Fast and accurate visual vibration measurement via derivative-enhanced phase-based optical flow

Visual vibration measurement using a digital camera is an emerging non-contact modality capable of enabling flexibility, high spatial resolution, and full field. However, the massive amounts of video data with vibration information (thousands of time-lapse images per measurement) to be handled lead to an actual bottleneck. This prevents the system from extracting the vibration information with high speed and fidelity. Here, a straightforward phase-based optical flow approach is proposed by introducing a derivative operation to perform vibration measurements in a more accurate and efficient manner, in contrast to the state-of-the-art phasebased visual method. This approach generates analytical signals by considering each raw gray image as the real part and its first-order derivative as the imaginary part. As a result, the physical vibration can be extracted from the phase variations of the analytical signals from one to the next. Numerical simulations and experiments are conducted to validate the effectiveness and accuracy of this simple but powerful approach. The results indicate that the proposed approach provides a significantly higher speed than current methods and a correlation coefficient of 99.2 % with the identification results.