FR3117654A1 - Image acquisition device - Google Patents

Abstract

Image acquisition device The present description relates to an image acquisition device comprising a stack comprising: an organic image sensor (19); an angle filter (21); a lighting system (23); And a liquid crystal screen (25). Figure for abstract: Fig. 2

Description

Image acquisition device

The present description relates generally to image acquisition devices and, more particularly, to biometric systems for acquiring fingerprint images.

Fingerprint image acquisition systems are used in many fields in order, for example, to secure devices, secure buildings, control access or control the identity of individuals.

Biometric checks carried out by image acquisition systems are becoming more democratic in order to best protect access to data, information and places.

There is a need to improve biometric image acquisition systems.

One embodiment overcomes all or part of the drawbacks of known biometric image acquisition systems.

One embodiment provides an image acquisition device comprising a stack comprising:
an organic image sensor;
an angular filter;
a lighting system; And
a liquid crystal display.

According to one embodiment, the lighting system comprises an organic light-emitting diode.

According to one embodiment, the lighting system comprises a waveguide layer with which is laterally associated one or more light-emitting diodes.

According to one embodiment, the light-emitting diode or diodes are adapted to emit radiation in the visible and/or the infrared.

According to one embodiment, the liquid crystal screen comprises a layer of liquid crystals, electrodes, polarizers and a layer comprising thin film transistors.

According to one embodiment, the device comprises one or more color filters.

According to one embodiment, the device comprises a touch panel.

1. mise sous tension du système d'éclairement ;
2. affichage d'une image sur l'écran à cristaux liquides ;
3. suppression de l'affichage de l'information sur l'écran à cristaux liquides ; et
4. acquisition d'une image.

One embodiment provides a method for acquiring an image, by the image acquisition device as described above, comprising the following successive steps:

1. switching on the lighting system;
2. displaying an image on the liquid crystal screen;
3. elimination of the display of information on the liquid crystal screen; And
4. acquiring an image.

According to one embodiment, the method comprises comprising a step e) of detecting the presence of at least one finger of a user by the device, step e) being carried out between step b) and step c) or before step a).

According to one embodiment, step e) is performed by disturbing an oscillation frequency.

According to one embodiment, the method comprises, in a step f), the switching off of the illumination source carried out before step e).

According to one embodiment, the method comprises, after step d), the display on the liquid crystal screen of another image informing of the correct performance of the method.

These characteristics and advantages, as well as others, will be set out in detail in the following description of particular embodiments given on a non-limiting basis in relation to the attached figures, among which:

there represents by a block diagram, partial and schematic, an example of an image acquisition system;

there represents by a sectional view, partial and schematic, an embodiment of an image acquisition device;

there represents by a sectional view, partial and schematic, another embodiment of an image acquisition device;

there represents three examples of images that can be displayed on the image acquisition devices of FIGS. 2 and 3;

there represents, by a block diagram, an example of implementation of an image acquisition method;

there represents, by a block diagram, another example of implementation of an image acquisition method; And

there represents, by a sectional, partial and schematic view, another embodiment of an image acquisition device.

The same elements have been designated by the same references in the various figures. In particular, the structural and/or functional elements common to the various embodiments may have the same references and may have identical structural, dimensional and material properties.

For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been represented and are detailed. In particular, the image processing unit of the system has not been detailed.

Unless otherwise specified, when reference is made to two elements connected together, this means directly connected without intermediate elements other than conductors, and when reference is made to two elements connected (in English "coupled") between them, this means that these two elements can be connected or be linked through one or more other elements.

In the following description, when referring to absolute position qualifiers, such as "front", "rear", "up", "down", "left", "right", etc., or relative, such as the terms "above", "below", "upper", "lower", etc., or to qualifiers of orientation, such as the terms "horizontal", "vertical", etc., it reference is made unless otherwise specified to the orientation of the figures.

