Removal of shadows from images in a video signal
First Claim
1. A method for detecting and removing shadows, the method comprising the steps of:
- (i) combining corresponding values from a plurality of frames that are carried by a digital video signal, obtained, directly or indirectly, from a video camera, any two frames of the video signal differing from each other owing to the field of view of the video camera changing by any camera action selected from tilting, panning, zooming or dollying or any combination thereof, said corresponding values being combined so as to create therefrom a background model image of the scene or of a portion thereof, said background model image covering a region greater than a field of view of at least one individual frame of the video signal;
(ii) processing the background model image to detect and define within the background model image model shadow zones;
(iii) calculating correction factors for some or all of said model shadow zones;
(iv) for each of a plurality of frames of the video signal, determining a region of said background model image corresponding to the field of view of the frame, and thereby deriving, in the frame carried by the signal, frame shadow zones that correspond to said model shadow zones; and
(v) correcting video signal values within said frame shadow zones.
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Abstract
Substantially removing shadows in video images obtained from a camera viewing a scene, at variable pointing angles and magnification, by digital processing of a sequence of frames in the video signal, the processing including—(a) creating and maintaining a model image of the scene, by accumulating image data from a plurality of video frames; (b) in the model image, detecting and defining model shadow zones; (c) calculating correction factors for the model shadow zones; (d) for each frame of the video signal—defining, in the image carried by the signal, shadow zones that correspond to respective model shadow zones; and (e) correcting video signal values in shadow zones accordingly.
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Citations
32 Claims
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1. A method for detecting and removing shadows, the method comprising the steps of:
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(i) combining corresponding values from a plurality of frames that are carried by a digital video signal, obtained, directly or indirectly, from a video camera, any two frames of the video signal differing from each other owing to the field of view of the video camera changing by any camera action selected from tilting, panning, zooming or dollying or any combination thereof, said corresponding values being combined so as to create therefrom a background model image of the scene or of a portion thereof, said background model image covering a region greater than a field of view of at least one individual frame of the video signal; (ii) processing the background model image to detect and define within the background model image model shadow zones; (iii) calculating correction factors for some or all of said model shadow zones; (iv) for each of a plurality of frames of the video signal, determining a region of said background model image corresponding to the field of view of the frame, and thereby deriving, in the frame carried by the signal, frame shadow zones that correspond to said model shadow zones; and (v) correcting video signal values within said frame shadow zones. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A shadows removal system, adapted to receive, directly or indirectly, a digital video signal from a video camera moving so as to view regions within a scene and to implement a method for detecting and removing shadows in images that are carried by the video signal, the method comprising:
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combining corresponding values from a plurality of frames that are carried by a digital video signal, obtained, directly or indirectly, from a video camera, any two frames of the video signal differing from each other owing to the field of view of the video camera changing by any camera action selected from tilting, panning, zooming or dollying or any combination thereof, said corresponding values being combined so as to create therefrom a background model image of the scene or of a portion thereof, said background model image covering a region greater than a field of view of at least one individual frame of the video signal; processing the background model image to detect and define within the background model image model shadow zones; calculating correction factors for some or all of said model shadow zones; for each of a plurality of frames of the video signal, determining a region of said background model image corresponding to the field of view of the frame, and thereby deriving, in the frame carried by the signal, frame shadow zones that correspond to said model shadow zones; and correcting video signal values within said frame shadow zones. - View Dependent Claims (31)
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32. A computer program product, comprising a non-transitory computer usable medium having a computer readable program code embodied therein, said computer readable program code adapted to be executed to implement a method for detecting and removing shadows in images that are carried by a digital video signal, obtained, directly or indirectly, from a video camera moving so as to view regions within a scene said method comprising:
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combining corresponding values from a plurality of frames that are carried by a digital video signal, obtained, directly or indirectly, from a video camera, any two frames of the video signal differing from each other owing to the field of view of the video camera changing by any camera action selected from tilting, panning, zooming or dollying or any combination thereof, said corresponding values being combined so as to create therefrom a background model image of the scene or of a portion thereof, said background model image covering a region greater than a field of view of at least one individual frame of the video signal; processing the background model image to detect and define within the background model image model shadow zones; calculating correction factors for some or all of said model shadow zones; for each of a plurality of frames of the video signal, determining a region of said background model image corresponding to the field of view of the frame, and thereby deriving, in the frame carried by the signal, frame shadow zones that correspond to said model shadow zones; and correcting video signal values within said frame shadow zones.
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Specification