System and method for image registration based on variable region of interest

Abstract

An image registration system for aligning first and second images. The novel system includes a first system for extracting a region of interest (ROI) from each image and a second system for coarsely aligning the regions of interest. The first system determines the size and location of the ROI based on the number of features contained within the region. The size of the ROI is enlarged until a number of features contained in the ROI is larger than a predetermined lower bound or until the size is greater than a predetermined upper bound. The second system computes a cross-correlation on the regions of interest using a plurality of transforms to find a coarse alignment transform having a highest correlation. The image registration system may also include a third system for performing sub-pixel alignment on the regions of interest.

1 . A system for finding a region of interest in an image comprising:
 a first system for detecting features in said image;   a second system for determining a location for said region of interest; and:   a third system for determining a size of said region of interest based on a number of features contained within a region of said size and at said location in said image.   
     
     
         2 . The invention of  claim 1  wherein said third system includes a system for enlarging said size until a number of features contained in said region is larger than a predetermined lower bound or until said size is greater than a predetermined upper bound. 
     
     
         3 . The invention of  claim 1  wherein said location is fixed. 
     
     
         4 . The invention of  claim 3  wherein said location is at a center of said image. 
     
     
         5 . The invention of  claim 1  wherein said location is dependent on a number of features contained in said region of interest. 
     
     
         6 . The invention of  claim 5  wherein said second system includes a system for counting a number of features in each row and each column of said image. 
     
     
         7 . The invention of  claim 6  wherein said second system further includes a system for finding a first subset of rows having a large number of features. 
     
     
         8 . The invention of  claim 7  wherein said second system further includes a system for finding a second subset of columns having a large number of features. 
     
     
         9 . The invention of  claim 8  wherein said location is at an intersection of said first and second subsets. 
     
     
         10 . A method for finding a region of interest in an image including the steps of: detecting features in said image;
 determining a location for said region of interest; and   determining a size of said region of interest based on a number of features contained within a region of said size and at said location in said image.   
     
     
         11 . The invention of  claim 10  wherein said method includes enlarging said size until a number of features contained in said region is larger than a predetermined lower bound or until said size is greater than a predetermined upper bound. 
     
     
         12 . The invention of  claim 10  wherein said location is determined by counting a number of features in each row and each column of said image, finding a first subset of rows having a large number of features and a second subset of columns having a large number of features, and choosing said location at an intersection of said first and second subsets. 
     
     
         13 . A method for aligning a first image and a second image including the steps detecting features in one of said images;
 determining a location for a region of interest;   determining a size of said region of interest based on a number of features contained within a region of said size and at said location in said image;   applying said size and location to said first and second images to extract a region of interest from each image; and   cross-correlating said regions of interest using a plurality of transforms to find a first transform that coarsely aligns said regions of interest.   
     
     
         14 . The invention of  claim 13  wherein said method further includes interpolating said regions of interest. 
     
     
         15 . The invention of  claim 14  wherein said method further includes crosscorrelating the interpolated regions of interest using a plurality of transforms to find a second transform that sub-pixel aligns said regions of interest. 
     
     
         16 . The invention of  claim 15  wherein said method further includes applying said first and second transforms to one or both of said first and second images.