Method to measure 3D deformation using defocused images of objects with artificial speckle features

A novel method to measure three-dimensional deformation based on defocused images of an object is presented in this paper. To do this, images of an object with artificial speckle features are taken by a camera. The in-plane coordinates of the points on a specimen surface are obtained according to the camera setup parameters and the defocused distance. The blur band width on the edges of the surface textures is used as a parameter to evaluate the blur degree of an image. Depth dimension is obtained by the relationship of the defocused distance and the blur degree. The relationship is given theoretically and experimentally. The digital image correlation method is used to trace each point on the specimen surface before and after deformation. Three-dimensional deformation can be obtained according to the displacement of each point. Reliability of the method is validated by two experiments.