EP2593904A1

EP2593904A1 - Multifunctional bispectral imaging method and device

Info

Publication number: EP2593904A1
Application number: EP11741667.7A
Authority: EP
Inventors: Jean-Claude Fontanella
Original assignee: Thales SA
Current assignee: Thales SA
Priority date: 2010-07-13
Filing date: 2011-07-13
Publication date: 2013-05-22
Also published as: US20130235211A1; FR2962827B1; WO2012007692A1; IL224156A; FR2962827A1

Abstract

The invention relates to a multifunctional device (2) and method for bispectral imaging, comprising acquiring a plurality of bispectral images (IBM), each bispectral image being the combination of two acquired images (I_M1, I_M2) in two different spectral bands, and generating a plurality of images, each of which gives an impression of depth by combining the two acquired images (I_M1, I_M2) and forming imaging information. The method includes simultaneously processing the plurality of bispectral images in order to generate, in addition to the imaging information, watch information and/or early threat information, comprising the following steps: searching for specific spectrum and time signatures, associated with a specific threat, in the plurality of bispectral images; and detecting a specific object in each bispectral image, and generating a time-tracking of the position of the object in the plurality of images in each spectral band, and detecting and tracking the object that forms the watch information.

Description

Multifunctional bi-spectral imaging method and device

The present invention relates to a multifunctional bi-spectral imaging method, of the type comprising a step of acquiring a plurality of bi-spectral images, each bi-spectral image being the combination of two images acquired in two different spectral bands. , and a step of generating a plurality of images each giving an impression of depth by combining the two images acquired in the two different bands, the plurality of images being an image information. The invention also relates to an imaging device implementing the imaging method.

A bi-spectral device is a device for acquiring an image in two spectral bands, for example the spectral bands 3-5 μηι and 8-12 μηι. A special case is that of bi-color devices that use two sub-bands of the same main spectral band. For example, if we consider the band between 3 and 5 μηι, some two-color infrared devices acquire an image in the sub-band of 3.4 to 4.2 μηι and another image in the sub-band of 4.5 at 5 μηι.

The invention applies to the field of optronic detection and panoramic vision systems. These systems are used in particular for the air platforms (transport aircraft, combat aircraft, drones and helicopters), maritime and land platforms (armored, troop transport ...) for surveillance and / or combat. Such platforms need a lot of information.

For example, they need to establish the tactical situation, ie to know the position of other actors (air and / or ground platforms) on a battlefield so that they can then develop a strategy. of fight.

It is also useful to have information, such as a very large field image and high resolution for example for a piloting aid or platform navigation.

Moreover on a battlefield, it is important to be able to detect what is called a threat departure and identify the type of threat, for example, a missile, a heavy weapon (cannon) or a gunshot.

All this information requires specific devices with appropriate sensors and treatment units for their acquisition.

For example, patent EP 0 759 674 describes a method for giving the impression of depth in an image, which is very useful information for the pilot of an air platform for example. The patent also discloses a camera designed to implement this method to provide an image giving the impression of depth. This camera is a bi-spectral camera that is to say adapted to provide two images in two distinct spectral bands in the infrared. The image giving the impression of depth is obtained by combining the two images acquired in the two spectral bands.

Another example: the DAIRS system for "Distributed Aperture InfraRed Systems" developed by Northrop Grumman for the "Joint Strike Fighter" (JSF) aircraft is a single-spectral imaging device, that is to say for acquire an image in a single spectral band. This system therefore delivers imagery information. Nevertheless, it does not present an impression of depth obtained by bi-spectral or two-color systems. In addition, the system is not able to detect a very brief event such as a threat start such as a shot.

In addition, there may be devices comprising several multi-spectral systems for example to provide depth imaging information or to perform a threat departure detection. Nevertheless, the multiplicity of this type of device leads especially to complexity and therefore to a cost of integration with the platform and very high equipment costs.

The object of the invention is to provide a method and an imaging device less cumbersome, easier to integrate and globally less expensive than a set of single-function devices for platforms such as surveillance or combat platforms.

To this end, the subject of the invention is an imaging method of the aforementioned type, characterized in that it comprises a step of simultaneous processing of the plurality of bi-spectral images to generate in addition to the information of imaging standby information and / or threat start information, comprising the following steps:

searching for particular spectral and temporal signatures in the plurality of bi-spectral images, a particular spectral and temporal signature being associated with a particular threat; and

detecting a particular object on each bi-spectral image, and generating a temporal tracking of the position of the object on the plurality of images in each spectral band, the detection and monitoring of the object forming the intelligence information .

