Twin Image Research Articles

Twin-Image-Free Holography: A Compressive Sensing Approach.

Holographic reconstruction is troubled by the phase-conjugate wave front arising from Hermitian symmetry of the complex field. The so-called twin image obfuscates the reconstruction in solving the inverse problem. Here we quantitatively reveal how and how much the twin image affects the reconstruction and propose a compressive sensing (CS) approach to reconstruct a hologram completely free from the twin image. Using the canonical basis, the incoherence condition of CS is naturally satisfied by the Fourier transformation associated with wave propagation. With the propagation kernel function related to the distance, the object wave diffracts into a sharp pattern while the phase-conjugate wave diffracts into a diffuse pattern. An iterative algorithm using a total variation sparsity constraint could filter out the diffuse conjugated signal and overcome the inherent physical symmetry of holographic reconstruction. The feasibility is verified by simulation and experimental results, as well as a comparative study to an existing phase retrieval method.

A Twin Image from Abeokuta, Nigeria

A Twin Image from Abeokuta, Nigeria

O que fabrica o historiador quando faz história, hoje?

O problema geral deste ensaio é o de continuar perseguindo as apropriações historiográficas do tempo pelos antigos e modernos, tema que já venho tratando em pesquisas anteriores. Mais especificamente, pretendo realizar uma genealogia conceitual do topos popularizado por Cícero de que a história é mestra da vida: historia magistra vitae. A longa duração é necessária como condição à análise das diferentes recepções, percepções e retratações que a formulação adquiriu até chegar ao nosso presente. Nessa longa travessia procurarei mapear situações em que a historia magistra vitae converte-se nas figuras gêmeas da autoridade e da tradição e, finalmente, em crença. Essas duas figurações quando aliadas a indeterminações historiográficas do tempo e suas formas discursivas têm a capacidade de produzir explicações para o movimento histórico do passado e do presente, uma movimentação normalmente silenciosa, cujos efeitos geram maneiras distintas de entendimento da experiência do tempo vivido.

Comparison of image properties in full-field phase X-ray microscopes based on grating interferometry and Zernike's phase contrast optics

A grating interferometer (GI) system has been installed in an X-ray microscope equipped with a Zernike phase contrast (ZPC) system and a Cu rotating anode X-ray source. The GI and ZPC systems are switchable, and their performances of phase information extraction have been compared. The GI system is based on a Lau interferometer consisting of an absorption grating and a π/2 phase grating, which extracts a magnified phase shift map of a sample via a phase-stepping measurement. The ZPC system generates a phase contrast image by using a phase plate and a corresponding condenser device. The ZPC system and the GI system are compared in terms of detectability of phase objects. By the Fourier analysis of images of a logarithmic ruler pattern, the spatial resolution was found to be identical between the two systems. Although the sensitivity depends on the sample size, the signal-to-noise ratio of polystyrene spheres with a few microns in diameter was used for sensitivity comparison, showing the superior sensitivity of the GI system to that of the ZPC system. The quantitativeness of the GI system with the phase-stepping measurement was also demonstrated over the ZPC system, which generates halo and shade-off artifacts. The GI system exhibits twin image artifacts that need to be resolved for practical applications of the technique.

The Metrics of Landscape. Stereo fieldwork by Francisco Afonso Chaves and other Portuguese Explorers

Although the invention of the stereoscope in 1832 shed new light on the anomalies of vision and on the constructive role of the mind in visual perception, this became no obstacle to its scientific uses throughout the 19th and 20th centuries. On the contrary, combined with photography, the stereoscope embodied both the imperialist politics of the 19th century and its scientific ideology. These pairs of twin images perfected photography as an accurate and credible scientific instrument and gave explorers the chance to map, calculate and “grab the world in an image”. The use of stereo photography in geodesic and topographic fieldworks is one of the best evidences of such scientific practices, largely overlooked by stereo photography studies. Here, we introduce the stereoviews by Portuguese explorers such as Francisco Afonso Chaves, an early-20th-century Azorean naturalist, and analyse a particular series of Verascope glass plates which represent theodolites photographed during his fieldwork. The identification of common uses of theodolites in the stereo collections of other explorers suggests the advantage of expanding fieldwork to the laboratory, a fact David Brewster (1856) would naturally recognise as a “rational pleasure”.

