Left frames: Application of RCM technique to a simple test image sequence, consisting of an expanding ring-shaped “wave” superimposed on a diffuse background (a) shows the original frames, (b) shows the expanding ring without the background, (c) shows the running difference, and (d) shows the RCM filter. Green indicates statistically significant brightenings, purple dimmings. Right: The time series for the point indicated by the circle in the frames on the left. Readers are encouraged to view the accompanying animation, RCM_RunningDifference_test_sequence.mpg, available in the online version of this paper.