In the rest of the description, unless otherwise specified, a layer or a film is said to be opaque to radiation when the transmittance of the radiation through the layer or the film is less than 10%. In the rest of the description, a layer or a film is said to be transparent to radiation when the transmittance of the radiation through the layer or the film is greater than 10%, preferably greater than 50%. According to one embodiment, for the same optical system, all the elements of the optical system which are opaque to radiation have a transmittance which is less than half, preferably less than a fifth, more preferably less than a tenth, of the transmittance the weakest of the elements of the optical system transparent to said radiation. In the remainder of the description, the term "useful radiation" is used to refer to the electromagnetic radiation passing through the optical system in operation.

In the remainder of the description, the term “optical element of micrometric size” is used to refer to an optical element formed on one face of a support whose maximum dimension, measured parallel to said face, is greater than 1 μm and less than 1 mm.

Embodiments of optical systems will now be described for optical systems comprising a matrix of micrometric-sized optical elements in the case where each micrometric-sized optical element corresponds to a micrometric-sized lens, or microlens, composed of two dioptres . However, it is clear that these embodiments can also be implemented with other types of optical elements of micrometric size, each optical element of micrometric size being able to correspond, for example, to a Fresnel lens of micrometric size, to a micron-sized gradient index lens or to a micron-sized diffraction grating.

In the rest of the description, visible light is called electromagnetic radiation whose wavelength is between 400 nm and 700 nm, and, in this range, red light is electromagnetic radiation whose wavelength is between 600 nm and nm and 700 nm. Infrared radiation is electromagnetic radiation with a wavelength between 700 nm and 1 mm. In infrared radiation, a distinction is made in particular between near infrared radiation, the wavelength of which is between 700 nm and 1.7 μm.

Unless specified otherwise, the expressions “about”, “approximately”, “substantially”, and “of the order of” mean to within 10%, preferably within 5%.

Unless specified otherwise, the expressions “all the elements”, “all the elements”, “each element”, mean between 95% and 100% of the elements.

Unless otherwise specified, the expression "it comprises only the elements" means that it comprises, at least 90% of the elements, preferably that it comprises at least 95% of the elements.

There represents, by a partial and schematic block diagram, an example of an image acquisition system.

The image acquisition system, illustrated in , understand :
an image acquisition device 11 (DEVICE); And
a processing unit 13 (PU).

The processing unit 13 preferably comprises means for processing the signals supplied by the device 11, not shown in . The processing unit 13 comprises, for example, a microprocessor.

The device 11 and the processing unit 13 are preferably connected by a link 15. The device 11 and the processing unit 13 are, for example, integrated in the same circuit.

According to one embodiment, not shown, the image acquisition system 11 comprises a battery allowing the electrical supply of the image acquisition device 11 and of the processing unit 13.

There represents, by a partial and schematic sectional view, an embodiment of an image acquisition device 17.

More specifically, the illustrates an embodiment of the device illustrated in . The device 17 can, for example, be coupled to a processing unit and be integrated into the image acquisition system as described in relation to the . The device 17 forms, for example, part of a module for the detection and recognition of individuals by the detection and recognition of fingerprints and/or veins, for example, in the fingers of a hand.

The image acquisition device 17, illustrated in , allows on the one hand to acquire useful images in the biometric recognition, preferably, the recognition of fingerprints and veins of one or more fingers of a user placed on the surface of the device on a crystal screen 25 or LCD (Liquid Crystal Display), that is to say a liquid crystal display device to be coupled to an illumination system. The image acquisition device 17 also makes it possible to communicate with the user by displaying texts or symbols on the surface of the device on the screen. This display, for example by symbols, allows the user to properly position his or her fingers on the surface of the device, on the screen, in order to acquire optimal fingerprint images.

The image acquisition device 17 comprises from bottom to top :
an organic image sensor 19 (SENSOR);
an angular filter 21 (ANGULAR FILTER);
an illumination system 23 (OLED PANEL); And
the LCD screen 25 ,
the organic image sensor 19, the angular filter 21 and the illumination system 23 defining an imaging module and the liquid crystal screen 25 making it possible to pixelate the information transmitted on demand.

According to one embodiment, not shown, device 17 comprises one or more color filters.

