Hard X-ray ptychography has become an indispensable tool for observing the microscopic structure of a thick specimen. It measures diffraction patterns by scanning an X-ray beam and visualizes the complex-valued refractive index of the specimen by a computational reconstruction called phase retrieval. The quality of imaging is dependent on the used phase-retrieval algorithm, especially when the intensity of the diffraction patterns in the high-spatial-frequency range is low and/or when the spatial overlap of the illumination area is small. In this paper, a phase-retrieval algorithm, AMPAM, based on the Poisson model and total variation (TV) is proposed. It applies alternating minimization using primal-dual splitting and gradient-descent algorithms to compute the result without matrix inversion. The imaging capability of the proposed algorithm from low-dose and/or sparsely scanned data was investigated by numerical simulations. The proposed algorithm was compared with ADPr, which is the state-of-the-art algorithm based on the TV-regularized Poisson model. The results indicated that AMPAM can provide good-quality images with a computational cost 7–11 times less than ADPr. In addition, ink toner and macroporous silica particles were imaged at SPring-8 BL24XU to confirm the applicability of the algorithm to actual measurements.

中文翻译：

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基于全变正则泊松模型的相位检索用于低对比度物体的 X 射线 ptychographic 成像

硬 X 射线 ptychography 已成为观察厚标本微观结构不可或缺的工具。它通过扫描 X 射线束来测量衍射图案，并通过称为相位检索的计算重建来可视化样品的复值折射率。成像质量取决于所使用的相位检索算法，特别是当高空间频率范围内的衍射图案强度较低和/或照明区域的空间重叠较小时。在本文中，提出了一种基于泊松模型和总变差 (TV) 的相位检索算法 AMPAM。它使用原始对偶分裂和梯度下降算法应用交替最小化来计算结果而无需矩阵求逆。通过数值模拟研究了所提出算法的低剂量和/或稀疏扫描数据的成像能力。所提出的算法与 ADPr 进行了比较，ADPr 是基于 TV 正则化 Poisson 模型的最先进算法。结果表明，AMPAM 可以提供高质量的图像，计算成本比 ADPr 低 7-11 倍。此外，在 SPring-8 BL24XU 上对墨粉和大孔二氧化硅颗粒进行成像，以确认该算法对实际测量的适用性。结果表明，AMPAM 可以提供高质量的图像，计算成本比 ADPr 低 7-11 倍。此外，在 SPring-8 BL24XU 上对墨粉和大孔二氧化硅颗粒进行成像，以确认该算法对实际测量的适用性。结果表明，AMPAM 可以提供高质量的图像，计算成本比 ADPr 低 7-11 倍。此外，在 SPring-8 BL24XU 上对墨粉和大孔二氧化硅颗粒进行成像，以确认该算法对实际测量的适用性。