DE102019132529A1 - Method for extracting, reading out and / or outputting information hidden in a printed and / or visually designed surface - Google Patents

Abstract

A method is proposed for extracting, reading out and / or outputting information hidden in a printed and / or visually designed surface of an object, comprising: a) creating, providing and / or at least using a digital image that is an image of a printed and / or or reproduces visually designed surface of an object, b) determining information hidden in the image of the printed and / or visually designed surface by examining the digital image and / or the image reproduced thereby and c) extracting, reading out and / or outputting the determined information, wherein the determination of the hidden information comprises that a grid consisting of a plurality of grid elements is constructed and / or reconstructed from the digital image and / or the image reproduced thereby, the grid being constructed and / or reconstructed given the boundary conditions, - that a for the grid for ver Adjacent grid base area within which the reproduced grid elements are distributed can be subdivided into a first partial area and a second partial area, the first partial area and / or the second partial area being optionally contiguous or multi-part, - that the grid has a deviation that corresponds to the second subarea, but not in the first subarea, so that the areal extent, extent and / or distribution of the deviation specifies the second subarea and / or its area distribution or contour, and that the hidden information or its negative image through the second subarea and / or is coded by its area distribution or contour.

Description

The application relates to a method for extracting, reading out and / or outputting information hidden in a printed and / or visually designed surface.

Printing on objects or their packaging is increasingly provided with security features with which, for example, their authenticity or authenticity, that is, their actual origin, can be checked by the specified manufacturer, licensee or supplier; for example by scanning or photographing the security feature (e.g. with the help of a smartphone) and comparing it with a verifiably real digital template file or digital template for the security feature used from the actual manufacturer.

Such graphically or visually functioning security features can be, for example, noise patterns; The security feature is often designed to be clearly recognizable as such and, for example, accommodated in a separate area of the printed surface reserved for it; partly also explicitly marked or framed as such.

The present application, on the other hand, is used to determine security features that are at least visually more or less hidden, i.e. are not readily recognizable as such. Since such hidden features often serve as information carriers, information transmitters and / or themselves as the actual, hidden information or at least as a key to it, the present application speaks of “hidden information” in summary; this hidden information can also serve as a (hidden) security feature at the same time, but does not necessarily have to represent a security feature.

There are objects, the surface of which has a printing in the form of a grid, in which a portion of the set of grid points or grid elements is arranged slightly offset (relative to the ideal, everywhere periodic grid), so that the hidden information is due to deviations from the ideal grid or grid is coded. With this type of security feature, the hidden information is made visible by placing a suitable filter film, which has a checkerboard-like arrangement of darkened (and between them transparent) fields, which typically have lateral dimensions of, for example, about 100 µm. If such a filter film is placed on the visually designed surface and brought into overlap with the visually designed surface by positioning it correctly, the hidden information suddenly becomes visible and readable for the human eye, which was not recognizable when looking at the visually designed surface itself if their font size or their other area is actually not an obstacle. Often the hidden information consists in the contour of those surface areas in which the grid elements are arranged laterally offset to the ideal grid, whereby e.g. alphanumeric character strings, barcodes or other information can be made visible by means of the filter film.

It is the object of the present application to provide a method for making visible, extracting and / or reading out information that is hidden in a printed and / or visually designed surface of an object, the method making visible, extracting and / or reading out the information to enable in a new way.

This object is achieved by the method according to claim 1.

• Figur leinen Ausschnitt eines schematischen Layouts zum Bedrucken oder anderweitigen Gestalten der Oberfläche eines Gegenstands,
• 2 einen Ausschnitt einer Digitalvorlage zum Bedrucken der Oberfläche eines Gegenstands mit dem Layout aus 1,
• die 3A bis 3E in schematischer Ansicht das bevorzugte Gestaltungsprinzip zum Verbergen einer Information in einer bedruckten oder anderweitig bearbeiteten Oberfläche eines Gegenstands,
• 4 den Ausschnitt eines Digitalbildes, aufgenommen von der Oberfläche eines Gegenstands, die unter Verwendung der Digitalvorlage aus 2 gemäß dem Layout aus 1 bedruckt oder anderweitig bearbeitet wurde,
• 5 den Ausschnitt des Digitalbildes aus 4 nach Vornahme einer Glättung zur Verringerung von Rauschen,
• 6 einen nochmals vergrößerten Teilausschnitt des Digitalbildes aus 5 mit Kennzeichnung erkannter oder zumindest zunächst angezeigter Zentren von Rasterelementen,
• 7A ein Histogramm über die Häufigkeit der Neigungswinkel von Verbindungslinien zwischen je zwei Rasterelementen eines Bildausschnitts gemäß 7C zur Bestimmung des Verdrehwinkels des fotografierten Rasters,
• 7B das Histogramm aus 7A nach Vornahme einer Glättung über die auftretenden Neigungswinkel,
• 7C den zur Ermittlung des Verdrehwinkels eines fotografierten Rasters verwendeten Bildausschnitt des Digitalbilds,
• 8A ein Histogramm für die Abstände zwischen je zwei Rasterelementen gemäß 7C,
• 8B die Funktionskurve über denkbare Startwerte für die Periodenlänge, zunächst aus 8A ermittelt und anschließend umskaliert zur Kompensation sich proportional zum Abstand zwischen je zwei Rasterelementen auswirkender Einflüsse,
• 9 ein Histogramm über die ermittelte Häufigkeit berechneter Zahlenwerte für den lateralen Versatz von Rasterelementen aus 6,
• 10 ein errechnetes, helligkeits-invertiertes und zuvor geglättetes Abbild eines Rasters gemäß 4 zur Verwendung bei der Ermittlung der zuvor verborgenen Information,
• 11 eine Veranschaulichung einer Hilfskonstruktion zum Positionieren, insbesondere Korrigieren der Orientierung der ermittelten Information relativ zur Bildfläche einer Digitalvorlage,
• 12 einen Teilausschnitt der aus dem Digitalbild rekonstruierten verborgenen Information,
• 13 einen zu 12 korrespondierenden Ausschnitt einer digitalen Dateivorlage, welche die verborgene Information enthält,
• 14 ein Flussdiagramm zur Erläuterung des Verfahrens zum Extrahieren, Auslesen und/oder Ausgeben einer verborgenen Information,
• die 15A und 15B zwei alternative Ausführungen hinsichtlich der Beschaffenheit der Rasterelemente,
• 16 eine Weiterbildung mit in sich weiter unterteilten Basiszellen zur pseudozufälligen Dezentrierung der Zentren von Rasterelementen, dargestellt für eine Basiszelle einer Digitalvorlage und
• 17A und 17B abgeleitete Digitalbilder zur Darstellung des errechneten Kontrasts und des invertierten Kontrasts.

Some exemplary embodiments are described below with reference to the figures. Show it:

• Figure is a section of a schematic layout for printing or otherwise designing the surface of an object,
• 2 a section of a digital template for printing the surface of an object with the layout 1 ,
• the 3A to 3E a schematic view of the preferred design principle for concealing information in a printed or otherwise processed surface of an object,
• 4th the section of a digital image, recorded from the surface of an object, made using the digital original 2 according to the layout 1 has been printed or otherwise processed,
• 5 the section of the digital image 4th after smoothing to reduce noise,
• 6th a further enlarged section of the digital image 5 with identification of recognized or at least initially displayed centers of grid elements,
• 7A a histogram of the frequency of the angles of inclination of connecting lines between two raster elements of an image section according to FIG 7C to determine the angle of rotation of the photographed grid,
• 7B the histogram 7A after smoothing over the inclination angle that occurs,
• 7C the image section of the digital image used to determine the angle of rotation of a photographed grid,
• 8A a histogram for the distances between two grid elements according to 7C ,
• 8B the function curve over conceivable starting values for the period length, initially 8A determined and then rescaled to compensate for influences proportional to the distance between two grid elements,
• 9 a histogram of the determined frequency of calculated numerical values for the lateral offset of grid elements 6th ,
• 10 a calculated, brightness-inverted and previously smoothed image of a grid according to 4th for use in discovering previously hidden information,
• 11 an illustration of an auxiliary construction for positioning, in particular correcting the orientation of the determined information relative to the image area of a digital original,
• 12th a partial section of the hidden information reconstructed from the digital image,
• 13th one to 12th Corresponding excerpt from a digital file template that contains the hidden information,
• 14th a flow chart to explain the method for extracting, reading out and / or outputting hidden information,
• the 15A and 15B two alternative versions with regard to the nature of the grid elements,
• 16 a further development with further subdivided basic cells for the pseudo-random decentering of the centers of raster elements, shown for a basic cell of a digital original and
• 17A and 17B Derived digital images to show the calculated contrast and the inverted contrast.

In this application, the respective reference symbols are used across all figures for all figures of the application; To explain the elements identified thereby, reference can therefore be made to the disclosure relating to the respective remaining figures. If a reference number mentioned in the description does not appear in a figure, reference is made in this regard to the other figures.

1 shows a section of a layout 8th for the visual design (e.g. by means of a printing process or another processing process) of the in 4th photographed surface 100a of an object 100 . 4th thus shows the image content of a digital image 6th , which is a digital image A. the surface 100a this item 100 shows. Unless otherwise noted, the representations of all figures are cut-out representations on a (sometimes greatly) enlarged scale. In 1 and 4th a surface section is shown, the height of which corresponds in practice, for example, to a fraction (for example between a quarter and a half) of the letter height of a word or letter appearing in a printed text. This text forms the actual visual and merely exemplary motif; concrete is in 1 and 4th a motif or motif section 3rd which corresponds to the top crossbar of a printed letter "s" or "S"; the downward bend is no longer shown. Inside the upper crossbar, the line width of which is 0.5 to 1.5 mm or even larger in the printed text, there is information that is much smaller and also hidden 4th inscribed (or as predefined information to be hidden 40 still to be inscribed), which is here exemplarily formed as an additional, again smaller printed lettering from the three letters "CPS" (cf. 1 and 12th ).

Because of its small size, this is hidden information 4th if the text of the subject 3rd is printed with a font height of, for example, 24 pt, can hardly be recognized without aids. In addition, however, there is this hidden, smaller lettering 4th even on the printed (or through other visual design techniques instead of printing, for example by embossing, etc.) surface not recognizable as such, but only coded as a change in a grid from whose grid points (more precisely, grid spots or spot-shaped grid elements) the actual motive 3rd is constructed. While here as a motif 3rd is a printed text (or only a partial section of the printed or to be printed letter “s”), any other motif, for example an image, logo or a printed photo, can be used as a motif 3rd exist; Information can be found in its grid - even with motifs with inhomogeneous color and brightness such as photos or graphics 4th conceal in the same way as in the homogeneously colored lines of a printed letter or alphanumeric character.

While 1 only the schematic layout 8th for the subject 3rd and for the information to be concealed therein 40 shows, shows 2 an assigned section of a digital template file, ie a digital template 9 for the print image as a whole, that for printing on the surface 100a this item 100 and / or a plurality of objects according to the layout 1 serves. By using this digital master 9 (or another copy of this digital master copy with identical content 9 that may have been used elsewhere and also at an earlier point in time), printed copies are or have been produced, for example, on the with the help of the digital master 9 printed surface 100a of an object 100 are embodied, for example on a surface 100a a packaging, a document, a tool or machine part or a housing 100 . As in 2 is recognizable, the motive exists 3rd or the actual larger lettering intended for reading 3rd technically from a grid 5 from many grid elements 1 which in general do not necessarily correspond to the printing dots of a printing technique used, but are each made up of several or many of them. The grid elements 1 the printing embodied on the object and / or other visual design or processing are therefore if the layout 8th out 1 (ie a digital original designed accordingly 9 out 2 ) was used for printing, typically made up of several printing “dots”, which means that the selected printing or processing technique is suitable, including cut areas of these grid elements 3rd to print as they are in 2 in the digital template 9 are provided.

