Spurious motion filter
A filter for filtering out spurious motion from a sequence of video images, for use in video image signal processing to identify objects in motion in the sequence of video images. Spurious motion is chaotic, repetitive, jittering portions of an image that constitute noise and interfere with motion detection in video signals. The filter keeps track of the location and the strengths of spurious motion, applies appropriate low pass filtering strengths according to the spurious motion strengths in real-time. Regular pixels without spurious motion will pass through the filter unaltered, while pixels with spurious motion will be “smoothed” to avoid being detected as noise.
1. A method of filtering a video signal in a surveillance system, comprising:
determining a measurement of a difference between two frames in the video signal;
applying a threshold to the video signal; and
filtering the video signal with a low pass filter wherein the low pass filter is implemented by S i =S i-1 ·(1−α)+P i ·α where S i is a filtered signal in the ith frame, P i is the input on the ith frame, α is a user defined parameter.
2. The method of claim 1 , further comprising:
generating a spurious motion map; and
displaying the spurious motion map.
3. The method of claim 1 , further comprising:
displaying the video signal;
generating and displaying a spurious motion map of the video signal; and
adjusting the threshold in accordance with the display of the video signal and the display of the spurious motion map.
4. The method of claim 1 , further comprising:
displaying the video signal;
generating and displaying a spurious motion map of the video signal; and
adjusting a parameter in the low pass filter in accordance with the display of the video signal and the display of the spurious motion map.
5. The method of claim 1 , further comprising:
displaying the video signal;
generating and displaying a spurious motion map of the video signal;
adjusting the threshold in accordance with the display of the video signal and the display of the spurious motion map; and
adjusting a parameter in the low pass filter in accordance with the display of the video signal and the display of the spurious motion map.
6. The method of claim 1 , wherein the step of determining a measurement of the difference between two frames is made using a differential filter.
7. The method of claim 1 , further comprising:
normalizing the video signal to generate a spurious motion map; and
dilating the spurious motion map to fill in holes.
8. The method of claim 7 , further comprising filtering the motion map with a low pass filter.
9. The method of claim 8 , further comprising processing the video signal to detect motion.
10. A surveillance system for processing a video signal, comprising:
a processor that receives the video signal;
a software application operable on the processor to:
determine a measurement of a difference between two frames in the video signal;
apply a threshold to the video signal; and
filter the video signal with a low pass filter wherein the low pass filter is implemented by S i =S i-1 ·(1−α)+P i ·α where S i is a filtered signal in the ith frame, P i is the input on the ith frame, α is a user defined parameter.
11. The system of claim 10 , wherein the software application is further operable to generate a spurious motion map and display the spurious motion map.
12. The system of claim 10 , wherein the software application is further operable to:
display the video signal;
generate and display a spurious motion map of the video signal; and
adjust the threshold in accordance with the display of the video signal and the display of the spurious motion map.
13. The system of claim 10 , wherein the software application is further operable to:
display the video signal;
generate and display a spurious motion map of the video signal; and
adjust a parameter in the low pass filter in accordance with the display of the video signal and the display of the spurious motion map.
14. The system of claim 10 , wherein the software application is further operable to:
display the video signal;
generate and display a spurious motion map of the video signal;
adjust the threshold in accordance with the display of the video signal and the display of the spurious motion map; and
adjust a parameter in the low pass filter in accordance with the display of the video signal and the display of the spurious motion map.
15. The system of claim 10 , wherein the determination of a measurement of the difference between two frames is made using a differential filter.
16. The system of claim 10 , wherein the software application is further operable to:
normalize the video signal to generate a spurious motion map; and
dilate the spurious motion map to fill in holes.
17. The system of claim 16 , wherein the software application is further operable to filtering the motion map with a low pass filter.
18. The system of claim 17 , wherein the software application is further operable to further process the video signal to detect motion.