Enhanced Resolution Images Research Articles

EDSR: Empowering super-resolution algorithms with high-quality DIV2K images

Remarkable strides have been made in Enhanced-resolution image reconstruction in recent times. In this research, we propose EDSR, a novel algorithm leveraging high-quality DIV2K images to enhance super-resolution algorithms’ performance. Our approach addresses challenges associated with capturing and reconstructing fine details and textures in low-resolution images. The training process utilizes a deep neural network fed with the extensive DIV2K dataset, comprising meticulously selected high-resolution images for super-resolution tasks. The network learns from these high-quality images to improve super-resolved outputs’ accuracy and fidelity. Extensive experimentation evaluates the effectiveness of the EDSR algorithm in achieving superior results. Experimental outcomes exhibit the remarkable progress made by EDSR compared to other leading super-resolution algorithms. The mean PSNR values obtained using EDSR on various test datasets indicate substantial improvement in image quality. The SSIM scores show enhanced preservation of fine details and textures. In the Nature category, the EDSR algorithm exhibits impressive performance, achieving a mean Peak Signal-to-Noise Ratio (PSNR) of 35.92 dB and a Structural Similarity Index (SSIM) of 0.9321. When analyzing Portrait images, the algorithm consistently maintains high quality, delivering a mean PSNR of 34.17 dB and an SSIM of 0.9125. For Cityscape images, EDSR showcases excellent capabilities with a mean PSNR of 36.05 dB and an SSIM of 0.9382, highlighting its exceptional handling in this category. Lastly, in the Still Life category, the algorithm demonstrates competence, achieving a mean PSNR of 33.79 dB and an SSIM of 0.9024. In conclusion, the proposed EDSR algorithm empowers super-resolution algorithms by leveraging high-quality DIV2K images. The empirical findings validate that EDSR is highly efficient in enhancing image quality and preserving fine details.

Wavelength domain spatial frequency modulation imaging: enabling fiber optic delivery and detection.

Spatial frequency modulation imaging (SPIFI) provides a simple architecture for modulating an extended illumination source that is compatible with single pixel imaging. We demonstrate wavelength domain SPIFI (WD-SPIFI) by encoding time-varying spatial frequencies in the spectral domain that can produce enhanced resolution images, like its spatial domain counterpart, spatial domain (SD) SPIFI. However, contrary to SD-SPIFI, WD-SPIFI enables remote delivery by single mode fiber, which can be attractive for applications where free-space imaging is not practical. Finally, we demonstrate a cascaded system incorporating WD-SPIFI in-line with SD-SPIFI enabling single pixel 2D imaging without any beam or sample scanning.

Cascaded domain multiphoton spatial frequency modulation imaging.

Multiphoton microscopy is a powerful imaging tool for biomedical applications. A variety of techniques and respective benefits exist for multiphoton microscopy, but an enhanced resolution is especially desired. Additionally multiphoton microscopy requires ultrafast pulses for excitation, so optimization of the pulse duration at the sample is critical for strong signals. We aim to perform enhanced resolution imaging that is robust to scattering using a structured illumination technique while also providing a rapid and easily repeatable means to optimize group delay dispersion (GDD) compensation through to the sample. Spatial frequency modulation imaging (SPIFI) is used in two domains: the spatial domain (SD) and the wavelength domain (WD). The WD-SPIFI system is an in-line tool enabling GDD optimization that considers all material through to the sample. The SD-SPIFI system follows and enables enhanced resolution imaging. The WD-SPIFI dispersion optimization performance is confirmed with independent pulse characterization, enabling rapid optimization of pulses for imaging with the SD-SPIFI system. The SD-SPIFI system demonstrates enhanced resolution imaging without the use of photon counting enabled by signal to noise improvements due to the WD-SPIFI system. Implementing SPIFI in-line in two domains enables full-path dispersion compensation optimization through to the sample for enhanced resolution multiphoton microscopy.

