Method and software for creating data for latent image prints

Abstract

To provide a method and software for generating latent image printing data for obtaining a latent image printout having good print quality regardless of the maker or model of a printer.SOLUTION: The invention relates to a method and software for generating data for a latent image printout in which an invisible image is visible under infrared light. An RGB image data is formed by forming pseudo-black, pseudo-cyan, pseudo-magenta, and pseudo-yellow patterns expressed in the RGB color space without overlapping each other.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to security printed materials that require anti-counterfeiting and anti-tampering functions, such as passports, securities, identification cards, other certificates, important documents, tickets, cards, etc., and relates to a method and software for creating data for latent image printed materials that require authenticity and security and can be output from a wide variety of printers, including those for general home use, without using special substrates, inks, or dedicated output machines. [Background technology]

[0002] It is important to provide high security to printed matter such as passports, securities, identification cards, other certificates, important documents, tickets, and cards by providing the printed matter with a forgery and tamper-proof effect. A common method for providing such printed matter with a forgery and tamper-proof effect is to apply some means and action to the printed matter to make an invisible image that cannot be recognized by the naked eye appear. Representative examples include providing the printed matter with functional ink that does not allow the color to be reproduced normally by a color copier, and providing the printed matter with copy prevention lines that are composed of lines that cannot be reproduced by copying.

[0003] However, in recent years, the performance of color copying machines has improved, and the copy resolution and image reproducibility have improved, so the copy prevention effect of the copy prevention lines has decreased. In addition, the use of functional inks such as fluorescent inks, which are invisible under normal light, on printed matter has also become less effective in preventing counterfeiting, because fluorescent ink materials are commercially available and easily available to anyone.

[0004] In order to solve the above problems, the applicant has filed a patent application for a latent image print, which, as a measure to prevent counterfeiting by copying using a high-resolution copier, does not require the use of special substrates or inks, and in which a gradation image is visible when observed with the naked eye under normal light, and a different gradation image (latent image) is visible when observed using an infrared camera (see Patent Document 1).

[0005] The above-mentioned latent image prints can be printed in large quantities and continuously using an offset printing machine, etc., or printed as needed using a printer. When printing using an offset printing machine, etc., the CMYK data in the data creation can be printed directly, so there is no particular difficulty in creating platemaking data by specifying the colors of black (K) ink, which will be the latent image, and cyan (C), magenta (M), and yellow (Y) inks, which will be the gradation image, in advance, and then printing and printing can be performed, as latent image prints having the desired print quality and effect can be easily created.

[0006] On the other hand, in recent years, the IT environment has been improved and computers and printers are in place as infrastructure, so a method of adding a latent image to various certificates that require anti-counterfeiting effects, such as resident cards, seal certificates, family register extracts and certified copies, and outputting them on a printer via a network to obtain a latent image printout has been attracting attention. However, there are various issues involved in creating a latent image printout using a printer.

[0007] The first problem is the low image resolution. In Patent Document 1, as shown in the printed pattern portion (2a) in FIG. 9(a), the visible image area (a) and the invisible image area (b) are arranged in a matrix shape with a desired positional relationship, and the visible image area (a) is printed with cyan (C), magenta (M) and yellow (Y) toner or pigment ink that does not contain infrared absorbing pigment, and the invisible image area (b) is printed with black (K) toner or pigment ink that contains infrared absorbing pigment in addition to cyan (C), magenta (M) and yellow (Y). The continuous gradation of the invisible image (5) can be expressed by the image area of ​​black (K) in the invisible image area (b).

[0008] At this time, in order to maintain the image resolution of the invisible image with continuous gradations, it was necessary to maintain the minimum number of pixels in the invisible image area (b). However, with output devices with low resolution, it was not possible to set sufficient pixels to create continuous gradations, and the image resolution was limited to the range that the output device could handle. For example, with a color printer with an output resolution of 600 dpi, the invisible image area (b) required at least four pixels in length and width to create an invisible image with 16 gradations, and the number of lines for the printing dots converted from this was an image resolution equivalent to 60 lines per inch.

[0009] In addition, the document file forming the image structure of the technology described in Patent Document 1 is basically a 32-bit CMYK image, and an output device is required that can print the information of each of the cyan (C), magenta (M), yellow (Y) and black (K) shown in the print pattern portion (2a) in Fig. 9(a) as is. In other words, the output device was limited to expensive color multifunction machines and digital printing machines equipped with a printer driver that can turn off color separation.

[0010] On the other hand, when using an inexpensive home printer, black and gray can be produced by mixing four colors of toner - cyan (C), magenta (M), yellow (Y) and black (K) - or pigment ink, but it is also possible to print with just black (K), so the printer driver's control system generally uses a UCR (Under Color Removal) method, which removes equal amounts of the three colors cyan (C), magenta (M) and yellow (Y) from the black areas and increases the amount of black (K) by that amount. For this reason, as shown in FIG. 9(b), if the visible image area (a) is printed in cyan (C), magenta (M), and yellow (Y), but the invisible image area (b) is printed only in black (K), the entire invisible image area (b) will be colored, and the line shape of the invisible image (5) that was originally composed of black (K) of the 32-bit CMYK image will not be expressed, resulting in the problem that the latent image will not be visible when the latent image print is viewed with an infrared light.

[0011] The second issue is uneven print quality due to differences in printer manufacturers and models. A wide variety of printer models are sold by various manufacturers, and the printer control methods, control programs, printer drivers, etc. are often developed independently by each manufacturer, which can lead to differences in print quality of printed matter output by the printer. For example, when the same print image data is input to an image processing device such as a computer and output by printers of different manufacturers, models, etc., the print images printed by each printer are printed with different densities, hues, etc.

[0012] If this is due to the toner density, color balance, output method, etc. of each printer, the density and hue can be adjusted by changing the output settings already installed in the printer. However, the third problem is uneven print quality caused by data conversion in computer processing. To be more specific, in Windows (registered trademark) and MacOS, etc., the RGB color gamut is supported as the standard color gamut at the OS level, and when CMYK data is processed by a personal computer, the data is converted from CMYK to RGB color space. Then, when the data created by the personal computer is output to the printer, it is again converted from RGB color space data to CMYK data, so the output latent image printout sometimes does not have the desired density or hue.

