Digital Fresnel Holography Research Articles

Autofocusing in off-axis digital Fresnel holography using S-th power weighted neighborhood correlation coefficient

Accurately determining the focus plane of the reconstructed image is crucial for obtaining high-quality reconstructed images in the process of digital hologram reconstruction. In this paper, a focusing evaluation function based on S-th power weighted neighborhood correlation coefficient (SPWNCC) is proposed to realize automatic focusing of the reconstructed image in off-axis digital Fresnel holography. The Fresnel transform method is utilized as the off-axis digital holographic reconstruction algorithm. Both the numerical simulation and optical experiment results are given to verify the validity of the proposed autofocusing method. The obtained focusing curve can maintain good unimodality and noise immunity performance over a large search range (approximately 800 mm). The proposed SPWNCC based focusing evaluation function has a certain guiding significance on the automatic focusing of off axis digital holographic reconstructed images of long distance recorded objects.

Deep convolutional neural network for three-dimensional objects classification using off-axis digital Fresnel holography

A Deep Convolutional Neural Network (CNN)-based three-dimensional (3D) objects classification using an augmented holographic phase image dataset is proposed. Off-axis Fresnel digital holography is used for retrieving 3D object information as phase images. The phase image dataset of the five different 3D objects considered in this study is prepared under various recording distances and rotational angles. The CNN based architecture classifies the 3D objects into two sets comprising of TRUE and FALSE classes with higher accuracy and minimal loss on the training set for the phase image dataset. The CNN has achieved higher precision, lower recall, and higher F1-score for the TRUE class on the test set. The experimental results demonstrate that the proposed CNN is capable of classifying 3D objects with an overall accuracy of 86% and AUC of 96% for the phase image dataset. The feasibility and classification performance are deduced from a proof of the concept experiment.

Optimal Fresnelet sparsification for compressive complex wave retrieval from an off-axis digital Fresnel hologram

Complex wave retrieval (CWR) from an off-axis digital Fresnel hologram proposed by Liebling et al. is a single-exposure scheme in which a non-linear holographic process is modeled using simultaneous linear equations. This linear model fits well into the compressive sensing (CS) framework. We propose a method in which the CS is applied to a CWR method with Fresnelet sparsification. This approach compensates for the noise in the retrieved Fresnel field that is aroused due to the linear modeling approximations involved in the reconstruction process. As a result, a superior intensity and phase reconstruction were obtained by this method. Four methods including the direct CWR (conventional) method, compressive CWR method without sparsification, compressive CWR method with Haar wavelet, and compressive CWR method were compared with Fresnelet sparsification. The simulation and the optical experimental results converge to the same conclusion: the Fresnelet sparsified case is the best choice for quantitative phase imaging using compressive off-axis digital Fresnel holography.

Compressive complex wave retrieval from a single off-axis digital Fresnel hologram for quantitative phase imaging and microlens characterization

A compressive sensing (CS) approach is proposed for the complex wave retrieval algorithm from single off-axis digital Fresnel holography to improve the accuracy of quantitative phase measurement. The linear model of non-linear holographic process used in the complex wave retrieval algorithm is utilized to meet the linearity requirement of the proposed CS implementation presented in this paper. The error in object wave reconstruction due to the approximations used in complex wave retrieval algorithm is compensated by combining it with CS approach. A Mach–Zehnder interferometric geometry in transmission and off-axis mode in the Fresnel domain is used to record the digital hologram. The numerical simulations and experimental results are presented to demonstrate and validate the proof of the concept and to compare CS frame work with conventional complex wave retrieval algorithm. The proposed algorithm is tested for the microlens sample characterization by considering the parameters such as height, diameter and radius of curvature. A Haar wavelet based object wave sparsification is used in the experiment for the prudent phase reconstruction in the CS approach. The proposed method enables an improved and accurate object phase reconstruction, with minimal noise such as distortions or speckles with respect to the conventional complex wave retrieval method.

