JP2006310988A - Image processing apparatus and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide image processing technology for making intervals between dots configuring a latent image inconspicuous while keeping the density of a latent image part. <P>SOLUTION: An image processing method for generating a pattern image including the latent image appearing at copying and a background whose density is thinned at the copying in comparison with that of the latent image in order that a received original image is different from a copied image calculates a space length between first dots on the basis of the arrangement of the first dots for configuring the latent image and discriminates whether or not the arrangement of second dots whose space length is smaller than that of the first dots is necessary on the basis of the space length between the first dots. When the arrangement of the second dots is required, a pattern for arranging the second dots around the first dots is generated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing technique for synthesizing and outputting a copy-suppressed copy-forgery-inhibited pattern on the background of a document for the purpose of suppressing illegal forgery and information leakage due to copying of an important document.

  Some receipts, securities, and certificates have a special pattern printed on the background that makes characters and images appear when they are copied so that they are not easily copied. This special pattern is generally called a “counterfeit deterrent pattern”, and implements a mechanism that prevents the original from being easily copied by copying, thereby realizing the effect of suppressing the copying of the original.

  In this forgery-inhibited tint block, an area where dots remain after copying and an area where dots disappear after copying or where the dots become lighter than the latent image portion are composed of two areas having substantially the same density. From a macro perspective, these two areas do not clearly show that characters and images such as “copy” are hidden, but microscopically have different characteristics. In the present invention, these hidden characters and images are referred to as “latent images”.

  For example, an area where dots remain after copying (hereinafter, this area is referred to as a “latent image portion” or “latent image area”) is composed of a cluster of dots in which each dot is concentrated, and an area where dots disappear after copying (hereinafter referred to as “latent image area”). This area is referred to as a “background portion” or “background area”). By configuring the dots with dispersed dots, two areas having substantially the same density and different characteristics can be created.

Concentrated dots and dispersed dots can be generated by halftone processing using halftone dots with different numbers of lines or dither processing using dither matrices with different characteristics in terms of image processing.
In halftone processing, halftone dots with a low number of lines can be used to obtain a concentrated dot arrangement, and halftone dots with a high number of lines can be used to obtain a dispersed dot arrangement.

  In the dither processing using a dither matrix, it is preferable to use a dot concentrated dither matrix to obtain a concentrated dot arrangement, and to use a dot dispersed dither matrix to obtain a dispersed dot arrangement.

  Therefore, when generating a tint block image using halftone processing, the latent image portion is suitable for halftone processing with a low number of lines, and the background portion is suitable for halftone processing with a high number of lines. For generation, dither processing using a dot concentration type dither matrix is suitable for the latent image portion, and dither processing using a dot dispersion type dither matrix is suitable for the background portion.

  In general, a copying machine has a limit of image reproduction capability that depends on an input resolution for reading minute dots of a copied document and an output resolution for reproducing minute dots. Therefore, if there are isolated minute dots in the document that exceed the limit of the image reproduction capability of the copying machine, the minute dots cannot be completely reproduced in the copied material, and the isolated minute dot portions are lost. .

  Therefore, if the background of the forgery-inhibited background pattern is created to exceed the limit of dots that can be reproduced by a copying machine, large dots (concentrated dots) in the forgery-inhibited background pattern can be reproduced by copying, but small dots (distributed) (Dot) cannot be reproduced, and a hidden image (latent image) appears. Further, even if the dots dispersed by copying do not disappear completely, even if the density difference after copying is clearly different compared to concentrated dots, a hidden image (latent image) appears.

  In the forgery-inhibited pattern, a technique called “camouflage” is well known as a technique for making it difficult to distinguish characters and images hidden as latent images.

  This camouflage is a method in which a pattern having a different density from the latent image portion and the background portion is arranged on the entire forgery-inhibited tint block image. At first glance, the camouflage having a different density from the latent image portion and the background portion is macroscopically. The pattern is conspicuous and the latent image is more inconspicuous.

  In addition, compared with a forgery-inhibiting background pattern having no camouflage pattern, the forgery-inhibiting background pattern having a camouflage pattern has an effect of giving a decorative impression to the printed matter. In this camouflage pattern, it is desirable that the dots inside the camouflage pattern disappear as much as possible after copying so that the latent image can be easily identified after copying. In the simplest implementation, camouflage can be achieved by not hitting dots at locations corresponding to camouflage patterns. The above is the outline of the counterfeit copy-forgery pattern.

  Conventionally, printing paper manufacturers have previously printed a copy-forgery-inhibited pattern including characters and images (latent images) such as “copy” on a dedicated paper and sold it as anti-copying paper. Then, government offices and companies purchased the copy-preventing paper and printed the document whose originality is to be guaranteed on the copy-preventing paper, thereby inhibiting the copying of the printed matter.

  However, conventional copy prevention paper is created by printing paper manufacturers by preprinting ground patterns on special paper, so the cost of using special paper, the cost caused by preparing more than the required number of preprinted paper, etc. There was a demerit in cost.

  On the other hand, in recent years, a technique for creating a forgery-inhibited tint block image in software and outputting a document in which a forgery-inhibiting tint block is arranged on the background by a laser printer (hereinafter referred to as “on-demand tint block output method using a printer”). .) Is realized.

  The on-demand copy-forgery-inhibited pattern output method using a printer can print a document with forgery-suppressed copy-forgery-inhibited patterns placed on the background using plain paper, so when necessary, print a document with forgery-suppressed copy-forgery-printed patterns on the background. Can do. Therefore, it is not necessary to prepare copy prevention paper more than necessary as in the prior art. That is, the on-demand copy-forgery-inhibited pattern output method using a printer can greatly reduce the cost of paper compared to a conventional document copy suppression method using copy-preventing paper.

  Further, users of conventional anti-copying paper can only use hidden characters and images (latent images) prepared in advance by a printing paper manufacturer, or custom-made characters and images (latent images).

  However, with the on-demand copy-forgery-inhibited pattern output method using a printer, the user can generate a copy-forgery-inhibited pattern image including any hidden characters and images (latent images) by software processing for each printing, and print it on-demand with the printer. There is an advantage that hidden characters and images (latent images) can be freely customized.

  By taking advantage of the ability to select this latent image on demand, not only the company logos and characters that have been used in the past as images and characters to be embedded as latent images, but also serial numbers that identify output printers, for example Number, IP address, computer name and IP address that identifies the computer that issued the print command, user name and login name that identifies the user who issued the print command, and print to identify when and who performed the printing process Various information such as a job number, printing date / time, printing location, and file name of the electronic document can be selected.

  As a result, the on-demand copy-forgery-inhibited pattern output method using a printer can realize a more advanced tracking function that cannot be realized with conventional preprinted copy-preventing paper.

As the above-described prior art, for example, there is one shown in Patent Document 1 below.
JP 2001-197297 A

  However, when a latent image portion of a forgery-inhibited background pattern printed by an on-demand background pattern output method by a printer is expressed by a dot array having a certain density and a low density, there is a problem that the space between the dots is easily noticeable. . Thereby, even if it is a copy-forgery-inhibited pattern image output as an original, the character string of a latent image part becomes easy to visually recognize, and the confidentiality of a character string will fall.

  The present invention has been made in view of this problem, and when a latent image portion is expressed by a dot-concentrated dither matrix, the density between the latent image portions is maintained and the dots are conspicuous. An object of the present invention is to provide an image processing technique that reduces this problem.

  In order to achieve the above object, the image processing method according to the present invention mainly includes the following steps.

That is, an image processing method for generating a copy-forgery-inhibited pattern image including a latent image that appears at the time of copying and a background that becomes lighter than the latent image at the time of copying in order to indicate that the copy is different from the input document image Is
A blank length calculating step for calculating a blank length between the first dots based on an arrangement of the first dots constituting the latent image;
A determination step of determining whether it is necessary to arrange a second dot smaller than the first dot based on the blank length calculated by the blank length calculation step;
A pattern generation step of generating a pattern for arranging the second dots around the first dots when the second dots need to be arranged in accordance with the determination in the determination step.

