FR3019426A1 - IMAGING DEVICE AND CORRESPONDING IMAGING METHOD - Google Patents

Abstract

The present invention relates to an imaging device (1) comprising: - a microwave sensor (2) configured to capture electromagnetic radiation emitted or reflected by bodies or objects, and to transform them into a first signal representative of said radiation, and a distance sensor (3) configured to determine the distance between said sensor (3) and different points, and to provide a second signal representative of said distance. The device (1) comprises a processing unit (5) receiving as input the first signal and the second signal, and configured to detect the spatial variations of the first signal for the body or objects situated at a determined distance from the distance sensor. (3). The invention also relates to a corresponding microwave imaging method, and a thermally emissive means.

Description

BACKGROUND OF THE INVENTION The present invention relates to an imaging device, and a corresponding imaging method. The present invention particularly relates to microwave imaging, and in particular radiometric imaging. The invention particularly aims to allow the automatic detection of hidden objects, including by people, reliably and easily, while respecting the privacy of said people. Such detection can especially be used in the control areas of airports, military sites or even sensitive sites that may require a search, for example prisons, nuclear power plants, etc.. The security requirements have been increased with the increase of risks, including attacks. A number of detection systems have thus been developed or are under development to meet these requirements. There are active systems that make images at distances of less than 1 meter. Such systems, for example airport gantries, use radiometry to detect any objects (metallic or not) carried by passengers, especially under clothing, with a resolution of less than 1 cm. Such systems include a high number of sensors associated with a scanning system to scan completely a person in a minimum of time and at short distances. However, such devices are bulky and can be difficult to move. Passive mobile systems are also available for imaging at distances of less than about 10 meters. Such systems are transportable and allow to view objects hidden by people under their clothing with a resolution ranging from 1 to 10 cm, or even to scan the contents of luggage left unattended. Such systems include a much smaller number of sensors than the active systems described above, and are associated with a mechanical scanning system for scanning a larger or smaller area. However, imaging devices based on microwave detection highlight the anatomical details of scanned people, which leads to ethical issues. There are thus systems in which the scanned person is represented by a figurine (or avatar) on which are reported elements detected by the system. However, in such systems, the posture of the figurine is frozen, for example standing up with arms and hands in the air, so that the scanned person must stand in the same posture as that of the figurine to allow the analysis and the correct location of the detected elements. Such a posture may involve a significant effort for some people, especially elderly or disabled, especially since it must be maintained during the scanning time of the system. Thus, some people are unable to put themselves in the imposed posture during the analysis period, thus preventing a reliable and correct detection of elements hidden by the system, making ineffective microwave detection and leading to a palpation of said people. OBJECT AND SUMMARY OF THE INVENTION The present invention aims at solving the various technical problems mentioned above. In particular, the present invention aims to provide a microwave imaging device for detecting hidden objects while preserving the privacy of people scanned by the device.

Preferably, the present invention aims to provide a device for detecting hidden objects and to represent them on a visible image of the person scanned by the device. Thus, in one aspect, there is provided an imaging device characterized in that it comprises: a microwave sensor, preferably a radiometric sensor, the microwave sensor being configured to capture electromagnetic radiation emitted or reflected by bodies or objects in a first detection zone corresponding to the detection zone of the microwave sensor, and to transform them into a first signal representative of said radiation, and - a distance sensor configured to determine, in a second detection zone corresponding to the detection zone of said distance sensor, the distance between said sensor and the different points of said second detection zone, and to provide a second signal representative of said distance. In particular, the sensors are arranged so that the first and second detection zones comprise a common detection zone. The device comprises a processing unit receiving as input the first signal and the second signal, and configured to detect the spatial variations, for example greater than a determined threshold, of the first signal for the body or objects located in the common area. , at a determined distance from the distance sensor. Thus, the combination of a microwave sensor and a distance sensor allows the device to distinguish the radiation variations resulting from the contours of the person scanned by the device, variations in radiation due to the presence of an object carried by the person scanned by the device. The distance sensor makes it possible to easily detect the contours of the person scanned by the device, and the microwave sensor makes it possible to identify the abnormal variations in radiation at the level of the person that may result from the presence of a suspicious object. The automatic detection of suspicious objects on the persons scanned by the device thus makes it possible to alert a manager without displaying the microwave image and thus the private parts of the person scanned by the device. Preferably, the microwave sensor is a radiometric sensor. A microwave sensor, and in particular a radiometric sensor, is understood to mean a sensor capable of measuring electromagnetic frequencies between 107 Hz and 1014 Hz, preferably between 109 Hz and 1013 Hz. Preferably, the distance sensor is an infrared sensor, comprising for example a transmitter and an infra-red receiver. Preferably, the device also comprises a visible sensor, for example a camera, configured to capture visible electromagnetic radiation in a third detection zone corresponding to the detection zone of the visible sensor, and to transform them into a third signal representative of said radiation. . Preferably, the first, second and third detection zones comprise a common detection zone. The processing unit is then configured to: form an image corresponding to the third signal, and superimpose, on the image corresponding to the third signal, the spatial variations of the first signal for the body or objects located in the common area , at a determined distance from the distance sensor. Preferably, the imaging device also comprises a display and the superposition of the spatial variations on the image is displayed on the display.

