Inspection method and inspection device for inspecting security markings

An inspection method is provided for checking the integrity of a combination of a security marking and an identification label, the security marking including at least one contrast field having a comparatively high reflectivity in a first and a second wavelength range, and a security field, having different reflection properties in the first wavelength range compared to the second wavelength range, and the identification label having at least one light background around mark components printed with dark color. The inspection method may include capturing possibly averaged gray values of the contrast field and the identification label background, comparing the gray values, and determining whether the gray value of the contrast field of the security marking deviates from the gray value of the background of the identification label by less than a predefined maximum amount.

The application relates to a readout unit and an inspection method for reading out and inspecting security markings, in particular security markings on packaging, such as those used as part of a deposit system, for example.

Security markings are used in a variety of ways in order to make counterfeiting more difficult and to offer the best possible guarantee for the authenticity of a document, a product, a banknote or the like. Security markings are used for products that are subject to a deposit because the deposit value is typically higher than the value of the packaging itself.

It is known to apply a security marking to an outer shell of the packaging or a label or a banderole of the packaging, which can consist for example of plastic, sheet metal or card-board, which has several fields arranged next to one another having different reflective properties. One of these fields is, for example, a contrast field with a comparatively high reflectivity in a broad wavelength range, which includes, for example, visible and infrared light. A second of these fields is a dark field which, compared to the contrast field, has a low reflectivity in the broad wavelength range. A third field is a security field having different reflection properties in at least one known wavelength range than in another known wavelength range. For example, the security field can have a low reflectivity in a first e.g. visible wavelength range of light. In contrast, in a second, different, visible or invisible wavelength range of the light, the security field has a higher reflectivity—or vice versa.

The reflectivity of the respective field for a respective wavelength depends on the color with which the respective field is applied, in particular printed, to a respective background. The color with which the contrast field is printed or the contrast fields are printed is typically a broadband reflective color, while the color with which the dark field or the dark fields are printed is a broadband absorbing color. The contrast field can also be formed by the background itself if it itself is broadband reflective. If this is the case, the contrast field is not printed, but is formed by the unprinted background.

In many cases, in addition to a security marking, an identification label is also provided, which identifies the product type, the manufacturer or the banknote, etc., for example by indicating the manufacturer, product or value of the banknote. The identification label can be, for example, a GTIN shown in the form of a barcode or a QR code. GTIN is the abbre-viation for Global Trade Item Number, i.e. a global article number.

In addition to mark components of the identification label typically printed with black or in a broad wavelength range of dark color, the background—i.e. the area around the mark components of the identification label printed with dark color—is light and in particular white in order to obtain a good contrast. The light, in particular white, background of the mark components of the identification label is typically formed by the unprinted background on which the dark mark components of the identification label are also printed. This is also regularly the same background that also forms the bright contrast field of the security marking. The contrast field (or the contrast fields) of the security marking and the background around the mark components of the identification label that are printed with dark color therefore regularly have the same light, e.g. white, color.

The mark components of the identification label printed with dark color and the dark fields of the security marking are usually printed with the same broadband dark color, e.g. carbon black, on a light background.

The color with which the security field is printed on the light background or the security fields are printed on the light background has a higher absorption in the first wavelength range than in the second wavelength range. Correspondingly, the color with which the security field is printed or the security fields are printed has a higher reflectivity or a higher transparency or both in the second wavelength range. If the color with which the security field is printed or the security fields are printed has a higher reflectivity in the second wavelength range than in the first wavelength range, the intensity of the reflected light in the second wavelength range is in any case greater than the intensity of the reflected light in the first wavelength range. If the color with which the security field is printed or the security fields are printed has a higher transparency in the second wavelength range than in the first wavelength range, the intensity of the reflected light in the second wavelength range is greater than the intensity of the reflected light in the first wavelength range in cases where the background under the color with which the security field is printed has a sufficiently high reflectivity in this second wavelength range. If the color with which the security field is printed or the security fields are printed already has a high reflectivity in the second wavelength range, the reflectivity of the background under the color with which the security field is printed or the security fields are printed is less or not at all decisive.