  According to the present invention, it is possible to generate a latent image that makes the area between the dots constituting the latent image inconspicuous while maintaining the density of the latent image portion.

[First embodiment]
Hereinafter, the present invention will be described in detail according to preferred embodiments with reference to the accompanying drawings. In the present embodiment, the image corresponding to the background portion is designed so that dots are discretely arranged using a dot dispersion type dither matrix, and the image corresponding to the latent image portion uses a dot concentration type dither matrix. The description will be made assuming that the dots are designed so as to be concentrated.

  Hereinafter, the dither matrix used for generating the background image is referred to as a background dither matrix, and the dither matrix used for generating the latent image portion is referred to as a latent image dither matrix.

  In each embodiment of the present invention, a portion that becomes visible at the time of copying is referred to as a latent image portion or a foreground portion, and a portion that disappears or becomes thinner than the latent image portion at the time of copying is referred to as a background portion. Then, text information such as “VOID” is input to the latent image portion. However, the copy-forgery-inhibited pattern image in the present invention is not limited to this, and text information may be expressed (visualized) like white characters with respect to surrounding images during copying. In this case, it is a matter of course that the above-described dot concentration and dispersion relationship between the latent image portion and the background portion is opposite to that which is not white. It will be apparent from the following description that the application of the present invention is not limited by the type, color, shape, size, etc. of the tint block image.

The dither method is a method in which a multi-value input image signal is compared with a threshold value calculated according to a certain rule, and a binary image is output based on the magnitude relationship. The dither matrix is a threshold matrix in which thresholds for binarizing an input image signal by the dither method are two-dimensionally arranged.
A binary image (threshold pattern) is obtained by binarizing the pixel value of the input image signal with the threshold value of the corresponding dither matrix, but the obtained binary image has a gradation of the dither matrix of the input image signal. If it is less than the threshold value, one bit (eg, “1”) is assigned to the pixel value, and if it is greater than or equal to the threshold value, the other bit (eg, “0”) is assigned.

  In this embodiment, the binary image constituting the background and the binary image constituting the latent image portion are respectively appropriate so that the background portion and the latent image portion have substantially the same density when printed on paper using a printer. Assume that an input image signal is input and generated in advance by a dither method.

A background threshold pattern and a method for generating a latent image threshold pattern, which will cause the background portion and the latent image portion to have substantially the same density when printed on paper using a printer, will be described in detail later.
In the following description, the binary image constituting the background portion is referred to as a background threshold pattern, and the binary image constituting the latent image portion is referred to as a latent image threshold pattern.

  FIG. 1A is a block diagram illustrating the internal processing of the tint block image generation device according to this embodiment. The tint block image generation apparatus includes a tint block image generation unit 101, a composition unit 102, a print data processing unit 103, and a printing unit 104.

  First, an input background image 111, color information 112, processing area information 113, latent image threshold pattern 114, background threshold pattern 115, latent image background area designation image 116, and camouflage area designation image 117 are input to the tint block image generation unit 101. Is done. The tint block image generation unit 101 performs image processing on the input background image 111 according to a predetermined rule, and outputs a tint block image 118. The input background image 111 may be a multi-value image or a binary image. The processing area information 113 is information indicating an area for embedding a background pattern in the input background image information.

  The latent image background area designation image 116 is an image for designating a latent image portion and a background portion, and is composed of one pixel and one bit. One bit (for example, “1”) of the latent image background area designation image 116 represents a latent image portion, and the other bit (for example, “0”) represents a background portion.

  The camouflage area designating image 117 is an image for designating an area for decreasing the density in order to have a camouflage effect, and is composed of one pixel and one bit like the latent image background area designating image 116. One bit (for example, “1”) of the camouflage area designation image 117 indicates that it is not a camouflage area where the density is lightened, and the other bit (for example, “0”) is a camouflage area where the density is lightened compared to the surroundings. It shows that there is. FIG. 1B is a diagram showing an example of a latent image background area designation image and a camouflage area designation image. In FIG. 1B, 1001 is an example of the latent image background area designation image 116, and 1002 is an example of a camouflage area designation image 117.

  As described above, the background threshold pattern 115 and the latent image threshold pattern 114 are subjected to threshold processing on appropriate image signals with the threshold values of the background dither matrix and the latent image dither matrix, respectively, so that they are output as equal densities at the time of print output. Generated. Here, FIG. 1C is a diagram illustrating an example of the latent image threshold pattern 114 and the background threshold pattern 115. In FIG. 1C, reference numeral 1101 denotes the latent image threshold pattern, and 1102 denotes the background threshold pattern.

  The tint block image 118 generated by the tint block image generation unit 101 is output to the synthesis unit 102. Since the method of generating the copy-forgery-inhibited pattern image 118 will be described in detail later, a detailed description thereof is omitted here.

  The synthesizing unit 102 synthesizes the input document image 119 and the copy-forgery-inhibited pattern image 118 generated by the copy-forgery-inhibited pattern image generation unit 101, and an output document image 120 (hereinafter referred to as a “copy-forgery-inhibited pattern output document image”) synthesized with the copy-forgery-inhibited pattern. Generate. Note that, when the copy-forgery-inhibited pattern image 118 is used as the copy-forgery-inhibited pattern synthesized output document image 120 as it is, regardless of the contents of the input document image 119, it is not necessary to refer to the input document image 119 by the combining unit 102.

  At this time, after performing color matching processing for each object constituting the copy-forgery-inhibited pattern image 118 and the input document image 119, the object constituting the input document image 119 and the copy-forgery-inhibited pattern image 118 are combined to generate a copy-forgery-inhibited pattern composite output document image 120. Alternatively, the color matching process may be executed on the copy-forgery-inhibited pattern composite output document image 120 in the print data processing unit 103 at the subsequent stage.

  The print data processing unit 103 is a drawing interface of an OS (Operating System) (for example, Graphic Device Interface (GDI) of the Windows (registered trademark) series that is the OS of Microsoft), QuickDraw of the MacOS series that is the OS of Apple Computer, etc. The copy-forgery-inhibited pattern combined output original image 120 combined by the combining unit 102 is received as drawing information and is sequentially converted into a print command. At this time, image processing such as color matching processing, RGB-CMYK conversion, and halftone processing is executed as necessary. The print data processing unit 103 then describes the data format (for example, a page description language) that can be interpreted by the printing unit 104 as the copy-forgery-inhibited pattern output document image data 130 (hereinafter referred to as “copy-forgery-inhibited pattern output document image data”). The data format and the data format expanded into the print bitmap) are sent to the printing unit 104 in the subsequent stage.

  The printing unit 104 prints out an output document 140 based on the copy-forgery-inhibited pattern combined output original image 120 in accordance with the information of the input copy-forgery-inhibited pattern output original image data 130.

  Here, to explain the case of a laser beam printer as an example, the printing unit 104 includes a printer controller and a printer engine (not shown). The printer controller includes a print information control unit, a page memory, an output control unit, and the like. The print information control unit analyzes the page description language (PDL) sent from the print data processing unit 103 and develops corresponding patterns for drawing and printing commands in the page memory.

  If necessary, image processing such as RGB-CMYK conversion and halftone processing is also executed. Note that if the print information control unit determines that the print bit map is not the data format described in the page description language, the image data is directly expanded in the page memory.

  The output control unit converts the contents of the page memory into a video signal and outputs it to the printer engine. The printer engine includes, for example, a recording medium transport mechanism, a semiconductor laser unit, a photosensitive drum, a developing unit, a fixing unit, a drum cloning unit, a separation unit, and the like, and performs printing by a known electrophotographic process.

