Optical acquisition device for biometric systems
The invention relates to a device for acquisition of images for a biometric system, which includes an optical assembly and at least one imager for acquisition of an image of an object to be analysed presented in front of the assembly at a non-determined distance from the latter. The assembly includes at least one diaphragm with a coded aperture. The optical assembly allows acquisition by the sensor(s) of an image of the object capable of being exploited to deduce therefrom the searched biometric information, and of an image of the object acquired via the coded aperture of the diaphragm. The device also includes a processing unit to determine the distance of the object to be analysed as a function of the image of the object acquired via the coded aperture of the diaphragm.
1. Method for acquiring images for a biometric system, wherein the method comprises steps of
providing an optical assembly which receives an input optical signal of an object,
providing a first optical filter configured to selectively transmit frequencies in a first frequency band and a diaphragm with a first coded aperture which convert the input optical signal into a coded optical signal having frequencies only in the first frequency band,
providing a second optical filter configured to selectively transmit frequencies comprises in a second frequency band different from the first frequency band, wherein the second optical filter filters the input optical signal so as to produce a biometric optical signal having frequencies only in the second frequency band,
acquiring a first image of the object from said biometric optical signal, wherein the first image carries biometric information deducible from the first image, and acquiring a second image of the object from the coded optical signal,
determining a distance between the object and the optical assembly from the second image.
2. Method as claimed in claim 1 , wherein the first image shows a face, an iris or a vein, wherein the method comprises carrying out a identification or authentication based on the first image.
3. The method according to claim 1 , wherein the first optical filter and the second optical filter are stacked together.
4. The method according to claim 1 , further comprising projecting an image in the second frequency band onto the object.
5. The method according to claim 1 , wherein the first frequency band is a blue frequency band.
6. The method according to claim 1 , wherein the diaphragm with the first coded aperture comprises a first semi-opaque surface opaque to the second frequency band and transparent to the first frequency band, and wherein the first coded aperture is transparent to the first frequency band and to the second frequency band.
7. The method according to claim 1 , comprising providing a second diaphragm comprising an aperture transparent at least to the first frequency band and to the second frequency band, and a second semi-opaque surface which is opaque to the first frequency band and transparent to the second frequency band.
8. The method according to claim 7 , wherein the aperture of the second diaphragm is a centred and circular aperture enabling acquisition of the first image in the first frequency band.
9. The method according to claim 7 , wherein the aperture of the second diaphragm is a second coded aperture separate from the first coded aperture, and wherein the first image is reconstituted from optical signals output by the diaphragm with the first coded aperture diaphragm and by the second diaphragm.
10. The method according to claim 1 , further comprising
splitting the input optical signal into a first optical signal in the first frequency band and a second optical signal in the second frequency band,
converting the second optical signal into the coded optical signal using the diaphragm with the first coded aperture,
acquiring the first image from the first optical signal using a first imager,
acquiring the second image from the coded optical signal using a second imager different from the first imager.