Albeit the printing technique of the digital original to be used later 9 in 2 is neither removable nor specified, the digital template shows 9 out 2 that printing of a variety of halftone elements 1 is planned, of which at least some are to be trimmed, ie only incompletely printed and / or at least some of which are to be printed in offset positions, which results in, for example, trimmed sections of grid elements. In 2 the outline of the lettering “CPS”, ie the outline of the hidden information, can be vaguely visualized 4th guess. With the information to be hidden 40 and the hidden information (embodied thereon after an item is printed) 4th In the context of this application, exactly the same information is meant in each case. The conceptual separation between the two expressions is only made if the distinction between the one (still "to be hidden" in the print image to be generated later, but) initially only through the digital original 49 ( 13th ) predefined information 40 on the one hand and the one in the finished print image on the object ( 4th ) embodied in the print image, already "hidden" therein 4th should be specially emphasized. Otherwise, however, as the respective information 4th ; 40 is identical in each case or should in any case be identical, both expressions in the following description are regarded as equivalent.

The 3A to 3E illustrate in a schematic view the preferred design principle for hiding information 4th in a printed surface 100a of an object 100 . At the same time they show 3A to 3E but also the design principle, like after photographing the surface 100a of an object 100 from the digital photo 6th (as in 4th shown) a grid 5 will be constructed and / or reconstructed, with the structure of which the hidden information 4th can be determined. Since this application does not include the production of the embodied printed copy of the object 100 or the digital master 9 in the foreground, but a process with which a digital photo 6th that is just an image A. of the object 100 embodied copy shows the hidden information 4th itself can be determined again, the following description of the 3A to 3E with regard to the construction and / or reconstruction of the grid according to the application, which will be explained in detail with reference to later figures 5 , with the structure of which the hidden information 4th should be determined.

In 3A is a grid 5 shown, but the placed grid elements do not yet match the grid elements printed on the object, but at least the basic structure is made up of a plurality of elementary unit areas, which are referred to in this application as basic cells become. Instead of being square (as shown), the unit areas or basic cells can, for example, also be selected to be rectangular or different. The basic cells are only geometrically defined patches of area, each around a grid element, for example 1 of the grid 5 out 2 to be thought around. But first goes 3A from a strictly periodic grid 5 in which each of its basic cells has a grid element 1 Is “filled” or occupied or occupied or at least one such grid element 1 assigned.

For the method proposed here, preference is given to grids based on that according to 3B , which are similar to those in 3C can be modified. If the photographed digital image A. ( 4th ) of a digital image 6th is examined in order to reconstruct the raster on which the imaged raster elements are based in order to use local deviations of some raster elements 2 within the grid shown 5 To determine the hidden information, a grid as in FIG 3C shown.

The grid to be constructed and / or reconstructed 5 is based on a basic structure in which the positions of the grid elements are thinned out like a checkerboard, as in 3B shown, so that only every second basic cell has a grid element 1 busy or assigned to it. Furthermore, as in 3C shown, the selection of those basic cells that are to have a grid element, inverted; ie in basic cells, in which there are actually no raster elements, raster elements are placed, and in basic cells, in which there are previously raster elements, these are removed.

While 3C although locally some irregular deviations from the grid that has not yet been modified 3B shows, shows 3D in the grid base 5a this grid 5 that area in which no inversion has taken place (which is called “first partial area 10” here) and that area in which the inversion was carried out (which is referred to here as “second partial area 20”). The grid elements forming the grid and the dividing lines between the empty or filled basic cells themselves are in 3D not shown, or only between the two partial surface areas 10 and 20th .

In 3D it can be seen that the second partial surface area formed or spanned by the inverted base surfaces 20th has a surface extension or outline contour which (apart from edge inaccuracies) is precisely the information that is hidden in the (to be concealed or in the photographed image) information 4th contained letter "P" corresponds to the lettering "CPS", which in 3E is shown without distortion of the edges.

So, as with the 3C and 3D apparent that for the grid 5 available grid base area 5a , within which the reproduced grid elements 5 are distributed, in a first partial area 10 and a second partial area 20th divisible, the first partial surface area 10 and / or the second partial surface area 20th is optionally contiguous or in several parts. The grid 5 exhibits a deviation, that is to say a systematic deviation, that is in the second partial surface area 20th , but not in the first partial area 10 is designed so that the two-dimensional extent, extent and / or distribution of the deviation the second partial surface area 20th and / or its area distribution or contour 20a pretends. The hidden information 4th or their negative image is thus through the second partial surface area 20th and / or by its area distribution or contour 20a coded.

Thus, in the proposed method, as will be explained further below, the raster sought is obtained 5 constructed and / or reconstructed under specification of the boundary condition that the deviation in the second partial surface area 20th a uniform change in the grid elements 2 of the second partial area 20th , in particular a uniform change in the position, the orientation, the size, the diameter, the contour, the brightness and / or the color of the grid elements 2 of the second partial area 20th compared to the grid elements 1 of the first partial area 10 is or includes.

• - nur in dem zweiten Teilflächenbereich 20 einen von Null verschiedenen Parameterwert besitzt und/oder
• - in dem zweiten Teilflächenbereich 20 einen anderen Parameterwert als in dem ersten Teilflächenbereich 10 besitzt; beispielsweise den Wert -1, der (als Multiplikationsfaktor oder in sonstiger Weise) die Invertierung der dortigen Basiszellen ausdrückt.

For example, the grid 5 constructed and / or reconstructed under specification of the boundary condition that it has a deviation that corresponds to a parameter, the parameter

• - only in the second partial area 20th has a non-zero parameter value and / or
• - in the second partial area 20th a different parameter value than in the first partial area 10 owns; for example the value -1, which (as a multiplication factor or in some other way) expresses the inversion of the basic cells there.

Alternatively it would be conceivable that the grid 5 it is constructed and / or reconstructed with the specification of the boundary condition that it has a deviation which corresponds to a parameter in the second partial surface area 20th depending on the position of the base cell assumes at least two different parameter values (for example for the base cells emptied by the inversion or the base cells filled thereby), each of which is based on a uniform parameter value for the first partial surface area 10 and / or is different from zero.

So if from the arrangement of the digital image 6th according to 4th reproduced grid elements later that grid is reconstructed which was originally when the object was printed 100 was already the basis, then the reconstruction takes place under the boundary condition that - preferably from a checkerboard thinned grid according to 3B starting - in the area that the hidden information takes up within the motif, all basic cells are inverted. These and the other boundary conditions, as formulated in the patent claims, enable and / or facilitate a successful reconstruction of the originally printed grid.

The digital template for printing according to 3C resulted from a checkerboard inversion of the hidden motif 3D . A chessboard-like inversion of the digital artwork according to FIG 3C therefore gives again the original hidden image according to 3D , at least apart from the fact that the negative image could also result if the basic cells selected for these two inversions are not identical but are shifted from one another by one basic cell. Now the digital artwork is not being used for printing 3C inverted like a checkerboard, but the image 6 of the actual printed pattern according to 4th , then of course there is also an image of the hidden image 3D . One type of basic cells of this image (either the light or the dark, depending on whether the negative image was produced or not) all together form the second partial surface area 20th the grid base area 5a , as its outline the information to be determined 4th is coded as this information 4th already in the digital template 9 out 2 according to (or with the layout 8th out 1 ) was intended as a local inversion or shift of the grid.

4th shows a section of a digital image 6th that of the printed item 100 was recorded and thus an image as a motif or image content A. from its surface 100a reproduces or contains. From this digital image 6th ; A. becomes that of the arrangement of (photographed or depicted) grid elements 1 , 2 underlying grid 5 determined. Thus is a grid 5 to be determined from basic cells of suitable size, orientation and position.

The size of the basic cells is limited downwards by the typical resolution capability of camera images, for which a maximum resolution of 800 dpi is assumed, which corresponds to a length of 31.75 µm. The size of the basic cells can be chosen, for example, between 30 and 150 µm. Assuming a resolution limit of the human eye at around 300 dpi, which corresponds to a length of almost 85 μm, the size of the dimension of the basic cell (ie its period or period length) can preferably be selected in the order of magnitude between 40 and 85 μm; especially with square basic cells. The shape of the grid elements can be circular (with a diameter that matches the size of the basic cell) or also square or in some other way (eg star-shaped). The center of a grid element 1 ; 2 can be assumed or defined as lying in the middle of a respective basic cell.

The recording or creation of the digital image 6th as well as its evaluation (and ultimately also the entire method according to the application for determining the hidden information) can take place, for example, with a smartphone, but also with a film or photo camera, a scanner, a webcam, a microscope (such as a USB microscope), a Tablet, augmented reality glasses or any other device that is provided with a camera, ie with any image recording device. The digital image 6th can be evaluated by the image recording device used, alternatively also by another fixed or portable computer (e.g. laptop or smartwatch) or on a server on the Internet.

The relevant image area of the digital image must be used to determine the hidden information 6th containing this information can be evaluated. This predefined image area results, for example, from the fact that the smartphone user uses the smartphone with the aid of the camera image shown on the screen or display with the aid of superimposed markings in relation to the motif shown 3rd and / or on others in the vicinity of the subject 3rd aligns visible elements or surface areas of the object. Alignment directly to the information to be determined itself, however, is not possible or not reliably possible, since this information is concealed, that is to say is not or barely perceptible.

wobei M(x,y) die nach dieser Glättung errechneten Bildwerte anstelle der ursprünglich aufgenommene Bildwerte bzw. Bildpunktwerte B(x,y) bezeichnet. Diese Bildpunktwerte sind im einfachsten Fall Helligkeitswerte, die zwischen absolutem Schwarz (dem Wert Null entsprechend) und einer Maximalhelligkeit liegen; alternativ können sie auch Buntwerte bzw. Helligkeitswerte für mehrere Farben (z.B. C,M,Y,K oder wie üblicherweise verwendet R,G,B) umfassen. 5 shows the section of the digital image 6th out 4th after smoothing the image content to remove or reduce the image noise. Starting from a digital image 6th or camera image B (x, y) with the image pixel coordinates x and y and brightness values B. For example, the recorded digital values of the pixels can be averaged over a pixel area of 3x3 pixels (or more generally over nxn pixels) in order to eliminate the noise, for example; for example according to the formula $$\text{M.}\left(\text{x}\text{, y}\right)=1/9\ast {\Sigma }_{\left(\text{i}=\mathrm{1.0,}+\mathrm{1,}\text{j}=-\mathrm{1.0,}+1\right)}\text{B.}\left(\text{x + i}\text{, y + i}\right),$$

where M (x, y) are the image values calculated after this smoothing instead of the originally recorded image values or image point values B (x, y) designated. In the simplest case, these pixel values are brightness values that lie between absolute black (corresponding to the value zero) and a maximum brightness; alternatively, they can also include chromatic values or brightness values for several colors (for example C, M, Y, K or, as is commonly used, R, G, B).

For clarification it should be mentioned here that the grid elements 1 , 2 (more precisely their image in the digital image 6th ) each themselves in turn can be composed of a plurality or multiplicity of pressure points (ie from the images of these pressure points) of an imprint (or visual design generated by other processing techniques) of the depicted object surface. The images of the raster elements are therefore mostly not images of individual printing dots, but images of a visually designed raster point or raster spot. In most cases, however, it is in the digital image 6th the resolution of the halftone dot or halftone dot 1 , 2 can no longer be recognized in several pressure points.

