rus
Issue #1/2021
S. B. Odinokov, I.K Tsyganov, V. E. Talalaev, V. V. Kolyuchkin, N. V. Piryutin
Diffraction Comparator for Authentication of Security Holograms on Documents. Modernization and Trial Operation
Diffraction Comparator for Authentication of Security Holograms on Documents. Modernization and Trial Operation
DOI: 10.22184/1993-7296.FRos.2021.15.1.86.98
The article discusses a new experimental sample of a high-performance optoelectronic scanner device for authentication of security holograms on documents. It increases the speed of result obtaining due to using modern scanning systems, high-speed image sensors, custom components of the optical system in the scanner design. Correlation filters in the recognition algorithm for the information received from the hologram, significantly reduce the time and raise the reliability of the security hologram authenticity control.
The article discusses a new experimental sample of a high-performance optoelectronic scanner device for authentication of security holograms on documents. It increases the speed of result obtaining due to using modern scanning systems, high-speed image sensors, custom components of the optical system in the scanner design. Correlation filters in the recognition algorithm for the information received from the hologram, significantly reduce the time and raise the reliability of the security hologram authenticity control.
Теги: authenticity control automatic control diffraction security elements holographic security elements security holograms security holograms on passport documents автоматический контроль голограммные защитные элементы дифракционные защитные элементы защитные голограммы защитные голограммы на документах контроль подлинности
Diffraction Comparator for Authentication of Security Holograms on Documents. Modernization and Trial Operation
S. B. Odinokov, I.K Tsyganov, V. E. Talalaev, V. V. Kolyuchkin, N. V. Piryutin
Research Institute of Radio Electronics and Laser Technology, Bauman Moscow State Technical University, Moscow, Russia
The article discusses a new experimental sample of a high-performance optoelectronic scanner device for authentication of security holograms on documents. It increases the speed of result obtaining due to using modern scanning systems, high-speed image sensors, custom components of the optical system in the scanner design. Correlation filters in the recognition algorithm for the information received from the hologram, significantly reduce the time and raise the reliability of the security hologram authenticity control.
Keywords: Security holograms, Diffraction security elements, Holographic security elements, Authenticity control, Automatic control, Security holograms on passport documents
Received on: 22.12.2020
Accepted on: 28.01.2021
Introduction
Rainbow holograms are widely used as one of the security elements for various documents: passports, driver’s licenses, various certificates and other security printing products [1]. The relevance of this topic is difficult to overestimate, even with the entry into our life of volume holograms on polymer carriers. Security rainbow holograms are used as a fighting tool against counterfeit goods in almost all spheres of human activity, which inevitably leads to the emergence certain people’s need to counterfeit them. Accordingly, the task of the authenticity control of security rainbow holograms will be in demand for a long time.
Team of the “Optical-Holographic Systems” laboratory under the guidance of Prof. S. B. Odinokov works on this and related topics for over 10 years at the Bauman Moscow State Technical University. During this time, both systems for expert control of security holograms and portable or desktop xpress control were developed, manufactured and delivered to customers. Main requirements for these devices are:
There are at least two approaches to the construction of devices for the express control of holograms. In both approaches, to make a decision about the authenticity of the hologram, the information obtained from the investigated hologram is compared with information from the reference hologram.
In the first approach, a colour image from a hologram illuminated by a source of incoherent multispectral “white” light and recorded by a digital camera is used as information for comparison. These devices include the Regula 2303 holographic image visualizer, the VSC 8000 video spectral comparator (Foster & Freeman), and the DOCUBOX HD device (Projectina) (See Figure 1 a-c).
The second approach compares diffraction spectra reconstructed by coherent radiation from the controlled hologram and from the reference hologram at one or more wavelengths. The method for analyzing coherent images of security holograms (hereinafter referred to as the SH) consists in the correlation image recognition of the spatial diffraction distribution of the intensity of laser radiation in the regions of the SH. If a coherently illuminated element of the hologram contains diffraction gratings with different spatial frequencies and orientations, then the diffraction pattern will include a zero order, as well as pairs of diffraction orders symmetrically located at a certain distance from it. The direction and distance between these maxima and the zero order correspond to the orientation and spatial frequency of the gratings existing on the illuminated element.