In the present description, the embodiments of the image acquisition devices of FIGS. 2 and 3 are represented in space according to a direct orthogonal XYZ frame, the Y axis of the XYZ frame being orthogonal to the upper face of the sensor. of pictures 19.

The angular filter 21 preferably covers the entire upper face of the image sensor 19. The illumination system 23 preferably covers the upper face of the angular filter 21 and the LCD screen 25 covers, preferably, the whole of the upper face of the lighting system 23.

The image sensor 19 is adapted to capture images from which are extracted information relating to the veins and to the fingerprint of a finger 26 of a user of the device 17, when the finger is located above the face upper part of the device 17. The extraction of this information, from an image acquired by the image sensor 19, is carried out by the processing unit illustrated in .

The image sensor 19 is a sensor with photodetectors or organic photodiodes (OPD, Organic Photodiode). The photodiodes are, for example, integrated on a substrate with MOS transistors (Metal Oxide Semiconductor, metal oxide semiconductor), a substrate with thin-film transistors (TFT or Thin-Film Transistor) or a substrate with organic transistors. The substrate is for example made of silicon, preferably of monocrystalline silicon. The substrate is, for example, a flexible substrate. The channel, source and drain regions of TFT transistors are for example made of amorphous silicon (a-Si or amorphous Silicon), of indium, gallium and zinc oxide (IGZO Indium Gallium Zinc Oxide) or of silicon low temperature polycrystalline (LTPS or Low Temperature Polycrystalline Silicon). The photodiodes of the image sensor 19 comprise, for example, a mixture of organic semiconductor polymers such as poly(3-hexylthiophene) or poly(3-hexylthiophene-2,5-diyl), known under the name P3HT, mixed with methyl [6,6]-phenyl-C61-butanoate (N-type semiconductor), known under the name PCBM. The photodiodes of the image sensor 19 comprise, for example, small molecules, that is to say molecules having molar masses of less than 500 g/mol, preferably less than 200 g/mol.

The angular filter 21 is adapted to filter the incident radiation according to the incidence of the radiation with respect to the Y axis.

According to one embodiment, the angular filter 21 corresponds to a stack of an array of lenses and a matrix of holes and/or to a high pass or band pass filter specific to certain wavelengths, and/or to one or more polarizers.

For example, the angular filter 21 is, more particularly, adapted so that the image sensor 19 only receives the rays whose respective incidences relative to the Y axis are less than a maximum incidence of less than 45°, preferably less than 30°, more preferably less than 10°, even more preferably less than 4°. The angular filter 21 is adapted to block the rays of the incident radiation whose respective incidences with respect to the Y axis are greater than the maximum incidence.

According to the embodiment illustrated in , the illumination system 23 corresponds to a panel of one or more organic light-emitting diodes (OLED, Organic Light-Emitting Diode) mounted on a support. The illumination system 23 is monochromatic or polychromatic. The illumination system 23 can, optionally, comprise a collimator and/or a polarizer between the OLED(s) and the LCD screen 25.

In , the illumination system 23 is located between the LCD screen 25 and the angular filter 21. Alternatively, the illumination system 23 is positioned between the angular filter 21 and the image sensor 19 or on the side of the sensor d images 19 opposite the angular filter 21. Alternatively, the illumination system 23 is positioned above the LCD screen 25. If the illumination system 23 is located on the side of the image sensor 19 opposite the angular filter , that is to say on the underside of the image sensor 19, the image sensor 19 comprises areas transparent to the light emitted by the illumination system 23 so that the light emitted by the lighting system illumination 23 passes through the image sensor 19 without it "dazzling" the image sensor 19. If the illumination system 23 is located between the image sensor 19 and the angular filter 21 or between the filter angular 21 and the LCD screen 25, it is transparent, or partly transparent (that is to say having a transmittance between between 10% and 40%) to the light reflected by the finger(s) 26.

