Granted Patent B2

US 10,068,125 · App. 15/315,511 · Granted Sep 4, 2018

Abstract

Claims (62)

1. A method for validation of whether an object is an element of the human body comprising at least the following steps:

illumination, by at least one first light source emitting in the infrared and by at least one second light source emitting in the visible spectrum, of an object whereof the aim is to validate that said object corresponds to an element of the human body, said second light source emitting light at wavelengths inferior to those of the first source;

acquisition of an image by an image sensor, the pixels of said image being associated with at least two characteristic values respectively of a first color component and of a second color component, said second component corresponding to at least one wavelength of the second source, the respective light powers of illumination of the first light source and of the second light source being previously calibrated so that the first color component and the second color component are statistically balanced for an authentic element of the human body, wherein the first color component and the second color component are statistically balanced for an authentic element of the human body when a difference between the first color component and the second color component in an area of an image corresponding to said authentic element of the human body is less than a threshold;

execution of a validation processing as a function of comparisons between the values of the second component of the pixels of an area of interest of the image and the values of the first component of said pixels;

validation or not of the authenticity of the object as a function of the result of the validation processing.

2. The method according to claim 1 , wherein the first light source emits incident light to the object outside the field of acquisition of the image sensor, and the second light source emits incident light to the object in the field of acquisition of the image sensor.

3. The method according to claim 1 , wherein a first polarizer is disposed on the light path between the first light source and the object, said first polarizer being a linear polarizer with a polarization axis in a first direction, and a second polarizer is disposed at the image sensor, said second polarizer being a linear polarizer with a polarization axis in a second direction orthogonal to the first direction, the first light source illuminating the object by polarized light in the first direction and the second light source illuminating the object by non-polarized light in the first direction.

4. The method according to claim 1 , wherein the first light source emits in wavelengths between 780 nm and 900 nm, and the second light source emits in wavelengths between 435 nm and 550 nm.

5. The method according to claim 1 , wherein the exposure time during which the object is illuminated is previously determined by a step during which the object is illuminated only by the first light source at a determined power, said exposure time corresponding to the time necessary so that the average level of exposure of the image sensor to light reaches a predetermined value.

6. The method according to claim 5 , wherein the validation processing is also a function of the exposure time.

7. The method according to claim 1 , wherein the power of the first light source is previously determined by a step during which the object is illuminated only by the first light source during a determined exposure time, said power corresponding to the power necessary so that the average level of exposure of the image sensor to light reaches a predetermined value.

8. The method according to claim 7 , wherein the validation processing is also a function of the power of the first light source thus determined.

9. The method according to claim 1 , wherein the validation processing comprises calculation of a reflection parameter which is a function of the sum of the values of the second component of the pixels of the area of interest whereof the first component is less by a predetermined value than the value of the second component.

10. The method according to claim 9 , wherein said sum is weighted by the inverse of weights, functions of the predetermined spatial distribution of the light intensity of the second light source.

11. The method according to claim 10 , wherein the reflection parameter β is determined according to the following formula:

β

=

1

N

ROI

⁢

∑

x

∈

ROI

⁢

⁢

x

g

·

H

⁡

(

x

g

-

(

x

r

+

ɛ

)

)

ω

x

with H the Heaviside function, N ROI the total number of pixels x of the area of interest ROI, x r the value of the first component of the pixel x, x g the value of the second component of the pixel x, ε a threshold constant, and ω x a predetermined weight, function of the light intensity of the second light source for the pixel x.

12. A non-transitory computer-readable non-volatile memory medium product storing program code instructions for executing the steps of the method according to claim 1 when said program is executed by a computer.

13. A validation device configured to execute a validation method according claim 1 , said validation device comprising

at least one first light source configured to emit light in the direction of the object;

at least one second light source configured to emit light in the direction of the object at wavelengths inferior to those of the first source;

an image sensor sensitive to a range of wavelengths covering at least partly the first range of wavelengths and the second range of wavelengths, configured to acquire an image of the object whereof the pixels are associated with at least two characteristic values respectively of a first color component and of a second color component, said second component corresponding to at least one wavelength of the second range of wavelengths,

a processing unit comprising a computer with a processor and a memory, said processing unit configured to execute a validation processing as a function of comparisons between the values of the second component of the pixels and the values of the first component in an area of interest of the image and configured to validate or not of the authenticity of the object as a function of the result of the validation processing,

wherein respective light powers of illumination of the first light source and of the second light source are calibrated so that the first color component and the second color component are statistically balanced for an authentic element of the human body, wherein the first color component and the second color component are statistically balanced for an authentic element of the human body when a difference between the first color component and the second color component in an area of an image corresponding to said authentic element of the human body is less than a threshold.

14. A method for calibrating a validation device according to claim 13 , comprising at least the following steps, for each of the authentic elements of the human body of a learning base:

illumination of the authentic element of the human body by the first light source,

determination of an exposure time corresponding to the time necessary so that the average level of exposure to the light of the image sensor reaches a predetermined value, the light power of the first light source being selected to make appear the venous network inside the authentic element of the human body on an image acquired by the image sensor,

iteratively until and as long as the difference between the first color component and the second color component in an area of interest of the image corresponding to the authentic element of the human body is less than an equilibrium threshold:

simultaneous illumination of the element of the human body by the first light source and by the second light source during said exposure time,

acquisition of an image by the image sensor,

acquisition of an image by the image sensor,

increase in the power of the second light source,

the light power of the second light source being selected so as to be statically representative of the powers associated with each of the authentic elements of the human body of the learning base.

Assignments (11)