A Practical Guide to Motion Magnification

Numerous algorithms and software packages have been developed to detect and magnify small motions in video recordings with applications to structural vibration analysis. While some techniques follow naturally from intuition or mathematical duality, others seem overly complex at face value. Due to this, it can be difficult to assess the best tool for analysis, especially in terms of an intuitive understanding of how the results came to be. To facilitate the development of this intuition, input videos with different test articles and vibration characteristics were processed through selected magnification schemes. For each input, the outputs of the different methods were compared in order to assess their differences, amplification potentials, and limitations. Beginning with single regions of interest, the investigation then moved into more complicated scenarios involving multiple areas of localized motion. Variations such as coherence and scale for objects in the frame were also examined. Unlike previous review papers, these magnification tools are introduced in a framework that is more geared toward the working acoustician; in particular, intensity-, Fourier-, multi-resolution-, and Hilbert-based methods are evaluated in a structural-acoustic context to garner a better understanding of the underlying principles and idiosyncrasies. The main result is a thorough evaluation of each method’s performance in order to develop a guide for choosing the best algorithm in a given scenario.