One possibility of inspecting a security marking of the type described is to illuminate the security marking for one thing with light in the first wavelength range and for another with light in the second wavelength range.

DE 10 2006 011 143, DE 102 47 252 and DE 43 19 555 each describe a security field that is printed with a color that strongly absorbs visible light and is transparent to infrared light, so that the reflectivity of the security field in the infrared wavelength range is determined by the background under the color with which the security field is printed. The background of the security field is white, so that the security field also appears just as white under infrared light as the background and the surroundings of the security field, because the color with which the security field is printed is transparent to infrared light and therefore invisible, so that under infrared light, the background is visible under the color with which the security field is printed.

Another inspection method aims to determine the extent to which the security field reflects more strongly in the second wavelength range than in the first wavelength range. This method has the advantage that the inspection of the security field does not have to refer to the surroundings of the security field or any reference field that has the same color as the background on which the color for the security field is printed.

In exchange, the other inspection method has the disadvantage that the intensity of the light reflected by the security field depends on the intensity of the illumination—also referred to below as the illuminance. The illuminance in turn depends not only on the intensity of a light source, but also, for example, on the distance that the security field to be inspected has from the light source, or on the angle at which the light from the light source strikes the security field.

The security marking is typically located on items with a value, for example beverage packaging subject to a deposit. If the valuable item is handed over, e.g. beverage packaging subject to a deposit is returned, the value (e.g. the deposit) is paid out and the payor charges the paid out value on—to whom results from the identification label, for example. Now, it is possible to replace the original identification label with a different identification label, so that the value paid out is charged to someone other than the actually obligated party.

The invention has the object of providing an improved inspection method and means for an improved inspection method.

According to the invention, this object is achieved by an inspection method which is configured in such a way that it inspects a combination of security marking and identification label to determine whether both are located on a uniform background, e.g. on the same substrate.

According to the invention, this is done by inspecting whether the background of the identification label and the contrast field of the security marking have the same gray value at at least one wavelength—that is, are equally bright under the same lighting. For this purpose, a grayscale image is captured from the combination of identification label and security marking by means of a corresponding camera. The camera converts the different brightnesses of the mark components of the identification label and security marking into numerical values, which, for example, can be between 0 and 255 in a digital camera with an image sensor with a dynamic range of 8 bits, wherein usually only a portion of the maximum avail-able dynamic range is utilized.

Since identical and, in particular, uniform illumination is not always given, a gray value correction is preferably carried out by means of corresponding local point operations during the image preprocessing.

In particular, an inspection method is proposed for checking the integrity of a combination of a security marking and an identification label. Said security marking comprises at least one contrast field, which has a comparatively high reflectivity in a first and a second wavelength range, and a security field, which has different reflection properties in the first wavelength range compared to the second wavelength range. Said identification label has at least one light background around mark components printed with dark color, comprising the following steps:illuminating the combination of security marking and identification label with light in a specified wavelength range,capturing an image of the combination of security marking and identification label,identifying the security marking and the identification label in the image,capturing a possibly averaged gray value of the contrast field of the security marking,capturing a possibly averaged gray value of the background of the identification label,comparing the gray value of the contrast field of the security marking with the gray value of the background of the identification label,determining whether the gray value of the contrast field of the security marking deviates from the gray value of the background of the identification label by less than a predefined maximum amount, andgenerating and outputting a signal indicating a lack of integrity if the gray value of the contrast field of the security marking deviates from the gray value of the background of the identification label by more than a predefined maximum.

Preferably, gray values of the contrast field of the security marking and gray values of the background of the identification label are each determined and averaged in different measurement fields.

A gray value histogram is preferably formed for each of the measurement fields.

The gray value histograms are preferably smoothed.

