Real-time hybrid fringe pattern analysis using a linear digital phase locked loop for demodulation and unwrapping

A new technique for fringe pattern demodulation using a linear digital phase locked loop (DPLL) is presented. The phase components of a fringe pattern are calculated using a way similar to the Fourier fringe analysis technique and a wrapped phase map is produced. The linear DPLL demodulates, tracks and unwraps the wrapped phase map simultaneously. Consequently, the proposed algorithm has good noise immunity. The proposed algorithm is tested using real fringe patterns and its suitability for demodulating real fringe patterns is confirmed. Also, the proposed algorithm is compared with the Fourier fringe analysis technique. The implementation of the linear DPLL in real time on a commercial parallel image processing system is described. Fringe patterns are grabbed, processed and the resultant phase maps are displayed concurrently. The parallel system is capable of analysing 25 images per second. There is a two-image delay between grabbed fringe patterns and displayed phase maps.