| Hard X-ray phase-contrast imaging is one of the novel fields of X-ray imaging. There are four main methods of X-ray phase contrast imaging. In-line imaging is easy to achieve and grating imaging is potential in application. So the imaging algorithms and algorithms of phase information retrieval of these two methods are studied in the paper, and phase information retrieval is emphasized.In the in-ling imaging technology, the direct method and iterative method are employed to recover the phase information of the object. The direct method is based on transport intensity of equation (TIE), and full multi-grid (FMG) algorithm is employed to resolve the Poisson equation. The error reduction algorithm (ER), which is a kind of iterative method, is employed to retrieve phase. TIE algorithm is not accurate in long region, since the Fresnel Diffraction Equation cannot be linearization in long region. ER is mainly used in the long region, since it converges fast in the long region. In order to overcome the limitation of the direct and iterative methods, TIE and ER algorithms are combined together. The retrieved image by TIE algorithm works as the initialization of the ER algorithm. TIE algorithm performs well in low frequency information recovery and ER algorithm performs well in high frequency, so the combined method converges fast. All the algorithms mentioned above are verified by computer simulation and experiment.It is necessary to extract the refractive angle to get the phase information of the object. So the extraction method of phase information is essential to grating-based phase-contrast imaging. The common extraction methods of phase information are the simplest method, Moire interferometry and phase stepping. The advantages and limitations of these methods are discussed and improved by reverse projection scheme. The reverse projection scheme is verified by computer simulation that it performs well compared with current methods. |
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