WO2009112240A2

WO2009112240A2 - Method for applying an image having embedded additional information onto a data carrier

Info

Publication number: WO2009112240A2
Application number: PCT/EP2009/001710
Authority: WO
Inventors: Thomas Kramer
Original assignee: Maurer Electronics Gmbh
Priority date: 2008-03-10
Filing date: 2009-03-10
Publication date: 2009-09-17
Also published as: EP2100747A1; EP2100747B1; WO2009112240A3

Abstract

The invention relates to a method for applying an image onto a data carrier (10), particularly a data or identification card (10), by means of an output device. In order to further increase protection against forgery of the data carrier, additional information that is invisible to the naked eye is integrated in an image to be applied as a novel safety feature. For this purpose, the invention provides that the image to be applied comprises a plurality of pixels, with which positive gray or brightness values are associated, the amount of the pixels of the image is adjusted to the spatial resolution capacity of the output device, additional information to be embedded in the recognizable image comprises a plurality of pixels according to the spatial resolution capacity of the output device, with which positive and negative gray or brightness values are associated, the gray or brightness values of the pixels of the additional information to be embedded are superimposed over the gray or brightness values of the pixels of the image, and the image to be applied is recorded onto the data carrier pixel by pixel utilizing the gray or brightness values obtained in this manner.

Description

Method for applying an image with embedded

Additional information on a data medium

description

The present invention relates to a method for applying an image by means of an output device to a data carrier, in particular to a data or ID card.

When applying image information to a data carrier, in particular when applying image information that individualizes a data carrier, such as in particular a value or ID card, these are nowadays often written into a corresponding layer of the data carrier with the aid of laser marking systems. In this case, the data carrier material is deliberately blackened by a laser beam modulated in its intensity in such a way that the desired image information, eg. a portrait photo of the cardholder as well as a name reflecting his name.

The image information, in particular the portrait photo, is present in digital form as a pixel matrix.

The number of stored pixels depends on the desired size of the image on the disk and the resolution of serving as an output device laser marking system.

Although such image information introduced by means of laser light ensures a high level of protection against counterfeiting, in the field of security documents there is still a need to further increase the security against counterfeiting.

In order to increase the falsification security of images on value and security documents, it has already been proposed to vary the shape of the individual pixels of an image composed of pixels, so that the image of a plurality of the same, not regularly shaped pixels, such as letters, numbers or fantasy shapes. To visualize the respective shapes of the pixels, a spe- In order to make the pixel shape visible as a moiré pattern (RL van Renesse, Optical Document Security, 3rd Edition, Artech House Optoelectronics Library, 2005, page 159), two dimensional point or perforated gratings are required.

It has also been proposed to provide microtext as a phase-modulated line raster over a background, whereby various images can be visualized by means of a special associated line raster (see above, page 157f.).

Furthermore, attempts have also been made to construct micro-font images in which all the pixels of the background have the same gray level or the same color value. Accordingly, the characters used for the individual pixels also have the same gray level or color among each other. The image is then generated by the arrangement of different characters with different filling factor, ie with different coverage of the respective associated pixel area. In this case, the text is not selectable. Conversely, if a given text is used, the gray levels or color values of the individual characters must be varied, but this leads to poor image quality.

Based on this, the present invention seeks to provide a further method for applying an image by means of an output device to a disk in which a novel security feature is provided to further increase the counterfeit security of the data carrier, which is invisible to the unaided human eye with simple optical means can be visualized.

This object is achieved by the method according to claim 1. Advantageous embodiments and further developments of the invention are described in the subclaims.

In order to provide a new optical security feature for a data carrier, in particular for a card-shaped data carrier, such as a data, value or ID card, additional or microinformation is embedded in an image to be applied to the data carrier, which consists of a plurality of pixels corresponding to the Resolution of the output consists of positive and negative gray or brightness values. The gray or brightness values of the pixels of the additional information are superimposed on the gray or brightness values of the pixels of the actual image, wherein the number of pixels of the image to be applied has possibly been previously adapted to the spatial resolution of the output device. The image to be applied is then recorded together with the additional or microinformation embedded in this way in accordance with the gray or brightness values of the picture elements pixel by pixel on the data carrier.

Although only positive gray or brightness values of the pixels may occur in an image, both positive and negative values are required for embedding the additional or microinformation to increase the gray or brightness values of some pixels and, in turn, the gray or brightness values other pixels to decrease so that the un-armed human eyes provide gray or brightness impression of the image with additional or microinformation does not change from that of the original image.