  When the copy-forgery-inhibited pattern image generation unit 101 creates a copy-forgery-inhibited pattern image with the intention that each pixel is printed and output only with the primary colors (cyan, yellow, magenta, and black) of the printer, It is not desirable that each pixel expressed assuming output in cyan, yellow, magenta, and black) is printed with a plurality of different colors of ink or toner. Therefore, in the print data processing unit 103 and the printing unit 104, for pixel values corresponding to the copy-forgery-inhibited pattern image in the copy-forgery-inhibited pattern output original image (for example, cyan, magenta, yellow, and black), It is desirable to set so that a plurality of inks and toners of different colors are expressed at the same time and are not mixed colors.

  Specifically, it is preferable to introduce a setting in which each pixel is always printed with a single color ink or toner even after color conversion processing such as color matching is passed and halftone processing is executed. However, this is not the case when one pixel of the copy-forgery-inhibited pattern image is expressed by light ink, dark ink, large ink dots, or small ink dots of the same color on an inkjet printer. In addition, as a color variation of the tint block image, it is possible to generate a tint block image that looks green at first glance by arranging cyan pixels and yellow pixels in a balanced manner. If the primary color of the printer (cyan, yellow, magenta, black) is used, it is desirable that one pixel of the copy-forgery-inhibited pattern image is output accurately only with the corresponding cyan or yellow toner or ink.

  However, it is possible to generate an image that realizes the effect of the tint block even if one pixel of the tint block image is not printed out only with the primary colors (cyan, yellow, magenta, black) of the printer. Even if one pixel of a copy-forgery-inhibited pattern image is expressed by a plurality of inks or toners of different colors, it can be used as a forgery-proof copy-forgery-inhibited pattern if a latent image remains after copying.

In this embodiment, the copy-forgery-inhibited pattern image 118, the input document image 119, the copy-forgery-inhibited pattern output document image 120, and the copy-forgery-inhibited pattern output document image data 130 are digital data, and the copy-forgery-inhibited pattern composite output document (output document) is a recording medium (for example, It represents an image printed on paper.
FIG. 2 is a flowchart for explaining the internal processing flow of the copy-forgery-inhibited pattern image generation unit 101 according to this embodiment. First, in step S201, the copy-forgery-inhibited pattern image generation unit 101 starts a copy-forgery-inhibited pattern image generation process through a user interface or the like. In step S202, the copy-forgery-inhibited pattern image generation unit 101 starts the input background image 111, the background threshold value pattern 115, and the latent image threshold value pattern. 114, the latent image background area designation image 116, the camouflage area designation image 117, and the like are read.

  Then, the process proceeds to step S203, and the tint block image generation unit 101 determines an initial pixel when generating the tint block image. For example, when the entire input image having a rectangular size is subjected to image processing from the pixel corresponding to the upper left vertex to the pixel corresponding to the lower right vertex to change to a tint block image in the raster scanning order, the upper left pixel is set as the initial position.

  In step S <b> 204, the tint block image generation unit 101 arranges the background threshold pattern 115, the latent image threshold pattern 114, the latent image background area designation image 116, and the camouflage image 117 in a tile shape from the upper left of the input background image 111. At this time, the following equation (1) is calculated for the pixels of the input background image to be processed, and it is determined whether or not to write the pixel values corresponding to the dots at the time of printing. At this time, the pixel value corresponds to the input color information.

Here, the definition of the component of Formula (1) is shown below.
nCamouflage: 0 if the pixel is a camouflage area in the camouflage area designation image, 1 otherwise
nSmallDotOn: 1 if the pixel value of the background threshold pattern is black, 0 if white
nLargeDotOn: 1 if the pixel value of the latent image threshold pattern is black, 0 if white
nHiddenMark: 1 if a pixel corresponding to a latent image portion in a latent image background area designation image, 0 if a pixel corresponding to a background portion
/ nHiddenMark: Denial of nHiddenMark. 0 in the latent image portion and 1 in the background portion.
Note that it may be determined whether or not to write a pixel value corresponding to a dot at the time of printing while referring to the pixel value of the input background image. In this case, the right side of Expression (1) may be multiplied by an item (nBackground) obtained by referring to the input background image. This nBackground is 1 if the input background image has a specific pixel value (white background area), and 0 otherwise.

  In addition, it is not necessary to perform calculation using all the elements of Expression (1) for each pixel to be processed, and it is possible to increase the processing speed by omitting unnecessary calculation.

  For example, if nHiddenMark = 1, / nHiddenMark = 0, and if nHiddenMark = 0, / nHiddenMark = 1. Therefore, if nHiddenMark = 1, the value of equation (2) can be the value of nLargeDotOn, and if nHiddenMark = 0, the value of equation (2) can be the value of nSmallDotOn.

  Further, the value of nCamouflage is an integration over the whole. If nCamouflage = 0, nWriteDotOn = 0. Therefore, in the case of nCamouflage = 0, the calculation of equation (2) after nCamouflage can be omitted.

In the generated tint block image 118, the background threshold pattern 115, the latent image threshold pattern 114, the latent image background area designating image 116, and the camouflage area designating image 117 have an image of the least common multiple of the vertical and horizontal lengths. Since the copy-forgery-inhibited pattern image generation unit 101 generates only a part of the copy-forgery-inhibited pattern image, which is the smallest unit of repetition, and repeatedly arranges a part of the copy-forgery-inhibited pattern image in the size of the input background image, the copy-forgery-inhibited pattern image 118 is generated. The processing time required for generating can be reduced.
Next, in step S205, the calculation result (value of nWriteDotOn) in step S204 is determined. Here, if nWriteDotOn = 1 (S205-YES), the process proceeds to step S206, and the dot writing process is executed. If nWriteDotOn = 0 in step S205 (S205-NO), the process proceeds to step S207.

  In the dot writing process of step S206, the tint block image generation unit 101 performs a process of writing a pixel value corresponding to a dot at the time of printing.

The value of the pixel value can be changed depending on the color of the tint block image 118. When creating a black background pattern, the pixel to be processed in the input background image 111 is set to black.
In addition, a color copy-forgery-inhibited pattern image can be created by setting cyan, magenta, and yellow according to the color of the toner or ink of the printer.

When the input background image 111 is 1 to several bits of image data per pixel, the pixel value may be expressed using an index color. Index color is a method of expressing image data. Color information that frequently appears in a target color image is set in the table of contents (for example, index 0 is white, index 1 is cyan, etc.), and the value of each pixel is color information. It is expressed by the described table of contents numbers (for example, the first pixel value is expressed as index 1 value, the second pixel value is expressed as index 2 value,...).
In step S207, the copy-forgery-inhibited pattern image generation unit 101 determines whether all the pixels in the processing target area of the input background image 111 have been processed. If all the pixels in the processing target area of the input background image 111 have not been processed (S207-NO), the process proceeds to step S208, the tint block image generation unit 101 selects an unprocessed pixel, and steps S204 to S204 again. The process of S206 is executed.

  If the processing for all the pixels in the processing target area of the input background image has been completed (S207—YES), the processing proceeds to step S209, and the image processing in the tint block image generation unit 101 ends.

  By the processing of the tint block image generation unit 101 described above, the tint block image 118 obtained by performing image processing on the input background image 111 is generated.

(Dot placement method in the latent image and background)
Next, a method for arranging dots in the latent image portion and the background portion in this embodiment of the present invention will be described. In the present embodiment, a case where the latent image portion is generated based on a dot concentration type dither matrix and the background portion is generated based on a dot dispersion type dither matrix will be described as an example. Here, as a representative of the dot concentration type dither matrix used when generating the latent image portion, there is a spiral dither matrix. FIG. 3 shows a 4 × 4 spiral dither matrix. The thresholds of the 4 × 4 spiral dither matrix are arranged in a spiral shape with numerical values increasing from the center.

  FIG. 4 shows a threshold pattern (dot arrangement) obtained by performing threshold processing on a predetermined input image signal using the 4 × 4 spiral dither matrix of FIG. 401, 402, and 403 are input image signals 3 (in 401 in the figure, the number of elements of the matrix filled with black is 3), and 6 and 9 are the dither matrix in FIG. The threshold patterns obtained by threshold processing are respectively shown in FIG. The obtained threshold pattern (dot arrangement) is a pattern in which each dot is concentrated.

