A biometric capture device

Abstract

A biometric capture device comprising: - an optical module (2) with an acquisition surface (3), - an optical acquisition system (4) arranged so that a first light ray propagating outside the optical module along an optical axis (6) of said optical acquisition system forms an angle (β) at the acquisition surface with the normal to the acquisition surface, the value of this angle being greater than the critical angle determined by the refractive indices of the optical module and of air, and in addition the optical system is arranged so that the optical axis forms an angle with the normal to the exit face which is less than said critical angle, - an illumination system (8) configured to illuminate said acquisition surface, said illumination system producing a light beam defined by an illumination axis (9), a second light ray propagating outside the optical module along the illumination axis, then propagating in the optical module so as to form at the acquisition surface a given incident light ray which is reflected on the acquisition surface so as to define a given reflected light ray, the illumination system and the optical acquisition system being arranged so that the angle (Ω) between: - the reflected light ray and - the first light ray is strictly greater than the angle (β).

Description

[0001] manual

[0002] This invention relates to the field of biometric identification, for example, for individual identification or verification of an individual's access rights to a location, item, or information. Background Technology

[0003] Typically, biometric identification methods involve comparing biometric data extracted from an image captured from a part of the body of the person to be identified with reference biometric data extracted from an image captured from the same part of the user's body previously, in order to pass or refuse identification.

[0004] There are now biometric capture devices, which include a housing with a collection surface, where the subject places one of their fingers on the collection surface, and a camera set in the housing to capture one or more images of the finger to activate the biometric recognition method.

[0005] Figure 1 The conventional structure of a biometric capture device is shown, including a transparent glass or plastic prism 1000, an illumination system 1001, and an optical acquisition system with a camera 1002.

[0006] The camera 1002 is connected to the side of the prism 1000, while the illumination system 1001 is connected to the small base of the prism 1000, which is opposite to the large base of the prism, and the large base is internally tangent to the acquisition surface 1003.

[0007] In use, the lighting system 1001 generates a light beam that passes through the base of the prism to the collection surface 1003 and exits from the device. The collection surface 1003 thus becomes the interface between the first medium (corresponding to the prism) and the second medium (corresponding to air or the user's finger).

[0008] The rays of the illumination beam diverge in a manner distributed around a principal illumination axis, which forms a small angle with the normal to the acquisition surface. Figure 1 The angle is 0°. The light diverges around the main illumination axis, illuminating the entire acquisition surface 1003. For example, the maximum divergence angle is 20°.

[0009] The light emitted by the lighting system 1001 is refracted by the smaller base, thus forming an angle θ less than the critical angle with the normal of the larger base. c The included angle, the critical angle θ c It is defined as the angle at which total internal reflection occurs when light reaches the interface between the first medium prism and the second medium air.

[0010] Thus, most of the light rays pass through the acquisition surface 1003, whether the external medium is air or a finger, because the refractive index of the finger is higher than that of air when the finger is placed on the acquisition surface.

[0011] When a finger is placed on the acquisition surface 1003, the light rays generated by the illumination system 1001 and shot on the acquisition surface are thus not totally reflected by this surface and do not illuminate the finger. The light rays then diffuse inside the finger and are re-emitted in all directions with the same light intensity: the finger behaves like a Lambertian surface or is isotropic.

[0012] However, the camera 1002 is arranged to receive only the light rays which form an angle with the normal to the base greater than a critical angle θ c . It is also arranged to receive only the light rays which form an angle with the normal to the acquisition surface 1003 less than a limit angle θ l , the critical angle θ l being defined as the angle beyond which total reflection occurs when a light ray reaches the interface between the first medium, the prism, and the second medium, the finger.

[0013] Thus, the light rays scattered by the finger and emitted from the finger in the recesses cannot reach the camera 1002, because when they pass through the layer of air separating them from the acquisition surface and are refracted by this surface, they necessarily propagate in the prism while forming an angle with the normal to the surface less than the critical angle θ c .

[0014] On the other hand, the light rays scattered by the finger and emitted from the finger in the raised parts of the finger in contact with the acquisition surface 1003 can propagate in the prism, whether or not they form an angle with the normal to the acquisition surface 1003 less than θ l . Thus, there are light rays emitted from the finger which propagate in the prism, forming an angle with the normal to the acquisition surface 1003 greater than θ c , which can be imaged by the camera.

[0015] Thus, the camera 1002 forms a high-contrast image of the fingerprint between the recesses and the raised parts, because:

[0016] - the raised parts in the image correspond to the light rays scattered by the finger which are emitted from the finger in the raised parts of the finger in contact with the acquisition surface 1003 to reach the camera,

[0017] - whereas the light rays scattered by the finger, emitted from the finger in the recesses, cannot reach the camera.

[0018] Thus, in the image of the fingerprint, the raised parts appear brighter than the recesses.

[0019] Due to the relative position between the camera 1002 and the sole, this device is called "frustrated total reflection", which means that the camera observes the acquisition surface without the finger being in contact with it: indeed, any light ray reaching the camera from the acquisition surface has been reflected at the acquisition surface 1003 and has thus propagated in the prism before this reflection, but since the air is in contact with the acquisition surface 1003, no light ray can pass through the acquisition surface and reach the camera. However, when the finger touches the acquisition surface 1003, the condition for the camera to observe the acquisition surface 1003 in total reflection is temporarily not met, since a light ray can propagate from the finger to the camera, and thus is called "frustrated total reflection".

[0020] Unfortunately, this type of device remains sensitive to dirt and scratches on the acquisition surface. Indeed, part of the light rays coming from the illumination system can be scattered by the finger and follow an angle with the normal to the acquisition surface 1003 greater than θ c propagates and reaches the camera.

[0021] The light path can thus be modeled by reflection and anisotropic scattering.

[0022] This can be modeled by, for example, the Henyey-Greenstein phase function.

[0023] The probability of a geometric reflection ray to follow an angle θ with the real ray is:

[0024] with μ = cos(θ),

[0025] with g the anisotropy coefficient, greater than 0 and less than 1. For a light dirt, it will be close to 1 and will decrease with the amount of deposit on the surface.

[0026] According to experiments, the observed values are always greater than 0.5.

[0027] This forms a decreasing energy curve away from the geometric condition of reflection.

[0028] This is particularly troublesome if the dirt comes from the trace left by a finger previously placed on the surface, since an image similar to that of the finger can appear.

[0029] Therefore, the detection threshold of the device is raised, so that the device does not take into account the fingerprint trace left by a previous object to be identified.

[0030] Unfortunately, this device is also unable to extract the real fingerprint of a new object to be identified, placed on the acquisition surface with a finger. For example, if the user places a "dry finger", that is to say a finger for which the coupling of light is limited and only a part of the light rays emitted by the finger pass through the acquisition surface.

