Study On Phase Unwrapping In Topography Measurement With Digital Holography

Digital holography is a technology that has characteristics of simple and convenient measurement, non-contact, high resolution in topography measurement of 3D object's surface, and has a wide perspective in application. Digital holography obtains phase information directly proportional to height of object's surface through interference. Phase information is wrapped in the image of reconstruction from hologram.Processing of phase unwrapping has to be adopted to come back to the real phase distribution, in order to obtain the 3D object's surface.This paper centering about 2D phase unwrapping algorithm is studied. The characteristics of main algorithms are analyzed systemically. Unweighted phase unwrapping algorithm of least-squares based on discrete cosine transform (DCT) has been analyzed theoretically and experimental research has also been done. The main work includes:1. The principle and mathematical model of phase unwrapping algorithm are analyzed in detail. The problems solved by 2D phase unwrapping algorithms are put forward.2. Branch cut algorithm and least-squares algorithm are analyzed systemically. Processing of phase unwrapping is done with the two algorithms. Based on the compare and analysis between the experiment results, characteristics of the two algorithms are explained and problems adapted for algorithms are specified.3. Unweighted phase unwrapping algorithm of least-squares based on DCT is studied. The least-squares algorithm with image filtering and post-processing is studied.4. The modified least-squares based on DCT is proposed to unwrap phase in the image of reconstruction from hologram, and experimental research of the algorithm is done based on the theories. The method of evaluating unwrapped phase quality is used to analyze experiment results.