6th shows a further enlarged section of the digital image 5 , namely in the area of the line bend in the left area of the upper crossbar of the letter "s", which (as shown by the 1 and 2 explained) as a motive 3rd or motif detail serves to illustrate the method according to the application with which the information hidden in the motif is to be determined. In addition to the smoothed grid elements 1 , 2 (their affiliation to either the first or the second subarea 10 , 20th has yet to be determined) are those within the pixel matrix of the digital image 6th indicated positions for which it has been determined that there are centers of grid elements 1 , 2 lie.

und $$\text{Z}\left(\text{x}\text{,y}\right)=0\text{ sonst}\text{.}$$

The centers Z can be defined, for example, as those image pixels whose brightness is a local minimum over a 3 × 3 pixel area of the smoothed camera image M (x, y) out 5 possesses what can be expressed by the logical function $$\text{Z}\left(\text{x}\text{, y}\right)=\mathrm{1,}\text{if M}\left(\text{x}\text{, y}\right)={\text{MIN}}_{\left(\text{i}\text{, j}=-\mathrm{4\; ..}+\mathrm{4th}\right)}\left(\text{M.}\left(\text{x + i}\text{, y + i}\right)\right)$$

and $$\text{Z}\left(\text{x}\text{, y}\right)=0\text{otherwise}\text{.}$$

For the sake of clarity, in 6th these centers are represented in the form of white crosses with a black outline. The formula for Z (x, y), on the other hand, only marks the image pixel with a value of 1 that lies in the center of the cross, i.e. where the crossbar of the cross and the vertical bar of the cross intersect.

Outside the left and top of the as a motif 3rd serving grid 5 from grid elements 1 , 2 a number of erroneously calculated centers, i.e. so-called pseudo-centers, which are not superimposed on any grid element, can be recognized. These are local, low-contrast brightness minima due to brightness fluctuations in the non-printed area of the object surface (or its image in the digital image 6th ).

To eliminate such erroneously calculable pseudo-centers, the condition can be defined that a pixel of the digital image should only be a center if the brightness minimum there is over the corresponding 3x3 or nxn pixel area of the smoothed camera image M (x, y) out 5 differs by a predetermined minimum value or minimum contrast from the (local) mean value over the smoothing area. For this purpose, a numerical value would then have to be defined for the absolute threshold of the minimum contrast, above which a (smoothed) pixel for recognition as the center Z of a grid element 1 or 2 is allowed.

In 6th multiple centers that are immediately adjacent can still be seen in some places, both outside of the motif 3rd serving grid 5 from grid elements 1 , 2 as well as within. These multiple centers come about because two or more neighboring smoothed pixels have the same, locally minimal brightness value. However, since each raster element in the digital image is always a plurality of image pixels and is also spaced from all surrounding, neighboring raster elements, the display of immediately adjacent double pixels or pixel groups is to be interpreted as meaning that the respective raster element is positioned exactly between two or more pixels.

The erroneous display of such multiple centers directly next to one another can be eliminated or prevented by adding to the brightness values of the pixels of the smoothed camera image M (x, y) in 5 A pseudo-random number, which varies depending on the pixel position, is added in an almost vanishing, i.e. very small, value range (for example between zero and 0.000001 or between zero and a maximum of 10 ^-n with n≥6), so that the pixel brightness is only ever locally on a single pixel can assume a local minimum.

The aim of the method according to the application is to use the recognized arrangement of positions of grid elements 1 , 2 of the grid 5 a grid, more precisely the grid originally used as the basis for printing the object 5 to reconstruct.

If the original grid or just another grid cannot be determined in this way, the registration speaks of the construction (instead of reconstruction) of a grid, because an attempt is always made by examining and evaluating the digital image 6th to determine how the originally used grid (cf. 2 ) must have looked. Even if the determined or constructed grid should turn out to be a wrong grid (which indicates, for example, that the photographed object is not an original, authentic product and the hidden information of the security feature is thus falsified), the procedure for constructing this grid is precise the same as in the reconstruction of the actual original grid. Incidentally, in the latter case too, statistical and error-related deviations from the original grid are unavoidable, if only because the reconstruction of the original grid can only take place with a certain degree of accuracy.

In the following, it is assumed that, if there is a need at all, a perspective correction to correct a tilting of the mount between the surface 100a of the subject 100 and the image capture device involved in creating the digital image 6th of the surface (preferably flat or planar, but not necessarily aligned parallel to the image plane or sensor plane of the image recording device used) 100a may have existed, has already been carried out. Thus is the digital image 6th (or the image saved as image content 6th from the surface 100a of the subject 100 ) already straightened out to such an extent that along the two grid-specific periodicity directions of the grid (already mapped, but not yet reconstructed) 5 the (imaginary) connecting lines between the respective grid elements run parallel to one another instead of convergent.

• - ein Verdrehwinkel θ zwischen einer der beiden Koordinatenrichtungen des Digitalbildes 6 und einer der beiden Periodenrichtungen des Rasters selbst,
• - eine Periode (hier auch Periodenlänge a genannt) entlang beider zueinander orthogonalen Periodizitätsrichtungen (oder, falls je nach Raster die Periodenlänge entlang beider orthogonalen Periodizitätsrichtungen unterschiedlich groß sein sollte, die Werte für beide dieser Periodenlängen),
• - die beiden Längen Vx, Vy für den Versatz bzw. die Verschiebung entlang der ersten und der zweiten Koordinatenrichtung des Digitalbildes 6, um das durch die Periodenlänge a und den Verdrehwinkel θ gebildete, durch den Koordinatenursprung verlaufende Raster so zu verschieben, dass es wie später beschrieben optimal mit den Zentren in Deckung gebracht werden kann.

For the (re-) construction of the grid you are looking for, the following must be determined:

• - a twist angle θ between one of the two coordinate directions of the digital image 6th and one of the two period directions of the grid itself,
• - a period (here also period length a called) along both orthogonal periodicity directions (or, if, depending on the grid, the period length should be different along both orthogonal periodicity directions, the values for both of these period lengths),
• - the two lengths Vx , Vy for the offset or the shift along the first and the second coordinate direction of the digital image 6th to do this by the period length a and the twist angle θ to move the grid that runs through the origin of coordinates so that it can be optimally aligned with the centers, as described later.

Thus, four parameters have to be determined in such a way that when (re-) designing the grid, the grid originally used when printing the object is created.

$$\text{y}\text{'}=1/\text{a}\ast \left(\left(\text{x}-\text{Vx}\right)\ast \text{sin}\left(\mathrm{\theta }\right)-\left(\text{y}-\text{Vy}\right)\ast \text{cos}\left(\mathrm{\theta }\right)\right),$$

wobei als Ursprung beispielsweise die linke obere Ecke des Digitalbilds 6 gewählt wird, beispielsweise die linke obere Ecke des in den 4, 5, 10 (und nochmals ausschnittsweise vergrößert in 6) dargestellten Bildausschnitts.When converting the image coordinates of all raster elements in the coordinate system of the digital image spanned by the image pixels 6th (Coordinates x and y ) into the changed image coordinates of all grid elements in the coordinate system of the grid to be reconstructed 5 (Coordinates x 'and y') the following conversion formulas apply to the image coordinates: $$\text{x}\text{'}=1/\text{a}\ast \left(\left(\text{x}-\text{Vx}\right)\ast \text{cos}\left(\mathrm{\theta }\right)-\left(\text{y}-\text{Vy}\right)\ast \text{sin}\left(\mathrm{\theta }\right)\right)$$

$$\text{y}\text{'}=1/\text{a}\ast \left(\left(\text{x}-\text{Vx}\right)\ast \text{sin}\left(\mathrm{\theta }\right)-\left(\text{y}-\text{Vy}\right)\ast \text{cos}\left(\mathrm{\theta }\right)\right),$$

where the origin is, for example, the top left corner of the digital image 6th is selected, for example the upper left corner of the 4th , 5 , 10 (and again enlarged in detail in 6th ) shown image section.

• - ein Verdrehwinkel θ einer Periodizitätsrichtung des zu konstruierenden und/oder zu rekonstruierenden Rasters 5 relativ zu einer Koordinatenrichtung des Digitalbildes 6 und
• - zumindest die Periodenlänge a des zu konstruierenden und/oder zu rekonstruierenden Rasters 5

gemeinsam in gegenseitiger Abhängigkeit voneinander ermittelt werden, ohne einen Gesamtversatz Vx, Vy des zu konstruierenden und/oder zu rekonstruierenden Rasters relativ zu dem Digitalbild festzulegen, und dass mit Hilfe der ermittelten Ergebniswerte für den Verdrehwinkel θ und für die Periodenlänge a erst danach ein lateraler Versatz Vx, Vy berechnet wird, durch welchen die Zentren bestmöglich mit den Kreuzungen des Rasters 5 in Deckung gebracht werden, was die Voraussetzung dazu ist, dass aus dem Digitalbild 6 die durch den zweiten Teilflächenbereich 20 dargestellte Information 4 rekonstruiert werden kann.With regard to the implementation of this determination of the actual (grid) parameters, it is proposed that the construction and / or reconstruction of the grid 5 from the digital image 6th includes that initially

• - a twist angle θ a periodicity direction of the grid to be constructed and / or reconstructed 5 relative to a coordinate direction of the digital image 6th and
• - at least the period length a of the grid 5 to be constructed and / or reconstructed

can be determined together in mutual dependence on one another, without an overall offset Vx , Vy of the grid to be constructed and / or to be reconstructed relative to the digital image, and that with the aid of the determined result values for the angle of rotation θ and for the period length a only then is there a lateral offset Vx , Vy is calculated by means of which the centers match the intersections of the grid in the best possible way 5 be brought into congruence, which is the prerequisite for that from the digital image 6th that through the second partial surface area 20th information presented 4th can be reconstructed.

It is therefore suggested not to use all four parameters in the optimization θ , a , Vx , Vy to optimize or vary at the same time, but initially only the angle of rotation or screen angle θ and the grid period a to be determined, while the initially unknown, but also to be determined offset shifts Vx , Vy can be appropriately estimated (to be described later).

It is also proposed that the two parameters should be optimized together first θ , a (disregarding the other parameters Vx , Vy ) apply a global algorithm, either a deterministic global algorithm or a randomized global algorithm. A conceivable example of a randomized global algorithm is the use of an evolutionary algorithm, the term "evolutionary algorithm" being understood as a collective term for genetic methods, a controlled random search (CRM; Controlled Random Search) and for evolutionary methods according to Rechenberg is.

This results in a global optimization of the screen angle θ and grid period a which have only local values for each individual of the evolutionary algorithm (ie for fixed values for the offset that cannot be further optimized) Vx and Vy ending) optimization of θ and a goes out.

• - eine Berechnung zur Eingrenzung des Bereichs in Frage kommender Zahlenwerte für das Endergebnis des Verdrehwinkels θ, vorzugsweise zur Eingrenzung auf einen Winkelbereich kleiner als 5°, beispielsweise kleiner als 2°, insbesondere kleiner als 0,5°, und
• - eine Berechnung zur Eingrenzung des Bereichs in Frage kommender Zahlenwerte für das Endergebnis der Periodenlänge a, vorzugsweise zur Eingrenzung auf einen Bereich von Zahlenwerten mit einer Bandbreite auf ±5 Pixel, beispielsweise bis auf maximal ±2 Pixel, insbesondere bis auf maximal ±0,5 Pixel

durchgeführt wird und dass erst nach dieser Eingrenzung des Verdrehwinkels θ und/oder der Periodenlänge a die gemeinsame Ermittlung der endgültigen Zahlenwerte für das Endergebnis des Verdrehwinkels θ und der Periodenlänge a in gegenseitiger Abhängigkeit voneinander durchgeführt wird.It is also proposed that the joint determination of the angle of rotation θ and the period length a is carried out in such a way that from the digital image and / or a partial area of the digital image first

• - a calculation to limit the range of possible numerical values for the final result of the angle of rotation θ , preferably to limit it to an angular range smaller than 5 °, for example smaller than 2 °, in particular smaller than 0.5 °, and
• - a calculation to limit the range of possible numerical values for the final result of the period length a , preferably for limiting to a range of numerical values with a bandwidth of ± 5 pixels, for example up to a maximum of ± 2 pixels, in particular up to a maximum of ± 0.5 pixels

is carried out and that only after this limitation of the angle of rotation θ and / or the period length a the joint determination of the final numerical values for the final result of the angle of rotation θ and the period length a is carried out in mutual dependence on each other.

