A Multi-Thresholding Algorithm for Sizing out of Focus Particles

A methodology is presented that enables efficient acquisition of sufficient droplet information (e.g. diameter and aspect ratio) from images of in and out of focus droplets. The newly developed multi-threshold algorithm is successfully implemented in the automatic particle/droplet image analysis (PDIA) system. Under the same optical hardware set-up, and compared to the dual threshold methods [1], the multi-threshold method increases the measurable/acceptable depth of field (DoF) of particles, especially for the small particles of diameters less than 50??m (1098?pixels in this optical set-up). When testing the 70??m~110??m and 100??m~200??m moving glass spheres, the dual threshold method can only detect 11%~29?% of the particles found by the multi-threshold method. The multi-threshold method is also capable of generating the aspect ratios of particles more accurately than dual threshold methods.