Fringe Thinning Algorithms

Three fringe thinning algorithms suitable for Interferograms recorded using the Mach-Zehnder interferometer are presented in this section. The first is an automatic technique for fringe thinning using the intensity minima within a dark band and does not require user intervention. This has been compared to two other methods of approximately locating the intensity minima. These are: (1) the midpoint search within a dark band, and (2) paintbrush drawing using a personal computer.

Automatic Fringe Thinning Algorithm

The algorithm under discussion is similar to the one proposed by Funnell [86], but in view of certain differences in the direction of the minimum intensity. The direction is decided by using the intensity information over a template of pixels. The computer code developed in the present study can run using different sizes of templates and handle complex fringe shapes. The input required for the code are the starting points arbitrarily selected for each of the fringes.

The algorithm uses the following ideas. The direction of the tracings are defined as: (a) forward, and (b) backward, (Fig 4.17)

Figure 4.17: Two major directions for tracing of fringes

The turning of fringes by more than degrees results in a change of direction and is a special case. Such areas of the fringes where a turning occurs has to be predefined in the form of a rectangle covering the area. These cases are classified into four categories depending on the angle of turning: (a) while in forward direction turning backward up, (b) while in forward direction turning backward down, (c) while in backward direction turning forward up, (d) while in backward direction turning forward down (fig.4.18).

Figure 4.18: Four Possible turning options of fringes.