- 标题
- 摘要
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- 实验方案
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Optimal pulse width modulation technique combined with stair phase-coding method for absolute phase retrieval with projector defocusing
摘要： The accurate three-dimensional shape measurement of a complex surface is significantly important in industrial testing. However, three-dimensional profilometry by conventional sinusoidal fringe projection using a phase-shifting algorithm performs suboptimally because of the nonlinear intensity response of projectors. To overcome this problem, the present paper proposes using a combined optimizing sinusoidal pulse width modulation (SPWM) technique and stair phase-coding approach to obtain the unwrapped phase. Properly optimizing SPWM with a small degree of a defocusing projector to generate sinusoidal fringe patterns can overcome the undesired harmonics and nonlinear gamma effect. Two groups of four-step phase-shifting fringe patterns are used. One group of the stripes contains four sinusoidal patterns generated by the SPWM technique, which is used to determine the wrapped phase. The other group of stripes contains four sinusoidal patterns with the codeword embedded into the stair phase, whose stair changes are perfectly aligned with the 2π discontinuities of the sinusoidal fringe phase, which is used to determine the fringe order for the phase unwrapping. Moreover, for the defocusing projection, because the frequency of the phase-coding fringe increases, the fringe order decision becomes less reliable. Thus, a self-correction phase unwrapping method is applied for phase retrieval. Experiments were conducted to verify the performance of the proposed method.
关键词： Phase-shifting,Phase retrieval,Stair phase-coding,Defocusing
更新于2025-09-23 15:23:52
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Compressive Phase Retrieval Realized by Combining Generalized Approximate Message Passing with Cartoon-Texture Model
摘要： Generalized approximate message passing (GAMP) can be applied to compressive phase retrieval (CPR) with excellent phase-transition behavior. In this paper, we introduced the cartoon-texture model into the denoising-based phase retrieval GAMP(D-prGAMP), and proposed a cartoon-texture model based D-prGAMP (C-T D-prGAMP) algorithm. Then, based on experiments and analyses on the variations of the performance of D-PrGAMP algorithms with iterations, we proposed a 2-stage D-prGAMP algorithm, which makes tradeoffs between the C-T D-prGAMP algorithm and general D-prGAMP algorithms. Finally, facing the non-convergence issues of D-prGAMP, we incorporated adaptive damping to 2-stage D-prGAMP, and proposed the adaptively damped 2-stage D-prGAMP (2-stage ADD-prGAMP) algorithm. Simulation results show that, runtime of 2-stage D-prGAMP is relatively equivalent to that of BM3D-prGAMP, but 2-stage D-prGAMP can achieve higher image reconstruction quality than BM3D-prGAMP. 2-stage ADD-prGAMP spends more reconstruction time than 2-stage D-prGAMP and BM3D-prGAMP. But, 2-stage ADD-prGAMP can achieve PSNRs 0.2 ～ 3 dB higher than those of 2-stage D-prGAMP and 0.3 ～ 3.1 dB higher than those of BM3D-prGAMP.
关键词： cartoon-texture model,generalized approximate message passing,adaptive damping,compressive phase retrieval
更新于2025-09-23 15:22:29
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Pr-Based Sar Reconstruction Autofocus Algorithm for Persistent Surveillance Change Detection
摘要： Random phase noises arising from frequency jitter of transmit signal and atmospheric turbulence result in corrupted synthetic aperture radar (SAR) imagery, which in turn degrades change detection (CD) performance. In this paper, a phase retrieval (PR) based SAR reconstruction autofocus framework by exploiting the hidden convexity is proposed with the goal of achieving reliable persistent surveillance CD. Firstly the original non-convex quartic SAR reconstruction is reformulated as a convex quadratic program. Under the minimum phase assumption, the auto-correlation retrieval-Kolmogorov factorization (CoRK) algorithm is then utilized to optimally and efficiently retrieve the underlying SAR reflectivity. The devised scheme possesses effective capabilities of phase noise mitigation, thus has a superior CD performance. Experimental results are provided to verify the effectiveness of the proposed method.