According to the embodiment illustrated in , the LCD 25 includes:
a layer of liquid crystals 27 (LC LAYER);
two electrodes located on either side of layer 27, one of electrodes 29T (T. ELECTRODE), called the top electrode, being located on the upper face of layer 27 and the other of electrodes 29B (B. ELECTRODE), called the bottom electrode, being located on the underside of the layer 27;
a layer 31 of thin-film transistors (TFT, Thin-Film Transistor) making it possible to control and command the electric current which passes through the electrodes 29B, 29T, the layer 31 being, preferably, located on the lower face of the lower electrode 29B;
two polarizers located on either side of the structure defined by the electrodes 29B, 29T, the layer 27 and the layer 31, one of the polarizers 33T (T. POLARIZER) called top polarizer or analyzer, being located on the face top of the top electrode 29T and the other of the polarizers 33B (B. POLARIZER), called the bottom polarizer, being located on the underside of the layer 31; And
two alignment layers 35B and 35T (AL), located respectively between layer 27 and bottom electrode 29B and between layer 27 and top electrode 29T.

The electrodes 29T and 29B are, for example, made from one or more metal oxides such as indium oxide doped with tin (ITO, Indium Tin Oxide), molybdenum trioxide (MoO3), zinc oxide doped with aluminum (AZO), zinc oxide (ZnO), and/or one or more metals such as aluminum, silver or copper and/or graphene and/or silver nanowires. The electrodes 29T and 29B preferably each have a sufficiently small thickness to be transparent. The electrodes 29T and 29B each have, for example, a thickness of between 5 nm and 500 nm, preferably between 50 nm and 200 nm. The electrodes 29T and 29B can, for example, be put at different potentials in order to produce an electric field through the layer 27.

By way of example, a layer of color filters, not shown, is located between electrode 29T and polarizer 33T.

Preferably, at least one of the two electrodes 29T or 29B is pixelated according to a matrix so that the LCD screen 25 is pixelated according to this same matrix. For example, electrode 29B is pixelated.

Layer 27 is composed of nematic liquid crystals which can preferably be arranged in a helix. The liquid crystals constituting the layer 27 have, for example, the property of being arranged parallel to an electric field which crosses the layer 27 (that is to say parallel to the Y axis) or perpendicular to the Y axis. at rest (i.e. for a zero electric field).

The liquid crystals of layer 27 can be N-(4-methoxybenzylidene)-4-butylaniline (MBBA), be derived from cholesterol or be derivatives of cyanobiphenyls or cyanophenylcyclohexanes and more generally any material suitable for the formation of liquid crystals . Layer 27 of liquid crystals has, for example, a thickness comprised between 2 μm and 30 μm, preferably between 5 μm and 20 μm.

The purpose of the layers 35B and 35T is to initiate the alignment of the liquid crystal molecules. In other words, layer 35B makes it possible to orient the liquid crystal molecules located in its vicinity in a first direction and layer 35T makes it possible to orient the liquid crystal molecules located in its vicinity in a second direction different from the first direction, preferably perpendicular to the first direction.

Layers 35B and 35T are, according to one embodiment, made of organic polymer, for example based on polyimide (PI) or polydimethylsiloxane (PDMS) in which grooves have been created. We then speak of rubbed polymer. The molecules present in layer 27 will then tend to line up in the direction of the grooves. Layers 35B and 35T each have, for example, a thickness comprised between 100 nm and 30 μm, preferably comprised between 500 nm and 25 μm. The grooves formed in layer 35T are then parallel to polarizer 33T and the grooves formed in layer 35B are then parallel to polarizer 33B.

Layers 35B and 35T are, according to a preferred embodiment, made from non-organic materials such as silica. Preferably, layers 35B and 35T are made from silicon oxide SiO _x , for example silicon dioxide SiO ₂ . The material of the layers 35B and 35T is, for example, deposited respectively on the upper face of the lower electrode 29B and the lower face of the upper electrode 29T by vacuum spraying. Layers 35B and 35T each have, for example, a nanometric thickness, that is to say a thickness comprised between 5 nm and 100 nm, preferably comprised between 10 nm and 50 nm.