Preferably, the imaging device comprises means for detecting closed contours formed by spatial variations of the first signal at a determined distance from the distance sensor. Preferably, the imaging device comprises a means for comparing the contours formed by spatial variations of the first signal at a determined distance from the distance sensor, between the front face and the rear face of the body or objects located in the zone. common. The means of comparison may in particular form closed contours from the difference between two different open contours 10 of the front face and the rear face of the body or objects. Preferably, the imaging device also comprises adjustment means with elements detectable by the microwave sensor and elements detectable by the distance sensor, in order to allow correspondence between the first signal and the second signal. Preferably, the adjustment means also comprises elements detectable by the visible sensor in order to allow the correspondence between the first, second and third signals. According to another aspect, the invention also relates to a microwave imaging method, preferably radiometric, comprising: a step of acquiring electromagnetic radiation emitted or reflected by bodies or objects in a first detection zone, for delivering a first signal representative of said radiation, a step of acquiring the position of the bodies or objects in a second detection zone, for delivering a second signal representative of said position of the bodies or objects in the second detection zone. The first zone and the second detection zone comprise a common detection zone and the method also comprises a step of detecting spatial variations, for example greater than a determined threshold, of the first signal for the body or objects located in the common area at a certain position. Preferably, the position of the bodies or objects is defined by their distance to a given point. Preferably, the method also comprises a step of acquiring visible electromagnetic radiation in a third detection zone, to deliver a third signal representative of said radiation.

Preferably, the first, second and third detection zones comprise a common detection zone and the method comprises the following steps: a step of forming an image corresponding to the third signal, and an overlay step, on the image corresponding to the third signal, spatial variations of the first signal for the body or objects located in the common area at a determined position. Preferably, the method also comprises an adjustment step comprising: a step of acquisition of electromagnetic radiation emitted or reflected by first elements; a step of acquiring the position of second elements; and a step of matching. the first signal and the second signal from the radiation acquisition of the first 25 elements and the position of the second elements. The first and second elements can be the same. According to another aspect, the invention also relates to a thermally emissive means. Preferably, the emissive means comprises: an insulating frame having an open side, an electrical resistive means mounted in the frame, an electromagnetic absorption means mounted on the electrical resistive means and an infrared-transparent protective screen disposed on the 'absorption. The protective screen closes the open side of the frame, with the electrical resistive means and the electromagnetic absorption means inside.

