Method and apparatus for acquiring a set of images illuminated by a flash

1. A method of obtaining a sequence of images of a scene via an imaging device having a plurality of photosensitive cells arranged in an array to form a frame region, the frame region being composed of a plurality of frame sub-regions, each frame sub-region corresponding to a sub-set of the photosensitive cells each sub-set of photosensitive cells having an exposure time duration, wherein the exposure of at least some of said frame sub-regions occurs at different times during a total time of exposure of the frame region, the method comprising:

illuminating the scene being imaged at a plurality of flash events;

acquiring a set of frames of the scene; and

constructing a sequence of images, each image being constructed from frame sub-regions of at least two acquired frames;

wherein the time interval between consecutive flash events is set, so as to shift temporally from frame to frame the time of occurrence of a flash event with respect to the start of a frame, the time interval being set to be greater than or equal to the sum of the exposure time duration of a subset of the plurality of photosensitive cells and the time duration of the flash event.

2. The method according to claim 1 , wherein each frame sub-region corresponds to a line of photosensitive cells of the array and exposure of the array is performed successively line by line.

3. The method according to claim 1 , wherein the flash events are timed such that each sub-set of photosensitive cells is illuminated by one flash event during capture of a frame.

4. The method according to claim 1 , wherein each image is constructed from frame sub-regions of at least two acquired frames.

5. The method according to claim 1 , wherein each image of the sequence of images is formed by reassembling the frame sub-regions of consecutive frames illuminated by the same flash event to form a reconstructed image.

6. The method according to claim 5 , comprising identifying frame sub regions for which the same flash event is shared between two consecutive frames and applying a weighted illumination intensity to said frame sub-regions to form the reconstructed image.

7. The method according to claim 1 , wherein the time duration of the flash event is determined to be a fraction of the exposure time duration of a frame sub-region such that:

Exposure time =n ×flash duration

where n is an integer greater than 0.

8. The method according to claim 1 , wherein the flash event duration changes from one frame to another frame and the flash interval is adjusted from frame to frame accordingly.

9. A non-transitory computer-readable medium having one or more executable instructions stored thereon, which when executed by a processor cause the processor to perform a method for obtaining a sequence of images of a scene via an imaging device having a plurality of photosensitive cells arranged in an array to form a frame region, wherein the frame region is composed of a plurality of frame sub-regions, each frame sub-region corresponding to a sub-set of the photosensitive cells each sub-set of photosensitive cells having an exposure time duration, and wherein the exposure of at least some of said frame sub-regions occurs at different times during a total time of exposure of the frame region, the method comprising:

illuminating the scene being imaged at a plurality of flash events;

acquiring a set of frames of the scene; and

constructing a sequence of images, each image being constructed from frame sub-regions of at least two acquired frames;

wherein the time interval between consecutive flash events is set, so as to shift temporally from frame to frame the time of occurrence of a flash event with respect to the start of a frame, the time interval being set to be greater than or equal to the sum of the exposure time duration of a subset of the plurality of photosensitive cells and the time duration of the flash event.

10. An electronic imaging device having a plurality of photosensitive cells arranged in an array to form a frame region, the frame region being composed of a plurality of frame sub-regions each frame sub-region corresponding to a sub-set of photosensitive cells, the device comprising:

an array controller configured to expose each of said frame sub-regions during an exposure time duration wherein the exposure of at least some of said frame sub-regions occurs at different times during a total time of exposure of the frame region;

a flash unit for illuminating a scene to be imaged during a flash time duration;

a flash controller for activating the flash unit to illuminate the scene being imaged at a plurality of flash events, the time interval between consecutive flash events being set to be greater than or equal to the sum of the exposure time duration of a subset of the plurality of photosensitive cells and the time duration of the flash event;

a processor configured to:

acquire a set of frames of the scene wherein the time of occurrence of a flash event with respect to the start of a frame is shifted temporally from frame to frame; and

construct a sequence of images from the frame sub-regions of the acquired frames.