[0031] OBJECT OF THE INVENTION

[0032] The object of the present invention is to provide a biometric capture device that makes it possible to more easily distinguish between the real imprint of an object to be authenticated and the residual imprint left on the acquisition surface. SUMMARY

[0033] To achieve this object, according to the invention, a biometric capture device is proposed, comprising:

[0034] - an optical module with an acquisition surface, on which, in use, a user places at least one body part with at least one imprint,

[0035] - an optical acquisition system configured to acquire at least one image of at least one imprint of said body part through at least one face of the module called exit face, wherein the optical system is arranged so that a first light ray propagating outside the optical module along an optical axis of said optical acquisition system forms an angle β at the acquisition surface with the normal to the acquisition surface, the value of this angle being greater than the critical angle determined by the refractive indices of the optical module and of the air, and in addition the optical system is arranged so that the optical axis forms an angle with the normal to the exit face that is less than said critical angle.

[0036] - an illumination system configured to illuminate the acquisition surface, the illumination system generating a light beam defined by an illumination axis,

[0037] a second light ray propagating outside the optical module along the illumination axis, then propagating in the optical module so as to form, at the acquisition surface, a given incident light ray that is reflected on the acquisition surface so as to define a given reflected light ray,

[0038] the illumination system and the optical acquisition system being arranged so that the angle Ω between:

[0039] - the reflected light ray, if the reflected light ray is in the plane defined by the normal to the acquisition surface and the first light ray, or the projection of the reflected light ray in said plane in the opposite case, and

[0040] - the first light ray

[0041] is strictly greater than the angle β.

[0042] Thus, in use, the light beam generated by the illumination system passes through at least one face of the optical module and finally reaches the acquisition surface. When the body part is placed on the acquisition surface, a part of the light rays of the light beam (extending along the illumination axis or parallel to it when they propagate outside the optical module) which are shot on the acquisition surface at the location of the body part and which are reflected by said acquisition surface do not reach the optical acquisition system because their direction is far from the exit face due to the specific structure between the illumination system and the optical acquisition system.

[0043] Moreover, the light rays of the light beam (extending along the illumination axis or parallel to it when they propagate outside the optical module) which are shot on the acquisition surface at the location of the convexity of the body part and / or which pass through the acquisition surface at the location of the concavity and thus reach the finger, are isotropically scattered by said body part.

[0044] However, due to the specific location of the optical acquisition system, said system can only receive the light rays which form an angle of incidence with the normal to the acquisition surface greater than the critical angle θ c . Thus, the light rays scattered by the body part and shot from the concavity of the body part cannot normally reach the optical acquisition system because they cannot normally pass through the air layer separating them from the acquisition surface and then propagate in the optical module while forming an angle of incidence with the normal to the acquisition surface greater than the critical angle θ c .

[0045] Thus, the light rays scattered by the body part and shot from the convexity of the finger can normally at least partially reach the optical acquisition system.

[0046] Thus, the optical acquisition system forms a high-contrast image of the imprint between the concavity and the convexity because:

[0047] - the convexity in the image corresponds to the light rays scattered by the body part which are shot from the body part at the convexity of said body part in contact with the acquisition surface to reach the optical acquisition system,

[0048] - while the light rays scattered by the body part and shot from the concavity of the body part do not normally reach the optical acquisition system.

[0049] Thus, in the image, the convexity appears brighter than the concavity.

[0050] Thus, the present application makes it possible to acquire a high-quality image of the imprint.

[0051] The scattering of the light rays by the body part is isotropic and the specific structure of the illumination system compared to the positioning of the illumination system in the prior art does not modify the scattering of the light rays by the body part and thus does not modify the amount of light scattered by the body part and reaching the optical acquisition system.

[0052] On the other hand, in the presence of a residual fingerprint, the light rays scattered by the dirt remaining on the acquisition surface will be scattered in a non-isotropic manner.

[0053] In fact, due to the specific configuration between the optical acquisition system and the illumination system, the angle Ω in the application is greater than the angle of the device in the prior art. However, far from the geometric reflection (in this case, a given reflected light ray or its projection), the non-isotropic scattering induced by the dirt remaining on the acquisition surface follows a rapidly decreasing energy curve: thus, the light intensity of the light rays scattered by the body part towards the optical acquisition system is reduced in the application compared to the device in the prior art.

[0054] Thus, in a given image, the light intensity of the corresponding points of the convexities of the body part placed on the acquisition surface is not modified in the application compared to the device in the prior art, whereas the light intensity of the corresponding points of the residual traces present on the acquisition surface is reduced in the application compared to the device in the prior art.

[0055] Thus, since the residual mark receives only light rays whose light intensity is very low, the application is not or almost not sensitive to the residual mark during the capture request.

[0056] The simple threshold of the detection level of the application makes it possible to eliminate the residual traces without modifying the image of the body part placed on the acquisition surface.

[0057] Thus, by advantageously taking advantage of the different optical properties between the residual mark and the real mark (the scattering effect of the human body is very strong, it is less sensitive to the direction of the light rays falling on it, the residual mark is more subtle, on the contrary) and the total reflection principle, more particularly the frustrated total reflection principle, the application makes it possible to more easily distinguish the residual mark from the real mark of the object to be authenticated.

[0058] Thus, the application proposes a simple solution to make the biometric acquisition device better distinguish the residual mark from the real mark, in particular to make the residual mark less visible in the image.

[0059] Furthermore, the application can be implemented in the housing of the prior art without having to modify the optical acquisition system, which is often complex, but only for the illumination system, so as to illuminate the acquisition surface according to an angle Ω greater than the angle β with the normal to the acquisition surface.

[0060] Note that the illumination system makes it so that the given incident light ray is inclined with respect to the normal to the acquisition surface, that is to say that the given incident light ray is strictly greater than zero degrees and strictly less than 90 degrees.

[0061] Note that the optical acquisition system makes it so that the first light ray is inclined with respect to the normal to the acquisition surface, that is to say that the first light ray is strictly greater than zero degrees and strictly less than 90 degrees.

[0062] The "acquisition surface" is the part of the device with which the object whose biological feature is to be identified will interact to ensure the taking of the image.

[0063] At least one part of the surface of the optical module can directly form the acquisition surface, or be covered with treatment means and / or dedicated elements, then form the acquisition surface with said part of the surface of the optical module.

[0064] Generally, the acquisition surface corresponds to only a part of the surface of the acquisition module (covered or not with treatment means and / or dedicated elements). For example, the upper surface of the acquisition module can be covered with a frame with a window: the inside of the window will define the acquisition surface, so the acquisition surface will consist of only a part of the upper surface of the optical module.

[0065] It is also noted that a given reflected light ray can also be called symmetrical with respect to the normal to the acquisition surface of a given incident light ray.

[0066] It is also noted that a given reflected light ray is not necessarily a total reflection of a given incident light ray, but can be a simple partial reflection of a given incident light ray.

[0067] The "optical axis" is the axis around which the field of view of the optical acquisition system (or "field of view" in English) is distributed.

