For example, human skin color varies slightly with blood circulation.
This variation, while invisible to the naked eye, can be exploited
to extract pulse rate [Verkruysse et al. 2008; Poh et al. 2010;
Philips 2011]. Similarly, motion with low spatial amplitude, while
hard or impossible for humans to see, can be magnified to reveal
interesting mechanical behavior [Liu et al. 2005]. The success of
these tools motivates the development of new techniques to reveal
invisible signals in videos. In this paper, we show that a combination
of spatial and temporal processing of videos can amplify subtle
variations that reveal important aspects of the world around us.