Preferably, an inspected combination of security marking and identification label is rejected as inadmissible if the gray value of the contrast field of the security marking deviates from the gray value of the background of the identification label by more than 10%.

The inspection method is preferably implemented by a readout unit that is designed to perform the inspection method.

According to further variants of the inspection method, the security marking and, in particular, the security field are inspected not only in two different wavelength ranges, but in multiple different wavelength ranges, so that the spectral properties of the fields of the security marking—in particular the spectral properties of the security field and the color or the colors with which it is printed—can be inspected with even greater differentiation and counterfeiting is made even more difficult.

The inventive concept is also embodied by a readout unit for a security marking on packaging of the type described above. According to the invention, the readout unit is designed to detect an intensity of the light reflected by the security field of the security marking in at least two different wavelength ranges, of which a first wavelength range is a wavelength range in which the security field is strongly absorbed, while the other, second wavelength range is a wavelength range in which the security field reflects comparatively more strongly.

The readout unit preferably possesses an image acquisition unit with an area sensor with light-sensitive sensor elements, which are preferably arranged in a matrix-like manner. The image acquisition unit with an area sensor is used to capture an image imaged on the sensor in two dimensions.

For this purpose, an optical system is usually attached in front of the area sensor, which maps the image of a respective security marking as sharply as possible on the area sensor.

The light-sensitive sensor elements are light-sensitive both in the first wavelength range of light and in the second wavelength range, and are therefore able to capture images of the security marking, and in particular of the security field, when illuminated with light in the first wavelength range as well as when illuminated with light in the second wavelength range.

In this embodiment, whether the image of the security marking is captured with light in the first wavelength range or with light in the second wavelength range thus depends on the light with which the packaging with the security marking is illuminated.

Correspondingly, in a preferred embodiment, the readout unit comprises an illumination module which is designed and arranged to illuminate a field of view of the image acquisition unit simultaneously or alternately with light in the first wavelength range and with light in the second wavelength range. The field of view of the image acquisition unit here means the area in which the security marking of a packaging is located when its image is sharply imaged on the area sensor.

Alternatively, an illumination module can also be provided which simultaneously illuminates the field of view of the image acquisition unit with light in the first wavelength range and with light in the second wavelength range—i.e. broadband. In this case, light filters can alternately be interposed in front of the image acquisition unit, one of which is transparent for light in the first wavelength range and another for light in the second wavelength range, which blocks the respective other wavelength range. Two illumination modules can also be provided, one for light in the first wavelength range and one for light in the second wavelength range, which are activated alternately. Likewise, two image acquisition units can be provided which, due to the properties of their area sensors or due to corresponding filters, on the one hand only capture images with light in the first wavelength range and on the other hand only capture images with light in the second wavelength range.

Finally, it is also possible to provide an illumination module that simultaneously emits both light in the first wavelength range and light in the second wavelength range and an image acquisition unit that is sensitive both to light in the first wavelength range and to light in the second wavelength range, without additional filters being required. The image of the security marking ultimately captured in this variant would be dark in the area of the dark fields, since the dark fields absorb both light in the first wavelength range and light in the second wavelength range. The contrast field would be bright, since the contrast field has a high reflectivity both for light in the first wavelength range and for light in the second wavelength range. The security field, on the other hand, would have a mean gray value, because the security field absorbs light in the first wavelength range, but has a relatively high reflectivity for light in the second wavelength range, which is in any case higher than the reflectivity of the dark fields for light in the second wavelength range. Even if the security field did have the same high reflectivity as the contrast field under light in the second wavelength range, in the last-mentioned embodiment, in which the security marking is illuminated both with light in the first wavelength range and with light in the second wavelength range and the reflected light is captured broadband, the security field will additionally not appear quite bright, but rather gray, since in any case it absorbs light in the first wavelength range.

