TIME-OF-FLIGHT SENSOR AND METHOD FOR ADJUSTING AN EXPOSURE TIME OF SUCH A SENSOR

1 . An indirect time-of-flight measurement sensor, comprising:

a photosensitive pixel array configured to acquire a succession of images of a scene during a given exposure time; and

a control unit configured to control an acquisition of a succession of images by the pixel array and to define an exposure time for the acquisition according to a pixel saturation rate of the array, distances between the sensor and elements of the scene, and a standard deviation of the distances between the sensor and the elements of the scene.

2 . The sensor according to claim 1 , wherein the control unit is configured to define the exposure time for the acquisition from the pixel saturation rate of the array and a precision of the sensor corresponding to a ratio between the distances between the sensor and elements of the scene and the standard deviation of the distances between the sensor and the elements of the scene.

3 . The sensor according to claim 2 , wherein the control unit is configured to compare the pixel saturation rate with a saturation rate threshold, and to:

if the pixel saturation rate is greater than the saturation rate threshold, reduce the exposure time,

otherwise compare the precision to a precision threshold, and

if the precision is greater than the precision threshold, reduce the exposure time,

otherwise, increase the exposure time.

4 . The sensor according to claim 3 , wherein the control unit is configured to adjust the exposure time of the sensor by increasing or by reducing the value of the exposure time by a percentage between a minimum step and a maximum step.

5 . The sensor according to claim 4 , wherein the precision is evaluated from the mathematical formula

z

2

σ

z

2

,

wherein z is a distance between an element of the scene with respect to the sensor and σ z is the standard deviation of the distances between the sensor and the elements of the scene.

6 . The sensor according to one of claim 5 , wherein, if the saturation rate threshold is incompatible with the precision threshold, then the control unit is configured to update the precision threshold with the saturation rate.

7 . A method, comprising:

acquiring a succession of images of a scene with pixels of a photosensitive pixel array of an indirect time-of-flight measurement sensor during a given exposure time; and

defining the exposure time for the acquisition based on a pixel saturation rate of the array, distances between the sensor and elements of the scene, and a standard deviation of the distances between the sensor and the elements of the scene.

8 . The method according to claim 7 , comprising defining the exposure time for the acquisition based on the pixel saturation rate of the array and a precision of the sensor corresponding to a ratio between the distances between the sensor and elements of the scene and the standard deviation of the distances between the sensor and the elements of the scene.

9 . The method according to claim 8 , comprising comparing the pixel saturation rate with a saturation rate threshold, and

if the pixel saturation rate is greater than the saturation rate threshold, reducing the exposure time,

otherwise comparing the precision with a precision threshold, and

if the precision is greater than the precision threshold, reducing the exposure time,

otherwise, increasing the exposure time.

10 . The method according to claim 9 , comprising adjusting the exposure time of the sensor by increasing or by reducing the value of the exposure time by a percentage between a minimum step and a maximum step.

11 . The method according to claim 10 , comprising evaluating the precision from the mathematical formula

z

2

σ

z

2

,

wherein z is a distance between an element of the scene with respect to the sensor and σ z is the standard deviation of the distances between the sensor and the elements of the scene.

12 . The method according to claim 11 , comprising updating the precision threshold with the saturation rate if the saturation rate threshold is incompatible with the precision threshold.

13 . A method, comprising:

sensing, for each of a plurality of objects, a distance between a sensor and the object;

calculating a standard deviation of the distances;

selecting, with a control unit of the sensor, an exposure time based on a pixel saturation rate of a photosensitive pixel array of the sensor and on the standard deviation of the distance;

acquiring, with a photosensitive pixel array of a sensor, a plurality of images of the objects with the selected exposure time.

14 . The method of claim 13 , comprising selecting the exposure time based on a precision of the sensor.

15 . The method of claim 14 , wherein the precision of the sensor corresponds to a ratio between the distances and the standard deviation of the distances.

16 . The method of claim 15 , comprising comparing, with the control unit, the pixel saturation rate with a saturation rate threshold.

17 . The method of claim 16 , comprising reducing the exposure time if the pixel saturation rate is greater than the saturation rate threshold.

18 . The method of claim 17 , comprising:

comparing the precision to a precision threshold if the pixel saturation rate is less than the saturation rate threshold;

reducing the exposure time if the precision is greater than the precision threshold; and

increasing the exposure time if the precision is less than the precision threshold.

19 . The method of claim 18 , comprising adjusting the exposure by increasing or by reducing the value of the exposure time by a percentage between a minimum step and a maximum step.

20 . The method of claim 19 , comprising evaluating, with the control unit, the precision from a mathematical formula

z

2

σ

z

2

,

wherein z is a distance between an object and the sensor, wherein σ z is the standard deviation of the distances between the sensor and the elements of the scene.