CROCODILE

Context.The investigation of the atmospheres of closely separated, directly imaged gas giant exoplanets is challenging due to the presence of stellar speckles that pollute their spectrum. To remedy this, the analysis of medium- to high-resolution spectroscopic data via cross-correlation with spectral templates (cross-correlation spectroscopy) is emerging as a leading technique.Aims.We aim to define a robust Bayesian framework combining, for the first time, three widespread direct-imaging techniques, namely photometry, low-resolution spectroscopy, and medium-resolution cross-correlation spectroscopy in order to derive the atmospheric properties of close-in directly imaged exoplanets. Current atmospheric characterisation frameworks are indeed either not compatible with all three observing techniques or they lack the commitment to efficient sampling strategies that allow high-dimensional forward models.Methods.Our frameworkCROCODILE(cross-correlation retrievals of directly imaged self-luminous exoplanets) naturally combines the three techniques by adopting adequate likelihood functions. To validate our routine, we simulated observations of gas giants similar to the well-studiedβPictoris b planet and we explored the parameter space of their atmospheres to search for potential biases.Results.We obtain more accurate measurements of atmospheric properties when combining photometry, low- and medium-resolution spectroscopy into atmospheric retrievals than when using the techniques separately as is usually done in the literature. Indeed, the combined fit is, on average, 20% more accurate than fitting only medium-resolution cross-correlation spectroscopy. We find that medium-resolution (R≈ 4000)K-band cross-correlation spectroscopy alone is not suitable to constrain the atmospheric properties of our synthetic datasets; however, this problem disappears when simultaneously fitting photometry throughout theYandMbands and low-resolution (R≈ 60) spectroscopy between theYandHbands. Our thorough testing demonstrates that free chemistry is a suitable forward model to retrieve the atmospheric thermal and chemical properties of cloudless gas giants at chemical equilibrium.Conclusions.CROCODILEprovides a robust statistical framework to interpret medium-resolution spectroscopic data of close-in directly imaged exoplanets, where speckles originating from stellar stray light render the extraction of the continuum difficult. Our framework allows the atmospheric characterisation of directly imaged exoplanets using the high-quality spectral data that will be provided by the new generation of instruments such as the Enhanced Resolution Imager and Spectrograph (ERIS) at the Very Large Telescope, the Mid-Infrared Instrument (MIRI) aboard theJames WebbSpace Telescope, and in the future the Mid-infrared ELT Imager and Spectrograph (METIS) at the Extremely Large Telescope.

The Enhanced Resolution Imager and Spectrograph for the VLT

The Enhanced Resolution Imager and Spectrograph (ERIS) is an instrument that both extends and enhances the fundamental diffraction limited imaging and spectroscopy capability for the VLT. It replaces two instruments that were being maintained beyond their operational lifetimes, combines their functionality on a single focus, provides a new wavefront sensing module for natural and laser guide stars that makes use of the Adaptive Optics Facility, and considerably improves on their performance. The observational modes ERIS provides are integral field spectroscopy at 1–2.5 μm, imaging at 1–5 μm with several options for high-contrast imaging, and long-slit spectroscopy at 3–4 μm. The instrument is installed at the Cassegrain focus of UT4 at the VLT and, following its commissioning during 2022, has been made available to the community.

Evaluating the effective resolution of enhanced resolution SMAP brightness temperature image products

The MEaSUREs Calibrated Enhanced-Resolution Passive Microwave Daily Equal-Area Scalable Earth Grid 2.0 Brightness Temperature (CETB) Earth System Data Record (ESDR) includes conventional- and enhanced-resolution radiometer brightness temperature (TB) images on standard, compatible grids from calibrated satellite radiometer measurements collected over a multi-decade period. Recently, the CETB team processed the first 4 years of enhanced resolution Soil Moisture Active Passive (SMAP) L-band (1.41 GHz) radiometer TB images. The CETB processing employs the radiometer form of the Scatterometer Image Reconstruction (rSIR) algorithm to create enhanced resolution images, which are posted on fine resolution grids. In this paper, we evaluate the effective resolution of the SMAP TB image products using coastline and island crossings. We similarly evaluate the effective resolution of the SMAP L1C_TB_E enhanced resolution product that is based on Backus-Gilbert processing. We present a comparison of the spatial resolution of the rSIR and L1C_TB_E enhanced resolution products with conventionally-processed (gridded) SMAP data. We find that the effective resolution of daily CETB rSIR SMAP TB images is slightly finer than that of L1C_TB_E and about 30% finer than conventionally processed data.

Dendritic spinule-mediated structural synaptic plasticity: Implications for development, aging, and psychiatric disease.