In our opinion, this method is more accurate and gives better results in the identification process, as opposed to comparing colour photographs of holograms. Fig. 1d shows the first version of an optoelectronic scanner developed by the “Optical-Holographic Systems” laboratory [2, 3], which works on the principle of comparing spatial spectra reconstructed by coherent radiation from a controlled hologram and spectra obtained earlier from a reference hologram. This device, in contrast to the proposed one, has two significant drawbacks: 1 – mechanical movement of the optical head, which leads to significant time expenditures in the investigation; 2 – due to design features, the number and position of control points is limited and fixed.
In the proposed device, as well as in its predecessor, mathematically synthesized invariant correlation filters are used, which contain information about the reference object, as well as about its possible distortions. This allows to some extent get rid of the noise influence of noise in the analyzed diffraction distribution pattern, as well as positioning errors of the probe radiation [4, 5]
Functional diagram of diffraction comparator of security holograms
Fig. 2 shows a functional diagram of the device. It can be seen that the comparator includes two channels: a control channel (items 1–11) and a guidance channel (items 12–14). The guidance channel is designed to determine the position of the investigated hologram relative to the device, and the control channel performs the actual hologram identification procedure, which consists in obtaining diffraction spectra from the designated control points and comparing the obtained spectra with the reference spectra obtained during the training of the device and stored in its database.
The control channel consists of a two-coordinate scanning illumination system 1, containing a laser diode 2, a collimating objective 3, a mirror scanning system 4, including, among other things, 2 galvanometric scanners 5 and an additional pupil transfer lens system 6, the controlled object 7, Fourier converting system 8, visualizer 9, reproduction lens 10 and array photodetector (recording device) 11.
The guidance channel consists of a matrix of LEDs 12 for illumination of the monitored object 7, a projection lens 13 and photodetector array (recording device) 14.
Experimental sample of diffraction comparator of security holograms
Based on the functional diagram, an optical scheme and a 3D model of the device structure were developed, which can be seen in Fig. 3a. The design of the device is based on the mezzanine principle and contains 3 levels. On the lower level there is an on-board integrated computer to which an external monitor, mouse and keyboard are connected. The integration of the computer into the device is caused by the need to organize a high-speed data bus for transmitting large amount of video information. Elements of the optical system of the comparator and electronic components are located on the two upper floors. An optical window is located on top of the comparator for placing on it the investigated hologram or document with the hologram. A cover is provided to eliminate external light.
To create an experimental sample of a diffraction comparator for security holograms, in accordance with the developed design documentation, optical, optoelectronic, electronic, mechanical parts, assemblies and units included in it were manufactured and purchased. Most of the optical and mechanical components are manufactured in Russia and Belarus. Optoelectronic and electronic assemblies have also been developed and manufactured by Russian development firms, but with the predominant use of foreign components.
Figures 3b‑3d show photographs of the appearance of the device. The overall dimensions of the scanner were 330 × 330 × 650 mm, and the weight was 20 kg, i. e. it is a tabletop device. From the photo in Fig. 3b, you can get an idea of its dimensions against the background of a in comparison with laptop. In the upper part of the scanner, under the cover, there is an optical entrance window through which the document is scanned (see Fig. 3c, 3d). Technical parameters of the comparator of security holograms are given in table 1.
Let us now consider the elements of the device’s subsystems and the principles of its operation in more detail. Let’s start with the guidance channel in Fig. 4. It consists of a multicomponent LED illuminator 1, a projection lens 2 and a photodetector array 3. There are also mirrors in the optical system for the convenience of arranging the device and reducing its overall dimensions.
