Method of flicker reduction

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

capturing a sequence of frames of the video, the frames each comprising a plurality of predefined regions each comprising a plurality of pixels;

characterizing a time-varying oscillation of the flicker based on variations, across the sequence of frames, of data relating to pixel intensities in at least one said predefined region, wherein characterizing the time-varying oscillation of the flicker comprises determining an amplitude and a phase of the flicker, and generating a sinusoid indicative of the flicker using the amplitude and the phase of the flicker; and

based on the characterizing of the time-varying oscillation of the flicker, applying a flicker correction to a frame of the video, wherein applying the flicker correction comprises inverting the generated sinusoid to generate a correction ratio, and using the correction ratio to apply the flicker correction to the frame of the video.

2. A method according to claim 1 , wherein:

the method comprises determining a frequency of the flicker; and

the characterizing of the time-varying oscillation of the flicker is based on the determined frequency.

3. A method according to claim 2 , wherein the determining of the frequency of the flicker is based on a geographical location at which the video was captured.

4. A method according to claim 1 , wherein the frame to which the flicker correction is applied is one of the sequence of frames.

5. A method according to claim 1 , wherein the frame to which the flicker correction is applied is subsequent to the sequence of frames.

6. A method according to claim 1 , wherein the sequence of frames comprises at least three frames.

7. A method according to claim 1 , wherein:

the video is captured using a rolling shutter; and

each said predetermined region comprises a line of pixels.

8. A method according to claim 1 , wherein the data relating to pixel intensities is an average intensity of pixels of the predetermined region.

9. A method according to claim 1 , wherein:

the sequence of frames comprises frames having a given exposure; and

the method comprises producing a high dynamic range frame for which the frame to which flicker correction is applied is a high dynamic range frame component.

10. A method according to claim 1 , wherein the frames comprise a plurality of zones, the method comprising:

identifying at least one said zone as a flicker-free zone; and

inhibiting the flicker correction in the at least one flicker-free zone.

11. A method according to claim 10 , wherein:

the at least one flicker-free zone is neglected in the characterizing of the time-varying oscillation of the flicker.

12. A method according to claim 10 , wherein identifying a given zone as a flicker-free zone comprises determining that a time variation of pixel intensity of the given zone is inconsistent with a presence of flicker in the given zone.

13. A method according to claim 12 , wherein the time variation of pixel intensity of a given zone is a time variation of an average pixel intensity of the given zone.

14. A method according to any of claim 10 , wherein inhibiting the flicker correction in a given zone comprises:

identifying an edge region of the given zone; and

applying a varying degree of flicker correction across the edge region.

15. An apparatus for reducing artefacts caused by the presence of flicker during capture of a video, the apparatus comprising:

a receiving module to capture a sequence of frames of the video, the frames each comprising a plurality of predefined regions each comprising a plurality of pixels;

a characterization module to characterize a time-varying oscillation of the flicker based on variations, across the sequence of frames, of data relating to pixel intensities in at least one said predefined region, wherein characterizing the time-varying oscillation of the flicker comprises determining an amplitude and a phase of the flicker, and generating a sinusoid indicative of the flicker using the amplitude and the phase of the flicker; and

a flicker correction module to, based on the characterizing of the time-varying oscillation of the flicker, apply a flicker correction to a frame of the video, wherein applying the flicker correction comprises inverting the generated sinusoid to generate a correction ratio, and using the correction ratio to apply the flicker correction to the frame of the video.

16. 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:

capture a sequence of frames of a video, the frames each comprising a plurality of predefined regions each comprising a plurality of pixels;

characterize a time-varying oscillation of flicker present during capture of the video, the characterizing being based on variations, across the sequence of frames, of data relating to pixel intensities in at least one said predefined region, wherein characterizing the time-varying oscillation of the flicker comprises determining an amplitude and a phase of the flicker, and generating a sinusoid indicative of the flicker using the amplitude and the phase of the flicker; and

based on the characterizing of the time-varying oscillation of the flicker, apply a flicker correction to a frame of the video, wherein applying the flicker correction comprises inverting the generated sinusoid to generate a correction ratio, and using the correction ratio to apply the flicker correction to the frame of the video.

17. A method for reducing artefacts caused by the presence of flicker during capture of a video, the method comprising:

capturing a sequence of frames of the video, the frames each comprising a plurality of predefined regions each comprising a plurality of pixels;

characterizing a time-varying oscillation of the flicker based on variations, across the sequence of frames, of data relating to pixel intensities in at least one said predefined region, wherein characterizing the time-varying oscillation of the flicker comprises determining an amplitude and a phase of the flicker; and

based on the characterizing of the time-varying oscillation of the flicker, applying a flicker correction to a frame of the video,

wherein the frame comprises a plurality of zones, and the method comprises identifying at least one of said zones as a flicker-free zone, and inhibiting the flicker correction in the at least one flicker-free zone.