In the non-broadband variants, the illumination module preferably comprises light sources that are narrow-banded, so that the spectral bandwidth (from half value of the maximum to half value of the maximum (FWHM: full width at half maximum)) is smaller than 60 nm in each case. The mean wavelength between these two half-value wavelengths is referred to in the context of this description as the central wavelength of the respective wavelength range.

The illumination module is preferably designed in such a way that it emits light in the visible wavelength range in at least two partial wavelength ranges, the central wavelengths of which are preferably more than 200 nm apart.

The intensity of the shorter of these two wavelength ranges is preferably between 25 and 40% of the total intensity of the visible light emitted in the two partial wavelength ranges. Light-emitting diodes are particularly well-suited light sources. These have short response times and narrow bandwidths.

The illumination module is preferably designed in such a way that the field of view of the image acquisition unit in which a packaging to be evaluated is located is illuminated uni-formly in such a way that the intensity difference over the field of view is at most 25%.

Furthermore, the illumination module is preferably arranged in such a way that the lighting angle in relation to a surface normal of the security marking to be illuminated is between 20° and 45°.

The image acquisition unit with associated optics for imaging a security marking to be evaluated on the area sensor is preferably designed in such a way that 1 mm2of the security marking is captured by at least four entire sensor elements (pixels).

The readout unit preferably comprises an evaluation unit which is connected to the image acquisition unit and which is designed to capture mean gray values for at least one contrast field, at least one dark field and the security field, preferably separately for light in the first wavelength range and for light in the second wavelength range. Finally, an assessment unit connected to the evaluation unit is designed to carry out an assessment of the respective security markings captured on the basis of the gray values of the security field captured for the two different wavelength ranges. If the assessment of the gray values by the assessment unit shows that, in particular, the gray values in the area of the image of the security field, when illuminated with light in the second wavelength range, deviate by a predetermined amount from the gray values when illuminated with light in the first wavelength range, the security marking is assessed as OK. Otherwise it is assessed as not OK. If used as intended in a reverse vending machine, the latter would have the effect that packaging would not be accepted, but would be taken back. In this case, the deposit value will not be refunded. If, on the other hand, a respective security marking captured is assessed as OK, the corresponding packaging is accepted by a reverse vending machine with the readout unit in accordance with the invention and the deposit value is refunded.

FIG.1shows, by way of example, a packaging10in the form of a can with a security marking12and an identification label50, which in the example shown is in the form of a barcode.

The security marking12serves to identify the packaging10as packaging for which a deposit is to be paid when purchased by a consumer, which the consumer receives back when the packaging is returned. The security marking is designed in such a way that it is not easily possible to equip such packaging for which no deposit has been paid with the security marking. Since the deposit value is greater than the packaging value, whoever takes back the packaging and pays out the deposit would suffer a loss in the case of packaging with forged security markings.

FIG.2shows the essential features of the security marking12, namely a comparatively strongly reflective contrast field14which encloses a security field16and a signal field18. The contrast field14is highly reflective in a broad wavelength range, in particular in the visible wavelength range of light and in the transition to the infrared wavelength range.

The security field16has the property that it is weakly reflective in a first, preferably visible wavelength range of the light, that is to say it is strongly absorbing and therefore appears dark.

In a second, likewise preferably visible wavelength range of the light, however, the security field16is highly reflective, for example just as strongly reflective as the contrast field14. The security field16obtains this property of different reflectivity at different wavelengths in that the color with which the security field16is printed has a lower absorption in the second wavelength range than in the first wavelength range.

As a result, when viewing the packaging10in the first wavelength range, for example in normal daylight, the security field16can be clearly seen as a dark field in front of a light background, whereas when viewed in the second wavelength range, for example with the aid of a corresponding camera, the security field16can be seen less strongly, since the security field16has a higher reflectivity in the second wavelength range, which is similar to that of the contrast field14.