As a variant, the layers 35B and 35T are made from organic materials whose alignment of the molecules is photo-induced, that is to say the organic layers are photo-aligned using UV light. polarized. As a variant, the organic layers are produced by molding.

The two polarizers 33T and 33B are crossed linear polarizers, that is to say they respectively have a polarization in a first direction which we will call horizontal polarization hereafter and in a second direction, preferably orthogonal to the first direction, which we will subsequently call vertical polarization. The high polarizer 33T polarizes, according to the embodiment illustrated in , in the second direction and the bottom polarizer 33B polarizes in the first direction.

The LCD 25 pixels are controlled separately. Each pixel is in particular controlled by one or more transistors present in layer 31. At rest, that is to say when the electrodes 29T and 29B of the same pixel are at the same potential, the liquid crystal molecules form between the layer 35B and layer 35T a helix having an angle of rotation of 90°. The liquid crystal molecules located in the vicinity of layer 35T are oriented in the second direction and the liquid crystal molecules located in the vicinity of layer 35B are oriented in the first direction. The unpolarized light emitted by the illumination system 23 passes through the polarizer 33B and becomes polarized. At the output of the polarizer 33B, the light passes through the layer of liquid crystals 27 and sees its polarization changed by 90°. At the output of the liquid crystal layer 27, the light has a polarization aligned with the polarizer 33T.

When the electrodes 29T and 29B of the same pixel are not at the same potential, the liquid crystals tend to orient themselves, throughout the thickness of the layer 27, parallel to the electric field created between the two electrodes 29T and 29B. The unpolarized light emitted by the illumination system 23 therefore passes through the bottom polarizer 33B and the layer 27 but is blocked by the top polarizer 33T. The non-polarized light emitted by the illumination system 23 therefore does not pass through the LCD screen 25.

The display of an image on the LCD screen 25 results from the activation of some of the pixels of the LCD screen 25. Indeed, some of the pixels of the LCD screen 25, by the passage of an electric field within the layer 27 will appear black while others will allow the radiation emitted by the illumination system 23 to pass. All of these pixels form a text or symbols.

The device 17 comprises, according to the embodiment illustrated in , on the upper face of the LCD screen 25, more precisely, on the upper face of the high polarizer 33T, a protective layer 41 (GLASS COVER). The protective layer 41 is preferably made of glass and has a thickness of less than one millimeter, preferably of the order of 0.7 mm.

According to the embodiment illustrated in , the device 17 comprises an optional touch panel 39 (TOUCH PANEL), of the resistive or capacitive type allowing detection of the contact of the finger(s) 26 with the device 17.

According to an embodiment not shown, the protective layer 41 is a plastic layer chosen from polyethylene terephthalate (PET), poly(ethylene naphthalate) (PEN), a cyclic olefin polymer (COP) and polyimide (PI) or a layer of an inorganic material chosen from silicon nitride (SiN), silicon dioxide (SiO ₂ ) deposited by plasma-enhanced chemical vapor deposition (PECVD, plasma-enhanced chemical vapor deposition) or by physical vapor deposition (PVD, physical vapor deposition) or a layer of an epoxy or acrylate glue.

According to an embodiment not shown in , the touch panel 39 is omitted and the finger detection is performed by means of one of the two electrodes 29T and 29B of the LCD screen 25 or by means of one of the two electrodes of the OLED panel 23.

According to an embodiment not shown in , the image acquisition device comprises an infrared filter in a layer covering the image sensor 19. The infrared filter is not necessarily in contact with the image sensor 19 or the OLED panel 23. It can be located in the structure of the LCD screen 25. The infrared filter blocks, for example, the infrared radiation emitted by the sun which risks saturating the image sensor 19 during use of the image acquisition device. outdoor 17 pictures.

There represents, by a partial and schematic sectional view, another embodiment of an image acquisition device 43.

More particularly, the image acquisition device 43 illustrated in is similar to the image acquisition device 17 illustrated in except that the illumination system 23 is a waveguide layer 45 (WAVEGUIDE) associated with one or more light-emitting diodes 47 (LED).