According to particular embodiments, the imaging method comprises one or more of the following characteristics:

- The two bands belong to the same infrared spectral band whose wavelength is between 3 and 5 μηι and are each located on either side of a wavelength substantially equal to 4.3 μηι;

the step of acquiring a plurality of bi-spectral images is performed at a high frequency at least equal to substantially 400 Hz; the step of acquiring a plurality of bi-spectral images comprises a micro-scanning step for generating a plurality of bi-spectral images of greater resolution;

it comprises a step of combining a plurality of pixels of each bi-spectral image of greater resolution in order to reduce the number of pixels and to improve the signal-to-noise ratio before the step of searching for the particular spectral and temporal signatures in the plurality of bi-spectral images of higher resolution;

the plurality of bi-spectral images is acquired by at least two cameras previously synchronized temporally.

The subject of the invention is also an imaging device comprising at least one bi-spectral camera, each comprising a bi-spectral matrix of a plurality of detectors able to acquire a plurality of bi-spectral images, each bi-spectral image being spectral being the combination of two images acquired in two different spectral bands, the imaging device comprising means for generating a plurality of images each giving an impression of depth from the two images acquired in the two different bands, the plurality of image being an image information and the device being characterized in that it comprises means for simultaneous processing of the plurality of bi-spectral images to generate at least two pieces of information from a standby information, a start information of threat and imaging information, the means of simultaneous processing being connected to the at least one bi-spectral camera and comprising :

the means for generating the imaging information;

means for searching for particular spectral and temporal signatures in the plurality of bi-spectral images, a particular spectral and temporal signature being associated with a particular threat; and

means for detecting a particular object on each bi-spectral image and for generating a temporal tracking of the position of the object on the plurality of images in each spectral band, the detection and monitoring of the object forming the watch information.

According to particular embodiments, the imaging device comprises one or more of the following characteristics:

it is adapted to implement the preceding method. The invention will be better understood on reading the description which follows, given solely by way of example, and with reference to the drawings, in which:

FIG. 1 is a block diagram of an embodiment of an imaging device according to the invention comprising a plurality of dual-spectral cameras,

FIG. 2 is a block diagram of an embodiment of an imaging device according to the invention comprising a bi-spectral camera,

FIG. 3 is a block diagram illustrating an imaging and processing method implemented by the imaging device according to the invention,

FIG. 4 is a block diagram of a bi-spectral mega-image according to the invention,

FIG. 5 is a graph representing the short and long-range atmospheric transmission in the infrared band between 3 and 5 μηι whose central wavelength is 4.3 μηι,

FIG. 6 is a graph representing the optical flux in the infrared band whose wavelength is between 3 and 5 μηι, for a missile jet, the terrestrial background and the solar radiation,

FIGS. 7 and 8 are schematic diagrams illustrating the notions of spectral and temporal signatures of an object detected by the imaging device according to the invention,

FIG. 9 is a block diagram of another embodiment of an imaging device according to the invention comprising a bi-spectral camera,

FIG. 10 is a block diagram illustrating the principle of a micro-scanning of a bi-spectral camera, and

- Figure 1 1 is a block diagram illustrating another embodiment of the imaging method according to the invention.

The invention relates to an imaging device intended to be integrated into an aerial or land platform such as an airplane, a helicopter, a drone, an armored vehicle ... This type of platform is intended for surveillance and / or combat . It allows, day and night and in real time, the acquisition and processing of images for example to effectively coordinate the self-defense maneuvers of the platform or to help pilot the platform .

This same device is suitable to allow the provision of an operator:

an imagery information, namely an image interpretable by the man of the zone considered,

a standby information, namely an image on which potential targets and their position appear, for example men, a tank, another platform ... and - A threat departure information, namely an image on which a threat departure is clearly identified and positioned, for example a shot, a missile or cannon fire.

FIG. 1 illustrates a device 2 according to the invention which comprises at least one bi-spectral camera 4, processing means 6 and a man / machine interface such as a screen 7. The processing means 6 are connected by a part to the or each bi-spectral camera 4 and secondly to the screen. The screen is intended to display the information processed by the processing means 6.