[0068] The "illumination axis" is the axis around which the rays of the light beam produced by the illumination system are distributed. Thus, when the light beam is in the shape of a straight cylinder, the illumination axis can be the generator of the light beam, or when the light beam is in the shape of a cone, the illumination axis can be the height of the light beam. For any other light beam shape, the direction in which the light beam has the highest intensity can be taken.

[0069] For the present application, the angles related to the illumination system are considered at the point of incidence on the acquisition surface of a given ray produced by the illumination system, that is to say once the ray has propagated in the optical module (unless it refers to a surface other than the acquisition surface, for example the surface of the optical module that is penetrated by the light beam on entry into the optical module). Thus, if we consider the Figure 7 , the angle a is considered at the point of incidence of the given ray, and not directly on the illumination system before the ray has propagated in the optical module. Thus, when the acquisition surface is considered, it is the given incident ray that is involved, and not the illumination axis of the illumination system, for example, which can undergo a slight refraction at the entrance to the optical module.

[0070] Likewise, the angles related to the optical acquisition system are considered to be at the acquisition surface, that is to say that the related light rays propagate in the optical module to reach the optical acquisition system (not including when it involves other surfaces than the acquisition surface, for example the exit face). Thus, if we consider the following angles which will be described in more detail below Figure 7 , the angle β is considered to be at the acquisition surface and not directly on the optical acquisition system after the propagation of said light rays in the optical module. Thus, when considering the acquisition surface, it is the first light rays which are involved and not the optical axis of the optical system.

[0071] For the present application, the angles in the plane defined by the first light rays and the normal to the acquisition surface will be considered: thus, these angles are defined by the light rays in said plane or the projection of the light rays on said plane.

[0072] Moreover, it is noted that the acquisition surface separates a first medium (corresponding to the optical module) from a second medium (corresponding to air or skin).

[0073] Then, the "critical angle θ c " refers to the angle beyond which the total reflection phenomenon occurs if the incident light rays reach the acquisition surface via the first medium and the second medium is air. The critical angle is derived according to the following formula:

[0074]

[0075] n1 is the refractive index of the optical module and n0 is the refractive index of air. Thus, if the refractive index of air is equal to 1 and the refractive index of the optical module is equal to for example 1.5, the critical angle θ c is 41.8 degrees.

[0076] The "limit angle θ1" refers to the angle beyond which the total reflection phenomenon occurs if the incident light rays reach the acquisition surface via the first medium and the second medium is skin.

[0077] The limit angle is derived according to the following formula:

[0078]

[0079] n1 is the refractive index of the optical module and n2 is the refractive index of the skin. In the visible range, the refractive index of human skin is between 1.41 and 1.47. Taking the minimum value 1.41, the limit angle θ1 is thus obtained as 70 degrees. Taking the maximum value, the limit angle θ1 is obtained as 76 degrees.

[0080] Optionally, the exit face is a lateral face of the optical module.

[0081] Optionally, the optical system is arranged so that its optical axis forms an angle with the normal to the exit face which is less than 2 degrees and preferably less than 1 degree and preferably equal to 0 degrees.

[0082] Optionally, the angle Ω is greater than 60 degrees (°) and preferably greater than 70°, preferably greater than 90°.

[0083] Optionally, the angle Ω is less than 2β.

[0084] Preferably, the angle Ω is greater than 70° and less than 2β.

[0085] Optionally, the angle Ω is greater than 90° and greater than 2β.

[0086] Optionally, the illumination system and the optical acquisition system are arranged so that the angle of the first light rays with the given incident light ray is strictly less than β.

[0087] Optionally, the angle γ is less than 35 degrees, preferably less than 25 degrees, preferably less than 15 degrees, preferably less than 10°.

[0088] Optionally, the given incident light ray forms an angle with the normal to the acquisition surface, the value of which is greater than the critical angle and less than the limiting angle determined by the refractive indices of the module and the skin.

[0089] Optionally, the angle of the given incident light ray with the normal to the acquisition surface is greater than β.

[0090] Optionally, the device comprises a single illumination system and / or a single optical acquisition system.

[0091] Optionally, the illumination system and the optical acquisition system are carried by a support extending in a plane that is either coincident or parallel.

[0092] Optionally, the optical module is in the form of a prism.

[0093] Optionally, the optical module is in the form of a glass sheet.

[0094] - has parallel faces, at least on one portion has inclined lateral faces, or

[0095] - a sheet, the bottom face of which has a plurality of microprisms.

[0096] The use of a glass sheet makes it possible to obtain a more compact device.

[0097] Indeed, the height of the glass sheet is lower than that of a prism, in particular because the exit face of the glass sheet is closer to the acquisition system than in a prism, which makes it possible to make the exit face smaller.

[0098] Optionally, the device comprises at least one region treated to absorb the light rays emitted by the illumination system and reflected at the acquisition surface.

[0099] Optionally, said region is coated with a dark coating.

[0100] Optionally, the optical acquisition system and the illumination system are close to each other.

[0101] Optionally, the illumination system illuminates through the exit face.

[0102] Optionally, the illumination system illuminates through a face of the optical module adjacent to the exit face.

[0103] By "adjacent face" is meant a face of the optical module having at least one common edge with the exit face.

[0104] Other characteristics and advantages of the application will appear from the following description of a non-limiting embodiment thereof. BRIEF DESCRIPTION OF DRAWINGS

[0105] Figure 1 The description has been made according to the state of the art and the relation of the application therewith: Figure 1 is a sectional view of a device not belonging to the state of the art and to the application.

[0106] The application will be better understood from the following description, given in connection with the attached drawings, in which:

[0107] - Figure 2 is a sectional view of a device according to a first embodiment of the application,

[0108] - Figure 3 is a sectional view of a device according to a second embodiment of the application,

[0109] - Figure 4 is a sectional view of a device according to a third embodiment of the application,

[0110] - Figure 5 is a sectional view of a device according to a fourth embodiment of the application,

[0111] - Figure 6 is a sectional view of a device according to a fifth embodiment of the application,

[0112] - Figure 7 is a sectional view of a device according to a sixth embodiment of the application,

[0113] - Figure 8 is a sectional view of a device according to a seventh embodiment of the application. DETAILED DESCRIPTION

[0114] With reference to Figure 2 , according to a first embodiment, a biometric capture device, generally indicated with 1, is a capture device for acquiring a fingerprint for performing biometric recognition.

[0115] However, this application is not limiting and the device 1 can be used to capture prints of other parts of the body, for example prints of a few fingers, of a whole hand, of a palm, etc.

[0116] The device 1 comprises an optical module 2 having:

[0117] - an upper surface,

[0118] - a lower surface parallel to the upper surface, and

[0119] - at least one lateral surface connecting the upper surface and the lower surface.

[0120] The optical module 2 is here made of a material transparent to visible light, for example glass or plastic, for example polycarbonate (PC) or poly(methyl methacrylate) (PMMA). The refractive index of the optical module 2 is greater than the refractive index of air and, optionally, greater than the refractive index of the skin.