The guidance channel functions as follows. The multicomponent LED illuminator consists of 32 LEDs located on a semicircle with a calculated radius at equal angular intervals. The vertical axis of the illuminator (semicircle) coincides with the vertical axis of the optical window with the hologram. During operation, the LEDs turn on discretely, illuminating the investigated hologram from a certain direction. All gratings perpendicular to this direction will diffract the incident radiation towards the lens of the matrix photodetector. As a result, the video camera registers the image of objects with certain orientations of the gratings (see Fig. 5). Anticipating the quite natural question: “Why not illuminate the hologram with all LEDs at once?”, the answer is that in this case it is much more difficult to isolate useful information against the noise background.
The frames of the investigated object, obtained in all directions of illumination, are processed using the software: noise removal, contrast enhancement, and then stitching into a single image. The obtained image is used to bind the hologram to the coordinate system of the device. In Fig. 6 shows the result of the search for support elements in the process of snapping. The colour defines the type of the supporting element: the inscription “РОССИЯ” (red), the inscription “RUSSIA” (green), Eagle (yellow); the circle indicates the position of the reference element in the standard, and the square indicates the position of the reference element on the image of the investigated hologram.
Also, at this stage, the primary comparison of the image of the investigated hologram with the reference one takes place, and in the case of a complete mismatch, it is recognized as counterfeit. In case of detection of reference objects that coincide with the reference ones, as a result of binding, information about the reference Fourier spectra at the assumed control points is loaded from the database. In the future, this information will be used in the correlation comparison with the images of the Fourier spectrum obtained in the control channel. The technical parameters of the guidance channel are given in table 2.
Now let’s switch to the control channel. A photograph with the principal subunits that make up this channel is shown in Fig. 7. It contains a two-coordinate scanning system of illumination 1, which allows to illuminate the investigated hologram or document with a hologram within the entrance window with a small beam aperture. One of the key components of the scanner is the Fourier transform lens 2, which forms parallel probing beams to illuminate the investigated object along the normal and, after reflection from the object, forms a diffraction spectrum on the visualizer 3. The diffraction distribution from the visualizer is recorded using the projection lens 4 and the photodetector array 5 and is transferred to a computer for subsequent comparison with reference information.
Consider the beam paths in the control channel. For this, we first turn to the two-coordinate scanning system, photographs of which are shown in Fig. 8. The radiation from the semiconductor laser 1, having passed through the collimator 2, first hits the mirror 3 (mounted on a galvanometric scanner, scanning along the X axis). Next, the image of the mirror 3 with the help of the mirror transfer system of the pupil 4 is built in the plane of the mirror 5 (in turn, fixed on a galvanometric scanner, which performs scanning along the Y axis). After that, the image of the mirror 5, using the lens transfer system of the pupil 6, forms a quasi-point source of coherent radiation at a given distance, scanning the space in a 12 × 12 degree cone. Thus, we illuminate the object in the plane of the sample installation with a size of 70 × 70 mm or a diameter of 50 mm.
Further, the radiation, passing through the Fourier transform lens 2 (see Fig. 7), falls along the normal to the small area of interest on the investigated object. Then, depending on the parameters of the diffraction gratings that hit the illumination spot, it diffracts in the opposite direction and, having passed through the Fourier transform lens 2 again, forms a diffraction spectrum in its focal plane, which coincides with the plane of the visualizer 3. Photographs of the passage of radiation in the control channel after the two-coordinate scanning system are shown in Fig. 9.
Only half of the diffraction distribution pattern is formed on the visualizer, containing only one of the diffraction orders +1st or –1st. The position of the illumination radiation in the plane of the visualizer and the position of the reflected zero order from the hologram coincide and are known to us. Thus, the location of the same diffraction order completely determines the parameters, period and orientation of the illuminated diffraction grating and allows the process of comparison with the standard. Fig. 10a shows a top view of a diffraction spectrum visualizer. In the photograph, we see three clearly distinguishable maxima, which indicates that the illumination area on the hologram has three diffraction gratings, the periods of which are determined by the distance from the center of the picture, and the angular orientations are determined by the position on the arc of the corresponding radius. Fig. 10b contains a photograph from the photodetector array 5 (see Fig. 7), the image of which is transmitted to the on-board computer for subsequent processing and comparison with reference information. The technical parameters of the control channel are shown in Table 3.