Of course, any number of bi-spectral cameras can be envisaged, three being represented in this figure. The dual-spectral cameras 4 are identical in principle and will be described in detail later. For example, they may differ in their resolution (number of pixels of the camera detector), their focal length and the field of optics.

Each camera looks, that is to say is oriented, in a different average direction from the others. The fields of vision of each camera can be totally distinct but without having areas uncovered or have a common part to obtain and / or reconstruct an image having a continuous field of view from a camera to the other. Thus the plurality of two-color cameras covers all or part of the space.

For example, a so-called frontal camera, because placed on the front of the aerial platform such as a helicopter, is intended to image the space located in front of the platform, while two side cameras, because located on the flanks of the platform, are able to look each in a direction substantially perpendicular to that of the front camera. In addition, the front camera usually has better spatial resolution than the front cameras.

The processing means 6 comprise means 14 for shaping the signals generated by each two-color camera 4 connected to means 16 for generating a watch information, means 18 for generating a threat information and means 20 generating an imaging information for driving or navigation.

Of course, the signal generated by each camera is representative of the image acquired by it. Subsequently, a processing of an image means processing of the signal associated with the image acquired by the camera, the image being converted into a signal by the camera.

The means 14 for formatting the signals comprise means for synchronizing all the signals delivered by a plurality M of two-dimensional cameras. spectral 4 of the imaging device 2 and means for generating an image called bi-spectral mega-image and formed by combining all the bi-spectral images acquired by the cameras of the device at the same time.

The means 16 for generating a watch information comprise bi-spectral mega-image processing means able to detect and identify at least one target by its radiometric and / or spectral signature and to generate a tracking of these targets.

In known manner, a target is a hot spot, that is to say that gives off heat in relation to its environment: a person, a material, a mobile platform ...

In addition, a spectral signature of an object is the dependence with the wavelength of a set of characteristics of the electromagnetic radiation of the object, which contributes to identifying the object, for example its relative intensity of light emission. between two spectral bands, its maximum emission wavelength ...

The radiometric signature of a target is defined by the intensity radiated by it relative to its environment, known in the known manner: background of the image.

Likewise, the means 18 for generating a threat information comprise means for searching for a spectral signature representative of a possible threat in the same bi-spectral mega-image.

They also include means to search for a temporal signature of this possible threat and of discrimination of the type of threat, for example by comparison with a databank, to confirm that it is indeed a threat and what kind.

By definition, a temporal signature of a threat is the time characteristic of the issuance of the threat. For example, a shot will be much shorter than a missile jet, and can be repeated quickly (for example, a burst of light weapons).

The means 20 for generating an imaging information for driving or navigation comprises means for generating an image with a depth impression as described in patent EP 0 759 674.

The dual-spectral cameras 4 will now be detailed next to the figure

2 which illustrates an imaging device 2 having only one camera so as not to overload the figure.

The dual-spectral camera 4 is a wide-field camera for covering part of the space to be analyzed. It comprises at least one large-field optical system 8 and a detector 10. Such a camera is for example described in patent EP 0 759 674. Such a wide-field optical system 8 has already been described, for example, in patent FR 2,692,369. Preferably, the field of optics 8 is substantially between 60 ° and 90 °.

The detector 10 is a bi-spectral detector for example as described in patent EP 0 759 674, which comprises a bi-spectral matrix, for example of multi-quantum well or super-array type, in particular for delivering signals in two directions. sub-bands of the same spectral band or in two different spectral bands. In the first case, the detector is said to be two-color. The size of the bi-spectral matrix is substantially at least 640 pixels x 480 pixels.

Preferably, the dimensions of the matrix are 1000 × 1000 pixels corresponding to an elementary field of 1.57 mrad or 500 × 500 pixels corresponding to an elementary field of 3.14 mrad.

In addition, the acquisition frequency of the dual-spectral camera 4 is high and preferably at least 400 Hz.

The camera simultaneously acquires two images of the same field of view of space: one in each spectral band.

For this, the optic 8 focuses the luminous flux on the bi-spectral detector 10 which converts it into an electrical signal transmitted to the processing means 6.

Moreover, the two spectral bands in which the bi-spectral camera 2 is sensitive are such that they have particular characteristics, in particular as regards the electromagnetic emission of the missile jets and the variation of the atmospheric transmission according to of the distance.

