WO2000037875A1

WO2000037875A1 - Aiming aid method and system for a light weapon

Info

Publication number: WO2000037875A1
Application number: PCT/FR1999/003185
Authority: WO
Inventors: Philippe Valery
Original assignee: Thomson-Csf Sextant
Priority date: 1998-12-18
Filing date: 1999-12-17
Publication date: 2000-06-29
Also published as: CA2354569A1; CA2354569C; EP1141648A1; FR2787566A1; FR2787566B1

Abstract

The invention concerns an aiming aid method and a system (1) for a light weapon (2) hand-held by the shooter. The system comprises a first imaging sensor (C1), called narrow-field sensor, fixed on the weapon (20) barrel (2) and whereof the optical axis (ΔC1) is structurally harmonised with the sighting axis (Δ20) and a second imaging sensor (C1), called wide-field sensor, fitted on the shooter's head (Te). Each of said sensors (C1, C2) is associated with devices (5, 6) measuring the lie and the bearing, so as to make a first rough estimate of the variation between the two optical axes (ΔC1, ΔC2) by calculating the matrix of rotation and the estimated variation between the sensors (C1, C2). Using said matrix and the fields, an image processing device (3) establishes the correlation between the images, so as to display a reticle in a visual display unit of the headgear (4) to represent physically the sighting axis.

Description

SIGHTING AID METHOD AND SYSTEM FOR LIGHT WEAPON

The present invention relates to a sighting aid method for a light weapon, more precisely a sighting aid method for a shooter carrying such a weapon in his hand.

The invention also relates to a sighting aid system for implementing such a method.

It is well known, to obtain a very precise shot with a light weapon, that is to say in the context of the invention a portable weapon, to provide it with a telescopic sight. This scope can also be coupled to a light intensifier, which allows night shooting.

However, this arrangement requires a shoulder of the weapon, or even requires having a stable support. The shooting can then be precise, but the aiming requires in this case a significant time.

However, in many situations, the shooter must be able to react very quickly and, therefore, must be able to use his weapon without supporting it, while ensuring a precise shot.

To do this, it has been proposed, for example, to provide the weapon with a laser pointer, that is to say with a collimated beam generator propagating parallel to the firing axis of the weapon or line of sight. The impact on the target results in a small diameter spot of light. The wavelength used can also be in the non-visible range, for example in the infrared. The shooter is therefore no longer obliged to support his weapon. It is enough that it locates the position of the spot, either directly (visible range), or using special glasses (infrared), to obtain a good aim. However, in all cases, the major shortcoming of this process is the lack of discretion. Indeed, the target can detect the radiation, either directly (at sight, for wavelengths in the visible), or using a detector appropriate to the wavelength used. On the other hand, the accuracy is limited by the visual discrimination of the spot, the dispersion of the beam and the limit of visual perception of the shooter.

The invention aims to remedy the shortcomings of the methods and devices of the known art, some of which have just been mentioned. It makes it possible to obtain a rapid fire, not requiring to support the weapon, and however precise, which appears contradictory a priori. It also ensures an aiming process not detectable by the opponent. In other words, the system remains entirely passive, that is to say does not generate radiated energy.

Taking into account the distances of use of the system according to the invention (typically in a range of distances greater than 25 m and less than 100 m), and the typical dimension of the targets (1.5 m according to the vertical dimension and 0, 5 m depending on the horizontal dimension), it is necessary to offer the shooter an accuracy better than 2.5 mrad on the direction of the barrel of his weapon, and this by a measuring device ensuring complete discretion, as he just to be called back.

To do this, the method according to the invention comprises the determination of the position of the line of sight of the weapon by correlation of images and the restitution of a symbol of sight (for example a reticle materializing the line of sight) on a display member, advantageously of the helmet type, visual type of helmet. The symbol can be displayed in an infinite collimated form. It can be superimposed on the scene observed by the shooter, in direct vision or through a camera. To determine the position of the line of sight, correlates an image obtained from a sensor carried by the gun and an image obtained from a sensor carried by the shooter's head. The spatial orientation data of the two sensors are identified with respect to each other by auxiliary means and are used to estimate the deviations in orientation between the two images in order to facilitate the correlation of the images. The correlation of the images makes it possible to determine in the second image the position of the first image. We can then determine the position in the second image of a reticle representing the line of sight of the weapon which carries the first sensor. The reticle thus determined by calculation is displayed on a display secured to the shooter's head and therefore to the sensor of the second image. It is displayed at a position corresponding to its place in the second image, and it is displayed superimposed on the scene observed by the shooter. The shooter can then point his weapon at a target by aligning the reticle on this target without having to shoulder the weapon.

The first sensor is preferably at a reduced field than the second sensor.

The system for implementing the method essentially comprises a first image sensor fixed on the weapon, a second image sensor fixed on the shooter's head, electronic image processing circuits making it possible to calculate the position of the field of the first sensor in the image of the second sensor, and a display device collimated to infinity making it possible to embed in the field of vision of the shooter a reticle or a similar symbol materializing the line of sight of the weapon. The set is completed by orientation sensors, independent of the image sensors, fixed respectively on the weapon and on the shooter's head, allowing an estimate (preferably continuous over time) of the deviations of orientation of the fields. aiming of the first and second image sensors to assist in determining the position of the field of the first sensor in the image of the second. The signals from these orientation sensors are also processed by the aforementioned electronic circuits.

