Computational reconstruction of images from optical holograms

This thesis describes the analysis, development and implementation of computational reconstruction of optical holograms, and its applications in marine biology and Holographic Particle Image Velocimetry (HPIV). Computational reconstruction of holograms is a process that recovers three-dimensional information from its holographic form computationally rather than optically. In this thesis, the reconstructions are represented by a sequence of plane images at programmable distances parallel to the associated hologram. The primary goal is to increase the reconstruction speed and improve the image quality, and ultimately lead to a computational platform that is efficient and robust for oceanographic applications such as for marine biology and HPIV. A signal processing path has been followed throughout this thesis. Reconstruction algorithms have been developed in wavenumber space and accelerated by the use of FFT algorithms. Modifications to the reconstruction kernel both in spatial domain and frequency domain have been incorporated to improve the reconstruction quality. The behavior of reconstruction process is described qualitatively. A number of focus measures are proposed for quantitative focus analysis based on a circular disc object. Optimal sampling of holograms is also discussed and found to be distancedependent. A PC based computational reconstruction system has been constructed which in addition consists of a commercial memory-enhanced DSP engine and a high-resolution scanner. As compared to optical reconstruction, by using this system the reconstruction time of one hologram has been reduced by a factor of 100 to 383.3 minutes for recovering one 24.8mm * 24.8mm * 250mm volume at a resolution of 315pixel/mm. Both simulation results of HPIV and experimental results of marine micro-organism are presented. A computationally efficient method has been devised for object-counting based on hologram images. Thesis Supervisor: Jerome H. Milgram Title: W. I. Koch Professor of Marine Technology Thesis Reader: Arthur B. Baggeroer Title: Ford Professor of Engineering

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