a b s t r a c tDigital holography is an effective 3D imaging technique, with the potential to be used for particle size measurements. A digital hologram can provide reconstructions of volume samples focused at different depths, overcoming the focusing problems encountered by other imaging based techniques. Several particle analysis methods discussed in the literature consider spherical particles only. With the object sphericity assumption in place, analysis of the holographic data can be significantly simplified. However, there are applications, such as particle analysis and crystallization monitoring, where non-spherical particles are often encountered. This paper discusses the processing of digital holograms for particle size and shape measurement for both spherical and arbitrarily shaped particles. An automated algorithm for identification of particles from recorded hologram and subsequent size and shape measurement is described. Experimental results using holograms of spherical and non-spherical particles demonstrate the performance of the proposed measuring algorithm.
Abstract:A method to measure the size, orientation, and location of opaque micro-fibers using digital holography is presented. The method involves the recording of a digital hologram followed by reconstruction at different depths. A novel combination of automated image analysis and statistical techniques, applied on the intensity of reconstructed digital holograms is used to accurately determine the characteristics of the microfibers. The performance of the proposed method is verified with a single fiber of known length and orientation. The potential of the method for measurement of fiber length is further demonstrated through its application to a suspension of fibers in a liquid medium.
Digital holography has been reported as an effective tool for particle analysis. Other image-based techniques have small depth of focus allowing only 2D analysis at microscopic level. On the other hand, digital holography offers the ability to study volume samples from a single recording as reconstructions at different depths can be obtained. This paper focuses on the processing of the digital hologram that follows its recording in order to obtain particle size. We present a stepwise processing procedure with discussion on aspects such as reconstruction, background correction, segmentation, focusing, magnification and particles' feature extraction. Solutions to common obstacles faced during particle analysis which include ways to obtain fixed size reconstructions, automatically determine the threshold value, calculate magnification, and locate particles' depth position using effective focusing metrics are highlighted. Real holograms of microparticles are used to illustrate and explain the different stages of the procedure. Experimental results show that the proposed algorithm can effectively extract particle size information from recorded digital holograms.
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