Dendritic spines are highly dynamic and changes in their density, size, and shape underlie structural synaptic plasticity in cognition and memory. Fine membranous protrusions of spines, termed dendritic spinules, can contact neighboring neurons or glial cells and are positively regulated by neuronal activity. Spinules are thinner than filopodia, variable in length, and often emerge from large mushroom spines. Due to their nanoscale, spinules have frequently been overlooked in diffraction-limited microscopy datasets. Until recently, our knowledge of spinules has been interpreted largely from single snapshots in time captured by electron microscopy. We summarize herein the current knowledge about the molecular mechanisms of spinule formation. Additionally, we discuss possible spinule functions in structural synaptic plasticity in the context of development, adulthood, aging, and psychiatric disorders. The literature collectively implicates spinules as a mode of structural synaptic plasticity and suggests the existence of morphologically and functionally distinct spinule subsets. A recent time-lapse, enhanced resolution imaging study demonstrated that the majority of spinules are small, short-lived, and dynamic, potentially exploring their environment or mediating retrograde signaling and membrane remodeling via trans-endocytosis. A subset of activity-enhanced, elongated, long-lived spinules is associated with complex PSDs, and preferentially contacts adjacent axonal boutons not presynaptic to the spine head. Hence, long-lived spinules can form secondary synapses with the potential to alter synaptic connectivity. Published studies further suggest that decreased spinules are associated with impaired synaptic plasticity and intellectual disability, while increased spinules are linked to hyperexcitability and neurodegenerative diseases. In summary, the literature indicates that spinules mediate structural synaptic plasticity and perturbations in spinules can contribute to synaptic dysfunction and psychiatric disease. Additional studies would be beneficial to further delineate the molecular mechanisms of spinule formation and determine the exact role of spinules in development, adulthood, aging, and psychiatric disorders.

Reliability, availability, and maintainability analysis of the Enhanced Resolution Imager and Spectrograph adaptive optics module and lesson learned before commissioning

Enhanced Resolution Imager and Spectrograph is an instrument currently under commissioning at the Cassegrain focus of the Very Large Telescope UT4. Its mission is to replace the suite of instruments NAOS-CONICA and SINFONI and push to the edge the capabilities of this 8-meter class telescope, by leveraging the adaptive optics module. The instrument has been designed for maximum lifetime and reliability and minimum downtime. We will present the instrument constraints and our approach to the reliability, availability, and maintainability (RAM) analysis. We identified the main actors in the system, then for each of them, we compiled a database of reliability parameters in order to build-up the reliability diagram, describing the failure sources. Starting from this information, we computed the system-wide reliability parameters and compared them with the requirements by the customer. Such a scheme is very general and may be taken as an example of RAM analysis for astronomical instrumentation; it may be also customized for the needs of other projects. In the end, we summarize the lessons learned.

An optimized survey strategy for the ERIS/NIX imager: searching for young giant exoplanets and very low mass brown dwarfs using the K-peak custom photometric filter

ABSTRACT We present optimal survey strategies for the upcoming NIX imager, part of the Enhanced Resolution Imager and Spectrograph instrument to be installed on the Very Large Telescope. We will use a custom 2.2 µm K-peak filter to optimize the efficiency of a future large-scale direct imaging survey, aiming to detect brown dwarfs and giant planets around nearby stars. We use the results of previous large-scale imaging surveys (primarily SPHERE SHINE and Gemini GPIES) to inform our choice of targets, as well as improved planet population distributions. We present four possible approaches to optimize survey target lists for the highest yield of detections: (i) targeting objects with anomalous proper motion trends, (ii) a follow-up survey of dense fields from SPHERE SHINE and Gemini GPIES, (iii) surveying nearby star-forming regions, and (iv) targeting newly discovered members of nearby young moving groups. We also compare the predicted performance of NIX to other state-of-the-art direct imaging instruments.

Cryogenic characterization of the grating vector apodizing phase plate coronagraph for the enhanced resolution imager and spectrograph at the Very Large Telescope

We present results on the laboratory characterization of the grating vector apodizing phase plate (gvAPP) coronagraph that will be included in the upcoming instrument enhanced resolution imager and spectrograph (ERIS) at the VLT. ERIS will include a 1 to 5 μm adaptive-optics-fed imager, NIX, that will greatly improve the capability of the VLT to perform high-contrast imaging of exoplanets especially in the 3 to 5 μm wavelength range. The gvAPP, one of the coronagraphs in the NIX suite, is a pupil plane coronagraph that uses a thin film of patterned liquid crystals to create two images of a star with a D-shaped dark hole on either side. The gvAPP is manufactured using an innovative direct-write system that produces precise patterns of liquid crystals. We utilized the upgraded infrared cryogenic test bench run by the Exoplanets and Habitability Group at ETH Zurich to measure the morphology of the gvAPP PSF and to test the accuracy of the liquid crystal manufacturing technique in the lab for the first time at contrast levels of ∼10 − 5. We find that the gvAPP can reach raw contrasts below ∼10 − 5 between ∼10 and 13 λ / D. This contrast upper limit translates to a writing accuracy of the orientation of the liquid crystal’s fast axis of better than 0.3 deg for the spatial frequencies corresponding to those separations. This is a sufficient accuracy such that the gvAPP will not be the limiting factor in achieving the required contrasts to image exoplanets.