The subject of the invention is therefore a method of assisting aiming for a light weapon carried by a shooter, characterized in that it comprises the following steps:

- the acquisition of a first image using a first image sensor, associated with a first field and fixed to said weapon, the optical axis of which is mechanically linked to the axis of the barrel of the weapon; said first image representing a front scene, seen from said cannon;

- the acquisition of a second image using a second image sensor, associated with a second field and carried by the head of said shooter, so as to encompass all or part of a front scene observed by that -this and likely to contain a target;

- The acquisition by orientation sensors carried respectively by the weapon and by the gunner's head, of an estimate of the angular differences between the field observed by the gunner and the field seen by the sensor carried by the weapon; - the correlation of the images of the two sensors to determine the position of the field seen by the first image sensor in the field seen by the second sensor, and to determine in particular the position in the image of the second sensor of a point of the first image representing the line of sight of the weapon, the correlation using the angular deviation determined previously;

- the display on a helmet display, at a corresponding position, of a symbol representing this line of sight. The symbol is preferably collimated to infinity. It is preferably superimposed on the scene observed in direct vision, but it can also be envisaged that it is superimposed on an image supplied by the second sensor or by another camera carried by the shooter's head. The orientation sensors can be of the magnetometric type, with for example a heading sensor and a two-axis inclinometer, these sensors being provided on the one hand on the shooter's head and on the other hand on the weapon.

Correlation is facilitated in particular in an acquisition phase where an image portion of the second sensor must coincide with the image of the first sensor. The orientation sensors indeed make it possible to develop a rotation matrix making it possible to rotate the two images relative to one another by an amount corresponding to the indication (approximate) given by the orientation sensors . The images are then found to be substantially identically oriented and the correlation can be continued more easily. In the subsequent phases of tracking, the correlation of images is the main element used to move the crosshair in the field of the display.

One determines in particular from the indications of the two orientation sensors a rotation matrix representing the relative positions in space of two reference trihedra linked one to the weapon, the other to the head. One can also, to help with the correlation, use a vector of translation, limited a priori to approximately 50 cm, representing the difference in position between the head and the weapon.

The invention also relates to a sighting aid system for the implementation of this method.

The invention will be better understood and other characteristics and advantages will appear on reading the description which follows with reference to the appended figures, among which:

- Figures 1A and 1B schematically illustrate the architecture of an aiming aid system according to the invention; - Figure 2 is a geometric diagram to explain the general operation of the system of Figures 1A and 1B;

- Figure 3 illustrates an example of a modular signal and image processing device used in the aiming assistance system of the invention;

- Figure 4 illustrates the nesting of images provided by imaging sensors used in the aiming aid system of the invention; - Figure 5 is a more detailed embodiment of one of the modules of the device of Figure 3;

- Figures 6A and 6B schematically illustrate one of the steps of the method according to the invention;

Figure 7 is a more detailed embodiment of a correlation module used in the device of Figure 3;

- And Figure 8 is a diagram illustrating the last step of the method according to the invention, consisting of a so-called fine correlation.

We will now, to explain the aiming method according to the invention, describe an exemplary embodiment of aiming system architecture 1 implementing it, with reference to FIGS. 1A and 1B. Figure 1A schematically illustrates _. its overall architecture and FIG. 1B is a detail figure showing one of the components used, in this case a display device 4, advantageously of the so-called visual helmet type.

The system 1 firstly comprises a sensor with imagery C in the visible or infrared domain, fixed on the weapon 2. In the first case (visible light), it is possible to use a standard matrix sensor, or a "IL-CCD" type component (light intensifier with charge coupled device). In the second case, we can use a component of the type "M IR" (Medium Wave Infrared: infrared in the wavelength ranges between 3 and 5 μm) or LWIR (Long Wave Infrared: infrared in the wavelength ranges between 8 and 12 μm). The direction of the optical axis, Δci _r of the sensor Ci is harmonized, by construction, with the axis, Δ _20. of the barrel 20. If this is not the case, it is taken into account in the calculations.

A device for measuring the position of the center of the field of the imaging sensor C of the weapon 2 is provided. This device is composed of a second imaging sensor C2 fixed on the shooter's head and of an electronic processing device. of signals and images 3 supplied by the sensor C ₂ , this device 3 having in particular the function of calculating the position of the field of the sensor Ci in the image of the sensor C2. In fact, the field of the sensor C is advantageously chosen to be smaller than the field of the sensor 2 •

The system 1 also includes an infinitely collimated rendering device 4 making it possible to embed in the shooter's field of vision a reticle 41, or any other suitable symbol, materializing the aim. This device is advantageously constituted by a display member of the so-called visual helmet type.

