JP2009081835A - Tint block image generation program and tint block image generation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a program and a device for generating a forgery suppressed tint block in which original concealment capability is improved. <P>SOLUTION: An image generation device generates, on a print medium, an image including a first image portion and a second image portion. The device has a first screen processing means which generates image data by an area modulation screen having a first screen ruling, for pixels of the first image portion; and a second screen processing means which generates image data by an area modulation screen or a density modulation screen having a second screen ruling which is higher than the first screen ruling for pixels of the second image portion. Then the first screen processing means generates a halftone dot at the center of gravity position of an image of a latent image portion in a cell corresponding to a halftone dot formation area in the area modulation screen processing. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a copy-forgery-inhibited pattern image generation program and a copy-forgery-inhibited pattern image generation device, and more particularly to a program and device for generating copy-forgery-inhibited pattern image data to be printed on a print medium. Furthermore, a copy-forgery-inhibited pattern image data generation program and copy-forgery-inhibited pattern image generation that have the effect of suppressing forgery by copying a print medium (original) on which a copy-forgery-inhibited pattern image is printed based on this copy-forgery-inhibited pattern image data Relates to the device.

The copy-forgery-inhibited pattern is combined with the original image of the original as a background, making it possible to distinguish whether the printed document is the original or a copy. Although it is difficult to identify the copy-forgery-inhibited pattern in the original, copying and copy-printing characters and images will emerge. By using this, it becomes possible to easily distinguish the original from the copy. In addition, since characters and images of the background pattern are revealed by copying, if the original is generated by synthesizing the background, an effect of psychologically suppressing the copy of the original can be obtained.

  The background pattern is described in Patent Document 1, and according to this description, it is as follows.

  The general structure of a background pattern consists of a “latent image portion” in which dots printed on the original remain after copying or a small reduction in dots, and a “background portion” where dots printed on the original due to copying disappear or dots are greatly reduced. It consists of two areas. That is, the latent image portion has a small density change due to copying and the original image is reproduced as it is, and the background portion has a large density change due to copying and the original image disappears. A copy-forgery-inhibited pattern character or image is formed by these two areas, and the copy-forgery-inhibited pattern character or image is referred to as a “latent image”.

  The two areas of the latent image part and the background part have almost the same density. In the original state, it is difficult to distinguish the characters and images of the copy-forgery-inhibited pattern such as “copy” at a glance. Each of the background portion and the latent image portion has different characteristics. When copied, a difference in density between the latent image portion and the background portion is generated due to the difference in density change, so that it is easy to distinguish the characters and images of the tint block formed in these two areas.

  The latent image part is composed of a cluster of concentrated dots to make it easier to read dots during copying (scanning by copying), and the background part is made up of dispersed dots to make it difficult to read dots during copying. . By doing so, the latent image portion has a characteristic that dots are likely to remain after copying, and the background portion has a characteristic that the dots are more easily erased than the latent image portion. Concentrated dots and dispersed dots can be realized by halftone dot processing using halftone dots with different numbers of lines. That is, a halftone dot with a low line number is used to obtain a concentrated dot arrangement, and a halftone dot with a high line number is used to obtain a dispersed dot arrangement.

  In general, a copying machine has an image reproduction capability that depends on the input resolution in the process of reading minute dots of the original to be copied with a scanner and the output resolution in the process of reproducing minute dots read by the scanner with a print engine. There are limits. Therefore, if there are small dots in the document that exceed the limit of the image reproduction capability of the copier, the small dots cannot be reproduced completely in the copy, and the isolated small dots will disappear. . That is, if the background of the background pattern is created to exceed the limit of dots that can be reproduced by a copier, large dots (concentrated dots) on the background pattern can be reproduced by copying, but small dots (distributed dots) can be copied. Due to this, the latent image hidden in the copied manuscript appears. In addition, even if the dispersed dots in the background area do not disappear completely due to copying, if the degree of dot disappearance is large compared to the dots in the latent image area, a density difference will occur between the background area and the latent image area after copying. Then, a latent image hidden in the copied manuscript emerges.

  In the background pattern, a technique called “camouflage” is used to make it more difficult to distinguish characters and images hidden as latent images. This camouflage technology is a method of arranging a pattern with a density different from that of the latent image portion and the background portion over the entire tint block image. At first glance, a camouflage pattern with a different density from the latent image portion and the background portion is conspicuous. This has the effect of making the latent image less noticeable. That is, since the contrast of the camouflage pattern is large and the contrast between the latent image portion and the background portion is small, the latent image is more effectively hidden by the optical illusion. Furthermore, the camouflage pattern has an advantage that it can give a decorative impression to the printed matter and can create a background pattern with excellent design. In general, the camouflage pattern is created with two values indicating whether dots are generated or not, and the camouflage pattern is formed by not generating dots of the background pattern in an area corresponding to the camouflage pattern. The binary camouflage pattern is described in Patent Document 2. The above is the outline of the background pattern.

  FIG. 1 is a diagram showing an example of a latent image of a tint block and a camouflage pattern. As shown in the enlarged view 10X, for example, the black portion corresponds to the latent image portion LI of the tint block and the white portion corresponds to the background portion BI of the tint block as shown in the enlarged view 10X. On the other hand, in the camouflage pattern 12, as shown in the enlarged view 12X, for example, a black portion CAM is a region where a background pattern dot is not formed, and a white portion is a region where a background pattern dot is formed. In other words, the camouflage pattern data is binary image data in which each pixel indicates a portion where the tint block image is printed and a portion where the tint block image is not printed.

  FIG. 2 is a diagram showing an example of an original on which a background pattern is printed. In the tint block 14, a latent image portion LI and a background portion BI are formed based on the latent image mask pattern 10 of FIG. The latent image portion LI is formed with dots with a low halftone line number (53 lpi) by the dot concentration type dither method, and the background portion BI is formed with dots with a high halftone line number (212 lpi) by the dot dispersion type dither method. . As is clear from the enlarged background pattern 14X, the entire background pattern has a constant output density, but the dots in the latent image portion LI are large dots because they are formed by a screen with a low number of dotted lines, and the background portion BI. These dots are minute dots because they are formed by a screen having a high number of dotted lines.

  The copy-forgery-inhibited pattern 16 is formed based on the latent image mask pattern 10 and the camouflage pattern 12 of FIG. 1 except that the latent image portion LI and the background portion BI are excluded from the black portion CAM region of the camouflage pattern. As shown in the enlarged tint block 16X, the entire tint block has a constant output density, and no dots are formed in the camouflage pattern area CAM. In other areas, a latent image composed of large dots is formed as in FIG. A portion LI and a background portion BI composed of minute dots are formed. Since the contrast of the camouflage pattern is large, the latent image (character “duplicate”) formed by the latent image portion LI and the background portion BI having a low contrast is inconspicuous.

  The original copy-forgery-inhibited pattern in FIG. 2 has the same output density of the latent image portion LI and the background portion BI, so that the latent image “double” formed thereby is concealed. This is called high concealment of the latent image in the original.

  FIG. 3 is a diagram showing an example of a copy of a background pattern. The copy 18 is formed through a scanning process by copying and a dot forming process (a process for printing on a print medium based on scan data generated by the scanning process). As shown in the enlarged view 18X, a latent image portion is formed. Although dots with large LI have hardly disappeared, minute dots in the background portion BI have disappeared considerably. As a result, in the copy 18, the output density of the latent image portion LI hardly decreases, but the output density of the background portion BI decreases considerably, and the latent image “duplicate” appears to float. That is, the recognizability of the latent image in the copy is high.

  Similarly, the copy 20 is the same as the copy 18 except for the camouflage pattern area CAM. The contrast of the camouflage pattern decreases due to the decrease in the output density of the background portion BI, and the latent image “double” appears to float.

4 is an enlarged view of the enlarged view of the original in FIG. 2 and the enlarged view of the copy in FIG. (A) In the original, the latent image portion LI is composed of dots (halftone dots) with a small number of halftone lines and a large area, and the background portion BI is composed of minute dots with a large number of halftone lines. No dot is formed in the black portion CAM of the camouflage pattern. On the other hand, in (b) the copied material, the size of the large dots (halftone dots) in the latent image portion LI has not changed so much, whereas a considerable number of small dots in the background portion BI have disappeared. . As a result, in the copied material, the output density of the latent image portion LI is hardly lowered, the output density of the background portion BI is greatly lowered, and the latent image “duplicate” of the tint block is manifested.
JP 2005-151456 A Japanese Patent Laid-Open No. 4-170569

  As described above, the copy-forgery-inhibited pattern is required to satisfy both the high concealability of the latent image in the original and the high distinguishability of the latent image in the copy. In the example of FIG. 2, the background portion BI is a dither matrix having a high number of halftone lines, and the latent image portion LI is a dither matrix having a low number of halftone lines, and is binarized according to the latent image mask 10.

  However, as shown in FIGS. 2 and 4, the first problem is that the dots of the background portion BI and the dots of the latent image portion LI are combined with the boundary portion between the background portion and the latent image portion of the original 14X, resulting in a density. A region 21 that is highly emphasized and a region 22 in which the distance between the dots of the background portion BI and the dots of the latent image portion LI is widened and the density is low (white) are generated. The latent image becomes conspicuous by such areas 21 and 22, and the concealment property of the latent image in the original is impaired.

  Japanese Patent Application Laid-Open No. H10-228561 proposes performing boundary processing so that dots generated in the background portion at the boundary portion of the latent image mask pattern do not combine with the latent image portion.

  FIG. 5 is a diagram showing a copy-forgery copy and an original copy of the tint block when the boundary processing according to Patent Document 1 is performed. FIG. 6 is an enlarged view thereof. In both figures, in the original 14 and its enlarged view 14X, although the combination of dots is prevented in the area 23, a white area in which the dots are separated is formed in the area 24. That is, the region 24 highlighted in white remains unresolved.

  As a second problem, when the low-resolution camouflage pattern shown in FIGS. 1 and 2 is employed, the area of the pattern for turning off the background pattern dots is wide and the contrast is high, so that the concealment property of the latent image is increased. be able to. However, there is a disadvantage that the contrast is too high and it is too conspicuous than the original printed image. In order to overcome this, there is a method using a camouflage pattern having a relatively high resolution.

  FIG. 7 is a diagram showing a camouflage pattern with high resolution and a tint block employing the camouflage pattern. The camouflage pattern 25 has a higher resolution than the camouflage pattern 12 of FIG. In the original copy-forgery-inhibited pattern 26 using the camouflage pattern 25, the black portion of the camouflage pattern is a portion where dots of the copy-forgery-inhibited pattern are not formed (dot off). FIG. 7 shows enlarged views 25X and 26X, respectively. If the camouflage pattern 25 has a high resolution, the conspicuousness of the pattern is suppressed, and the distinguishability of the original printed image does not deteriorate.