Imaging through a scattering medium: the Fisher information and the generalized Abbe limit.

Enhanced-resolution imaging in complex scattering media is revisited from a parameter estimation perspective. A suitably defined Fisher information is shown to offer useful insights into the limiting precision of parameter estimation in a scattering environment and, hence, into the limiting spatial resolution that can be achieved in imaging-through-scattering settings. The Fisher information that defines this resolution limit via the Cramér-Rao lower bound is shown to scale with the number of adaptively controlled space-time modes of the probe field, suggesting a physically intuitive generalization of the Abbe limit to the spatial resolution attainable for complex scattering systems. In a conventional, direct-imaging microscopy setting, this bound is shown to converge to the canonical Abbe limit.

Applications of STED fluorescence nanoscopy in unravelling nanoscale structure and dynamics of biological systems

Fluorescence microscopy, especially confocal microscopy, has revolutionized the field of biological imaging. Breaking the optical diffraction barrier of conventional light microscopy, through the advent of super-resolution microscopy, has ushered in the potential for a second revolution through unprecedented insight into nanoscale structure and dynamics in biological systems. Stimulated emission depletion (STED) microscopy is one such super-resolution microscopy technique which provides real-time enhanced-resolution imaging capabilities. In addition, it can be easily integrated with well-established fluorescence-based techniques such as fluorescence correlation spectroscopy (FCS) in order to capture the structure of cellular membranes at the nanoscale with high temporal resolution. In this review, we discuss the theory of STED and different modalities of operation in order to achieve the best resolution. Various applications of this technique in cell imaging, especially that of neuronal cell imaging, are discussed as well as examples of application of STED imaging in unravelling structure formation on biological membranes. Finally, we have discussed examples from some of our recent studies on nanoscale structure and dynamics of lipids in model membranes, due to interaction with proteins, as revealed by combination of STED and FCS techniques.

Enhanced resolution imaging of ultrathin ZnO layers on Ag(111) by multiple hydrogen molecules in a scanning tunneling microscope junction

Molecular hydrogen in a scanning tunneling microscope (STM) junction has been found to enhance the lateral spatial resolution of the STM imaging, referred to as scanning tunneling hydrogen microscopy (STHM). Here we report atomic resolution imaging of 2- and 3-monolayer (ML) thick ZnO layers epitaxially grown on Ag(111) using STHM. The enhanced resolution can be obtained at a relatively large tip to surface distance and resolves a more defective structure exhibiting dislocation defects for 3-ML-thick ZnO than for 2 ML. In order to elucidate the enhanced imaging mechanism, the electric and mechanical properties of the hydrogen molecular junction (HMJ) are investigated by a combination of STM and atomic force microscopy. It is found that the HMJ shows multiple kinklike features in the tip to surface distance dependence of the conductance and frequency shift curves, which are absent in a hydrogen-free junction. Based on a simple modeling, we propose that the junction contains several hydrogen molecules and sequential squeezing of the molecules out of the junction results in the kinklike features in the conductance and frequency shift curves. The model also qualitatively reproduces the enhanced resolution image of the ZnO films.

Sparsity-based reconstruction for super-resolved limited-view photoacoustic computed tomography deep in a scattering medium.

Delay-and-sum beamforming (DSB) of photoacoustic data does not incorporate a priori spatial sparsity of the imaging target. By incorporating this information into beamforming for limited-view photoacoustic computed tomography, we experimentally obtained enhanced resolution images of wires at a depth of 8.5mm in a tissue mimicking scattering medium. Using a 21MHz transducer, we improved the resolution from the 200 to 250μm achieved by DSB to 75μm. The sparsity-based technique also generated a cleaner image with a background signal level of roughly -50 dB, much lower than the roughly -18 dB background signal level of DSB.

