Fig. 3. Experimental results of tracking a moving star object over many static dots via speckle correlations.

a Three representative still frames of the moving scene on the DMD, made of a large number of static dots, and a single moving star. b The cross-correlation between the measured speckle patterns at t₀ and the speckle patterns at successive times. The cross-correlation decreases with distance from the centre due to the finite memory effect range. c Plot of I(t_n) ⋆ I(t_n−2) − I(t_n) ⋆ I(t_n), where I(t_n) is the measured speckle pattern at frame n (see Supplementary Video 3). The red arrow follows the cross-correlations between one of the static background dots and the moving star. In the first panel, the background dot is at the edge of the memory effect range from the moving star, and it is thus barely visible, becoming brighter as it gets closer to the centre of the picture (i.e. closer to the moving star). The dashed circle in the last panel of b and c shows the memory range.