  On the other hand, a Bayer type dither matrix is a representative example of the dot dispersion type dither matrix that constitutes the background portion. The Bayer type N × N dither matrix is expressed by the following equation.

However, N is a power of 2, UN is an N × N matrix with 1 element.
FIG. 5 is a diagram illustrating an example of a 4 × 4 Bayer-type dither matrix. A threshold pattern generated by dithering an arbitrary input image signal with a Bayer-type dither matrix is designed so that each dot is arranged in a distributed manner.

  FIG. 6 is a diagram illustrating a threshold pattern (dot arrangement) obtained by performing threshold processing on a predetermined input image signal using the 4 × 4 Bayer-type dither matrix of FIG. 6, reference numerals 601, 602, and 603 denote threshold patterns obtained by performing threshold processing on the input image signals 2, 4, and 5 using the dither matrix shown in FIG. The threshold pattern (dot arrangement) obtained here is a pattern in which each dot is arranged dispersedly. In the Bayer-type dither matrix, the elements of the threshold matrix are sequentially arranged at positions where they do not touch each other as much as possible, and the threshold pattern takes an isolated grid-like dot arrangement. In the Bayer-type dither matrix, the elements of the threshold matrix are sequentially arranged at positions where they do not touch each other as much as possible, and the threshold pattern takes an isolated grid-like dot arrangement. In the Bayer type dither, when the size of the dither matrix increases, periodic textures due to the matrix may be conspicuous, but there is an advantage that a periodic and beautiful pattern can be obtained at a specific gradation.

  In the present embodiment, the case where a Bayer type dither matrix is used as a background dither matrix will be mainly described below. However, the gist of the present invention is not limited to the Bayer type dither matrix, and other dot dispersion type dither matrices are used. May be used.

  For example, a blue noise mask is an example of a dot dispersion type dither matrix used for the background. In this blue noise mask, all threshold patterns in an arbitrary gradation have blue noise characteristics, and the distribution of black pixels forming the threshold pattern is random but highly uniform, and the graininess is not conspicuous. The blue noise characteristic means that the output pattern of points when set to an arbitrary gradation is locally aperiodic and isotropic and has low frequency components. . The threshold pattern obtained from the blue noise mask has advantages in that a visually preferable output pattern can be obtained, for example, by preventing the occurrence of moire and making paper feed unevenness inconspicuous.

  In addition to a blue noise mask, a dot dispersion type dither matrix may be used in which a threshold pattern at a specific or arbitrary gradation is periodic (or pseudo-periodic) and anisotropic and has low frequency components.

  FIG. 7 is a diagram for comparing the area ratios of the black pixels of the background threshold pattern 115 and the latent image threshold pattern 114. As shown in FIG. 7, the vertical and horizontal sizes of the dither matrix in the background portion are X_S and Y_S, the gradation of the input image signal is T_S, and the vertical and horizontal sizes of the dither matrix in the latent image portion are X_L. , Y_L, and the gradation of the input image signal is T_L.

  At that time, the ratio of black pixels in the background threshold pattern 115 is P_S = T_S / (X_S * Y_S), and the ratio of black pixels in the latent image threshold pattern is P_L = T_L / (X_L * Y_L) ( “*” Means multiplication).

  FIG. 8 is a diagram showing the relationship between the black pixel area ratio of the threshold pattern obtained by threshold processing of the input image signal with a dither matrix and the density when the threshold pattern is printed. In the dither processing, the area ratio of the black pixels changes according to the gradation of the input image signal, so the horizontal axis in FIG. 8 may be regarded as the gradation of the input image signal.

  Here, the dither matrix (background threshold pattern) of the background portion and the dither matrix (latent image threshold pattern) of the latent image portion do not have to have the same side size, and may be different sizes. For example, the gradation characteristics of the dither matrix in the background portion (hereinafter referred to as “background dither matrix”) and the dither matrix in the latent image portion (hereinafter referred to as “latent image dither matrix”) are as indicated by reference numeral 801 in FIG. In the case of linear gradation characteristics, the horizontal axis value (area ratio of black pixels) is substantially equal regardless of the size of the background dither matrix and the latent image dither matrix, that is, black pixels in the background threshold pattern 115 If the values of the gradations T_S and T_L of the input image signal such that the ratio (P_S) occupied by black and the ratio (P_L) occupied by black pixels in the latent image threshold pattern are substantially equal are used, the background threshold pattern and the latent image threshold The density of the pattern is almost equal, and a tint block image in which the latent image is not conspicuous can be generated.

In practice, however, the gradation characteristics of the dither matrix of the background portion and the dither matrix of the latent image portion are not necessarily the same due to the characteristics of the printer.
For example, it is assumed that the gradation characteristic of the latent image dither matrix is represented by a gentle S-shaped curve as indicated by 802, and the gradation characteristic of the background dither matrix is represented by a steep S-shaped curve as indicated by 803. In such a case, the density of the background portion and the latent image portion at the time of printing is not the same even if the area ratio of the black pixels of the background threshold pattern and the latent image threshold pattern is set to be approximately equal.

  By appropriately adjusting the input image signal for the dither matrix of one or both of the background portion and the latent image portion, the density at the time of printing can be made as close as possible. If the number of gradations that can be expressed by the background dither matrix or the latent image dither matrix is large, the density of the background portion or latent image portion can be finely adjusted by adjusting the gradation of the input image signal.

  When the latent image dither matrix is a dot-concentrated dither matrix as shown in FIG. 3, when the gradation of the input image signal is below a certain level, it becomes close to an isolated dot, and the latent image portion tends to disappear during copying. On the other hand, when the gradation of the input image signal exceeds a certain level, the dots are concentrated and the clustered dots constituting the latent image are easily recognized clearly by human eyes.

  Therefore, in the latent image dither matrix, it is preferable to keep the gradation of the possible input image signal within a certain range. In the latent image dither matrix as shown in FIG. 3, even if the size of the dither matrix changes, if the gradation of the input image signal is the same, substantially the same concentrated dot arrangement can be obtained. Therefore, it is possible to change the density per unit area by keeping the gradation of the input image signal with respect to the latent image dither matrix constant and changing the size of the dither matrix.

(Satellite dot arrangement)
If the size of the dither matrix is increased and the density per unit area is reduced, when the dot-concentrated dither matrix is arranged in a tile pattern, the space between the dots spreads to be discernible to the human eye. Due to the visual characteristics, there arises a problem that the latent image and the visible image in the original anti-counterfeiting tint block are easily distinguished.

  As a countermeasure for this problem, the diameter of the dot represented by the dot-concentrated dither matrix (hereinafter referred to as “large dot”) was reduced, and the diameter was reduced between the arranged large dot and large dot. It is conceivable to arrange new dots (hereinafter referred to as “satellite dots”) different from the large dots according to the area, around the large dots.

  With the arrangement of satellite dots, the black pixel area ratio and the relationship between gradation and density (gradation characteristics) as described in 801 of FIG. 8 are maintained, and even when large dots are arranged by the latent image threshold pattern, The space between the large dot and the large dot becomes inconspicuous due to the arrangement of satellite dots arranged around the large dot, and it becomes possible to make it difficult to distinguish the latent image and the visible image in the anti-counterfeiting tint block of the original image. .

  The latent image threshold pattern is assumed to remain after copying, and when the latent image threshold pattern includes a satellite dot, the density of the latent image threshold pattern is large even if the density of the satellite dot decreases. If dots remain, it will make sense as a latent image. Therefore, whether the satellite dots disappear or remain after copying, the role as a latent image is secured by the remaining large dots. Further, in order to know parameters for the latent image threshold pattern including satellite dots to remain after copying, a test printing sheet described later can be used.