The reflectivity of the respective field for a respective wavelength—and thus the intensity with which light is reflected in a respective wavelength range—depends on the color with which the respective field is printed on a respective background and on the background itself. The color with which the contrast field14is printed or the contrast fields are printed is typically a broadband reflective color, while the color with which the potentially provided dark fields20and22are printed (seeFIG.3) is a broadband absorbing color. The contrast field14can also be formed by the background itself if this is itself broadband reflective, so that the contrast field14does not necessarily have to be printed.

The identification label50is formed by mark components52in the form of bars that are printed with black or in a broad wavelength range of dark colors and are surrounded by a light, for example white, background54. The background54is also located between the mark components52printed with dark color in the form of bars. The light, in particular white, background of the mark components of the identification label50is typically formed by the background from which the dark mark components52of the identification label are also printed. This is the same background that also forms the bright contrast field14of the security marking12. The contrast field (or the contrast fields)14of the security marking12and the background52around the mark components52of the identification label50, which are printed with dark color, therefore have the same light, e.g. white, color.

If the combination of security marking12and identification label50has been manipulated in an impermissible manner, for example by pasting over the original identification label52(the barcode), the contrast field14and the background52can also have brightnesses that differ slightly from one another. According to the invention, this difference can be used to detect counterfeits or impermissible manipulations.

The mark components52of the identification label50printed with dark color and the dark fields20and22of the security marking12are usually printed with the same broadband dark color, e.g. carbon black, on a light background.

The color with which the security field16is printed has a higher absorption in the first wavelength range than in the second wavelength range. Accordingly, the color with which the security field16is printed has a higher reflectivity or a higher transparency or both in the second wavelength range compared to the first wavelength range. If the color with which the security field16is printed has a higher reflectivity in the second wavelength range than in the first wavelength range, the intensity of the reflected light in the second wavelength range is in any case greater than the intensity of the reflected light in the first wavelength range. If the color with which the security field16is printed has a higher transparency in the second wavelength range than in the first wavelength range, the intensity of the reflected light in the second wavelength range is greater than the intensity of the reflected light in the first wavelength range in cases where the background under the color with which the security field16is printed has a sufficiently high reflectivity in this second wavelength range. If the color with which the security field16is printed already has a high reflectivity in the second wavelength range, the reflectivity of the background under the color with which the security field16is printed is less or not at all decisive.

For security reasons, however, it is advantageous if the background under the color with which the security field16is printed has a reflectivity that deviates from the reflectivity of the contrast field14. This means that the security field16can be printed with two colors, namely initially with a first color with reflective properties that differ from those of the contrast field14, and then with a second color so that the second color covers the first color. The second color with which the security field16is printed is then that color which, as described above, has a higher reflectivity and/or transparency in the second wavelength range than in the first wavelength range.

The security field16has an asymmetrical shape, so that its orientation in relation to the rest of the security marking can be clearly recognized.

A further component of the security marking12is a signal field18which, depending on the type of packaging, is either highly absorbent (as shown inFIG.2) or highly reflective in a broad wavelength range that includes visible and infrared light. In the last-mentioned case—highly reflective signal field18—the signal field18has the same color as the background14and is therefore practically non-existent, but determined exclusively by the abstract def-inition of its intended location. In the exemplary embodiment according toFIG.2, the signal field18is shown in a strongly absorbing color, that is to say weakly reflective and therefore dark.

The signal field18serves to signal to a device for reading out the security marking whether and, if so, which stored parameters are to be taken into account when inspecting the security marking. Parameters can be stored correction factors, for example.

In order to make it easier to find the security marking12′ (seeFIG.3) on a packaging10and to find the signal field18within the security marking12′, the security marking12′ preferably comprises further fields, namely dark fields first in the form of corner markings20and second in the form of orientation markings22.

The dark fields20and22have the property of being strongly absorbing in the first wavelength range as well as in the second wavelength range, that is to say being weakly reflective and thus appearing dark.

The corner markings20have the shape of right-angled, isosceles triangles. This shape is particularly suitable because such shapes practically do not occur in the rest of the packaging. The legs of the respective isosceles triangle20run parallel to the edges of the security marking12′. The hypotenuses of the corner markings20are thus turned inwards with respect to the security marking12′.

