Dense and refined microstructure 3D measurement method based on an optical microscope and varying illuminations

We propose a novel microscopic photometric stereo (MPS) method based on a conventional optical microscope and varying illuminations for dense and refined microstructure 3D measurement. To guarantee the flexibility of the MPS, an uncalibrated photometric stereo (UPS) method, which does not require a priori knowledge of the light-source direction or the light-source intensity, is employed to recover surface normals and albedos from the captured multiple micro-images. Although the UPS has been studied before, there are some particular issues to be addressed to make it suitable for microscopic cases. For resolving the inherent generalized bas-relief (GBR) ambiguity of the UPS, we present a GBR disambiguation method based on a framework of entropy minimization, and extend it using a graph-cut energy minimization to decrease the influence of noise and further refine the recovered surface normal. The proposed MPS method has been tested on synthetic as well as real images and very encouraging results have been obtained. The experimental results show that this novel method can reconstruct dense and refined 3D points for the microstructure. It is an easy-to-implement yet effective alternative method for microstructure 3D measurement and can be applied to many potential fields. © 2011 IOP Publishing Ltd.