  However, the second problem is that dots are formed with a high number of halftone lines in the background portion BI, so dots are formed corresponding to high-resolution camouflage patterns, and the patterns are reproduced almost faithfully. On the other hand, since dots are formed with a low number of halftone lines in the latent image portion LI, the area of the dot off corresponding to the camouflage pattern becomes rough, and the appearance of the pattern differs from the background portion. For example, in region 27 in FIG. 7, dot off occurs in a relatively large region. Thus, if the appearance of the camouflage pattern is different between the background portion and the latent image portion, the latent image becomes conspicuous and the concealment property of the original latent image is impaired.

  As described above, the first problem is that the latent image portion and the background portion are formed by a screening process using a dither matrix having different numbers of halftone lines. There is a generation of a high density emphasis area and a low density emphasis area by dot separation. This problem is not limited to the tint block, and the same problem occurs in the boundary portion of a plurality of areas formed by the dither matrix screening process with different numbers of halftone lines. Alternatively, a first process using an area modulation (AM) screen with a low halftone number and a second process using an area modulation (AM) screen with a high halftone number or a density modulation (FM) screen using an error diffusion method or a distributed dither matrix. The same applies to the boundary portion of the image area formed by the above processing.

  As a second problem, when a high-resolution camouflage pattern is superimposed on a background pattern consisting of a latent image portion and a background portion, the appearance of the camouflage pattern differs between the latent image portion and the background portion due to the difference in the number of dotted lines. , The latent image concealment is impaired.

  Accordingly, an object of the present invention is to provide a program and an apparatus for generating a tint block in which a high density emphasis area and a low density emphasis area do not occur at a boundary portion between a latent image portion and a background portion.

  Another object of the present invention is to provide a program and an apparatus for generating an image in which a high density emphasis area and a low density emphasis area do not occur at the boundary between the first and second image areas.

  Furthermore, another object of the present invention is to provide a program and an apparatus for generating a tint block that makes the appearance of the camouflage pattern in the latent image portion and the background portion equal.

In order to achieve the above object, according to the first aspect of the present invention, a tint block image data for forming a tint block image including a latent image portion and a background portion having different output densities reproduced on a print medium, which are reproduced at the time of copying. In a tint block image generation program for causing a computer to execute a tint block image generation process for generating
The tint block image generation step includes:
For the pixels of the latent image portion, a first screening processing step of generating latent image portion image data by an area modulation screen having a first halftone line number;
The background pixel includes a second screening process step of generating background image data by an area modulation screen or a density modulation screen having a second halftone number higher than the first halftone number. ,
The first screening processing step generates the latent image portion image data forming a halftone dot with a position shifted from a center of a cell corresponding to a halftone dot formation region in the area modulation screen as a center. .

  Said 1st side surface WHEREIN: The position shifted from the center of the said cell is a gravity center position in the image of the said latent image part in the cell corresponding to the halftone dot formation area in the said area modulation screen, It is characterized by the above-mentioned. .

  In the first aspect described above, according to a preferred embodiment, the halftone dots formed in the first screening process have an upper limit on the size corresponding to the gradation value of the latent image portion in the cell.

In the first aspect described above, according to a preferred embodiment, the first screening process step comprises:
A center-of-gravity position generation step for obtaining a center-of-gravity position of the image of the latent image portion in the cell;
An average input tone value generation step of obtaining an average input tone value obtained by dividing the total tone value of the image of the pixel portion in the cell by the number of pixels in the cell;
An ideal output dot number generation step of obtaining, as an ideal output dot number, the number of dots generated when an image in which all pixels have the average input gradation value is screened by the area modulation screen;
A halftone dot generating step of generating a halftone dot having a size with the upper limit of the number of ideal output dots at the center of gravity position.

In the first aspect described above, according to a preferred embodiment, the area modulation screen having the first number of halftone lines is a dot-concentrated dither matrix, and the latent image portion image data is input to the latent image portion. Image data that forms halftone dots of a size corresponding to the tone value,
The area modulation screen having the second halftone line number is a dot dispersion type dither matrix, and the background image data has a density corresponding to the input gradation value of the background portion, and the latent image portion image data This is image data for forming halftone dots smaller than halftone dots.

In the first aspect described above, according to a preferred embodiment, the tint block image has a camouflage pattern synthesized on the latent image portion and the background portion,
And a step of generating a corrected camouflage pattern gradation value obtained by correcting the gradation value of the camouflage pattern according to the input gradation values of the latent image portion and the background portion,
The first screen processing step generates the latent image portion image data with reference to a dither matrix of the area modulation screen having the first halftone number for the corrected camouflage pattern gradation value,
In the second screen processing step, the background image data is generated by referring to the dither matrix of the area modulation screen having the second halftone number for the corrected camouflage pattern gradation value.

In order to achieve the above object, according to the second aspect of the present invention,
In an image generation program for causing a computer to execute an image generation process for generating image data for forming an image including a first image portion and a second image portion on a print medium.
The image generation process includes:
For the first pixel, a first screening processing step of generating image data by an area modulation screen having a first halftone line number;
The second pixel has a second screening processing step of generating image data by an area modulation screen or a density modulation screen having a second halftone line number higher than the first halftone line number;
In the first screening processing step, a halftone dot is formed at the center of gravity of the image of the latent image portion in the cell corresponding to the halftone dot formation region in the area modulation screen processing.

  In order to achieve the above object, a third aspect of the present invention is the tint block image generation device according to the first or second aspect.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.

  FIG. 8 is a diagram showing the configuration of the tint block image forming apparatus according to the present embodiment. The tint block image forming apparatus includes a printer driver program 32 installed in a host computer 30, a latent image portion dither matrix 33, a background portion dither matrix 34, camouflage pattern data 35, and a printer 40. The latent image portion dither matrix 33 and the background portion dither matrix 34 are included in the printer driver program 32 distributed to the user by the printer manufacturer via a recording medium or via a network line such as the Internet. When 32 is installed in the host computer, it is stored in the storage unit in the host computer. The host computer 30 further includes a CPU, a RAM, and an application program 31, and executes the application program 31 to generate image data (print document image data) including characters, images, graphics, and the like.

  Further, in response to a request from the user, the host computer 30 executes the printer driver 32 to generate the camouflage-patterned tint block data 37. When a print request is received from the user for the image data generated by the application 31, the printer driver 32 generates print job data of the image data 36 to be printed based on a printer control language that can be interpreted by the printer device 40. If the print request from the user includes adding copy-forgery-inhibited pattern data to the image data 36 to be printed, the printer driver 32 generates the copy-forgery-inhibited pattern data and adds the copy-forgery-inhibited pattern data 37 to the print job. Including them and transmitting them to the interface IF of the printer 40

  The image data 36 can take various forms, for example, data described in a page description language, data expanded in an intermediate code of a printer, or RGB bitmap data expanded in pixels. The camouflage pattern-added tint block data 37 is obtained by performing screening processing on tone data obtained by correcting (or modulating) binary (0 or 255) camouflage pattern tone data with the input tone of the tint block. Image data. The camouflage pattern-added copy-forgery-inhibited pattern data 37 may be represented by binary values of 0 and 1 for each pixel. When the image data to be printed is represented by 8-bit gradation values for each color of RGB, the pattern data 37 The value 255 corresponding to the maximum gradation value and the value 0 corresponding to the minimum gradation value may be expressed by 8 bits.

  On the other hand, the printer 40 includes a print engine 46 including a print medium feeding unit, a print execution unit that forms an image on the print medium, a print medium discharge unit, and the like, and a predetermined image for the received image data 36 and copy-forgery-inhibited pattern data 37. And a controller 41 that performs processing and further controls the print engine 42. The CPU of the controller 41 executes the image forming program 42 and generates bitmap data expanded into pixels from the received image data 36. If the received image data 36 is in the form of bitmap data, the bitmap data can be used as it is.

  Then, the synthesis unit 43 synthesizes the bitmap data having the gradation value for each pixel of the image data 36 and the dot data of the tint block data 37. This composition is performed by, for example, a process of superimposing the image of the image data 36 on the image of the copy-forgery-inhibited pattern data 37. Further, the RGB data synthesized by the color conversion unit 44 is color-converted into CMYK data, and the binarization unit 45 converts the CMYK bitmap data into dot data in the pixel using a predetermined screen. Output to the print engine 46. As a result, the print engine 46 prints an image obtained by combining the image to be printed generated by the application program and the copy-forgery-inhibited pattern image generated by the printer driver 32 on the print medium. This is the original copy of the background pattern.

  Alternatively, according to another synthesis method, before the RGB bitmap data of the image data 36 and the copy-forgery-inhibited pattern image image data are synthesized, the RGB bitmap data of the image data 36 is color-converted into CMYK bitmap data, and the CMYK The copy-forgery-inhibited pattern data 37 is combined with bitmap data of any color. In this case, the copy-forgery-inhibited pattern data 37 has the dot ON / OFF information for each pixel as the maximum gradation value / minimum gradation value of the bitmap data, and the copy-forgery-inhibited pattern data 37 has any one of CMYK colors of the image data 36. Overwrite bitmap data. For example, if the image data 36 is black K character data, the CMY bitmap data is converted into the tint block data 37. Alternatively, the copy-forgery-inhibited pattern data 37 is overwritten on the pixel of the gradation value of the minimum density of the bitmap data of any color of the image data 36.

  In the embodiment of FIG. 8, the printer driver 32 of the host computer 30 generates a tint block data 37 corresponding to the tint block image generation program. However, as a modified example, copy-forgery-inhibited pattern data and camouflage pattern data may be generated in the printer, and a copy-forgery-inhibited pattern image may be generated based on the generated copy-forgery-inhibited pattern data and camouflage pattern data. In this case, the printer driver 32 generates print job data including designation to print a copy-forgery-inhibited pattern image on the image data 36 to be printed, and the controller 41 of the printer 40 executes the copy-forgery-inhibited pattern image generation program. Using the latent image portion dither matrix and the background portion dither matrix stored in, the print pattern data with the camouflage pattern is generated from the print job data instructed to generate the print pattern with the camouflage. The print job data for generation of copy-forgery-inhibited pattern data includes data necessary for generating copy-forgery-inhibited pattern data with camouflage patterns, such as designation of characters and patterns that are lost or reproduced during copying, designation of density of copy-forgery-inhibited patterns, and designation of camouflage patterns. It is. The copy-forgery-inhibited pattern generation processing in the printer 40 may be executed by the CPU of the printer executing an image generation program, or may be executed by a dedicated image processing generation device such as an ASIC.

[Overview of tint block generation procedure]
Hereinafter, an outline of the tint block generation method by the tint block image generation device according to the present embodiment will be described. The copy-forgery-inhibited pattern image generating device refers to the host computer when the copy-forgery-inhibited pattern image is generated by the printer driver 32, and the printer 40 when the copy-forgery-inhibited pattern image is generated by the image forming program 42. In the present embodiment, the copy-forgery-inhibited pattern image generation apparatus corresponds to the latent image mask pattern selected from the default pattern by the user or the latent image mask pattern uniquely generated by the user, and the copy-forgery-inhibited pattern image composed of the latent image portion and the background portion. Generate data. In some cases, a camouflage pattern is combined with the copy-forgery-inhibited pattern image data.