The orientation markings22act, on the one hand, as corner markings for locating two further corners of the overall square security marking12′. In addition, they enclose the signal field18between them, so that it is easy to find even if it has the same color as the background14, as is shown by way of example inFIG.3.

Both the corner markings20and the orientation markings22can also have shapes other than those shown in the exemplary embodiment and, for example, be composed of several partial areas, so that information can be encoded with the corner markings20and/or orientation markings22, in a similar manner as with the aid of the signal field18.

FIG.4basically shows the same security marking12″ asFIG.3. The only difference between the security marking12″ fromFIG.4compared to the security marking12′ fromFIG.3is that the security field18in the security marking12″ fromFIG.4is weakly reflective, i.e. dark, and thus has the same color as the orientation markings22and the corner markings20, while the security field18′ of the security marking12′ fromFIG.3is highly reflective and thus has the same color as the contrast field14.

FIG.5shows a variant of a security marking12′″ with a signal field18″ divided into a total of 8 partial signal fields, which are either strongly or weakly reflective. In this way, the eight subfields can reproduce a code comprising 8 bits (1 byte). Depending on the value of the respective bit—0 or 1—the associated subfield is highly or weakly reflective. In the exemplary embodiment, the signal field18″ reproduces the byte 10100110 or 01011001, depending on whether the bit value 1 is assigned a strong or weak reflectivity. With such a subdivided signal field18″, not only bivalent information (directionally reflective or diffusely reflective) can be reproduced, but 256-valent information can be reproduced in the exemplary embodiment, for example as a plurality of different correction factors for different packaging, for example.

Referring to the schematic, sketch-like representation of a readout device30for reading out security markings12on packaging such as the packaging10, the essential components and the mode of operation will now be described.

The readout device30, which can be, for example, part of a reverse vending machine for beverage packaging, may comprise a transport means32with which a packaging10′ can be positioned in front of a readout unit34such that it is in the field of view of the image acquisition unit36of the readout unit34. The field of view is indicated inFIG.5by dashed oblique lines. The transport means may comprise conveyor belts and/or rollers. Rollers can be used to rotate a beverage packaging in such a way that the security marking is in the acquisition area of the image acquisition unit36.

To illuminate the field of view, an illumination module is provided comprising two illumination units38.1and38.2. The direction of illumination and thus the angle at which the illu-urination falls on a packaging10to be read out is indicated by dotted arrows. The angle of illumination should be in an angular range between 20° and 45° with respect to the surface normal of the packaging10. The illumination units38.1and38.2of the illumination module are arranged and aligned accordingly. However, other illumination angles and, accordingly, other arrangements of the illumination module are also possible. In particular, the illumination module may also have only a single illumination unit which is able to emit light in several wavelength ranges or in a broadband wavelength range.

The illumination units38.1and38.2possess a large number of light-emitting diodes (LED) as light sources. The illumination unit38.1is designed to illuminate the packaging10with light intensity of the reflected light in the second wavelength range, while the illumination unit38.2illuminates the packaging unit10with light intensity of the reflected light in the first wavelength range. The illumination unit38.2possesses two types of light-emitting diodes, namely a first type of light-emitting diodes that emit blue, visible light and a second type of light-emitting diodes that emit red, visible light. The visible light which the illumination unit38.2emits is thus composed of two wavelength ranges, each with a central wavelength in the blue range of the visible spectrum and a central wavelength in the red range of the visible spectrum. The half-value bandwidth of the two partial wavelength ranges emitted by the illumination unit38.2for visible light is in each case less than 50 nm.

With the aid of the illumination module and its illumination units38.1and38.2, targeted lighting scenarios can thus be set. In normal operation, the illumination units38.1and38.2are operated alternately so that the packaging10is either only illuminated with light in the second wavelength range from the illumination unit38.1or with light in the first wavelength range from the illumination unit38.2. As explained at the beginning, however, it is also possible to permanently illuminate the packaging10by means of both illumination units38.1and38.2.

