Twin Image Elimination Research Articles

Single-beam digital holographic reconstruction: a phase-support enhanced complex wavefront on phase-only function for twin-image elimination.

In in-line digital holographic microscopy (DHM), twin-image artifacts pose a significant challenge, and reduction or complete elimination is essential for object reconstruction. To facilitate object reconstruction using a single hologram, significantly reduce inaccuracies, and avoid iterative processing, a digital holographic reconstruction algorithm called phase-support constraint on phase-only function (PCOF) is presented. In-line DHM simulations and tabletop experiments employing the sliding-window approach are used to compute the arithmetic mean and variance of the phase values in the reconstructed image. A support constraint mask, through variance thresholding, effectively enabled twin-image artifacts. Quantitative evaluations using metrics such as mean squared error, peak signal-to-noise ratio, and mean structural similarity index show PCOF's superior capability in eliminating twin-image artifacts and achieving high-fidelity reconstructions compared with conventional methods such as angular spectrum and iterative phase retrieval methods. PCOF stands as a promising approach to in-line digital holographic reconstruction, offering a robust solution to mitigate twin-image artifacts and enhance the fidelity of reconstructed objects.

Asymmetric wavefront shaping with nonreciprocal 3D nonlinear detour phase hologram.

Asymmetric control of light with nonlinear material is of great significance in the design of novel micro-photonic components, such as asymmetric imaging devices and nonreciprocal directional optical filters. However, the use of nonlinear photonic crystals for asymmetric optical transmission, to the best of our knowledge, is still an untouched area of research. Herein we propose the 3D nonlinear detour phase holography for realizing asymmetric SH wavefront shaping by taking advantage of the dependence of the SH phase on the propagation direction of the excitation beam. With the proposed method, the designed nonreciprocal 3D nonlinear detour phase hologram yields SH phases with opposite signs for the forward and backward transmission situations. Moreover, the quasi-phase-matching scheme and orbital angular momentum conservation in the asymmetric SH wavefront shaping process are also discussed. This study conceptually extends the 2D nonlinear detour phase holography into 3D space to build the nonreciprocal 3D nonlinear detour phase hologram for achieving SH twin-image elimination and asymmetric SH wavefront shaping, offering new possibilities for the design of nonreciprocal optical devices.

Quantitative phase imaging of biological cells using lensless inline holographic microscopy through sparsity-assisted iterative phase retrieval algorithm

The twin image-free phase reconstruction is still a challenge with single-shot inline holographic systems. Existing solutions mostly are based on the inverse problem approaches or alternating projections. However, there exists a trade-off between phase retrieval and twin image elimination. Recent studies have introduced a hybrid method involving both the approaches to mitigate this trade-off. Following these works, we propose a single-shot sparsity-assisted iterative phase retrieval approach that applies a sparsity constraint in the object domain and formulates phase retrieval as a minimization problem. We demonstrate lensless digital inline holographic microscopy for imaging transparent and weakly scattering biological samples over a large field-of-view of ∼29mm2. The proposed method achieves high fidelity phase reconstruction with faster convergence compared to the existing single-shot phase retrieval methods. We further demonstrate the phase quantification of label-free biological samples, such as cervical cells and RBCs, to highlight the potential of our technique in clinical applications.

HoloPhaseNet: fully automated deep-learning-based hologram reconstruction using a conditional generative adversarial model.

Quantitative phase imaging with off-axis digital holography in a microscopic configuration provides insight into the cells' intracellular content and morphology. This imaging is conventionally achieved by numerical reconstruction of the recorded hologram, which requires the precise setting of the reconstruction parameters, including reconstruction distance, a proper phase unwrapping algorithm, and component of wave vectors. This paper shows that deep learning can perform the complex light propagation task independent of the reconstruction parameters. We also show that the super-imposed twin-image elimination technique is not required to retrieve the quantitative phase image. The hologram at the single-cell level is fed into a trained image generator (part of a conditional generative adversarial network model), which produces the phase image. Also, the model's generalization is demonstrated by training it with holograms of size 512×512 pixels, and the resulting quantitative analysis is shown.

Iterative denoising phase retrieval method for twin-image elimination in continuous-wave terahertz in-line digital holography

In this paper, an iterative denoising phase retrieval method is proposed to solve the twin-image problem in continuous-wave terahertz in-line digital holography. The iterative algorithm is based on the classical error reduction algorithm by adding the positive absorption constraint and a new image denoising for the object field to improve the quality of the reconstructed images. At certain geometrical parameter, the twin-image can be treated as noise superimposed in the object plane. The object field is considered as a complex function affected by the twin-image, and then the denoising process embedded in each iteration is applied to the real and imaginary parts of the object field, respectively. The validity of this approach is demonstrated by the high-quality imaging of samples like the Siemens star and the cicada's wing, which are almost free from the twin-image. Also, the proposed method exhibits good robustness to noises existing in the hologram, and the reconstructed images show better quality compared with other popular phase retrieval methods and denoising algorithm. This work would be helpful to expand the application of continuous-wave terahertz in-line digital holography in biomedical imaging and nondestructive testing.

