Fig. 5

One-dimensional DFT of a single moving square. a The video frames of a moving square of width d at a constant speed v. b The differential footprint images of the square in different colors. c The color-coded DFT images of the square. d A turning point in the plot of the DFT area \(a_{1} \left( {t_{i} } \right)\) as a function of time \(t_{i}\)