Method of flicker reduction

1. A method for reducing artefacts caused by the presence of flicker during image capture, the method comprising:

performing image capture to produce image capture data corresponding to an image capture scene, the image capture data including a first image having a first exposure and a second image having a second exposure;

processing the image capture data to:

(a) detect a discrepancy in the second image with respect to the first image; and

(b) determine flicker indication data indicative of a presence of flicker in the second image;

determining from the flicker indication data whether the discrepancy is due to the presence of flicker in the second image;

if the discrepancy is determined to be due to the presence of flicker in the second image, applying a flicker reduction correction to said second image, the flicker reduction correction comprising processing the image capture data to correct the discrepancy in said second image to produce a flicker-reduced version of the second image; and

if the discrepancy is determined not to be due to the presence of flicker in the second image, not applying the flicker reduction correction to said second image.

2. The method according to claim 1 , wherein determining said flicker indication data comprises calculating at least one parameter indicative of a likelihood of flicker being present in the second image, the at least one parameter comprising a parameter calculated in dependence on the detected discrepancy.

3. The method according to claim 2 , wherein:

the first image is a video frame of a first sequence of video frames;

the second image is a video frame of a second sequence of video frames; and

the at least one parameter comprises a parameter calculated from a detected discrepancy between a prior video frame of the first sequence and a corresponding prior video frame of the second sequence.

4. The method according to claim 2 , wherein:

the first image is a video frame of a first sequence of video frames;

the second image is a video frame of a second sequence of video frames; and

the at least one parameter comprises a parameter calculated from a detected discrepancy between the second image and a flicker-reduced version of a prior video frame of the second sequence.

5. The method according to claim 3 , wherein the correcting of the discrepancy in said second image comprises combining said second image with a flicker-reduced version of said prior video frame of the second sequence.

6. The method according to claim 3 , wherein the method is performed in real time to produce a flicker-reduced version of the second sequence.

7. The method according to claim 1 , wherein the second exposure is smaller than the first exposure.

8. The method according to claim 1 , comprising:

capturing the first image with a first array of image sensor pixels; and

capturing the second image with a second array of image sensor pixels, the pixels of the second array having a lower sensitivity than the pixels of the first array.

9. The method according to claim 1 , comprising forming an output high dynamic range image based on the first image and the flicker-reduced version of the second image.

10. The method according to claim 9 , comprising forming the output high dynamic range image based on the flicker indication data.

11. The method according to claim 1 , comprising detecting the discrepancy between the first and second images based on a predicted version of one of the first and second images, the predicted version being based on the other of the first and second images.

12. The method according to claim 11 , comprising:

if the discrepancy is determined not to be due to the presence of flicker in the second image, applying a motion correction to said second image.

13. The method according to claim 1 , wherein the first image is captured over a number of flicker cycles which exceeds a threshold number for the first image to be substantially resilient to flicker.

14. The method according to claim 1 , wherein the first image is captured over at least ten flicker cycles.

15. The method according to claim 1 , wherein the second image is captured over a smaller number of flicker cycles than the first image.

16. An apparatus for reducing artefacts caused by the presence of flicker during image capture, the apparatus comprising:

a receiver configured to receive image capture data corresponding to an image capture scene, the image capture data including a first image having a first exposure and a second image having a second exposure; and

a processor configured to process the image capture data to:

(a) detect a discrepancy in the second image with respect to the first image; and

(b) determine flicker indication data indicative of a presence of flicker in the second image,

the processor being configured to:

determine from the flicker indication data whether the discrepancy is due to the presence of flicker in the second image;

if the discrepancy is determined to be due to the presence of flicker in the second image, apply a flicker reduction correction to said second image, the flicker reduction correction comprising processing the image capture data to correct the discrepancy in said second image to produce a flicker-reduced version of the second image; and

if the discrepancy is determined not to be due to the presence of flicker in the second image, not apply the flicker reduction correction to said second image.

17. The apparatus according to claim 16 , wherein:

the first image is a video frame of a first sequence of video frames;

the second image is a video frame of a second sequence of video frames; and

determining said flicker indication data comprises calculating at least one parameter indicative of a likelihood of flicker being present in the second image, the at least one parameter comprising a parameter calculated from a detected discrepancy between a prior video frame of the first sequence and a corresponding prior video frame of the second sequence.

18. The apparatus according to claim 16 , wherein:

the first image is a video frame of a first sequence of video frames;

the second image is a video frame of a second sequence of video frames; and

the at least one parameter comprises a parameter calculated from a detected discrepancy between the second image and a flicker-reduced version of a prior video frame of the second sequence.

19. A non-transitory computer-readable storage medium comprising a set of computer-readable instructions stored thereon which, when executed by at least one processor, cause the at least one processor to:

receive image capture data corresponding to an image capture scene, the image capture data including a first image having a first exposure and a second image having a second exposure;

process the image capture data to:

(a) detect a discrepancy in the second image with respect to the first image; and

(b) determine flicker indication data indicative of a presence of flicker in the second image;

determine from the flicker indication data whether the discrepancy is due to the presence of flicker in the second image;

if the discrepancy is determined to be due to the presence of flicker in the second image, apply a flicker reduction correction to said second image, the flicker reduction correction comprising processing the image capture data to correct the discrepancy in said second image to produce a flicker-reduced version of the second image; and

if the discrepancy is determined not to be due to the presence of flicker in the second image, not apply the flicker reduction correction to said second image.

20. The non-transitory computer-readable storage medium according to claim 19 , wherein:

the first image is a video frame of a first sequence of video frames;

the second image is a video frame of a second sequence of video frames; and

determining said flicker indication data comprises calculating at least one parameter indicative of a likelihood of flicker being present in the second image, the at least one parameter comprising a parameter calculated from a detected discrepancy between a prior video frame of the first sequence and a corresponding prior video frame of the second sequence.