关键词： Synthetic aperture radar (SAR),hidden convexity,change detection (CD),phase retrieval (PR),random phase noises
更新于2025-09-23 15:21:21
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SAR Slow Moving Target Imaging Based on Over-Sampling Smooth Algorithm
摘要： A novel Synthetic aperture radar (SAR) signal processing technique has been proposed which re-focused slow moving targets based on phase retrieval algorithm. After theoretical derivation, we can get that the raw data Fourier magnitude of slow moving targets is approximate to the stationary ones in the SAR system. By applying the Fourier magnitude of received data to phase retrieval algorithms, the blur and defocusing effect caused by the moving of the targets can be eliminated. The simulated results demonstrate the validity of this algorithm.
关键词： Over-sampling smooth,Slow moving target imaging,Synthetic aperture radar,Phase retrieval
更新于2025-09-23 15:21:21
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Beam phase retrieval based on higher order modes in cylindrical superconducting radio frequency cavities
摘要： The control of beam phase relative to the accelerating RF field within a superconducting cavity is important in many accelerator applications and is of particular importance for a free electron laser facility. As standard practice, the phase is usually inferred from the beam-induced transient field with respect to a timing reference. We report here on an alternative and novel means of beam phase determination based on beam-excited higher order electromagnetic modes and the accelerating electromagnetic mode, which are conveniently available from the same coupler. The monopole modes are immune to the electron beam offset and therefore are best suited for the task. A coupled circuit model is used to assist the development and to rapidly assess the facility of the method. Simulations based on the circuit model indicate that the resolution of this system depends critically on the signal to noise ratio. Beam-based measurements with a test setup were carried out at the European X-ray Free Electron Laser (XFEL), Germany. Based on this new method, we have routinely obtained a resolution of 0.1°. The best resolution observed with the current setup was 0.03°. These results agree very well with the predictions from those predicted by a circuit model. The system investigated here can be used to provide diagnostic information for the current low level RF system employed in the European XFEL. To this end, the associated electronics are under development. This monitor is the first of its kind that can deliver direct and online measurements of the beam phase with respect to the RF field.
关键词： higher order modes,accelerator applications,beam phase retrieval,free electron laser,superconducting radio frequency cavities
更新于2025-09-23 15:21:21
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Assessment of Fringe Pattern Decomposition with a Cross-Correlation Index for Phase Retrieval in Fringe Projection 3D Measurements
摘要： Phase retrieval from single frame projection fringe patterns, a fundamental and challenging problem in fringe projection measurement, attracts wide attention and various new methods have emerged to address this challenge. Many phase retrieval methods are based on the decomposition of fringe patterns into a background part and a fringe part, and then the phase is obtained from the decomposed fringe part. However, the decomposition results are subject to the selection of model parameters, which is usually performed manually by trial and error due to the lack of decomposition assessment rules under a no ground truth data situation. In this paper, we propose a cross-correlation index to assess the decomposition and phase retrieval results without the need of ground truth data. The feasibility of the proposed metric is verified by simulated and real fringe patterns with the well-known Fourier transform method and recently proposed Shearlet transform method. This work contributes to the automatic phase retrieval and three-dimensional (3D) measurement with less human intervention, and can be potentially employed in other fields such as phase retrieval in digital holography.
关键词： parameter selection,cross-correlation,Fourier transform,phase retrieval,Shearlet transform,fringe pattern decomposition
更新于2025-09-23 15:21:21
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Color image encryption based on enhanced optical interference with different diffraction distances and linear phase color-blend
摘要： We develop a novel method to encrypt a color image by combining enhanced optical interference with phase retrieval algorithm (PRA) and linear phase color-blend (LPCB). In this method, the original color image is encoded into three phase only masks (POMs) with different Fresnel diffraction distances and one fixed random phase mask (RPM). For the decryption in an optical interference system, the three individual POMs are placed in the red, green and blue channels, respectively, and the RPM is placed in the public channel. Only if the right POMs and RPM are fixed their positions properly, one could achieve the expected information. Compared with traditional interference-based color image method, our method eliminates the silhouette problem fully. LPCB is also introduced to modulate the phase value of each pixel of the three POMs to further enhance the security. Numerical simulation results are presented to illustrate the feasibility and effectiveness of the proposed scheme.
