At 11:27 AM 13/09/2007, Stephen Koehler wrote:
>Mike, Kieran, or anyone else: Is this technique mentioned in the
>literature on phase unwrapping, e.g., Ghiglia and Pritt? It's so
>simple, and so apparently effective, that I'm surprised that I haven't
>heard of it, before. Unless I am thinking of this problem wrong, I
>see no problem with unwrapping twice with a removal of tilt, defocus
>and SA in the middle.
The idea of removing some background level of phase (with significant phase
gradient) is rather like the sub-Nyquist idea of John Greivenkamp. There
is a nice explanation of it on the following website:
I have also seen early, oblique suggestions of essentially removing linear
and quadratic phase terms in Bones' papers:
1. D. J. Bone, "Fourier fringe analysis: the two-dimensional phase
unwrapping problem," Applied Optics 30, 3627(1991).
2. D. J. Bone, H.-A. Bachor, and R. J. Sandeman, "Fringe-pattern
analysis using a 2-D Fourier transform," Applied Optics 25, 1653-1660 (1986).
3 J. E. Greivenkamp, "Sub-Nyquist interferometry," Appl. Opt. 26,
One possible interpretation is that in your example the fringes are below
the Nyquist limit, but by removing the local phase gradient your are
shifting the residual phase to very low variation whilst the noise is still
fairly high frequency and more easily removed.