Thus, the above-mentioned algorithmic methods are used to determine the angle of rotation or screen angle θ and the period length a only apply after for both parameters θ , a first the possible numerical values or final result values have been narrowed down to such an extent that the range possible numerical values turns out to be considerably smaller than the fundamentally relevant parameter range that is available for a complete search.

For example, the parameter range for the angle of rotation includes θ after taking symmetries into account, in principle a maximum of an angle range from 0 ° to 90 °, or an angle range between -45 ° to 45 °; all other conceivable angles can be mapped to an angle within this angular range.

• Zum Auffinden der Mitte eines geeigneten Suchbereichs für den Rasterwinkel θ wird die folgende Vorgehensweise gemäß den 7A bis 7C vorgeschlagen:
  • Innerhalb des im Digitalbild 6 abgebildeten Motivs wird ein geeignet großer, rechteckiger (Bildflächen-)Bereich (beispielsweise mit einem Seitenverhältnis von 2:1) ausgewählt, in dem mindestens 100 Zentren Z von Rasterelementen 1, 2 angeordnet sind (ob ein bestimmtes Rasterelement im ersten oder zweiten Teilflächenbereich positioniert und demnach mit 1 oder 2 zu bezeichnen ist, lässt sich erst nach Rekonstruktion des Rasters, d.h. erst im Nachhinein feststellen). Wie in 7C dargestellt, ist der ausgewählte Bildflächenbereich z.B. in ein linkes und ein rechtes Quadrat unterteilbar. Für alle Kombinationen aus jeweils einem Raster-Zentrum Z im linken Quadrat bzw. der linken Hälfte des rechteckigen Bildflächenbereichs (in Bezug auf die lange, obere oder untere Kante dieses Rechtecks) und jeweils einem Raster-Zentrum Z im rechten Quadrat bzw. der rechten Hälfte des rechteckigen Bildflächenbereichs wird der Neigungs- oder Steigungswinkel θ der Verbindungslinie zwischen diesen beiden Zentren Z berechnet gemäß

$$\mathrm{\theta }\left({\text{x}}_{\text{1}}{\text{,<figure-callout id="1" label="y" filenames="DE102019132529A1\_0033.png,DE102019132529A1\_0034.png" state="{{state}}">y</figure-callout>}}_{\text{1}};{\text{x}}_2{\text{,y}}_2\right)=-\text{arctan }\left(\left({\text{<figure-callout id="2" label="y" filenames="DE102019132529A1\_0030.png,DE102019132529A1\_0033.png" state="{{state}}">y</figure-callout>}}_{\text{2}}-{\text{y}}_{\text{2}}\right)/\left({\text{<figure-callout id="2" label="x" filenames="DE102019132529A1\_0030.png,DE102019132529A1\_0033.png" state="{{state}}">x</figure-callout>}}_{\text{2}}-{\text{x}}_{\text{1}}\right)\right).$$

For finding suitable initial values (ie for the middle of the search areas) for the screen angle θ and the period length a (for insertion or use, for example, in the evolutionary algorithm), especially those that have the most suitable value for the screen angle θ and the period length a can be done as follows:

• To find the center of a suitable search area for the screen angle θ the following procedure is carried out according to the 7A to 7C suggested:
  • Inside the in the digital image 6th Depicted motif, a suitably large, rectangular (image area) area (for example with an aspect ratio of 2: 1) is selected in which at least 100 centers Z of grid elements 1 , 2 are arranged (whether a certain grid element is positioned in the first or second partial surface area and is therefore to be designated as 1 or 2 can only be determined after the grid has been reconstructed, ie only afterwards). As in 7C shown, the selected image area can be subdivided into a left and a right square, for example. For all combinations of one grid center each Z in the left square or the left half of the rectangular image area (in relation to the long, upper or lower edge of this rectangle) and in each case a grid center Z in the right square or the right half of the rectangular image area is the angle of inclination or slope θ the line connecting these two centers Z calculated according to

$$\mathrm{\theta }\left({\text{x}}_{\text{1}}{\text{, <figure-callout id="1" label="y" filenames="DE102019132529A1\_0033.png,DE102019132529A1\_0034.png" state="{{state}}">y</figure-callout>}}_{\text{1}};{\text{x}}_2{\text{, y}}_2\right)=-\text{arctan}\left(\left({\text{y}}_{\text{2}}-{\text{y}}_{\text{2}}\right)/\left({\text{x}}_{\text{2}}-{\text{x}}_{\text{1}}\right)\right).$$

The in 7A the histogram shown is plotted, ie over the angular range from -45 ° to + 45 °; for example in 0.1 ° steps.

This histogram is then smoothed; for example by calculating the mean value over a range of ± 0.5 °; the mean value over a comparatively larger angular range (e.g. averaged over an angular range of ± 3 °) is subtracted from this mean value over the ± 0.5 ° angular range, whereby the in 7B The smoothed histogram shown for the slope angle is created.

Due to the fact that with a periodic grid at the angle of rotation that leads to the rotation in the direction of one of the period directions of this grid, a particularly large number of connecting lines (between two centers of grid elements) have precisely this angle of inclination or at least an angle of inclination that deviates only slightly from it in the search area 7C angle of inclination occurring with a particularly high frequency than one with a high probability of the final value for the angle of rotation θ of the grid identify only slightly deviating, ie very suitable, initial value for a more precise calculation of the actual, final and exact value for the angle of rotation θ with the help of one of the algorithms mentioned above is particularly suitable and with a high probability of a correct end result for θ that is the value in the histogram in 7B that has the greatest frequency, i.e. the global maximum of this histogram. In the smoothed histogram in 7B this value of the (inclination) angle, which occurs with the greatest frequency, is approx. -2 °.

Also for the period length a that together with the twist angle θ should be optimized or determined algorithmically, a suitable initial value is required.

The start parameter for the grid period a (expressed as the number of image pixels), ie the center of the search area for the raster period a , could be estimated from the known screen period of the printed screen using the image resolution. The image resolution itself could be estimated from the known size of other surrounding clearly visible elements inside or outside the grid.

If no suitable, clear graphic or visual element is available to estimate the grid period, a suitable initial value or starting parameter for the grid period is determined a the following procedure is suggested:

For all those combinations or pairs of grid element centers Z the preceding calculation of the start parameter for the screen angle θ , for which the angle difference between the angle of inclination of the line connecting the two raster point centers Z ₁ , Z ₂ (with the coordinates x ₁ , y ₁ and x ₂ , y ₂ ) and the start parameter for the raster angle is below 0.5 ° following distance L. calculated: $$\text{L.}={\left[{\left({\text{x}}_{\text{1}}-{\text{x}}_{\text{2}}\right)}^2+{\left({\text{y}}_{\text{1}}-{\text{y}}_{\text{2}}\right)}^2\right]}^{0.5}$$

Furthermore, a histogram is calculated using these distances between two centers in each case, specifically in a value range of between 0 and 100 pixels. This histogram is in 8A shown; it shows the frequency of the distances between any two centers as in 7C described.

The frequency H (a) of the occurrence of potential period lengths a between 2 and 18 pixels in size is applied with a step size of 0.02; for example using the following function, which is the weighted square distance to the nearest integer multiple of the period length under consideration a represents: $$\text{H}\left(\text{a}\right)={\left[{\mathrm{\Sigma }}_{\text{L.}}\left(\text{H}\left(\text{L.}\right)/\text{Total number *}{\left(\text{L.}-\text{a *}\left(\text{L div a}\right)\right)}^2\right)\right]}^{0.5}$$

Dadurch entsteht die obere Funktionskurve in 8B.Div represents the whole number division and total number represents the sum of all in 8A plotted frequencies, ie $\text{Total number}={\mathrm{\Sigma }}_{\text{L.}}\text{H}\left(\text{L.}\right).$

This creates the upper function curve in 8B .

According to the procedure in 7C the frequency of encountering a corresponding distance increases linearly with larger distances (namely proportional to the circumference of a circular line 2rπ). This leads to the overall linear rise of this upper function curve in 8B . About the plausibility of the potential period lengths a The values of this upper function curve are to be assessed independently of this geometric peculiarity in 8B then linearly rescaled according to the following formula in order to be able to assess the deflections relative to the linear fit: $${\text{H}}_{\text{rescaled}}\left(\text{a}\right)=\left(\text{H}\left(\text{a}\right)-\left({\text{pitch}}_{\text{H}\left(\text{a}\right)}*\text{a}+{\text{Offset}}_{\text{H}\left(\text{a}\right)}\right)\right)/\left({\text{pitch}}_{\text{H}\left(\text{a}\right)}*\text{a}+{\text{Offset}}_{\text{H}\left(\text{a}\right)}\right)$$

Here, with the slope _{H (a)} the slope and with the offset _{H (a)} the y-axis intercept of the linear fit to the upper curve H (a) in 8B designated. The formula first determines the difference to the linear fit for H (a) (numerator, this has the effect that the slope of the linear fit is eliminated) and this difference is then transformed linearly in such a way that the deflections around the x-axis are proportional to the height of the linear fit at this point (slope _{H (a)} * a), which means that not the absolute deflections are considered, but the relative deflections.

The function rescaled in this way is shown as the lower function curve in 8B applied. The minimum of this rescaled, lower function curve in 8B corresponds to a suitable value for the start parameter a0 for the grid period; According to 8B for example, it is 6.1. This starting value for the grid period a is therefore together with the start value for θ for the joint algorithmic calculation of the exact values or final results for the angle of rotation θ and the period length a of the grid.

• - Raster-Verdrehwinkel θ: ±1,0° um den Startparameter für θ herum und
• - Rasterperiode a: ±0,5 Bildpixel um den Startwert a0 herum.

With the joint optimization of the angle of rotation or grid angle θ and the grid period a (by means of a deterministic or randomized global algorithm), for example, the following boundary conditions are used:

• - Raster rotation angle θ : ± 1.0 ° around the start parameter for θ around and
• - grid period a : ± 0.5 image pixels around the starting value a0 around.