基于深度学习的离轴菲涅耳数字全息非线性重构

基于深度学习的离轴菲涅耳数字全息非线性重构

Fresnel incoherent digital holography with large field-of-view

Incoherent digital holography (IDH) is a recently proposed technique to record three-dimensional (3D) information about the object under incoherent illumination, which breaks the limitation that the holographic recording must be illuminated by coherent light sources and thus makes it usable in white-light and fluorescence illuminating circumstance. In particular, the fresnel incoherent correlation holography (FINCH) is an exemplary method which improves the imaging resolution power and efficiency of incoherent digital holography, and it can obtain 3D distribution of objects swiftly without scanning and moving. However, compared with the conventional optical holography, the FINCH system has a very small field-of-view due to the limitation of the pixel number and size of spatial light modulator (SLM). Therefore, expanding the recording field-of-view of FINCH system is very significant for the application of IDH. In the FINCH, the SLM is used as a diffractive beam splitter so that each spherical beam, originating from each object point, is split into two spherical beams with two different curve radii. Then the interference fringes between the two beams are recorded by CCD. In this paper, the field-of-view angle recorded by the SLM is proposed and analyzed based on the physical and numerical principles of the FINCH system. The field-of-view of imaging system is improved by increasing the effective diameter of SLM through moving the center of the dual-lens optical axis mounted on the SLM to the edge in different directions respectively. An optical setup of reflection mode is constructed to verify the theoretical analysis of this study, and the sub-holograms in different field-of-views are obtained by CCD through changing the masks displayed on the SLM sequentially. Then, the complex holograms in different field-of-views are obtained by using the three-step phase-shifting method, and the reconstructed images are acquired respectively through the angular spectrum method (ASM) by using a computer. Finally, the large field-of-view image is obtained by stitching the reconstructed images in each field-of-view by utilizing the matlab program. The experimental results show that the efficient recording field-of-view of SLM can be increased by 2.77 times with our proposed method. Accordingly, the recording field-of-view of the system is improved significantly. The recording field-of-view of the FINCH system will increase further if the center of the dual-lens optical axis continues to move toward the edge. Therefore, this study provides an important support for the further application of high resolution microscopic imaging with large field-of-view.

Algorithm for extracting multiple object waves without Fourier transform from a single image recorded by spatial frequency-division multiplexing and its application to digital holography

We propose a novel algorithm that does not require any Fourier transform to extract multiple object waves in a single image recorded with spatial frequency-division multiplexing. Smoothing is utilized to extract the desired object-wave information from a spatially multiplexed image. Numerical and experimental results show its validity and applicability for image and Fresnel digital holography. Our investigations clarify the speeding up of both the object-wave extractions and multiple object–image reconstructions quantitatively.

Reduction of speckle noise in holographic images using spatial jittering in numerical reconstructions.

This Letter presents an easy, fast, and efficient single-shot method to reduce speckle noise in digital Fresnel holography. In this method, several images from a single hologram are reconstructed by introducing spatial displacements in the Fresnel kernel. Spatial jitters produce images with different speckle positions. Averaging the set of numerically produced images leads to a strong reduction of speckle noise in both amplitude and phase difference images. The experimental results show the suitability of the proposed approach and confirm its applicability to digital holographic interferometry.

Refocus criterion based on maximization of the coherence factor in digital three-wavelength holographic interferometry.

This Letter presents an alternative approach for image refocusing in digital Fresnel holography. In the literature, a large majority of reported focus detection criteria is based on amplitude contrast or phase contrast. We propose a focus detection criterion based on the speckle phase coherence factor. This factor reaches its maximum value at the best focus distance. At any reconstruction distance, estimation of the coherence factor is based on robust noise estimation from anisotropic diffusion. We propose a theoretical relation to estimate the coherence factor from the measured standard deviation. Experimental results for the case of three-color holographic imaging and interferometry are provided. Experimental results show the suitability of the proposed approach for image plane refocusing.

Digital holographic image fusion for a larger size object using compressive sensing

Digital holographic imaging fusion for a larger size object using compressive sensing is proposed. In this method, the high frequency component of the digital hologram under discrete wavelet transform is represented sparsely by using compressive sensing so that the data redundancy of digital holographic recording can be resolved validly, the low frequency component is retained totally to ensure the image quality, and multiple reconstructed images with different clear parts corresponding to a laser spot size are fused to realize the high quality reconstructed image of a larger size object. In addition, a filter combing high-pass and low-pass filters is designed to remove the zero-order term from a digital hologram effectively. The digital holographic experimental setup based on off-axis Fresnel digital holography was constructed. The feasible and comparative experiments were carried out. The fused image was evaluated by using the Tamura texture features. The experimental results demonstrated that the proposed method can improve the processing efficiency and visual characteristics of the fused image and enlarge the size of the measured object effectively.

