Mapping of Moving, Deformable Surfaces Using the Defocusing Principle

Abstract

Mapping of deformable surfaces is important in biomechanics, biofluidics, and many other braches of the life sciences. We have adapted the digital defocusing technique originally developed for particle image velocimetry for mapping deformation of a flexible surface using a single camera. The aperture of a lens is replaced with a plate with three openings arranged in an equilateral triangle, and the subject is filmed outside the focal plane of the camera so that each point of light in the subject creates a triangle of points on the image sensor. A set of images of a target at known distances is used to establish a relationship between the distance of the subject and the size of the triangle of points it creates. We applied this technique to imaging the wings of live insects in flight to quantify wing deformation. A plate with three 2.4 mm openings was constructed and inserted into a 20 mm wide-angle lens. The wing surface was marked with small, reflective points, and the animals were filmed at 500 fps with a high-speed video camera. The videos were analyzed with previously published software which detects triplets of points and outputs three-dimensional coordinates of the source point based on triangle size. The clouds of points were then interpolated to create a three-dimensional model of the wing for each frame.

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