• - für den Rasterwinkel θ (zu optimieren): 0,1°
• - für die Rasterperiode a (zu optimieren): 0,01 Pixel

The optimizations are carried out, for example, with the following accuracy:

• - for the screen angle θ (to be optimized): 0.1 °
• - for the grid period a (to be optimized): 0.01 pixels

wobei die Koordinaten x' und y' im Koordinatensystem des gesuchten, zu rekonstruierenden Rasters 5 verwendet werden, in dem die Rasterlinen entlang der ganzzahligen Koordinaten verlaufen. Die gemeinsame Optimierung von θ und a, deren geeignete Startparameter bereits wie oben erläutert errechnet wurden, erfolgt zunächst, indem Vx und Vy wie im Folgenden berechnet werden. Erst wenn die Optimierung von θ und a abgeschlossen ist und deren endgültige, korrekte Werte feststehen, werden die Versatz-Koordinaten Vx und Vy ihrereseits optimiert, beispielsweise mittels eines Gradientenabstiegs-Verfahrens. Dabei werden die schon errechneten, korrekten Werte für den Rasterwinkel θ und die Rasterperiode a eingesetzt und nicht mehr verändert.The mean square distance of the centers to the next grid intersection serves as the optimization measure to be minimized or as the optimization function F for all optimizations, i.e. F is calculated from the mean value of this expression for each center (i.e. Z (x, y) = 1) according to $${\text{F = mean}}_{\text{x}\text{, y | Z}\left(\text{x}\text{, y}\right)=1}\left[{\left(0.5-|0.5-{\text{x '}}_{\text{Fractional part}}|\right)}^2+{\left(0.5-|0.5-{\text{y '}}_{\text{Fractional part}}|\right)}^2\right],$$

where the coordinates x 'and y' are in the coordinate system of the grid to be reconstructed 5 can be used in which the grid lines run along the integer coordinates. The joint optimization of θ and a, the suitable starting parameters of which have already been calculated as explained above, are initially carried out by calculating Vx and Vy as follows. Only when the optimization of θ and a is complete and their final, correct values are established, become the offset coordinates Vx and Vy optimized on their part, for example by means of a gradient descent method. The correct values already calculated for the screen angle are thereby used θ and the grid period a used and no longer changed.

$$\text{hY}\left(\text{x}\text{,y}\right)=\text{x}*\text{sin}\left(\mathrm{\theta }\right)-\text{y*cos}\left(\mathrm{\theta }\right)\text{ mod a}$$

berechnet, wobei mod den Rest einer ganzzahligen Division darstellt. Anschließend werden für alle Rasterelement-Zentren Z die Werte $$\text{Vx}\left(\text{x}\text{,y}\right)=\text{hX}\left(\text{x}\text{,y}\right)*\text{cos}\left(\mathrm{-\theta }\right)-\text{hY}\left(\text{x}\text{,y}\right)*\text{sin}\left(\mathrm{-\theta }\right)$$

$$\text{Vy}\left(\text{x}\text{,y}\right)=\text{hX}\left(\text{x}\text{,y}\right)*\text{sin}\left(\mathrm{-\theta }\right)+\text{hY}\left(\text{x}\text{,y}\right)*\text{cos}\left(\mathrm{-\theta }\right)$$

berechnet. Die Häufigkeit der erhaltenen Zahlenwerte für die beiden Versatzwert-Komponenten Vx, Vy der Zentren aus 6 sind in 9 in Form eines Histogramms aufgetragen.As part of the optimization for the screen angle θ and the grid period a become the values for the offset Vx and Vy calculated as follows: For all grid element centers Z become the auxiliary variables $$\text{hX}\left(\text{x}\text{, y}\right)=\text{x}*\text{cos}\left(\mathrm{\theta }\right)-\text{y * sin}\left(\mathrm{\theta }\right)\text{mod a}$$

$$\text{hY}\left(\text{x}\text{, y}\right)=\text{x}*\text{sin}\left(\mathrm{\theta }\right)-\text{y * cos}\left(\mathrm{\theta }\right)\text{mod a}$$

calculated, where mod represents the remainder of an integer division. Then for all grid element centers Z the values $$\text{Vx}\left(\text{x}\text{, y}\right)=\text{hX}\left(\text{x}\text{, y}\right)*\text{cos}\left(\mathrm{-\theta }\right)-\text{hY}\left(\text{x}\text{, y}\right)*\text{sin}\left(\mathrm{-\theta }\right)$$

$$\text{Vy}\left(\text{x}\text{, y}\right)=\text{hX}\left(\text{x}\text{, y}\right)*\text{sin}\left(\mathrm{-\theta }\right)+\text{hY}\left(\text{x}\text{, y}\right)*\text{cos}\left(\mathrm{-\theta }\right)$$

calculated. The frequency of the numerical values obtained for the two offset value components Vx , Vy of the centers 6th are in 9 plotted in the form of a histogram.

By shifting by a value in the range from -a / 2 to + a / 2, each pixel can be shifted to a grid intersection, where a is the determined period of the grid. Therefore, in the figure, the greatest frequency value becomes precisely within this range from -a / 2 to + a / 2 H for the components Vx and Vy chosen as the end result for the general offset affecting the grid as a whole (or for its two components Vx and Vy ). Albeit in 9 Within the range from -a / 2 to + a / 2 for Vx and Vy, several similarly high maxima can sometimes occur, the maximum is always selected which has the largest numerical value on the H-axis, ie most frequently in the digital image of the grid is or occurs in most grid elements; this numerical value is used as the final result for the offset value Vx or for the offset value Vy determined.

• - für den Versatz Vx (fester Wert): 0,1 Pixel
• - für den Versatz Vy (fester Wert): 0,1 Pixel und mit den folgenden Randbedingungen:
• - Vx und Vy: jeweils Wertebereich von -a0/1,9 bis +a0/1,9.

After optimizing θ and a are their final, correct values, which are no longer changed. Now the offset coordinates Vx and Vy optimized on their part, for example by means of a gradient descent method. The optimizations are carried out with the following accuracy, for example

• - for the offset Vx (fixed value): 0.1 pixel
• - for the offset Vy (fixed value): 0.1 pixel and with the following boundary conditions:
• - Vx and Vy: each value range from -a0 / 1.9 to + a0 / 1.9.

With the help of global optimization (in which the screen angle θ and the grid period a have been optimized, the offset Vx and Vy was calculated) and the subsequent local optimization of the offset Vx and Vy (where the results for the screen angle θ and the grid period a of the global optimization), the four position parameters became parameters θ , a , Vx , Vy des in the digital image 6th shown grid 5 determined.

Using the grid, the digital image can now 6th the hidden information 4th can be reconstructed, ie an image in which a brightness value is determined for each basic cell.

For this purpose, first of all, one as in 10 brightness-inverted averaged representation of the smoothed digital image 5 needed. If M (x, y) the brightness of all digital image pixels (with its coordinates x , y ) of the (smoothed) image content 5 indicates so designated M _inv (x, y) this image content after brightness inversion, ie mirroring of all brightness values around the mean value of the local brightness; light pixels become dark and vice versa.

wobei MIN den niedrigesten und MAX den höchsten Helligkeitswert in der lokalen Umgebung bezeichnet. Diese Helligkeits-Invertierung erfolgt über einen quadratischen Bildflächenbereich B innerhalb des Digitalbildes 6 von 5, wobei der quadratische Bildflächenbereich B beispielsweise eine Seitenlänge besitzt, die einer Anzahl von (2*a+1) Pixeln entspricht, d.h. die etwas größer ist als zwei Rasterperioden a, damit neben dem höchsten Helligkeitswert des nächstgelegenen Rasterelements auch noch der niedrigste Helligkeitswert der Lücken zwischen den umliegenden Rasterelementen einfließen kann.The calculation of M _inv (x, y) is done by changing the brightness values M (x, y) all pixels (i.e. for all pixel coordinates x , y ) from the digital image 6th of 5 are brightness-inverted, namely around a local mean brightness value, for example around the mean value MW from the local highest and the local lowest brightness value, ie around $$\text{MW}\left[{\text{MIN}}_{\text{B.}}\left(\text{M.}\left(\text{x}\text{, y}\right)\right){\text{;MAX}}_{\text{B.}}\left(\text{M.}\left(\text{x}\text{, y}\right)\right)\right],$$

where MIN denotes the lowest and MAX the highest brightness value in the local area. This brightness inversion takes place over a square image area B. within the digital image 6th of 5 , where the square screen area B. for example has a side length which corresponds to a number of (2 * a + 1) pixels, ie which is slightly larger than two raster periods a so that, in addition to the highest brightness value of the closest grid element, the lowest brightness value of the gaps between the surrounding grid elements can also flow into it.

The resulting, inverted brightness values are $$\begin{array}{l}{\text{M.}}_{\text{inv}}\left(\text{x}\text{, y}\right)=\text{MW}\left({\text{MIN}}_{\text{B.}}\left(\text{M.}\left(\text{x}\text{, y}\right)\right){\text{;MAX}}_{\text{B.}}\left(\text{M.}\left(\text{x}\text{, y}\right)\right)\right)\\ -\left[\text{M.}\left(\text{x}\text{, y}\right)-\text{MW}\left({\text{MIN}}_{\text{B.}}\left(\text{M.}\left(\text{x}\text{, y}\right)\right){\text{;MAX}}_{\text{B.}}\left(\text{M.}\left(\text{x}\text{, y}\right)\right)\right)\right]\\ =2*\text{MW}\left({\text{MIN}}_{\text{B.}}\left(\text{M.}\left(\text{x}\text{, y}\right)\right){\text{;MAX}}_{\text{B.}}\left(\text{M.}\left(\text{x}\text{, y}\right)\right)\right)-\text{M.}\left(\text{x}\text{, y}\right)\end{array}$$

The reconstruction of the image can now be carried out according to the digital template of the hidden information 4th in the form of the upright, untwisted grid, which enables a direct comparison with the digital original 49 out 13th aims, as with the 11 to 13th is explained.

For this purpose, for example, as a rectangle R. designed image section (in 11 hatched) of the digital image 6th , the information hidden in it 4th safely contains, selected and repositioned, namely brought into the same position and orientation as the position and orientation of the hidden information 49 in the file template 9 according to 13th . The selected (eg rectangular) image area is used for this purpose R. that is the image of the visual motif 3rd includes (here the upper part of the letter "s", which contains the hidden information 4th contains), transformed into an upright, ie untwisted rectangle. The location of the twisted, the hidden information 4th containing rectangle R. is in 11 in relation to the digital image 6th (Rectangle R ' , dotted line). The transformation therefore only means that the image information of the digital image instead of the image coordinates as before x , y now in the coordinates of the coordinate system of the grid to be reconstructed 5 and thus in the coordinate system of the hidden information 4th is pictured. The result is an upright rotated image V (x ', y') in the coordinates x 'and y'.