FIG. 9 is a flowchart showing a procedure for generating the tint block data in the present embodiment.
First, the tint block image generation device generates latent image mask pattern data (S1). The latent image mask pattern data is, for example, the data of the latent image mask pattern 10 of the character “double” shown in FIG. 1, and is composed of data 0 and 1 indicating whether each pixel is the latent image portion LI or the background portion BI. . Then, the tint block image generation device acquires camouflage pattern data (S2). Data selected from a plurality of camouflage pattern data 35 stored in advance in the memory in the host computer 30 becomes camouflage pattern data. As the camouflage pattern, various patterns such as those having the low resolution shown in FIG. 1 and those having the high resolution shown in FIG. 7 can be adopted.

  The camouflage pattern data in this embodiment is 8-bit gradation value data for each pixel, but binary data of black (gradation value 0) and white (gradation value 255). In addition, a background pattern dot is not formed in a black portion of the camouflage pattern, and a background pattern dot is formed in a white portion. Alternatively, the camouflage pattern data may have gradation values exceeding two values. That is, it may be composed of 8-bit gradation data and have 256 gradations with gradation values 0 to 255.

In order to synthesize the camouflage pattern with the background pattern, the background pattern image generation device generates corrected camouflage pattern gradation data based on the input gradation of the latent image portion and the background portion (S3). The input gradation values (0 ≦ In ≦ 255) of the latent image portion and the background portion correspond to the output density of the copy-forgery-inhibited pattern image, and the gradation value determined by default or the copy-forgery-inhibited pattern arbitrarily selected by the user The gradation value corresponds to the output density of the image. On the other hand, the camouflage pattern is composed of black (gradation value 0) and white (gradation value 255), and the dot is turned off in black. Therefore, when the gradation value of the camouflage pattern is A (= 0, 255), the gradation value Ai of the corrected camouflage pattern in consideration of the input gradation value In of the latent image portion and the background portion is expressed by the following equation (1). Is required.
Ai = (A / 255) × In (1)
The camouflage pattern-added tint block image is an image obtained by modulating the tint block image composed of the latent image portion and the background portion with the camouflage pattern gradation value. In other words, it is an image in which the gradation value of the camouflage pattern is modulated by the input gradation value of the tint block image. In the above step S3, this modulation process is performed to obtain a corrected camouflage pattern gradation value.

  When the camouflage pattern is not used, all the gradation values A of the camouflage pattern may be set to white (255). In this case, by setting the size of the camouflage pattern to one pixel, the memory capacity of the camouflage pattern can be minimized.

  Next, according to the latent image portion mask pattern, for the background portion pixels, the background portion screen 34 such as an area modulation (AM) screen having a high number of halftone lines or a density modulation (FM) screen by error diffusion or distributed dither matrix. The screening process is performed (S4). For example, with respect to the corrected camouflage pattern gradation value, image data having pixel dots on or off is generated with reference to a dither matrix constituting the background screen 34.

  Furthermore, according to the latent image portion mask pattern, the latent image portion image is also subjected to a screening process using a latent image portion screen 33 such as an area modulation (AM) screen having a low number of halftone lines (S5). However, in the latent image portion screening process, special screening processing is performed in which the center of a dot-concentrated halftone dot is formed at the center of gravity of the image of the latent image portion in the cell corresponding to the halftone dot formation region. Do. This special screening process will be described in detail later. By performing a special screening process on the latent image part with a low number of halftone lines, a high density emphasis region and a low density area at the boundary between the latent image part and the background part are obtained. The emphasis area can be suppressed. Furthermore, the appearance of the camouflage pattern can be made equal between the latent image portion and the background portion.

  The latent image portion screen 33 is preferably an AM screen having a low number of halftone lines, and is a dot concentration type dither matrix such as a threshold matrix or a gradation conversion matrix. The background screen 34 is preferably an AM screen having a higher number of dotted lines than the latent image screen, and is a dot dispersion type dither matrix such as a threshold matrix or a gradation conversion matrix. Alternatively, the background screen 34 may be a density modulation (FM) screen using an error diffusion method or a distributed dither matrix. As an original function of the tint block image, the latent image portion and the background portion need to have different output densities reproduced at the time of copying. Therefore, a screen that can realize this is required.

  Through the above rough processing, the ground pattern data with a camouflage pattern or the ground pattern data 37 without a camouflage pattern can be generated.

  Hereinafter, a procedure for generating the background pattern data with a camouflage pattern in the present embodiment will be described in detail.

[Latent image part dither matrix and background part dither matrix]
FIG. 10 is a diagram showing an example of the background screen and the latent image screen in the present embodiment. FIG. 10 shows, as an example of a background screen and a latent image screen for generating images of the background portion BI of the background pattern and the latent image portion LI, a low-line-number AM screen and a high-line-number AM having a distributed shape. A screen dither matrix is shown.

  The background portion basic dither matrix DM-BI in FIG. 10A is a dot dispersion type dither matrix having threshold values 1 to 8 for each element of the 4 × 4 matrix. The threshold “1” is assigned to the element at the position of the displacement vector (−2, 2), (2, 2), the threshold “2” is arranged at a position separated from the element of the threshold “1”, 8 "is placed between them. In the copy-forgery-inhibited pattern image forming process, the input gradation value of the background portion is compared with the threshold value of each element of the background portion basic dither matrix DM-BI. If the input gradation value is equal to or greater than the threshold value, a dot is formed in that pixel. The For the background portion basic dither matrix DM-BI in FIG. 10A, the input gradation value is set to “1”, and the second dot D2 is formed at the black pixel position with the threshold value “1”. Is done. The enlarged view is shown in the background portion BI of FIG. 4A, and the background portion BI has minute dots D2 formed by the number of halftone dots 212 lpi.

  On the other hand, the latent image portion basic dither matrix DM-LI in FIG. 10B is one of the dot concentration type dither matrix having threshold values 1 to 128 of each element of the 32 × 32 matrix, that is, an AM screen. The threshold “1” is assigned to the element at the position of the displacement vector (−8, 8) (8, 8), and corresponds to the center position of the first dot (halftone dot) D1. The threshold values “2 to 128” are distributed in order from the threshold value “1” corresponding to the center position of the first dot (halftone dot) D1. In the copy-forgery-inhibited pattern image forming process, the input tone value of the latent image portion and the threshold value of each element of the latent image portion basic dither matrix DM-LI are compared. If the input tone value is equal to or greater than the threshold value, a dot is formed at that pixel. Is done. For the latent image portion basic dither matrix DM-LI in FIG. 10B, when the input gradation value “31” is set, a dot is formed at the element position of the threshold value “1 to 31”, and a large dot is formed. (Halftone dot) D1 is formed. An enlarged view thereof is shown in the latent image portion LI of FIG. 4A, and a large dot D1 is formed with a dot number of 53 lpi.

  The background portion basic dither matrix DM-BI may be a dot concentration type dither matrix that forms minute halftone dots in the same manner as the latent image portion basic dither matrix DM-LI. However, the halftone dot size generated in the background portion is required to be smaller than the halftone dot size in the latent image portion.

  As described above, the background pattern is required to maintain high concealment capability of the latent image by making the output density of the background portion and the latent image portion equal in the original. Further, in a copied material, it is required to increase the difference in output density between the background portion and the latent image portion and to increase the output density of the latent image portion so that the latent image can be distinguished. The large first dots D1 are less likely to disappear in the copy, while the smaller second dots D2 tend to disappear in the copy. As a result, the output density during copying differs between the latent image portion and the background portion.

  However, the image formed by the dither matrixes DM-BI and DM-LI shown in FIG. 10 has a low output density region used for the background pattern, for example, an output density region of 10 to 15%, the number of output density gradations (resolution). ) Is limited. In the basic dither matrix DM-BI for the background portion, the minute dot D2 is formed at the position of the threshold value “1”, so that the background portion is formed with the output density corresponding to it. On the other hand, in the latent image portion forming step, an input gradation value that can generate the same output density as that of the background portion is selected, and the input gradation value is compared with the latent image portion basic dither matrix DM-LI. As a result, an image of the latent image portion is formed. However, since the number of gradations (resolution) of the output density of the latent image portion LI is limited as described above, an output density that matches the output density of the background portion cannot always be formed in the latent image portion LI. .

  FIG. 11 is a diagram showing characteristics of input gradation and output density of the background portion basic dither matrix DM-BI and the latent image portion basic dither matrix DM-LI. For the characteristics shown in FIG. 11, for the sake of simplicity, the number of dots formed in pixels having a threshold value equal to or lower than the input gradation in the basic dither matrix and the output density of the tint block image generated by the printer engine are ideal. It is assumed that there is a linear relationship.

  The copy-forgery-inhibited pattern image generating apparatus uses the latent image portion basic dither matrix DM-LI shown in FIG. 10B as the latent image portion dither matrix 33 and the background portion basic dither shown in FIG. When the matrix DM-BI is used, the characteristics of the output density according to the input gradation value and the corresponding latent image portion image data and background portion image data are as shown in FIG. That is, in the case of the background portion, when the output density OUT includes “0” with respect to the input gradation value IN = 0 to 7, eight output density values can be taken. That is, the number of gradations (or resolution) of the output density from paper white where all pixels are dot off to the maximum output density where all pixels are dot on is 8. Then, as shown in FIG. 10A, in the background portion, for the input gradation value IN = 1, the minute second dots D2 dispersed at the pixel positions of the threshold value “1” of the dither matrix DM-BI. Become an image. On the other hand, in the case of the latent image portion, if the output density OUT includes “0” with respect to the input gradation value IN = 0 to 127, it can take 128 output density values. That is, the number of gradations (or resolution) of the output density from paper white to the maximum output density is 128.

  However, the output density corresponding to the input gradation IN = 1 in the background portion is located between the two output densities corresponding to the input gradation In = 12, 13 in the latent image portion. For this reason, the output density cannot be equal between the background portion and the latent image portion.

  The output density range employed as the copy-forgery-inhibited pattern image is 10% to 15% of the maximum output density. In the range of 10 to 15% output density, the number of output density gradations that can be reproduced by the latent image portion basic dither matrix is about 20 gradations at most. Therefore, even if the number of halftone lines in the latent image portion dither matrix is reduced and the number of gradations of the output density of the latent image portion is increased, the output can be adjusted by changing the input gradation value of the latent image portion by one step. Since the amount of change in density becomes larger than a certain level, it is difficult or impossible to match the output density of the latent image portion with the output density of the background portion with high accuracy.

  In addition, the background dither matrix size can be doubled or quadrupled to increase the number of gradations in the background output density, and the output density of the tint block image can be changed within a range of 10 to 15%. Even in this case, for the same reason as described above, it is difficult or impossible to match the output density of the background portion and the output density of the latent image portion with high accuracy.

  FIG. 12 is a diagram illustrating an example in which the concealment property of the latent image in the original is deteriorated. Regarding the latent image mask pattern “copy” in FIG. 12A, FIG. 12B shows a copy-forgery-inhibited pattern image when the input gradation value of the latent image portion is “12”, and FIG. 12C shows the latent image portion. A tint block image when the input gradation value is “13” is shown. In FIG. 12B, the output density of the latent image mask pattern is lower than that of the background portion, and the concealability of the latent image “copy” is lowered. Similarly, in FIG. 12C, the output density of the latent image mask pattern is higher than that of the background portion, and similarly, the concealability of the latent image “copy” is lowered.

