The microscopic environmental changes in the surroundings are imperceptible to humans. What is impossible to perceive with the naked eye includes minor changes, such as color variations due to blood flow to the face, or motion variations, like the subtle movement of veins beneath human skin.
For detecting these variations, an optical microscope aid is required to the human eye. As an alternative, cheaper and newer technologies like high-speed imagery and image processing help to detect such subtle variations. Eulerian video magnification (EVM) is the most popular technique for achieving this. This method, takes a standard video sequence as input, and applies spatial decomposition, followed by temporal filtering to the sequence of frames. Amplification of the resulting signal reveals the hidden information, resulting in color and motion magnified videos. Using this method, we can successfully visualize the flow of blood as it fills the face and also to amplify and reveal invisible motions.
@article{Wu12Eulerian,
author = {Hao-Yu Wu and Michael Rubinstein and Eugene Shih and John Guttag and Fr\'{e}do Durand and
William T. Freeman},
title = {Eulerian Video Magnification for Revealing Subtle Changes in the World},
journal = {ACM Transactions on Graphics (Proc. SIGGRAPH 2012)},
year = {2012},
volume = {31},
number = {4},
}