gilt und ansonsten, d.h. für alle dazwischen schachbrettartig verteilten Pixel $$\text{V}\left(\text{x'}\text{,y'}\right)={\text{M}}_{inv}\left(\text{x}\text{,y}\right)$$

gilt, d.h. zusammenfassend $$\text{V}\left(\text{x'}\text{,y'}\right)=\text{M}\left(\text{x}\text{,y}\right),\text{ falls x'}+\text{y';}=\text{2n}$$

und $$\text{V}\left(\text{x'}\text{,y'}\right)={\text{M}}_{\text{inv}}\left(\text{x}\text{,y}\right),\text{ falls x'}+\text{y';}=\text{2n}+\text{1}\text{,}$$

wobei n eine beliebig wählbare ganze Zahl darstellt. 12 zeigt einen Teilausschnitt der aus dem Digitalbild 6 rekonstruierten verborgenen Information 4. Diese verborgene Information 4 ist rekonstruiert worden, indem wie oben geschildert aus dem verwendeten Digitalbild 6 das Rauschen eliminiert wurde, die exakten Positionen der Zentren Z der Rasterelemente ermittelt wurden, darauf basierend das Raster (mit Hilfe der ermittelten Raster-Parameter, nämlich des Rasterwinkels θ, der Rasterperiode a und der Offset-Verschiebungskomponenten Vx und Vy) rekonstruiert wurde und anhand der Lage der Rasterkreuzungen des rekonstruierten Rasters 5 das verborgene Motiv 4 rekonstruiert wurde, das als Flächenverteilung und/oder Kontur des zweiten, invertierten Teilflächenbereichs 20 (3D) codiert war.After the previous steps and this transformation, which adapts the rotation as well as the origin, the checkerboard-like inversion with which the hidden information has to be reversed 4th was originally encoded or hidden. Therefore, the pixels of the hidden image V (x ', y') become checkerboard-like either from the averaged image M (x, y) or from the inverted averaged image M _inv (x, y) determined, the coordinates x ', y' of the pixels corresponding to the coordinates in the coordinate system of the grid and into the coordinates x ; y in digital image 6th are to be converted; for example according to the condition that, if the sum of the coordinates (x '+ y') is even, $$\text{V}\left(\text{x '}\text{, y '}\right)=\text{M.}\left(\text{x}\text{, y}\right)$$

applies and otherwise, ie for all pixels distributed in a checkerboard manner in between $$\text{V}\left(\text{x '}\text{, y '}\right)={\text{M.}}_{inv}\left(\text{x}\text{, y}\right)$$

applies, ie in summary $$\text{V}\left(\text{x '}\text{, y '}\right)=\text{M.}\left(\text{x}\text{, y}\right),\text{if x '}+\text{y ';}=\text{2n}$$

and $$\text{V}\left(\text{x '}\text{, y '}\right)={\text{M.}}_{\text{inv}}\left(\text{x}\text{, y}\right),\text{if x '}+\text{y ';}=\text{2n}+\text{1}\text{,}$$

where n represents an arbitrarily selectable whole number. 12th shows a partial section from the digital image 6th reconstructed hidden information 4th . This hidden information 4th has been reconstructed from the digital image used as described above 6th the noise has been eliminated, the exact positions of the centers Z of the raster elements were determined, based thereon the raster (with the help of the determined raster parameters, namely the raster angle θ , the grid period a and the offset displacement components Vx and Vy ) was reconstructed and based on the position of the grid intersections of the reconstructed grid 5 the hidden motive 4th was reconstructed as the area distribution and / or contour of the second, inverted subarea 20th ( 3D ) was coded.

13th shows a corresponding excerpt from the file template 49 for the information to be hidden 40 . This file template 49 for the information to be hidden 40 represents the hidden information 4th which is also shown schematically as a layout in 1 was shown, where in 13th the information to be hidden 40 and their environment was divided into basic cells (namely into basic cells with one for the creation of the actual print template 9 , ie the digital master 9 for printing according to 2 suitable cell size adapted to the resolution and with each base cell completely filled in either black or white. This leads to the angular contour of the information to be hidden 40 in 13th .

To align the motif detail relative to the hidden or originally defined information for concealment 40 from the digital template 49 the repositioned, upright hidden image V (x ', y') becomes a digital template with base cell accuracy by lateral and / or vertical displacement 49 aligned, for example in that for each possible shift the correlation coefficient between the information V (x ', y') repositioned (experimentally by this offset amount) and the digital original 49 is calculated and that offset is selected which leads to the highest absolute value of the correlation coefficient.

The absolute value of the correlation coefficient for the correlation between the digital original 49 for the information to be hidden 40 and that from the corresponding surface area of the motif 3rd in the processed digital image 6th created image V (x, y), which surface area also contains the hidden, but meanwhile determined information 4th is a measure of the correspondence between the initially hidden but now determined information 4th with the one originally in the further digital template 49 saved to hide within the design to be printed 3rd certain information 40 . The absolute value of the correlation coefficient is between 0 and 1; the higher the absolute value of the correlation coefficient, the greater the correspondence between the hidden information 4th of the created, provided or at least used digital image 6th and the digital master 49 . If the correlation coefficient or a quality measure based on it is above a certain minimum threshold value, the result of the authenticity check of the confidential information serving as a security feature, for example, falls 4th positive from; otherwise the non- Authenticity of the information is established, which is an indicator that this is only an image A. in digital image 6th examined, but previously on the surface 100a of the photographed object 100 embodied motif 3rd is an unauthorized copy or counterfeit.

14th shows a flowchart in which the above-explained method steps of the method with which information hidden in a printed and / or visually designed surface of an object 4th can be extracted, read out and / or output, are summarized.

After the creation or at least procurement of the camera image to be used 6th ( 4th ), which is the image A. the surface as image content from image values B (x, y) contains, an optional smoothing of M (x, y) made taking into account neighboring pixel values ( 5 ).

From the smoothed image function M (x, y) on the one hand the grid was reconstructed ( 6th to 9 and 11 ); on the other hand, the image brightness became M (x, y) the inverted image brightness M _inv (x , y ) calculated.

For the raster points or raster elements recognized within the image area of the digital image, the position of their respective raster element center was calculated; then became the grid formed from it 5 reconstructed.

After calculating the start parameter for the rotation of the coordinate system of the grid relative to the format frame of the digital image, ie for the angle of rotation θ ( 7A to 7C ) and the calculation of the start parameter for the period length a of the grid ( 8A , 8B and 9 ) these two parameters were optimized simultaneously, ie together, using a global optimization method. Then the optimal offset values were made Vx and Vy for the fine offset determined by the angle of rotation θ twisted grid 5 with the period a relative to the digital image along its coordinate axes x , y to move so the reconstructed grid 5 - Subject to a subsequent coarse offset, ie an alignment or shift by an integral multiple of the (respective) period lengths along both directions of periodicity of the grid - as closely as possible with those in the image 6th or. A. detected grid element positions is congruent.

For the one with the reconstructed grid 5 corresponding image section R. were made from the averaged brightness values M (x, y) or from the inverted averaged brightness values M _inv (x , y ) existing images ( 5 and 10 ) both images using the selection function V (x ', y') (quasi “checkerboard”) M (x, y) and M _inv (x, y) linked with each other, in that, for example, for all "even" basic cells (x ', y'), for which x '+ y' = 2n applies, the brightness values of the non-inverted image M (x, y) , on the other hand for all "odd" basic cells (x ', y'), for which x '+ y' = 2n + 1 applies, the brightness values of the inverted image M _inv (x, y) selected and combined into a single image V (x ', y') ( 12th ) or the other way around.

The relevant image section V (x ', y') of the image obtained in this way was made with the digital master 49 or with the information to be hidden contained therein 40 compared; A quality measure was derived from the degree of similarity in order to decide whether this was concealed information 4th coded security feature (or the photographed print image containing it on the surface of the object) is to be assessed as real or authentic or not. In particular, it is immediately apparent from the comparison whether the hidden information 4th (specifically: here the letter sequence "CPS") with that 40 that are in an original digital artwork 49 is included, matches or not.

The 2 and 4th was based on a grid in which the (e.g. printed on the object and in the digital image 6th shown) grid elements 1 , 2 themselves are in turn composed of a plurality or multiplicity of technical printing pressure points of the printing technology used and / or other grid-shaped processing technology. Thus, the grid elements were not technically conditioned elementary areas of the printing or other processing technology that could not be produced smaller, but rather aggregates ("motif points") from a respective multitude of such technically conditioned elementary areas ("pressure points"). So far, the term “grid element” has always been understood as an aggregate of connected and / or overlapping pressure points, ie as a “motif point” of the visual (grid) motif.

Alternatively, however, the method of this application can also be used to reconstruct rasters 5 (from their image A. in the digital image 6th ) are applied in which the grid elements 1 , 2 actually individual, elementary areas that cannot be further subdivided from a printing or processing point of view 1' , 2 ' , ie "pressure points" in the true sense of the word. Such elementary pressure points 1' , 2 ' , are significantly smaller; they own with one Print resolution of 600 dpi, for example a diameter of 42 µm, and this is then identical for each print point.

Even with such pressure point grids, as in 15A shown can be made up of two interlocking sub-patterns from the first elementary surfaces 1' (eg on straight grid intersections with x + y = 2n) and offset second elementary surfaces 2 ' (eg on odd grid intersections with x + y = 2n + 1) hide or code information according to which the pattern area 5a into a first and a second partial surface area 10 , 20th is divisible. The in 15A illustrated grid section designed; it corresponds roughly to the left quarter of the grid area for the hidden lettering "CPS" in 2 and essentially comprises the first hidden letter "C".

• Zunächst müssen anstelle der Helligkeitswerte des (geglätteten) Digitalbildes 6 Kontrastwerte verwendet werden, insbesondere lokale Kontrastwerte, die unabhängig von einem globalen Helligkeitsgradienten sind. Die daraus erhaltenen, abgeleiteten Digitalbilder sind dann dergestalt, dass die Helligkeitswerte eines solchen Bildes jeweils die Stärke des lokalen Kontrasts des eigentlichen (optional allenfalls geglätteten) Bildes wiedergeben.

If the method is applied to such elementary printing point or elementary surface rasters, the printing density is considerably lower. The differences in brightness are then typically smaller, so that a brightness gradient across the entire digital image leads to the (global) mean value of the brightnesses (as in the calculation of M _inv (x, y) used) is no longer a suitable value for exchanging or inverting the dark brightness values belonging to a raster element with the bright brightness values of their surroundings over the entire digital image. For such print grids this is based on the 1 to 15th Modify the explained method in two ways, with the following alternative features both individually and in combination with one another (and of course combined with the other, unchanged features of the flowchart 15th ) are possible:

• First, instead of the brightness values of the (smoothed) digital image 6th Contrast values are used, in particular local contrast values that are independent of a global brightness gradient. The derived digital images obtained therefrom are then such that the brightness values of such an image each reflect the strength of the local contrast of the actual (optionally possibly smoothed) image.

The local contrast K (x, y) can be calculated according to, for example $$\text{K}\left(\text{x}\text{, y}\right)={\text{MAX}}_{\left(\text{i}\text{, j}=-\mathrm{3\; ..}+\mathrm{3rd}\right)}\left(\text{M.}\left(\text{x}+\text{i}\text{, y}+\text{j}\right)\right)-{\text{MIN}}_{\left(\text{k}\text{,1}=-\mathrm{2\; ..}+2\right)}\left(\text{M.}\left(\text{x}+\text{k}\text{, y}+\text{1}\right)\right)$$

17A shows a digital image derived in this way, with high local contrasts being shown light and low local contrasts being shown dark. The size of the search area for the local maximum brightness used in the formula can, for example, have a spacing (here an example of 7 image pixels) that is slightly smaller than the grid period (here an example of 7.5 image pixels) of the underlying grid, so that usually only the Value of the only, very next gap between grid elements 1' or. 2 ' is included.