[0013] In addition, some simple home printers and mobile printers that run on rechargeable batteries can only accept RGB data, and if CMYK data is input, it is forcibly converted to RGB data, so the color tone of the initially created data may differ from the density and hue of the output printed image.

[0014] The above-mentioned variations in print quality (density and hue of the printed image) output from the printer not only result in colors that were not intended when the data was created, but also cause problems such as the latent image being invisible when the latent image print is observed under infrared light, or a latent image that should not be visible is visible when the print is observed with the naked eye under normal light. In addition, there is also the problem that the variations in print quality affect the determination of the authenticity of the print.

[0015] Therefore, the applicant has applied for a method for creating a halftone print characterized in that each of the four primary colors of CMYK is divided and arranged in its own specified area without overlapping, with the objective of printing an appropriate latent image even with a printer that uses a print control method that converts the color of image data, by converting CMYK data into the three primary colors of light (RGB) and processing it as an sRGB color gamut without using a color management function, converting the image data processed as the above-mentioned sRGB color gamut into the three primary colors of colorants (CMY and K), and outputting it as the desired colorants (see, for example, Patent Document 2).

[0016] Also, to solve the same problem, another known technology has been disclosed, which is a printing control method that combines K, which is an encoding pattern, and CMY, which is graphic information, and when a printer receives RGB data and converts it into CMYK data, at least one of the RGB component values ​​is mapped below the mixing threshold of the corresponding CMY component so that the K component is not used in printing the graphic information (see, for example, Patent Document 3).

[0017] Another technique involves automatically selecting a specific printer driver from among multiple printer drivers that is capable of printing data in the CMYK color space without first converting it to data in another color space, and automatically selecting a high-definition mode as the print mode, which prints data in the CMYK color space without first converting it to data in another color space, and printing the document to be printed with an identification image added (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0018] [Patent Document 1] Patent No. 3544536 [Patent Document 2] Patent No. 4214262 [Patent Document 3] Patent No. 5564498 [Patent Document 4] Patent No. 4506345 Summary of the Invention [Problem to be solved by the invention]

[0019] However, while the technology in Patent Document 2 can be applied to output devices that can print each CMYK color information as is, or to expensive color multifunction machines or digital printing machines equipped with printer drivers that can turn off color separation in the output device, when CMYK data is input to simple home printers that can only input RGB data or mobile printers that run on rechargeable batteries, the data is forcibly converted to RGB data when it is input and then printed again as CMYK data by the printer, so even when this technology is used, the colors of the data for printed material may not be reproduced as they are in the printed material.

[0020] Furthermore, the technology in Patent Document 3 is a color control method using a printer, which maps the RGB component values ​​below the mixing threshold of the CMY components corresponding to the RGB component values ​​to prevent the K component from being used in printing graphic information (CMY). However, this mapping affects the hue of the printed graphic information, making it difficult to reproduce the colors as they were when they were created in the printed material.

[0021] In addition, the technology of Patent Document 4 is also a printer control method that aims to prevent data conversion to a different color space, and it was necessary to provide a function to prevent conversion to a different color space for each manufacturer and model of personal computer or printer. As mentioned above, printer control methods, control programs, printer drivers, etc. are often developed independently by each manufacturer, so there remains the issue of differences in print quality between prints output by each printer.

[0022] In particular, in recent years, the environments in which users use printers have become increasingly diverse, with a wide variety of manufacturers and models available, and there has been a demand for printers to be able to print latent image prints with good print quality, even on simple printers for general household use that do not have special control functions, or on mobile printers that run on rechargeable batteries.

[0023] In view of the above circumstances, the present invention aims to provide a method and software for creating data for latent image prints in order to obtain latent image prints having good print quality (concealment of the latent image when observed with the naked eye, visibility of the latent image when observed with infrared vision, and clarity of the print) regardless of the printer manufacturer or model. [Means for solving the problem]

[0024] The present invention is a method for creating printing data for a latent image print in which an invisible image is visible under infrared light, comprising the steps of acquiring first image data that is the base image of the invisible image and obtaining black and white (monotone) RGB image data, inverting the black and white (monotone) RGB image data to obtain negative image data, adjusting the tone curves of the black and white (monotone) RGB image data and the negative image data, forming the black and white (monotone) RGB image data after the tone curve adjustment using a pseudo-black pattern expressed in RGB color space, forming the negative image data using pseudo-cyan, pseudo-magenta and pseudo-yellow patterns each expressed in RGB color space as the three pure primary colors of cyan, magenta and yellow, forming the pseudo-black, pseudo-cyan, pseudo-magenta and pseudo-yellow patterns without overlapping with each other, and combining the pseudo-black, pseudo-cyan, pseudo-magenta and pseudo-yellow patterns.

[0025] The present invention also provides a method for creating printing data for a latent image print in which a visible image is visible to the naked eye under normal light and an invisible image is visible under infrared light, the method including the steps of: acquiring first image data that is a base image for the invisible image, and acquiring black and white (monotone) RGB image data; inverting the black and white (monotone) RGB image data to acquire negative image data; adjusting tone curves of the black and white (monotone) RGB image data and the negative image data; acquiring second image data that is a base image for the visible image, and acquiring RGB image data for a visible image; adjusting a tone curve of the RGB image data of the visible image; and acquiring the negative image data after the tone curve adjustment. The method includes the steps of: synthesizing the RGB image data of the visible image after tone curve adjustment to obtain composite image data; forming the black and white (monotone) RGB image data after tone curve adjustment using a pseudo black pattern expressed in RGB color space; forming the composite image data using pseudo cyan, pseudo magenta and pseudo yellow patterns expressed in RGB color space as the three pure primary colors of cyan, magenta and yellow, respectively, to form the pseudo black, pseudo cyan, pseudo magenta and pseudo yellow patterns without overlapping with each other; and synthesizing the pseudo black, pseudo cyan, pseudo magenta and pseudo yellow patterns.

[0026] The method for creating data for a latent image print of the present invention is characterized in that the pseudo cyan, pseudo magenta, pseudo yellow and pseudo black patterns are arranged in a matrix or randomly.

[0027] The method for creating data for a latent image print of the present invention is characterized in that the gradation of an invisible image and / or a visible image is expressed by the image coverage of pseudo cyan, pseudo magenta, pseudo yellow and pseudo black patterns.