For example and preferably, the spectral band is located in the infrared and its wavelength is between 3 and 5 μηι. The two sub-bands are located on either side of a wavelength substantially equal to 4.3 μηι. The first sub-band has a wavelength substantially between 3.4 and 4.2 μηι and the second a wavelength substantially between 4.5 and 5 μηι.

In a known manner, the red or hot band is defined as the spectral subband whose wavelengths are the greatest compared with those of the second spectral subband, called the blue or cold band.

The imaging device according to the invention implements the imaging method 100 which will now be described with reference to FIG.

Each bi-spectral camera 4 of the imaging device 2 acquires a plurality of bi-spectral images denoted IB _M where M is the number of the camera during a step 102 of acquisition of a plurality of bi images. -spectrals of the process 100. The acquisition is performed at the high frequency F, preferably substantially equal to 400 Hz.

Each image of a sub-band l _M i, IM 2 has a dimension of L pixels x H pixels (the dimensions of the bi-spectral matrix of the camera), ie N pixels in total (N = LxH).

Each pair of images I _M i, IM 2 is then combined to form a bi-spectral image IB _M of 2xLxH, for example by juxtaposing them.

In known manner, the M cameras (for M≥ 1) are synchronized by construction before the acquisition of bi-spectral images. For example, they use a common clock.

Next, these means 14 combine the M bi-spectral images of the cameras to form a bi-spectral megapixel MIB during a step 106 of generating a bi-spectral mega-image.

For example, the bi-spectral mega-image MIB is generated by juxtaposing the bi-spectral images IB _M of each camera, as shown in FIG. 4.

Thus, a plurality of bi-spectral mega-images is obtained at the same frequency F of acquisition of the images by the cameras.

Each bi-spectral megapixel MIB has a dimension of 2xMxN pixels where N is the total number of pixels of an image in a band of a camera (N = LxH).

This plurality of bi-spectral mega-images forms a single signal at the frequency F.

This is exploited by the processing means 16, 18, 20 simultaneously to generate at least two pieces of information from imaging, watch and threat starting information during steps 108, 1 10, 1 12 respectively.

The step 108 of generating an imaging information implemented by the means 20 for generating a control information will now be detailed.

The imaging information includes a mega-image of high spatial resolution formed from the images of each camera having a resolution of 1000 pixels x 1000 pixels.

This step 108 comprises a sub-step 1 14 for generating a mega-image having a depth impression by combining the images acquired in the red band and the blue band.

A measurement of the distance of the objects present in the image is performed as described in patent EP 0 759 674 by comparing the image obtained in each band. The exploitation of the bi-spectral images for the evaluation of the distance is unchanged compared to that described in this document. The red band is chosen to be partially absorbed. In the case of the band 3-5 μηι, for a natural object (black body or solar reflection) the blue band is little absorbed by the carbon dioxide, while the red band undergoes a variable effect with the distance. The comparison of the signals of the two bands makes it possible to estimate the distance.

The ratio of the intensity of each pixel of the image in the red band and the blue band is calculated. The ratio is a function of the atmospheric transmission which is a function of the distance of the object imaged on the pixel. FIG. 5 is an example of atmospheric transmission, in the spectral bands situated on either side of 4.5 μηι between 3 and 5 μηι, for two different distances.

Then during a step 1 16 an image is displayed by the screen 7. This image is either the image having a depth impression resulting from the step 108, or the image of one or the other band depending on weather conditions.

Indeed, it is known that in cold climates the image acquired in the red band, for example of wavelengths greater than 4.5 μηι, is generally better than that acquired in the blue band of wavelengths per second. examples below 4.5 μηι.

The step 1 of generating a watch information implemented by the means 16 for generating a watch information will now be detailed.

The watch is to search for and detect targets and track them, that is to say, track their movement by measuring their position over time.

In known manner the objects or targets to be monitored are almost punctual in the images and evolve relatively slowly over time.

Therefore a radiometric contrast is fundamental on the images in order to detect a target and to deduce the information of standby, that is why we use preferably bi-spectral images of minimum dimensions 1000 pixels x 1000 pixels produced by the ( or the camera (s).