According to another aspect, the invention also relates to a device for imaging a body or object, comprising a microwave sensor, preferably a radiometric sensor, and a thermally emissive means as described above, intended to be positioned at a distance from the microwave sensor. so that said body or object is between the emissive means and the microwave sensor. According to another aspect, the invention also relates to a method for imaging a body or object in which a thermal radiation is emitted, said body or object is positioned in front of the thermal radiation and the electromagnetic radiation emitted or transmitted by bodies or objects. BRIEF DESCRIPTION OF THE DRAWINGS The invention and its advantages will be better understood on reading the detailed description of two particular embodiments, taken as non-limiting examples and illustrated by the appended drawings in which: FIG. schematic representation of a first embodiment of an imaging device according to the invention, - Figure 2 is a schematic representation of a second embodiment of an imaging device according to the invention, - the FIG. 3 is a diagrammatic sectional view of a thermally emissive means that can be used with an imaging device according to the invention; FIG. 4 represents an exemplary flow chart of an embodiment of a method; according to the invention.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 schematically illustrates a first exemplary embodiment of an imaging device 1 according to the invention. In the first embodiment, the imaging device 1 5 comprises a microwave sensor 2, a distance sensor 3, a camera 4, a processing unit 5 and a display means 6. The microwave sensor 2 is configured to to capture the radiation emitted or reflected by bodies or objects in its detection zone which will be designated below by first detection zone. The microwave sensor 2 may be an active or passive sensor. Preferably, the microwave sensor 2 is a radiometric sensor, such as a radiometric passive sensor measuring a Gaussian noise signal corresponding to the radiation emitted by the bodies whose temperature is different from zero degrees Kelvin. Alternatively, the microwave sensor 2 may be an active sensor in which a signal is emitted towards the body, for example a noise signal, in order to increase the sensitivity and / or the accuracy of the measurement made by the microwave sensor 2 Alternatively, the microwave sensor 2 may be an active sensor in which a known periodic signal is emitted in the direction of the body and wherein the microwave sensor determines the amplitude and phase differences of the measured signal with respect to the transmitted signal. In the example described below, we consider that the microwave sensor 2 is a radiometric sensor or radiometer. The microwave sensor 2 comprises in particular an antenna for sensing the radiation of the first detection zone, and a receiver processing the radiation picked up by the antenna and delivering a first signal representative of said radiation. Optionally, microwave sensor specific optics may be provided in the imaging device between the antenna and the body or object to be scanned. The microwave sensor 2 then transmits the first signal representative of the radiation to the processing unit 5. The distance sensor 3, or depth sensor, makes it possible to determine, in its detection zone designated below by a second detection zone, the distance separating it from the different points of the second detection zone. Thus, the distance sensor 3 makes it possible to obtain an image of the second detection zone translating the distance separating each element from the second detection zone of the distance sensor 3. Such an image may for example translate into color shades, the measured distances in the second detection zone. The distance sensor 3 may for example be an infrared sensor. The infrared sensor may comprise an infra-red transmitter and an infra-red antenna to determine the distance between the distance sensor 3 and the different elements (bodies or objects) of the second detection zone: the infra-red transmitter red emits infrared radiation which is reflected by said elements of the second detection zone before being measured by the infra-red antenna. Depending on the duration or amplitude between the infra-red radiation emitted and the infra-red radiation received, the distance sensor 3 determines the distance between it and the element that reflected the infra-red. Thus, the distance sensor 3, or depth sensor, provides an image representative of the depth of the second detection zone, such as a radar for example.

The distance sensor 3 then delivers a second signal representative of said distance, and transmits it to the processing unit 5. The camera 4 is a visible sensor configured to capture electromagnetic radiation from the visible range, in its detection zone designated here. below by third detection zone. The purpose of the camera 4 is, in particular, to protect the privacy of the person being scanned, by making it possible to display, on the display means 6, the visible image picked up by the camera and not the radiometric image captured by the microwave sensor 2. The camera 4 may be a conventional camera, formed of photosensitive cells such as can be found in digital cameras. An optics may be provided in the imaging device 1, in front of the lens of the camera 4, in order to improve the optical properties thereof. The camera 4 then delivers a third signal corresponding to the visible image of the third detection zone, and transmits it to the processing unit 5. The processing unit 5 receives the first signal, the second signal and the third signal , and outputting an image by means of display 6. The image transmitted to (and displayed by) the display means 6 corresponds to the visible image captured by the camera 4, in order to preserve the intimacy of the person scanned by the imaging device 1. On the displayed image are also represented and positioned the hidden objects that have been detected by the imaging device 1. The operator can thus quickly and easily determine the type and the location of a hidden object at the origin of an alarm of the imaging device: it can thus easily check directly on the person scanned by the imaging device 1, the detected object without having to make a palpation complete. For this purpose, the processing unit 5 comprises a first means 7 for detecting the contours. The first means 7 receives as input the first signal from the microwave sensor 2 and determines the spatial variations of the microwave radiation which form a contour, in particular closed. Indeed, in the event of the presence of an object on the body of a person, said object modifies the radiation emitted by the person, which causes a spatial variation of the radiation captured by the sensor 2: the object then appears on the body. microwave image by its radiation different from that of the body of the person. The first means 7 thus makes it possible to detect the radiation gradients in the microwave image and to isolate the contours, in particular closed, having a variation greater than a determined threshold. It is thus possible to detect the presence of an object on a person, but also its shape and position on the person. The first means 7 then provides a signal to a second means 8 for determining the depth of said contours. The second means 8 is intended to verify that the variations detected by the first means take place in the same plane, and are due to the presence of an object. In fact, the first detection zone comprises several planes: there is the swept person who is in the foreground and there is the background which has a radiation different from that of the person. Thus, when the imaging device 1 scans the first detection zone, it observes both the first plane and the background. The latter having a radiation different from that of the person, the areas where the background is visible can be analyzed by the imaging device 1 as a hidden object. In order to avoid such an error, the second means 8 receives as input the signal of the first means 7 with the variation contours, and the second signal from the distance sensor 3. The second means 8 then verifies that the contours detected by the first means 7 are well at the person scanned by the imaging device 1 (foreground), and do not correspond to parts of the background visible from the imaging device 1.