When applying or printing a colorful image, the embedding of the additional or microinformation can also be effected by a variation of the color values of the individual pixels, that is, by changes in the color or the color saturation. Again, the changes in chroma or color saturation of the individual pixels should be selected so that the change in chroma or chroma in some pixels is compensated for by an opposite change in chroma or chroma in other pixels so as not to alter the overall impression of the image.

In this way, additional or microinformation, ie image information that is not visible to the naked eye, can be embedded in an image, for example in a portrait photo or in any other image, that the actual image, when viewed with the naked eye will appear exactly as it would appear if it had been applied to the data carrier without the additional information.

The invention thus uses the high spatial frequencies of the image, which are in the range of the spatial resolution of the output device and above the resolution ability of the human eye to embed additional information into the image such that the low spatial frequencies corresponding to the resolving power of the human eye are not affected thereby. Due to the integrating perception of the human eye for structures that are smaller than its resolution, the additional information is invisible, but can be made visible by a simple magnification with a magnifying glass or the like.

The method according to the invention can be carried out with any output device for applying an image to a data carrier whose resolution is higher than that of the human eye, which can thus produce such fine pixels so close together that they are no longer perceived separately by the human eye can.

In order to ensure that low spatial frequencies of the gray or brightness curve or color gradient in the image remain unchanged, it is provided according to the invention that the integral of the gray or brightness values or color values over all pixels of each region of pixels of the additional information, the size of a recognizable with the naked eye Pixel corresponds to zero.

According to an advantageous development of the invention, it is provided that the additional information to be embedded is embedded in regions of the image to be applied which have average gray or brightness values or color values. In this way it can be achieved that the additional information can be integrated into the actual image in a particularly inconspicuous manner, and yet is easily recognizable by simple enlargement with the aid of a simple magnifying glass.

Conveniently, the additional information to be embedded is a text. Thus, for example, the name of the cardholder can be used as micro or additional information for the security feature according to the invention.

Instead of such a microtext or in addition, guilloche may also be provided as micro or additional information to be embedded.

In principle, it is also conceivable to use laser or inkjet printers with high resolution for the method according to the invention. Especially suitable However, net for the implementation of the method according to the invention is a laser marking system with a pixel size of less than 50 microns, preferably less than 40 microns and in particular in the range of about 20 to 30 microns.

The higher the spatial resolution of the output device, the more diverse it is to design the additional or microinformation to be embedded in the image to be applied, which leads to a further improvement of the security against counterfeiting.

The invention will be explained in more detail below, for example, with reference to the drawing. Show it:

FIG. 1 shows a card-shaped data carrier with a security feature according to the present invention,

FIG. 2 shows a representation of the portrait photograph on the data carrier of FIG. 1 for illustrating the security feature integrated therein;

FIGS. 3a and 3b show a schematic simplified illustration of gray values of different pixels in an image with a security feature integrated therein according to the present invention, and FIGS

FIG. 4 shows the course of gray values in an image above the location; the gray values of the security feature to be embedded over the location, as well as the gray scale value over the location in an image with an embedded security feature.

In the various figures of the drawing corresponding elements are provided with the same reference numerals.

Figure 1 shows as a data carrier a data card, which is shown for example as ID card or bank card. The data card 10 has a recording surface 1 on which the name 2 of the owner and his portrait photo 3 are recorded in a personalization area. Furthermore, general security features 4, such as tilted images or the like and the name 5 of the issuing institution can be recorded on the recording surface. be done. Furthermore, a security background 6 made of guilloches or the like can be provided partially or completely.

As shown in FIG. 2, in the owner's portrait photograph 3, which looks like a common portrait photo with the naked eye, a security feature 7 according to the invention is integrated so that it is not noticeable to the naked eye. For the naked eye, the gray value course within the portrait photo 3 is as expected in the case of a standard passport photo or the like.

However, if one looks at the portrait photo 3 in the area of the security feature 7 with a magnifying glass, it can be seen, as in the enlarged illustration 7a of the security feature, that additional information can be recognized, which is shown here as a microtext.

In order to be able to introduce the micro or additional information into the image, it is first necessary for the image to be present in digital form, that is to say it is subdivided into individual pixels. If the number of pixels present is smaller than the resolving power of the recording apparatus, such an image consisting of pixels can be scaled by suitable interpolation methods to the maximum spatial resolution of the output apparatus.

If, for example, a portrait photo, which is intended for a format of 3 x 4 cm, with 600 x 800 pixels, results in a resolution in the recorded image of 500 dpi. In order to be able to record an image which can be recognized by the human eye as sharp, however, a resolution of 70 dpi would already be sufficient, which would correspond to approximately 21 × 280 pixels. However, if the recorder operates at a resolution of 1000 dpi, approximately 1200 x 1600 pixels are required for the image.

