1. A method of high precision sub-pixel spatial alignment of digital images comprising the steps of: capturing a reference image from a reference video signal as one of the digital images and a corresponding test image from a test video signal as another of the digital images, where the test video signal represents the reference video signal after processing; overlaying an arbitrary test block on the reference and test images at corresponding locations that include texture; performing a fast Fourier transform for the portions of each image that lie within the test block to produce a reference FFT and a test FFT; cross-correlating the reference and test FFTs to produce a correlation surface having a peak correlation value, the position of the peak correlation value on the correlation surface being representative of a shift position between the reference and test images; fitting a curve to the peak and neighboring correlation values to determine an integer pixel shift position; updating the position of the test block overlaying the test image by the integer pixel shift position; and repeating the performing step for the test image, the correlating step for finding fractional pixel shift positions, and the updating step by adding the fractional pixel shift positions to the integer pixel shift position until an end condition is achieved, the final position of the test block in the test image from the updating step relative to the initial position of the test block in the test image providing the high precision sub-pixel shift alignment between the reference and test images.