Method and apparatus for detecting object movement within an image sequence
First Claim
1. In a vehicular traffic monitoring system including a video camera having a given field of view for recording successive image frames of road traffic within its field of view, and digital image processing means responsive to pixel information defined by each of said successive image frames;
- the improvement wherein said digital image processing means comprises;
first means responsive to an initial train of said successive image frames for deriving a stored initial reference image defining only stationary objects within said field of view and thereafter updating said stored initial reference image with a reference image derived from an image frame recorded later than said initial train, with each pixel'"'"'s digital amplitude level of each of said reference images being determined by illumination conditions existing when said initial train and when said later recorded frame were recorded;
second means for modifying each pixel'"'"'s digital amplitude level of one of a current image frame and said stored reference image then being stored to make their corresponding pixels defining stationary objects substantially equal to one another;
third means responsive to the digital amplitude-level difference between corresponding pixels of each of successively-occurring ones of said successive image frames and the then stored reference image for deriving successive images defining only moving objects within said field of view;
fourth means for discriminating between those moving objects that remain substantially fixed in position with respect to one another in each of said successively-occurring ones of said successively-occurring images and those moving objects that substantially change in position with respect to one another in each of said successively-occurring ones of said successively-occurring images; and
a fifth means responsive to the variance of the digital amplitude levels of the pixels of those ones of said objects that remain substantially fixed in position with respect to one another for distinguishing those ones of said moving objects that remain substantially fixed in position with respect to one another that define non-physical moving objects, from said moving objects that remain substantially fixed in position with respect to one another that define physical moving objects, and then eliminating those ones of said moving objects that define non-physical moving objects.
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Abstract
Method and apparatus for processing a sequence of images to detect object movement within the sequence. Specifically, the method comprises the steps of: (a) supplying a sequence of image frames; (b) initializing a reference image that contains image information regarding stationary objects within a scene represented by the sequence of images; (c) supplying a next image frame which temporally follows the sequence of image frames; (d) comparing the next image to the reference image to produce a motion image representing motion information regarding movement of objects within the scene; (e) updating the reference image with information within the next image that represents stationary objects within the scene; and (f) repeating steps (c), (d), and (e) for each next image supplied. The method is implemented by image processing apparatus. A specific embodiment of the method and apparatus is a traffic monitoring system that identifies vehicles in varying illumination levels and eliminates erroneous identification of non-physical movement in the scene such as shadows and headlight reflections.
181 Citations
40 Claims
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1. In a vehicular traffic monitoring system including a video camera having a given field of view for recording successive image frames of road traffic within its field of view, and digital image processing means responsive to pixel information defined by each of said successive image frames;
- the improvement wherein said digital image processing means comprises;
first means responsive to an initial train of said successive image frames for deriving a stored initial reference image defining only stationary objects within said field of view and thereafter updating said stored initial reference image with a reference image derived from an image frame recorded later than said initial train, with each pixel'"'"'s digital amplitude level of each of said reference images being determined by illumination conditions existing when said initial train and when said later recorded frame were recorded; second means for modifying each pixel'"'"'s digital amplitude level of one of a current image frame and said stored reference image then being stored to make their corresponding pixels defining stationary objects substantially equal to one another; third means responsive to the digital amplitude-level difference between corresponding pixels of each of successively-occurring ones of said successive image frames and the then stored reference image for deriving successive images defining only moving objects within said field of view; fourth means for discriminating between those moving objects that remain substantially fixed in position with respect to one another in each of said successively-occurring ones of said successively-occurring images and those moving objects that substantially change in position with respect to one another in each of said successively-occurring ones of said successively-occurring images; and a fifth means responsive to the variance of the digital amplitude levels of the pixels of those ones of said objects that remain substantially fixed in position with respect to one another for distinguishing those ones of said moving objects that remain substantially fixed in position with respect to one another that define non-physical moving objects, from said moving objects that remain substantially fixed in position with respect to one another that define physical moving objects, and then eliminating those ones of said moving objects that define non-physical moving objects. - View Dependent Claims (2, 3, 4, 5, 6)
- the improvement wherein said digital image processing means comprises;
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7. A method of image processing comprising the steps of:
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(a) supplying a first sequence of image frames; (b) initializing a reference image that contains image information regarding stationary objects within a scene represented by said first sequence of images; (c) supplying a next image frame which temporally follows said first sequence of image frames; (d) comparing said next image frame to said reference image to produce a two-dimensional motion image representing motion information regarding movement of objects within the scene; (e) updating said reference image with information within said next image frame, where said information used for updating the reference image only represents stationary objects within the scene and substantially disregards moving objects and temporarily stationary objects within the scene; and (f) repeating steps (c), (d), and (e) for each next image supplied. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. Apparatus for image processing comprising:
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imaging means for supplying a continuous sequence of image frames representing a scene; reference image initializing means, connected to said imaging means, for initializing a reference image that contains image information regarding stationary objects within the scene; comparator means, connected to said imaging means and said reference image initializing means, for comparing an image frame supplied by said imaging means to said reference image to produce a two-dimensional motion image representing motion information regarding movement of objects within the scene; means for updating said reference image with information within said image frame, where said information used for updating the reference image only represents stationary objects within the scene and substantially disregards moving objects and temporarily stationary objects within the scene. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
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Specification