Multi-threshold algorithm for analyzing out of focus particles and droplets

摘要

A methodology is presented that enables efficient acquisition of sufficient particle/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. It employs continuous thresholds until the local background level to process each particle/droplet in the images, rather than only two thresholds implemented in the dual threshold methods (which are widely used in the commercial software). It uses a curve matching method to compare the results with the calibrated data, to acquire the particle/droplet size, aspect ratio and the distance from the focal plane, which provides a possibility to get the three-dimensional position of the particles/droplets from the two-dimensional images. The multi-threshold method significantly increases the depth of field (DoF) of small particles with diameter smaller than 50µm, and it performs more efficiently than the dual threshold methods. The multi-threshold method is also capable of generating the aspect ratios of particles/droplets more accurately than the dual threshold methods.