Finally, there is a device made up of two devices, 5 and 6, which are orientation sensors making it possible, by combining the information which they deliver, to determine the difference between the orientation of the weapon and the orientation of the head. The simplest is to provide that each of the orientation sensors comprises two sensors: a heading sensor and a two-axis inclinometer (not shown separately). These devices, 5 and 6, which generate heading and attitude data, are fixed, respectively, on the weapon 2 and on the shooter's head Te in order to give a continuous preference estimate of the orientation deviation of the two aiming axes, Δi and Δ ₂ , sensors C and C2. These sensors are independent of the image sensors. This double device, 5 and 6, provides, in cooperation with specific circuits of the electronic signal and image processing device 3, an estimate of the rotation matrix MR of passage between the sensor Ci and the sensor 2. The vector translation T is not known. Knowing that the weapon is held by the shooter, we can estimate the standard of T at an average value of 0.7 meters and an upper limit of 1 meter. The weapon can for example be held at the hip.

The electronic signal and image processing device 3 receives the signals generated at the output of the imaging sensor C and of the sensors 6, fixed on the head Te of the shooter, via the link 60, and receives the signals generated at the output of the sensor with C2 imagery and sensors 5, carried by the weapon 2, via the link 50. The device 3 transmits as output the signals processed for display on the visual display member of the helmet 4 (in the example described), thus than the power supply necessary for the proper functioning of this organ.

FIG. 1B illustrates the display member 4 in front view, that is to say on the side observed by the shooter. It allows to embed in the front scene 40, actually observed by the shooter, a reticle 41 materializing the targeted target, or other indications, for example an arrow indicating which side he must turn the weapon 2, for a period initial aiming process, as shown below. The image provided by the wide field sensor 2 encompasses all or part of the scene observed by the shooter.

FIG. 2 is a geometric diagram illustrating the relationships existing between a reference trihedron Rc2 associated with the devices carried by the shooter's head Te, and in particular with the sensor 2, and a reference trihedron TRci associated with the devices carried by the weapon 2, and in particular to sensor C. We have represented on this diagram, the translation vector T and we have superimposed on the reference trihedron TRC1 a reference trihedron TR 'C2 (in dotted lines), representing the reference trihedron TRC2, after translation according to the vector T. This superposition allows to calculate the rotation matrix MR.

The aiming process includes two initial steps, carried out using the two positioning sensor devices 5 and 6.

The first step, which will be called "automatic rallying", consists in using the signals generated by the orientation sensors 5 and 6, on the weapon 2 and on the gunner's head Te, to help the gunner to point his weapon in the same direction as his head. This is done by the signal and image processing device 3. The processed signals include heading and tilt information of the reference frames, T-Ci and T.RC2, linked to the sensors, Ci and C2 with respect to a landmark - At the output, the processing device 3 generates signals making it possible to estimate the difference in orientation of the fields of sight of the sensors, and C2, at least in direction and direction. These signals are transmitted to the display member 4, so as to display a specific symbol on the screen, for example an arrow 42, in place of the reticle 41 materializing the aim. The shooter then knows that he must move the barrel of his weapon 2, in the general direction symbolized by the arrow 42, so that the reticle 41 symbolizing the aim enters his field of vision and is displayed on the screen. of the display unit. It is therefore an automatic aid, very coarse, to obtain an approximate score of weapon 2, so that the stages of the aid to the aiming process itself can begin. However, an approximate initial score can be performed manually, without the assistance of any symbology. The second initial step consists in calculating an estimate of the aforementioned rotation matrix MR, still using the data provided by the two orientation sensors, 5 and 6. This estimate of the rotation matrix MR is obtained by comparing the data (attitude and heading) provided by the two devices, 5 and 6, and possibly using the estimate of the translation vector T.

Once this or these initial steps have been performed, the correlation of the images is performed using the rotation matrix to facilitate the acquisition of identical image areas in the images supplied by the two image sensors; by rotating the image of the first sensor of angles defined by the rotation matrix, the images of the two sensors are given substantially the same orientation, which facilitates correlation.

This correlation will then make it possible to determine in the field of the head sensor what is the position of the line of sight, this being represented by a well determined point (for example a central point) of the field of the weapon sensor Cl and the field of the weapon sensor being located, by correlation, in the field of the head sensor.

It is therefore possible to display on the screen of the display member 4 a reticle 41 materializing the aiming and being embedded in the scene 40 observed by the shooter, and therefore superimposed on the target that he wishes to reach, since the reticle 41 will move in synchronism with the movements of weapon 2 (tracking phase after the acquisition phase of the correlation operation).

The electronic circuits of the device 3 can be cut into modules for the execution of the various necessary steps.

FIG. 3 illustrates the modular configuration of an image processing device 3 for the implementation of the aiming method, according to a preferred embodiment of the invention. The circuits allowing the execution of the above-mentioned initial step or steps have not been shown.

In the following, a certain number of conventions concerning signals and other parameters used by the method of the invention will be respected. These conventions are listed in the "TABLE OF NOTATIONS" appended at the end of this description.

The device 3 comprises two analog / digital acquisition modules, 30 and 34, respectively for the channels for acquiring the output signals of the sensors Ci and C2.

The output signals of the analog / digital acquisition modules, 30 and 34, are transmitted to modules for extracting contours of homogeneous zones, or objects, contained in the digital images, modules 31 and 35, respectively.

A module 32 then calculates the pyramid of contours of the image supplied by the small field sensor Ci, after extraction of the contours.

Similarly, the signals at the output of the module 35 are transmitted to a first module 36 for establishing the images of the distances to the contours of the wide field image, followed by a module 37 for establishing the pyramid of images called " chamfer ", that is, distances to the nearest contour.

