Real-Time Optical Measurement of Displacements Using Subpixel Image Registration

An open-source tool for a real-time measurement of relative displacements based on image registration is presented. The use of upsampled matrix-multiplication discrete Fourier transform and measurement limited to predefined points of interest by virtual extensometers allows high sampling frequencies with a subpixel accuracy. This solution was designed primarily for laboratory testing in order to eliminate the problem with inaccurate measurement of cross-head displacement due to compliance of testing frames and difficulties connected to the attachment of strain-gauges or extensometers. However, the portable hardware allows for outdoor applications in which remote monitoring of displacements and deformations is required. The accuracy of the system was assessed, and the software was successfully verified through experimental testing.