PHASE-STEPPING HOLOGRAPHIC-INTERFEROMETRY IN STUDYING TRANSPARENT DENSITY FIELDS AROUND 2-D OBJECTS OF ARBITRARY SHAPE

The image-processing routines executed in the quantitative experimental investigation of transparent density fields around 2-D objects of arbitrary shape by means of phase-stepping holographic interferometry are presented. A crucial step is to automatically distinguish between the foreground pixels (i.e., the pixels not lying in the shadow of the object) and the background pixels. This is done by thresholding into a binary mask a discriminative parameter which is computed from the digitized interferograms. To remove the 2π-discontinuities from the phase surface in the phase-integration process, an algorithm was implemented to successively address all foreground pixels starting from one central foreground pixel while circumventing the background pixels and less reliable foreground pixels. The complete procedure is illustrated by measuring the 2-D density (temperature) field around a heated horizontal cylindrical bar in free convection. © 1990.