove reduced moire generated when an image including a periodic pattern is reduced.

It is a block diagram which shows one Example of the reduction | restoration moire removal apparatus which concerns on this invention. 3 is a flowchart showing an operation of the reduced moire removing apparatus shown in FIG. 1. It is a schematic diagram which shows an example of reduction of binary image data. (A) shows an image before the reduction moiré removal processing, (b) shows an image when the reduction processing and resolution conversion are performed, and (c) shows an image after the reduction moiré removal processing according to the present invention. Show. 6 is a flowchart illustrating an operation of the reduced moire removing apparatus according to the second embodiment. 1 is a block diagram illustrating an embodiment of a printing apparatus. 7 is a flowchart illustrating an operation of the printing apparatus illustrated in FIG. 6. 10 is a flowchart illustrating an operation of a printing apparatus according to a fourth embodiment. It is an enlarged view which shows an example of a screen tone. FIG. 10 is an enlarged view including a moire generated when the screen tone shown in FIG. 9 is reduced.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Reduction | restoration moire removal apparatus 101 Memory | storage device 102 Holding means 103 Control means 104 Image data acquisition means 105 Conversion means 106 Reduction means 107 Reduction means 108 FM screening means

Claims (9)

In a reduced moire removal method for removing reduced moire generated when an image including a periodic pattern is reduced,
The image is acquired as two gradation data at the first resolution,
Converting the two gradation data into continuous gradation data;
By acquiring the continuous tone data of the second resolution by reducing the pixel size of the continuous tone data,
Acquiring the third resolution continuous tone data by reducing the number of pixels of the second resolution continuous tone data;
A reduced moire removal method, wherein the continuous grayscale data having the third resolution is converted into two grayscale data having the fourth resolution by FM screening. In a reduced moire removal method for removing reduced moire generated when an image including a periodic pattern is reduced,
The image is acquired as two gradation data at the first resolution,
By obtaining the second resolution two-gradation data by reducing the pixel size of the two-gradation data;
Converting the two gradation data into continuous gradation data;
Acquiring the third resolution continuous tone data by reducing the number of pixels of the second resolution continuous tone data;
A reduced moire removal method, wherein the continuous grayscale data having the third resolution is converted into two grayscale data having the fourth resolution by FM screening.   3. The reduced moire removal method according to claim 1, wherein the third resolution is 1 / n (n is a natural number) of the fourth resolution. In a reduced moire removal device that removes reduced moire generated when an image including a periodic pattern is reduced,
Image data acquisition means for acquiring the image as two gradation data at a first resolution;
Conversion means for converting the two-tone data into continuous-tone data;
A reduction means for reducing the size of the pixels of the continuous tone data to obtain the continuous tone data of the second resolution;
Reducing means for reducing the number of pixels of the second resolution continuous tone data to obtain the third resolution continuous tone data;
An apparatus for removing reduced moiré, comprising FM screening means for converting the continuous gradation data of the third resolution into two gradation data of the fourth resolution. In a reduced moire removal device that removes reduced moire generated when an image including a periodic pattern is reduced,
Image data acquisition means for acquiring the image as two gradation data at a first resolution;
Reduction means for reducing the pixel size of the two gradation data to obtain the two gradation data of the second resolution;
Conversion means for converting the two-tone data into continuous-tone data;
Reducing means for reducing the number of pixels of the second resolution continuous tone data to obtain the third resolution continuous tone data;
An apparatus for removing reduced moiré, comprising FM screening means for converting the continuous gradation data of the third resolution into two gradation data of the fourth resolution.   6. The reduced moire removing apparatus according to claim 4, wherein the third resolution is 1 / n (n is a natural number) of the fourth resolution. In the printed matter printed by removing the moire generated when the image including the periodic pattern is reduced,
The image is acquired as two gradation data at the first resolution,
Converting the two gradation data into continuous gradation data;
By acquiring the continuous tone data of the second resolution by reducing the pixel size of the continuous tone data,
Acquiring the third resolution continuous tone data by reducing the number of pixels of the second resolution continuous tone data;
An image obtained by printing an image obtained by converting the continuous tone data of the third resolution into two tone data of the fourth resolution by FM screening. In the printed matter printed by removing the reduction moire generated when the image including the periodic pattern is reduced,
The image is acquired as two gradation data at the first resolution,
By obtaining the second resolution two-gradation data by reducing the pixel size of the two-gradation data;
Converting the two gradation data into continuous gradation data;
Acquiring the third resolution continuous tone data by reducing the number of pixels of the second resolution continuous tone data;
An image obtained by printing an image obtained by converting the continuous tone data of the third resolution into two tone data of the fourth resolution by FM screening.   The printed matter according to claim 7 or 8, wherein the third resolution is 1 / n (n is a natural number) of the fourth resolution.

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