A speckle image correlation method is proposed for the application to 3D topography at ultra-high speeds. With random densely-seeded laser speckles projected onto an object to be measured, taking snapshots from two different viewing angles using a pair of CCD cameras, we are able to correlate the two speckle images in real time, 30 Hz, by a sparse-array compressed-image correlation algorithm. As soon as the correlation is established, a fast triangulation reconstruction gives the 3D coordinates of the speckles on the object in the global coordinate system, and thus the topography of the surface of the object is obtained. This method has an accuracy of plus or minus 0.2 pixels and a resolution equal to that of its cameras. Most image correlation algorithms suffer from their lack of speed. The method discussed here has overcome this barrier and made wide applications possible. Real-time correlation enables applications in areas such as on-line inspection, non-still object measurement, and instant 3D model acquisition.
Douglas P. Hart,
"Real-time 3D topography by speckle image correlation", Proc. SPIE 3422, Input/Output and Imaging Technologies, (18 June 1998); doi: 10.1117/12.311076; https://doi.org/10.1117/12.311076