Four channels multi-illumination single-holographic-exposure lensless Fresnel (MISHELF) microscopy

MISHELF microscopy [Opt. Express 23, 21352 (2015)] has been recently reported as the background technology of a new concept of compact, cost-effective and field-portable lensless microscope [Sci. Rep. 7, 43291 (2017)] based on wavelength multiplexing and a fast and robust algorithm for twin image minimization and noise reduction. In this manuscript, MISHELF microscopy is expanded beyond its actual configuration by considering 4 illumination/detection channels while retaining its working principle concerning single-shot, twin image mitigation and noise averaging. Proof of principle validation of the proposed improvement is conducted through experiments with a resolution test target and a micro sphere sample.

Cross and trophy

Crosses and trophies are twin images in the Roman visual world of the first century CE, omnipresent as signposts of imperial power over the bodies and minds of the conquered. While crosses expose armour-less human bodies to torturous dying, the cruciform trophies are the body-less armour of an already dead enemy. Both are images of triumph and merciless retaliation against the non-compliant. Seen through the lens of the trophy, Paul's theology of cross and justification by faith emerges as a resistant messianic counter-visualization, as the body of the crucified empowers a rebellious re-embodiment of the dis-embodied.

Twin-image reduction method using a diffuser for phase imaging in-line digital holography.

Phase imaging by digital holography is widely used. An in-line optical setup is preferable for a practical use. A twin image, however, is a serious obstacle to achievement of high-quality phase imaging in in-line digital holography. For in-line digital holography, a time-division phase-shifting method or a wave-splitting phase-shifting method is used to eliminate the twin image. The former requires multiple exposures, and the latter requires specially designed optical elements. To solve these problems, a twin-image reduction method using a diffuser is proposed. In the proposed method, recording a digital hologram using a diffuser and signal processing enable reduction of the twin image on a reconstructed plane. A preliminary experimental result confirms the feasibility of the proposed method.

Continuous-wave off-axis and in-line terahertz digital holography with phase unwrapping and phase autofocusing

Continuous-wave terahertz digital holography is a practical tool to obtain the complete wave-front information of a sample in the terahertz region that has offered unique advantages in various fields. The propagation distance plays a decisive role in the numerical reconstruction of both in-line and off-axis digital holograms. Only when a terahertz hologram is propagated back to a focal object plane can the authentic amplitude and phase distribution be reconstructed, which is actually a troublesome task. In this manuscript, the combination of hologram enhancement, spectrum filtering, phase retrieval and phase unwrapping algorithms is illustrated and organized to benefit the decision-making process of the autofocusing method not only for the amplitude distribution but also for the phase image. To guarantee the accuracy of the autofocusing results, the noise of the hologram, the intrinsic twin image in the amplitude and phase results and the wrapped ambiguity in the phase distribution are suppressed or lessened by using the four techniques stated above. The focused amplitude and unwrapped phase distributions of the sample are reconstructed, and experimental verification confirms that the present hybrid autofocusing method is a feasible, effective and promising technology with broad application prospects.

Achromatic phase shifting self-interference incoherent digital holography using linear polarizer and geometric phase lens.

A simple Fresnel-type self-interference incoherent digital holographic recording system is proposed. The main part of the system consists of the two linear polarizers and geometric phase lens. The geometric phase lens is employed as a polarization selective common-path interferometer. One of the polarizers is rotated by the motor and serves as a phase-shifter with the geometric phase lens, to eliminate the bias and twin image noise. A topological phase is obtained by the relative angle between the polarizer and geometric phase lens. Since this phase shifting method does not depend on the change of the optical path length, the phase shifting performance is almost constant in the broad spectral range. Using the proposed achromatic phase shifting method, a simultaneous three-color phase shifting digital hologram recording under the incoherent light source is demonstrated.

Twin imaging phenomenon of integral imaging.

The imaging principles and phenomena of integral imaging technique have been studied in detail using geometrical optics, wave optics, or light filed theory. However, most of the conclusions are only suit for the integral imaging systems using diffused illumination. In this work, a kind of twin imaging phenomenon and mechanism has been observed in a non-diffused illumination reflective integral imaging system. Interactive twin images including a real and a virtual 3D image of one object can be activated in the system. The imaging phenomenon is similar to the conjugate imaging effect of hologram, but it base on the refraction and reflection instead of diffraction. The imaging characteristics and mechanisms different from traditional integral imaging are deduced analytically. Thin film integral imaging systems with 80μm thickness have also been made to verify the imaging phenomenon. Vivid lighting interactive twin 3D images have been realized using a light-emitting diode (LED) light source. When the LED is moving, the twin 3D images are moving synchronously. This interesting phenomenon shows a good application prospect in interactive 3D display, argument reality, and security authentication.