In view of the fact that the resolution limit of the human eye is approximately 70 dpi, 5 x 5 to 6 x 6 pixels are available for every pixel that can be recognized by the human eye.

FIG. 3 a shows three pixels Pl, P 2, P 3 with their gray values over the location. If an image is then recorded on the basis of these gray values, the result is a picture which is pleasing to the human eye. In order to integrate or embed microinformation as a security feature in an image, a pixel is now subdivided into finer pixels Pmi. Now, each of the micro-pixels Pmi can be assigned a gray value such that the average of the gray values of the micro-pixels Pmi is equal to the original gray value of the pixel P2.

In this case, the procedure can be such that one of the pixels is assigned a gray value twice as large as the pixel P2, while the two adjacent micro-pixels Pmi are assigned gray values which amount to only half.

This results in a certain increase in contrast, which, as in FIG. 2, is represented in the enlarged security feature 7a by a certain overexposure of the letters.

However, as illustrated in Figure 3b, the smaller gray levels required to compensate for the increased gray level may also be distributed evenly or arbitrarily over a particular area.

The procedure for introducing a security feature according to the invention into the stored image for recording will now be explained with reference to FIG. For the sake of simplicity, the image is viewed in one direction only.

FIG. 4 a schematically shows the gray value profile in an image over the location, a light-dark transition 8 being illustrated. The areas P here indicate the resolution limit of the human eye, while the areas Pm represent the resolution of the recording apparatus. If an image is already recorded with a corresponding resolution, the digitally recorded image can be further processed in this form immediately. However, if the pixels of the recorded image are not sufficient, appropriate scaling must be carried out with suitable interpolation programs which prevent blocking in the recorded image.

The microinformation to be introduced into the image is then arranged in the form of positive and negative gray values, as shown in FIG. 4b, in such a way that each information pixel of the security feature has more than one image. corresponding to the resolution limit of the recording device corresponding micro-pixels, wherein the sum of the gray values of these pixels, which are in an area whose size corresponds approximately to the size of the visible pixels with the naked eye, is always equal to zero.

The values thus obtained are then added to the pixels of the recorded image, so that, as shown in Figure 4c, results in a gray value course, although the human eye can not be perceived, but is easy to recognize with a corresponding magnifying glass.

Although the embedding of additional information has been described only by the example of changes in the gray or brightness values, it is also possible for color images to have the color values, for example the values for chromaticity and / or color saturation of individual pixels of the resolution capability of the respective output or printing device corresponding image as the gray or brightness values to vary to integrate additional information in the applied, for example, printed image without disturbing the colorful overall impression.

The advantage of the security feature according to the invention is that it can be generated on the one hand only with very high resolution recording devices, such as those used in Laserpersonalisierungsanlagen, and thus is virtually impossible to fake. On the other hand, the security feature according to the invention can be detected with any good magnifying glass, so that no special equipment is required for its recognition and testing.

The security feature according to the invention can be integrated not only in portrait photos on identification cards and the like, but in any image representation, for example also on bills, documents and other documents to be protected against counterfeiting.

Claims

claims

1. A method for applying an image by means of an output device to a data carrier, in particular on a data or ID card, in which - the image to be applied consists of a plurality of pixels, which each positive gray or brightness values or color values are assigned, the number of Is adapted to the recognizable image additional information from a plurality of pixels according to the spatial resolution of the output device to which each positive and negative gray or brightness values or color values are assigned, the gray or brightness values or Color values of the pixels of the additional information to be embedded are superimposed on the gray or brightness values or color values of the pixels of the image, and the image to be applied using the thus obtained gray or brightness values or color values pixel by pixel on the image is recorded.

2. The method according to claim 1, characterized in that the spatial resolution of the output device is higher than that of the human eye.

3. The method according to claim 1 or 2, characterized in that the integral of the gray or brightness values or color values over all pixels of each area of pixels of the additional information that corresponds to the size of a detectable with the naked eye pixel is equal to zero.

4. The method according to any one of the preceding claims, characterized in that the einzubettende additional information is embedded in areas of the image to be applied, the average gray or brightness values or color values.

5. The method according to any one of the preceding claims, characterized in that the additional information to be embedded is a text.

6. The method according to any one of the preceding claims, characterized in that the additional information to be embedded comprises guilloches.

7. The method according to any one of the preceding claims, characterized in that the output device is a laser marking system with a pixel size less than 50 microns, preferably less than 40 microns, in particular from about 20 to 30 microns is used.