[0028] The present invention is also characterized in that it is software for causing a computer to execute the method for creating data for latent image prints.

[0029] According to the method and software for creating printing data for latent image prints of the present invention, latent image prints of good print quality can be obtained without using special substrates or inks, and there are no particular constraints on the printer's printing control method or output device, etc., and latent image prints can be output from a wide variety of printers to obtain prints that require authenticity and security.

[0030] Furthermore, according to the method and software for creating printing data for latent image prints of the present invention, it is not necessary to create data for latent image prints that is specialized for each printer, and one-source, multi-use usage is possible, so that it does not incur effort or cost for those creating the data for latent image prints, and also eliminates the need for users to make complicated environment settings for the printer. [Brief description of the drawings]

[0031] [Figure 1] 1A and 1B are diagrams showing a state in which a latent image print according to an embodiment of the present invention is observed with the naked eye under normal light and a state in which it is observed under infrared light. [Diagram 2] 13A and 13B are diagrams showing a state in which a latent image print according to another embodiment of the present invention is observed with the naked eye under normal light and a state in which it is observed under infrared light. [Diagram 3] 1 is a block diagram showing an apparatus for creating data for a latent image print according to an embodiment of the present invention; [Figure 4] 4 is a flowchart showing a method for creating data for a latent image print according to an embodiment of the present invention. [Diagram 5] 1A and 1B are diagrams showing an example of data conversion in a printer of data for a latent image print created in an embodiment of the present invention, and a diagram showing a conventional technique. [Figure 6] 1A and 1B are diagrams showing data for a latent image print created in an embodiment of the present invention and a latent image print outputted from the data by a printer; [Figure 7] FIG. 1 is a diagram for explaining an embodiment of the present invention. [Figure 8] FIG. 1 is a diagram for explaining an embodiment of the present invention. [Figure 9]1A and 1B are diagrams showing an example of data for a latent image print according to a conventional technique and a partially enlarged view thereof; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The following describes an embodiment of the present invention with reference to the drawings. However, the present invention is not limited to the embodiment described below, and includes various other embodiments within the scope of the technical idea described in the claims.

[0033] (First embodiment) Regarding the method of creating data for a latent image print in the embodiment of the present invention, first, a latent image print (1) to be created will be described with reference to FIGS.

[0034] (Latent image print) The latent image print (1) is a print that is printed on a substrate (2), and is a print that, as shown in Fig. 1(a), shows a visible image (4) (here, a gray image) when viewed with the normal naked eye (T1), or, as shown in Fig. 2(a), shows a visible image (4) (here, the letters "PB") when viewed with the normal naked eye (T1). On the other hand, as shown in Fig. 1(b) and Fig. 2(b), shows an invisible image (5) (in this embodiment, a facial image) that is not visible when viewed with the normal naked eye (T1) when viewed with infrared light (T2) using a camera, optical scanner, or the like.

[0035] There are no limitations on the images used in the visible image (4) and the invisible image (5), and the visible image (4) may be a flat, solid-color image as shown in Fig. 1(a) as well as letters, numbers, symbols, marks, designs, facial images, landscapes, etc. Similarly, any image may be used for the invisible image (5), such as letters, numbers, symbols, marks, designs, facial images, landscapes, etc. Both the visible image (4) and the invisible image (5) may be binary images or images having continuous gradations such as facial images.

[0036] (Printer) The latent image print (1) to be created is printed by a printer, and the type of printer can be electrophotographic, inkjet, or laser printer, and does not matter. In addition, printing can be done with expensive color multifunction machines and digital printing machines, as well as simple printers for general households and mobile printers that run on rechargeable batteries.

[0037] (base material) Furthermore, the material of the substrate (2) used in the latent image print (1) is not particularly limited as long as it has a surface that the printer can print on, and examples of the material that can be used include high-quality paper, coated paper, art paper, plastic, film, and composite substrates in which paper is coated with a film.

[0038] (ink) The latent image print (1) is printed using the four color materials (CMYK) that come standard with the printer. At this time, the invisible image (5) is printed with black (K) toner containing infrared absorbing pigment or pigment ink. Images other than the invisible image (5) that can be seen with the naked eye are printed with cyan (C), magenta (M), and yellow (Y) toner or pigment ink that do not contain infrared absorbing pigment.

[0039] Specifically, the visible image (4) of the latent image print (1) shown in Figure 1 (a) that can be seen with the naked eye is formed in gray by mixing cyan (C), magenta (M), and yellow (Y) except for the invisible image (5). Under visible light, the invisible image (5) printed in black (K) containing an infrared absorbing pigment and the mixed gray visible image (4) are seen as being almost the same color, making it possible to conceal the invisible image (5). Similarly, the visible image (4) of the latent image print (1) shown in Figure 2(a) can be formed in the same manner by forming the parts other than the invisible image (5) in cyan (C), magenta (M), and yellow (Y), thereby concealing the invisible image (5) printed in black (K) containing an infrared absorbing pigment under visible light and forming any visible image (4).

[0040] (Device for creating data for latent image prints (M)) Next, the device (M) for creating data for latent image prints will be described. Fig. 3 is a block diagram showing the configuration of the device (M) for creating data for latent image prints, which includes an input unit (M1), an editing unit (M2), a communication interface (M3), a database (M4), and a display unit (M5).

[0041] The input means (M1) has at least an invisible image input means (M1a), and if necessary, a visible image input means (M1b). The invisible image input means (M1a) is a means for inputting an invisible image (5) that is the basis of the invisible image (5) that is visible when observed under an infrared light source. The visible pattern input means (M1b) is a means for inputting a visible image (4) that is the basis of the visible image that is observed when viewed with the naked eye under normal light. The invisible image (5) and the visible image (4) are inputted by capturing an image with a digital camera, scanning with a scanner, or by reading out any image previously recorded in the communication interface (M3) and / or the database (M4).

[0042] The invisible image input means (M1a) or the visible pattern input means (M1b) is composed of a mouse, a keyboard, etc., and may directly create the invisible image (5) and the visible image (4) using commercially available image processing software, such as Photoshop (registered trademark), manufactured by Adobe (registered trademark). The invisible image input means (M1a) or the visible pattern input means (M1b) may also input values ​​for tone curve adjustment used in the editing means (M2) and may input instructions for executing various image processes.