As a search area for the local minimum brightness, which corresponds to a raster element, a smaller track width is sufficient (here, for example, 5 image pixels or less); according to 15A even the brightness value at the local pixel of the raster element is sufficient, since these pixels either have an elementary pressure point 1' ; 2 ' are busy or not.

oder kürzer $${\text{K}}_{\text{inv}}=2*\text{MW}\left({\text{MIN}}_{\left(\text{i}\text{,j}=-\mathrm{6..}+6\right)}\left(\text{K}\left(\text{x}+\text{i}\text{,y}+\text{j}\right)\right);{\text{MAX}}_{\left(\text{i}\text{,j}=-\mathrm{6..}+6\right)}\left(\text{K}\left(\text{x}+\text{i}\text{,y}+\text{j}\right)\right)\right)-\text{K}\left(\text{x}\text{,y}\right).$$

_{Furthermore, the inverted contrast K inv} (x, y) of the (smoothed) digital image can be derived from K (x, y) 6th calculate by for each pixel ( x , y) the value of the contrast K (x, y) there is inverted around the mean value MW of the extreme values of the contrast over a little less than 2 raster periods (here as an example over a square area with a side length of 13 pixels): $$\begin{array}{l}{\text{K}}_{\text{inv}}\left(\text{x}\text{, y}\right)=\text{MW}\left({\text{MIN}}_{\left(\text{i}\text{, j}=-\mathrm{6\; ..}+\mathrm{6th}\right)}\left(\text{K}\left(\text{x}+\text{i}\text{, y}+\text{j}\right)\right);{\text{MAX}}_{\left(\text{i}\text{, j}=-\mathrm{6\; ..}+\mathrm{6th}\right)}\left(\text{K}\left(\text{x}+\text{i}\text{, y}+\text{j}\right)\right)\right)\\ -\left(\text{K}\left(\text{x}\text{, y}\right)\text{MW}\left({\text{MIN}}_{\left(\text{i}\text{, j}=-\mathrm{6\; ..}+\mathrm{6th}\right)}\left(\text{K}\left(\text{x}+\text{i}\text{, y}+\text{j}\right)\right);{\text{MAX}}_{\left(\text{i}\text{, j}=-\mathrm{6\; ..}+\mathrm{6th}\right)}\left(\text{K}\left(\text{x}+\text{i}\text{, y}+\text{j}\right)\right)\right)\right)\end{array}$$

or shorter $${\text{K}}_{\text{inv}}=2*\text{MW}\left({\text{MIN}}_{\left(\text{i}\text{, j}=-\mathrm{6\; ..}+\mathrm{6th}\right)}\left(\text{K}\left(\text{x}+\text{i}\text{, y}+\text{j}\right)\right);{\text{MAX}}_{\left(\text{i}\text{, j}=-\mathrm{6\; ..}+\mathrm{6th}\right)}\left(\text{K}\left(\text{x}+\text{i}\text{, y}+\text{j}\right)\right)\right)-\text{K}\left(\text{x}\text{, y}\right).$$

The inverted contrast K _inv (x, y) calculated in this way is in 17B shown. Instead of the images based on brightness values M (x, y) and M _inv (x, y) the images K (x, y) and K _inv (x, y) based on contrast values are thus calculated and used for the subsequent calculation.

und $${\text{V}}_{\text{K}}\left(\text{x'}\text{,y'}\right)={\text{K}}_{\text{inv}}\left(\text{x}\text{,y}\right),\text{ falls x'}+\text{y';}=\text{2n}+\text{1}$$

oder umgekehrt.After calculating these contrast images K (x, y) and K _inv (x, y), the grid elements can be selected for the alternating checkerboard-like selection 1' , 2 ' the following selection function V _K (x ', y') can be calculated: $${\text{V}}_{\text{K}}\left(\text{x '}\text{, y '}\right)=\text{K}\left(\text{x}\text{, y}\right),\text{if x '}+\text{y ';}=\text{2n}$$

and $${\text{V}}_{\text{K}}\left(\text{x '}\text{, y '}\right)={\text{K}}_{\text{inv}}\left(\text{x}\text{, y}\right),\text{if x '}+\text{y ';}=\text{2n}+\text{1}$$

or the other way around.

Thus, the selection function V uses _K (x ', y') instead of M (x, y) and M _inv (x, y) now the contrast images K (x, y) and K _inv (x, y), which is indicated by the use of the index K.

If the method is applied to such elementary pressure point or elementary surface rasters, secondly, the centers may no longer be calculated as only those extreme values that represent extreme values within a smallest area of ± 1 image pixel, but this area must be dependent on the raster period can be selected so that random fluctuations in brightness between grid elements are not incorrectly identified as centers.

und $$\text{Y}\left(\text{x}\text{,y}\right)=0\text{ sonst}\text{.}$$

Those image pixels that have a local minimum brightness over an mx m-pixel comparison area of the smoothed camera image M (x, y) can then be identified as the “centers” of the grid elements, for example according to the logical function $$\text{Y}\left(\text{x}\text{, y}\right)=\mathrm{1,}\text{if M}\left(\text{x}\text{, y}\right)={\text{MIN}}_{\left(\text{i}\text{, j}=-\mathrm{4\; ..}+\mathrm{4th}\right)}\left(\text{M.}\left(\text{x + i}\text{, y + i}\right)\right)$$

and $$\text{Y}\left(\text{x}\text{, y}\right)=0\text{otherwise}\text{.}$$

The size of the comparison area specified here in the form of the widths of the indices depends on the grid period and thus also on the image resolution. This exemplary embodiment with a side length or width of the comparison area of 9 × 9 image pixels applies to a raster period of 212 μm, which corresponds to a raster period of 7.5 image pixels _{with the present image resolution of A image, reference = 900 dpi.} This ensures that the centers are not denser than the underlying raster and that no random variations in brightness between raster elements are identified as the center. In the case of other image resolutions or raster periods, the dimensions of the comparison area must be scaled linearly and rounded to the nearest odd number; For example, for an image resolution of A _image = 1200 dpi, a side length of A _{image / image, reference} * (grid period + 1), rounded to the nearest odd number, would be ideal. The image resolution can be estimated from the real size of the surrounding printed elements and is not critical in terms of accuracy.

The rest of the process can then be carried out in a similar manner to that on the basis of 15th and the other previous figures already explained.

In all embodiments of the method, an additional concealment of the grid can also be provided (and likewise to be reconstructed again), the effect of which - exemplarily for a likewise made up of elementary pressure points 1' , 2 ' existing grid as in 15A - in 15B is shown; there are the respective (here elementary; otherwise, however, aggregate-shaped) grid elements 1' , 2 ' in relation to their ideal positions, ie the centers of the basic cells or grid intersections, respectively, arranged offset. This irregularity makes it difficult to recognize both partial surface areas 10 , 20th further.

For example, there is an additional, optional obfuscation of the grid 5 every basic cell already when planning its layout B. of the grid divided into a matrix of nxn, for example 5x5 sub-cells, as in 16 is shown (in the area of the digital original 9 ), with per base cell B. only a single one of the 25 or nxn subcells is covered with a grid element 15 (size or brightness yet to be defined) and later on the object surface 100a is printed; the average print density is then 1/25 = 4% (and if only every second basic cell is occupied by a grid element, even only 1/50 = 2%).

To later, if the same, on an object surface 100a imprinted print raster is photographed from there, to enable the reconstruction and evaluation of the raster to be carried out with the method according to the application (for example in the smartphone), it can optionally be provided that in (according to 16 originally in the digital master 9 defined) grid 5 at least exactly one and the same row and column per basic cell B. is never occupied with a pressure point. In order to facilitate the reconstruction of the grid, several, for example two rows and columns per basic cell can be used B. (in 16 for example the subcells of the top and bottom rows and those of the leftmost and rightmost columns of the further subdivided basic cell B. ) is never occupied with a pressure point, ie always remain empty. If the edge-side or outer pixels remain empty, this raster element 15 is assigned to one of the remaining inner 3x3 or nine pixels (if the respective basic cell is to be occupied by a raster element 415) 6th are outlined together by the thicker dashed line. In 16 the grid element 15 lies, for example, on the second pixel from the left in the middle line. Since two basic cells are always adjacent to one another, two adjacent columns and rows are always free of grid elements, over the entire image area of the digital original 9 (and therefore also later on the corresponding print raster on the object as well as on the digital photo taken 6th reconstructed grid 15 in the reconstruction and examination method for evaluating the photographed print pattern.

This further subdivision of the basic cells, which can be combined with all the embodiments (or, viewed conversely: the combination of the pixels in super-cells) B. of nxn pixels, in each of which at most only a single raster element is positioned) is an optional additional feature that can be combined with all other embodiments, which merely provides additional, further concealment of the actual security feature (namely the hidden information coded as population inversion 4th ) is used and superimposed on it.

Provided such a concealment according to 16 is provided, the search area only needs to be sufficiently large to determine K (x, y), for example, as already described above, have a track width that is slightly smaller than the grid period of the underlying grid. This ensures that even if the centers of the raster elements are varied, the local contrast value is still present at the position of a raster crossing of the reconstructed raster, which corresponds to the now slightly shifted but still closest raster element.

The proposed method for extracting, reading out and / or outputting hidden information enables a security feature (in the form of hidden information) to be photographed and checked for authenticity; e.g. with the help of a smartphone. The security feature, ie the hidden incorporation of hidden information 4th in one motif 3rd is as a design of the grid that is not immediately perceptible, changed in certain areas or deviates from the area's surroundings 5 executed and in particular coded as a deviation or variation within the grid. To check the authenticity of the security feature, a recorded or used digital image is used 6th the hidden information encoded in the raster is reconstructed or repositioned, and it becomes a quantitative measure for the correspondence of the hidden, but now ascertained, information 4th with the original, separate digital master 49 determined to define this hidden information.

• - der seitens eines Smartphones etwa bestehenden Anforderungen an die Druckqualität eines mit der Kamera eines Smartphone aufzunehmenden Druckbildes oder sonstigen Bildmotivs (z.B. hinsichtlich Bildauflösung, Schärfe und/oder Helligkeitskontrast),
• - der Reproduzierbarkeit der Druckqualität, insbesondere der Reproduzierbarkeit der Relativposition der unterschiedlichen Rasterelemente zueinander;
• - der optischen Dichte und/oder des Helligkeitskontrasts des Druckbildes, auch im Vergleich zu einem visuellen Hintergrund,
• - der herstellerseitig erreichten Qualität der mit einem Smartphone und/oder dessen Kamera erstellbaren Digitalbilder, insbesondere unter Berücksichtigung der vielen unterschiedlichen verfügbaren Smartphonemodelle,
• - des Kontrasts, der Beleuchtung, der Bildhelligkeit, der Tonwertkurve, der Bildschärfe, der Bildauflösung, des Aufnahmeabstands, des Aufnahmemittelpunkts und der Aufnahmeverdrehung bzw. des Verdrehwinkels des Rasters (diese Eigenschaften müssen zwar mitunter innerhalb großzügiger Grenzen liegen; mit ihnen sind aber keine besonderen Anforderungen verknüpft).

As the surface contour of the second partial surface area 20th encoded hidden information 4th can be easily integrated into any, even full-surface graphic or visual surface design and does not require any additional surface on the surface 100a of objects 100 . The method described in this application is particularly robust, ie uncritical with regard to the following influences:

• - the requirements on the part of a smartphone for the print quality of a print image or other image motif to be recorded with the camera of a smartphone (e.g. with regard to image resolution, sharpness and / or brightness contrast),
• the reproducibility of the print quality, in particular the reproducibility of the relative position of the different raster elements to one another;
• - the optical density and / or the brightness contrast of the print image, also in comparison to a visual background,
• - the quality achieved by the manufacturer of the digital images that can be created with a smartphone and / or its camera, in particular taking into account the many different smartphone models available,
• - the contrast, the lighting, the image brightness, the tone value curve, the image sharpness, the image resolution, the recording distance, the recording center point and the recording rotation or the rotation angle of the grid (these properties must sometimes be within generous limits, but they are not special Requirements linked).

Thus, the presented method for reconstructing hidden information or a security feature is particularly user-friendly, since there are no hard requirements or restrictions with regard to the way in which the image recording is made with the smartphone or other image recording device or the image quality.

The presented method for reconstructing the hidden information or for checking the security feature does not depend on a specific software or app for producing the digital image. The creation of the digital image does not require any special interaction; A special area does not have to be displayed, nor do image sharpness and / or image brightness need to be further controlled than is already done in conventional smartphone or camera apps or the autofocus and auto-exposure modes available for them.

The proposed method for extracting, reading out and / or outputting and in particular for reconstructing and / or (repositioning and subsequent) checking the authenticity of the security feature or the hidden information can therefore also be carried out by checking personnel independently using a digital image made with a smartphone and by subsequent uploading this smartphone recording (e.g. on a server on the Internet, on which it is then evaluated); In particular, it is not necessary to check the security feature with an app or your own test program. No additional devices are necessary for the application of the proposed method; E.g. no special lighting device that could limit the universal testability of hidden security features with the help of smartphones. Otherwise, the proposed method can of course also be carried out without the connection or use of a server.

