Local Illumination Research Articles

Real-Time Computed Tomography Volume Visualization with Ambient Occlusion of Hand-Drawn Transfer Function Using Local Vicinity Statistic.

ObjectivesIn this paper, we present an efficient method to visualize computed tomography (CT) datasets using ambient occlusion, which is a global illumination technique that adds depth cues to the output image. We can change the transfer function (TF) for volume rendering and generate output images in real time.MethodsIn preprocessing, the mean and standard deviation of each local vicinity are calculated. During rendering, the ambient light intensity is calculated. The calculation is accelerated on the assumption that the CT value of the local vicinity of each point follows the normal distribution. We approximate complex TF forms with a smaller number of connected line segments to achieve additional acceleration. Ambient occlusion is combined with the existing local illumination technique to produce images with depth in real time.ResultsWe tested the proposed method on various CT datasets using hand-drawn TFs. The proposed method enabled real-time rendering that was approximately 40 times faster than the previous method. As a result of comparing the output image quality with that of the conventional method, the average signal-to-noise ratio was approximately 40 dB, and the image quality did not significantly deteriorate.ConclusionsWhen rendering CT images with various TFs, the proposed method generated depth-sensing images in real time.

Kinematic model for simulating mucosal wave phenomena on vocal folds

Mucosal waves have been found to be important for evaluating vocal fold vibrations in laryngological practice. While they are routinely evaluated visually, the knowledge on the physical phenomena related to mucosal wave propagation is limited. Kymographic imaging, in particular, reveals various mucosal wave features that deserve more understanding in order to advance functional diagnostics of voice disorders. Here, a kinematic model is presented which simulates mucosal waves on human vocal folds. The vocal fold geometry is based on a parametrically adjustable M5 model. A kinematic rule is used for simulating the propagation of the mucosal wave from the bottom of the vocal folds upwards and laterally over the upper vocal fold surface. The model maps the changes of the coronal shape of the vocal folds through vibration cycles. The vibration characteristics including the mucosal wave movements are then visualized using a synthetic kymogram graphically obtained through a local illumination method. The model can serve as an educational and research tool for studying the mucosal wave features and their appearance in laryngeal kymographic images.

Patch-based Stereo Direct Visual Odometry Robust to Illumination Changes

In this paper, we present a patch-based direct visual odometry (DVO) that is robust to illumination changes at a sequence of stereo images. Illumination change violates the photo-consistency assumption and degrades the performance of DVO, thus, it should be carefully handled during minimizing the photometric error. Our approach divides an incoming image into several buckets, and patches inside each bucket own its unique affine illumination parameter to account for local illumination changes for which the global affine model fails to account, then it aligns small patches placed at temporal images. We do not distribute affine parameters to each patch since this yields huge computational load. Furthermore, we propose a prior weight as a function of the previous pose in a constant velocity model which implies that the faster a camera moves, the more likely it maintains the constant velocity model. Lastly, we verify that the proposed algorithm outperforms the global affine illumination model at the publicly available micro aerial vehicle and the planetary rover dataset which exhibit irregular and partial illumination changes due to the automatic exposure of the camera and the strong outdoor sunlight, respectively.

Simultaneous acquisition of polarimetric SVBRDF and normals

Capturing appearance often requires dense sampling in light-view space, which is often achieved in specialized, expensive hardware setups. With the aim of realizing a compact acquisition setup without multiple angular samples of light and view, we sought to leverage an alternative optical property of light, polarization. To this end, we capture a set of polarimetric images with linear polarizers in front of a single projector and camera to obtain the appearance and normals of real-world objects. We encountered two technical challenges: First, no complete polarimetric BRDF model is available for modeling mixed polarization of both specular and diffuse reflection. Second, existing polarization-based inverse rendering methods are not applicable to a single local illumination setup since they are formulated with the assumption of spherical illumination. To this end, we first present a complete polarimetric BRDF (pBRDF) model that can define mixed polarization of both specular and diffuse reflection. Second, by leveraging our pBRDF model, we propose a novel inverse-rendering method with joint optimization of pBRDF and normals to capture spatially-varying material appearance: per-material specular properties (including the refractive index, specular roughness and specular coefficient), per-pixel diffuse albedo and normals. Our method can solve the severely ill-posed inverse-rendering problem by carefully accounting for the physical relationship between polarimetric appearance and geometric properties. We demonstrate how our method overcomes limited sampling in light-view space for inverse rendering by means of polarization.

Energy-Reduced Arrhythmia Termination Using Global Photostimulation in Optogenetic Murine Hearts.