11. The device according to claim 10 , wherein the flash events are timed such that each subset of photosensitive cells is flashed only once during capture of a frame.

12. The device according to claim 10 , wherein each image is constructed from frame sub-regions of at least two acquired frames.

13. The device according to claim 10 , wherein each image of the sequence of images is formed by reassembling the frame sub-regions of consecutive frames illuminated by the same flash event to form a reconstructed image.

14. The device according to claim 13 , wherein the processor is configured to identify sub regions for which the same flash event is shared between two consecutive frames and to apply a weighted illumination intensity to said frame sub-regions to form the reconstructed image.

15. The device according to claim 10 , further comprising a clock to synchronise operation of the array controller and the flash controller.

16. A flash control device for an electronic imaging device, the electronic image device having a plurality of photosensitive cells arranged in an array to form a frame region, the frame region being composed of a plurality of frame sub-regions each frame sub-region corresponding to a sub-set of photosensitive cells, and being exposed during an exposure time duration wherein the exposure of at least some of said frame sub-regions occurs at different times during a total time of exposure of the frame region, the flash control device comprising:

a flash controller for activating a flash unit to illuminate the scene being imaged at a plurality of flash events, the time interval between consecutive flash events being set to shift temporally from frame to frame the time of occurrence of a flash event with respect to the start of a frame, the time interval between consecutive flash events being greater than or equal to the sum of the exposure time duration of a subset of photosensitive cells and the time duration of the flash event.

17. A method of controlling a flash unit for an electronic imaging device, the electronic image device having a plurality of photosensitive cells arranged in an array to form a frame region, the frame region being composed of a plurality of frame sub-regions each frame sub-region corresponding to a sub-set of photosensitive cells, and being exposed during an exposure time duration wherein the exposure of at least some of said frame sub-regions occurs at different times during a total time of exposure of the frame region, the method comprising

activating the flash unit to illuminate the scene being imaged at a plurality of flash events, the time interval between consecutive flash events being set to shift temporally from frame to frame the time of occurrence of a flash event with respect to the start of a frame, the time interval between consecutive flash events being greater than or equal to the sum of the exposure time duration of a subset of photosensitive cells and the time duration of the flash event.

18. A method of obtaining a sequence of images of a scene via an imaging device having a plurality of photosensitive cells arranged in an array to form a frame region, the frame region being composed of a plurality of frame sub-regions, each frame sub-region corresponding to a sub-set of the photosensitive cells each sub-set of photosensitive cells having an exposure time duration, wherein the exposure of at least some of said frame sub-regions occurs at different times during a total time of exposure of the frame region, the method comprising:

the scene being imaged receiving an illumination at a plurality of flash events;

acquiring a set of frames of the scene; and

constructing a sequence of images, each image being constructed from frame sub-regions of at least two acquired frames;

wherein the time interval between consecutive flash events is set, so as to shift temporally from frame to frame the time of occurrence of a flash event with respect to the start of a frame, the time interval being set to be greater than or equal to the sum of the exposure time duration of a subset of the plurality of photosensitive cells and the time duration of the flash event.

19. An electronic imaging device having a plurality of photosensitive cells arranged in an array to form a frame region, the frame region being composed of a plurality of frame sub-regions each frame sub-region corresponding to a sub-set of photosensitive cells, the device comprising:

an array controller configured to expose each of said frame sub-regions during an exposure time duration wherein the exposure of at least some of said frame sub-regions occurs at different times during a total time of exposure of the frame region;

a scene to be imaged receiving an illumination from a flash unit during a flash time duration;

a flash controller for activating the flash unit to illuminate the scene being imaged at a plurality of flash events, the time interval between consecutive flash events being set to be greater than or equal to the sum of the exposure time duration of a subset of the plurality of photosensitive cells and the time duration of the flash event; and

a processor configured to:

acquire a set of frames of the scene wherein the time of occurrence of a flash event with respect to the start of a frame is shifted temporally from frame to frame; and

construct a sequence of images from the frame sub-regions of the acquired frames.