Artifactless, lens-free coherent microscopy with quasi-3D scanning

We propose a quasi-3D scheme to solve imaging artifacts from the laser source for lens-free holographic imaging. The scheme includes three steps: background noise removal, image alignment and twin-image elimination. The sample moves along the lateral direction and the imaging sensor is sequentially placed at different axial distances for data recording. With this volume data, the artifacts from the laser source can be effectively mitigated. The experiments show that a pixel-level imaging resolution (1.55 µm) over a field-of-view larger than 20 mm2 can be achieved. The experiments with biological samples, including kidney and intestine pathological slides of rats, validate that this technique can realize dramatic image contrast and resolution enhancements compared to conventional lens-free holographic methods. Our work provides a new framework to suppress laser source artifacts for holographic imaging.

Automatic filtering for zero-order and twin-image elimination in off-axis digital holography

Windowing the Fourier spectra is usually used to filter the zero-order and twin image in off-axis digital holography (DH). However, during the filtering process, manual operation is often needed. In our work, we present an automatic filtering method. The filtered zone is a circle in the Fourier domain. The point with the highest intensity in the +1st order is chosen as its center, the location of which is related to the angle between the reference and the objective beams. Considering that the size of the zero-order spectra is twice of that of the +1st order, the radius of the circle is set to be a third of the distance between the circle center and the very center of the Fourier spectra. With this filtering method, the desired spectra can be filtered out automatically and noniteratively. This method has been tested and validated on several samples. Compared with the iterative filtering method, it spends about 2‰ of the processing time and obtains the reconstructed images with high similarity. This approach can result in real-time use of the off-axis DH and holographic microscopy.

Compact, cost-effective and field-portable microscope prototype based on MISHELF microscopy

We report on a reduced cost, portable and compact prototype design of lensless holographic microscope with an illumination/detection scheme based on wavelength multiplexing, working with single hologram acquisition and using a fast convergence algorithm for image processing. All together, MISHELF (initials coming from Multi-Illumination Single-Holographic-Exposure Lensless Fresnel) microscopy allows the recording of three Fresnel domain diffraction patterns in a single camera snap-shot incoming from illuminating the sample with three coherent lights at once. Previous implementations have proposed an illumination/detection procedure based on a tuned (illumination wavelengths centered at the maximum sensitivity of the camera detection channels) configuration but here we report on a detuned (non-centered ones) scheme resulting in prototype miniaturization and cost reduction. Thus, MISHELF microscopy in combination with a novel and fast iterative algorithm allows high-resolution (μm range) phase-retrieved (twin image elimination) quantitative phase imaging of dynamic events (video rate recording speed). The performance of this microscope prototype is validated through experiments using both amplitude (USAF resolution test) and complex (live swine sperm cells and flowing microbeads) samples. The proposed method becomes in an alternative instrument improving some capabilities of existing lensless microscopes.

Improved quantitative phase imaging in lensless microscopy by single-shot multi-wavelength illumination using a fast convergence algorithm.

We report on a novel algorithm for high-resolution quantitative phase imaging in a new concept of lensless holographic microscope based on single-shot multi-wavelength illumination. This new microscope layout, reported by Noom et al. along the past year and named by us as MISHELF (initials incoming from Multi-Illumination Single-Holographic-Exposure Lensless Fresnel) microscopy, rises from the simultaneous illumination and recording of multiple diffraction patterns in the Fresnel domain. In combination with a novel and fast iterative phase retrieval algorithm, MISHELF microscopy is capable of high-resolution (micron range) phase-retrieved (twin image elimination) biological imaging of dynamic events. In this contribution, MISHELF microscopy is demonstrated through qualitative concept description, algorithm implementation, and experimental validation using both a synthetic object (resolution test target) and a biological sample (swine sperm sample) for the case of three (RGB) illumination wavelengths. The proposed method becomes in an alternative instrument improving the capabilities of existing lensless microscopes.

Twin image elimination in digital holography by combination of Fourier transformations

We present a new technique for removing twin image in in-line digital Fourier holography using a combination of Fourier transformations. Instead of recording only a Fourier transform hologram of the object, we propose to record a combined Fourier transform hologram by simultaneously recording the hologram of the Fourier transform and the inverse Fourier transform of the object with suitable weighting coefficients. Twin image is eliminated by appropriate inverse combined Fourier transformation and proper choice of the weighting coefficients. An optical configuration is presented for recording combined Fourier transform holograms. Simulations demonstrate the feasibility of twin image elimination. The hologram reconstruction is sensitive to phase aberrations of the object, thereby opening a way for holographic phase sensing.

In-line hologram segmentation for volumetric samples

We propose a fast, noniterative method to segment an in-line hologram of a volumetric sample into in-line subholograms according to its constituent objects. In contrast to the phase retrieval or twin image elimination algorithms, we do not aim or require to reconstruct the complex wave field of all the objects, which would be a more complex task, but only provide a good estimate about the contribution of the particular objects to the original hologram quickly. The introduced hologram segmentation algorithm exploits the special inner structure of the in-line holograms and applies only the estimated supports and reconstruction distances of the corresponding objects as parameters. The performance of the proposed method is demonstrated and analyzed experimentally both on synthetic and measured holograms. We discussed how the proposed algorithm can be efficiently applied for object reconstruction and phase retrieval tasks.

