Flicker detection method and flicker detection apparatus

Patent metadata

Field	Value
Publication number	US-9148583-B2
Application number	US-201414336281-A
Country	US
Kind code	B2
Filing date	Jul 21, 2014
Priority date	Jul 19, 2013
Publication date	Sep 29, 2015
Grant date	Sep 29, 2015

Abstract

The present invention discloses a flicker detection method and a flicker detection apparatus. The method includes: calculating the mean values of selected rows of image frames to constitute a mean value vector; calculating a differential vector between the mean value vectors of a current frame and a previous frame; calculating a DC-free difference vector by subtracting a direct current component from respective elements of the differential vector; calculating a power spectrum corresponding to the DC-free difference vector; obtaining a first frequency reference value; obtaining a second frequency reference value; and if the difference between the first and second frequency reference values is above a threshold, then it is determined that flicker is present in the current frame; otherwise, it is determined that no flicker is present.

First claim

The invention claimed is:

1. A flicker detection method of detecting flicker in a sequence of image frames, the method comprising:
calculating mean values of selected rows of the image frames, the mean values constituting a mean value vector mean_row(k) in an order of the rows;
calculating a differential vector diff_frame(k) between the mean value vector mean_row(k) of a current frame and the mean value vector mean_row(k−1) of a previous frame;
calculating a DC-free difference vector diff_mean_row(k) by subtracting a direct current component of the differential vector diff_frame(k) from respective elements of the differential vector diff_frame(k);
calculating a power spectrum corresponding to the DC-free difference vector diff_mean_row(k);
obtaining one of a value of the power spectrum at a first frequency and a mean value of the power spectrum in a predetermined range around the first frequency as a first frequency reference value;
obtaining one of the value of the power spectrum at a second frequency and the mean value of the power spectrum in a predetermined range around the second frequency as a second frequency reference value; and
if a difference between the first frequency reference value and the second frequency reference value is above a predetermined difference threshold, it is determined flicker is present in the current frame;
otherwise, it is determined no flicker is present in the current frame.

2. The method according to claim 1 , wherein where flicker is present in the current frame,
if the first frequency reference value is above the second frequency reference value, it is determined the frequency of the flicker is the first frequency; and
if the second frequency reference value is above the first frequency reference value, it is determined the frequency of the flicker is the second frequency.

3. The method according to claim 1 , wherein the selected rows are all of rows of the image frames or sampled rows as a result of sampling all of rows of the image frames uniformly.

4. The method according to claim 3 , wherein the image frames are gray scale images.

5. The method according to claim 2 , further comprising a second-level determination of:
for three first-level determination results of the current frame and first and second frames previous to the current frame,
if at least two of the determination results are that the flicker at the first frequency is present and none of the determination results are that the flicker at the second frequency is present, it is determined the flicker at the first frequency is present in the current frame;
if at least two of the determination results are that the flicker at the second frequency is present and none of the determination results are that the flicker at the first frequency is present, it is determined the flicker at the second frequency is present in the current frame;
otherwise, it is determined no flicker is present in the current frame.

6. The method according to claim 5 , further comprising a third-level determination of:
counting a first proportion of second-level determination results that the flicker at the first frequency is present and a second proportion of second-level determination results that the flicker at the second frequency is present among second-level determination results of M frames comprising the current frame and previous M−1 frames thereof;
counting a first number of second-level determination results that the flicker at the first frequency is present and a second number of second-level determination results that the flicker at the second frequency is present among second-level determination results of N frames comprising the current frame and previous N−1 frames thereof;
if the first proportion is above a first proportion threshold and the second number is below 1, it is determined the flicker at the first frequency is present in the current frame;
if the second proportion is above a second proportion threshold and the first number is below 1, it is determined the flicker at the second frequency is present in the current frame;
otherwise, it is determined no flicker is present in the current frame,
wherein M and N are integers above 1 and M>N.

7. The method according to claim 6 , wherein it is determined whether there is motion of the current frame relative to the previous frame in the case where it is determined no flicker is present in the current frame.

8. The method according to claim 1 , wherein before the step of building, the method further comprises:
detecting whether there is motion of the current frame relative to the previous frame; and
where a detection result indicates that there is motion of the current frame relative to the previous frame, calculating the DC-free difference vector diff_mean_row(k) by:
obtaining a truncated mean value vector MS_mean_row(k) of the current frame, the truncated mean value vector MS_mean_row(k) being a vector result of removing predetermined parts of a head and a tail of the mean value vector mean_row(k) of the current frame;
searching the mean value vector mean_row(k−1) of the previous frame of the current frame for a segment with a same length as and a most approximate to the truncated mean value vector MS_mean_row(k) of the current frame as a matching truncated mean value vector Mt_mean_row(k−1);
calculating a differential vector diff_frame_MM(k) between the truncated mean value vector MS_mean_row(k) of the current frame and the matching truncated mean value vector Mt_mean_row(k−1) of the previous frame; and
calculating the DC-free difference vector diff_mean_row(k) by subtracting a direct current component of the differential vector diff_frame_MM(k) from respective elements of the differential vector diff_frame_MM(k).

9. The method according to claim 8 , wherein searching for the matching truncated mean value vector Mt_mean_row(k−1) comprises:
cropping segments of the mean value vector mean_row(k−1) of the previous frame of the current frame by shifting a window with the same length as the truncated mean value vector MS_mean_row(k) of the current frame as candidate segments;
calculating mean values of absolute values of respective elements of difference vectors between the truncated mean value vector MS_mean_row(k) of the current frame and respective candidate segments; and
selecting a candidate segment with a lowest mean value as the matching truncated mean value vector Mt_mean_row(k−1).

10. The method according to claim 8 , wherein the predetermined parts are related to the length of the mean value vector mean_row(k) of the image frame and a predetermined proportion.

11. The method according to claim 8 , wherein the detecting whether there is motion of the current frame relative to the previous frame comprises:
if the mean values of the absolute values of respective elements of the DC-free difference vector diff_mean_row(k) are above a predetermined motion threshold, it is determined there is motion of the current frame relative to the previous frame;
otherwise, it is determined there is no motion of the current frame relative to the previous frame.

12. A flicker detection apparatus for detecting flicker in a sequence of image frames, the apparatus comprising:
a mean value vector calculating device configured to calculate mean values of selected rows of the image frames, the mean values constituting a mean value vector mean_row(k) in an order of the rows;
a differential vector calculating device configured to calculate a differential vector diff_frame(k) between the mean value vector mean_row(k) of a current frame and the mean value vector mean_row(k−1) of a previous frame;
a DC-free difference vec

Assignees

• Fujitsu Ltd

Inventors

• Wu Jianrong
• Fu Xuan
• Higashi Akihiro

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

• H04N5/144

  Movement detection (for video coding H04N19/503; analysis of motion in general G06T7/20) · CPC title

• H04N25/60

  Noise processing, e.g. detecting, correcting, reducing or removing noise · CPC title

• H04N5/2357 Primary

  Electricity · mapped topic