[0121] In particular, the optical module 2 is here in the form of a prism. The optical module 2 is for example a prism having four lateral surfaces. The optical module 2 is for example a circular truncated cone, thereby comprising a large base (upper surface) and a small base (lower surface).

[0122] In the present example, only a portion of the upper surface constitutes the acquisition surface 3 on which the biometric object to be identified places his finger. Optionally, the optical module 2 is partially framed by a frame 11 with a window 12: the interior of the window defines the acquisition surface 3.

[0123] The acquisition surface 3 is flat.

[0124] In the following, these angles are to be considered when no part of the body is placed on the acquisition surface.

[0125] In addition, the device 1 also comprises an optical acquisition system 4 configured to capture at least one image of the fingerprint of the biometric object to be identified placed on the acquisition surface 3.

[0126] In the present example, the optical acquisition system 4 is the only optical acquisition system of the device 1.

[0127] The optical acquisition system 4 comprises for example at least one optical sensor, for example here a camera sensitive to visible light, and optionally one or more auxiliary optical elements, for example one or more lenses and diaphragms.

[0128] In the present example, the optical acquisition system 4, and therefore the device 1, comprises a single optical sensor.

[0129] The optical acquisition system 4 is optionally arranged to acquire images through a first side of the optical module 2, hereinafter referred to as the exit face 5. The exit face 5 is thus inclined with respect to the upper face associated with the acquisition surface 3.

[0130] In the present case, the optical acquisition system 4 is actually arranged outside the optical module behind said exit face 5, so that its field of view is directed towards the exit face 5.

[0131] The field of view of the optical acquisition system 4 is defined by an optical axis 6. The optical axis 6 is thus maintained here directed towards the acquisition surface and inclined with respect to the normal 13 to the acquisition surface 3 (i.e. neither parallel nor perpendicular to it).

[0132] Preferably, the optical axis 6 constitutes the normal to the exit face 5. The optical axis thus forms an angle with the normal to the exit face 5 which is less than the critical angle θ c .

[0133] Furthermore, the optical acquisition system 4 is also arranged so that a first light ray coming from the acquisition surface and propagating along the optical axis 6 to reach the acquisition surface again forms an angle β with the normal 13 to the acquisition surface 3 which is greater than the critical angle θ c (while being less than the limit angle θ1), so that when there is air above the acquisition surface 3, a light ray coming from outside the optical module 2 cannot pass through the acquisition surface 3 and be directed towards the acquisition system 4. In the present case, since the optical axis 6 is orthogonal to the exit face 5 and directed towards the acquisition surface 3, the first light ray coincides directly with the optical axis 6 even when it propagates in the optical module 2. The optical axis will thus be discussed below only for the first embodiment.

[0134] Furthermore, the device 1 comprises an illumination system 8.

[0135] In the example shown, the illumination system 8 is the only illumination system 8 of the device 1.

[0136] The illumination system 8 comprises at least one light source arranged to be able to emit visible light.

[0137] Alternatively or in addition, the illumination system 8 and the optical acquisition system can work in other wavelength ranges, for example in the near infrared (i.e. wavelengths less than 1.1 microns) or in the ultraviolet, provided that the optical module is transparent to these wavelengths. The at least one light source of the illumination system 8 consists of one or more light-emitting diodes (LEDs) and / or one or more superluminescent diodes (more commonly known by the English name Super Luminescent Diodes or SLDs) and / or one or more laser diodes.

[0138] In the present case, the lighting system 8 (and therefore the device 1) is limited to a single light source. In the present case, the light source (and therefore the lighting system 8 and the device 1) consists of a single LED.

[0139] The lighting system 8 thus comprises here a single lighting axis 9, i.e. the lighting axis of the LED. In the present case, the lighting system 8 is capable of producing a light beam diverging around the lighting axis, the light beam being directed towards the acquisition surface 3. The divergence is such that the entire acquisition surface 3 is illuminated. The divergence angle is for example maximum 20°.

[0140] The lighting system 8 is here arranged to illuminate through the exit face 5. In the present case, the lighting system 8 is in fact arranged outside the optical module 2 behind said exit face 5, so that the light beam it produces is directed directly towards the exit face 5. Furthermore, the lighting axis 9 is inclined with respect to the exit face 5. The light rays forming the light beam are thus refracted by said face.

[0141] The light rays propagating along the lighting axis 9 are thus subsequently propagated in the optical module 2 so as to form, at the acquisition surface 3, a given incident light ray 14 which does not coincide with the lighting axis 9. The given incident light ray 14 forms an angle a with the normal 13.

[0142] The given incident light ray 14 is reflected on the acquisition surface 3, thus defining a given reflected light ray 15. Furthermore, the lighting system 8 and the optical acquisition system 4 are arranged so that the given reflected light ray 15 forms an angle Ω with the optical axis 6 which is strictly greater than the angle β.

[0143] In the present case, the angle Ω is greater than 60 degrees and is here greater than 70 degrees. The angle Ω is for example 75 degrees.

[0144] In the present case, the angle Ω is less than 2β. In fact β is equal to 45 degrees in the present case.

[0145] The lighting system 8 is arranged close to the optical acquisition system 4.

[0146] The lighting system 8 is arranged below the optical acquisition system 4. The lighting system 8 is thus not directed towards the optical acquisition system 4. In fact, the lighting system 8 and the optical acquisition system 4 are generally directed towards the same angle and the same direction.

[0147] Optionally, the lighting system 8 and the optical acquisition system 4 are arranged so that the angle γ of the optical axis 6 with the given incident light ray 14 is strictly less than β.

[0148] Optionally, the angle γ is less than 35 degrees, preferably less than 25 degrees. In the present case, for example, the angle γ is taken equal to 15 degrees (the angle a being taken equal to 30 degrees).

[0149] The lighting system 8 is here arranged so that the angle a is less than the angle β.

[0150] The lighting system 8 is thus here arranged so that the angle a is less than the critical angle θc .

[0151] Furthermore, the optical module 2 comprises at least one area 10 treated so as to absorb the light rays emitted by the illumination system 8 and reflected at the acquisition surface 3.

[0152] For example, said area 10 is covered with a coating (directly on the whole and / or indirectly on the outside and / or on the inside of at least one face of the optical module 2: thus, this treated area 10 can be provided on the outside and / or on the inside of the optical module 2) which absorbs at least 95%, preferably at least 98% of the light rays reaching said area. The coating is for example a dark coating (i.e. a coloured coating which absorbs at least 95%, preferably at least 98% of the light rays) and for example black.

[0153] Optionally, said area 10 is provided on at least one lateral face of the optical module 2 and here preferably on the face opposite the exit face 5. Preferably, said area 10 extends over at least the whole of said lateral face opposite the exit face 5.

[0154] The illumination system 8 is here provided so that all the light rays emitted by the illumination system 8 and reflected by the acquisition surface 3, after any number of reflections on the surface of the optical module 2, finally reach the area 10.