Finally a double correlation module called "Gros-Fin" 33, receives the output signals from modules 32 and 37, as well as gradient signals supplied by the contour extraction module 35, and, supplied by the respective modules 30 and 34 for acquiring image signals, iP and iG, the definition of which is given in the aforementioned rating table. The calculations performed by the so-called "Big" part of the correlation module 33 are based on a valued correlation type algorithm.

The calculations carried out by the so-called "End" part are based on an algorithm for estimating the positioning difference between the center of the image of the small field sensor Ci and the center of the positioning zone F ^G in the image. large field of the sensor C _∑ , calculated by the "large" module.

The different modules making up the device 3 will now be detailed.

Once the model and type of sensors, Ci and C2, are selected, the respective fields of these sensors are known. These are data supplied by the manufacturer, as well as other associated characteristics: resolution, etc.

The analog / digital conversion of the image signals generated by the sensors C and C2, conversion carried out in the modules 30 and 34, is ensured synchronously by a conventional image scanning device, on a typical dynamic of 28 levels of Grey.

The estimation of the rotation matrix MR, and its application to the images from the sensor, as well as the knowledge of the fields of the sensors, i and C2, makes it possible to construct, by a spatial resampling processing, from the digitized image from the small field sensor i two derived images iP and I 'P of axes parallel to the axes of the image iG _r assuming that it is rectangular, or more generally of an orthonormal reference frame linked to that -this. These images, i and I 'P, are such that the following relation is satisfied:

C∑G ≈ QxciP (1),

with Q whole number, and ClG = CI 'P (1 bis),

with CJ ^G , ClP and CI 'P, the instantaneous fields of jG images. jP and I 'P, respectively.

Spatial re-sampling is carried out by a conventional interpolation function, of bilinear or bicubic type.

The value of Q is chosen as shown below.

The desired field of the “raw” image ClGβrute at the output of the sensor C2 is less than the instantaneous field of the “raw” image ClPβrute of the small field sensor Ci- The relationships linking these two “raw” images are as follows:

ClGβru te = λxClPBru te (2),

with λ a real number greater than unity and Q whole part of λ.

FIG. 4 is a diagram schematically illustrating the images J ^G , ∑P and I 'P. The cutting of the useful area of the resampled images is such that the image I ′ P is included in the image I ^G of the wide field sensor C ₂ • The diagrams have shown schematically in FIG. 4 positions of the images ∑ and I 'P before application of the rotation matrix MR. The XYZ axes symbolize the T-RCi reference system (Figure 2).

The digital signals representing the images iP and i are transmitted to the module 33.

. . A ⁰ At the end of this operation, we define by ™ * the maximum value of the apparent residual roll of I 'P in image i. The modules 31 and 35 extract the object contours present in the two digitized images. The process is similar in both modules.

FIG. 5 illustrates in more detail, in the form of block diagrams, one of the modules, for example the module 31.

The extraction parameters are chosen so as to introduce an identical low-pass filtering level on the two scanned images.

An input module 310 calculates images of gradients Gx and Gy along two orthonormal axes X and Y attached to the image. This operation can be carried out by any conventional method in the field of image processing. One can have recourse, for example, to recursive treatments like those described in the article of Rachid DERICHE, entitled: "Using Canny 's detector to drift a recursively implemented Optimal Edge Detector", "Computer Vision 1987", pages 167- 187, article to which we will profitably refer.

The images of calculated gradients, along the X and Y axes, are transmitted to a first module 311 intended to calculate, at each point, the norm of the gradient NG, in accordance with the following relation:

NG = | G (/, /) | (/, _/.) - G!. (/, _/ )! (3),

with i and j the coordinates of pixels in the image, along two orthonormal axes.

The images of calculated gradients are also transmitted to a second module 312, intended to calculate at each point the orientation of the gradient OG, in accordance with the following relation:

The output signals produced by the modules 311 and 312, represent, respectively, the images of the standard and of the orientation of the gradients, are transmitted to an output module 314 drawing up a list of the contour points of the objects detected in the digitized image, as digital coordinates. This step includes the following sub-steps: binarization, removal of non-maxima and application of a threshold by hysteresis. The binarization sub-step requires knowing the high and low thresholds. These thresholds are estimated by an additional module 313, according to an iterative process. The module 313 indeed receives the data associated with the list of contour points in feedback. It also receives on a second input the image of the gradient norm calculated by the module 311.

From the list of contour points extracted from the previous image and from the standard of the gradients of the current image, the object of the module 313 is to dynamically control, zone of the image by zone of the image, high and low thresholds.

The current image is divided into areas of equal size. On each zone, of arbitrary index z, the module 313 calculates a high threshold, which we will refer to SH _Z , and a low threshold, which we will refer to SB _Z , for the image being processed at an instant t arbitrary, this as a function of the high and low thresholds obtained on the area at an instant t-1 corresponding to the previous image. The following relationship is used:

SH _z (t) = αχβ ^χ Sff _z (tl) -t- (la) S _n elm (5),

with α e [0, 1], the exact value being fixed by the application, depending on the type of sensor selected, the value α = 0.8 being a typical value, β depends on the number of contour points extracted in the previous image, at time t-1. If the number of points is too high to maintain a rate in real time, β is chosen to be less than unity. On the other hand, if the number of points is insufficient to obtain contour information, one chooses β greater than unity. Typically the value of β is between 0.8 and 1.25.