[0043] The editing means (M2) shown in FIG. 3 includes at least a black and white (monotone) conversion means (M2a), an inversion means (M2b), a tone curve adjustment means (M2c), a pseudo pattern application means (M2d), and a synthesis means (M2e).

[0044] The black and white (monotone) conversion means (M2a) converts the image data input by the invisible pattern input means (M1a) into RGB black and white (monotone) image data (5a).

[0045] The inversion means (M2b) performs negative-positive inversion to obtain negative image data (5c) of the black-and-white (monotone) image data (5a) converted by the black-and-white (monotone) conversion means (M2a).

[0046] The tone curve adjustment means (M2c) performs tone curve adjustment on the black and white (monotone) image data (5a) obtained by the black and white (monotone) conversion means (M2a) and the negative image data (5c) obtained by the inversion means (M2b). In addition, when the latent image print (1) has a visible image (4) containing meaningful information, rather than a flat plain image as shown in Fig. 1(a), the tone curve adjustment is performed on the visible image data (4a) input by the visible image input means (M1b).

[0047] The pseudo pattern application means (M2d) applies the pseudo black (iK), pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) patterns to the image data after tone curve adjustment.

[0048] The combining means (M2e) combines the pseudo cyan (iC), pseudo magenta (iM), pseudo yellow (iY) and pseudo black (K) patterns obtained by the pseudo pattern applying means (M2b).

[0049] The display means (M5) is not particularly limited and may be a monitor of a personal computer, a dedicated monitor, etc. Furthermore, the display means (M5) is not an essential component for creating data for a latent image print.

[0050] The output means (P) shown in FIG. 3 is a means for printing data created by the device for creating data for latent image prints (M) onto a substrate (2), and is not an essential component for creating data for latent image prints. However, by configuring the output means (P) with a color laser printer, color inkjet printer, etc., and connecting it to the device for creating data for latent image prints (M), it is possible to carry out operations from data creation to the creation of latent image prints (1) as a single device.

[0051] (How to create data for latent image prints) Next, a method for creating data for latent image prints using the above-mentioned device (M) for creating data for latent image prints and software for the method will be described with reference to Fig. 4. Note that the process flow shown in Fig. 4 will be described together with images after processing in order to make the process easier to understand.

[0052] The method for creating data for a latent image print includes at least a main process flow (F1) surrounded by a solid line in Fig. 4, and further includes a sub-process flow (F2) surrounded by a dotted line in Fig. 4, as necessary. In the case of only the main process flow (F1) in Fig. 4, a flat gray image is observed with normal naked eye as shown in Fig. 1(a), but when observed under an infrared light source (T2), a latent image print (1) is obtained in which an invisible image (5) not visible with normal naked eye (T1) is visible as shown in Fig. 1(b). In addition, in the case of including both the main process flow (F1) and the sub-process flow (F2) in Fig. 4, a latent image print (1) is obtained in which a visible image (4) containing significant information is visible with normal naked eye (T1) as shown in Fig. 2(a), and an invisible image (5) not visible with normal naked eye (T1) is visible with infrared light (T2), as shown in Fig. 2(b).

[0053] (Main processing flow (F1)) First, a main processing flow (F1) enclosed by a solid line in FIG. 4 will be described.

[0054] (Step 1 Specify invisible image and convert to black and white) In Step 1 shown in Fig. 4, the first image data (5a) that will be the base image of the invisible image (5) is specified by the invisible image input means (M1a) of the latent image print data creation device (M). In this embodiment, an image such as a facial image having continuous gradations that will be the original image of the invisible image (5) is input from the communication interface (M3) or the database (M4). At this time, RGB image data is used as the input source. Note that in this embodiment, the invisible image (5) is a facial image having continuous gradations, but the type of image is not limited in any way.

[0055] Since the invisible image (5) is an image printed by a printer using black (K) toner or pigment ink containing infrared absorbing pigment, it is expressed in monotone (black and white) with all 256 gradations of each RGB channel being the same. Therefore, if the image input from the invisible image input means (M1a) is 24-bit RGB image data in color, the black and white (monotone) conversion means (M2a) of the editing means (M2) adds a process of converting it to black and white (monotone) to obtain black and white (monotone) RGB image data (5a'). Also, if the image input from the invisible image input means (M1a) is an 8-bit grayscale image or, assuming that it is a 32-bit CMYK image, a separate process of converting it to a monotone 24-bit RGB image is added to obtain black and white (monotone) RGB image data (5a'). Note that if the image input from the invisible image input means (M1a) is monotone (black and white), this conversion can be omitted. This is Step 1.

[0056] (Step 2 Negative-positive inversion) Next, in Step 2, the black and white (monotone) RGB image data (5a') obtained in Step 1 is inverted to obtain negative image data (5c). That is, the invisible image data (5a) and the negative image data (5c) of the invisible image data are in a negative-positive relationship. In this embodiment, since the black and white (monotone) RGB image data (5a') has continuous gradation, the invisible image data (5c) obtained by inverting it also has continuous gradation.

[0057] (Step 3: Adjusting the tone curve) In Step 3, first, the tone curve of the black and white (monotone) RGB image data (5a') is adjusted to obtain black and white (monotone) RGB image data (5b) after tone curve adjustment. The black and white (monotone) RGB image data (5b) after tone curve adjustment becomes an image to be printed in black (K) containing infrared absorbing pigment by the printer. Next, in Step 3, the tone curve of the negative image data (5c) is further adjusted to obtain negative image data (5d) after tone curve adjustment. The negative image data (5d) after tone curve adjustment becomes an image to be printed in cyan (C), magenta (M) and yellow (Y) without infrared absorbing pigment by the printer.

