Method of and apparatus for improved image correlation

Apparatus for correlating a first image and a second image, said first image being in the form of a first real array having a size M by N and said second image being in the form of a second real array having a size M by N, M and N being positive integers, the apparatus comprising:

• a first domain transformer for performing a first domain transform on said first real array to produce a first complex array having a size M by (N/2+1);
• a second domain transformer for performing a second domain transform on said second real array to produce a second complex array having a size M by (N/2 +1);
• a multiplier, responsive to said first domain transformer and said second domain transformer, for multiplying a conjugate of said first complex array by said second complex array to produce an intermediate complex array having a size M by (N/2+1);
• first inverse domain transform means, responsive to the multiplier, for performing a first inverse domain transform on each of the columns of the intermediate complex array to produce an inverse transformed intermediate complex array;
• supplementing means, responsive to the first inverse domain transform means, for producing a supplemented complex array having size M by N from said inverse transformed intermediate complex array by determining elements for additional columns by symmetry for each row;
• second inverse domain transform means, responsive to the supplementing means, for performing a second inverse domain transform on each of the M rows of the completed complex array to produce a real correlation matrix having a size M by N;
• and
• correlating means, responsive to the second inverse transform means, for correlating said first image and said second image on the basis of said real correlation matrix.