  Therefore, in the present embodiment, the background portion dither matrix and the latent image portion dither matrix are generated based on the basic dither matrix in FIG. 10, and the output density is 0 to 15 with respect to the input gradation values 0 to 255, for example. A dither matrix having a characteristic of increasing in a low concentration region of about% is adopted.

  FIGS. 13 and 14 are diagrams showing a low density area expanded dither matrix 33 for a latent image portion and a low density area expanded dither matrix 34 for a background portion, which are employed in the present embodiment. FIG. 15 is a diagram showing output density characteristics with respect to input gradation values of the latent image portion dither matrix 33 and the background portion dither matrix 34.

  The basic dither matrices DM-BI and DM-LI in FIG. 10 are enlarged in size until the number of gradations is sufficient. For example, it is expanded to a matrix size of 128 × 128. However, in FIG. 13 and FIG. 14, a 32 × 32 matrix size is shown for convenience. Then, all the threshold values of the enlarged dither matrix are distributed and diffused so that all the threshold values are different in the order in which dots are generated corresponding to the increase of the input gradation value. This is called a diffusion dither matrix.

  Next, a background portion and a latent image portion for a plurality of input gradation values are printed by a printer using a diffusion dither matrix, and an output density is measured by a colorimeter. Based on the measurement result of the output density, the threshold value is corrected so that an ideal output density characteristic, for example, a linear characteristic, is obtained with respect to the input gradations 0 to 255. This correction is the same as the correction performed in the normal calibration process of the screen gamma table. As a result, a corrected diffusion dither matrix is generated.

  Finally, the low-density area expanded dither matrices 33 and 34 are generated by multiplying the threshold value of the corrected diffusion dither matrix by 15/100 so that about 15% of the maximum output density becomes the maximum value. That is, when the screening process is performed using the low-density area expanded dither matrix, the output density characteristic is such that the output density increases only up to about 15% with respect to the input gradations 0 to 255.

  In the low density area expanded dither matrix 33 of the latent image portion in FIG. 13, the elements (black elements) at the positions of the displacement vectors (−8, 8) and (8, 8) are given thresholds 1 to 7, Threshold values 8 to 254 are given to gray (or white) elements around. That is, black and surrounding gray (or white) pixels correspond to the maximum size of the first dot D1. A threshold value 255 is given to the other elements. In this case, dots are generated in pixels with a threshold value lower than that for input gradations 0 to 254, but for the input gradation 255, pixels with threshold values are controlled to be dot off. Alternatively, the input gradation 255 is prohibited in the latent image portion.

  Therefore, by using the low density area expansion dither matrix 33 of the latent image portion, the first dot D1 is displaced from the input tone 0 to 255 in the latent image portion by the displacement vector (−8, 8). , (8, 8), the minimum size due to the element at the position, and the maximum size due to the black and gray (or white) element. Since the output density at the maximum size of the first dot D1 is 15% of the solid black, the output density changes from 0 to 15% with respect to the input gradation 0 to 255. Therefore, it has a large number of gradations (254 gradations) in the output density range of 0 to 15%.

  In the latent image portion basic dither matrix DM-LI in FIG. 10B, threshold values 1 to 31 are given to the gray elements in which the first dot D1 of the maximum size is generated. On the other hand, in the low density area expanded dither matrix 33 of the latent image portion in FIG. 10, threshold values 1 to 254 are given to the gray (or white) elements in which the first dot D1 of the maximum size is generated. Yes. That is, the number of gradations (resolution) of the output density is remarkably increased. Therefore, the resolution in density adjustment is increased, and the output density of the latent image portion can be adjusted to the same output density as the background portion with high accuracy.

  The low density region expanded dither matrix 34 in the background portion of FIG. 14 is given threshold values 1 to 254 distributed to the elements at the positions of the displacement vectors (−2, 2) and (2, 2), and the other elements. Is given a threshold of 255. Also in this case, for input gradations 0 to 254, a dot is generated in a pixel corresponding to an element having a threshold value lower than that. However, for convenience, for input gradation 255, the threshold pixel is set to dot off. Be controlled. Alternatively, the input gradation 255 is prohibited in the background portion.

  If this background low density area expanded dither matrix 34 is used, a minute dot D2 is applied only to the pixels at the positions of the displacement vectors (-2, 2) and (2, 2) with respect to the input gradation values 0 to 255. Are sequentially generated, and dots are not generated for other pixels. Therefore, the background image has only the minute dots D2 dispersed at the position of the number of halftone lines 212 lpi, and no more dots are formed. When the minute dot D2 is generated in all the pixels at the positions of the displacement vectors (−2, 2) and (2, 2), the output density is about 12% of the black solid. That is, in the low density area expanded dither matrix 34 in the background portion, the output density increases or decreases within the range of 0 to about 12% with respect to the input gradations 0 to 255. As a result, a stable arrangement of minute dots that can maximize the characteristics of the background is assured.

  FIG. 15 shows output density characteristics with respect to input gradation values of the low density area expanded dither matrices 33 and 34 shown in FIGS. As described above, the output density characteristic with respect to the input gradation value of the dither matrix 34 in the background portion is in the range of 0 to about 12% with respect to the input gradation 0 to 255. On the other hand, the output density characteristic with respect to the input gradation value of the dither matrix 33 of the latent image portion is in the range of 0 to 15% with respect to the input gradation 0 to 255. In both cases, the output density has a linear relationship with a simple increase with respect to the input gradation value by calibration.

  The above is the description of the dither matrices 33 and 34 constituting the background screen and the latent image screen in the present embodiment.

[Generation method of copy-forgery-inhibited pattern image data]
Hereinafter, a method for generating copy-forgery-inhibited pattern image data with a multi-tone camouflage pattern according to the present embodiment will be described.

  FIG. 16 is a flowchart showing a method of generating copy-forgery-inhibited pattern image data in the present embodiment. The printer user selects a copy-forgery-inhibited pattern generation menu in the printer driver 32 of the host computer 30, and executes generation of copy-forgery-inhibited pattern image data according to the flowchart of FIG. First, the user inputs the text of the background pattern (S10). For example, words such as “copy”, “copy”, and “confidential”. Further, the size of the tint block word such as 48 points is input (S11), the angle of the tint block word such as 40 degrees is input (S12), and the tint block effect and arrangement are selected (S13). The copy-forgery-inhibited pattern effect is one in which the wording is white (the wording is white and the surrounding is black) or the wording is black (the wording is black and the surrounding is white). In the case of white, the wording becomes the latent image portion around the background portion, and in the case of the relief, the wording becomes the latent image portion and the surrounding portion becomes the background portion. In addition, the arrangement of the tint block includes a square arrangement, a diagonal arrangement, a reverse arrangement, and the like.

  FIG. 17 is a diagram illustrating an example of the tint block effect. The copy-forgery-inhibited pattern patterns 50 and 51 are examples of the copy-forgery-inhibited pattern effect in which the wording is “copy” and “copy” and the wording appears in the original or a copy. The copy-forgery-inhibited pattern patterns 52 and 53 are examples of the copy-forgery-inhibited pattern effect in which the same wording is used to white out the original or a copy. In both cases, the wording angle is set to 40 degrees.

  FIG. 18 is a diagram illustrating an example of the arrangement of a background pattern. In all cases, the wording is “copy”, the angle is 40 degrees, and the tint block effect is revealed. (A) In the square arrangement, a tint block image is generated so that the latent image mask pattern is pasted in a tile shape. (B) In the oblique arrangement, the latent image mask pattern is arranged so as to be shifted by a predetermined phase for each line feed. (C) In the reverse arrangement, the latent image mask pattern is arranged upside down at each line feed.

  When the input or selection by the user is completed in steps S10 to S13, the printer driver 32 generates a latent image mask pattern (S14). As shown in FIG. 17, the example of the latent image mask pattern is composed of 1-bit data capable of distinguishing the latent image area from the background area.

  Next, the printer driver 32 sets the input gradation value of the tint block image (S16). When the latent image portion dither matrix 33 and the background portion dither matrix 34 shown in FIGS. 13 and 14 are used, the background portion has an input gradation value of “255” as the maximum value, and the latent image portion has an output of the background portion. An input gradation value In = 170 that matches the density (12% of the solid black) is selected. That is, in the background portion, the input gradation value is set to “255”, so that the black values at the positions of the displacement vectors (−2, 2) and (2, 2) of the background portion dither matrix 34 (FIG. 14) are very small. Dot D2 is generated. The output density at this time is 12% of the black solid, and the dispersed second minute dots are generated to the maximum, so that the output density becomes high and is optimal as a tint block image. On the other hand, in the latent image portion, by setting the input gradation value In = 170, a halftone dot composed of pixels corresponding to black elements and gray (or white) elements of the latent image portion dither matrix 33 (FIG. 13). A number of dots corresponding to In = 170 are generated in the region. As a result, a large dot D1 having a size corresponding to the input gradation value In = 170 is formed.

  As shown in the output density characteristics of FIG. 15, the latent image portion dither matrix 33 and the background portion dither matrix 34 of FIGS. 13 and 14 have different output density characteristics with respect to the input gradation. That is, the gradient of the output density with respect to the input gradation is larger in the latent image portion dither matrix. Therefore, when the input gradation “255” capable of reproducing the optimum output image in the background portion is selected, the input gradation In = 170 whose output density matches that is selected in the latent image portion.

  The printer driver 32 acquires camouflage pattern data in response to the user's selection request (S17). Camouflage pattern data is stored in a memory in the host computer or in an external memory, and the camouflage pattern data is acquired in response to a user's selection request.

  Further, the printer driver 32 selects a tint block color (black, cyan, magenta, etc.) in response to a user's selection request (S18). The tint block color should be a single color.

When S10 to S17 such as the above input by the user are completed, the printer driver 32 executes a tint block image generation process (S19). The copy-forgery-inhibited pattern image generation processing is performed according to the flowcharts of FIGS.

  19 and 20 are flowcharts of the tint block image generation processing in the present embodiment. The tint block image generation processing S19 of FIG. 16 is shown in the flowcharts of FIGS. First, the corrected camouflage pattern data is generated by correcting the gradation value of the camouflage pattern data based on the input gradation values of the latent image portion and the background portion (S21). This procedure corresponds to procedure S3 in FIG. That is, when the gradation value of the camouflage pattern is A (0, 255) and the input gradation of the latent image portion and the background portion constituting the tint block is In (1 ≦ In ≦ 254), the gradation value of the corrected camouflage pattern Ai is calculated by the aforementioned equation (1). When the camouflage pattern is not used, the gradation value of the camouflage pattern is set to “255”, and the corrected camouflage pattern gradation value becomes equal to the input gradation value In by the calculation of the above-described equation (1).