The software, in addition to conducting express control of holograms on documents, also allows you to analyze the parameters of the gratings contained in the holograms to create diffraction “maps” of holograms. In Fig. 11 shows visualizations of diffraction responses – spectra at single probing (Fig. 11a), the spectrum of a fragment of the “Eagle” hologram (Fig. 11b), the spectrum of a fragment of the “RF” hologram (Fig. 11c) and the spectrum of the entire hologram.
Conclusion
In conclusion, let us highlight the main design and software solutions implemented in the automatic diffraction comparator for express control of the authenticity of security holograms on documents. Galvanometric scanners are used in the design of the device. Their use made it possible to significantly reduce the time required to control the security hologram with the dimensions of the passport page. The use of a high-speed image sensor has also resulted in reduced inspection times. Custom components of the optical system have improved the quality of the recorded diffraction distribution patterns, which has reduced errors in authenticity control.
The absence of moving elements in the comparator, except for scanning mirrors, increased the positioning accuracy of the probe beam on the sample under study, which in turn increased the probability of correct identification of the security hologram, as well as the mechanical reliability of the device as the whole. The use of correlation filters in the recognition algorithm for information obtained from the hologram also increased the reliability of the authenticity control process.
Acknowledgments
The work was carried out at the Bauman Moscow State Technical University with the financial support of the Ministry of Education and Science of the Russian Federation under agreement No. 14.577.21.0223 (ID PRFMEFI57716X0223).
Authors
S. B. Odinokov, Doctor of Technical Sciences, Research Institute of Radio Electronics and Laser Technology BMSTU, odinokov@bmstu.ru, Moscow, Russia.
ORCID: 0000-0003-2730-9545
I. K. Tsyganov, Research Institute of Radio Electronics and Laser Technology, BMSTU, Moscow, Russia.
ORCID: 0000-0002-9538-5673
V. E. Talalaev, Research Institute of Radio Electronics and Laser Technology, BMSTU, Moscow, Russia.
ORCID: 0000-0003-4244-6898
V. V. Kolyuchkin, Candidate of Technical Science, Research Institute of Radio Electronics and Laser Technology, BMSTU, Moscow, Russia.
ORCID: 0000-0002-7294-7143
N. V. Piryutin, Research Institute of Radio Electronics and Laser Technology, Bauman MSTU, Moscow, Russia.
ORCID: 0000-0002-5493-8796
Contribution of the authors
The article was prepared based on many years of work by all members of the authors team.
Conflict of interests
The authors declare no conflicts of interests. All authors took part in writing the article and supplemented the manuscript in their part of the work.
S. B. Odinokov, I.K Tsyganov, V. E. Talalaev, V. V. Kolyuchkin, N. V. Piryutin
Research Institute of Radio Electronics and Laser Technology, Bauman Moscow State Technical University, Moscow, Russia
The article discusses a new experimental sample of a high-performance optoelectronic scanner device for authentication of security holograms on documents. It increases the speed of result obtaining due to using modern scanning systems, high-speed image sensors, custom components of the optical system in the scanner design. Correlation filters in the recognition algorithm for the information received from the hologram, significantly reduce the time and raise the reliability of the security hologram authenticity control.
Keywords: Security holograms, Diffraction security elements, Holographic security elements, Authenticity control, Automatic control, Security holograms on passport documents
Received on: 22.12.2020
Accepted on: 28.01.2021
Introduction
Rainbow holograms are widely used as one of the security elements for various documents: passports, driver’s licenses, various certificates and other security printing products [1]. The relevance of this topic is difficult to overestimate, even with the entry into our life of volume holograms on polymer carriers. Security rainbow holograms are used as a fighting tool against counterfeit goods in almost all spheres of human activity, which inevitably leads to the emergence certain people’s need to counterfeit them. Accordingly, the task of the authenticity control of security rainbow holograms will be in demand for a long time.
