Ring shaped object detector for non-isotropic 2D images using optimized distance transform weights

A detector has been developed for finding ring shaped objects occurring in clusters in 2D images with non-isotropic pixel dimensions. The rings are characterized as having a closed border and a void interior. We assume that the thickness of the rings is approximately constant and their void shape smooth. We initially find candidates that could be possible ring voids, then by using a distance transform (DT) based technique, a DT histogram of the surrounding material is created. If the DT histogram fulfills certain constraints, a ring has been found. A second DT based step marks the pixels surrounding the void with a unique label. By this approach, we impose only loose constraints on the shape of the rings. In addition to the ring detector itself, the paper illustrates that if proper DTs are used, non-isotropic images can be analysed without interpolation to a square grid.