The algorithm is thoroughly described in Supporting Note II. Briefly, the video is scanned in twodimensions using a 3x3 pixels window, the Pearson correlation coefficient in time between the central pixel (cPx in Figure ) and its direct neighbors is computed, yielding 8 correlation relationship values for each pixel. Figure provides examples of such a window for high and low correlation regions of the movie. Based on these correlation relationships, the pixels are clustered together akin to reconstructing a family tree (see Figure ). During this process, a threshold is used to determine if the correlation values are high enough to group pixels together or not.