Figure 5.

Frangi's filter identifies beam location and orientation in micro-CT images. We applied a modified version of Frangi's filter to enhance plate-like objects in this three-dimensional image stack (eye A). (a) An example slice yields (b) a probability map that each voxel is a member of a beam, which can then be (c) binarized to segment the beams. Simultaneously, the eigenvectors of the Hessian matrix provide (d,e) information on beam orientation in three dimensions, where blue vectors correspond to the smallest eigenvalue and orange vectors correspond to the second-largest. Shown here is a two-dimensional projection of three-dimensional vectors that are orthogonal. For a three-dimensional rendering of these vectors, see the electronic supplementary video. Scale bar, 1.0 mm.