Step 1 comprises a sub-step 1 17 for detecting a radiometric contrast by the means 16 for generating a watch information. During this sub-step, the intensity of each pixel is compared to the intensity of a pixel representative of the background of the image, that is to say of a normal environment. The pixels representative of a possible target have an intensity different from that of the background for at least one of the two bands.

Then, during a step 1 18, the means 16 for generating a watch information identify the target (s) by their respective spectral signature, comparing the images produced in each of the bands.

For this, the intensities of the pixels are compared in the two bands pixel by pixel or group of pixels per group of pixels. This comparison allows example to evaluate the apparent temperature of the target and thus to deduce a class of object (man, tank ...).

For example, an object whose radiation in both bands follows the laws of the black body is probably a natural object.

Then, a tracking of each target is generated during a step 120, that is to say a tracking of the position of the target. The track is performed on at least a plurality of images acquired in the same band.

For example, a target may be detected in a so-called "sensitive band" band but not in the other, then called "blind band". This non-detection in the blind band and the value of the light intensity emitted by the target in the sensitive band form identification elements of the target.

To estimate the radiation in the blind band, the detections made in the sensitive band are then used to identify the pixels of the blind band where the target is located and thereby obtain the spectral signature information in that band.

In addition, the tracking of targets generated in each band is complementary.

For example, a target is detected in the first band during a first period T1 and then in the second band in a second period T2 consecutive to T1. In this case the track is preferably made in the first band during T1, then in the second for the period T2.

Then, the step 1 12 of generating a threat information implemented by the means 18 for generating threat information is executed in order to establish whether the target is a threat. This step 1 12 will now be detailed.

A threat departure information includes the detection of the departure of this threat, that is to say a fugitive emission or having a temporal signature characteristic of a type of threat (related to the propulsion of this threat). To generate this information it is preponderant to have both a radiometric sensitivity and a high temporal response.

Thus, the processing for generating threat start information is performed on images of dimensions at least equal to 500 pixels × 500 pixels and delivered at a rate of at least 400 Hz.

Step 1 12 comprises a substep 122 for searching for a signature or radiometric contrast and then for a spectral signature followed by a sub-step 124 for searching for a temporal signature and for discriminating the type of threat. As previously described, an intensity different from that of the background for a pixel is a radiometric signature and is associated with a possible threat. In the case of a flame or a jet, the intensity is stronger than that of the bottom. During sub-step 122, the images from the two Sr and blue Sb red bands are combined to distinguish the threats from the bright points caused by the solar reflections by comparing the radiation in the two subbands.

With reference to FIGS. 6 and 7, each Sr, Sb image in the infrared spectral band between 3 and 5 μηι is the result of the light emission of three contributions: the terrestrial background, the solar radiation and the missile jet if a missile is fired or the jet of mouth if ammunition is fired.

The purpose of combining the two images Sr and Sb is to cancel the contribution of the natural background in the two subbands.

For this and in a known manner, for each pixel a quantity S is calculated according to the formula S = Sr - A.Sb by adjusting the parameter A. The parameter A is generally chosen for all the pixels of the image.

A positive signal S highlights a missile jet or a jet of mouth. A negative S signal corresponds to a solar reflection and a null signal to the terrestrial background.

An advantage of this method is that the probability of false alarm for missile detection is decreased compared to the use of single-spectral camera. Indeed, the combination of these bands makes it possible to get rid of solar reflections and distinguish the emission of the missile from natural sources, unlike a single-spectral imaging system. For such a mono-spectral device, it is easy to detect the "hot" pixels that is to say having a strong intensity, nevertheless it is difficult to differentiate if they are associated with a threat departure or a reflection solar on a surface.

It also helps to determine the direction of potential threats.

Then, during step 124 and with respect to FIG. 8, the luminous intensity of these pixels, identified as possible threats, is tracked over time in one or both bands. The temporal profile of the luminous intensity then makes it possible to discriminate the type of threat, by what is called their temporal signature.

For example, a shot has a very short emission, of the order of a millisecond, compared to the missiles which are thus detected by the emission of their jet or flame whose emission is long, of the order of several seconds.

In addition, tracking can be performed as in step 120 to track the threat. For example, to track the movement of a missile.

Standby and threat information is then displayed on screen 7.