[0058] Here, the tone curve adjustment in Step 3 will be described. In adjusting the tone curve, the black and white (monotone) RGB image data (5b) after tone curve adjustment and the negative image data (5d) after tone curve adjustment are adjusted so that when they are combined in negative and positive, they become uniformly flat densities of cyan (C), magenta (M), yellow (Y), and black (K). In this case, the image area ratio of each pattern needs to be 25% or less so that the four types of patterns of cyan (C), magenta (M), yellow (Y), and black (K) do not overlap with each other, that is, so that the halftone dots printed by the printer do not overlap with each other. To achieve this configuration, the tone curve applied to the RGB image is adjusted to a range of image area ratio of approximately 0% to 25% (a range of 191 to 255 for RGB images). As shown in FIG. 4, the black and white (monotone) RGB image data (5b) and negative image data (5d) after the tone curve adjustment are paler black and white (monotone) image data compared to the black and white (monotone) RGB image data (5a') and negative image data (5c) before the tone curve adjustment.

[0059] The tone curve can be adjusted by setting a predetermined tone curve using, for example, a tone curve change function of Photoshop (registered trademark), which is a commercially available image processing software made by Adobe (registered trademark). The tone curve can also be adjusted according to the characteristics of the printer used for printing. This concludes the explanation of Step 3.

[0060] (Step 4 Applying pseudo-pattern) In Step 4, pseudo patterns are applied to the black and white (monotone) RGB image data (5b) after tone curve adjustment and the negative image data (5d) after tone curve adjustment. In Step 4, first, a pseudo black (iK) pattern is applied to the black and white (monotone) RGB image data (5b) after tone curve adjustment. Next, pseudo cyan (iC), pseudo magenta (iM), and pseudo yellow (iY) patterns are applied to the negative image data (5d) after tone curve adjustment.

[0061] Here, we will explain pseudo black (iK), pseudo cyan (iC), pseudo magenta (iM), and pseudo yellow (iY) in Step 4. Pseudo black (iK), pseudo cyan (iC), pseudo magenta (iM), and pseudo yellow (iY) are the pure primary colors of CMYK printing, black (K), cyan (C), magenta (M), and yellow (Y), expressed in the RGB color space.

[0062] The RGB color space is a color space expressed by the three primary colors of light, red, green, and blue, and colors are expressed by a combination of numerical values ​​from 0 to 255 for each of the RGB colors. The numerical values ​​of RGB are not absolute, but are relative to the width of the color gamut. In this embodiment, as an example, the pure primary color (100% color) of cyan (C) in the CMYK printing color is expressed as pseudo-cyan (iC) in the RGB color space by R0, G159, and B230. Furthermore, the pure primary color (100% color) of magenta (M) is expressed as pseudo-magenta (iM) by R194, G0, and B123. Similarly, the pure primary color (100% color) of yellow (Y) is expressed as pseudo-yellow (iY) by R255, G240, and B0. Furthermore, the pure primary color of black (K) is expressed as R0, G0, and B0.

[0063] In the above, pseudo cyan (iC) is expressed as R0, G159, B230, but pseudo cyan (iC) can also be expressed with a combination of different values, such as R0, G255, B255. Similarly, pseudo magenta (iM) can be expressed with a combination of R255, G0, B255, and pseudo yellow (iY) can be expressed with a combination of R255, G255, B0, etc. In other words, pseudo black (iK), pseudo cyan (iC), pseudo magenta (iM), and pseudo yellow (iY) must be expressed as the CMYK printing colors cyan (C), magenta (M), yellow (Y), and black (K).

[0064] Here, the effects of the above-mentioned configuration will be explained in comparison with the conventional technology. Figure 5 shows an example of data conversion when data for latent image prints is output by an output device, and Figure 5(a) explains the present invention, and Figure 5(b) explains the conventional technology. The prior art pattern in FIG. 5(b) is composed of cyan (C), magenta (M), yellow (Y) and black (K), whereas the pseudo pattern of the present invention shown in FIG. 5(a) is composed of pseudo cyan (iC), pseudo magenta (iM), pseudo yellow (iY) and pseudo black (iK) patterns.

[0065] As shown in Fig. 5(b), in the conventional technology, when the input source is a CMYK image (e1), the printer driver converts it to an RGB image (e2), and the printer driver applies a dedicated color profile optimal for the output device, converts it again to a CMYK image (e3) and prints it. At that time, when the cyan (C), magenta (M), yellow (Y) and black (K) of the CMYK image (e1) are converted to the RGB image (e2), they become pseudo cyan (iC), pseudo magenta (iM), pseudo yellow (iY) and pseudo black (iK) expressed in RGB colors, and the color components that were expressed as black by mixing the dots and lines of cyan (C), magenta (M) and yellow (Y) become pseudo black (iK).

[0066] Furthermore, when the RGB image (e2) is converted back to a CMYK image (e3), depending on the dedicated color profile, the pseudo black (iK) is replaced with a color component consisting only of black (K) or a color component consisting mainly of black (K) with small amounts of cyan (C), magenta (M) and yellow (Y). Because the user cannot rewrite this dedicated color profile, it is difficult to print latent image print data such as that shown in Figures 1 and 2 on an inexpensive home printer.

[0067] In the present invention, as shown in Fig. 5(a), since the input source is RGB image data (d1), when output by the printer, it is converted to CMYK image data (d2) via a dedicated color profile by the printer driver, but as described above, the pseudo cyan (iC), pseudo magenta (iM), pseudo yellow (iY), and pseudo black (iK) provided in the RGB image data (d1) before conversion are roughly cyan (C), magenta (M), yellow (Y), and black (K), so the color composition of the input source RGB image data (d1) and the converted CMYK image data (d2) is equivalent. In this way, since there are no restrictions on the printer driver or the dedicated color profile, the present invention makes it possible to reproduce the color of the latent image print data as it is in the print.

[0068] (Shape and arrangement of pseudo patterns) Next, the pattern shapes and arrangements when applying pseudo cyan (iC), pseudo magenta (iM), pseudo yellow (iY) and pseudo black (iK) in Step 4 will be described. First, a pseudo black (K) pattern (5e) is arranged on the black and white (monotone) RGB image (5b) after tone curve adjustment obtained in Step 3, as shown in FIG. 4. Also, in Step 4, pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) patterns (5f) are arranged on the negative image data (5d) after tone curve adjustment obtained in Step 3. At this time, as shown in FIG. 4, the pseudo black (iK) pattern (5e) and the pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) patterns (5f) are arranged so as not to overlap each other.