^s norm is the threshold value to be applied to the gradient norm to perform a threshold operation on n% of the points in the area. The number n is chosen according to the characteristics of the sensors (spatial richness of the image) and is typically between 5% and 15%.

The following relationship is satisfied:

SB _Z = E (yx (SH _z (t)) (6),

with E integer value and γ fixed once and for all by the application, γ is generally less than 0.5.

To avoid the effects of inter-zone discontinuities, a process of smoothing the thresholds obtained is implemented. Each zone z is divided into four contiguous sub-zones and the high and low thresholds are recalculated for the sub-zones by a conventional interpolation algorithm, using the zones adjacent to the zone z.

The module 314 performs the binarization of the contours and the suppression of the local non-maxima, according to a hysteresis method. This module 314 determines the contour chains (that is to say the sets of connected contours according to the principle of connexity to eight) such that at least one point of each chain exceeds the local high threshold of its zone and that all other points in the chain exceed their local low threshold.

In addition, each point in the chain is kept if it constitutes a local maximum of the standard. To verify this, we compare the gradient norm at this point, which we will call P, with the gradient norm of two other points, Pi and P2, which are closest to point P, in a direction achieving the best approximation on a 3x3 neighborhood of the normal to the contour at point P. The direction of this normal is calculated from the orientation of the gradient at point P which gives the direction of the tangent at point P.

The process which has just been explained is illustrated very schematically by FIGS. 6A and 6B. In FIG. 6A, an image is represented representing the scene seen by the wide field sensor C2, comprising, in the example illustrated, two remarkable objects constituted by a tree Ar and a building Bt. At the end of the contour extraction process, there is a list of contour points CAr and CBt, represented, for example, by zeros. The two objects, symbolized by these contours, can represent potential targets that stand out from the background.

Apart from the contour points, the points or pixels of the image are represented by numbers other than zero (1, 2, 3, ...) and the value of which is all the greater the further these points are from contours (distance in connectivity to 4 from a pixel to the nearest contour, the distance being expressed in pixels).

Naturally, the zeros in the list are associated with digital coordinates, according to an orthonormal reference frame XY, the axes of which are advantageously parallel to the edges of the image, if the latter is rectangular. These coordinates are stored, at least temporarily, in conventional memory circuits (not shown), so as to be used by the next module, 32 or 36, depending on the channel considered (FIG. 3).

We will refer again to Figure 3.

On the upper channel (image processing from the small field sensor Ci), module 32 allows the establishment of the pyramid of contours, from the list calculated by module 31.

For reasons of speed of execution, the constitution of the pyramid consists in using the image of the contours C ^F ₀ determined by the module 311 at the maximum level of resolution and in constituting the sequence of images C ^P _k of the pyramid in accordance to equation (7): C [(ιj) = _ (2, 2) v _, (2ι, 2j + 1) v Q ^p _, (2 / + 1.2 /) v _Cf. , (2 / _τ 1,2 d + 1) '

relation in which ke [0, K], with K integer, such that 2 ^k ≥ tg (- A ^a m-- _A ) -

, 'and Δ (n. »the maximum value of the residual roll previously defined.

Pixels are considered booleans (the proposition is true if there are contours, false otherwise). The parameter T ^p is the maximum of the sizes of ∑P according to the orthonormal axes X and Y.

The number of non-zero points (i.e. the number of contour points) in the imaαeCV is noted Ωf

On the lower channel (processing of the image from the wide field sensor 2), the gradients calculated by the module 310 (FIG. 5) are transmitted to an input of the module 33.

The module 36 allows the establishment of the image of the distances to the nearest contour. This image is made up from the image of the contours of the wide field image given by the sensor C2. To do this, we can use a known algorithmic method, for example that disclosed by the article by Gunilla BORGEFORS, entitled: "Hierarchical Chamfer Matching: A parametric edge matching algorithm", published in "IEEE Transactions on Pattern Analysis and Machine Intelligence", November 1988, Vol 10, n ° 6, pages 849-865, to which we will profitably refer. The module 37 makes it possible to establish the pyramid of the so-called "chamfer" images calculated from the image provided by the previous module 36.

For reasons of speed of execution, the constitution of the pyramid consists in using the image of the "chamfer" distances constituted from the image of the contours of the large field image D ^G _Q determined by the module 36 at maximum level of resolution and to constitute the sequence of images D ^G of the pyramid in accordance with the following relation (8):

D ^G _r (i, j) = Max (D ^G _, (2,2), D ° _, (2 / .2; + 1). D ^G , (2 / + 1,2 /), ^G , (2 / + 1.2 + 1)) div 2,

relation in which r e [0, R], with -R = K + g, and div represents the integer division function.

The correlation module 33 is actually subdivided into two modules, as indicated.

The so-called "large" module, 33G, is represented in the form of a block diagram by FIG. 7, and comprises three cascaded sub-modules: 330 to 332.

The 33G module performs a valued correlation, at the same level of resolution, between the images of the contour pyramid of the small field image and the images of the pyramid of distance images with contours obtained from the large field image.

