Although animated and live action films are composed of a series of still images, we perceive them as smooth/coherent motion. The present study proposes a method of analyzing motion smoothness by using a spatio-temporal frequency analysis applied to the spatio-temporal difference between two frames of sequential images. There has been no objective explanation for the mechanism of motion smoothness perceived in animated films (which are composed of a lesser number of still images than live action films). With respect to the analysis of motion smoothness, two-dimensional Fourier transformation was applied, in such a way that spatio-temporal frequency components on a given motion can be visualized and this allows us to quantitatively compare the difference of two sample frames in motion. The present study aimed to investigate the physical factors of motion smoothness and further discusses the perception of such smooth/coherent motions in the “limited animation" technique.