关键词： Optical interference,Linear phase color-blend,Phase retrieval algorithm,Color image encryption
更新于2025-09-23 15:21:01
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Phase Retrieval of Real-valued Functions in Sobolev Space
摘要： The Sobolev space H s(Rd) with s > d/2 contains many important functions such as the bandlimited or rational ones. In this paper we propose a sequence of measurement functions { (cid:2)φγ j,k} ? H ?s(Rd) to the phase retrieval problem for the real-valued functions in H s(Rd). We prove that any real-valued function f ∈ H s(Rd) can be determined, up to a global sign, by the phaseless measurements {|(cid:4)f, (cid:2)φγ j,k(cid:5)|}. It is known that phase retrieval is unstable in in?nite dimensional spaces with respect to perturbations of the measurement functions. We examine a special type of perturbations that ensures the stability for the phase-retrieval problem for all the real-valued functions in H s(Rd) ∩ C 1(Rd), and prove that our iterated reconstruction procedure guarantees uniform convergence for any function f ∈ H s(Rd) ∩ C 1(Rd) whose Fourier transform (cid:3)f is L1-integrable. Moreover, numerical simulations are conducted to test the e?ciency of the reconstruction algorithm.
关键词： measurement function perturbation,phase retrieval,retrievable stability,reconstruction stability,Sobolev space
更新于2025-09-23 15:21:01
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Fast reconstruction of two-wavelength off-axis multiplexed holograms using division-multiplexing and critical sampling
摘要： Benefiting from two-wavelength information multiplexed into one hologram, two-wavelength off-axis holography can perform simultaneous quantitative phase imaging in an extended thickness range. However, its present phase processing still adopts the traditional Fourier-based method at the expense of the reconstruction speed. Hence, we propose a fast approach by combining critical sampling with division multiplexing. In our approach, the critical sampling is used to remove the redundant data, and the division multiplexing is developed to eliminate the redundant calculation processes. Experimental results illustrate that our approach can yield faster reconstruction with frame rates up to 46 fps even for one megapixel multiplexed holograms at two wavelengths on a single-core personal computer.
关键词： Critical sampling,Multiplex holography,Dual-wavelength digital holography,Fast phase retrieval
更新于2025-09-23 15:21:01
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Experimental analysis and designing strategies of lens-less microscopy with partially coherent illumination
摘要： Lens-less microscopy can achieve a wide field of view imaging (FOV) through a simple configuration compared to conventional microscopy, and it’s very attractive in resource-limited areas because of its cost-effectiveness and portability. Featuring a small package and cheapness, LEDs and LDs both show the potential to act as a reasonable illumination source for lens-less microscopes, especially for portable ones. However, based on holographic theorem, the complex light-field reconstruction algorithms consider the light source as a highly coherent one, while both LEDs and LDs can only provide partially coherent illumination. In this manuscript, we would systematically and experimentally analyze the imaging performances of lens-less microscopy with partially coherent illumination. The analysis covers autofocusing under LED/LD illumination, imaging performances under different LED spatial coherence and imaging performances under LED/LD illumination. Furthermore, based on the analysis, some conclusions about designing a lens-less microscope are presented. We think that the experiments and conclusions can provide effective guidance to construct a low-cost lens-less microscope with trade-off hardware parameters in practices.
关键词： Computational imaging,Digital holography,Microscopy,Portable imaging device,Phase retrieval
更新于2025-09-23 15:21:01