  In step S16 of setting the input gradation value of the tint block image in FIG. 16, the input gradation is set to “255” in the background portion, and the input gradation is set to In = 170 in the latent image portion. When different input gradations are set for the background portion and the latent image portion in this way, the latent image portion and the background portion are calculated according to the latent image mask pattern in the calculation of the corrected camouflage pattern gradation data according to the above equation (1). Therefore, it is necessary to change the input gradation In to be modulated. This is because the latent image portion dither matrix 33 and the background portion dither matrix 34 have different output density characteristics as shown in FIG.

  Therefore, in this embodiment, in order to simplify the calculation, the input gradation is shared by In = 170 in both the latent image portion and the background portion. However, the background portion dither matrix 34 is normalized so that the maximum output density (12%) is obtained at the input gradation In = 170 (for example, FIG. 22), and screening processing is performed with reference to the normalized background portion dither matrix. .

  Alternatively, as described in a modification of the embodiment described later (FIG. 37), the maximum gradation value (for example, 255) that can take the input gradation in both the latent image portion and the background portion is set. The image portion dither matrix 33 is normalized so that the input gradation value “255” has an output density (12%) corresponding to the input gradation value In = 170. That is, the input tone values 0 to 170 and the output density characteristics of the latent image portion dither matrix 33 in FIGS. 13 and 15 are normalized to the input tone values 0 to 255.

  Hereinafter, a case where the input gradation In is set to 170 will be described. In step S21, the gradation value data of the corrected camouflage pattern is calculated based on the expression (1) for the input gradation In = 170. Then, the printer driver 32 normalizes the background portion dither matrix 34 of FIGS. 14 and 15 to generate a normalized background portion dither matrix (S22).

  FIG. 21 is a diagram showing a normalized background portion dither matrix 34N. The threshold values 0 to 245 of the black elements at the positions of the displacement vectors (−2, 2) and (2, 2) in the background portion dither matrix 34 of FIG. 14 are changed to new threshold values 0 to 170 (= Normalize to In).

Normalization threshold = (threshold / 254) × In (2)
Therefore, in the normalized background portion dither matrix 34N in FIG. 21, the threshold value of the black element is replaced with 0 to 170, and when the input gradation value is “170”, dots are formed in the pixels corresponding to all the black elements, and the maximum The output density (12% of solid black) is obtained.

  FIG. 22 is a diagram showing the input / output density characteristics of the normalized background portion dither matrix, the background portion dither matrix before normalization, and the latent image portion dither matrix. The output density characteristics of the background portion dither matrix 34 and the latent image portion dither matrix 33 are the same as those in FIG. In the above-described example, the input gradation “255” for generating dots in all the pixels corresponding to the elements on the displacement vector is adopted in the background portion, and the input gradation value In == 170 was adopted. Therefore, in order to adopt the input gradation value In = 170 in the background portion, the background portion dither matrix 34 is normalized by the input gradation In = 170, and the normalized background portion indicated by the broken line characteristic 34N in FIG. A dither matrix 34N is generated. The normalized background dither matrix 34N can be easily generated by the calculation according to the above equation (2).

  In some cases, the input gradation value In of the latent image portion varies depending on the aging of the engine. Therefore, it is possible to absorb the secular change by generating the normalized background dither matrix 34N using the input gradation value In that is changed at the same time.

19 and 20, the corrected camouflage pattern gradation data is subjected to a screening process with reference to the latent image portion dither matrix 33 or the normalized background portion dither matrix 34N according to the latent image mask pattern, and the background pattern with the camouflage pattern is obtained. Generate image data (
S23 to S41). The camouflage pattern-attached copy-forgery-inhibited pattern image data is image data indicating the presence or absence of dots for each pixel. The screening process is performed for each cell that defines the halftone dot generation region of the latent image portion dither matrix 33.

  The latent image portion dither matrix 33 shown in FIG. 13 includes eight cells CELL that do not overlap with the black element of the two displacement vectors (8, 8) and (−8, 8) as the center (halftone dot center). Yes. A large dot D1, which is a halftone dot, is formed in each cell CELL. In the cell CELL shown in the latent image portion dither matrix 33 in FIG. 13, when the upper left element of the latent image portion dither matrix 33 is the origin (0, 0), the black element (0, 0) indicated by D1 is displayed. ), (16, 0), (8, 8), (8, 24), (0, 16), (16, 16), (8, 24), (24, 24). Eight rhombus regions each consisting of 128 elements. Cell regions A to H are shown in the matrix showing the latent image mask pattern 10 of FIG. The areas other than A to H form cells together with the adjacent dither matrix side area. The cell CELL is also shown in the normalized background portion dither matrix 34N of FIG.

  FIG. 23 is a diagram for explaining the tint block image generation processing of FIGS. FIG. 23A shows a tint block image in which a plurality of latent image mask patterns 10 are squarely arranged in a print size 60 of A4. In the case of the A4 size, the number of pixels is 4720 dots in the horizontal direction and 6776 dots in the vertical direction. FIG. 23B shows the positional relationship between the latent image mask pattern 10 in the upper left of FIG. 23A and the camouflage pattern 12 arranged in a tile shape. The latent image mask pattern 10 is a square pattern having 2030 dots in the horizontal direction and 2030 dots in the vertical direction. On the other hand, as shown in FIG. 23C, the camouflage pattern 12 is a square pattern having 215 dots in the horizontal direction and 215 dots in the vertical direction.

  FIG. 23 (D) is an enlarged view of the upper left end region of FIG. 23 (C). Each of the latent image portion dither matrix 33-4 and the background portion dither matrix 34-5 is a matrix of 32 cells × 32 cells, and is made to correspond to the pixels so as to be attached in a tile shape in order from the upper left. However, in the latent image portion screening process, as will be described in detail later, the latent image portion dither matrix is shifted and associated with the barycentric position in the cell so that the dot center of the dither matrix overlaps.

  Then, the printer driver compares the gradation value of the correction camouflage pattern with the threshold value of the dither matrix 33-4, 34-5. If the gradation value is equal to or greater than the threshold value, the pixel dot is ON, and the gradation value is less than the threshold value. If so, the pixel dot is turned off. However, the gradation value of the correction camouflage pattern is set so that only 0 to 254 can be taken. Alternatively, when the input gradation value is 255, uniform pixel dots are turned off. The dither matrix to be compared is selected corresponding to black or white of the latent image mask pattern.

  The copy-forgery-inhibited pattern image generation processing in this embodiment is performed for each cell (S23, S40, S41), background portion screening processing (S25 to S28 in FIG. 19), and latent image portion screening processing (S30 to S39 in FIG. 20). ), And each screening process is different. Therefore, first, cell No = 0 is set as an initial value (S23).

[Background screening]
The background screening process shown in FIG. 19 will be described. First, if the latent image mask pattern is not black for pixel (i, j) (NO in S24), that pixel is the background portion, so the corresponding camouflage pattern gradation value In and the corresponding element of the normalized background portion dither matrix 34N Is compared with the threshold value (S25). If the correction gradation value Ai is equal to or greater than the threshold value, the copy-forgery-inhibited pattern image data (i, j) is ON (S26), and if the correction gradation value Ai is less than the threshold value, the copy-forgery-inhibited pattern image data (i, j) is dot OFF. (S27). On the other hand, if the latent image portion mask pattern is black (YES in S24), since it is a latent image portion, nothing is done at this time. The above processing is performed for all the pixels in the cell (S28), and each pixel in the background portion in the cell is turned ON or OFF.

  With the above processing, the number of second dots corresponding to the corrected camouflage pattern gradation value Ai in the background portion in the cell corresponds to the black element at the position of the displacement vectors (−2, 2) and (2, 2). Generated on the pixel.

[Latent image screening]
Next, the screening process of the latent image portion in the cell is performed according to the flowchart of FIG. Since the screening process of the latent image part is more complicated than the background part, it will be described with a specific example. In addition, the latent image portion screening process is similar to the process described in the patent document WO2005 / 109851.

  FIG. 24 is a diagram illustrating an example of a latent image mask pattern. A latent image mask pattern 10 is formed in a 32 × 32 matrix. The inside of the pattern 10A corresponds to the latent image portion, and the outside of the pattern 10A corresponds to the background portion. Therefore, the matrix data of the latent image mask pattern has 1 bit of “0” (latent image portion) or “1” (background portion) in each pixel of the 32 × 32 matrix. Further, the latent image portion mask pattern 10 shows eight cells A to H.

  FIG. 25 shows corrected camouflage pattern gradation value data Ai. In order to facilitate understanding, a gradation value Ai is written in each element of the 32 × 32 matrix. This specific example is an example in which the camouflage pattern is not used. Therefore, the corrected camouflage pattern gradation value Ai is equal to the input gradation value In = 170 according to the equation (1).

Returning to the flowchart of FIG. 20, first, the gravity center position in the cell is calculated for the latent image portion image (S30). The barycentric coordinates (X (center of gravity), Y (center of gravity I)) in the cell are calculated by the following equations (3) and (4). Here, “the gradation value of the pixel” and “the gradation value in the cell” are the corrected camouflage pattern gradation value Ai for the pixel of the latent image portion indicated by the latent image mask pattern and the gradation of the pixel of the background portion. The value 0 is given.
X (centroid) = Σ {(X coordinate of each pixel) × (gradation value of each pixel)} / total of gradation values in the cell (3)
Y (centroid) = Σ {(Y coordinate of each pixel) × (gradation value of each pixel)} / total of gradation values in the cell (4)
In the example of FIG. 25, the coordinates of the center of gravity G of the image of the latent image portion in the cell CELL (C) are (2.7, 2.5).

Next, the average input gradation value in the cell is calculated (S31). This calculation is based on the following equation (5). Here, the “pixel gradation value” gives a corrected camouflage pattern gradation value Ai for the pixels in the latent image portion indicated by the latent image mask pattern, and a gradation value 0 for the pixels in the background portion. The number of elements in the cell is 128.
Average input tone value = Σ (tone value of each pixel) / number of elements in the cell (5)
In the corrected camouflage pattern gradation value Ai of FIG. 25, the cell CELL (C) will be described as a specific example. There are 46 gray elements indicating the latent image portion (latent image mask pattern 10A) in the cell CELL (C). Yes, since the gradation value Ai of each element is 170, the average input gradation value is 46 × 170/128 = 61.09 according to the above equation (5).

  Next, assuming that the average input gradation value “61.09” is input to all the pixels in the cell, a dot generated by comparing the average input gradation value and the threshold value of the latent image portion dither matrix 33. Count the number. This number of dots becomes the ideal number of output dots indicating the upper limit value of the number of dots to be generated in the latent image portion in the cell (S32). This is because the average input gradation value corresponds to the output density in the latent image portion in the cell.

  FIG. 26 is a diagram for explaining the ideal output dot count process. Each pixel in the cell CELL (C) has an average input gradation value “61”. Then, the central element of the latent image portion dither matrix 33 is associated with the central pixel of the cell CELL (C), and the threshold value of the latent image portion dither matrix 33 is compared with the average input gradation value “61”. The ideal number of output dots satisfying the input gradation value ≧ the latent image portion dither matrix threshold is 8.