Waveguide layer 45 preferably covers the stack of image sensor 19, angular filter 21 and LCD screen 25. LEDs 47 are, for example, laterally coupled to layer 45 and are, for example, located out of plumb, in the Y direction, with the stack of the image sensor 19, the angular filter 21 and the layer 45. According to one embodiment, the LEDs are coupled to the waveguide layer 45 and located on one, two, three or four sides of the waveguide layer 45.

Preferably, the LEDs 47 can be organized in "bars" along the layer 45.

According to one embodiment, the LEDs 47 are adapted to emit radiation in the visible and/or the infrared.

Layer 45 called the waveguide layer comprises a structure of two or three media with different refractive indices (not shown in ).

For the purposes of the present description, the refractive index of a medium is defined as being the refractive index of the material constituting the medium for the range of wavelengths of the radiation picked up by the image sensor. The refractive index is considered to be substantially constant over the range of wavelengths of the useful radiation, for example equal to the average of the index of refraction over the range of wavelengths of the radiation picked up by the image sensor .

A waveguide layer is structurally adapted to allow the confinement and propagation of electromagnetic waves. The media are, for example, arranged in the form of a stack of three sub-layers, a central layer sandwiched between an upper sheath and a lower sheath, the refractive indices of the materials making up the sheaths being lower than the index refraction of the material making up the central layer, the lower sheath being located on the side of the image sensor 19. Preferably, microstructures are formed between the central layer and the lower sheath. The microstructures preferably have the shapes of prisms or teeth whose points are oriented in the direction of the object to be imaged and whose bases are flush with the rear face of the central layer. Each microstructure has a face slightly inclined in the direction of propagation of the wave so that the propagated wave is deflected and follows the geometry of the microstructure. The inclination of the face of the microstructure is, for example, between 5° and 80°. The inclination is preferably of the order of 45°. For example, the microstructures are not evenly distributed along the wave path. The density of the microstructures is preferably higher and higher as one moves away from the system of the radiation deflected by these microstructures. Alternatively, microstructures are present in the walls of the sheath.

According to one embodiment, the waveguide layer 45 is associated with a collimator, located on its upper face.

The network of microstructures formed in the layer 45 is, for example, suitable for guiding the waves emitted by the LEDs 47. The network then comprises microstructures inclined in the direction of the waves emitted by the LEDs 47. Optionally, the network of microstructures is adapted to extract light in a collimated manner.

According to one embodiment, the infrared filter (not shown) mentioned in relation to the embodiment illustrated in is, for example, located between the LEDs 47 and the waveguide layer 45.

There shows three examples of images that can be displayed on the image acquisition devices of Figures 2 and 3.

More specifically, the represents by views A, B and C, images displayed by the LCD screen 25 which define the outline of fingers.

The LCD screen 25 illustrated in FIGS. 2 and 3 allows the display of images, preferably texts or symbols, comprising one or more pieces of information allowing the guidance of a user of the device 17 or 43.

The display of images makes it possible, for example, initially to welcome the user, to indicate to him that a biometric analysis is going to be carried out. It allows, for example, in a second time to illustrate which fingers are concerned by the analysis and how to place them. It allows, for example, in a third time to inform the user that the analysis is finished, that it went well and possibly to wish the user a pleasant day.

View A of the shows an example of an image indicating the position of the fingers for an analysis of the fingers of the left hand.

View B of the shows an example of an image indicating the position of the fingers for a finger analysis of the right hand.

View C of the shows an example of an image indicating the position of the thumbs for an analysis of the thumbs of both hands.

There represents, by a block diagram, an example of implementation of an image acquisition method.

More specifically, the illustrates a method allowing the acquisition of images in the case of the devices illustrated in or 3.

The process illustrated in includes a step 49 of powering up the lighting system 23 (Source ON) or verifying that the lighting system 23 is indeed powered up.

Step 49 is followed by a step 51 of displaying an image on the LCD screen 25 (Information display on LCD screen). During step 51, the pixels of the LCD screen 25 are divided into two parts, a first part of the pixels intended to allow the radiation from the illumination source 23 to pass through and do not undergo any modification and a second part of the pixels. pixels intended to be black or dark undergo a modification.