[0155] Thus, a device 1 is described having an angle Ω of 75°: with an anisotropy factor g greater than 0.6, the attenuation factor of the light intensity of the light rays scattered by the residual imprint when using the device 1 is greater than Figure 1 the attenuation factor 3 of the device in the prior art shown. For example, with an anisotropy factor g of 0.7, the attenuation of the device 1 is Figure 1 5 times greater than the device in the prior art shown.

[0156] Obviously, Figure 1 the device 1 shown is only one of the many possible arrangements for implementing the application.

[0157] Thus, Figure 3 a second arrangement is illustrated which has the same structure as in Figure 2 , with the difference that the illumination system 8 is not illuminated through the exit face 5 but through a face of the optical module adjacent to said exit face 5. In this example, the illumination system 8 is illuminated through the lower face 16.

[0158] The rest of the description made for the first embodiment thus also applies to the second embodiment, in particular concerning the angles a, β, γ and Ω.

[0159] Furthermore, the illumination system 8 is here cleverly provided so that its illumination axis 9 is parallel to the optical axis 6.

[0160] Preferably, the illumination system 8 and the optical acquisition system 4 are also arranged so that their respective bases extend in the same plane.

[0161] Generally, the illumination system 8 and the optical acquisition system 4 are mounted on the same support or on two distinct but parallel supports to each other and optionally extend in the same plane.

[0162] Thus, Figure 4 Another structure is shown which is identical to that in Figure 2 except at the optical module 2.

[0163] Thus, the optical module 2 is a glass sheet, called thin glass sheet, having:

[0164] - an upper surface,

[0165] - a lower surface parallel to the upper surface, and

[0166] - at least one lateral surface connecting the upper surface and the lower surface (at least one lateral surface connecting the upper surface and the lower surface is orthogonal to the lower surface and to the upper surface).

[0167] The optical module 2 is here made of a material transparent to visible light, for example glass or plastic, for example polycarbonate (PC) or poly(methyl methacrylate) (PMMA). The refractive index of the optical module 2 is greater than the refractive index of air and optionally greater than the refractive index of the skin.

[0168] In the present case, only a portion of the upper surface constitutes the acquisition surface 3 on which the subject whose biological feature is to be identified places his finger. Optionally, the optical module 2 is partially framed by a frame 11 with a window 12: the interior of the window defines the acquisition surface 3.

[0169] The acquisition surface 3 is flat.

[0170] On the other hand, the lower surface 16 of the optical module 2 is not flat but has a plurality of microprisms on the outside of the optical module.

[0171] There is thus no longer a single exit face and a single face illuminated by the illumination system 8 but a plurality of exit faces and a plurality of faces illuminated by the illumination system 8.

[0172] However, due to the particular structure of the thin glass sheet with microprisms, the behavior of the light rays would be identical to that of the first embodiment if they were respectively located at each exit face of one of the given microprisms.

[0173] The remaining parts described for the first embodiment thus also apply to the third embodiment, in particular concerning the angles a, β, γ and Ω.

[0174] Reference is made to Figure 5According to a fourth embodiment, a biometric capture device, generally designated 1, is a capture device for capturing a fingerprint for performing biometric recognition.

[0175] However, this application is not limiting and the device 1 can be used to capture imprints of other parts of the body, for example of several fingers, of a whole hand, of a palm, etc.

[0176] The device 1 comprises an optical module 2 having:

[0177] - an upper surface,

[0178] - a lower surface parallel to the upper surface, and

[0179] - at least one lateral surface connecting the upper surface and the lower surface.

[0180] The optical module 2 is here made of a material transparent to visible light, for example glass or plastic, for example polycarbonate (PC) or poly(methyl methacrylate) (PMMA). The refractive index of the optical module 2 is greater than the refractive index of air and optionally greater than the refractive index of the skin.

[0181] In particular, the optical module 2 is here in the form of a prism.

[0182] In the present case, only a portion of the upper surface constitutes the acquisition surface 3 on which the biometric object to be recognized places his finger. Optionally, the optical module 2 is partially framed by a frame 11 with a window 12: the interior of the window defines the acquisition surface 3.

[0183] The acquisition surface 3 is flat.

[0184] In the following, these angles are to be considered when no part of the body is placed on the acquisition surface.

[0185] In addition, the device 1 also comprises an optical acquisition system 4 configured to capture at least one image of the fingerprint of the biometric object to be recognized placed on the acquisition surface 3.

[0186] In the present case, the optical acquisition system 4 is the only optical acquisition system of the device 1.

[0187] The optical acquisition system 4 comprises for example at least one optical sensor, for example here a camera sensitive to visible light, and optionally one or more auxiliary optical elements, for example one or more lenses and diaphragms.

[0188] In the present case, the optical acquisition system 4 and therefore the device 1 both comprise a single optical sensor.

[0189] The optical acquisition system 4 is optionally arranged to acquire images through a first side of the optical module 2, hereinafter referred to as the exit face 5. The exit face 5 is thus inclined with respect to the upper face associated with the acquisition surface 3.

[0190] In the present case, the optical acquisition system 4 is actually arranged outside the optical module behind said exit face 5, so that its field of view (or "field of view" in English) is directed towards the exit face 5.

[0191] The field of view of the optical acquisition system 4 is defined by an optical axis 6. The optical axis 6 is thus maintained here directed towards the acquisition surface and inclined with respect to the normal 13 to the acquisition surface 3 (i.e. neither parallel nor perpendicular to it).

[0192] Preferably, the optical axis 6 constitutes the normal to the exit face 5. The optical axis thus forms an angle with the normal to the exit face 5 which is less than the critical angle θ c .

[0193] Furthermore, the optical acquisition system 4 is also arranged so that a first light ray coming from the acquisition surface and propagating along the optical axis 6 to reach the acquisition surface again forms an angle β with the normal 13 to the acquisition surface 3 which is greater than the critical angle θ c (while being less than the limit angle θ1), so that when there is air above the acquisition surface 3, a light ray coming from outside the optical module 2 cannot pass through the acquisition surface 3 and be directed towards the acquisition system 4. In the present case, since the optical axis 6 is orthogonal to the exit face 5 and directed towards the acquisition surface 3, the first light ray coincides directly with the optical axis 6 even when it propagates in the optical module 2. The optical axis will thus be discussed below only for the first embodiment.

[0194] Furthermore, the device 1 comprises an illumination system 8.

[0195] In the example shown, the illumination system 8 is the only illumination system 8 of the device 1.

[0196] The illumination system 8 comprises at least one light source arranged to be able to emit visible light.

[0197] Alternatively or in addition, the illumination system 8 and the optical acquisition system can work in other wavelength ranges, for example in the near infrared (i.e. wavelengths less than 1.1 microns) or in the ultraviolet, provided that the optical module is transparent to these wavelengths. The at least one light source of the illumination system 8 consists of one or more light-emitting diodes (LEDs) and / or one or more superluminescent diodes (more commonly known by the English name Super Luminescent Diodes or SLDs) and / or one or more laser diodes.