The input sub-module 330 allows the constitution of the correlation table N] ζ (u, v), in accordance with the following relation:

N _κ (^ ^, ) = ∑ ∑ (D ^c ( _l J) - C _κ ^p (ι -r, j + v)) _{(9) /}

relation in which, u and v are orthogonal coordinates in the correlation table, with U ^ ≤ u ≤ U ^ and Vf ≤ v ≤ T, inequalities in which V ^ ^nf and ϋi ^nf are typically equal to -2, and v ^ ^up and U ^sup are typically equal to +2.

The module 331 is intended for the selection of local minima. This selection is made in two stages.

We first select couples (u, v) such that

N (u, v) N (u, v) has a local minimum and - <S. 5 is a

threshold which depends on the spectral density of the input image. The threshold S is determined by a conventional calibration procedure of the image processing device.

The set of local minima at level K of the pyramid is noted Ξ

Finally, in module 332, an iterative process is carried out, raising the levels of the pyramids and filtering the values.

For any level n of the pyramid of images C ^'kp , we constitute a set Ξ _n as shown below.

For any couple (u, v) of Ε. _n + ±, we calculate a correlation table N _n reduced to 4 points, at level n, such that:

^ ( '') = ΧΣ (° _<, (/, /) _c;.. (T + / _+. ')) (Io),

relation in which (u ', \ ") e [2u, 2u + l] x [2 v, 2 v + l].

We keep a point P for each layer N _n . This point P is that for which the value of the tablecloth is minimum if this one checks the relation:

NAP) n

with S the previously defined threshold. Thus we constitute a sequence of sets Ξ _j for I [0, K-1].

The point selected by the "large" module 33G is the point u such that: πeΞ „and \ Jp e Ξ ₀ , p ≠ τi => N _Q (p)> N ₀ (π) (12).

The correlation process can stop at this stage. Indeed, the point π constitutes the best selected point. It is possible to display in the display device 4 a reticle 41 corresponding to the impact of the aiming axis Δ2 ₀ of the weapon 2 on the intended target, and superimposed on the scene observed 40 by the shooter through the device screen 4.

However, it is possible to further improve the accuracy of the sighting. Also, according to another aspect of the present invention, applicable to other contexts where a correlation is necessary, it is proposed to carry out a so-called "fine" correlation operation, using an estimate of a subpixel difference between a window selected in 1 image of the first sensor and a corresponding window selected in the image of the second sensor.

We will consider, as illustrated by the diagram in FIG. 8, a window F 'P of a few pixels, centered in the image' G, and a window FG of center FI, also of a few pixels, in the image I ^G . The pixels are delimited by lines, vertical and horizontal, in dotted lines, the pixels being supposed to be square. More precisely, the point π is the center of the central pixel of the window ^G , and a point O 'P, the center of the central pixel of the window F' P. The vector E represents the offset between the two "grids" of pixels, on the axis Yl-O 'P, that is to say in amplitude and in direction. The size of the window F ′ P is chosen so as to guarantee the presence of minimal information in this window FP. In other words, it should not be a uniform area. An indication of the information can be obtained by checking the value of the sum of the gradient standards on this window.

The window F ^G guarantees a margin of 1 pixel around the window FP.

A priori, there is no reason for the pixels of the two windows to coincide. It is assumed, in fact, that the small field image iP has an intrinsic resolution greater than the large field image ∑G.

We will therefore seek to estimate the sub-pixel difference E = \ of positioning between the center of the window F ^G and

the center of window F.

Given the compatibility of the spectral bands of the two imaging sensors, Ci and C2, an equivalence is used between the image of the window F ^G and the image of the window FP.

In general, if we consider any digital image I, of a few pixels in two dimensions, and a point M also included inside the image J, we can define a single-column vector Iv (M) containing the values of image I on the neighborhood V of point M. If the point M corresponds to a whole pixel, the values are directly the values of the pixels of J, while in the case where the point M has sub-pixel coordinates, the values of the vector Iv (M) are obtained by a mechanism classic interpolation. The precise choice of the interpolation mechanism must be made on a case-by-case basis, according to constraints specific to the specific application envisaged: speed of execution, precision of the result, etc. In the case of the process of the invention, the working neighborhood V is defined with the same sizes along X and Y as the window F ′ P. The total number of points in the neighborhood V is equal to L ^v .

We obtain the following identity: F ° (U) ≡ F ' ^p (-E). The offset \\ E \\ is less than one pixel.

We define H = matrix of L v lines and

of 2 columns. We then obtain the following relation:

F _v (-E) = F ^P (O ^p ) + H - (-E) (13), and

E = - (H ^T H) - H ^T - (F ^G (O ^a ) - F (O ^p )) (14).

The point 0 ^G is equivalent to the point π, but constitutes an origin of a reference for F ^G •

To take advantage of the higher intrinsic resolution of l, a magnification operation of the window FG 'is carried out by a factor Q. This operation is carried out by a conventional interpolation process, for example bilinear or bicubic. The resulting window is called G ^G.

F ^p is a centered window of JP, of size in X (respectively in Y) equal to the size of F 'P multiplied by Q.