For example, the threat is indicated on the image having a depth impression made in step 1 14 and displayed on the screen in step 7. In addition, the track of a target is displayed by overlay on this same image. According to a second embodiment of the imaging device 2 shown in FIG. 9, the detector of the or each bi-spectral camera 4 has a minimum dimension of 500 pixels × 500 pixels. In a known manner, this device makes it possible to improve the image intended for observation to the detriment of the temporal resolution.

In addition, the dual-spectral camera 4 comprises a micro-scanning system 12, such as for example that described in patent EP 0 759 674.

The microsweep is performed on a plurality k of consecutive positions and preferably on at least 4 positions.

For example, the micro-scanning system is of the diasporameter type.

With reference to FIG. 10, an example of a four-position micro-scan is illustrated by the displacement in four successive positions denoted Im T1 to Im T4 of the image of a point object on four adjacent pixels denoted P1 to P4 of the detector. 10.

For example, a bi-spectral matrix of dimensions of 500 pixels × 500 pixels and 400 Hz acquisition frequency then generates 400 frames per second, each of dimensions 500 pixels × 500 pixels. An image comprises the four consecutive bi-spectral fields generated by the micro-scan.

It is known that a micro-scanning device makes it possible to generate additional pixels and thus to improve the sampling of the image and to increase its resolution.

Thus, each bi-spectral image reconstructed after a micro-scan has a size of 1000 pixels x 1000 pixels x 2 spectral bands.

In addition and in a manner also known, the micro-scan makes it possible to perform non-uniformity corrections (NUC).

With reference to FIG. 11, another embodiment of the method will now be detailed. This embodiment is intended to be implemented by an imaging device comprising a micro-scanning device as shown in FIG. 9. The steps identical to the previous embodiment bear the same reference and will not be detailed here. -after.

The step 102 of acquiring a plurality of bi-spectral images by M cameras comprises a sub-step 130 of micro-scanning in a plurality k of positions of the detector pixels. Thus, the optical flux sweeps each pixel of the array of the detector in a plurality k of positions through the micro-scan system 12. Preferably, k is equal to 4.

The k positions of the scanning of the optical flux thus generate k frames shifted on the matrix of photodetectors forming an image. At the end of step 102, a plurality of bi-spectral images of k two-color frames are generated at the frequency F.

Each frame of a strip has dimensions of at least 500 pixels x 500 pixels.

Then the images resulting from the microsweep and the two spectral bands are treated in different ways according to the information to be generated.

The imaging information generation step 108 comprises a sub-step 132 of combining two successive two-color mega-images before generating in step 1 an image having an impression of depth. This sub-step 132 is executed by means of combining a plurality of two-color mega-images of the processing means 6 of the imaging device 2.

Thus the pixels of k successive frames of an image are combined in order to generate an oversampled image thus having a better resolution. This image is then produced at a slower frequency.

For example, an imaging device having a two-color camera whose matrix has a dimension of 500 pixels × 500 pixels, an acquisition frequency of 400 Hz and comprising a 4-position micro-scanning device will make it possible to generate images. in each spectral band of resolution 1000 pixels x 1000 pixels at the frequency of 100 Hz.

This temporal resolution is sufficient to display imaging information for example for flight aid that requires a temporal resolution at least equal to that of the human visual system.

Similarly, the step 1 of generating a standby information comprises a substep 134 identical to the substep 132 before carrying out the steps 11 and 18 for detecting a radiometric contrast and identification. of targets by spectral signature.

According to one variant, these sub-steps are common and implemented by common means of processing the plurality of bi-spectral mega-images at means 16 and 20 in order to reduce the processing time of the images.

Finally, the step 1 12 for generating a threat information comprises a substep 136 of summation of k adjacent pixels for each bi-spectral mega-image before carrying out the step 122 of searching for a radiometric contrast and spectral signature.

This sub-step 136 is intended to improve the spatial resolution of the images. It is performed by calculation means integrated in the processing means 6 of the imaging device 2. Indeed, the micro-scanning dilutes the signal caused by the emission of a point object. For example, in FIG. 3, during the acquisition of the image Im T4, the signal is shared between the 4 pixels P1, P2, P3 and P4.

In order to avoid this effect, the signals of 4 adjacent pixels are summed for each image of the same frame, the set of 4 pixels seeing at each instant almost the entire signal emitted by a point.