[0198] In the present case, the lighting system 8 (and therefore the device 1) is limited to a single light source. In the present case, the light source (and therefore the lighting system 8 and the device 1) consists of a single LED.

[0199] The lighting system 8 thus comprises a single lighting axis 9, i.e. the lighting axis of the LED. In the present case, the lighting system 8 is capable of producing a light beam that diverges around the lighting axis, the light beam being directed towards the acquisition surface 3. The divergence is such that the entire acquisition surface 3 is illuminated. The divergence angle is for example maximum 20°.

[0200] The lighting system 8 is here arranged to illuminate by a face of the optical module adjacent to the exit face 5. In the present case, the lighting system 8 illuminates by a face 17 that connects the exit face 5 and the upper face of the optical module 2, the output face 5 itself then connecting the face 17 and the lower face of the optical module. The optical module 2 thus has two lateral faces between its upper face and its lower face on the side of the lighting system 8 and of the optical acquisition system 4. The face 17 here extends orthogonally to the upper face of the optical module 2, unlike the exit face 5.

[0201] In the present case, the lighting system 8 is actually arranged outside the optical module 2 behind said face 17, so that the light beam it produces is directed directly towards this face 17. Furthermore, the lighting axis 9 is inclined with respect to the face 17. The light rays forming the light beam are thus refracted by said face 17.

[0202] The light rays propagating along the lighting axis 9 are then propagated in the optical module 2 so as to form, at the acquisition surface 3, a given incident light ray 14 that does not coincide with the lighting axis 9. The given incident light ray 14 forms an angle a with the normal 13.

[0203] The given incident light ray 14 is reflected on the acquisition surface 3, thus defining a given reflected light ray 15. Furthermore, the lighting system 8 and the optical acquisition system 4 are arranged so that the given reflected light ray 15 forms an angle Ω with the optical axis 6 that is strictly greater than the angle β.

[0204] In the present case, the angle Ω is greater than 60 degrees, and here greater than 70 degrees, and here greater than 90 degrees. The angle Ω is for example 105 degrees.

[0205] In the present case, the angle Ω is greater than 2β. In fact β is equal to 45 degrees in the present case.

[0206] The lighting system 8 is arranged close to the optical acquisition system 4.

[0207] The lighting system 8 is arranged above the optical acquisition system 4. The lighting system 8 is thus not directed towards the optical acquisition system 4. In fact, the lighting system 8 and the optical acquisition system 4 are generally directed towards the same angle and the same direction.

[0208] Optionally, the illumination system 8 and the optical acquisition system 4 are arranged so that the angle γ between the optical axis 6 and a given incident light ray 14 is strictly less than β.

[0209] Optionally, the angle γ is less than 35 degrees, and preferably less than 25 degrees. In this example, for example, the angle γ is equal to 15 degrees (and the angle α is equal to 60 degrees).

[0210] The illumination system 8 is here arranged so that the angle α is less than the angle β.

[0211] The illumination system 8 is here therefore arranged so that the angle α is greater than the critical angle θ c (and obviously still less than the limit angle θ1).

[0212] Furthermore, the illumination system 8 is here cleverly arranged so that its illumination axis 9 is parallel to the optical axis 6.

[0213] Preferably, the illumination system 8 and the optical acquisition system 4 are also arranged so that their respective bases extend in the same plane.

[0214] Generally, the illumination system 8 and the optical acquisition system 4 are mounted on the same support or on two distinct but parallel supports, and optionally extend in the same plane.

[0215] Furthermore, the optical module 2 comprises at least one area 10 treated so as to absorb the light rays emitted by the illumination system 8 and reflected at the acquisition surface 3.

[0216] For example, said area 10 is covered with a coating (directly on the bulk and / or indirectly on the outside and / or the inside of at least one face of the optical module 2: this treated area 10 can therefore be arranged on the outside and / or on the inside of the optical module 2) which absorbs at least 95%, and preferably at least 98%, of the light rays reaching said area. The coating is for example a dark coating (i.e. a coloured coating which absorbs at least 95% of the light rays, and preferably at least 98% of the light rays) and for example black.

[0217] Optionally, said area 10 is arranged on at least one lateral face of the optical module 2, and preferably here on the face opposite the exit face 5 and the surface 17 (on this side of the optical module 2, the optical module 2 therefore comprises only a single lateral face connecting the upper face and the lower face). Preferably, said area 10 extends over at least the entire opposite lateral face.

[0218] The illumination system 8 is here arranged so that all the light rays emitted by the illumination system 8 and reflected by the acquisition surface 3 finally reach the area 10 after any number of reflections on the surfaces of the optical module 2.

[0219] An apparatus 1 having an angle Ω of 105° is thus described: with an anisotropy factor g greater than 0.6, the attenuation factor of the light intensity of the light rays scattered by the residual mark when using the apparatus 1 is at least greater than Figure 1 the attenuation factor 3 of the apparatus in the prior art illustrated.

[0220] Figure 6 Another structure identical to that in Figure 3 is illustrated, except at the optical module 2.

[0221] Thus, the optical module 2 is a glass sheet, called thin glass sheet, having:

[0222] - an upper surface,

[0223] - a lower surface parallel to the upper surface, and

[0224] - at least one lateral surface connecting the upper surface and the lower surface, said surface extending obliquely between the upper surface and the lower surface. This surface constitutes the exit face 5.

[0225] In addition, at least another lateral surface is also orthogonal to the lower surface and to the upper surface.

[0226] The optical module 2 is here made of a material transparent to visible light, for example glass or plastic, for example polycarbonate (PC) or poly(methyl methacrylate) (PMMA). The refractive index of the optical module 2 is greater than the refractive index of air and optionally greater than the refractive index of the skin.

[0227] In the present case, only a portion of the upper surface constitutes the acquisition surface 3 on which the subject whose biological feature is to be identified places his finger. Optionally, the optical module 2 is partially framed by a frame 11 with a window 12: the interior of the window defines the acquisition surface 3.

[0228] The acquisition surface 3 is flat.

[0229] In addition, since the optical module 2 is in the form of a glass sheet, the first light rays can be reflected one to several times before propagating outside the optical module 2 along the optical axis 6.

[0230] In addition to this, the remaining parts described for the second embodiment thus also apply to the fifth embodiment, in particular concerning the angles a, β, γ and Ω.

[0231] With reference to Figure 7 , according to a sixth embodiment, a biological feature capture apparatus, generally designated 1, is a capture apparatus for acquiring a fingerprint to perform a biological feature recognition.

[0232] However, this application is not limiting and the apparatus 1 can be used to capture marks of other parts of the body, for example of several fingers, of a whole hand, of a palm, etc.

[0233] The device 1 comprises an optical module 2, which has:

[0234] - an upper surface,

[0235] - a lower surface parallel to the upper surface, and

[0236] - at least one lateral surface connecting the upper surface and the lower surface.