Dual-plane slightly off-axis digital holography based on a single cube beam splitter.

In order to recover the holographic object information, a method based on the recording of two digital holograms, not only at different planes but also in a slightly off-axis scheme, is presented. By introducing a π-phase shift in the reference wave, the zero-order diffracted term and the twin image are removed in the frequency domain during the processing of the recorded holograms. We show that the zero-order elimination by the phase-shifted holograms is better than working with weak-order beam and average intensity removal methods. For recording experimentally two π-shifted holograms at different planes slightly off-axis, a single cube beam splitter is used. Computer simulations and experimental results, carried out to validate our proposal, show a high accuracy of π/14 that can be comparable with phase-shifting digital holography. For high fringe spacing, our proposal could be applied in electron holography, avoiding high voltage in a biprism.

Spatially incoherent common-path off-axis color digital holography.

We describe a new method for recording spatially incoherent common-path off-axis color digital holograms. We present the theoretical and experimental evidence to demonstrate an incoherent common-path off-axis color digital holographic (ICOCH) system capable of capturing information from three-dimensional color objects under incoherent illumination, both in transmission and reflection modes. Fresnel incoherent correlation holography (FINCH), a common-path system, is a frequently used incoherent holography technique. Our proposed system is conceptually similar to an advanced form of FINCH; moreover, it has three advantages over this advanced form of FINCH. First, removal of the spatial light modulator makes our system simpler and more cost-effective. Second, removal of the polarizer or analyzer allows for greater light throughput. Third, the off-axis optical configuration enables separation of zero-order and twin images with only a single exposure per color rather than requiring three exposures per color for in-line holography FINCH. Therefore, we believe that this simple and cost-effective system with high light throughput can acquire incoherent holograms for different colors involving single exposure for each color, which makes the ICOCH system suitable for many applications.

Genetics of the human face: Identification of large-effect single gene variants

To discover specific variants with relatively large effects on the human face, we have devised an approach to identifying facial features with high heritability. This is based on using twin data to estimate the additive genetic value of each point on a face, as provided by a 3D camera system. In addition, we have used the ethnic difference between East Asian and European faces as a further source of face genetic variation. We use principal components (PCs) analysis to provide a fine definition of the surface features of human faces around the eyes and of the profile, and chose upper and lower 10% extremes of the most heritable PCs for looking for genetic associations. Using this strategy for the analysis of 3D images of 1,832 unique volunteers from the well-characterized People of the British Isles study and 1,567 unique twin images from the TwinsUK cohort, together with genetic data for 500,000 SNPs, we have identified three specific genetic variants with notable effects on facial profiles and eyes.

Increasing Perspectival Obliqueness Increases the Leaning Tower Illusion

The leaning tower illusion is a perceptual illusion in which two identical images of a tower photographed from below appear to diverge when juxtaposed. We manipulated the perceived obliqueness of the (upright) St Mark bell tower in Venice by modifying two parameters both related to the position of the camera with respect to the tower: (a) increasing the peripherality of the tower and (b) reducing the distance between the camera and the tower. The resulting images clearly show that the illusory leaning effect increases as a function of the obliqueness. Another crucial condition for the leaning tower effect must be that the twin images are perceived as parts of a unitary display: The illusion increases when the distance between the photos is progressively increased, but beyond a certain level of separation, the integration of the images should, of course, break down, and the illusion vanish.

Point spread function of incoherent digital holography based on spiral phase modulation