In the preceding example, a plurality of 400 Hz images of bi-spectral fields are generated, the image of which in a strip is 500 pixels × 500 pixels. Thus the spatial resolution of an image is decreased by 2, but at least one of the pixels contains the entire signal.

The spectral signature search step 122 is then performed on this frame.

In this embodiment of the method, the images or signals generated during the micro-scanning step are exploited differently and optimally according to the information sought.

The method according to the invention thus makes it possible to generate, simultaneously and by the same device, at least two of:

- Very large field imaging information useful for navigation, steering ...,

- a watch information, and

- information of detection of departure of threats (shots, missile, gun ...).

An advantage of a multi-function imaging system according to the invention is the reduction of the number of detectors and means necessary to perform all the functions considered and thus the cost reduction of the entire system and the reduction of costs. integration with a platform.

Other advantages are better performance of functions performed by dual-spectral cameras compared to single-spectral cameras, improved discrimination for watch and threat detection functions and a useful relief / depth impression in images. for piloting or navigation.

The invention is not limited to the embodiments described and shown, in particular it can be extended to other bands of the infrared band or other spectral bands, for example in the 8-12 μηι band.

Claims

1. - Imaging process (100) comprising a step (102) for acquiring a plurality of bi-spectral images (IB _M ), each bi-spectral image being the combination of two acquired images (I _M i, in two different spectral bands, and a step (108) of generating a plurality of images each giving an impression of depth by combining the two images acquired in the two different bands, the plurality of images being an image information, the method being characterized in that it comprises a step of simultaneous processing of the plurality of bi-spectral images for generating, in addition to the imagery information, a watch information and / or a threat departure information, comprising the following steps:

searching for (1 12) particular spectral and temporal signatures in the plurality of bi-spectral images, a particular spectral and temporal signature being associated with a particular threat; and

detecting (1 10) a particular object on each bi-spectral image, and generating a temporal tracking of the position of the object on the plurality of images in each spectral band, the detection and tracking of the object forming the information.

2. - Method according to claim 1, characterized in that the two bands belong to the same infrared spectral band whose wavelength is between 3 and 5 μηι and are each located on either side of a length wave substantially equal to 4.3 μηι.

3. - Method according to any one of claims 1 to 2, characterized in that the step (102) of acquisition of a plurality of bi-spectral images is performed at a high frequency at least equal to substantially 400 Hz.

4. - Method according to any one of claims 1 to 3, characterized in that the step (102) for acquiring a plurality of bi-spectral images comprises a step (130) of micro-scanning to generate a plurality of bi-spectral images of greater resolution.

5. - Method according to claim 4, characterized in that it comprises a step (132, 134) of combining a plurality of pixels of each bi-spectral image of greater resolution to reduce the number of pixels and improve the signal-to-noise ratio before the step (122, 124) of searching for particular spectral and temporal signatures in the plurality of bi-spectral images of higher resolution.

6. - Method according to any one of claims 1 to 5, characterized in that the plurality of bi-spectral images is acquired by at least two cameras previously synchronized temporally.

7. - Imaging device (2) comprising at least one bi-spectral camera (4), each comprising a bi-spectral matrix (10) of a plurality of detectors (10) capable of acquiring a plurality of bi-spectral images -spectrales, each bi-spectral image being the combination of two images acquired in two different spectral bands, the imaging device comprising means (20) for generating a plurality of images each giving an impression of depth from the two images acquired in the two different bands, the plurality of images being an image information and the device being characterized in that it comprises means (6) for simultaneous processing of the plurality of bi-spectral images to generate at least two information among a watch information, a threat start information and an imaging information, the means (6) for simultaneous processing being connected to the at least one bi-spectral camera (4) and comprising t:

the means (20) for generating the imaging information;

means (18) for finding particular spectral and temporal signatures in the plurality of bi-spectral images, a particular spectral and temporal signature being associated with a particular threat; and

means (16) for detecting a particular object on each bi-spectral image and for generating a temporal tracking of the position of the object on the plurality of images in each spectral band, detection and monitoring of the object forming the watch information.

8. - An imaging device according to claim 7, characterized in that the two bands belong to the same infrared spectral band whose wavelength is between 3 and 5 μηι and are located on both sides of a wavelength substantially equal to 4.3 μηι.

9. - Imaging device according to claim 7 or 8, characterized in that it is adapted to implement the method according to any one of claims 1 to 6.