<title>Progress in phase unwrapping</title>

This paper reviews some of the main developments in numerical phase unwrapping techniques that have been introduced over the past five years. In quality control applications of wholefield optical techniques it is often necessary for the phase unwrapping to be both robust and performed within a guaranteed time period of a few seconds or less. Deterministic algorithms that have data-independent run times are therefore desirable. The temporal phase unwrapping algorithm has been implemented on a pipeline image processor which is able to calculate phase maps from phase-shifted fringe patterns acquired at 30 frames s^-1, and to unwrap the resulting phase maps in real time. One application of the system is measurement of surface profile. The fringe patterns are projected at 30 frames s^-1 using a high resolution data projector. The spatial frequency is reduced exponentially from the maximum value. The sequence of phase values at a given pixel is then unwrapped independently of the other image pixels, and all the intermediate phase values contribute in a least squares sense to the final range estimate for the pixel. A total acquisition and processing time of 0.7 s has been achieved for a maximum spatial frequency of 16 fringes across the field of view.