Finally, visual designs of objects or surfaces can be printed in any printing colors (black, red, green, etc., white on black, etc.) and using any printing method (inkjet, flexographic, screen printing, letterpress, gravure, etc.) using the proposed method can be reconstructed and checked for authenticity, as long as it contains a grid of grid elements from which a digital image can be created and used for further investigation. The same applies to labeling or processing methods that are alternative to printing methods, such as punching, embossing, laser cutting, laser marking or the like.

Instead of an orthogonal grid, any other, e.g. non-orthogonal grid (with different angles between the two axes or periodicity directions) can also be used; even the basic cells of the underlying grid do not need to be square or rectangular. If necessary, the determination of the start parameter for the screen angle would be modified, but this could also be determined, for example, by determining the orientation of another graphic element. In view of the three color channels red, green and blue of a smartphone, the examinations can be carried out jointly or simultaneously, but separately for each color channel and thus independently of the other color channels, so that a hidden motif can be determined through each of the color channels.

List of reference symbols

1, 2

Grid element

1'; 2 '

Elementary surface

3

motive

4th

hidden information

5

Grid

5a

Grid footprint

6th

Digital image

8th

layout

9

Digital template (printing template for the grid)

10

first partial area

20th

second partial area

20a

contour

40

Information to be hidden

49

Digital template (for information to be hidden)

100

object

100a

surface

A.

image

a

Period length

a0

Initial value for determining the period length

B.

Base cell

H

frequency

L.

Distance between two centers

B (x, y)

Camera image

M (x, y)

averaged image

Minv (x, y)

brightness-inverted image

R; R '

rectangle

Vx, Vy

Offset

x; y

Periodicity direction

θ

Twist angle

Z

Center of a grid element

Claims (19)

A method for extracting, reading out and / or outputting information (4) hidden in a printed and / or visually designed surface of an object, the method comprising at least the following: a) creating, providing and / or at least using a digital image (6), which reproduces an image (A) of a printed and / or visually designed surface of an object, b) determining information (4) hidden in the image (A) of the printed and / or visually designed surface by examining the digital image (6) and / or the image (A) reproduced thereby and c) extracting, reading out and / or outputting the ascertained information (4), the ascertaining of the hidden information (4) comprising that from the digital image (6) and / or the image reproduced thereby (A) a grid (5) consisting of a plurality of grid elements (5) is constructed and / or reconstructed, wherein the grid (5) is constructed and / or reconstructed under the specification of the boundary conditions, - that a grid base area (5a) available for the grid (5), within which the reproduced grid elements (5) are distributed, is divided into a first partial area ( 10) and a second partial surface area (20) can be subdivided, the first partial surface area (10) and / or the second partial surface area (20) optionally being contiguous or multi-part, - that the grid (5) has a deviation that occurs in the second partial surface area (20), but not in the first subarea (10), so that the areal extent, extent and / or distribution of the deviation specifies the second subarea (20) and / or its area distribution or contour (20a), and - that the hidden information (4) or the negative image thereof is coded by the second partial surface area (20) and / or by its surface distribution or contour (20a). Procedure according to Claim 1 , characterized in that the grid (5) is constructed and / or reconstructed under the specification of the boundary conditions that the deviation in the second partial surface area (20) results in a uniform change in the grid elements (2) of the second partial surface area (20), in particular a uniform change the position, the orientation, the size, the diameter, the contour, the brightness and / or the color of the grid elements (2) of the second sub-area (20) compared to the grid elements (1) of the first sub-area (10) . Procedure according to Claim 1 or 2 , characterized in that the grid (5) is constructed and / or reconstructed with the specification of the boundary conditions that the grid (5) has a deviation which is or includes an inversion of occupation numbers, the occupation numbers indicating whether a respective intersection of the to be constructed and / or to be reconstructed grid (5) with a grid element (1; 2) is occupied or not. Method according to one of the Claims 1 to 3rd , characterized in that the grid (5) is constructed and / or reconstructed in such a way that its grid base area (5a) can be subdivided into a periodic arrangement of square, rectangular, diamond-shaped, parallelogram-shaped or other basic cells of the same size, with the first (10) and a periodically arranged and / or periodically distributed subset of the basic cells is filled with a respective grid element (1; 2) and / or assigned to a respective grid element (1; 2) in the second partial surface area (20) of the grid base area (5a). Method according to one of the Claims 1 to 4th , characterized in that a grid (5) is constructed and / or reconstructed from the digital image (6) and / or the image (A) reproduced thereby, the basic cells of which are in the first partial surface area (10) and also in the second partial surface area (20) along both periodicity directions (x, y) alternately either filled with a respective grid element (1; 2) and / or assigned to it or otherwise unfilled and / or assigned to no grid element, the grid (5) in the second partial surface area (20) being a relative to the grid (5) of the first partial surface area (10) is occupied grid inverted, - in which in the second partial surface area (20) exactly those basic cells are filled with a respective grid element (2) and / or assigned to it, which with periodic continuation of the grid of first partial surface area (10) into the second partial surface area (20) would be unfilled and / or not assigned to a grid element, whereas in the second n partial surface area (20) precisely those basic cells unfilled and / or not assigned to a grid element which, with periodic continuation of the grid of the first partial area (10) into the second partial area (20), are filled with and / or assigned to a respective grid element (2) would be. Procedure according to Claim 4 or 5 , characterized in that a grid (5) is constructed and / or reconstructed from the digital image (6) and / or the image (A) reproduced thereby, which raster is composed of a first that runs in the first partial surface area (10) and is strictly periodically occupied there Grid and a second grid running in the second partial surface area (10) and there strictly periodically occupied, the positions in which the second grid, continued periodically over the entire image area, has basic cells filled with a respective grid element (2), relative to positions , in which the first grid, continued periodically over the entire image area, has basic cells filled with a respective grid element (1), offset, in particular - by a period length (a) along a periodicity direction (x; y) or - are offset by half a diagonal of a basic cell along its diagonal direction. Method according to one of the Claims 1 to 6th , characterized in that a digital image (6) is created, provided and / or used which reproduces an image (A) of a grid (5) formed from grid elements (1; 2) of a printed and / or visually designed surface of an object, wherein the digital image (6) is made up of a plurality of digital pixels and wherein the reproduced raster elements (1; 2) raster elements of the image (A) reproduced as a motif of the printed and / or visually designed surface of an object, which are derived from the pixels of the digital image (6) are different, in particular larger than the pixels of the digital image (6). Method according to one of the Claims 1 to 7th , characterized in that a digital image (6) is created, provided and / or used which reproduces an image (A) of a grid (5) formed from grid elements (1; 2) of a printed and / or visually designed surface, the Image (A) reproduces raster elements (1; 2), which are each individual pressure points and / or elementary areas (1 ';2') of a printing technique or other processing technique for raster-shaped processing of a surface, which cannot be further subdivided. Method according to one of the Claims 1 to 7th , characterized in that a digital image (6) is created, provided and / or used which reproduces an image (A) of a grid (5) formed from grid elements (1; 2) of a printed and / or visually designed surface, the Image (A) reproduces raster elements (1; 2), which in turn are aggregates of a respective plurality and / or plurality of pressure points and / or elementary areas of a printing or other processing technique for raster-shaped processing of a surface. Method according to one of the Claims 1 to 9 , characterized in that the construction and / or reconstruction of the grid (5) from the digital image (6) and / or the image (A) reproduced thereby comprises that initially - a rotation angle (θ) of a periodicity direction of the to be constructed and / or to be reconstructed grid (5) relative to a coordinate direction of the digital image (6) and - at least one period length (a) of the grid to be constructed and / or to be reconstructed (5) are determined together in mutual dependence on each other, without a total offset (Vx, Vy ) to optimize the grid (5) to be constructed and / or reconstructed relative to the digital image (6), and that a lateral offset (Vx , Vy) is optimized, by means of which all grid elements are brought into congruence with the generated grid (5). Procedure according to Claim 10 , characterized in that the joint determination of the angle of rotation (θ) and the period length (a) is carried out in such a way that from the digital image (6) and / or a partial area of the digital image (6) first - a calculation to limit the area in question Coming numerical values for the end result of the angle of rotation (θ), preferably to limit the range to an angle of less than 5 °, for example less than 2 °, in particular less than 0.5 °, and / or a calculation to limit the range of possible numerical values for the end result of the period length (a), preferably to limit it to ± 5 pixels, for example to a maximum of ± 2 pixels, in particular to a maximum of ± 0.5 pixels, and that only after this limitation of the angle of rotation (θ) and / or the period length (a) the joint determination of the final numerical values for the final result of the angle of rotation (θ) and the period length (a) in mutual dependence on each other durc is managed. Method according to one of the Claims 1 to 11 , characterized in that the grid (5) is constructed and / or reconstructed under the specification of the boundary conditions that the grid elements (1; 2) relative to intersection points of the grid (5) to be constructed and / or reconstructed individually and / or pseudo are randomly offset. Procedure according to Claim 12 , characterized in that a grid (5) is constructed and / or reconstructed, the unit cells (B) of which are each subdivided into nxn sub-cells, the center ( Z) of the respective, individually and / or pseudo-randomly offset grid element (1; 2) is arranged in one of the sub-cells of the basic cell (B), in particular in one of the inner sub-cells of the basic cell (B). Method according to one of the Claims 1 to 13th , characterized in that the construction and / or reconstruction of the grid (5) comprises that - from the digital image (6) and / or the image (A) reproduced thereby for a plurality of grid elements (5) the position of the center (Z ) of the respective grid element (5) is calculated and - that the calculated positions of the centers (Z) of the grid elements (5) and / or an optimization function dependent on these positions are used for the construction and / or reconstruction of the grid (5). Procedure according to Claim 14 , characterized in that the construction and / or reconstruction of the grid (5) includes that the calculated positions of the centers (Z) of the grid elements (5) - for limiting a respective range of values for the angle of rotation (θ) and the period length (a ) of the grid (5) to be constructed and / or reconstructed, - for the joint optimization of the final numerical values of the angle of rotation (θ) and the period length (a) in mutual dependence on one another and / or - for the calculation of the lateral offset serving as a fine offset (Vx, Vy) can be used. Method according to one of the Claims 1 to 15th , further comprising: d) comparing the information (4) determined, extracted, read out and / or outputted from the digital image (6) with a digital template (49) for information to be concealed (40) and e) checking whether and / or to what extent the information (4) determined from the digital image (6) corresponds to the information (40) to be concealed contained in the digital original (49). Procedure according to Claim 16 , characterized in that step e) comprises: - determining a degree of similarity for the degree of similarity of the information (4) determined from the digital image (6) with information (40) contained in the digital original (49), - evaluating whether the information (4) determined from the digital image (6) is to be assessed as coinciding with the information (40) contained in the digital original (49), and / or - assessing whether the digital image (6) reproduced, printed and / or the visually designed surface of the object is to be assessed as an authentic copy of the digital original (49) for the information (40) to be concealed, a result of the determination and / or assessment being output. Method according to one of the Claims 16 or 17th , characterized in that the comparison between the information (4) determined, extracted, read out and / or output from the digital image (6) and the digital original (49) for this or other information (49) to be concealed is dependent on the Size of the magnitude of the correlation coefficient is performed. Method according to one of the Claims 16 to 18th , characterized in that an optimal displacement and / or alignment of a surface area (20), which is assumed, extracted, read out and / or output information (4) in the digital image (6), relative to a digital original (49), which contains information (49) to be concealed, is determined on the basis of the magnitude of the magnitude of the correlation coefficient.

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