Pulse chain-driven infrared imaging assembly

1. An infrared imaging assembly for capturing an infrared image of a scene, the infrared imaging assembly comprising:

an infrared-sensitive image sensor;

an irradiator comprising an array of individually addressable infrared-emitting LEDs, each infrared-emitting LED arranged to illuminate a scene region of a scene;

a driver configured to actuate the irradiator by applying a switching pulse train to each infrared-emitting LED during dead time of a previous image acquisition event in which analog-digital conversion and three dimensional (3D) map computation are taking place;

an image analysis module configured to analyze a preliminary infrared image to determine exposure levels for each of a plurality of image regions; and

a pulse train adjusting unit configured to adjust a duration of the switching pulse train based on the exposure levels.

2. An infrared imaging assembly according to claim 1 , wherein the image analysis module is configured to determine the exposure level of one of the image regions illuminated by a corresponding infrared-emitting LED of the irradiator.

3. An infrared imaging assembly according to claim 1 , wherein the pulse train adjusting unit is configured to decrease the duration of the switching pulse train for an infrared-emitting LED corresponding to an overexposed image region.

4. An infrared imaging assembly according to claim 1 , wherein the pulse train adjusting unit is configured to increase the duration of the switching pulse train for an infrared-emitting LED corresponding to an underexposed image region.

5. An infrared imaging assembly according to claim 1 , wherein the infrared-sensitive image sensor is a single infrared-sensitive image sensor realized as an array of infrared-sensitive pixels, and the single infrared-sensitive image sensor is arranged to capture the preliminary infrared image and a final image.

6. An infrared imaging assembly according to claim 1 , further comprising a single infrared-sensitive photosensor arranged to record a mean illumination value for the scene region, the preliminary image comprising a sequence of mean illumination values, the infrared-sensitive image sensor being a single infrared-sensitive image sensor realized as an array of infrared-sensitive pixels arranged to capture a final image.

7. An infrared imaging assembly according to claim 1 , wherein the driver is configured to apply the switching pulse train to each infrared-emitting LED for at most about a few percent of an integration time of the infrared-sensitive image sensor.

8. An infrared imaging assembly according to claim 1 , wherein each pixel of the array comprises at least two phase detectors for demodulation at two distinct phase shifts, the at least two phase detectors configured to shift detection by the infrared-sensitive image sensor by a corresponding phase shift.

9. An infrared imaging assembly according to claim 8 , wherein:

each pixel of the array comprises demodulation channels at phase shifts of about 0°, 90°, 180°, and 270°, and

the image analysis module is configured to determine a distance between the infrared-sensitive image sensor and the scene dependent on a combined phase shift that combines signal strengths at each of the phase shifts of the demodulation channels.

10. An infrared imaging assembly according to claim 1 , wherein the driver is configured to apply the switching pulse train to each infrared-emitting LED at a different time such that the switching pulse train to applied to each infrared-emitting LED does not overlap with the switching pulse train to applied to any other infrared-emitting LED.

11. A method of generating a depth map for a scene using an infrared imaging assembly, the method comprising:

actuating an infrared irradiator, comprising an array of individually addressable infrared-emitting LEDs, each infrared-emitting LED arranged to illuminate a scene region of a scene, by applying switching pulse trains of equal duration to each infrared-emitting LED;

capturing a preliminary image obtained when the infrared irradiator is actuated by applying the switching pulse trains of equal duration to each infrared-emitting LED during dead time of a previous image acquisition event in which analog-digital conversion and three dimensional (3D) map computation are taking place;

analyzing the preliminary image to determine an exposure level for each of a plurality of image regions;

adjusting the durations of the switching pulse trains according to the exposure levels;

actuating the infrared irradiator by applying the adjusted switching pulse trains to the infrared-emitting LEDs;

capturing a subsequent image obtained when the infrared irradiator is actuated by applying the adjusted switching pulse trains to each infrared-emitting LED; and

computing a depth map from the subsequent image.

12. A method according to claim 11 , further comprising, prior to capturing the preliminary image, applying a scanning sequence in which the switching pulse train is applied to each infrared-emitting LED at a different time such that the switching pulse train to applied to each infrared-emitting LED does not overlap with the switching pulse train to applied to any other infrared-emitting LED.

13. A method according to claim 12 , further comprising limiting the duration of the scanning sequence to at most 2% of an integration time of an image sensor used to capture the preliminary image.

14. A method according to claim 11 , further comprising repeating capturing the preliminary image and adjusting pulse train durations at least twice before capturing the subsequent image.

15. A method according to claim 11 , further comprising setting at least one of each of the switching pulse trains or adjusted ones of the switching pulse trains such that the at least one of each of the switching pulse trains or adjusted ones of the switching pulse trains comprises a series of uniform pulses with a duty cycle of 50%.

16. A camera comprising:

an infrared imaging assembly comprising:

an infrared-sensitive image sensor;

an irradiator comprising an array of individually addressable infrared-emitting LEDs, each infrared-emitting LED arranged to illuminate a scene region of a scene;

a driver configured to actuate the irradiator by applying a switching pulse train to each infrared-emitting LED during dead time of a previous image acquisition event in which analog-digital conversion and three dimensional (3D) map computation are taking place;

an image analysis module configured to analyze a preliminary infrared image to determine exposure levels for each of a plurality of image regions; and

a pulse train adjusting unit configured to adjust a duration of the switching pulse train based on the exposure levels.

17. A camera according to claim 16 , wherein in the infrared imaging assembly:

each pixel of the array comprises demodulation channels at phase shifts of about 0°, 90°, 180°, and 270°, and

the image analysis module, to determine a depth map of the scene, is configured to determine a distance between the infrared-sensitive image sensor and the scene dependent on a combined phase shift that combines signal strengths at each of the phase shifts of the demodulation channels.