Real-time object tracking system

Abstract

A real-time computer vision system tracks one or more objects moving in a scene using a target location technique which does not involve searching. The imaging hardware includes a color camera, frame grabber, and processor. The software consists of the low-level image grabbing software and a tracking algorithm. The system tracks objects based on the color, motion and/or shape of the object in the image. A color matching function is used to compute three measures of the target's probable location based on the target color, shape and motion. The method then computes the most probable location of the target using a weighting technique. Once the system is running, a graphical user interface displays the live image from the color camera on the computer screen. The operator can then use the mouse to select a target for tracking. The system will then keep track of the moving target in the scene in real-time.

We claim:  
     
         1 . A method of tracking a target, comprising the steps of: 
 inputting a sequence of images of a scene;    selecting a target in the scene;    computing the center of the target in an initial one of the images using one or more visual characteristics of the target region;    computing the center of the target in a subsequent one of the images using the visual characteristics; and    comparing the center of the target in the subsequent image to the center of the target in the initial image to determine movement of the target within the scene.    
     
     
         2 . The method of    claim 1   , wherein the visual characteristics include the color, shape or the location of the target.  
     
     
         3 . The method of    claim 1   , wherein the visual characteristics include a combination of static and dynamic characteristics.  
     
     
         4 . The method of    claim 3   , further including the step of modeling of the dynamic characteristics to yield an estimate the location of the target in the current image based on the location of the target in previous images.  
     
     
         5 . The method of    claim 1   , wherein the step of selecting a target in the scene includes the step of user-selecting the target on a computer screen through a graphical user interface.  
     
     
         6 . The method of    claim 5   , wherein the graphical user interface provides a bounding box surrounding the target superimposed on each image as it is displayed on the screen.  
     
     
         7 . The method of    claim 2   , wherein step of computing the center of the target with respect to color further includes the steps of: 
 enabling a match between the color of the target in the subsequent image to the color of the target in a previous image despite differences arising from target lighting and shadows.    
     
     
         8 . The method of    claim 2   , wherein step of computing the center of the target with respect to color further includes the steps of: 
 enabling a match between the color of the target in the subsequent image to the color of the target in a previous image within a threshold of hue.    
     
     
         9 . The method of    claim 2   , wherein step of comparing the center of the target in the subsequent image to the center of the target in the initial image includes a comparison of pixel in an RGB format.  
     
     
         10 . The method of    claim 1   , further including the step of determining if the target has moved outside of the scene.  
     
     
         11 . The method of    claim 1   , wherein: 
 the visual characteristic is color; and    further including the step of finding a weighted average of color to compute the center of the target based upon color alone.    
     
     
         12 . The method of    claim 1   , further including the step of segmented a region defined by a predetermined closeness of color as an estimate of target shape.  
     
     
         13 . The method of    claim 1   , further including the step of continuing to track the target when the target moves in front of or behind a similarly colored object in the scene.  
     
     
         14 . The method of    claim 1   , further including the step of continuing to track the target when the target and input image move in relation to one another.