  Next, the latent image portion dither matrix 33 is shifted so that the halftone dot center element of the latent image portion dither matrix 33 coincides with the position of the center of gravity G (S33), and the corrected camouflage pattern gradation value Ai and the latent image portion dither matrix are shifted. The threshold value of 33 is compared (S34, S35), the dot on (S36) is performed for the pixel of Ai ≧ threshold, the dot off (S37) is screened for the pixel of Ai <threshold, and the number of generated dots is the ideal output. The process is repeated until either the number of dots (= 8) is reached (YES in S38) or the pixel in the cell is completed (YES in S39).

  Here, the latent image portion dither matrix 33 is shifted so that the halftone dot center element of the latent image portion dither matrix 33 coincides with the position of the center of gravity G. However, in the latent image in the cell, from the center of the cell. You may shift so that the halftone dot center element of the latent image portion dither matrix 33 may coincide with the shifted position.

  That is, as shown in FIG. 25, the gravity center G of the latent image portion in the cell CELL (C) is associated with the halftone dot center element of the latent image portion dither matrix 33, and correction is performed in the order from the halftone dot center (centroid). The camouflage pattern gradation value Ai = 170 is compared with the threshold value of the latent image portion dither matrix 33. Then, dots are generated in the pixels of Ai ≧ threshold value. However, the number of dots generated in a cell is limited to the ideal number of output dots.

  The screening process in the latent image portion has the following merits. First, the average of the input gradation values in the latent image portion in the cell is obtained to obtain the ideal output dot number, the halftone dot center element of the dither matrix is shifted to the center of gravity position of the latent image portion image, and the ideal output Since dots are generated with the upper limit of the number of dots, the density of the latent image portion is reliably reproduced. Second, since the dot center element of the dither matrix is shifted to the position of the center of gravity, it is possible to generate dots (first dots D1) concentrated at the position of the center of gravity of the latent image portion in the cell. The first dot D1 in the portion and the second dot D2 in the background portion are not combined. Third, since the dot center element is shifted to the position of the center of gravity, even if the camouflage pattern of the background portion and the dot off occupies the center region of the cell, dots are generated in the latent image portion in the cell. The low density emphasis area is not generated at the boundary with the background portion.

  Then, the background screening process (S25 to S28 in FIG. 19) and the latent image screening process (S30 to S39 in FIG. 20) are repeated for all cells (S40).

  The synthesis of the generated tint block image data and the image data 36 to be printed is as follows.

  After the image data to be printed is converted from RGB bitmap data having RGB gradation values to CMYK bitmap data that is the color of the printer, the user specifies the CMYK bitmap data of the image data to be printed A tint block image is synthesized with the bitmap data of the tint block color (in this embodiment, any one of cyan, magenta, and black).

  In this synthesis method, first, the dot ON data of the tint block image is converted into a gradation value corresponding to the maximum density of the bitmap data, and the dot OFF data corresponds to the minimum density “0” of the bitmap data. Convert to gradation value. When the RGB value for each pixel in the printer is an 8-bit gradation value for each color, the gradation value corresponding to the maximum density is “255” and the gradation value corresponding to the minimum density is “0”. A pixel having a gradation value larger than the gradation value “0” in the bitmap data of the background pattern designation color of the image data to be printed is added to the background pattern image data converted to the maximum gradation value or the minimum gradation value. Overwrite the gradation data. As a result, a copy-forgery-inhibited pattern image is formed in the pixel of the gradation value “0” of the image to be printed, and the image to be printed is formed in the other pixels.

  Alternatively, another composition method overwrites the copy-forgery-inhibited pattern image data on the bitmap data of the copy-forgery-inhibited pattern specified color of the image data to be printed. For example, when the print target image data is data that forms a black character, the CMY bitmap data has a gradation value of “0” for all pixels. Therefore, since the bitmap data of the background pattern designated color in CMY does not have information as the image data to be printed, all the bitmap data of that color are replaced with the background pattern image data.

  The composition method is not limited to the above-described overwriting, and based on the image type (text, image, graphic, etc.) for each pixel of the image data to be printed and the gradation value, the image to be printed and the copy-forgery-inhibited pattern image are determined in advance. Blending processing may be performed at a ratio. Furthermore, among the bitmap data of the tint block designation color, all the CMYK data have the gradation value of the data to be printed being “0”, that is, the tint block data is overwritten only on the portion of the print target image data where no image is formed on the print medium. You may make it do.

  The synthesized image data is printed on a print medium through binarization processing (screen processing) of a normal printer.

  Of the synthesized image data, the portion consisting only of the copy-forgery-inhibited pattern image is composed of pixels having gradation values consisting of the maximum density gradation value and the minimum gradation value. In such a case, even after the screen processing, the portion of the highest density “255” is subjected to gradation conversion so that the density value is stored, and the portion of the minimum density “0” is set to “0”. Tone conversion is performed. As a result, the background pattern image generated by the background pattern generation process is printed on the print medium.

[Example of background pattern image without camouflage pattern]
FIG. 27 is a diagram illustrating an example of a tint block image generated by the screening process according to the present embodiment. Through the processes S24 to S28 in FIG. 19, the dispersed dot D2 having a high number of halftone lines is generated in the background portion BI. By the process in FIG. 20, the latent image portion LI has a large number of low halftone lines in each cell. Dot D1 is generated. In the latent image portion LI in the one-dot chain line circle, a large dot D1 having a size corresponding to the output density of the latent image in the cell is reproduced for each cell at the center of gravity of the latent image in the cell. The As a result, in the cell F, a large dot D1 (F) of a size (19 dots) corresponding to the input gradation value 170 is generated at the center of the cell, and the inside of the surrounding cells C, D, E, G, H The smaller large dots D1 (C), D1 (D), D1 (E), D1 (G), and D1 (H) are generated at positions shifted from the center of the cell (center of gravity position). However, these large dots make the shape of the latent image LI closer to the latent image mask pattern.

  FIG. 28 is a diagram showing an example of a tint block image generated by a general screening process in which both the latent image portion and the background portion are referred to the dither matrices 33 and 34N. That is, it is a result of screening processing in which all the cells are associated with the center pixel of the cell and the halftone dot center element of the latent image portion dither matrix. As apparent from comparison with FIG. 27, in FIG. 28, the dots D1 (C), D1 (D), D1 (G), and D1 (H) generated in the cells C, D, G, and H are shown in FIG. It is smaller than that and is formed near the boundary with the background portion BI. Further, no large dot D1 is generated in the cell E. As a result, in the boundary region, the small dot D2 in the background portion BI and the large dot D1 in the latent image portion are combined to form a high density emphasis region (cells C, D, G, H), or the large dot D1 is A low concentration emphasis region (cell E) is formed without being generated.

[Example of tint block image with camouflage pattern]
FIG. 29 is a diagram illustrating an example of a camouflage pattern. This example is a camouflage pattern CAM composed of two bands extending in the horizontal direction. In the black part, the dots of the background pattern are turned off.

  FIG. 30 is a diagram showing corrected camouflage pattern gradation values, and corresponds to FIG. When the corrected camouflage pattern gradation value Ai is obtained by reflecting the camouflage pattern of FIG. 29, the area of the camouflage pattern CAM is Ai = 0, and the other areas are Ai = In = 170. FIG. 30 shows the relationship among the cell CELL, the latent image mask pattern 10A, and the correction camouflage pattern gradation value in a 32 × 32 matrix.

  In the background area, the small dot D2 is formed at the halftone dot center position in accordance with the normalized background portion dither matrix 34N. In the area of the latent image portion, the center of gravity position of the latent image portion in the cell is obtained according to the procedure shown in FIG. 20, the average input gradation value is calculated, the number of ideal output dots is counted, and the center of gravity position G is obtained. The center of the halftone dot of the latent image portion dither matrix is shifted, the corrected camouflage pattern gradation value is compared with the threshold value of the shifted latent image portion dither matrix, and the dot on / off of the pixel is determined.

  FIG. 31 is a diagram showing an example of a tint block image generated by the screening process of the present embodiment for the corrected camouflage pattern threshold value of FIG.

  First, in the cell A, all pixels are screened as a background portion. Here, since the threshold value of the dither matrix in the background portion is normalized by the input gradation value as shown in FIGS. 21 and 22, as a result, the dot D2 is generated only at the halftone dot center of the background portion.

  Subsequently, in cell B, although there is a latent image portion area, the corrected camouflage pattern gradation value of the latent image portion is “0” due to the camouflage pattern, so that the dot D2 is generated only in the background portion.

  Next, in cell C, corrected camouflage pattern gradation values are generated in the background portion and the latent image portion, and the background portion is processed in the same manner as in cells A and B. On the other hand, for the latent image portion, the centroid position is X centroid = 1.1, Y centroid = 4.6, and the average input tone value is 29. Therefore, when the threshold value of the latent image portion dither matrix 33 in FIG. 13 is compared with the average input gradation value “29”, the ideal number of output dots to be generated is “4” dots. Therefore, if the latent image part dither matrix is moved to the center of gravity, and the input gradation is set to 170 and screening processing is performed in the order of the pixels closest to the center of gravity, the dots of the four pixels at the center, bottom, right, and left are turned on and the number of ideal output dots The process ends when “4” is reached. That is, a large dot D1 (C) composed of four pixel dots is generated in the latent image portion LI in the cell CELL (C).

  Similarly, in the cell D, the corrected gradation value is generated at the position indicating the background portion and the latent image portion. In particular, for the latent image portion, X centroid = −1.0, Y centroid = 4.6, the average input gradation value is 31, and the ideal number of output dots is “4” dots. Therefore, the dots of the four pixels at the center, bottom, right, and left with respect to the center of gravity position are turned on and the ideal output dot count is reached, and the process is terminated. As a result, a large dot D1 (D) composed of four pixel dots is generated in the latent image portion LI in the cell D.

  Similarly, in the cell E, the corrected gradation value is generated at the position indicating the background portion and the latent image portion. In particular, for the latent image portion, X centroid = 6.7, Y centroid = 0, the average input gradation value is 9.3, and the ideal number of output dots is “2” dots. Therefore, the dots of the two pixels at the center and the bottom with respect to the center of gravity position are turned on, and the ideal output dot count is reached and the processing is terminated. As a result, a large dot D1 (E) composed of two pixel dots is generated in the latent image portion LI in the cell E.

  Next, in cell F, a corrected gradation value is generated only in the latent image portion. Here, X centroid = 0.2, Y centroid = 0, the average input gradation value is 154, and the ideal number of output dots is “19” dots. Therefore, the dot of 19 pixels centering on the center of gravity position is turned on, and the ideal output dot number is reached and the process is terminated. As a result, a large dot D1 (F) composed of 19 pixel dots is generated in the latent image portion LI in the cell F.

  Even in the cell G, the corrected gradation value is generated at the position indicating the background portion and the latent image portion. In particular, for the latent image portion, X centroid = 1.0, Y centroid = −5.0, the average input tone value is 31, and the ideal output dot is “4” dots. Therefore, the dots of the four pixels at the center, bottom, right, and left with respect to the center of gravity position are turned on and the ideal output dot number is reached, and the process is terminated. As a result, a large dot D1 (G) composed of four pixel dots is generated in the latent image portion LI in the cell G.

