  An object's interior material properties, while invisible to the human eye,
determine motion observed on its surface. We propose an approach that estimates
heterogeneous material properties of an object directly from a monocular video
of its surface vibrations. Specifically, we estimate Young's modulus and
density throughout a 3D object with known geometry. Knowledge of how these
values change across the object is useful for characterizing defects and
simulating how the object will interact with different environments.
Traditional non-destructive testing approaches, which generally estimate
homogenized material properties or the presence of defects, are expensive and
use specialized instruments. We propose an approach that leverages monocular
video to (1) measure and object's sub-pixel motion and decompose this motion
into image-space modes, and (2) directly infer spatially-varying Young's
modulus and density values from the observed image-space modes. On both
simulated and real videos, we demonstrate that our approach is able to image
material properties simply by analyzing surface motion. In particular, our
method allows us to identify unseen defects on a 2D drum head from real,
high-speed video.
