System and method for acquiring images of veins of a finger
A system for acquiring an image of veins of a finger includes a camera designed to acquire an image of said finger when it is passed in front of it, a lighting device designed to illuminate said finger and a control unit for controlling the illumination intensity of said lighting device. Also, at least one system measures the transmission power of said finger upstream of the camera with respect to the passage of said finger towards said camera, said control unit being designed to control the illumination intensity of said lighting device according to the transmission power measured by said measuring system. Additionally, a method for acquiring images of veins of a finger is provided.
1. An acquisition system comprising:
a camera designed to acquire an image of a finger when the finger is in front of the camera, a lighting device designed to illuminate said finger;
a control unit comprising a processor for controlling an intensity of illumination of said lighting device; and
at least one system for measuring a transmission power of said finger upstream of the camera with respect to the passage of said finger towards said camera,
the control unit being designed to control the illumination intensity of said lighting device according to the transmission power measured by said measuring system,
wherein the system is adapted to:
(1) check an exposure of the image acquired during the acquisition by the camera and adjust the illumination intensity of the lighting device if the exposure of said image is judged to be incorrect to:
an illumination intensity lower than previous illumination intensity if the exposure of said image is judged to be overexposed, and
an illumination intensity higher than the previous illumination intensity if the exposure of said image is judged to be underexposed, and/or,
(2) check an exposure of a particular channel of the image acquired during the acquisition by the camera, and
select:
either said particular channel of the acquired image if the exposure of said image is judged to be correct, or
another channel of the acquired image overexposed compared with said particular channel if the exposure of said image is judged to be underexposed,
or another channel of the acquired image underexposed compared with said particular channel if the exposure of said image is judged to be overexposed, and/or,
(3) measure the transmission power of the finger, the image of which is to be acquired, the acquisition system comprising a photoemitter and a photodetector, the acquisition system being adapted to control the light intensity of the photoemitter to:
a light intensity lower than the light intensity of the measure if the light intensity measured by the photodetector is higher than a threshold intensity,
a light intensity higher than the light intensity of the measure if the light intensity measured by the photodetector is higher than a threshold intensity, and
perform a new measure.
2. The acquisition system according to claim 1 , wherein said control unit functions in a learning mode for an elaboration and storage of a function linking the illumination intensity of said lighting device to said transmission power.
3. The acquisition system according to claim 1 , wherein said control unit receives an image signal from said camera and is designed to complete an adjustment of the illumination intensity of said lighting device) by servocontrolling from one or more images acquired by means of said camera.
4. The acquisition system according to claim 1 , wherein said camera is designed to deliver an image on a plurality of channels, a first channel being more sensitive than a second channel, which is itself more sensitive than a third channel, said control unit receiving one of said channels and being designed to control the intensity of illumination of said lighting device so that said one of said channels is exposed to an acceptable level, said acquisition system further comprising a selector controlled by said control unit in order to select a channel among said channels that is exposed to a certain level.
5. The acquisition system according to claim 1 , further comprising two measuring systems comprising a photoemitter and a photodetector, the photoemitter of one being designed to emit at a higher light intensity than the other.
6. The acquisition system according to claim 1 , wherein a photoemitter of said measuring system has its light intensity controlled by said control unit.
7. An acquisition method implemented by means of an acquisition system comprising a camera designed to acquire an image of a finger when the finger is in front of the camera and a lighting device for illuminating said finger, said method comprising:
a step of adjusting an intensity of illumination of said lighting device;
a step of acquisition of said image by said camera; and
a step of measuring a transmission power of a finger implemented prior to the presentation of said finger in front of the camera,
the step of adjusting said lighting device comprising controlling the illumination intensity of said lighting device according to the transmission power measured at the measuring step,
wherein:
(1) the acquisition step comprises a step of checking an exposure of the image acquired during said acquisition step, a new step of adjusting the illumination intensity of said lighting device being implemented if the exposure of said image is judged to be incorrect to:
an illumination intensity lower than previous illumination intensity if the exposure of said image is judged to be overexposed, and
an illumination intensity higher than the previous illumination intensity if the exposure of said image is judged to be underexposed, and/or,
(2) the acquisition method further comprises:
a step of checking an exposure of a particular channel of the image acquired during the acquisition step, and
a step of selecting:
either said particular channel of the acquired image if the exposure of said image is judged to be correct at the checking step, or
another channel of the acquired image overexposed compared with said particular channel if the exposure of said image is judged to be underexposed at the checking step,
or another channel of the acquired image underexposed compared with said particular channel if the exposure of said image is judged to be overexposed at the checking step, and/or,
(3) the step of measuring the transmission power of the finger, the image of which is to be acquired, is implemented by means of a photoemitter and a photodetector, said measuring step comprising a first measuring substep, a substep of controlling the light intensity of said photoemitter to:
a light intensity lower than the light intensity of the first measuring substep if the light intensity measured by the photodetector is higher than a threshold intensity,
a light intensity higher than the light intensity of the first measuring substep if the light intensity measured by the photodetector is higher than a threshold intensity, and
a new measuring step.
8. The acquisition method according to claim 7 , wherein a function linking the illumination intensity of said lighting device to said transmission power is obtained by learning.