Study On Deterministic Phase Retrieval Based On The Intensity Measurement

When a wave, such a light, interacts with a body, details of the body are imprinted on the wave's three properties:amplitude (brightness),wavelength(colour) and phase(in a wavelength, the phase is equivalent to the depth). Phase is an inherent characteristic of any wave field. Statistics show that greater than25%of the information is encoded in the amplitude term and75%of the information is in the phase term. However, the oscillations of light waves about1015Hz, there are not existing light-sensing devices can record the amplitude and phase of diffraction field directly and simultaneously. In other words, the intensity of the light field can be directly measured through the CCD camera, film and other detector. Therefore, complex conversion and processing are needed to get depth information.At present, the phase retrieval based on the intensity measurement includes four typical techniques:the iterative phase retrieval algorithm, depth from defocus, deterministic phase retrieval based on the intensity measurement and optimization phase retrieval based on quadratic constraints. Among them, intensity data of the object and image plane is used to recover the phase distribution of the input and output of the light field in iterative phase retrieval. There are many shortcomings such as poor real-time. Blur information is used to obtain depth information of the three-dimensional scene in depth from defocus. The technique requires adjusting the camera parameters in order to achieve correspondence between point and point. The transport of intensity equation is solved to recover the phase information through the combination of optics and calculation in the method of phase retrieval based on the intensity measurement. This method is proved to be a feasible way to obtain phase information theoretically and experimentally. Optimization phase retrieval based on quadratic constraints is a new idea by the development of the matrix complete theory recently. So far, this method is merely in the theoretical exploration stage.Both technologies of depth from defocus and deterministic phase retrieval based on the intensity measurement are studied. Deterministic phase retrieval based on the intensity measurement which recovers phase information from the transport of intensity equation using the intensity images is focused in this thesis.The main research works and contributions of this thesis are outlined as follows:(1) Information-divergence algorithm in depth from defocus is improved. The original algorithm is yet based on equifocal assumption and ignores the fact that the image sizes of same object are changed in different parameters of the camera. In the improved algorithm, the homography between the original defocus images is calculated. Then original images are rectified and new defocus images of the same size are obtained. Space-variant window scheme is studied to overcome the limitation of equifocal assumption. Simulation and real experimental results prove the proposed algorithm can avoid smoothing depth in discontinuities and improve the precision.(2) On the basis of summing up various algorithms to solve the transport of intensity equation, such as the Green's function method, Zernike polynomial method, the multi-grid method and the Fourier transform, total variation is introduced to solve the transport of intensity equation in this theies. The experiments show that information in edge is remained at the same time of phase retrieval compared with the Fourier transform method.(3) A new derivation of Green function method in Neumann and Dirichlet boundary conditions is deduced. Because the Green's function itself is a four-dimensional matrix, large memory space will be occupied with the improvement of image resolution by solving the Green's function directly. The numerical solutions of Green's function method to solve the problems of the large-scale calculation and slow speed are presented in this thesis.(4) Imaging usually needs to apply the lens condenser in natural light conditions. The transfer function is more complex than that in the physical environment which is widely used in optical microscopy, electron microscopy and other microscopic fields. Fresnel propagation physics and phase reconstruction model are described detailedly. A phase retrieval method in this model is proposed.(5) A single CCD image data acquisition optical system is designed in this thesis. The system is equipped with a mobile focal mechanical device in order to give the accurately measurement of image in focal and defocal planes. The system is simple and portable. A patent for this system has been granted. At same time, a3-CCD image optical data collection platform is built. More accurate experimental results are achieved in this stable optical platform.