Parallel-mode scanning optical sectioning using digital Fresnel holography with three-wave interference phase-shifting.

The Fresnel incoherent correlation holography (FINCH) method is applicable to various techniques of imaging, including fluorescence microscopy. Recently, a FINCH configuration capable of optical sectioning, using a scanning phase pinhole, has been suggested [Optica 1, 70 (2014)]. This capability is highly important in situations that demand the suppression of out-of-focus information from the hologram reconstruction of a specific plane of interest, such as the imaging of thick samples in biology. In this study, parallel-mode scanning using multiple phase pinholes is suggested as a means to shorten the acquisition time in an optical sectioning FINCH configuration. The parallel-mode scanning is enabled through a phase-shifting procedure that extracts the mixed term of two out of three interfering beams.

Three-dimensional object recognition using joint fractional Fourier transform correlators with the help of digital Fresnel holography

Digital holography (DH) helps record true three-dimensional (3D) perspective of a 3D object. The technique of DH can be used for various applications, including 3D object recognition, which can be implemented optically. In this paper, 3D object recognition with joint fractional Fourier transform (JFRT) correlators is proposed in which the technique of digital Fresnel holography is used. Digital Fresnel hologram of a 3D object is synthesized and reconstructed digitally. After removal of the dc and twin image terms from the reconstructed image, two different target objects have been compared using linear and nonlinear JFRT correlators. The results are also verified using an optically recorded digital Fresnel hologram. The performance measure parameters, such as, discrimination ratio, peak-to-correlation energy, and peak-to-sidelobe ratio have been computed to compare the two proposed correlation schemes.

Recognition of three-dimensional objects using joint fractional correlator and nonlinear joint fractional correlator with the help of digital Fresnel holography: a comparative study

In this paper, real three-dimensional (3D) object recognition with joint fractional correlator (conventional) and nonlinear joint fractional correlator has been demonstrated. Digital Fresnel holograms of various 3D objects have been experimentally recorded and numerically reconstructed. Since the fringes of digital holograms record the complete 3D information, the 3D correlation has been performed by comparing two holograms using conventional and nonlinear joint fractional correlators. The correlation has also been carried out by comparing the two 3D images reconstructed from corresponding digital holograms using the two correlators. The performance measure parameters, such as discrimination ratio, peak-to-correlation energy, and peak-to-sidelobe ratio have been computed for both the correlators. With the calculated performance measure parameters, it is inferred that the nonlinear joint fractional correlator performs better as compared to the conventional correlator.

Compressive Fresnel digital holography using Fresnelet based sparse representation

Compressive sensing (CS) in digital holography requires only very less number of pixel level detections in hologram plane for accurate image reconstruction and this is achieved by exploiting the sparsity of the object wave. When the input object fields are non-sparse in spatial domain, CS demands a suitable sparsification method like wavelet decomposition. The Fresnelet, a suitable wavelet basis for processing Fresnel digital holograms is an efficient sparsifier for the complex Fresnel field obtained by the Fresnel transform of the object field and minimizes the mutual coherence between sensing and sparsifying matrices involved in CS. The paper demonstrates the merits of Fresnelet based sparsification in compressive digital Fresnel holography over conventional method of sparsifying the input object field. The phase shifting digital Fresnel holography (PSDH) is used to retrieve the complex Fresnel field for the chosen problem. The results are presented from a numerical experiment to show the proof of the concept.

Phase Contrast Imaging of the Fingerprint by Digital Holography

Aiming to the special demand of the criminal investigation, a non-invasive and non-contact fingerprint acquisition method is proposed based on digital holography. The off-axis Fresnel digital holography is designed to record the digital hologram. The reconstruction of the complex amplitude from fingerprint is analyzed, and the phase aberration is corrected by the surface fitting based on the least square approach. In the scene of the crime, the fingerprint of suspects is easily left on some smooth surfaces. In the experiments, the CD-ROM disk with fingerprint information is used as the sample. The results show that the amplitude and phase images can be obtained and combined to capture more information of latent fingerprints, which demonstrates digital holography is effective for the acquisition of latent fingerprints and can be applied to the criminal investigation field.