The configuration and processing flow of the pattern generation unit that generates a latent image threshold pattern that can include satellite dots will be described with reference to the block diagram of FIG. 9 and the flowchart of FIG.
A pattern generation unit 900 shown in FIG. 9 includes a large inter-dot space length calculation unit 901, a satellite dot necessity determination unit 902, a large dot gradation and satellite dot gradation determination unit 903, a large dot pattern generation unit 904, and satellite dots. The pattern generation unit 905, the latent image threshold pattern synthesis unit 906, and the latent image threshold pattern output unit 907 are configured.

  A large inter-dot space length calculation unit 901 calculates a large inter-dot space length from the latent image threshold pattern gradation 911 and the dot-concentrated dither matrix 910. Here, the space length between large dots is the length of a space portion (blank length) between large dots as shown in FIG. In FIG. 12, the inter-dot space length (x, y) in the x and y directions is shown. When large dots are arranged on an equally spaced grid, the large dot blank lengths in the x and y directions are the same. The space length calculation unit 901 between large dots can calculate the space length between large dots in the x direction and the y direction based on the arrangement of large dots that form the latent image. In determining whether satellite dots are necessary, the satellite dot necessity determining unit 902 refers to one of the values.

  In addition, when calculating the space length between large dots, the gray level 911 of the latent image threshold pattern referred to by the large dot space length calculation unit 901 is the pixel of the black pixel in the latent image threshold pattern 114 (FIG. 1A). This is the sum of the number of satellite dots, which will be described later, and the number of large dots.

  The satellite dot necessity determination unit 902 is a part that determines whether a satellite dot is necessary. Specifically, the space length between large dots calculated by the space length calculation unit 901 between large dots, and the space length upper limit value between large dots (a value determined in advance in consideration of human visual characteristics). If the calculated space length between the large dots is larger than the space length upper limit value between the large dots, the satellite dot necessity determining unit 902 determines that the satellite dot is necessary, and if not, the satellite dot is Judge that it is unnecessary.

  The large dot gradation / satellite dot gradation determination unit 903 determines the determination result of the satellite dot necessity determination unit 902, the gradation 911 of the latent image threshold pattern, and the satellite dot gradation initial value 912 (an appropriate size is determined in advance). And a satellite dot gradation (the number of black pixels constituting the satellite dot) and a large dot gradation (the number of black pixels constituting the large dot). Details of the determination method will be described later. If the satellite dot necessity determination unit 902 determines that no satellite dot is necessary, the output satellite dot gradation is 0, and the large dot gradation is equal to the gradation of the latent image threshold pattern 114. .

  The large dot pattern generation unit 904 generates a large dot pattern (dot concentration type dither matrix) based on the large dot gradation determined by the dot concentration type dither matrix 910 and the large dot gradation and satellite dot gradation determination unit 903. Is one of the elements that make up the latent image threshold pattern.)

  The satellite dot pattern generation unit 905 is a satellite dot pattern (large dot pattern) based on the satellite dot pattern gradation calculated by the dot concentration type dither matrix 910 and the large dot gradation and satellite dot gradation determination unit 903. One of the elements constituting the latent image threshold pattern is generated. This generation procedure will be described later in detail.

  The latent image threshold pattern composition unit 906 is a part that composes a latent image threshold pattern from the satellite dot pattern and the large dot pattern.

  The latent image threshold pattern output unit 907 is a part that outputs the latent image threshold pattern synthesized by the latent image threshold pattern synthesis unit 906.

  Here, a large dot pattern and a satellite dot pattern are considered as elements of the latent image threshold pattern, and it is assumed that both the large dot pattern and the satellite dot pattern are binary images of 1 bit per pixel.

When the satellite dot necessity determination unit 902 determines that there is no need for satellite dots, the satellite dot gradation is set to 0, and the satellite dot pattern is not used as an element of the latent image threshold pattern. .
Next, the flow of processing of the pattern generation unit 900 will be described using the flowchart of FIG.

  In order to indicate that the copy is different from the input original image (input original image 119 in FIG. 1A), a tint block image including a latent image that appears during copying and a background that becomes lighter than the latent image during copying is displayed. The generated tint block image generation method is based on the arrangement of large dots (first dots) constituting a latent image, for example, a blank length calculation step for calculating a blank length between first dots shown in FIG. 12 (S1004 in FIG. 10). And a determination step (S1005 in FIG. 10) for determining whether a satellite dot (second dot) smaller than the first dot is necessary based on the blank length obtained by the calculation in the blank length calculation step, and the determination of the determination step When the arrangement of the second dots is necessary, a pattern generation step (S1008 in FIG. 10) for generating a pattern for arranging the second dots around the first dots is provided.

  Specifically, first, in step S1001, the gradation 911 of the latent image threshold pattern is input. In step S1002, the dot-concentrated dither matrix 910 is input, and in step S1003, the inter-large dot space length upper limit is input, and the inter-dot space length is calculated (S1004). Then, based on the calculation result of the space length between the large dots, it is determined whether satellite dots are necessary (S1005).

  If it is determined that a satellite dot is necessary, the process proceeds to step S1006 to determine a satellite dot gradation and a large dot gradation (S1006). In step S1007, it is determined whether the satellite dot gradation is 0 or not ( If it is not 0 (S1007-NO), the process proceeds to step S1008. If the satellite dot gradation is 0 (S1007-YES), the process proceeds to step S1011.

  In step S1008, the satellite dot pattern generation unit 905 generates a satellite dot pattern. In step S1009, the large dot pattern generation unit 904 generates a large dot pattern, and then the latent image threshold pattern synthesis unit 906 generates a latent image. An image threshold pattern is synthesized (S1009).

  On the other hand, if it is determined in step S1005 that no satellite dot is necessary, or if the satellite dot gradation is determined to be 0 in step S1007, the large dot pattern generation unit 904 determines that the large dot pattern generation unit 904 in step S1011. A pattern is generated, and in step S1012, the latent image threshold pattern synthesis unit 906 performs synthesis of the latent image threshold pattern. Then, the last synthesized latent image threshold pattern (S1010 or S1012) is output (S1011).

  The above is the processing flow of the pattern generation unit 900 that generates a latent image threshold pattern that can include satellite dots.

(Procedure for generating satellite dot pattern and synthetic latent image threshold pattern)
Next, details of the procedure for generating the satellite dot pattern and the synthetic latent image threshold pattern including the satellite dot pattern will be described with reference to FIG.
FIG. 11 shows three examples (a), (b), and (c) as examples of the arrangement of satellite dot patterns. In the drawing, a large dot indicates a large dot, and a small dot indicates a satellite dot.

  Note that the pattern generation unit 900 that generates the latent image threshold pattern that can include satellite dots can arrange satellite dots as shown in FIG. 11 as an example. The present invention is not limited to the examples, and is not limited to the three arrangement examples (a), (b), and (c) in FIG.

  An example of the arrangement of satellite dots shown in FIG. 11 will be specifically described.

  First, as shown in FIG. 11A, the large dots are arranged on a line connected in a lattice pattern, and four satellite dots are arranged around the large dots, that is, the large dots. 4 shows a state in which four satellite dots are arranged at the midpoint of the arrangement interval.

  In FIG. 11 (b), as in (a), four satellite dots are arranged around the large dot, but as shown in the figure, the midpoint (arrangement) on the line connecting the large dots at an angle of 45 degrees is arranged. The difference is that a large dot is placed at the middle point of the interval.

  FIG. 11C shows the result of superposing the logical sum of (a) and (b).

FIG. 13 is a diagram exemplifying a latent image threshold pattern showing one large dot and satellite dots arranged around the large dot in the satellite dot arrangement example of FIG. 11 including the arrangement boundary. At this time, the latent image threshold pattern in FIG. 13C is obtained by superposing the logical sum of the large dot pattern and the satellite dot pattern. If attention is paid to only one latent image threshold pattern, the satellite dots may be divided into 2 to 4, so that the satellite dot gradation is appropriately determined in advance in consideration of the arrangement of the satellite dots. To do.
In creating the satellite dot pattern, a dot-concentrated dither matrix is used as in the creation of the large dot pattern. For each of the three cases (a), (b), and (c) described above, the procedure for creating the satellite dot pattern and the latent image threshold value pattern will be described while showing each pattern being generated.

