These artifacts contaminate the science template with features not present in the ITF window and are temporarily masked during the correlation procedure. The template is sequentially positioned throughout the window, and at each position a linear cross correlation is performed. By virtue of the sizes of the template and search windows, a total of forty-nine correlation coefficients are computed to determine the best pattern match location to pixel accuracy for each sampling location. The maximum coefficient in this sample is assumed to be the best representation for a true match. Summations are performed over the coordinates common to both w and t . 4.
Sigma is the standard deviation of the correlation coefficient matrix.
The maximum correlation coefficient must be at least two sigma greater than the rest of the coefficients in the matrix. If the coefficient is deemed valid, the position of the pattern match is then determined to sub-pixel accuracy.