Phase fitting method for sub-pixel displacement measurements using digital speckle images

This paper presents a technique to measure the minute displacement using digital speckle images. We firstly de-noise the speckle images using wavelet transform. And then the phase correlation algorithm is employed to calculate the integer pixel displacement. To get the sub-pixel accuracy, we make use of the pixels around the highest phase impulse to construct a continuous surface. The final displacement is obtained by computing the regional extreme point of the surface function. In this way, we boost up the phase correlation and get the sub-pixel information without the time-consuming template matching as used in DSCM (Digital Speckle Correlation Method). We demonstrated the feasibility and effectiveness of our method on practical measuring results.