Twin image elimination from two in-line holograms via phase retrieval

The reconstruction quality of in-line holography suffers from the superposition of twin images that have different foci but identical information content. We propose a phase retrieval method using two axially displaced holograms and a finite transmission constraint to eliminate the conjugate image. The simulation and experimental results demonstrate a better elimination effect and a faster rate of convergence compared with those of previously reported methods. Two holograms can be recorded simultaneously using two cameras, thus this technique can be used in real-time imaging.

Spatial filtering for zero-order and twin-image elimination in digital off-axis holography

Off-axis holograms recorded with a CCD camera are numerically reconstructed with a calculation of scalar diffraction in the Fresnel approximation. We show that the zero order of diffraction and the twin image can be digitally eliminated by means of filtering their associated spatial frequencies in the computed Fourier transform of the hologram. We show that this operation enhances the contrast of the reconstructed images and reduces the noise produced by parasitic reflections reaching the hologram plane with an incidence angle other than that of the object wave.

Twin-image elimination experiments for three-dimensional images in optical scanning holography

Twin-image elimination in the context of optical scanning holography has recently been proposed. The proposed technique involves simultaneously acquiring sine and cosine Fresnel holograms. A complex hologram is then formed by complex addition of the holograms, and twin-image rejection is predicted by computer simulations. An experimental verification of the technique by optical acquisition of the two holograms and subsequent reconstruction of the complex hologram digitally is reported. Three-dimensional image reconstruction without twin-image noise is demonstrated.

Off-axis reconstruction of in-line holograms for twin-image elimination

In-line holography is an important experimental tool in particle-field analysis and soft X-ray holography. The sole disadvantage of in-line holography is the inherent twin-image problem. In this paper, a new method for twin-image elimination is proposed. This method is based on the principle of off-axis reconstruction of in-line holograms which is a new approach in the field of optical holography. Theoretical analysis and computer simulation, as well as initial experimental results, show that it is a simple and efficient method to eliminate the twin-image of in-line holograms.

Twin-image elimination in optical scanning holography

We propose a novel multiplexing technique to solve the twin image problem in optical scanning holography without the use of a spatial carrier, as commonly used in conventional off-axis holography. The technique involves simultaneously acquiring sine and cosine Fresnel zone-lens plate coded images by optical scanning. A complex addition of the two coded images will then be performed and decoded to give a twin-image rejection reconstruction. Computer simulations will be presented to demonstrate the validity of the idea.

Iterative algorithms for twin-image elimination in in-line holography using finite-support constraints

The quality of reconstructed images from in-line holograms can be seriously degraded by the linear superposition of twin images having the same information but different foci. Starting from the reconstructed field at the real image plane, we make use of the uncontaminated information contained in the out-of-focus wave (virtual image) outside the in-focus wave (real image) support, together with a finite-support constraint, to form an iterative procedure for twin-image elimination. This algorithm can reconstruct complex objects, provided that they are not recorded in very near-field conditions. For real objects additional constraints can be imposed, extending the algorithm application to very near-field conditions. The algorithm’s convergence properties are studied in both cases, and some examples are shown.

Twin-image elimination in in-line holography of finite-support complex objects

Reconstruction of in-line holograms suffers from the superposition of two twin images having different foci but identical information content. A simple iterative method of twin-image elimination is presented here. It is based on the fact that, if the object has a finite support and the recording distance is not too small, the out-of-focus field is known on a large part of the reconstruction plane and is only superposed by the in-focus one inside a restricted support. An iterative procedure is developed to recover the out-of-focus wave inside the in-focus image support. Inverse diffraction then gives the reconstructed image. This procedure can be easily automated and works for finite-support real or complex objects, recorded in geometries with a Fresnel number of ~1.

Twin-image elimination in Gabor holography

It is shown that the “twin-image” may be eliminated from images of real (e.g., thin and purely absorptive) objects generated by Gabor holography using straightforward linear filtering. The technique tends to emphasize otherwise small contributions from the “intermodulation term” and an algorithm is demonstrated that can estimate the intermodulation term and, therefore, largely eliminate its effects from the processed image. Holograms of complex objects are analyzed and it is shown that they may be reconstructed without twin image effects provided the objects obey a size constraint that is similar to, but less stringent and more precise than, the conventional Fraunhofer condition.

Object reconstruction from noisy holograms

The inappropriate processing and digitization of an optical hologram to become a digital hologram can be modeled by additive noise superimposed on the hologram and followed by a clipping operator. Direct reconstruction of this noisy digital hologram will usually yield unsatisfactory results because the noise will be the dominating term on the reconstruction plane. The constrained iterative twin image elimination algorithm for an in-line Fresnel hologram is modified by incorporating the noise constraint into the hologram constraint domain to estimate the additive noise function while eliminating the twin image. The result of the object reconstruction is shown to be improved.