Highly Accurate 3D Shape and Deformation Measurements Using Fluorescent Stereo Microscopy

Biomechanics has been developing at rapid pace in recent decades. For investigation of the biotissues, biomaterials or biofilms under the microscale or the nanoscale, it urgently demands an accurate measurement technique for three-dimensional (3D) surface profilometry and deformation in real-time. Traditional stereo microscope with stereo-based digital image correlation (DIC) works well on common materials, but it is hard to apply to moisture sample due to the specular reflections which could cause large decorrelation among those stereo images. In this paper, we described a fluorescent stereo microscopy (FSM) measurement method for surface profilometry and deformation based on stereo-based DIC. Due to the complex lens combination of a microscope, the distortion of the optical system is hard to formulate accurately using ordinary distortion models. Thus, it could cause large reconstruction errors, particularly in Z-direction in height. In order to improve the accuracy, a new distortion correction scheme is introduced along with a new calibration board. This distortion correction method is intended for use prior to stereo-vision calibration by mapping sensor coordinates of generic image coordinates to a virtual ideal plane. In order to demonstrate this technique, a sequence pair of images of a biofilm is captured during growth, and the 3D surface profilometry and deformation was measured with high accuracy accordingly. A detailed description of this technique is presented in this paper.