Our temporal filtering approach not only amplifies color variation,
but can also reveal low-amplitude motion. For example, in the supplemental
video, we show that we can enhance the subtle motions
around the chest of a breathing baby. We provide a mathematical
analysis that explains how temporal filtering interplays with spatial
motion in videos. Our analysis relies on a linear approximation related
to the brightness constancy assumption used in optical flow
formulations. We also derive the conditions under which this approximation
holds. This leads to a multiscale approach to magnify
motion without feature tracking or motion estimation.