From the difference E calculated previously, we find, by translation, a point Eh. π.χ corresponds to the center of a pixel of the window G ^G whose integer coordinates are the best possible approximation of the difference E. The coordinates of this point E ± are as follows:

XE_I = rounded (Q.Eχ) (15), and

YlTx≈ rounded (Q. E _Y ) (16). We will try to estimate the sub-pixel difference E, of positioning between ITι and the center of the window F ^p , using the same approach as above.

To do this, we define a working neighborhood W of the same sizes along X and Y as the window F ^p .

The total number of points in the neighborhood W is equal to # • We then obtain the identity: ^G ^ ( ^π ι) ^{≡ F} w ( ^{~ E)} ).

As before we define H =

matrix of i ⁷ rows and 2 columns.

We then obtain the following relation:

^F W ^ 1> = ^F W <° ^P > ^{+ H} l ^• ( ^{~ E} l (17), and

£, = - (H ^τ H) - H ^τ - (F ^G (0 ^G ) ~ F (O ^p )) (18).

E is a reduced deviation from E. It is possible to display, on the screen of the display member 4, a reticle 41 positioned at the point (T1-E-Ei) with respect to a point which corresponds to the center of the field of the wide field sensor C2.

The point π is obtained with a typical precision of the order of 2 to 3 pixels on the wide field image. The difference E corresponds to 1 pixel of the resolution of the small field image. It is therefore possible to obtain precision in the positioning of the reticle 41 typically in the range of 2 to 3 mrad, which corresponds to the objective that the method according to the invention sets.

On reading the above, it is easy to see that the invention achieves the goals it has set for itself.

The shooting assistance method allows both to obtain a high accuracy of sight and a great speed, since it does not require a shoulder of the weapon. In further, according to another advantageous characteristic, the process, since it is not accompanied by the emission of radiant energy, remains completely discreet. In other words, even if the target has a sensor sensitive to the wavelengths used, it will not be able to detect the shooter, at least due to the implementation of the method specific to the invention.

It should be clear, however, that the invention is not limited only to the examples of embodiments explicitly described, in particular in relation to FIGS. 1A to 8.

In particular, the numerical values have been specified only to fix ideas. They essentially depend on the precise application targeted.

Likewise, the components that can be used: imaging sensors, electronic circuits for processing digital signals, etc., participate in a simple technological choice within the reach of those skilled in the art. In particular, as has been indicated, several types and technologies of imaging sensors can be used, in particular depending on the choice of wavelengths used (visible or infrared).

TABLE OF RATINGS

Claims

1. A method of assisting aiming for a light weapon carried by a shooter, characterized in that it comprises the following steps: - the acquisition of a first image using a first image sensor ( Cl), associated with a first field and fixed to said weapon, and the optical axis of which is mechanically linked to the axis of the barrel of the weapon; said first image representing a front scene, seen from said cannon; - the acquisition of a second image using a second image sensor (C2), associated with a second field and carried by the head of said shooter, so as to encompass all or part of a front scene observed by it and likely to contain a target; - the acquisition by orientation sensors (5,6) carried respectively by the weapon and by the shooter's head, of an estimate of the angular differences between the field observed by the shooter and the field seen by the carried sensor by the weapon; - the correlation of the images of the two sensors to determine the position of the field seen by the first image sensor in the field seen by the second sensor, and to determine in particular the position in the image of the second sensor of a point of the first image representing the line of sight of the weapon, the correlation using the angular deviation estimated previously;

- the display on a helmet display, at a corresponding position, of a symbol representing this line of sight.

2. Method according to claim 1, characterized in that the symbol is displayed in collimated form at infinity.

3. Method according to one of claims 1 and 2, characterized in that the symbol is displayed superimposed on the scene directly observed by the shooter.

4. Method according to one of claims 1 to 3, characterized in that the orientation sensors each comprise a heading sensor and a two-axis inclinometer.

5. Method according to one of claims 1 to 4, characterized in that it comprises a preliminary step consisting, from the estimation of the angular deviations, in the estimation of the orientation deviation of the sight lines. (Δci, Δc2) of said first (Ci) and second (C2) image sensors, at least in direction and direction, so as to display on said display member (4) a second determined symbol (42) indicating to said shooter the direction in which it must move said barrel (20) of the weapon (2).

6. Method according to claims 1 to 5, characterized in that said weapon (2) being held in the hand by the shooter, the correlation uses an estimate of a translation vector (T) between the positions of the two sensors of image, this vector having an upper bound estimated at around 1 meter.

7. Method according to any one of claims 4 to 6, characterized in that said first field of said first image sensor (Ci) is less than said second field of said second image sensor (C2), in that, said first and second images being analog, said acquisition comprises analog / digital conversion (30, 34) of the output signals of said first (Ci) and second (C2) image sensors, so as to construct two digital images associated with first (TRci) and second (TRc2) orthonormal repositories, representing respectively the images from said first (Ci) and second (C2) sensors in imaging, in that there is a step consisting in the construction, from the digital image from said first imaging sensor (C), and by application of said rotation matrix, from at least one first derived digital image (I ^p ), with the same orthonormal reference frame as the digital image (I ^G ) from said second sensor (C2), the instantaneous field of which is proportional, by a factor Q, to the instantaneous field of said digital image from the second imaging sensor (I ^p ), Q being an integer, and in that he is carried out in subsequent image processing steps comprising the correlation (33) of said derived digital image and said digital image from said second sensor in imaging, to determine the position of said first field of said first image sensor (Ci) in said second image acquired by said second image sensor (C2) and the position of said line of sight in this second image.

