Method of flicker reduction

Patent metadata

Field	Value
Publication number	US-11082628-B2
Application number	US-201816206306-A
Country	US
Kind code	B2
Filing date	Nov 30, 2018
Priority date	Nov 30, 2017
Publication date	Aug 3, 2021
Grant date	Aug 3, 2021

Abstract

Examples of the present disclosure relate to a method for reducing artefacts caused by the presence of flicker during capture of a video. A sequence of frames of the video are captured, the frames each comprising a plurality of predefined regions each comprising a plurality of pixels. A time-varying oscillation of the flicker is characterized based on variations, across the sequence of frames, of data relating to pixel intensities in at least one said region. Based on the characterizing of the time-varying oscillation of the flicker, a flicker correction is applied to a frame of the video.

First claim

What is claimed is:

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.

Assignees

• Apical Ltd
• Advanced Risc Mach Ltd

Inventors

• Tasdizen Ozgur
• Kornienko Alexey

Classifications

• H04N23/745 Primary

  Detection of flicker frequency or suppression of flicker wherein the flicker is caused by illumination, e.g. due to fluorescent tube illumination or pulsed LED illumination · CPC title

• H04N25/62

  Detection or reduction of noise due to excess charges produced by the exposure, e.g. smear, blooming, ghost image, crosstalk or leakage between pixels · CPC title

• H04N25/531

  by controlling rolling shutters in CMOS SSIS · CPC title

• H04N23/73

  by influencing the exposure time · CPC title

• H04N21/2368

  Multiplexing of audio and video streams · CPC title