Team of the “Optical-Holographic Systems” laboratory under the guidance of Prof. S. B. Odinokov works on this and related topics for over 10 years at the Bauman Moscow State Technical University. During this time, both systems for expert control of security holograms and portable or desktop xpress control were developed, manufactured and delivered to customers. Main requirements for these devices are:
- short time for scanning a sample and making a decision on its authenticity / forgery;
- low qualification of personnel who will use express scanners.
There are at least two approaches to the construction of devices for the express control of holograms. In both approaches, to make a decision about the authenticity of the hologram, the information obtained from the investigated hologram is compared with information from the reference hologram.
In the first approach, a colour image from a hologram illuminated by a source of incoherent multispectral “white” light and recorded by a digital camera is used as information for comparison. These devices include the Regula 2303 holographic image visualizer, the VSC 8000 video spectral comparator (Foster & Freeman), and the DOCUBOX HD device (Projectina) (See Figure 1 a-c).
The second approach compares diffraction spectra reconstructed by coherent radiation from the controlled hologram and from the reference hologram at one or more wavelengths. The method for analyzing coherent images of security holograms (hereinafter referred to as the SH) consists in the correlation image recognition of the spatial diffraction distribution of the intensity of laser radiation in the regions of the SH. If a coherently illuminated element of the hologram contains diffraction gratings with different spatial frequencies and orientations, then the diffraction pattern will include a zero order, as well as pairs of diffraction orders symmetrically located at a certain distance from it. The direction and distance between these maxima and the zero order correspond to the orientation and spatial frequency of the gratings existing on the illuminated element.
In our opinion, this method is more accurate and gives better results in the identification process, as opposed to comparing colour photographs of holograms. Fig. 1d shows the first version of an optoelectronic scanner developed by the “Optical-Holographic Systems” laboratory [2, 3], which works on the principle of comparing spatial spectra reconstructed by coherent radiation from a controlled hologram and spectra obtained earlier from a reference hologram. This device, in contrast to the proposed one, has two significant drawbacks: 1 – mechanical movement of the optical head, which leads to significant time expenditures in the investigation; 2 – due to design features, the number and position of control points is limited and fixed.
In the proposed device, as well as in its predecessor, mathematically synthesized invariant correlation filters are used, which contain information about the reference object, as well as about its possible distortions. This allows to some extent get rid of the noise influence of noise in the analyzed diffraction distribution pattern, as well as positioning errors of the probe radiation [4, 5]
Functional diagram of diffraction comparator of security holograms
Fig. 2 shows a functional diagram of the device. It can be seen that the comparator includes two channels: a control channel (items 1–11) and a guidance channel (items 12–14). The guidance channel is designed to determine the position of the investigated hologram relative to the device, and the control channel performs the actual hologram identification procedure, which consists in obtaining diffraction spectra from the designated control points and comparing the obtained spectra with the reference spectra obtained during the training of the device and stored in its database.
The control channel consists of a two-coordinate scanning illumination system 1, containing a laser diode 2, a collimating objective 3, a mirror scanning system 4, including, among other things, 2 galvanometric scanners 5 and an additional pupil transfer lens system 6, the controlled object 7, Fourier converting system 8, visualizer 9, reproduction lens 10 and array photodetector (recording device) 11.
The guidance channel consists of a matrix of LEDs 12 for illumination of the monitored object 7, a projection lens 13 and photodetector array (recording device) 14.
Experimental sample of diffraction comparator of security holograms
Based on the functional diagram, an optical scheme and a 3D model of the device structure were developed, which can be seen in Fig. 3a. The design of the device is based on the mezzanine principle and contains 3 levels. On the lower level there is an on-board integrated computer to which an external monitor, mouse and keyboard are connected. The integration of the computer into the device is caused by the need to organize a high-speed data bus for transmitting large amount of video information. Elements of the optical system of the comparator and electronic components are located on the two upper floors. An optical window is located on top of the comparator for placing on it the investigated hologram or document with the hologram. A cover is provided to eliminate external light.