  Finally, also in the cell H, corrected gradation values are generated at the positions of the background portion and the latent image portion. In particular, for the latent image portion, X centroid = −1.0, Y centroid = −5.0, the average input tone value is 31, and the ideal output dot is “4” dots. Therefore, the dots of the four pixels at the center, bottom, right, and left with respect to the center of gravity position are turned on and the ideal output dot count is reached, and the process is terminated. As a result, a large dot D1 (H) composed of four pixel dots is generated in the latent image portion LI in the cell H.

  As shown in FIG. 31, the first dot D1 is generated in the circular latent image portion LI except for the camouflage pattern dot off region CAM. In particular, large dots D1 are generated in the cells C, D, E, G, and H, although they are smaller than the first dot D1 of the cell F.

  FIG. 32 is a diagram showing an example of a tint block image generated by a general screening process with reference to the dither matrices 33 and 34N for both the latent image portion and the background portion for the corrected camouflage pattern threshold value of FIG. Comparing FIG. 31 and FIG. 32, in FIG. 32, no large dot D1 is generated in the cells C, D, E, G, and H in the circle indicating the latent image portion LI. A large dot D1 is generated only in the cell F. Therefore, in FIG. 32, a space is generated at the boundary between the latent image portion and the background portion, and the space is emphasized with a low density (white). On the other hand, in FIG. 31 according to the present embodiment, such a low-density space does not occur, and the shape of the latent image portion LI is faithfully reproduced.

[Other tint block image examples]
FIG. 33 is a diagram showing the operational effects of the present embodiment for an example of a tint block image without a camouflage pattern. FIG. 33A shows a copy-forgery-inhibited pattern image generated by a general screening process, and FIG. 33B shows a copy-forgery-inhibited pattern image generated by the screening process of this embodiment. In each of the cells CELL1 and 2, the background portion BI and the latent image portion LI are positioned as illustrated. In general processing (A), a small dot D2 is formed in the background portion BI in the cell CELL1, and a large dot D1 (1) is formed in the latent image portion LI. Corresponds to the lower right part of the large dot D1 (2) in the cell CELL2 and is connected to the small dot D2 in the background portion BI. On the other hand, in the process (B) of the present embodiment, the small dot D2 is formed in the background portion BI in the cell CELL1, and the large dot D1 (1) is formed in the latent image portion LI at a position away from the background portion BI. It is formed. That is, since the halftone dot center of the latent image portion dither matrix is shifted to the position of the center of gravity of the latent image portion LI, the large dot D1 (1) does not combine with the small dot D2 of the background portion BI. Further, the large dot D1 (1) has a size corresponding to the output density of the latent image portion LI in the cell CELL1.

  FIG. 34 is a diagram illustrating the operational effects of the present embodiment for a tint block image example without a camouflage pattern. FIG. 34A shows a copy-forgery-inhibited pattern image generated by a general screening process, and FIG. 34B shows a copy-forgery-inhibited pattern image generated by the screening process of the present embodiment. In this example, the area of the background portion BI in the cell CELL1 is larger than that in FIG.

  Therefore, in the example of the general processing in FIG. 34A, since the background portion BI in the cell CELL1 occupies the region where the large dot D1 is to be formed, the large portion of the latent image portion LI is formed in the cell CELL1. Dots are not generated. Therefore, the region 100 in which the low density is emphasized is formed at the boundary between the background portion BI and the latent image portion LI. On the other hand, in the example of the processing of the present embodiment shown in FIG. 34B, a relatively small large dot D1 (1) is formed in the area of the latent image portion LI in the cell CELL1. That is, a region where low density is emphasized is not formed.

  FIG. 35 is a diagram illustrating the effects of the present embodiment on an example of a tint block image with a camouflage pattern. (A) is a copy-forgery-inhibited pattern image generated by a general process, and (B) is a copy-forgery-inhibited pattern image generated by the process of the present embodiment. In this example, the cells CELL1, 2, 3 are all latent image areas, and a dot-off camouflage pattern CAM is located in a part of the cells CELL1,2.

  In the case of the general process (A), a partial large dot D1 (1) is generated outside the camouflage pattern CAM in the cell CELL1, and is not generated in the cell CELL2, but a large dot d1 (3) in the cell CELL3. Is generated. That is, the low concentration emphasis region 102 is formed in the cells CELL 2 and 3.

  On the other hand, in the case of the present embodiment in (B), relatively small large dots D1 (1) are generated outside the camouflage pattern CAM in the cell CELL1 at positions separated from the pattern. Further, in the cell CELL2, a relatively small large dot D1 (2) is generated outside the camouflage pattern CAM. In this way, in the present embodiment (B), since the dots are formed by shifting so that the halftone dot center of the latent image dither matrix corresponds to the center of gravity position in the latent image portion, the dots D1 (1), D1 (2) is formed, a large dot D1 is generated so as to faithfully reproduce the shape of the camouflage pattern CAM, and no low density emphasis region is formed.

  FIG. 36 is a diagram showing the operational effect of the present embodiment for an example of a tint block image with a camouflage pattern. In this example, the boundary between the background portion BI and the latent image portion LI and the camouflage pattern CAM with dot off are located in the cell CELL1. In the case of the general process (A), since the camouflage pattern CAM occupies a region where a large dot is to be formed (a rectangular region indicated by a broken line) in the cell CELL1, a large dot is not formed, and a low density emphasis region 104 is formed. On the other hand, in the case of the processing of the present embodiment of (B), a relatively small large dot D1 (1) is formed in the cell CELL1. Therefore, the low density emphasis region is not formed, and the camouflage pattern CAM is reproduced more faithfully.

[Modification example]
FIG. 37 is a diagram showing the input / output density characteristics of the background portion dither matrix and the normalized latent image portion dither matrix in the variation of the present embodiment. In the above-described embodiment, the screen processing is performed with reference to the normalized background portion dither matrix 34N shown in FIG. 21 and the latent image portion dither matrix 33 shown in FIG. In the modified example of FIG. 37, the background portion dither matrix 34 is the same as in FIG. 14, but the latent image portion dither matrix has an output density (12%) with respect to the input gradation value “170” of the maximum input gradation value “255”. The normalized latent image portion dither matrix 33N normalized so as to become “is used.

  The normalization formulas are as shown in the following formulas (6) and (7).

Normalization threshold = (threshold / In) × 254 (1 ≦ threshold ≦ In) (6)
Normalization threshold = 255 (if In <threshold) (7)
That is, the threshold values 1 to In (= 170) in the latent image portion dither matrix 33 in FIG. 13 are converted into normalized threshold values 1 to 254, and the threshold values In to 254 are converted into normalized threshold values “255”. Thus, image data having an output density in the range of 0 to 12% with respect to the gradation value Ai is generated.

When the background portion dither matrix 34 and the normalized latent image portion dither matrix 33N of FIG. 37 are used, the input gradation value In of the tint block image is set to In = 255. In other words, the background pattern and the latent image portion of the copy-forgery-inhibited pattern image have an output density of 12%. As a result, the above equation (1) is obtained when A i = (A / 255) × In = A when In = 255.
Thus, the gradation value Ai of the camouflage pattern after correction is equal to the gradation value A of the camouflage pattern before correction.

  That is, the step of calculating the gradation value of the corrected camouflage pattern (S3 in FIG. 9 and S21 in FIG. 19) is not necessary. The gradation value Ai of the camouflage pattern after correction is one of the maximum gradation ranges 0 to 255. Therefore, the multi-tone expression of the camouflage pattern can be utilized to the maximum.

  However, the latent image portion dither matrix 33N and the background portion dither matrix 34 have the same output density characteristics with respect to the range 0 to 255 that can be taken by the input gradation value, and the input image level of the latent image portion and background portion of the tint block image. The tone value In needs to be the maximum input tone value “255” within the range that the input tone values of the latent image portion dither matrix and the background portion dither matrix can take. In other words, if the dither matrix of the latent image portion and the background portion is designed so that the optimum output density is obtained with the maximum input gradation value In = 255 as described above, the gradation value (0 of the camouflage pattern) Alternatively, by performing halftone processing referring to the dither matrix in accordance with the latent image mask pattern for 255), a ground pattern image with a camouflage pattern can be generated.

  As the normalized dither matrix 34N in FIG. 21 and the normalized dither matrix 33N in FIG. 37, those generated based on engine characteristics at the time of factory shipment are adopted. However, when the output density characteristics of the engine change over time, it is desirable to normalize each time when generating a tint block image at an appropriate timing.

[Experiment example of tint block image]
FIG. 38 is a diagram showing an experimental example of a tint block image generated by the screening process in the present embodiment. FIG. 39 is an enlarged view thereof. This experimental example is a tint block image without a camouflage pattern. The original 14 and its copy 18 are shown. In particular, as shown in the original 14 and its enlarged view 14X, in the boundary regions 21A and 22A between the background portion BI and the latent image portion LI, a high density emphasis region due to dot combination or a low dot due to the absence of dot formation in the latent image portion. The density emphasis area does not occur. Compared with FIGS. 4 and 6, the degree of improvement is clear. In other words, the concealment property of the latent image “double” in the original can be kept high.

  FIG. 40 is a diagram illustrating an experimental example of a tint block image generated by the screening process according to the present embodiment. This experimental example is a copy-forgery-inhibited pattern image when the camouflage pattern 25 of FIG. 6 is used, and both are original copy-forgery-inhibited pattern images. The copy-forgery-inhibited pattern image 28 in FIG. 40A is an example in which the mask pattern of the latent image “double” becomes the latent image portion LI, and the copy-forgery-inhibited pattern image 26 in FIG. This is an example of becoming a BI. The tint block image 26 corresponds to the tint block image 26 of FIG.

  When the copy-forgery-inhibited pattern image 26 in FIG. 40B is compared with the copy-forgery-inhibited pattern image 26 in FIG. 7B, it can be seen that formation of a low-density region due to large missing dots in the region 29 is suppressed in the latent image portion LI. .

  According to the above-described embodiment, dot concatenation and dot missing can be eliminated in the boundary area between the background portion and the latent image portion of the original, and the latent image concealment property can be improved. In addition, high-resolution camouflage patterns can be reproduced more faithfully.

[Second Embodiment]
Next, a second embodiment in which the present invention is applied to other than the copy-forgery-inhibited pattern image will be described. In the above-described embodiment, the background pattern having the latent image portion and the background portion has been described. However, in the present invention, there are two areas in which screen processing by an AM screen with a small number of halftone lines and an AM screen with a large number of halftone lines, or screen processing by an error diffusion method or a distributed FM screen are mixed. It can be applied to various images.

  FIG. 41 is a flowchart showing an image data generation procedure in the second embodiment. FIG. 42 is a diagram illustrating an image example according to the second embodiment. The image data generation procedure in FIG. 41 will be described with reference to FIG.