Fresnel incoherent correlation holography (FINCH) has attracted much attention because it is able to record the holograms of three-dimensional (3D) samples under incoherent illumination with just a charge coupled device (CCD) and spatial light modulator (SLM). The FINCH technology achieves the splitting and phase shifting of the incident beam by loading a phase mask on an SLM. Three holograms, whose phase factors are different from each other, are recorded sequentially by a CCD. After the three holograms are superposed in the computer, the zero order image and a twin image are eliminated, and a complex hologram is obtained. The 3D properties of the object are revealed when the complex hologram is reconstructed in the computer. Spiral phase filters (SPFs) are commonly used to produce optical vortices, which can enhance and recognize image edges. In this paper, the spiral phase modulated FINCH system illuminated by Xenon lamp is built, in which the phase-only SLM is space-division multiplexed by a helical lens (superposed by an SPF and a lens) and a conventional lens. The mathematical model of spiral phase modulated FINCH system is established based on wave optics theory. The specific forms of the point spread function (PSF) and the reconstruction distance of the system are given for the first time. Experiments are conducted by using a small aperture with a diameter of 20 nm as a point source, the point source hologram recorded by CCD and the reconstructed image are consistent with the simulated ones. When the system is used for imaging resolution target and unstained onion cells, the edge contrast enhancement effects are obtained without the loss of resolution. The results show that the spiral phase modulated FINCH system can not only improve the edge contrast of the amplitude object, but also extract the edge information or recognition of the phase objects. This method has an important application prospect in the quantitative imaging of phase objects such as in real-time monitoring cell division and deformation of living cells.

Extreme ultraviolet holography using a laser-plasma source based on xenon/helium gas puff target

AbstractIn this paper, we present the application of partially spatially coherent extreme ultraviolet (EUV) radiation from xenon plasma from a laser-plasma source, based on a double stream gas puff target, in coherent imaging. The radiation at the wavelength of 13.5 ± 0.5 nm was employed to record Gabor-type holograms. An iterative algorithm, based on a phase retrieval technique, was developed and used to remove the twin image from the reconstructed EUV image of test objects. Using partially coherent radiation from a compact, laser-plasma source based on a double stream gas puff target, which is intrinsically incoherent, a Gabor EUV holography was successfully demonstrated.

Fast Method of Recovering Reference-Wave Intensity in Two-Step-Only Quadrature Phase-Shifting Holography

We present a simple yet effective method, without the need for any additional recording of intensity maps or tremendous iterative computations, to recover reference-wave intensity resulting from the complex hologram acquired by quadrature phase-shifting holography. This is achieved by utilizing a certain area of interest in the complex hologram. We select a particular area in the complex hologram where there is negligible diffraction from the test sample to estimate the reference-wave intensity. The calculated intensity value allows us to extract exact phase distribution of the object in the context of two-step-only quadrature phase-shifting holography (TSO-PSH) without the zeroth-order beam and the twin image noise on the reconstruction plane. Computer simulation and experimental results have been performed to verify the effectiveness and feasibility of our proposed method.

High resolution near on-axis digital holography using constrained optimization approach with faster convergence

A constrained optimization approach with faster convergence is proposed to recover the complex object field from a near on-axis digital holography (DH). We subtract the DC from the hologram after recording the object beam and reference beam intensities separately. The DC-subtracted hologram is used to recover the complex object information using a constrained optimization approach with faster convergence. The recovered complex object field is back propagated to the image plane using the Fresnel back-propagation method. The results reported in this approach provide high-resolution images compared with the conventional Fourier filtering approach and is 25% faster than the previously reported constrained optimization approach due to the subtraction of two DC terms in the cost function. We report this approach in DH and digital holographic microscopy using the U.S. Air Force resolution target as the object to retrieve the high-resolution image without DC and twin image interference. We also demonstrate the high potential of this technique in transparent microelectrode patterned on indium tin oxide-coated glass, by reconstructing a high-resolution quantitative phase microscope image. We also demonstrate this technique by imaging yeast cells.

현대 패션에 나타난 트위닝 경향과 내적 의미

The purpose of this study is to determine the trend of the twinning in contemporary fashion and to find its internal meaning. The research method adopts an examination of the literature and a case study on the twinning from 2013 S/S to 2017 S/S. The results show that, in the fashion collection, the twinning was used as a tool to highlight the season’s concept or design and in the designers’ presentation in an experimental trial. In fashion advertising, this was utilized as a marketing strategy, whereby models that represent a twin image, twin sisters, or a mother and daughter pair were selected to portray differentiated visual images of homosexuality or ambiguous sexual identity. In the fashion magazines, the emphasis was placed on the twinning look trend, portrayed on the cover or in pictorial articles, and the sensible mode was presented. In social media, the twinning has mainly been expressed in images of the daily routine of a well-known star, whereby the social media platform provides the public with easy access to the star. In the social media, space was provided for communication to describe the star’s personality and sensual fashion style. However, the model type and presentation method of the twinning were similar among the media. This examination demonstrates that the twinning stresses a differentiated personality and style, overcomes a sense of alienation through a shared aesthetic, and generates a fashion culture developed from the change in society on the perception of gender.