Filtering role of the sensor pixel in Fourier and Fresnel digital holography

Digital holography is a modern imaging technique whereby a propagated object wave interferes with a known (spherical or plane) reference wave at a plane where a digital sensor is situated. The resulting intensity distribution is recorded by a CCD or CMOS sensor array to produce a digital hologram. This digital hologram can be processed in several ways to isolate the real image term. Using a propagation algorithm, the object wave can be numerically reconstructed from this real image term. Several factors limit the performance of such imaging systems, such as the finite extent of the sensor array and the finite size of the equally spaced sensor pixels, which average the light intensity incident upon them. Theoretical results indicate that in a Fresnel-based system the role of these finite-size pixels is to attenuate higher spatial frequencies by convolving the reconstructed signal with a rectangular function of equal size to the light-sensitive area of the pixel. However, when a spherical reference wave is used, as is the case with "lensless" Fourier-based systems, spatial frequencies will not be attenuated; rather it is the complex amplitude of the reconstructed signal that will be attenuated. In this manuscript we explore this question in more detail, providing new theoretical and experimental results. By assuming a fully developed speckle field for the object wave, we examine the first-order statistical distributions for the integrated intensity of the object wave, and the interference term, using numerical simulations. We show that the statistical distribution of the interference term can be changed, by varying the sphericity of the reference wave. Experimental results are provided where we compare the performance of a Fresnel and Fourier holographic system as a function of pixel size.

Comparison between Digital Fresnel Holography and Digital Image-Plane Holography: The Role of the Imaging Aperture

Optical techniques are now broadly used in the field of experimental mechanics. The main advantages are they are non intrusive and no contact. Moreover optical techniques lead to full spatial resolution displacement maps enabling the computing of mechanical value also in high spatial resolution. For mesoscopic measurements, digital image correlation can be used. Digital holographic interferometry is well suited for quantitative measurement of very small displacement maps on the microscopic scale. This paper presents a detailed analysis so as to compare digital Fresnel holography and digital image-plane holography. The analysis is based on both theoretical and experimental analysis. Particularly, a theoretical analysis of the influence of the aperture and lens in the case of image-plane holography is proposed. Optimal filtering and image recovering conditions are thus established. Experimental results show the appropriateness of the theoretical analysis.

Digital color holography applied to fluid and structural mechanics

In various domains such as acoustics, vibrations or fluid mechanics, non-invasive metrological tools, giving full-field measurements with very high spatial and temporal resolutions, need to be developed to validate the models and/or numerical simulations of the studied phenomena. In this way, ONERA and LAUM have developed optical real-time methods based on three-wavelength digital holographic interferometry to analyze either unsteady wake flows or vibrating kinematics or complex fields. These digital color holographic methods aim at avoiding panchromatic holographic plates and their related constraints. In the domain of fluids mechanics, an interferometric set-up is presented to generate micro fringes from the observed area. The data are processed thanks to direct and inverse Fourier transforms to obtain a gas density field and to study its evolution in time. In structural mechanics, a versatile interferometric imaging set-up, based on digital Fresnel holography, is presented. These new optical imaging methods result in full-field measurements with a high spatial resolution. This research ultimately aims at analyzing, in time, unsteady complex wake flows, vibrating kinematics and acoustic fields. A few examples are given and the possibilities and limits of these methods are discussed.

Compressive Fresnel Holography

Compressive sensing is a relatively new measurement paradigm which seeks to capture the “essential” aspects of a high-dimensional object using as few measurements as possible. In this work we demonstrate successful application of compressive sensing framework to digital Fresnel holography. It is shown that when applying compressive sensing approach to Fresnel fields a special sampling scheme should be adopted for improved results.

Improvement of Quality of Reconstructed Images in Multi-Frame Fresnel Digital Holography

A modified reconstruction algorithm to improve the quality of reconstructed images of multi-frame Fresnel digital holography is presented. When the reference beams are plane or spherical waves with azimuth encoding, by introducing two spherical wave factors, images can be reconstructed with only one time Fourier transform. In numerical simulation, this algorithm could simplify the reconstruction process and improve the signal-to-noise ratio of the reconstructed images. In single-frame reconstruction experiments, the accurate reconstructed image is obtained with this simplified algorithm.