Patent ID: 7397938

Claim:
A method of identifying spherical objects in a digital image, wherein said image comprises a plurality of intensities corresponding to a domain of points in a D-dimensional space, said method comprising the steps of: calculating a local cross-correlation between a point in the domain of the image and a Gaussian spatial filter G K of standard deviation σ K about a Gaussian neighborhood G N of standard deviation σ N about the point, wherein the local cross-correlation is calculated by convolving over a difference of the Gaussians G N and G K according to the formula < I,G K > P =K ·(G N,K −G N )* I ( p ) wherein I(p) is the image at the point p, G N G K =K.G N,K with K = 1 ( 2 ⁢ π ⁡ ( σ N 2 + σ K 2 ) ) D being constant, σ N , K = σ N ⁢ σ K ( σ N 2 + σ K 2 ) , and * is a convolution operator; calculating a local standard deviation of the point in the image; calculating a local standard deviation of the spatial filter; calculating a cross-correlation ratio by dividing the local cross-correlation by the product of the local standard deviation of the image and the local standard deviation of the spatial filter; and analyzing the cross-correlation ratio to determine whether an object about said point is spherically symmetric.