To create an experimental sample of a diffraction comparator for security holograms, in accordance with the developed design documentation, optical, optoelectronic, electronic, mechanical parts, assemblies and units included in it were manufactured and purchased. Most of the optical and mechanical components are manufactured in Russia and Belarus. Optoelectronic and electronic assemblies have also been developed and manufactured by Russian development firms, but with the predominant use of foreign components.
Figures 3b‑3d show photographs of the appearance of the device. The overall dimensions of the scanner were 330 × 330 × 650 mm, and the weight was 20 kg, i. e. it is a tabletop device. From the photo in Fig. 3b, you can get an idea of its dimensions against the background of a in comparison with laptop. In the upper part of the scanner, under the cover, there is an optical entrance window through which the document is scanned (see Fig. 3c, 3d). Technical parameters of the comparator of security holograms are given in table 1.
Let us now consider the elements of the device’s subsystems and the principles of its operation in more detail. Let’s start with the guidance channel in Fig. 4. It consists of a multicomponent LED illuminator 1, a projection lens 2 and a photodetector array 3. There are also mirrors in the optical system for the convenience of arranging the device and reducing its overall dimensions.
The guidance channel functions as follows. The multicomponent LED illuminator consists of 32 LEDs located on a semicircle with a calculated radius at equal angular intervals. The vertical axis of the illuminator (semicircle) coincides with the vertical axis of the optical window with the hologram. During operation, the LEDs turn on discretely, illuminating the investigated hologram from a certain direction. All gratings perpendicular to this direction will diffract the incident radiation towards the lens of the matrix photodetector. As a result, the video camera registers the image of objects with certain orientations of the gratings (see Fig. 5). Anticipating the quite natural question: “Why not illuminate the hologram with all LEDs at once?”, the answer is that in this case it is much more difficult to isolate useful information against the noise background.
The frames of the investigated object, obtained in all directions of illumination, are processed using the software: noise removal, contrast enhancement, and then stitching into a single image. The obtained image is used to bind the hologram to the coordinate system of the device. In Fig. 6 shows the result of the search for support elements in the process of snapping. The colour defines the type of the supporting element: the inscription “РОССИЯ” (red), the inscription “RUSSIA” (green), Eagle (yellow); the circle indicates the position of the reference element in the standard, and the square indicates the position of the reference element on the image of the investigated hologram.
Also, at this stage, the primary comparison of the image of the investigated hologram with the reference one takes place, and in the case of a complete mismatch, it is recognized as counterfeit. In case of detection of reference objects that coincide with the reference ones, as a result of binding, information about the reference Fourier spectra at the assumed control points is loaded from the database. In the future, this information will be used in the correlation comparison with the images of the Fourier spectrum obtained in the control channel. The technical parameters of the guidance channel are given in table 2.
Now let’s switch to the control channel. A photograph with the principal subunits that make up this channel is shown in Fig. 7. It contains a two-coordinate scanning system of illumination 1, which allows to illuminate the investigated hologram or document with a hologram within the entrance window with a small beam aperture. One of the key components of the scanner is the Fourier transform lens 2, which forms parallel probing beams to illuminate the investigated object along the normal and, after reflection from the object, forms a diffraction spectrum on the visualizer 3. The diffraction distribution from the visualizer is recorded using the projection lens 4 and the photodetector array 5 and is transferred to a computer for subsequent comparison with reference information.
Consider the beam paths in the control channel. For this, we first turn to the two-coordinate scanning system, photographs of which are shown in Fig. 8. The radiation from the semiconductor laser 1, having passed through the collimator 2, first hits the mirror 3 (mounted on a galvanometric scanner, scanning along the X axis). Next, the image of the mirror 3 with the help of the mirror transfer system of the pupil 4 is built in the plane of the mirror 5 (in turn, fixed on a galvanometric scanner, which performs scanning along the Y axis). After that, the image of the mirror 5, using the lens transfer system of the pupil 6, forms a quasi-point source of coherent radiation at a given distance, scanning the space in a 12 × 12 degree cone. Thus, we illuminate the object in the plane of the sample installation with a size of 70 × 70 mm or a diameter of 50 mm.
