Tracking algorithms for low-contrast extended objects

We studied the effectiveness of two algorithms, of cross-correlation coefficient and of absolute difference in the case of extended, low-contrast objects, such as solar granulation and sunspots. Wave-front overall tilt signals, acquired via post-processing of sampled solar granulation and sunspot images, are presented. Furthermore, long-exposure images of solar granulation before and after the tilt elimination are compared as regards rms contrast.