The light reflected from the surface of the packaging10is captured by the image acquisition unit36. For this purpose, the image acquisition unit36possesses an area sensor40and optics42, which sharply maps an image of the surface of the packaging10on a surface of the area sensor40. The surface of the area sensor40is formed by a plurality of light-sensitive sensor elements. These are preferably arranged in a matrix-like manner. The sensor elements of the area sensor40and the optics42are designed so that a square millimeter of the surface of the packaging10is mapped onto a partial surface of the area sensor40in such a way that the partial surface contains at least four complete sensor elements. Thus, the imaging scale with which the optics42maps an image of the surface of the packaging10on the surface of the area sensor40depends on the size that the sensor elements occupy on the surface of the area sensor40and the distance between the sensor elements. It goes without saying that the optics42is designed in such a way that it maps the surface of the packaging10sharply on the surface sensor40in the area of a depth of field that is required by varying packaging diameters.

The sensor elements of the surface sensor40are broadband light-sensitive, that is to say at least in the partial wavelength ranges of the light emitted simultaneously or alternately by the illumination units38.1and38.2. The output value delivered by each individual sensor element of the area sensor40—also referred to here as a gray value—corresponds to the total intensity of all light in the various wavelength ranges that is captured by the respective sensor element.

The greater the total intensity of the light that strikes the respective sensor element, the greater the output value delivered by a respective sensor element of the surface sensor40, which is also referred to here as the gray value. The total intensity of the light that strikes the respective sensor element is made up of the partial intensities of the light in the different wavelength ranges from which the light that strikes a respective sensor element is composed.

This total intensity is the intensity of the light captured by the sensor element in the second wavelength range when the packaging is illuminated exclusively by the illumination unit38.1with light in the second wavelength range. In the same way, the output value of a respective sensor element corresponds to the respective intensity in the first wavelength range of the light if the packaging surface is illuminated exclusively by the illumination unit38.2with light in the first wavelength range.

If, in contrast, the surface of the packaging10is illuminated by both the illumination unit38.1and the illumination unit38.2simultaneously with light in the second wavelength range and with light in the first wavelength range, the light intensity detected by a respective sensor element—and thus the gray value output—depends on the sum of the intensity with which a respective surface element assigned to the sensor element via the image reflects light in the first wavelength range and in the second wavelength range.

This means that sensor elements which capture, for example, part of the contrast field14of the security marking12always capture a high brightness value and thus deliver a large output value—and thus a high gray value wi. In contrast, sensor elements that capture part of an orientation marking22or a corner marking20will always detect a low brightness value and thus also deliver a low output value and gray value si, regardless of whether the illumination is with light in the first wavelength range or with light in the second wavelength range. Conversely, the gray value d1delivered by a sensor element onto which a part of the security field16is mapped depends on the type of lighting.

When the packaging is illuminated with light in the first wavelength range, the intensity reflected by the security field16is low, so that a sensor element detecting part of the security field16only delivers a low gray value d1. However, if the packaging is illuminated with light in the second wavelength range, the intensity of the light reflected by the security field is significantly higher—depending on the background—and can, for example, corre-spond to the intensity reflected by the contrast field14. Correspondingly, a sensor element on which part of the security field is imaged delivers a high gray value d2when the packaging10is illuminated with light in the second wavelength range. If, on the other hand, the packaging10is simultaneously illuminated with light in the first wavelength range and in the second wavelength range, the gray value delivered by a sensor element capturing the security field is a mean gray value.

Within the image acquisition unit36, preprocessing of the gray values delivered by the area sensor40takes place in a preprocessing unit44. The processed gray values (output values of the sensor elements of the area sensor40) are supplied to an evaluation unit46in which, firstly, the various areas of the security marking are sensed with the aid of basically known pattern recognition methods.