(Procedure for creating FIG. 13A)
The satellite dot pattern generation unit 905 performs horizontal and horizontal operations on the large dot 1101 (first dot) based on the gradation of the input satellite dot (second dot) and the input dot concentration type dither matrix. Satellite dots (second dots: for example, 1104) are arranged at the midpoint of arrangement intervals (P1, P2: see FIG. 11A) with other large dots (1102, 1103...) Arranged in the vertical direction. 1105... The same applies to the relationship with other satellite dots (1106, 1107) arranged around the large dot 1101 (first dot) of interest.

  FIG. 14 is a diagram showing a procedure for creating a latent image threshold pattern (FIG. 13A) corresponding to the arrangement of the satellite dot patterns in FIG. First, a pattern 1401 is created using a dot concentration type dither matrix. As shown in the figure, the created pattern 1401 is equally divided into four parts, upper left, upper right, lower left and lower right, and numbers 1 to 4 are assigned to the divided areas as shown in the figure. Then, a pattern 1402 and a pattern 1403 are created by exchanging four areas of the 1401 pattern. In the pattern 1402, the four areas into which the pattern 1401 is divided are replaced with the upper left as the lower left, the upper right as the lower right, the lower left as the upper left, and the lower right as the upper right. In the pattern 1403, the four areas divided by the pattern 1401 4 Two areas are swapped with the upper left as the upper right, the upper right as the upper left, the lower left as the lower right, and the lower right as the lower left. Then, the logical sum of the pattern 1402 and the pattern 1403 is obtained to form one pattern such as 1404. This pattern 1404 is a satellite dot pattern. This process is executed by the satellite dot pattern generation unit 905.

  Then, the latent image threshold pattern composition unit 906 composes the large dot pattern 1405 generated by the large dot pattern generation unit 904 and the satellite dot pattern 1404 to create a latent image threshold pattern 1406.

Here, when determining the gradation of the large dot, the large dot gradation and satellite dot gradation determination unit 903 performs the following calculation and determines it according to the calculation result.
(Latent image threshold pattern gradation) -2 * (satellite dot gradation) (4)
If the calculation result of Expression (4) is not 0 or less, the large dot gradation and satellite dot gradation determination unit 903 determines the value of Expression (4) as the large dot gradation. When the value of the expression (4) is 0 or less, the large dot gradation and satellite dot gradation determination unit 903 makes the large dot gradation equal to the gradation of the latent image threshold pattern and sets the satellite dot gradation to 0. . That is, no satellite dot is arranged.

(Procedure of FIG. 13B)
The satellite dot pattern generation unit 905 focuses on, for example, the large dot (first dot) 1110 based on the input gradation of the satellite dot (second dot) and the input dot concentration type dither matrix, Satellite dots (second dots) (1113, 1114) at the midpoint of the arrangement interval (P3, P4) with other first dots (1111, 1112) arranged in an oblique direction (for example, ± 45 ° direction) Place. The same applies to the relationship with other satellite dots (1115, 1116) arranged around the large dot 1110 (first dot) of interest.

FIG. 15 is a diagram showing a procedure for creating a latent image threshold pattern (FIG. 13B) corresponding to the arrangement of the satellite dot patterns in FIG. First, a pattern 1501 is created using a dot concentration type dither matrix. As shown in the figure, the created pattern 1501 is equally divided into four parts, upper left, upper right, lower left, and lower right, and numbers 1 to 4 are assigned to the divided areas as shown in the figure. Then, a pattern 1502 is created by replacing the four areas of the 1501 pattern. In the pattern 1502, the four areas obtained by dividing the pattern 1501 are replaced with the upper left as the lower right, the upper right as the lower left, the lower left as the upper right, and the lower right as the upper left. This pattern 1502 becomes a satellite dot pattern. This process is executed by the satellite dot pattern generation unit 905. Then, the latent image threshold pattern composition unit 906 composes the large dot pattern 1503 generated by the large dot pattern generation unit 904 and the satellite dot pattern 1502 to create a latent image threshold pattern 1504.
Here, when determining the gradation of the large dot, the large dot gradation and satellite dot gradation determination unit 903 performs the following calculation and determines it according to the calculation result.

(Gradation of latent image threshold pattern)-(satellite dot gradation) (5)
If the calculation result of Expression (5) is not 0 or less, the large dot gradation and satellite dot gradation determination unit 903 determines the value of Expression (5) as the large dot gradation. When the value of the expression (5) is 0 or less, the large dot gradation and satellite dot gradation determination unit 903 makes the large dot gradation equal to the gradation of the latent image threshold pattern and sets the satellite dot gradation to 0. . That is, no satellite dot is arranged.

(Procedure for creating FIG. 13C)
The satellite dot pattern generation unit 905 performs horizontal and horizontal operations for the large dot 1120 (first dot) based on the gradation of the input satellite dot (second dot) and the input dot concentration type dither matrix. A second dot (1131, 1132) at the first midpoint of the first arrangement interval with the other first dots (1121, 1122) arranged in the vertical direction, and an oblique direction with respect to the first dot 1120 The second dots (1133, 1134) are arranged at the second midpoints of the second arrangement interval with the other first dots (1123, 124) arranged in the, respectively. The same applies to the relationship with other satellite dots arranged around the large dot 1120 of interest.

FIG. 16 is a diagram showing a procedure for creating a latent image threshold pattern (FIG. 13C) corresponding to the satellite dot pattern arrangement of FIG. First, a pattern 1601 is created using a dot concentration type dither matrix. As shown in the figure, the created pattern 1601 is equally divided into four parts, upper left, upper right, lower left and lower right, and numbers 1 to 4 are assigned to the divided areas as shown in the figure. Then, the following three patterns are created.
(1) In the pattern 1602, the four areas into which the pattern 1601 is divided are replaced with the upper left as the lower right, the upper right as the lower left, the lower left as the upper right, and the lower right as the upper left.
(2) In the pattern 1603, the four areas obtained by dividing the pattern 1601 are replaced with the lower left at the upper left, the lower right at the upper right, the upper left at the lower left, and the upper right at the lower right.
(3) In the pattern 1604, the four areas obtained by dividing the pattern 1601 are replaced with the upper left as the upper right, the upper right as the upper left, the lower left as the lower right, and the lower right as the lower left.

  The pattern 1605 is created by taking the logical sum of the above three patterns (1602, 1603, 1604). This pattern 1605 becomes a satellite dot pattern. This process is executed by the satellite dot pattern generation unit 905. Then, the latent image threshold pattern composition unit 906 composes the large dot pattern 1607 generated by the large dot pattern generation unit 904 and the satellite dot pattern 1605 to create a latent image threshold pattern 1608.

  Here, when determining the gradation of the large dot, the large dot gradation and satellite dot gradation determination unit 903 performs the following calculation and determines it according to the calculation result.

(Gradation of latent image threshold pattern) -3 * (gradation of satellite dots) (6)
If the calculation result of the expression (6) is not 0 or less, the large dot gradation and satellite dot gradation determination unit 903 determines the value of the expression (6) as the large dot gradation. When the value of the expression (6) is 0 or less, the large dot gradation and satellite dot gradation determination unit 903 makes the large dot gradation equal to the gradation of the latent image threshold pattern and sets the satellite dot gradation to 0. . That is, no satellite dot is arranged.

  The above is the details of the generation procedure of the satellite dot pattern and the latent image threshold pattern.

(Background pattern density calibration function)
Differences in printer engine characteristics and dither matrix that outputs threshold patterns, individual printer differences, printing environment such as humidity and temperature, engine durability, paper (media) differences, printer ink and toner differences, etc. Concentration instability depending on various conditions. Accordingly, the optimum input gradation for each of the background portion and the latent image portion dither matrix may differ depending on the printer model, dither matrix, individual printer, printing environment, paper, ink, toner, and the like. .