Indeed, the contours detected by the first means 7 could correspond to the space between the legs of the person swept by the imaging device 1, or to the space delimited by the arms when the hands are pressed on the hips. In this case, the measured radiation variation corresponds to the passage from the first plane to the background.

Thus, the second means 8 verifies from the second signal from the distance sensor 3 that the radiation variations detected by the first means 7 correspond to elements (objects or persons) located in the same plane. If this is the case, the second means 8 transmits the signal to an insertion means 9. The second means 8 also makes it possible to verify that an unclosed contour, for example a metal belt surrounding the person to be scanned and " cutting, "on the image of the first signal, the person in two, does not correspond to the background but is indeed an object worn by the person scanned.

The insertion means 9 receives, on the one hand, the signal from the second means 8 and, on the other hand, the third signal from the camera 4. The insertion means 9 makes it possible to add to the image filmed by the camera 4 , the outlines of objects detected by the means 7 and 8. The contours of suspicious objects thus become visible on the image of the camera 4, without the intimacy of the person scanned by the imaging device 1 being shown. The insertion means 9 then provides an image with the objects detected automatically by the processing unit 5 to the display 6 to allow the display of the image by an operator. In particular, the addition of the contours of the objects detected by the processing unit facilitates the work of the operator without displaying the intimacy of the persons scanned by the imaging device 1. Thus, the distance sensor 3 allows to verify that the spatial variations of the first signal correspond to elements situated in the same plane as that of the person scanned by the imaging device 1, and not to elements of the background. Moreover, the distance sensor 3 can also make it possible to trigger the scanning of the person by the imaging device, for example when the distance sensor 3 detects the presence of a person in the zone intended for scanning. Thus, the imaging device 1 may comprise a triggering means 10 receiving as input the second signal coming from the distance sensor 3 and outputting a control signal from the imaging device 1. Alternatively, the triggering means 10 may also be used to allow the scanning of the person by the imaging device 1 only when it is at a suitable distance to allow a correct analysis of the first signal by the processing unit 5. Indeed, as the analysis of the first signal by the processing unit 5 (automatic detection of hidden objects) is based on the signals of several sensors (microwave sensor 2, distance sensor 3 and camera 4), it is important to ensure that the signals sent by these different sensors correspond to the same parts of the scanned area. Such a correspondence can be obtained for example for a certain distance between the imaging device 1 and the person to be scanned, in which case the triggering means 10 can make it possible to trigger the scanning of the person only if it is at the desired distance of the imaging device 1. Alternatively, the triggering means 10 may also provide, as a function of the distance between the imaging device 1 and the person to be scanned, correction elements making it possible to correct the difference between the detection zones of the different sensors 2, 3 can take place at such a distance. FIG. 2 represents a second embodiment of the invention in which the references identical to FIG. 1 denote the same elements. FIG. 2 represents an imaging device 1 also comprising a comparison means 11. The comparison means 11 makes it possible to refine the detection of hidden objects, by comparing the spatial variations of the first signal detected on two different scans of the same nobody.