This image sensing of the image of the security marking also serves to determine the location of the signal field18in order to be able to read out its intensity. Depending on the intensity of the light reflected by the signal field18, the evaluation unit46switches on a different reference threshold for evaluating the intensity of the light reflected by the security field16in the second wavelength range.

Secondly, the intensity values delivered by the various fields of the security marking are compared with the respective reference thresholds in order to assess the respective security marking. This assessment is carried out by an assessment unit which is part of the evaluation unit46and is therefore not shown in greater detail inFIG.5. The reference threshold for the intensity values that were captured when the security marking was illuminated with light in the second wavelength range in the area of the security field16is of particular importance for the assessment.

The assessment of the intensity values represented by corresponding gray values d2, which are to be assigned to the security field16when illuminated with light in the second wavelength range, takes place with reference to the gray values d1—and thus the intensity values—that are to be assigned to the security field16when illuminated with light in the first wavelength range. Depending on how much the intensity of the reflected light in the second wavelength range deviates from the intensity of the reflected light in the first wavelength range, packaging is accepted and the deposit is either paid out or not.

The inspection by the evaluation unit46takes place according to the following procedure:

To inspect the security marking, the intensities of the light reflected by the security field16in two different wavelength ranges are recorded in the form of gray values d1, d2. In addition, the intensities of the light reflected by the contrast field14in the first wavelength range are recorded in the form of an optionally averaged gray value w1.

The gray values are preferably scaled—and thus normalized—in such a way that the difference between the averaged numerical gray value of the contrast field and the averaged numerical gray value of one or more dark fields of an image (a capture) of the security marking12is set to 100% (contrast normalization). This enables gray values from different images of the security marking12to be compared.

To check the integrity of the combination of security marking12and identification label50, this combination is illuminated in one or the other wavelength range and, in addition to the gray value of the contrast field14w1or w2, the gray value of the background52of the identification label50b1or b2is determined. If the gray value of the contrast field14w1or w2deviates from the gray value of the background52of the identification label50b1or b2by more than 10%, the combination of security marking12and identification label50is rejected as inadmissible. For this purpose, a signal indicating a lack of integrity of the combination of security marking and identification label is generated and output if the gray value of the contrast field of the security marking deviates from the gray value of the background of the identification label by more than a predefined maximum—namely by more than 5% or 10%, for example.

Since the brightness of the contrast field14and/or the background52can be uneven, for example as a result of uneven lighting or a non-level surface, it regularly occurs that the sensor elements of the area sensor40, onto which the corresponding partial areas of the contrast field14and the background52are mapped, will not all deliver the same gray value. A gray value histogram is therefore preferably formed and smoothed.

It is also advantageous to provide several measurement windows for determining the gray value of the contrast field14or of the background52. For example, each light field between the bars of the barcode50can be its own measurement field.

This is preferably done separately for the gray values of the contrast field14and the gray values of the background52as follows:Calculate the histogram.Smooth the histogram five times (kernel: [1,1,1,1,1]).Determine the histogram maximum (HistMax) (highest peak with the lowest gray value).Remove all histogram values that are smaller than ClipFactor (0.5)*HistMax.Calculate the mean value from the modified histogram.Calculate the gray value of the contrast field or the background at the end as the mean value of the individual gray values in the measurement windows.

Instead of or in addition to the integrity check based on the brightness values of the contrast field and background, a geometry check can also be provided in which, for example, the parallelism of mark components of the security marking12and the identification label is checked.

The evaluation unit46is also connected to a control unit48which is used, for example, to control the illumination units38.1and38.2and which also controls the transport means32in order, for example, to rotate the packaging10by means of the transport means32, so that the security marking on the surface of the packaging10is located in the field of view of the readout unit36. The image acquisition by the evaluation unit46is also used for this purpose.

The control unit also controls the refund of the deposit and the takebacks of packaging.