  Therefore, even when the engine characteristics and the printing environment of the printer are different, it is necessary to generate a copy-forgery-inhibited pattern image after obtaining a background threshold pattern and a latent image threshold pattern having substantially the same density during printing.

  However, it is actually difficult to automatically calculate the optimum background threshold pattern and latent image threshold pattern in consideration of all the fluctuation factors including fluctuations due to the printing environment. For each printer, it is necessary to implement a function for obtaining a background threshold pattern and a latent image threshold pattern in which the density of the background portion and the latent image portion is substantially the same, that is, a tint block density calibration function.

  As a method for mounting the background pattern density calibration function, a method of adjusting the gradation of the input image signal with respect to one or both of the background dither matrix and the latent image dither matrix and adjusting the density so as to be almost equal can be considered.

  FIG. 17 is a block diagram showing the internal configuration of the tint block density test printing apparatus, and the functions of the tint block density test printing apparatus can be implemented in an application on a computer or a printer driver.

  The copy-forgery-inhibited pattern density test printing apparatus includes a setting information input unit 1701, a pattern generation unit 1702, a trial-printed copy-forgery-inhibited pattern image generation unit 1703, a print data processing unit 1704, and a printing unit 1705.

  First, the setting information input unit 1701 performs a process of reading the setting information from the initial setting file in which the setting information is stored, or a process of receiving the setting information input through the user interface.

  The pattern generation unit 1702 generates a pattern necessary for generating a tint block based on the setting information input from the setting information input unit 1701 and outputs the pattern to the subsequent test print tint block image generation unit. In the case of the present embodiment, the pattern generated from the input setting information is a background threshold pattern and a latent image threshold pattern (this latent image threshold pattern is based on the arrangement of the large dots and satellite dots described above). It becomes. In the tint block density test printing apparatus, the pattern generation unit 1702 generates a plurality of background threshold patterns and latent image threshold patterns.

  Next, the trial-printed tint block image generation unit 1703 generates a trial-printed tint block pattern image based on the pattern input from the pattern generation unit 1702.

  The print data processing unit 1704 performs necessary image processing on the test print copy-forgery-inhibited pattern image generated by the test print copy-forgery-inhibited pattern image generation unit 1703. However, the print data processing unit takes into account the pixel values (cyan, magenta, yellow, black) of the copy-forgery-inhibited pattern image in the copy-forgery-inhibited pattern composite output original image in consideration of the color mixture of a plurality of inks and toners during printing. Perform image processing. The trial print copy-forgery-inhibited pattern image that has undergone the necessary image processing is converted into a data format that can be interpreted by the printer (for example, a data format described in a page description language or a data format that has been expanded into a print bitmap), and is printed later. Sent to the unit 1704.

  The printing unit 1704 prints out a test-printed tint block image according to the input data.

  Next, a description will be given of a test print sheet in which a plurality of copy-forgery-inhibited pattern images (patches) generated by the test-printed copy-forgery-inhibited pattern image generation unit 1703 are arranged in a two-dimensional manner. Based on this test printed sheet, it is possible to evaluate the latent image threshold pattern including satellite dots.

  A test printing sheet in which the density of the background portion and the latent image portion is two-dimensionally changed is printed with a background pattern having a light density to a dark density, and a plurality of background portions and latent images are printed on one sheet. There are patches where the density of the parts is almost the same. Therefore, it is possible to realize an effect that the density of the background pattern can be selected as a parameter.

  Conventionally, the user can freely select the latent image background area designation image, the camouflage area designation image, and the color information. However, if the density of the tint block can be selected using a test printing sheet, the user has more choices. There are benefits. The test printing sheet arranged two-dimensionally by changing the density of both the background portion and the latent image portion has an effect of further increasing the added value in the tint block synthesis printing apparatus.

FIG. 17 shows an example of a test printing sheet in which patches having different densities in the background portion and the latent image portion are two-dimensionally arranged. Each patch always includes a latent image portion and a background portion, and may include a camouflage. In each patch in FIG. 17, a hatched portion indicates a latent image portion, and a plain portion indicates a background portion. In FIG. 17, the latent image background area designating image for designating the latent image portion and the background portion is a rectangular rectangle. However, the latent image portion and the background portion are arranged side by side. It may be arranged so that it can be easily determined.
In the test printing sheet of FIG. 17, the density of the latent image portion is changed in the horizontal direction of the paper, and the density of the background portion is changed in the vertical direction.

In advance, considering the engine characteristics of the printer, the gradation of the dither matrix, etc., the patch existing at the center of the patch array arranged in the vertical direction is set so that the densities of the latent image portion and the background portion are substantially equal. Even when there are density fluctuations due to deterioration of the environment and engine performance, it is easy to find a patch in which the density of the latent image portion and the background portion are substantially equal.
However, since there is actually a density fluctuation depending on the characteristics of the printer and the printing environment, the density of the latent image portion and the background portion are almost equal in the patch at the center of the patch array arranged in the vertical direction in the test printing sheet. Do not mean.

  In the test print sheet, the density of the background portion is high in one direction in the vertical direction (upward direction of the paper in FIG. 17), and the density of the background portion is light in the other direction (downward direction of the paper in FIG. 17). It is set to be.

  In FIG. 17, the density of the background portion of the background pattern is changed with respect to the vertical direction. However, as described above, the gradation of the input image signal with respect to the background portion dither matrix can be changed as a method of changing the density of the background portion. There are ways to change.

  FIG. 18 is a diagram showing an image processing apparatus having a tint block density calibration function. A selection information input unit 1801 and a pattern generation unit 1802 are arranged in the previous stage of the tint block image generation device 1803 described in FIG. 1A.

  The selection information input unit 1801 inputs information about a patch determined to be optimal (for example, a number printed in the vicinity of the patch) as selection information through the user interface. At this time, the optimum copy-forgery-inhibited pattern image patch has the darkness desired by the user, and the background portion and the latent image portion have substantially the same density, and the test printing sheet is copied by the target copying machine. In this patch, the latent image portion remains and the background portion disappears. With this setting, it is also possible to set so that satellite dots remain after copying. If there is no target copying machine, it is possible to check whether the latent image portion remains and the background portion disappears after copying with an available copying machine.

  Next, the pattern generation unit 1802 generates a pattern necessary for generating a background pattern based on the selection information input from the selection information input unit 1801, and inputs the pattern to the background pattern image generation device 1803 at the subsequent stage. In the case of the present embodiment, patterns generated from input selection information are a background threshold pattern and a latent image threshold pattern (this latent image threshold pattern is based on the arrangement of large dots and satellite dots described above). .

  The copy-forgery-inhibited pattern image generation device 1803 generates a copy-forgery-inhibited pattern image based on the background threshold pattern and the latent image threshold pattern input from the preceding pattern generation unit 1802, combines the copy-forgery-inhibited pattern image with the input document image, and prints out the output document. . Since the processing in the tint block image generation apparatus 1803 has already been described in detail, the description thereof is omitted.

  As described above, according to the present embodiment, it is possible to generate a latent image that makes the area between the dots constituting the latent image inconspicuous while maintaining the density of the latent image portion.

[Second Embodiment]
Next, a second embodiment according to the present invention will be described. The present embodiment relates to a configuration in which the above processing is performed by a computer. FIG. 19 is a diagram showing a basic configuration of an information processing apparatus (hereinafter referred to as “computer”) according to the present embodiment. For example, in this computer, when all functions except the printing unit (or the printer engine of the printing unit) in FIGS. 1A, 17 and 18 of the first embodiment are executed, each functional configuration is expressed by a program. Such a function can be realized by reading it into a computer.

  In the figure, reference numeral 1911 denotes a CPU, which controls the entire computer using programs and data stored in a RAM 1912 and ROM 1913 and performs each process described in the first embodiment.

