Fourier ptychographic microscopy is a newly developed method to extend the resolution beyond the conventional limit defined by a microscope optics. The positions of the LED sources strongly determine the quality of the reconstructed result. In this paper, we propose a new positional misalignment correction method, which is based on the distribution of the incident LED intensity. When the LED matrix panel has displacements along x-axis, or y-axis, the incident LED intensity distribution which propagates to the sample plane will be changed. An optimization method to correct positional misalignment is introduced, as well as the light intensity correction. Simulation has been performed to verify the effectiveness of the proposed method, which demonstrates that the reconstructed result shows a better quality.
Fourier ptychographic microscopy has the advantages of large field of view, high resolution and quantitative phase imaging, which magically compromises contradiction between the resolution and the field of view. In the traditional reconstruction process, the spectrum is always updated partly step by step, which would result in error accumulation. In order to improve the reconstruction precision, based on its working principle, the paper proposes a global iterative optimization method, which updates the spectrum holistically. And experimental results demonstrate its better performance and effectiveness.
An approach for constructing optical hash function has been proposed based on the interaction between multiple scattering media and coherent radiation. Unlike the traditional Hash function via mathematical transformations or complex logic operations, the proposed method employs a multiple scattering media and Sobel filters for data scrambling and features extraction. An arbitrary length input data can be compressed into a fixed length (256-bit) Hash value after a cascade iterative processing. Its safety relies on the unpredicted and non-duplicated disorder multiple scattering media, in other word, there is tremendous difficulty of knowing the multiple scatting media with a specific internal state or efficiently simulating the light interaction effect between the multiple scattering media. Simulation results are presented to demonstrate the avalanche effect and collision resistance performance of the proposed designing strategy of the optical Hash function.
A generalized amplitude-phase retrieval algorithm (GAPRA) attack on ‘double images encryption method with resistance against the special attack based on an asymmetric algorithm’ (DIEM) is presented in this paper. The analysis shows that the DIEM is a cascaded cryptosystem, which consist of a joint transform correlator architecture and a phasetruncated Fourier transform scheme. A GAPRA attack is proposed and the potential risk of the cascaded cryptosystems is discussed. By using our method, an attacker could crack high-quality results of the plaintexts. A set of simulation results demonstrate the validity and feasibility of the proposed method.
KEYWORDS: Calibration, Cameras, 3D image processing, 3D acquisition, Distortion, Imaging systems, 3D metrology, 3D modeling, Projection systems, Image processing
In this paper, we proposed a novel method for correcting the 2D calibration target. Firstly, we captured
multiple images of the inaccurate calibration target from multi-views and located the coordinates of
those circle landmarks in these images. Secondly, homonymous landmarks in different images could be
detected by a scheme for a special topology relation. Thirdly, we could accurately reconstruct the 3D
coordinates of landmarks with a scale constraint using bundle adjustment strategy. And finally, the
scale was computed from an accurate distance between any two landmarks. Then we could obtain the
truly coordinates of landmarks, which multiplied by the scale. The experimental results validated that
our method is efficient, high-precision, low-cost and easy-implementation, which can be widely
applied in vision measurement and system calibration.
A phase reconstruction method using frequency-shifting is proposed. The frequency-shifting method is
developed based on the properties of trigonometric functions. The computer simulation and the
experimental result are also presented to demonstrate the feasibility and validity of the proposed
approach in phase reconstruction.
Circular targets are commonly used in vision measurement and photogrammetry. Due to the asymmetric projection, the geometric centroid of the ellipse projection and the true projection of the target center are not identical, which leads to a systematic center location error. A method to correct the center location error is presented in this paper. Surface normal directions of circular targets are determined by camera calibration in advance. Then the correction values of the geometric centroids are calculated with space analytic geometry. The experimental results show the improvement of accuracy can be achieved after error correction by our method.
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