More particularly, the imaging device 1 performs either two successive scans of the person, one face and one behind, before analysis by the processing unit 5, or includes two microwave sensors and two distance sensors, mounted next to each other. each other, to allow simultaneous scans of the front and rear of the person, before analysis by the processing unit 5. It is considered in the following description that the imaging device performs two successive scans of the person, one from the front and the back.

The imaging device 1 comprises a comparison means 11. The comparison means 11 receives the signal supplied by the second means 8 and allows, from the contours detected by the second means 8 on the front scan and on the scan of behind, to exclude false alerts and refine the detection of hidden objects.

For this purpose, the comparison means 11 reverses one of the two scans with the detected contours, then a comparison by superposition with the other scan. The overlapping of the contours makes it possible, for the contours coinciding on the two sweeps, to suppress false alerts. Thus, a person wearing loose clothing, can cause the detection of contours by the second means 8 under the arms or between the legs, that is to say where the clothes no longer cover the person. The superposition of the images by the comparison means 11 makes it possible to find the same contours on the front and back scans, and thus to detect the contours due to the clothes and not to the hidden objects. Such outlines may not be taken into account, thus avoiding false alarms. On the other hand, the contours detected on the front or back scan only, will correspond to elements present only on the front or back of the individual and may constitute hidden elements. Such contours are thus transmitted to the insertion means 9 in order to be displayed on the display means 6. Moreover, the comparison means 11 also makes it possible to consider the open contours, for example those appearing on the edge of the swept person. . By comparing the contours, it is also possible to compare the contour of the person scanned, and thus to visualize open contours that may correspond to a hidden object located on the side of the person. The comparison means 11 thus makes it possible to improve the detection of hidden objects, while avoiding false alerts. FIG. 3 represents a sectional view of a thermally emissive means 12 that can be used in combination with the imaging device 1 described above in order to calibrate said device or in order to generalize the detection described above to any type of element, in particular Objects. The thermally emissive means 12 is in the form of a plate, for example rectangular, a sectional view of which is shown in FIG. 3. The thermally emissive means 12 thus comprises an open frame 13 made of thermal insulating material, in which is placed an electrical resistive means 14. The means 14 is the source of the radiation emitted by the thermally emissive means 12, by the opening of the frame 13. In order to homogenize the radiation emitted by the thermally emissive means 12, the means 14 is disposed on a thermal conductive plate 15 for obtaining a homogeneous temperature on the opening surface of the frame 13. The thermal conductive plate 15 is disposed on an electromagnetic absorbent 16, limiting the electromagnetic reflections on the surface of the plate 15: thus obtaining a homogeneous radiation corresponding to that of the electrical resistive means 14.

Finally, a protective plate 17, transparent to the electromagnetic radiation emitted by the means 14 and the plate 15, closes the opening of the frame 13 and holds the elements 14, 15 and 16 in the frame 13.

The thermally emissive means 12 makes it possible to obtain a homogeneous emissive background, or "white noise", that can be used to calibrate the various sensors of the imaging device. Thus, the thermally emissive means 12 may be used in combination with a plate transparent to electromagnetic radiation on which are arranged geometric patterns of metal. An adjustment means is thus obtained comprising whose geometric elements are detectable both in the visible and by the microwave sensor. It is then possible to calibrate the imaging device so that the same element, detected by at least two sensors, is located at the same place on the signals of said sensors. The calibration thus makes it possible to correctly superimpose the images corresponding to the signals of the different sensors, by making the different objects of the common detection zone coincide with one another. In particular, it is possible to define the calibration of the imaging device for the different distances between said device and the person or object to be scanned. FIG. 4 represents a flowchart of an exemplary implementation of an imaging method 18 according to the invention. The imaging method 18 thus comprises a first step 19 for acquiring the electromagnetic radiation, for example with a microwave sensor, transmitted or reflected by bodies or objects located in a first detection zone, in order to obtain a first signal. In a second step 20, the method realizes an acquisition of the position of the bodies or objects located in a second detection zone, to obtain a second signal. Then, in a third step 21, the method detects spatial variations of the first signal for the body or objects located at a given position, for example at a distance to a given point. The imaging method 18 also comprises a fourth step 22 for acquiring visible electromagnetic radiation in a third detection zone. Then, in a fifth step 23, an image is formed corresponding to the visible electromagnetic radiation in the third detection zone, and in a sixth step 24, the spatial variations of the first signal for the body or bodies are superimposed on said image. or objects located at a specific position. Some of the steps 19 to 22 may be performed in a different order or at the same time, depending on the chosen embodiment. Thus, the object according to the invention makes it easy to detect hidden elements by a person, for example under his clothes, while preserving his privacy. In addition, the automatic detection facilitates the work of the operator, who can then, if necessary, only palpate the area detected by the imaging device. Finally, the various controls used make it possible to limit false detections and to improve the quality of detection of hidden objects. 20