  Reference numeral 1912 denotes a RAM which has an area for temporarily storing programs and data loaded from the external storage device 1918 and programs and data downloaded from other computer systems 1924 via an I / F (interface) 1923. An area required for the CPU 1911 to perform various processes is provided.

  Reference numeral 1913 denotes a ROM which stores computer function programs and setting data. Reference numeral 1914 denotes a display control device, which performs control processing for displaying images, characters, and the like on the display 1915. Reference numeral 1915 denotes a display that displays images, characters, and the like. As a display, a CRT, a liquid crystal screen or the like can be applied.

Reference numeral 1916 denotes an operation input device, which includes a device such as a keyboard and a mouse that can input various instructions to the CPU 1911. When manually inputting a camouflage area designation image, a latent image background area designation image, or the like, these can be inputted via the operation input device 1916.
Reference numeral 1917 denotes an I / O for notifying the CPU 1911 of various instructions input via the operation input device 1916.

  An external storage device 1918 that functions as a large-capacity information storage device such as a hard disk is an OS (operating system) and a program for causing the CPU 1911 to execute processing according to each of the above embodiments, a background dither matrix, a latent image dither matrix, and generation The copy-forgery-inhibited pattern image, the input document image, and the like are stored. Writing information to the external storage device 1918 and reading information from the external storage device 1918 are performed via the I / O 1919.

Reference numeral 1921 denotes a printer for outputting documents and images. Output data is sent from the RAM 1912 or the external storage device 1918 via the I / O 1922.
Examples of printers for outputting documents and images include ink jet printers, laser beam printers, thermal transfer printers, and dot impact printers.

  Reference numeral 1930 denotes a bus connecting the CPU 1911, ROM 1913, RAM 1912, I / O 1922, I / O 1919, display control device 1914, I / F 1923, and I / O 1917.

  In the present embodiment, the processing except the printing unit of the copy-forgery-inhibited pattern image generation device and the image processing device having a trial printing function is performed by a computer, but the processing performed by the computer is performed using a dedicated hardware circuit in the printer. It is also possible.

  Each of the above-described embodiments is merely a specific example for carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

[Other Embodiments]
Note that, even if the present embodiment is applied to a system composed of a plurality of devices (for example, a host computer, interface device, reader, printer, etc.), a device composed of a single device (for example, a copier, a facsimile machine, etc.) ).

  Also, an object of the present invention is to supply a recording medium (or storage medium) in which a program code of software that realizes the functions of the above-described embodiments is recorded to a system or apparatus, and a computer (or CPU or CPU) of the system or apparatus. Needless to say, this can also be achieved when the MPU) reads and executes the program code stored in the recording medium. In this case, the program code itself read from the recording medium realizes the functions of the above-described embodiment, and the recording medium on which the program code is recorded constitutes the present embodiment. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  Further, after the program code read from the recording medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the CPU or the like provided in the card or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  When this embodiment is applied to the recording medium, the recording medium stores program codes corresponding to the flowcharts and functional configurations described above.

It is a block diagram explaining the internal process of the tint block image generation device in this embodiment. It is the figure which showed the example of the latent image background area | region designation | designated image and the camouflage area | region designation | designated image. It is a figure showing an example of a latent image threshold pattern and a background threshold pattern. 5 is a flowchart for explaining a flow of internal processing of a tint block image generation unit 101; FIG. 4 is a diagram illustrating an example of a 4 × 4 spiral dither matrix. FIG. 4 is a diagram illustrating an example of a threshold pattern (dot arrangement) obtained by performing threshold processing on an input image signal using the 4 × 4 spiral dither matrix of FIG. 3. It is a figure which shows the example of a 4x4 Bayer type dither matrix. FIG. 6 is a diagram illustrating a threshold pattern (dot arrangement) obtained by performing threshold processing on a predetermined input image signal using the 4 × 4 Bayer type dither matrix of FIG. 5. It is a figure for comparing the area ratio of the black pixel of the background threshold value pattern 115 and the latent image threshold value pattern 114. FIG. It is a figure which shows the relationship between the area ratio of the black pixel of the threshold pattern obtained by carrying out threshold processing of the input image signal with a dither matrix, and the density when the threshold pattern is printed. It is a block diagram which shows the structure of the pattern generation part which produces | generates the latent image threshold value pattern which can contain a satellite dot. It is a flowchart explaining the flow of a process of the pattern generation part which produces | generates the latent image threshold value pattern which can contain a satellite dot. It is a figure which shows the example of arrangement | positioning of a satellite dot pattern. It is a figure explaining the space length between large dots. FIG. 12 is a diagram exemplifying a latent image threshold pattern that shows one large dot and satellite dots arranged around the large dot in the satellite dot arrangement example of FIG. 11 including the arrangement boundary. It is a figure which shows the preparation procedure of the latent image threshold value pattern (FIG.13 (a)) corresponding to arrangement | positioning of the satellite dot pattern of Fig.11 (a). It is a figure which shows the preparation procedure of the latent image threshold value pattern (FIG.13 (b)) corresponding to arrangement | positioning of the satellite dot pattern of FIG.11 (b). It is a figure which shows the preparation procedure of the latent image threshold value pattern (FIG.13 (c)) corresponding to arrangement | positioning of the satellite dot pattern of FIG.11 (c). It is a block diagram showing an internal configuration of a tint block density test printing apparatus. It is a figure which shows the tint block image generation apparatus provided with the tint block density calibration function. It is a block diagram which shows the structure of the information processing apparatus concerning this embodiment.

Claims (10)

An image processing method for generating a copy-forgery-inhibited pattern image including a latent image that appears at the time of copying and a background that becomes lighter than the latent image at the time of copying in order to indicate that the copy is different from the input original image. And
A blank length calculating step for calculating a blank length between the first dots based on an arrangement of the first dots constituting the latent image;
A determination step of determining whether it is necessary to arrange a second dot smaller than the first dot based on the blank length calculated by the blank length calculation step;
A pattern generation step of generating a pattern for arranging the second dots around the first dots when the second dots need to be arranged in accordance with the judgment of the judgment step. Method. 2. The image according to claim 1, wherein the pattern generation step generates an arrangement pattern of the second dots based on a gradation of the second dots and an input dot concentration type dither matrix. Processing method. The pattern generation step includes arranging the second dots at a midpoint of an arrangement interval with other first dots arranged in a horizontal direction and a vertical direction with respect to the first dots. 3. The image processing method according to 1 or 2. The pattern generation step includes arranging the second dots at a midpoint of an arrangement interval between the first dots and other first dots arranged in an oblique direction. 3. The image processing method according to 2. In the pattern generation step, the first midpoint of the first arrangement interval with the other first dots arranged in the horizontal direction and the vertical direction with respect to the first dots and the diagonal direction with respect to the first dots 3. The image processing method according to claim 1, wherein the second dot is arranged at a second midpoint of a second arrangement interval with another arranged first dot. A gradation determining step for determining the gradation of the first dot from the gradation of the second dot and the gradation of the latent image threshold pattern;
A first dot pattern determination step for determining a pattern of the first dot based on the gradation of the first dot determined in the gradation determination step and the input dot-concentrated dither matrix. The image processing method according to claim 1, further comprising: The method further comprises a pattern synthesis step for synthesizing the arrangement of the second dots generated by the pattern generation step and the pattern of the first dots determined by the first dot pattern determination step. The image processing method according to claim 1. An image processing apparatus that generates a copy-forgery-inhibited pattern image that includes a latent image that appears during copying and a background that becomes lighter than the latent image during copying to indicate that the copy is different from the input original image. And
A blank length calculation means for calculating a blank length between the first dots based on an arrangement of the first dots constituting the latent image;
Determination means for determining whether the arrangement of the second dots smaller than the first dots is necessary based on the blank length calculated by the blank length calculation means;
And a pattern generation unit configured to generate a pattern for arranging the second dots around the first dots when the second dots need to be arranged in accordance with the determination by the determination unit. apparatus. A program for causing a computer to execute the image processing method according to claim 1. A computer-readable storage medium storing the program according to claim 9.

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