Image processing for shearing interferometer fringe patterns

It is dificult to analyze fringe pattterns by phase-step technique because of the unstable fluid field when employing shearing interferometer to measure the temperature-gradient field of free convection. To overcome this difficulty, a new method is presented to proces the carrier fringe patterns. The fringes before and after disturbance are thinned to locate their centers and encoded into numerical data. The value of firnge order on every pixel can be acquired by surface fitting to these data. By subtracting the two fringe fields, the fringe order distribution caused uniquely by the temperature change can be obtained. This method can also eliminate the aberrations of the optical system. The method is applied to this recent experiment to obtain new results.