[0069] In this embodiment, the pseudo black (iK) pattern is arranged as dots. For example, if the image resolution of the black and white (monotone) RGB image data (5a) before the tone curve adjustment is 600 dpi, the dot size is 336 μm, which corresponds to 75 lines per inch in printed matter. The pseudo black (iK) pattern is arranged as dots in an image of 32 pixels horizontally and 16 pixels vertically, and the dots of the pseudo black (iK) pattern are arranged according to the continuous gradation of the black and white (monotone) RGB image data (5b) after the tone curve adjustment.

[0070] Similarly, the pseudo cyan (iC), pseudo magenta (iM), and pseudo yellow (iY) patterns (5f) are also arranged in dots. For example, in this embodiment, the pseudo cyan (iC), pseudo magenta (iM), and pseudo yellow (iY) are each configured with dots consisting of connected components of 8×8 pixels, and the dots of the pseudo cyan (iC), pseudo magenta (iM), and pseudo yellow (iY) patterns are arranged according to the continuous gradation of the negative image data (5d) after tone curve adjustment.

[0071] The size of the dots can be changed as appropriate for each of the pseudo black (iK), pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) patterns. The dot size can be increased by connecting dots together to increase the image coverage ratio, which allows the invisible image (5) to be expressed in continuous gradation. In the present invention, the image coverage ratio refers to the ratio of dots, pixels or images per unit area.

[0072] In this embodiment, the pseudo patterns are formed by dots, but each pseudo pattern may be a dot as shown in FIG. 4 or a pixel as shown in FIG. 8. Also, it may be a line (not shown) or a combination of these. Also, as described above, in order to express continuous gradation, the size of the elements constituting the pseudo pattern can be changed by connecting dots to dots or connecting pixels to pixels. Furthermore, the pseudo patterns are formed in the order of pseudo cyan (iC), pseudo magenta (iM), pseudo yellow (iY) and pseudo black (iK) from the left in FIG. 4, but they do not need to be arranged in order and may be random. Also, as in the printed pattern portion (2a) shown in FIG. 9 of the conventional technology, the visible image area (a) and the invisible image area (b) may be arranged in a matrix with a desired positional relationship. Furthermore, the shape of the pseudo pattern may not be arranged regularly in a matrix, but may be arranged randomly.

[0073] In the present invention, a "dot" refers to a printed dot or pixel, which is the smallest unit that forms a printed pattern, or a group of image elements formed by assembling a plurality of printed dots or pixels, and includes various figures such as circles, triangles, and polygons including rectangles. Also, a "line" refers to an image element formed by continuously arranging printed dots or pixels, which are the smallest units that form a printed pattern, in a specific direction, and includes dotted or dashed divided lines, straight lines, curved lines, and wavy lines. In the present embodiment, it is sufficient that the dots, pixels, or lines are arranged so as not to overlap each other when they are finally combined in Step 5.

[0074] As will be described later, since the pseudo black (iK) pattern (5e) and the pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) patterns (5f) are combined in step 5, the pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) patterns (5f) are adjusted to the desired color balance as necessary so that the invisible image (5) composed of the pseudo black (iK) pattern (5e) is not visually recognized in the combined composite image data (5g).

[0075] (Step 5: Synthesis of pseudo-patterns) Next, the synthesis of the pseudo pattern in Step 5 will be described. In Step 5, the pseudo black (K) pattern (5e) obtained in Step 4 is synthesized with each of the pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) patterns (5f) to obtain synthetic image data (5g). In other words, in the synthesis of the pseudo pattern in Step 5, a group of pseudo black (iK) dots and a group of pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) dots are synthesized as RGB image data. The synthetic image data (5g) is image data printed in a printer with cyan (C), magenta (M), yellow (Y) and black (K) toners or pigment inks.

[0076] The latent image print (1) printed by the printer from the composite image data (5g) obtained in Step 5 has cyan (C), magenta (M), yellow (Y) and black (K) that reflect the size and positional relationship of dots consisting of pseudo cyan (iC), pseudo magenta (iM), pseudo yellow (iY) and pseudo black (iK) shown in the composite image data (5g) in Fig. 4. When this latent image print (1) is viewed with the naked eye under normal light, a flat gray visible image (4) as shown in Fig. 1(a) is observed, but when viewed under an infrared light source (T2), an invisible image (5) that was not visible to the naked eye (T1) as shown in Fig. 1(b) is visible. The above is the main processing flow (F1) surrounded by a solid line in Fig. 4.

[0077] Next, a sub-process flow (F2) enclosed by a dotted line in FIG. 4 will be described.

[0078] (Step 6: Specifying visible images) In Step 6 shown in Fig. 4, the second image data (4a) that will be the base image of the visible image (4) is specified by the visible image input means (M1b) of the latent image print data creation device (M). In this embodiment, the visible image data (4a) that will be the original image of the visible image (4) is input from the communication interface (M3) or the database (M4). At this time, 24-bit RGB image data is used as the input source, as in Step 1. Note that, in this embodiment, the visible image data (4a) is described as an example of the alphabet, but the type of image is not limited in any way.

[0079] In this embodiment, the visible image data (4a) is a 24-bit RGB image, but if the image input from the visible image input means (M1b) is an 8-bit grayscale image or a 32-bit CMYK image, a separate process is added to convert it to a 24-bit RGB image.

[0080] (Step 7 Adjusting the tone curve) Next, in Step 7, the tone curve of the visible image data (4a) obtained in Step 6 is adjusted to obtain RGB image data (4b) of the visible image after tone curve adjustment. The tone curve in Step 7 can be adjusted as desired, and in this embodiment, the tone curve is adjusted so that the maximum densities of cyan (C), magenta (M) and yellow (Y) after printing do not exceed 50%. The RGB image data (4b) of the visible image after tone curve adjustment is an image that is printed in the printer using cyan (C), magenta (M) and yellow (Y) that do not contain infrared absorbing pigments.

[0081] (Step 8 Image synthesis) Next, in image synthesis in Step 8, the RGB image data (4b) of the visible image after tone curve adjustment and the RGB image data of the negative image data (5d) after tone curve adjustment are multiplied together to obtain synthesized image data (6) after tone curve adjustment. The synthesized image data (6) after tone curve adjustment is an image that will be printed in cyan (C), magenta (M) and yellow (Y) after printing. This is the sub-processing flow (F2) enclosed by the dotted line in Figure 4.

