Reducing Distortion at the Edges of the Retreived Phase Map
Processing a fringe pattern using the WTP method produces errors at the image edges. In order to alleviate these distortions, the fringe pattern image can be extended or extrapolated at the right hand and left hand borders. Fringe pattern extension is performed using zero padding. Despite the fact that this method is still found to be common-place in practice, the errors that occur at the borders of fringe patterns are still large. The use of linear prediction coding (LPC) in order to extrapolate the fringes at the left and right borders of the image (supposing that the fringes are parallel to the y axis) produces better results than using the zero padding method. The LPC method is especially successful at extrapolating signals that are smooth and oscillatory, though not necessarily periodic. In such cases, linear prediction often extrapolates accurately through many cycles of the signal .
We have implemented this method in our WTP C software. You can download this software from our website.
 Chapter 13.6, Numerical recipes in C, second edition (1992), Cambridge Press.