Unorthodox approach toward microscopic shape from image focus using optical microscopy

Abstract

Shallow depth-of-field is an inherent property of optical microscope. Because of this limitation, it is usually impossible to image large three-dimensional (3D) objects entirely in focus. However, the in-focus information of the object's surface can be acquired over a range of images by optical sectioning of the object in consideration. These images can then be processed to generate a single in-focus image and further for 3D shape reconstruction using methods like Shape from focus (SFF). SFF represents a passive technique for recovering object shapes. Although numerous methods for SFF have been recently proposed, all follow similar precedent of focus measure application and depth recovery by maximizing the focus curves. As the conventional techniques assume the presence of prominent texture in the scene, the shape of weak textured surfaces are not recovered properly. In this manuscript, we have followed an unorthodox approach to recover shapes of microscopic objects using SFF. At first, the in-focus image is obtained, pursued by computing depth along the edges and their neighbors present in scene. Empty spaces in the final depth map are then calculated by surface interpolation. The proposed approach works well even for objects with weak textures.