[0082] In this embodiment, for the tone curve adjusted composite image data (6) obtained by composing the images in Step 8, each of the pseudo cyan (iC), pseudo magenta (iM), and pseudo yellow (iY) patterns is formed with dots consisting of connected components of 8×8 pixels, and the connected components of each pixel are increased or decreased according to the continuous gradation of the tone curve adjusted composite image data (6). In this way, the size of the dots in each of the pseudo cyan (iC), pseudo magenta (iM), and pseudo yellow (iY) patterns can be changed as appropriate, and the visible image (4) can be expressed in continuous gradation depending on the size of the dots. Note that the application of the pseudo CMY pattern to the obtained tone curve adjusted composite image data (6) is similar to the application of the pseudo CMY pattern in Step 4 described above, so a description thereof will be omitted.

[0083] The image data (5g') obtained in Step 5 is shown in FIG. 4. The image data (5g') obtained in Step 5 and its enlarged view are shown in FIG. 6(a). As shown in FIG. 4 and FIG. 6(a), the image data (5g') has dots of pseudo cyan (iC), pseudo magenta (iM), pseudo yellow (iY) and pseudo black (iK) arranged so that they do not overlap. FIG. 6(b) shows the latent image print (1) obtained by outputting the image data (5g') from a printer and its enlarged view. The latent image print (1) is formed of the color materials of cyan (C), magenta, (M), yellow (Y) and black (K) that directly reflect the size and positional relationship of the dots in the image (5g').

[0084] When this latent image print (1) is viewed with the naked eye under normal light, a visible image (4) as shown in Figure 2(a) is observed, and when viewed under an infrared light source (T2), an invisible image (5) that is not visible with the naked eye (T1) as shown in Figure 2(b) is visible.

[0085] (software) The present invention also provides creation software for causing a computer to execute the method for creating data for latent image prints.

[0086] Although the embodiment of the present invention has been described, this embodiment is presented as an example and is not intended to limit the technical scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. This embodiment and its modifications are included in the technical scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

[0087] Example 1 Using the device (M) for creating data for latent image prints shown in FIG. 3, the latent image print (1) shown in FIG. 2 was created according to the flow shown in FIG.

[0088] In Step 1, 24-bit RGB image data (5a) with a resolution of 600 dpi is input as the first image data in the invisible image input means (M1a), and a process of converting the data to black and white (monotone) is performed by the black and white (monotone) conversion means (M2a) of the editing means (M2), to obtain black and white (monotone) RGB image data (5a'). In Step 6, 24-bit RGB image data (letters "PB") with a resolution of 600 dpi is input as the second image data in the visible image input means (M1b), to obtain visible image data (4a).

[0089] In Step 2, the black and white (monotone) RGB image data (5a') obtained in Step 1 is inverted to create negative image data (5c) of the facial image.

[0090] In Step 3, the tone curve of the black and white (monotone) RGB image data (5a') is adjusted to obtain black and white (monotone) RGB image data (5b) after tone curve adjustment. Furthermore, the tone curve of the negative image data (5c) is adjusted to obtain negative image data (5d) after tone curve adjustment.

[0091] Furthermore, in Step 7, the tone curve of the input visible image data (4a) is adjusted to generate visible image data (4b) after tone curve adjustment.

[0092] In Step 8, the RGB image data of the tone curve adjusted visible image data (4b) and the tone curve adjusted negative image data (5d) are combined by multiplication to create tone curve adjusted combined image data (6).

[0093] Next, in Step 4, a pseudo black (K) pattern (5e) was arranged by dots on the black and white (monotone) RGB image (5b) after tone curve adjustment obtained in Step 3. Also, each of the pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) patterns (5f) was arranged by dots on the composite image data (6) after tone curve adjustment obtained in Step 8. At this time, as shown in Fig. 4, the dots of the pseudo black (iK) pattern (5e) and each of the pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) patterns (5f) were arranged so that they would not overlap each other when combined.

[0094] In Step 5, the pseudo black (K) pattern (5e) obtained in Step 4 and the pseudo cyan (iC), pseudo magenta (iM), and pseudo yellow (iY) patterns (5f) are synthesized to obtain composite image data (5g).

[0095] The composite image data (5g) obtained in Step 5 was printed on white high-quality color copy paper (Ncolor081, manufactured by Fuji Xerox Co., Ltd.) using cyan (C), magenta (M), yellow (Y) and black (K) toners, using an output means (P) of a laser printer SP-740 manufactured by Ricoh Co., Ltd. with a resolution of 600 dpi.

[0096] When the latent image print (1) created in this way was observed with the naked eye under normal light, the alphabet "PB" was visible as shown in Figure 2(a). Furthermore, when this latent image print (1) was observed with an infrared camera, an invisible image (5) (face image) that was not visible with normal naked eye (T1) was visible as shown in Figure 2(b).

[0097] In this way, the present invention can obtain latent image prints (1) with desired density and hue from a wide variety of printers without any particular restrictions on the printer print control method, output device, etc. This saves time and money for the party creating the data for the latent image print, and also eliminates the need for users to make complicated environment settings for the printer.

[0098] Example 2 As shown in FIG. 7, the second embodiment is an example of a disaster certificate that needs to be issued in the event of a disaster, and is an example of creating image data for a latent image print (1), in which a visible image (4) observable with the naked eye under normal light is the logo (letter "PB") of the local government issuing the disaster certificate, and an invisible image (5) observable with an infrared camera is a facial image of an individual requesting the issuance of the disaster certificate. In the second embodiment, a smartphone is a latent image print data creating device (M) shown in FIG. 3, and is equipped with the process flow of FIG. 4. In other words, data for a latent image print is created using a dedicated application in which the software of the present invention is installed on a smartphone. In the second embodiment, Steps 1, 4, and 6 will be described, and the rest is the same as in the first embodiment, so description will be omitted.