8. Method according to claim 7, characterized in that, said digital images originating from said first (C) and second (C2) imaging sensors comprising non-uniform areas (Ar, Bt), the image processing steps comprise at minus the following steps:

- a step (31, 35) of extracting contours (CAr, CBt) from said non-uniform zones (Ar, Bt), so as to generate a list of points of coordinates of said digital image corresponding to said contours and associating them with a determined digital value;

- for the digital image from said first sensor (Ci), a step (32) consisting in establishing, from the image of said contours (CAr, CBt), a series of images forming a pyramid of contours, on a number of levels determined;

for the digital image coming from said second image sensor (C2), a step (36, 37) consisting in establishing, from the image of said contours (CAr, CBt) and for each point of the image, an image of the distances to the nearest contour and, from this image of the distances to the nearest contour, a series of images forming a pyramid of the distances of contours, over a determined number of levels; and

a valued correlation step (33) between said series of images forming a pyramid of contours and said series of images forming a pyramid of contour distances, so as to select a point of said digital image originating from said second image sensor image (C ₂ ) constituting the position closest to the center of the field of this image, and to display, on said display member (4), said first symbol (41) determined, at this position of said second image, superimposed of said observed front scene (40).

9. Method according to claim 8, characterized in that said step of extracting contours (CAr, CBt) from said non-uniform areas (Ar, Bt) of said digital images from said first (Ci) and second (C2) sensors image includes the following substeps:

- determining (310) images of gradients along two axes of orthonormal coordinates linked to said digital images; - determining (311) the norm of said gradients at each point of said images;

- determining (312) the orientation of said gradients at each point of said images; and

- the establishment (313, 314), from said standards and said gradient orientations, of a list of contour points.

10. Method according to claim 8, characterized in that said valued correlation step (33G) comprises the following substeps:

- The constitution (330), from said series of images forming a pyramid of outlines and from said series of images forming a pyramid of the distances of outlines, of a correlation sheet;

- the selection (331, 332) in said layer of values representing local minima below a determined threshold, for one of said pyramid levels, and the constitution, at each level of said pyramids, of a set of local minima; and

- selection of a point (1 ^~ 1) corresponding to the smallest of the minima to estimate the position of the center of a positioning area of said digital image from said first image sensor (Ci) in said digital image from said second image sensor (C ₂ ), this position representing said line of sight.

11. Method according to claims 8 or 10, characterized in that said valued correlation step (33G) is followed by an additional correlation step, called "fine", implementing an algorithm for estimating the positioning deviation (E), in amplitude and in direction, between the center (O 'P) of said digital image from said first image sensor (Ci) and the center (El) of said area for positioning this digital image in said digital image from said second image sensor (Ci), the positioning of said center (II) being obtained during said valued correlation step (33G), and in that at the end of said additional step, a new position of said center is determined by a translation of amplitude and direction in accordance with said deviation (E).

12. Aiming aid system intended for a light weapon carried by a shooter, characterized in that it comprises:

- a first image sensor (Ci) making it possible to acquire said first image, said first image sensor (Ci) being associated with a first field and being fixed to said weapon (2), the optical axis (I) this sensor (Ci) being mechanically linked to the axis A20) of the barrel (20) of the weapon (2) and representing the line of sight of this weapon (2);

- a second image sensor (C2) making it possible to acquire said second image, said second image sensor (C2) being associated with a second field and fixed on the head (Te) of said shooter, so as to encompass all or part of a front scene (40) observed by the latter, said scene (40) being capable of containing a target for said shooting;

- orientation sensors (5,6) making it possible to determine the angular difference between the direction of the weapon and the direction of the shooter's head;

- a signal and image processing device (3) received from said first (Ci) and second (C2) imaging sensors and orientation sensors (5,6) to correlate the images received from two image sensors, using the determined angular deviation, in order to determine the position of the field of the first image sensor in the field of the second image sensor,

- And a display member (4) for the display of a determined symbol (41), materializing said position of the line of sight in said second image, or a second determined symbol (42), indicating to said shooter a following direction which he must move the barrel of said weapon (2), said determined symbols (41, 42) being displayed superimposed on said front scene (40) observed by said shooter.

13. The system as claimed in claim 12, characterized in that said display member (4) is a helmet display comprising a screen on which said determined symbols are displayed (41, 42) and through which said shooter observes said front scene ( 40).

14. System according to claims 12 or 13, characterized in that said first (Ci) and second (C ₂ ) image sensors are sensors of the coupled charge type sensitive to radiation in the visible spectrum.

15. System according to claims 12 or 13, characterized in that said first (Ci) and second (C2) image sensors are sensors sensitive to radiation in the infrared spectrum.

16. System according to any one of claims 12 to 15, characterized in that the orientation sensors each comprise a heading sensor and a two axis inclinometer, so as to generate heading and attitude data for the weapon and the head.

17. System according to any one of claims 12 to 16, characterized in that, said first and second images being analog, said signal and image processing device (3) comprises acquisition modules (30, 34 ) comprising an analog / digital converter for each of said images.