마커 및 필터 설계를 통한 다양한 조도 조건에서의 영상 위상기반 2차원 변위 측정 기법

Abstract

The advanced displacement measurement technique using computer vision has shown several advantages, such as a high spatial resolution and no mass loading effect, compared to the conventional contact-sensing techniques. However, the accuracy and robustness of vision-based techniques are subjected to various illumination conditions, including uneven illumination and insufficient lighting. This study introduced an accurate displacement measurement technique, with high robustness with respect to the illumination changes, that used two complex Gabor filters and a specially designed marker with orthogonal features. The parameters of the two complex Gabor filters, including the center frequency, bandwidth, and direction, were selected based on the marker size and attitude to extract the accurate phase motion information on two directions with dense features. The noise caused by insufficient light and/or uneven illumination could also be reduced by emphasizing the orthogonal features using the proper filter parameters. Further, motion phase-based optical flow was applied to calculate the 2D displacement signal of the marker. The excellent performance of displacement measurement was confirmed by comparing to that by a laser doppler vibrometer(LDV) under various lighting conditions. Tracking of multiple markers on a plate was performed to demonstrate the capability of measuring the out-plane motion using the proposed technique.