Method and device for processing asynchronous signals generated by an event-based light sensor

1. A method for processing asynchronous signals generated by a light sensor, the light sensor having a matrix of sensing elements, the method comprising:

receiving, from each sensing element of the matrix, a respective event-based signal sequence including events asynchronously produced as a function of variations of light incident on the sensing element and light level values respectively associated with at least some of the events;

generating an image comprising pixels corresponding spatially to the sensing elements of the matrix; and

repeatedly determining a set of edge pixels among the pixels of the image,

wherein generating the image comprises updating each pixel of the image based on a light level value associated with a most recent event in the event-based signal sequence received from the sensing element corresponding to said pixel of the image,

wherein determining the set of edge pixels comprises:

selecting pixels of the image, wherein the selected pixels comprise pixels of the image corresponding to sensing elements from which the received event-based signal sequences include at least one event after a previous determination of the set of edge pixels, and pixels of the previously determined set of edge pixels;

evaluating respective local contrast measures with respect to the selected pixels of the image; and

deciding whether or not the selected pixels belong to the set of edge pixels based on the evaluated local contrast measures.

2. The method of claim 1 , wherein the selected pixels comprise each pixel of the image corresponding to a sensing element from which the received event-based signal sequence includes at least one event after the previous determination of the set of edge pixels.

3. The method of claim 2 , wherein the selected pixels further include each pixel of the previously determined set of edge pixels.

4. The method of claim 2 , wherein the selected pixels consist only of the pixels selected in response to events included in the respective event-based signal sequences received from the sensing elements.

5. The method of claim 1 , wherein the set of edge pixels is determined periodically, with a period in a range of 1 to 100 milliseconds, preferably in a range of 10 to 100 milliseconds.

6. The method of claim 1 , further comprising outputting a contour representation as a matrix of time-varying bits,

wherein each of the time-varying bits of the contour representation corresponds spatially to a respective pixel of the image and has a first value when the respective pixel of the image belongs to the set of edge pixels, and a second value when the respective pixel of the image does not belong to the set of edge pixels.

7. The method of claim 6 , wherein the contour representation is used to control a light modulator.

8. The method of claim 6 , wherein the contour representation is transmitted to a retinal implant for stimulation of retina cells.

9. A signal processing unit comprising:

an interface for connecting to a light sensor having a matrix of sensing elements and receiving, from each sensing element of the matrix, a respective event-based signal sequence including events asynchronously produced as a function of variations of light incident on the sensing element and light level values respectively associated with at least some of the events; and

a processor for generating an image comprising pixels corresponding spatially to the sensing elements of the matrix, and repeatedly determining a set of edge pixels among the pixels of the image,

wherein the processor is configured to update a respective pixel value of each pixel of the image based on a light level value associated with a most recent event in the event-based signal sequence received from the sensing element corresponding to said pixel of the image,

wherein the processor is configured to determine the set of edge pixels by:

selecting pixels of the image, wherein the selected pixels comprise pixels of the image corresponding to sensing elements from which the received event-based signal sequences include at least one event after a previous determination of the set of edge pixels, and pixels of the previously determined set of edge pixels;

evaluating respective local contrast measures with respect to the selected pixels of the image; and

deciding whether or not the selected pixels belong to the set of edge pixels based on the evaluated local contrast measures.

10. A computer program product comprising stored instructions to be executed in a processor associated with a light sensor having a matrix of sensing elements, wherein execution of the instructions by the processor controls steps of:

receiving, from each sensing element of the matrix, a respective event-based signal sequence including events asynchronously produced as a function of variations of light incident on the sensing element and light level values respectively associated with at least some of the events;

generating an image comprising pixels corresponding spatially to the sensing elements of the matrix; and

repeatedly determining a set of edge pixels among the pixels of the image,

wherein generating the image comprises updating each pixel of the image based on a light level value associated with a most recent event in the event-based signal sequence received from the sensing element corresponding to said pixel of the image,

wherein determining the set of edge pixels comprises:

selecting pixels of the image, wherein the selected pixels comprise pixels of the image corresponding to sensing elements from which the received event-based signal sequences include at least one event after a previous determination of the set of edge pixels, and pixels of the previously determined set of edge pixels;

evaluating respective local contrast measures with respect to the selected pixels of the image; and

deciding whether or not the selected pixels belong to the set of edge pixels based on the evaluated local contrast measures.