A new method of image processing in the analysis of axisymmetric drop shapes

A new method is presented to analyze drop images for the measurement of surface tension. The method, termed theoretical image fitting analysis (TIFA), eliminates the need for an independent edge detection module, and enhances the range of applicability of drop-shape techniques such as axisymmetric drop shape analysis (ADSA). In the current schemes of ADSA, edge detection techniques are used to extract the experimental drop profile from a digital image. Then the surface tension is calculated by fitting theoretical curves to the experimental profiles, taking the surface tension as an adjustable parameter. Edge detection is an important part of current drop-shape techniques. However, edge detectors fail when acquisition of sharp images is not possible due to experimental or optical limitations. Examples are captive bubble experiments for lung surfactant research and surface tension measurements of molten metal. The new method generates theoretical images of the drop (instead of theoretical profiles as in the current schemes), and generates an error function that describes the pixel-by-pixel deviation of the theoretical image from the experimental one. It then calculates the surface tension by matching the theoretical to the experimental image. The accuracy and versatility of TIFA were examined by comparing the results with other available advanced methods.