Step 51 comprises three successive sub-steps. Step 51 thus comprises a step 53 during which an electric field is imposed between the two electrodes 29T and 29B (Voltage accross electrodes ON) of certain pixels of the LCD screen 25. The presence of an electric field tends to modify the orientation of the liquid crystal molecules (55, Orientation of liquid crystals) in these pixels, which then become black or gray depending on the intensity of the electric field emitted between the two electrodes 29T and 29B. At the scale of the device, an image is displayed (57, Information display on LCD screen). The image displayed during step 51 preferably includes information relating to the number of fingers to be positioned on the device and to their positions on the surface of the device.

Step 51 is followed by a step 59 during which the user positions one or more fingers on the surface of the device respecting the information previously indicated (Finger on display).

Step 59 is followed by a step 61 of detection of the finger or fingers by the device and more precisely by the touch panel 39 (Finger on display detected).

As soon as the finger is detected in step 61, the image displayed on the LCD screen 25 relating to the position of the finger(s) is removed during a step 63 (Information display OFF).

Step 63 comprises three sub-steps. Initially, in a step 65, the electrodes 29T and 29B of all the pixels are set to the same potential (Voltage across electrodes OFF) so that the electric field no longer crosses the layer 27. As soon as the electric field which crosses layer 27 is zero, the liquid crystal molecules are oriented perpendicular to the Y axis and in the form of a helix (67, Changing the orientation of liquid crystals). The change in orientation of the molecules of liquid crystals, in certain pixels, generates uniformity in the passage of light throughout the LCD screen 25. All the pixels thus allow light to pass in the same way, which causes the deletion of the image displayed on the LCD screen 25 (69, Information display OFF).

An image of the finger(s) can then be acquired (71, Image acquisition). The acquired image can, for example, be more resolved in predetermined zones and indicated by the display during step 51. As a variant, only the photodetectors located in the predetermined zones are activated in order to reduce the volume of data to be processed, increase the speed of image processing and, for example, increase the life of image sensors.

Following step 71, the image is for example processed and used during a step not shown.

Step 71 is followed by an optional step 51' similar to step 51 described above, during which an image is displayed on the LCD screen 25. During step 51', the image displayed includes, for example, a message indicating that the acquisition of the image of the finger(s) was successful.

It can be envisaged that at the start of the method, several different images displayed follow one another as mentioned above in relation to the .

There represents, by a block diagram, an example of implementation of an image acquisition method.

More specifically, the illustrates a method allowing the acquisition of images in the case of the device illustrated in .

The process illustrated in comprises a first step 73 consisting in the de-energization of the OLED 23 (OLED OFF) or in the verification of the de-energization of the latter. Step 73 corresponds to an initial module state, the OLED is off and the device is awaiting an event (positioning of a finger on the device).

At the end of step 73, the user touches the device, at a step 59 identical to step 59 mentioned in . The purpose of this step is to indicate to the image acquisition device that a user is ready for biometric recognition or analysis. In other words, the purpose of this step is, for example, to bring the device out of standby mode. Proceeding to step 75 when the finger or fingers are detected and the device has come out of standby mode (Finger on display detected). During step 75, the detection of the finger or fingers is carried out, for example advantageously, by the electrodes of the OLED 23. The power supply control of the OLED 23 is ensured via a microcontroller where a detection function of a finger is allowed through the comparator which is put into a state of relaxation oscillation. The output of the comparator is used to charge and discharge the detection capacitor, connected to one of the electrodes of the OLED (preferably electrode 29T). As a person's finger nears the OLED 23, an additional capacitance causes a frequency change in the oscillations of the comparator. This change in frequency is measured by the microcontroller which thus performs the function of detection layer. Alternatively, the sense capacitor is connected to electrode 29T of LCD screen 25.

As a variant, rather than using the electrodes of the OLED 23, the same detection could be done using the electrodes 29B and 29T of the LCD screen 25.