[0099] In Step 1, the first image data input from the invisible image input means (M1a) is a facial image of an individual requesting the issuance of a disaster damage certificate, and the facial image of the individual is captured by a smartphone, and a process of converting it to black and white (monotone) is performed using a function provided in the smartphone as the black and white (monotone) conversion means (M2a) of the editing means (M2), to obtain black and white (monotone) RGB image data (5a) with a resolution of 600 dpi. In Step 6, 24-bit RGB image data with a resolution of 600 dpi, which is the logo mark (letter "PB") of the local government issuing the disaster damage certificate, is input as the second image data in the visible image input means (M1b), and visible image data (4a) is obtained.

[0100] In Step 4, a pseudo black (K) pattern (5e) was arranged by pixels on the black and white (monotone) RGB image (5b) after tone curve adjustment obtained in Step 3. Also, each of the pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) patterns (5f) was arranged by pixels on the composite image data (6) after tone curve adjustment obtained in Step 8. At this time, as shown in Fig. 4, the pixels of the pseudo black (iK) pattern (5e) and each of the pseudo cyan (iC), pseudo magenta (iM) and yellow (iY) patterns (5f) were arranged so that they would not overlap when combined.

[0101] In addition, the color balance of the pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) patterns was adjusted so that the invisible image (5) composed of the pseudo black (iK) pattern was not visually recognized.

[0102] The pseudo patterns were arranged as shown in the upper part of Figure 8, with pseudo black (iK), pseudo cyan (iC), pseudo magenta (iM) and pseudo yellow (iY) patterns formed in a grainy random arrangement of pixels.

[0103] The composite image data (5g) obtained in Step 5 was wirelessly transmitted from the smartphone to the output means (P), which was a mobile printer PIXUS (registered trademark) iP110 manufactured by Canon (registered trademark), and printed on white high-quality color copy paper (Ncolor081 manufactured by Fuji Xerox Co., Ltd.) using black (K), cyan (C), magenta (M) and yellow (Y) inks.

[0104] In this way, the present invention can be used for quickly issuing disaster certificates and the like when networks cannot be used during disasters such as earthquakes, as well as for easily issuing certificates and the like that require authenticity and security.

[0105] Furthermore, as in the second embodiment, if a grainy pixel array such as an error diffusion dither is used, when the resolution of the output device is 600 dpi, a visible image (4) and an invisible image (5) having an image resolution equivalent to 600 dpi can be formed on the latent image print (1). In other words, the image can be expressed at the maximum image resolution of the output device. This allows the image resolution to be increased to the pixel unit of the set image resolution even in an inexpensive simple home printer or a mobile printer that runs on rechargeable batteries.

[0106] In addition, in Example 2, pseudo cyan (iC), pseudo magenta (iM), pseudo yellow (iY), and pseudo black (iK) patterns are randomly arranged using grained pixels, and since there is a degree of freedom, it is possible to create any design such as letters or figures with the detail that can be expressed using the maximum image resolution of the output device. [Explanation of symbols]

[0107] 1 Latent image prints 2 Base material 3. Infrared camera 4. Visible images 4a Second image data 4b RGB image data of a visible image after tone curve adjustment 5. Invisible Images 5a First image data 5a' Monotone RGB image data 5b Monotone RGB image data after tone curve adjustment 5c Negative image data 5d Negative image data after tone curve adjustment 5e Pseudo Black (K) Pattern 5f Pseudo Cyan (iC), Pseudo Magenta (iM), and Pseudo Yellow (iY) patterns 5g Synthetic image data 6 Composite image data after tone curve adjustment M: Device for creating data for latent image printing M1 Input Method M1a Invisible image input means M1b Visible image input means M2 editing method M2a Black and White (monotone conversion method) M2b Reversal Method M2c tone curve adjustment method M2d Pseudo-Pattern Application Method M2e synthesis means M3 Communication Interface M4 Database M5 Display means P output means F1 Main processing flow F2 Sub-processing flow T1 Normal naked eye vision T2 Infrared Vision

Claims

1. A method for creating printing data for a latent image print in which an invisible image is visible under infrared light, comprising the steps of: obtaining first image data that is a base image of the invisible image, and obtaining black and white (monotone) RGB image data; inverting the black and white (monotone) RGB image data to obtain negative image data; adjusting tone curves of the black and white (monotone) RGB image data and the negative image data; forming the black and white (monotone) RGB image data after tone curve adjustment using a pseudo black pattern expressed in RGB color space, forming the negative image data using pseudo cyan, pseudo magenta and pseudo yellow patterns expressed in RGB color space as the three pure primary colors of cyan, magenta and yellow, respectively, and forming the pseudo black, pseudo cyan, pseudo magenta and pseudo yellow patterns without overlapping with each other; combining the pseudo black, the pseudo cyan, the pseudo magenta and the pseudo yellow patterns; A method for creating data for a latent image print, comprising:

2. 2. The method for creating data for a latent image print according to claim 1, wherein the gradation of the invisible image is expressed by the image coverage of the pseudo cyan, pseudo magenta, pseudo yellow and pseudo black patterns.

3. A method for creating printing data for a latent image print in which a visible image is visible to the naked eye under normal light and an invisible image is visible under infrared light, comprising the steps of: obtaining first image data that is a base image of the invisible image, and obtaining black and white (monotone) RGB image data; inverting the black and white (monotone) RGB image data to obtain negative image data; adjusting tone curves of the black and white (monotone) RGB image data and the negative image data; obtaining second image data that is a base image of the visible image, and obtaining RGB image data of the visible image; adjusting a tone curve of RGB image data of the visible image; a step of combining the negative image data after tone curve adjustment with the RGB image data of the visible image after tone curve adjustment to obtain combined image data; forming the black and white (monotone) RGB image data after tone curve adjustment using a pseudo black pattern expressed in RGB color space, forming the composite image data using pseudo cyan, pseudo magenta and pseudo yellow patterns expressed in RGB color space as the three pure primary colors of cyan, magenta and yellow, respectively, and forming the pseudo black, pseudo cyan, pseudo magenta and pseudo yellow patterns without overlapping with each other; combining the pseudo black, the pseudo cyan, the pseudo magenta and the pseudo yellow patterns; A method for creating data for a latent image print, comprising:

4. 4. The method for creating data for a latent image print according to claim 1, wherein the pseudo cyan, pseudo magenta, pseudo yellow and pseudo black patterns are arranged in a matrix or randomly.

5. Creation software for causing a computer to execute the method for creating data for latent image prints described in any one of claims 1 to 4.

Images