[0237] The optical module 2 is here made of a material transparent to visible light, for example glass or plastic, for example polycarbonate (PC) or poly(methyl methacrylate) (PMMA). The refractive index of the optical module 2 is greater than the refractive index of air and optionally greater than the refractive index of the skin.

[0238] In particular, the optical module 2 is here in the form of a glass sheet, known as a thin glass sheet.

[0239] In the present example, only a portion of the upper surface constitutes the acquisition surface 3 on which the biometric object to be identified places his finger.

[0240] Optionally, the optical module 2 is partially framed by a frame 11 with a window 12: the interior of the window defines the acquisition surface 3.

[0241] The acquisition surface 3 is flat.

[0242] In the following, these angles are to be considered when no body part is placed on the acquisition surface.

[0243] In addition, the device 1 also comprises an optical acquisition system 4 configured to capture at least one image of the fingerprint of the biometric object to be identified placed on the acquisition surface 3.

[0244] In the present example, the optical acquisition system 4 is the only optical acquisition system of the device 1.

[0245] The optical acquisition system 4 comprises for example at least one optical sensor, for example here a camera sensitive to visible light, and optionally one or more auxiliary optical elements, for example one or more lenses and diaphragms.

[0246] In the present example, the optical acquisition system 4, and therefore the device 1, both comprise a single optical sensor.

[0247] The optical acquisition system 4 is optionally arranged to acquire images through a first lateral surface of the optical module 2, hereafter called the exit face 5. The exit face 5 is therefore inclined with respect to the upper surface associated with the acquisition surface 3.

[0248] In the present case, the optical acquisition system 4 is in fact external to the optical module behind the exit face 5, so that its field of view (or "field of view" in English) is directed towards the exit face 5.

[0249] The field of view of the optical acquisition system 4 is defined by the optical axis 6.

[0250] Preferably, the optical axis 6 constitutes the normal to the exit face 5. Thus, the optical axis forms an angle with the normal to the exit face 5 which is less than the critical angle θ c .

[0251] In addition, the optical acquisition system 4 is also arranged so that a first light ray 18 coming from the acquisition surface and propagating along the optical axis 6 to reach the acquisition surface again forms an angle β with the normal 13 to the acquisition surface 3 which is greater than the critical angle θ c (while being less than the limit angle θ1), so that when there is air above the acquisition surface 3, a light ray coming from outside the optical module 2 cannot pass through the acquisition surface 3 and be directed towards the acquisition system 4.

[0252] Since the optical module 2 is in the form of a glass sheet, the first light ray 18 can be reflected one or more times before propagating outside the optical module 2 along the optical axis 6.

[0253] The first light ray 18 is directed towards the acquisition surface and is inclined with respect to the normal 13 to the acquisition surface 3 (i.e. neither parallel nor perpendicular to it).

[0254] In addition, the device 1 comprises an illumination system 8.

[0255] In the example shown, the illumination system 8 is the only illumination system 8 of the device 1.

[0256] The illumination system 8 comprises at least one light source arranged so as to be able to emit visible light.

[0257] Alternatively or in addition, the illumination system 8 and the optical acquisition system can work in other wavelength ranges, for example in the near infrared (i.e. wavelengths less than 1.1 microns) or in the ultraviolet, provided that the optical module is transparent to these wavelengths. The at least one light source of the illumination system 8 consists of one or more light-emitting diodes (LEDs) and / or one or more superluminescent diodes (more commonly known by the English name Super Luminescent Diodes or SLDs) and / or one or more laser diodes.

[0258] In the present case, the illumination system 8 (and therefore the device 1) is limited to a single light source. In the present case, the light source (and therefore the illumination system 8 and the device 1) consists of a single LED.

[0259] The lighting system 8 thus comprises here a single lighting axis 9, i.e. the lighting axis of the LEDs. In the present case, the lighting system 8 is capable of generating a light beam diverging around the lighting axis, the light beam being directed towards the acquisition surface 3. The divergence is such that the entire acquisition surface 3 is illuminated. The divergence angle is for example maximum 20°.

[0260] The lighting system 8 is here arranged to illuminate by a face of the optical module adjacent to the exit face 5. In the present case, the lighting system 8 illuminates by a face 17 connecting the exit face 5 and the upper face of the optical module 2, the output face 5 itself then connecting the face 17 and the lower face of the optical module. The optical module 2 thus has two lateral faces between its upper face and its lower face on the side of the lighting system 8 and of the optical acquisition system 4. The face 17 is here inclined with respect to the upper face of the optical module 2.

[0261] In the present case, the lighting system 8 is actually arranged outside the optical module 2 behind said face 17, so that the light beam it generates is directed directly towards this face 17. In addition, the lighting axis 9 is inclined with respect to the face 17 (the light rays forming the light beam are refracted by said face 17) or is orthogonal to said face 17.

[0262] The light rays propagating along the lighting axis 9 then propagate in the optical module 2 so as to form, at the acquisition surface 3, a given incident light ray 14 which does not coincide with the lighting axis 9. The given incident light ray 14 forms an angle a with the normal 13.

[0263] The given incident light ray 14 is reflected on the acquisition surface 3, thus defining a given reflected light ray 15. In addition, the lighting system 8 and the optical acquisition system 4 are arranged so that the included angle Ω of the given reflected light ray 15 and the first light ray 18 is strictly greater than the angle β.

[0264] In the present case, the angle Ω is greater than 60 degrees, and here greater than 70 degrees, and here greater than 90 degrees. The angle Ω is for example 101 degrees.

[0265] In the present case, the angle Ω is greater than 2β. In fact β is equal to 45 degrees in the present case.

[0266] The lighting system 8 is arranged close to the optical acquisition system 4.

[0267] The lighting system 8 is arranged above the optical acquisition system 4. The lighting system 8 is thus not directed towards the optical acquisition system 4.

[0268] Optionally, the lighting system 8 and the optical acquisition system 4 are arranged so that the included angle γ of the first light ray 18 and the given incident light ray 14 is strictly less than β.

[0269] Optionally, the angle γ is less than 35 degrees, preferably less than 25 degrees. In the present case, for example the angle γ is equal to 11 degrees (the angle a is equal to 56 degrees).

[0270] The lighting system 8 is here arranged so that the angle a is smaller than the angle β.

[0271] The lighting system 8 is here thus arranged so that the angle a is greater than the critical angle θ c (but obviously still smaller than the limit angle θ1).

[0272] Furthermore, the optical module 2 comprises at least one zone 10 treated so as to absorb the light rays emitted by the lighting system 8 and reflected at the acquisition surface 3.

[0273] For example, said zone 10 is covered with a coating (directly on the whole and / or indirectly on the outside and / or on the inside of at least one face of the optical module 2: this treated zone 10 can thus be arranged on the outside and / or on the inside of the optical module 2) which absorbs at least 95%, and preferably at least 98%, of the light rays which reach it. The coating is for example a dark coating (i.e. a coloured coating which absorbs at least 95%, and preferably at least 98%, of the light rays) and for example black.