Enhanced-Resolution Optical Coherence Tomography Imaging

Purpose: The effect of the enhanced-resolution imaging (ERI) technique on optical coherence tomography (OCT) images was evaluated. Methods: A total of 5 healthy subjects and 20 patients diagnosed with various eye diseases were recruited into the study. ERI, a novel image processing technique, was accomplished by using super-resolution technology, and was assessed by objectively and subjectively comparing the image quality among three different image groups: images enlarged without bicubic interpolation (NONE), with bicubic interpolation (IP), and with ERI. Results: ERI showed a higher ratio of the detailed variance to the background variance than NONE, whereas no significant difference was detected between NONE and IP. The mean opinion score of 5 experienced retinal specialists for ERI was significantly higher than that for IP. Conclusions: ERI generated a sharper image and clearly visualized small objects. Additionally, it is effective in enhancing OCT image quality.

Vapor-enhanced covalently bound ultra-thin films on oxidized surfaces for enhanced resolution imaging

Vapor-phase covalently bound siloxane thin films of various functionalities on a variety of surfaces, including glass, aluminum, and polyester, were demonstrated in a one-step process.

Analysis of a Veselago lens in the quasistatic regime

The resolution of conventional optical lenses is limited by the wavelength. Materials with a negative refractive index have been shown to enable the generation of an enhanced resolution image where both propagating and nonpropagating waves are employed. We analyze such a Veselago lens by exploiting some exact one-dimensional integral expressions for the quasistatic electric potential of a point charge in that system. These were recently obtained by expanding that potential in the quasistatic eigenfunctions of a three-flat-slabs composite structure. Numerical evaluations of those integrals, using realistic values for physical parameters like the electric permittivities of the constituent slabs and their thickness, reveal some surprising effects: For example, the maximum concentration of the electric field occurs not at the geometric optics foci but at the interfaces between the negative permittivity slab and the positive permittivity slabs. The analysis provides simple computational guides for designing such structures to achieve enhanced resolution of an optical image.

Application of phase extension method to sub-Å transmission electron microscopy

A sub-A resolution analysis of a Si crystal structure was performed successfully using a phase extension technique that combined the high-voltage electron microscopy (HVEM) and energy-filtered precession electron diffraction (EF-PED) methods. The high resolution electron microscopy (HREM) image of Si [211] was obtained with a spatial resolution of 0.12 nm using HVEM. The electron diffraction of Si [211] was acquired with a spatial resolution of 0.06 nm by employing the EF-PED method. The phase information of Si [211] was extracted from a deconvoluted image by applying instrumental parameters. Its amplitude information with higher spatial resolution was quasi-kinematically extracted from EF-PED data. Finally, it was revealed that Si atoms were clearly separated with a resolution of 0.78 A in the enhanced resolution image. Therefore, it is expected that the combination of the HVEM and EF-PED methods will be a useful and powerful tool for the quantitative characterization of nanostructured materials.

Structured oblique illumination microscopy for enhanced resolution imaging of non-fluorescent, coherently scattering samples

Many biological structures of interest are beyond the diffraction limit of conventional microscopes and their visualization requires application of super-resolution techniques. Such techniques have found remarkable success in surpassing the diffraction limit to achieve sub-diffraction limited resolution; however, they are predominantly limited to fluorescent samples. Here, we introduce a non-fluorescent analogue to structured illumination microscopy, termed structured oblique illumination microscopy (SOIM), where we use simultaneous oblique illuminations of the sample to multiplex high spatial-frequency content into the frequency support of the system. We introduce a theoretical framework describing how to demodulate this multiplexed information to reconstruct an image with a spatial-frequency support exceeding that of the system’s classical diffraction limit. This approach allows enhanced-resolution imaging of non-fluorescent samples. Experimental confirmation of the approach is obtained in a reflection test target with moderate numerical aperture.

Dynamic saturation optical microscopy: employing dark-state formation kinetics for resolution enhancement

Fluorescence microscopy has become one of the most rapidly developing observation techniques in the field of molecular biology, since its high sensitivity, contrast and labeling specificity together with being non-invasive fulfill the most important requirements of live cell imaging. The biggest limitation of the technique seems to be the spatial resolution which is, based on Abbe's diffraction law, restricted to some hundreds of nanometres. Recently, various approaches have been developed that overcome the limit imposed by the diffraction barrier and these methods currently lead the development in the field of fluorescence microscopy. In this contribution, we present dynamic saturation optical microscopy (DSOM)--a new technique that monitors the temporal decay of the excited singlet state due to a dark state formation. By mapping the intensity dependent decay kinetics, enhanced resolution images can be obtained. Generally, any dark state of fluorescent molecules can be employed in DSOM. Here, we focus our attention on triplet state formation.