Claims (12)

REVENDICATIONS1. Imaging device (1) characterized in that it comprises: - a microwave sensor (2), preferably radiometric, the microwave sensor (2) being configured to capture electromagnetic radiation emitted or reflected by bodies or objects in a first detection zone corresponding to the detection zone of the microwave sensor (2), and to transform them into a first signal representative of said radiation, and - a distance sensor (3) configured to determine, in a second detection zone corresponding to the detection zone of said distance sensor (3), the distance between said sensor (3) and the different points of said second detection zone, and for providing a second signal representative of said distance, in which the sensors (2, 3 ) are arranged in such a way that the first and second detection zones comprise a common detection zone and in which the device (1) co comprises a processing unit (5) receiving as input the first signal and the second signal and is configured to detect the spatial variations of the first signal for the body or objects located in the common area at a determined distance from the sensor of the first signal. distance (3). 2. The imaging device (1) according to claim 1, wherein the distance sensor (3) is an infra-red sensor, comprising for example a transmitter and an infra-red receiver. 3. An imaging device (1) according to claim 1 or 2, also comprising a visible sensor, for example a camera (4), configured to capture the electromagnetic radiation visible in a third detection zone corresponding to the sensor detection zone. visible, and to transform them into a third signal representative of said radiations. An imaging device (1) according to claim 3 wherein the first, second and third detection zones comprise a common detection zone and wherein the processing unit (5) is configured to: form an image corresponding to the third signal, and superimpose, on the image corresponding to the third signal, the spatial variations of the first signal for the body or objects located in the common area, at a determined distance from the distance sensor. An imaging device (1) according to claim 4, further comprising a display (6) and wherein the superposition of the spatial variations on the image is displayed on the display (6). An imaging device (1) according to any one of claims 1 to 5, further comprising adjustment means with elements detectable by the microwave sensor (2) and elements detectable by the distance sensor (3), to allow correspondence between the first signal and the second signal. An imaging device (1) according to claim 6 and any one of claims 3 to 5 wherein the adjusting means also comprises elements detectable by the visible sensor (4) to enable correspondence between the first, the second and the third signal. 8. Microwave imaging method (18), preferably radiometric, comprising: a step (19) for acquiring the electromagnetic radiation emitted or reflected by bodies or objects in a first detection zone, for delivering a first representative signal said radiation, - a step (20) of acquiring the position of the bodies or objects in a second detection zone, for delivering a second signal representative of said position of the bodies or objects in the second detection zone, in which the first zone and the second detection zone comprise a common detection zone and wherein the method (18) also comprises a step (21) for detecting the spatial variations of the first signal for the body or objects located in the common zone, at a certain position. 9. The method (18) of claim 8 wherein the position of the bodies or objects is defined by their distance to a specific point. The method (18) of claim 8 or 9, further comprising a step (22) for acquiring electromagnetic radiation visible in a third detection zone, for providing a third signal representative of said radiation. The method (18) of claim 10 wherein the first, second and third detection zones comprise a common detection zone and wherein the method comprises the following steps: a step (23) of forming a corresponding image at the third signal, and - a step (24) of superposition, on the image corresponding to the third signal, of the spatial variations of the first signal for the body or objects located, in the common area, at a determined position. 12. Method (18) according to any one of claims 8 to 11, also comprising an adjustment step comprising: - a step of acquisition of electromagnetic radiation emitted or reflected by first elements, - a step of acquisition of the position of second elements, and - a step of matching the first signal and the second signal from the acquisition of the radiation of the first elements and the position of the second elements.