As soon as one or more fingers are detected, the OLED 23 is powered up (77, OLED ON) and an image is displayed on the LCD screen during a step 51 identical to step 51 mentioned in . The displayed image preferably includes an indication of the number, type and position of the finger(s) to be analyzed. At the end of the display of the image on the LCD screen 25, the user repositions or shifts his or her fingers to the locations indicated (79, Finger on display good position).

As for the process illustrated in , the process illustrated in continues with the deletion of the image in step 63, the acquisition of an image of the finger(s) in step 71 and possibly the display of another image in step 51'.

An advantage of this embodiment is the energy saving generated by putting the OLED 23 on standby.

Another advantage of this embodiment is that it makes it possible to dispense with a touch panel, which makes it possible to reduce the thickness of the image acquisition device.

There represents by a sectional view, partial and schematic, another embodiment of an image acquisition device 81.

More particularly, the image acquisition device 81 is similar to the image acquisition device 17 illustrated in with the difference that it does not include either the LCD screen 25 or the touch panel 39. Indeed, the image acquisition device 81 represents a device for which the acquisition of images is activated by the detection of a finger through one of the electrodes of the OLED 23. In other words, in the image acquisition device 81, the presence of a finger is detected by one of the electrodes of the OLED 23.

The image acquisition method adapted to the device 81 comprises a step of detecting a finger on the surface of the device which is carried out by the disturbance of an electric field, the electric field being generated by the polarization of the electrodes of an OLED.

The sequence of steps of the image acquisition method adapted to device 81 is, for example, the following:
the OLED 23 is switched off, for example, in standby;
generation of a state of oscillations of the comparator of the microcontroller;
detection of the disturbance of the frequency of the oscillations when the user touches the surface of the device;
the OLED comes out of sleep mode and is powered on; And
the image of the finger(s) is acquired.

An advantage of the embodiments and modes of implementation described in FIGS. 1 to 6 is that they make it possible to display information to the user, for example, to indicate to the user the type of analysis which is done.

Another advantage of the embodiments and modes of implementation described in FIGS. 1 to 6 is that they make it possible to automate the taking of fingerprints or fingerprints without requiring an external control.

Various embodiments and variants have been described. The person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to the person skilled in the art. The embodiments described are not limited to the examples of dimensions and materials mentioned above.

Finally, the practical implementation of the embodiments and variants described is within the abilities of those skilled in the art based on the functional indications given above.

Claims (12)

Image acquisition device comprising a stack comprising:
an organic image sensor (19);
an angular filter (21);
an illumination system (23); And
a liquid crystal display (25). Device according to Claim 1, in which the illumination system (23) comprises an organic light-emitting diode. Device according to Claim 1, in which the illumination system (23) comprises a waveguide layer with which one or more light-emitting diodes are laterally associated. Device according to Claim 3, in which the light-emitting diode or diodes are adapted to emit radiation in the visible and/or the infrared. Device according to any one of Claims 1 to 4, in which the liquid crystal screen (25) comprises a layer of liquid crystals (27), electrodes (29T, 29B), polarizers (33T, 33B) and a layer comprising thin film transistors (31). Device according to any one of Claims 1 to 5, comprising one or more color filters. Device according to any one of claims 1 to 6, comprising a touch panel (39). Method for acquiring an image, by the image acquisition device according to any one of Claims 1 to 7, comprising the following successive steps:

1. switching on the lighting system (23);
2. displaying an image on the liquid crystal screen (25);
3. elimination of the display of information on the liquid crystal screen; And
4. acquiring an image.

Method according to claim 8, comprising a step e) of detecting the presence of at least one finger of a user by the device, step e) being carried out between step b) and step c) or before step a). A method according to claim 9, wherein step e) is performed by disturbing an oscillation frequency. Method according to Claim 9 to 10, comprising, in a step f), the switching off of the illumination source carried out before step e). Method according to any one of Claims 8 to 11, comprising, after step d), the display on the liquid crystal screen of another image indicating that the method has been carried out correctly.