[0274] Optionally, said zone 10 is arranged on at least one lateral face of the optical module 2 and preferably here on the lateral face opposite the exit face 5 and the surface 17 (on this side of the optical module 2, the optical module 2 thus comprises only a single lateral face connecting the upper face and the lower face, said face extending orthogonally to the upper face and to the lower face). Preferably, said zone 10 extends over at least the whole of said opposite lateral face.

[0275] The lighting system 8 is here arranged so that all the light rays emitted by the lighting system 8 and reflected by the acquisition surface 3, after any number of reflections on the surfaces of the optical module 2, finally reach the zone 10.

[0276] A device 1 is thus described having an angle Ω of 101°. For example, with an anisotropy factor g of 0.7, the attenuation of the device 1 is Figure 1 10 times greater than that of the device of the prior art shown.

[0277] Figure 8 A seventh embodiment is shown which is identical to Figure 7 that shown, with the difference that the lighting system 8 is cleverly arranged so that its lighting axis 9 is parallel to the optical axis 6.

[0278] Preferably, the lighting system 8 and the optical acquisition system 4 are also arranged so that their respective bases extend in the same plane.

[0279] Generally, the lighting system 8 and the optical acquisition system 4 are mounted on the same support or on two different but parallel supports and optionally extend in the same plane.

[0280] The rest of the description made for the sixth embodiment thus also applies to the seventh embodiment, in particular concerning the angles a, B, g and Q.

[0281] It is noted that the application is not limited to the above embodiments, any modification being within the scope of the application as defined by the claims.

[0282] The device can thus comprise different forms of optical module, which have been described as prismatic forms but with different numbers of facets. The optical module can have other shapes and for example be opaque overall. The shape of the optical module obviously allows the passage of the optical path through said module, in particular the acquisition surface, from the illumination system to the optical acquisition system.

[0283] The illumination system can be placed beside the optical system, below or above the optical system, between the optical acquisition system and the acquisition system, etc. The illumination system and / or the optical acquisition can be carried by a printed circuit board and optionally by the same printed circuit board.

[0284] Optionally, the illumination system will be placed so that its illumination axis is parallel to or coincides with the optical axis of the optical system.

[0285] The placement of the illumination system can be different from that shown. For example, the illumination system can comprise a plurality of light sources, which can comprise a plurality of LED light sources, the illumination system can comprise or be associated with one or more backlights, etc. In the case where the illumination system comprises a plurality of light sources, for example a plurality of LED light sources, the light sources will preferably be placed so that all their illumination axes are parallel to one another (the illumination system then having a total illumination axis parallel to each of the illumination axes of each of the light sources). More preferably, the light sources will all be placed in the same plane. For example, the light sources can be mounted on the same support, for example a printed circuit board. The illumination system can comprise a light guide.

[0286] The area treated to absorb the light rays emitted by the illumination system 8 and reflected at the acquisition surface 3 can not be carried by the optical module but for example by other elements outside the device, for example the frame shown in the figures. It is of course understood that this aspect can apply to the other embodiments, just as the optical module of the third embodiment can carry said treated area. Figure 4 The device can not comprise a frame or can comprise a frame different from that shown. For example, the entire upper surface of the optical module can form the entire acquisition surface.

[0287] The device can not comprise a frame or can comprise a frame different from that shown. For example, the entire upper surface of the optical module can form the entire acquisition surface.

[0288] Of course, the device can be configured so that the number of reflections of the first light rays before reaching the optical acquisition system is different from that described and / or so that the number of reflections of the light rays propagating along the illumination axis before reaching the acquisition surface is different from that described.

[0289] The arrangement of the illumination system can be different from that described. For example with reference to Figure 2 An illumination system can be obtained which is arranged symmetrically with respect to the optical axis.

[0290] It is clear that one or more of the described embodiments can be combined.

Claims

1. A biometric capture device comprising: - an optical module (2) with an acquisition surface (3) on which, in use, a user places at least one body part with at least one mark, - an optical acquisition system (4) configured to acquire at least one image of at least one mark of said body part through at least one face of said module, called exit face (5), wherein said optical acquisition system is arranged so that a first light ray propagating outside said optical module along an optical axis (6) of said optical acquisition system forms an angle β with the normal (13) to said acquisition surface at said acquisition surface (3), the value of said angle being greater than the critical angle determined by the refractive indices of said optical module and air, and further so that said optical axis (6) forms an angle with the normal to said exit face (5) which is less than said critical angle, - an illumination system (8) configured to illuminate said acquisition surface (3), said illumination system generating a light beam defined by an illumination axis (9), a second light ray propagating outside said optical module along said illumination axis (9) and then propagating in said optical module so as to form a given incident light ray (14) at said acquisition surface (3), said given incident light ray (14) being reflected on said acquisition surface (3) so as to define a given reflected light ray (15), said illumination system and said optical acquisition system being arranged so that the angle Ω between: - said given reflected light ray (15), if said given reflected light ray (15) is in the plane defined by the normal (13) to said acquisition surface (3) and said first light ray, or the projection of said given reflected light ray (15) in said plane in the opposite case, and - the first light ray is strictly greater than the angle β.

2. The device according to claim 1, wherein said illumination system (8) illuminates through a face (16) of said optical module adjacent to said exit face (5).

3. The device according to claim 1 or 2, wherein said optical acquisition system (4) is arranged so that said optical axis (6) forms an angle with the normal to said exit face (5) which is less than 2 degrees.

4. The device according to one of claims 1 to 3, wherein said angle Ω is greater than 60 degrees.

5. The device according to one of claims 1 to 4, wherein said angle Ω is less than 2β.

6. The device according to one of claims 1 to 5, wherein said illumination system (8) and said optical acquisition system (4) are arranged so that the angle γ between said first light ray and said given incident light ray (14) is strictly less than β.

7. The device according to claim 6, wherein said angle γ is less than 35 degrees.

8. The device according to one of claims 1 to 7, wherein the angle of said given incident light ray (14) with the normal (13) to said acquisition surface (3) is greater than β.

9. The device according to one of claims 1 to 8, comprising a single illumination system and / or a single optical acquisition system.

10. Apparatus according to one of claims 1 to 9, wherein the illumination system (8) and the optical acquisition system (4) are carried by supports extending in coincident or parallel planes.

11. Apparatus according to one of claims 1 to 10, wherein the optical module (2) is in the form of a prism.

12. Apparatus according to one of claims 1 to 11, wherein the optical module (2) is in the form of a glass sheet: - with parallel faces, at least one of which has a lateral face that is inclined over a portion, or - a wafer, the bottom face of which has a plurality of microprisms.

13. Apparatus according to one of claims 1 to 12, comprising at least one zone (10) treated to absorb the light rays emitted by the illumination system (8) and reflected at the acquisition surface (3).

14. Apparatus according to claim 13, wherein the zone (10) is coated with a dark colour.

15. Apparatus according to one of claims 1 to 14, wherein the optical acquisition system (4) and the illumination system (8) are close to one another.

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