Event detector and method of generating textural image based on event count decay factor and net polarity

1. A method for producing a textural image from event information generated by an event camera comprising:

accumulating event information from a plurality of events occurring during successive event cycles across a field of view of the event camera, each event indicating an x,y location within said field of view, a polarity for a change of detected light intensity incident at said x,y location and an event cycle at which said event occurred;

responsive to a threshold event criterion for a region of interest being met, generating a textural image for the region of interest from event information accumulated from within the region of interest by:

obtaining a count (p c ) of events occurring at each pixel location of the output image in a time window preceding the threshold event criterion;

determining a net polarity (p v ) of events occurring at each pixel location of the output image in the time window preceding the threshold event criterion;

generating a decay factor (p h ) for each pixel location as a function of said count;

applying said decay factor to a textural image (p t-1 ) generated for said region of interest prior to said time window; and

adding said net polarity (p v ) of events occurring at each pixel location to corresponding locations of said decayed textural image (p t-1 ) to produce said textural image (p t ).

2. The method according to claim 1 wherein the region of interest comprises the field of view of the event camera.

3. The method according to claim 1 further comprising:

in response to selected event cycles, analysing event information for one or more preceding event cycles to identify one or more regions of interest bounding a respective object to be tracked;

wherein said region of interest comprises a region of said one or more regions of interest.

4. The method of claim 1 wherein said threshold event criterion includes either: a threshold number of events; a threshold number of event cycles; or a threshold number of events occurring within a threshold number of event cycles.

5. The method of claim 1 wherein the decay factor is proportional to said count.

6. The method of claim 1 wherein the decay factor for a pixel P h (i,j) is calculated according to the following function:

P h ( i,j )= g ( p c ( i,j ))*heatmap max

where

p c (i,j) is the pixel count value;

g(.): is a function mapping values in a range between [0, ∞[to a range [0, 1 [; and

heatmap max is a maximum allowed value.

7. The method of claim 1 wherein the decay factor for a pixel P h (i,j) is calculated according to the following function:

P

h

⁡

(

i

,

j

)

=

2

⁢

(

1

-

1

1

+

e

-

f

⁢

p

c

⁡

(

i

,

j

)

)

*

heatmap

max

where

p c (i,j) is the pixel count value;

f is a cutoff frequency; and

heatmap max is a maximum allowed value.

8. The method of claim 6 wherein the decay factor for a pixel P h (i,j) is in the range [0, 1[.

9. The method of claim 1 wherein the resolution of the textural image is less than the resolution of event camera information.

10. A system comprising an event camera, a memory for accumulating event information generated by the event camera and a processor configured to process said accumulated event information according to the method of claim 1 .

11. A driver monitoring systems (DMS) comprising the system of claim 10 .