System and method for automatic calculation of scene geometry in crowded video scenes
View Patent ↗A system or method for automatic calculation of scene geometry may include receiving, by a processor, a video stream including a plurality of video frames. A video frame may be divided into blocks, and a vertical vanishing point of the video stream may be determined based on a dominant orientation of detected edges in the blocks. A horizon and scale of the video stream may be estimated based on optical flow of pixels between two consecutive video frames. A set of human heads may be detected in a video frame of the video stream based on the estimated horizon and scale of the video stream.
1. A method for automatic calculation of scene geometry, comprising:
receiving, by a processor, a video stream including a plurality of video frames;
dividing, by the processor, a video frame into blocks;
determining a vertical vanishing point of the video stream based on a dominant orientation of detected edges in the blocks;
estimating a horizon and scale of the video stream based on optical flow of pixels between two consecutive video frames; and
detecting a set of human heads in a video frame of the video stream based on the estimated horizon and scale of the video stream.
2. The method of claim 1 , wherein estimating the horizon and scale of the video stream comprises generating a set of estimated human head sizes at different locations within a video frame.
3. The method of claim 1 , wherein detecting the set of human heads in the video frame comprises generating a set of candidate points locating a human head's center.
4. The method of claim 3 , wherein detecting the set of human heads in the video frame further comprises creating a Hough transform using the generated set of candidate points.
5. The method of claim 4 , wherein the Hough transform extracts ellipses from the video frame which approximate a human head's size.
6. The method of claim 1 , comprising adjusting the estimated horizon and scale if a standard deviation of y-coordinates of the detected set of human heads is less than a threshold.
7. The method of claim 6 , wherein adjusting the estimated horizon and scale comprises detecting a set of human heads in a second video frame of the video stream using a different estimated horizon and scale.
8. The method of claim 1 , wherein estimating the horizon and scale of the video stream is further based on the detected edges in the blocks.
9. A system for automatic calculation of scene geometry, comprising:
a memory; and
a processor configured to:
receive a video stream including a plurality of video frames;
divide a video frame into blocks;
determine a vertical vanishing point of the video stream based on a dominant orientation of edges in the blocks;
estimate a horizon and scale of the video stream based on optical flow of pixels between two consecutive video frames; and
detect a set of human heads in a video frame of the video stream based on the estimated horizon and scale of the video stream.
10. The system of claim 9 , wherein the processor is configured to estimate the horizon and scale of the video stream by generating a set of estimated human head sizes at different locations within a video frame.
11. The system of claim 9 , wherein the processor is configured to detect the set of human heads in the video frame comprises generating a set of candidate points locating a human head's center.
12. The system of claim 11 , wherein the processor is configured to detect the set of human heads in the video frame by further creating a Hough transform using the generated set of candidate points.
13. The system of claim 12 , wherein the Hough transform extracts ellipses from the video frame which approximate a human head's size.
14. The system of claim 9 , wherein the processor is configured to adjust the estimated horizon and scale if a standard deviation of y-coordinates of the detected set of human heads is less than a threshold.
15. The system of claim 14 , wherein the processor is configured to adjust the estimated horizon and scale by detecting a set of human heads in a second video frame of the video stream using a different estimated horizon and scale.
16. The system of claim 9 , wherein the processor is configured to determine a vertical vanishing point of the video stream based on a set of vanishing points, wherein each vanishing point is an intersection between a pair of detected edges in a pair of blocks.
17. The system of claim 9 , wherein the processor is configured to detect humans using the vertical vanishing point, horizon, and scale and refine the horizon and scale based on the detected humans.