  First, an image data generation program is executed on the host computer to generate image data (S61). As shown in FIG. 42, this image includes a circular first image 71 subjected to screen processing using an AM screen with a small number of halftone lines, an AM screen with a large number of halftone lines, an error diffusion method, or a distributed FM screen. And a second image 72 of concentric circles for performing the screen processing. In the example of FIG. 42, the outer periphery of the circular first image 71 is formed by the second image 72. For example, the inside of the circle is a first image 71 that emphasizes gradation expression, and the border of the circle is set to a second image 72 that increases the resolution. Therefore, the generated image data includes a mask pattern 60 for distinguishing whether each pixel is the first image 71 or the second image 72, and gradation value data 61 having the gradation value of each pixel. The mask pattern 60 can be composed of 1 bit for each pixel. Further, the gradation value data 61 is composed of 8 bits for each pixel RGB and a total of 24 bits.

  Then, the image data generation program of the host computer performs the first screening process on the first image 71 using the first screen 133 such as an AM screen having a low number of dotted lines. Further, the second image 72 is subjected to the second screening process by a second screen 134 such as an AM screen having a higher number of dotted lines than the first screen 133 or an FM screen using an error diffusion method or a distributed dither matrix. I do. As a result, as shown in FIG. 42, a large dot D1 having a small number of dotted lines is formed in the region of the first image 71, and a dotted line is formed in the region of the second image 72 as shown in the enlarged view in the figure. Small dots D2 having a high number are formed.

  In the second embodiment, it is desirable that the first screen 133 and the second screen 134 have the same output density characteristic for the same input gradation value. When the generated image includes only a low density image, the first and second screens are dither matrices 133-1 and 134-1 having low output density regions for all input gradation values as described above. Can be. When the generated image includes a wide range of images having the minimum density to the maximum density, the first and second screens are changed from the minimum output density to the maximum output density for all input gradation values. 133-2 and 134-2.

  Also in the second embodiment, the screening process is as described with reference to FIGS. That is, for each cell, first, the second screening process (S25, S26, S27, S28) is performed on the pixels of the second image 72, and then the first screening process ( S30 to S39) are performed. By performing the screening process in this way, high density emphasis due to dot coupling and low density emphasis due to the absence of dots at the boundary between the first and second images 71 and 72 are suppressed, and high image quality is possible. .

  As described above, the present invention is applicable not only to a copy-forgery-inhibited pattern image for preventing forgery but also to a general image. In this case, for the pixels of the first image 71, the barycentric position, average input tone value, and ideal dot number of the first image are obtained for each cell, and the dot center of the dither matrix 33 is used as the barycenter of the first image. Since the screen processing is performed by shifting to the position, high image quality can be achieved.

It is a figure which shows the example of a latent image of a tint block, and a camouflage pattern. It is a figure which shows the example of the original copy-forgery-inhibited pattern. It is a figure which shows the example of the copy of a background pattern. FIG. 4 is a further enlarged view of the enlarged view of the original in FIG. 2 and the enlarged view of the copy in FIG. 3. It is a figure which shows the original copy of a tint block at the time of performing the boundary process by patent document 1, and a copy. FIG. 6 is an enlarged view of FIG. 5. It is a figure which shows the camouflage pattern with high resolution, and the tint block which employ | adopted it. It is a figure which shows the structure of the tint block image forming apparatus in this Embodiment. It is a flowchart figure which shows the production | generation procedure of the copy-forgery-inhibited pattern data in this Embodiment. It is a figure which shows an example of the background part screen in this Embodiment, and a latent image part screen. It is a figure which shows the characteristic of the input gradation and output density of background part basic dither matrix DM-BI and latent image part basic dither matrix DM-LI. It is a figure which shows the characteristic of the output density with respect to the input gradation value of a background part dither matrix and a latent image part dither matrix in 1st Embodiment. It is a figure which shows the low density area | region expansion dither matrix 33 of the latent image part employ | adopted by this Embodiment. It is a figure which shows the low concentration area | region expansion dither matrix 34 of the background part employ | adopted by this Embodiment. FIG. 6 is a diagram illustrating output density characteristics with respect to input gradation values of a latent image portion dither matrix 33 and a background portion dither matrix 34; It is a flowchart figure which shows the production | generation method of the copy-forgery-inhibited pattern image data in this Embodiment. It is a figure which shows the example of a tint block effect. It is a figure which shows the example of arrangement | positioning of a background pattern. It is a flowchart figure of a tint block image generation process in this Embodiment. It is a flowchart figure of a tint block image generation process in this Embodiment. It is a figure which shows the normalization background part dither matrix 34N. It is a figure which shows the input / output density characteristic of the normalization background part dither matrix, the background part dither matrix before normalization, and a latent image part dither matrix. It is a figure explaining the tint block image generation processing of FIG. It is a figure which shows an example of a latent image mask pattern. It is a figure which shows the correction camouflage pattern gradation value data Ai. It is a figure explaining the count process of the number of ideal output dots. It is a figure which shows the tint block image example produced | generated by the screening process of this Embodiment. It is a figure which shows the example of a tint block image produced | generated by the general screening process which referred the dither matrix 33 and 34N for both the latent image part and the background part. It is a figure which shows an example of a camouflage pattern. It is a figure which shows a correction | amendment camouflage pattern gradation value. It is a figure which shows the tint block image example produced | generated by the screening process of this Embodiment about the correction | amendment camouflage pattern threshold value of FIG. FIG. 31 is a diagram showing an example of a tint block image generated by a general screening process with reference to the dither matrices 33 and 34N for both the latent image portion and the background portion with respect to the corrected camouflage pattern threshold value of FIG. 30; It is a figure which shows the effect of this Embodiment about the example of a tint block image without a camouflage pattern. It is a figure which shows the effect of this Embodiment about the example of a tint block image without a camouflage pattern. It is a figure which shows the effect of this Embodiment about the tint block image example with a camouflage pattern. It is a figure which shows the effect of this Embodiment about the tint block image example with a camouflage pattern. It is a figure which shows the input / output density characteristic of the background part dither matrix and the normalization latent image part dither matrix in the modification of this Embodiment. It is a figure which shows the experiment example of the copy-forgery-inhibited pattern image produced | generated by the screening process in this Embodiment. It is an enlarged view of FIG. It is a figure which shows the experiment example of the copy-forgery-inhibited pattern image produced | generated by the screening process in this Embodiment. It is a flowchart figure which shows the image data production | generation procedure in 2nd Embodiment. It is a figure which shows the example of an image in 2nd Embodiment.

Explanation of symbols

16: Original 20: Copy LI: Latent image portion BI: Background portion 16X: Enlarged image of original 20X: Enlarged image of copy 33: Latent image portion dither matrix 34: Background portion dither matrix

Claims (10)

A copy-forgery-inhibited pattern image generation program for causing a computer to execute a copy-forgery-inhibited pattern image generation process for generating a copy-forgery-inhibited pattern image data on a print medium, including a latent image portion and a background portion that are reproduced at different output densities,
The tint block image generation step includes:
For the pixels of the latent image portion, a first screening processing step of generating latent image portion image data by an area modulation screen having a first halftone line number;
The background pixel includes a second screening process step of generating background image data by an area modulation screen or a density modulation screen having a second halftone number higher than the first halftone number. ,
The first screening processing step generates the latent image portion image data forming a halftone dot with a position shifted from a center of a cell corresponding to a halftone dot formation region in the area modulation screen as a center. Computer-readable copy-forgery-inhibited pattern image generation program.   2. The tint block image generation according to claim 1, wherein the position shifted from the center of the cell is a barycentric position in the image of the latent image portion in the cell corresponding to a halftone dot formation region in the area modulation screen. program. In claim 1,
A tint block image generation program characterized in that a halftone dot formed in the first screening processing step has an upper limit on a size corresponding to a gradation value of a latent image portion in the cell. In claim 2,
The first screening process step includes:
A center-of-gravity position generation step for obtaining a center-of-gravity position of the image of the latent image portion in the cell;
An average input tone value generation step of obtaining an average input tone value obtained by dividing the total tone value of the image of the pixel portion in the cell by the number of pixels in the cell;
An ideal output dot number generation step of obtaining, as an ideal output dot number, the number of dots generated when an image in which all pixels have the average input gradation value is screened by the area modulation screen;
A tint block image generation program, comprising: a halftone dot generation step of generating a halftone dot having a size up to the ideal output dot number at the center of gravity position. In claim 1,
The area modulation screen having the first halftone line number is a dot concentration type dither matrix, and the latent image portion image data is image data forming a halftone dot having a size corresponding to an input gradation value of the latent image portion. And
The area modulation screen having the second halftone line number is a dot dispersion type dither matrix, and the background image data has a density corresponding to the input gradation value of the background portion, and the latent image portion image data A copy-forgery-inhibited pattern image generation program characterized by being image data for forming halftone dots smaller than halftone dots. In claim 1,
The copy-forgery-inhibited pattern image is composed of a camouflage pattern on the latent image portion and the background portion,
And a step of generating a corrected camouflage pattern gradation value obtained by correcting the gradation value of the camouflage pattern according to the input gradation values of the latent image portion and the background portion,
The first screen processing step generates the latent image portion image data with reference to a dither matrix of the area modulation screen having the first halftone number for the corrected camouflage pattern gradation value,
The second screen processing step generates the background image data with reference to a dither matrix of the area modulation screen having the second halftone number for the corrected camouflage pattern gradation value. Generation program. In claim 6,
The latent image portion and the background portion are given the same input gradation value,
The area modulation screen having the first halftone line number and the area modulation screen having the second halftone line number have the same output density characteristics in a range of possible input gradation values, and can be read by a computer A tint block image generation program. In an image generation program for causing a computer to execute an image generation process for generating image data for forming an image including a first image portion and a second image portion on a print medium.
The image generation process includes:
For the first pixel, a first screening processing step of generating image data by an area modulation screen having a first halftone line number;
The second pixel has a second screening processing step of generating image data by an area modulation screen or a density modulation screen having a second halftone line number higher than the first halftone line number;
In the first screening processing step, a halftone dot is formed at the center of gravity of the image of the latent image portion in the cell corresponding to the halftone dot formation region in the area modulation screen processing. Image generation program. In a tint block image generating device for generating a tint block image on a print medium, including a latent image portion and a background portion that have different output densities reproduced at the time of copying,
For the pixels of the latent image portion, first screening processing means for generating latent image portion image data by an area modulation screen having a first halftone line number;
The background pixel includes second screening processing means for generating background image data by an area modulation screen or a density modulation screen having a second halftone line number higher than the first halftone line number. ,
The first screening processing means generates the latent image portion image data for forming a halftone dot at a gravity center position of the image of the latent image portion in a cell corresponding to a halftone dot formation region in the area modulation screen. A tint block image generation device. In an image generation apparatus for generating an image including a first image portion and a second image portion on a print medium,
For the first pixel, first screening processing means for generating image data by an area modulation screen having a first halftone dot number;
The second pixel has a second screening processing means for generating image data by an area modulation screen or a density modulation screen having a second halftone line number higher than the first halftone line number,
The copy-forgery-inhibited pattern image generation apparatus, wherein the first screening processing unit forms a halftone dot at a center of gravity of an image of the latent image portion in a cell corresponding to a halftone dot formation region in the area modulation screen process.