Further, the radiation, passing through the Fourier transform lens 2 (see Fig. 7), falls along the normal to the small area of interest on the investigated object. Then, depending on the parameters of the diffraction gratings that hit the illumination spot, it diffracts in the opposite direction and, having passed through the Fourier transform lens 2 again, forms a diffraction spectrum in its focal plane, which coincides with the plane of the visualizer 3. Photographs of the passage of radiation in the control channel after the two-coordinate scanning system are shown in Fig. 9.
Only half of the diffraction distribution pattern is formed on the visualizer, containing only one of the diffraction orders +1st or –1st. The position of the illumination radiation in the plane of the visualizer and the position of the reflected zero order from the hologram coincide and are known to us. Thus, the location of the same diffraction order completely determines the parameters, period and orientation of the illuminated diffraction grating and allows the process of comparison with the standard. Fig. 10a shows a top view of a diffraction spectrum visualizer. In the photograph, we see three clearly distinguishable maxima, which indicates that the illumination area on the hologram has three diffraction gratings, the periods of which are determined by the distance from the center of the picture, and the angular orientations are determined by the position on the arc of the corresponding radius. Fig. 10b contains a photograph from the photodetector array 5 (see Fig. 7), the image of which is transmitted to the on-board computer for subsequent processing and comparison with reference information. The technical parameters of the control channel are shown in Table 3.
The software, in addition to conducting express control of holograms on documents, also allows you to analyze the parameters of the gratings contained in the holograms to create diffraction “maps” of holograms. In Fig. 11 shows visualizations of diffraction responses – spectra at single probing (Fig. 11a), the spectrum of a fragment of the “Eagle” hologram (Fig. 11b), the spectrum of a fragment of the “RF” hologram (Fig. 11c) and the spectrum of the entire hologram.
Conclusion
In conclusion, let us highlight the main design and software solutions implemented in the automatic diffraction comparator for express control of the authenticity of security holograms on documents. Galvanometric scanners are used in the design of the device. Their use made it possible to significantly reduce the time required to control the security hologram with the dimensions of the passport page. The use of a high-speed image sensor has also resulted in reduced inspection times. Custom components of the optical system have improved the quality of the recorded diffraction distribution patterns, which has reduced errors in authenticity control.
The absence of moving elements in the comparator, except for scanning mirrors, increased the positioning accuracy of the probe beam on the sample under study, which in turn increased the probability of correct identification of the security hologram, as well as the mechanical reliability of the device as the whole. The use of correlation filters in the recognition algorithm for information obtained from the hologram also increased the reliability of the authenticity control process.
Acknowledgments
The work was carried out at the Bauman Moscow State Technical University with the financial support of the Ministry of Education and Science of the Russian Federation under agreement No. 14.577.21.0223 (ID PRFMEFI57716X0223).
Authors
S. B. Odinokov, Doctor of Technical Sciences, Research Institute of Radio Electronics and Laser Technology BMSTU, odinokov@bmstu.ru, Moscow, Russia.
ORCID: 0000-0003-2730-9545
I. K. Tsyganov, Research Institute of Radio Electronics and Laser Technology, BMSTU, Moscow, Russia.
ORCID: 0000-0002-9538-5673
V. E. Talalaev, Research Institute of Radio Electronics and Laser Technology, BMSTU, Moscow, Russia.
ORCID: 0000-0003-4244-6898
V. V. Kolyuchkin, Candidate of Technical Science, Research Institute of Radio Electronics and Laser Technology, BMSTU, Moscow, Russia.
ORCID: 0000-0002-7294-7143
N. V. Piryutin, Research Institute of Radio Electronics and Laser Technology, Bauman MSTU, Moscow, Russia.
ORCID: 0000-0002-5493-8796
Contribution of the authors
The article was prepared based on many years of work by all members of the authors team.
Conflict of interests
The authors declare no conflicts of interests. All authors took part in writing the article and supplemented the manuscript in their part of the work.
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