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

Abstract

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