Complex spatiotemporal non-linearity as observed during cardiac arrhythmia strongly correlates with vortex-like excitation wavelengths and tissue characteristics. Therefore, the control of arrhythmic patterns requires fundamental understanding of dependencies between onset and perpetuation of arrhythmia and substrate instabilities. Available treatments, such as drug application or high-energy electrical shocks, are discussed for potential side effects resulting in prognosis worsening due to the lack of specificity and spatiotemporal precision. In contrast, cardiac optogenetics relies on light sensitive ion channels stimulated to trigger excitation of cardiomyocytes solely making use of the inner cell mechanisms. This enables low-energy, non-damaging optical control of cardiac excitation with high resolution. Recently, the capability of optogenetic cardioversion was shown in Channelrhodopsin-2 (ChR2) transgenic mice. But these studies used mainly structured and local illumination for cardiac stimulation. In addition, since optogenetic and electrical stimulus work on different principles to control the electrical activity of cardiac tissue, a better understanding of the phenomena behind optogenetic cardioversion is still needed. The present study aims to investigate global illumination with regard to parameter characterization and its potential for cardioversion. Our results show that by tuning the light intensity without exceeding 1.10 mW mm-2, a single pulse in the range of 10–1,000 ms is sufficient to reliably reset the heart into sinus rhythm. The combination of our panoramic low-intensity photostimulation with optical mapping techniques visualized wave collision resulting in annihilation as well as propagation perturbations as mechanisms leading to optogenetic cardioversion, which seem to base on other processes than electrical defibrillation. This study contributes to the understanding of the roles played by epicardial illumination, pulse duration and light intensity in optogenetic cardioversion, which are the main variables influencing cardiac optogenetic control, highlighting the advantages and insights of global stimulation. Therefore, the presented results can be modules in the design of novel illumination technologies with specific energy requirements on the way toward tissue-protective defibrillation techniques.

On illumination-invariant variational optical flow for weakly textured scenes

This paper deals with variational optical flow approaches for motion estimation under varying illumination conditions in weakly textured scenes. It proposes a systematic and complete study on descriptor-based data-terms that lead to a robust variational optical flow model. Unlike the literature which most often only experimentally shows that a descriptor is illumination invariant, this contribution gives a theoretical proof of this invariance. First, a local illumination change model is proposed and used to mathematically check whether a descriptor is invariant or not with respect to illumination variations between images. Then, this contribution proposes two general mathematical formulations which can be used to design a wide variety of new illumination-invariant descriptors. To illustrate the interest of the proposed approach, two novel illumination-invariant descriptors are constructed using the proposed general formulations. Moreover, the performance of the descriptors was evaluated on numerous datasets with known ground truth optical flow, while the robustness of the variational optical flow approach was highlighted using complex medical image sequences without ground truth. These experimental results have shown that data-terms based on the proposed descriptors led to accurate and constant optical flow under varying illumination conditions.

A microfabricated nerve-on-a-chip platform for rapid assessment of neural conduction in explanted peripheral nerve fibers

Peripheral nerves are anisotropic and heterogeneous neural tissues. Their complex physiology restricts realistic in vitro models, and high resolution and selective probing of axonal activity. Here, we present a nerve-on-a-chip platform that enables rapid extracellular recording and axonal tracking of action potentials collected from tens of myelinated fibers. The platform consists of microfabricated stimulation and recording microchannel electrode arrays. First, we identify conduction velocities of action potentials traveling through the microchannel and propose a robust data-sorting algorithm using velocity selective recording. We optimize channel geometry and electrode spacing to enhance the algorithm reliability. Second, we demonstrate selective heat-induced neuro-inhibition of peripheral nerve activity upon local illumination of a conjugated polymer (P3HT) blended with a fullerene derivative (PCBM) coated on the floor of the microchannel. We demonstrate the nerve-on-a-chip platform is a versatile tool to optimize the design of implantable peripheral nerve interfaces and test selective neuromodulation techniques ex vivo.

Evaluation for Synergistic Effects by Combinations of Photodynamic Therapy (PDT) with Temoporfin (mTHPC) and Pt(II) Complexes Carboplatin, Cisplatin or Oxaliplatin in a Set of Five Human Cancer Cell Lines.

The platinum(II) complexes carboplatin (CBDCA), cisplatin (CDDP) and oxaliplatin (1-OHP) are used as anticancer drugs in a large number of tumour chemotherapy regimens. Many attempts have been made to combine Pt(II)-based chemotherapy with alternative treatment strategies. One such alternative anticancer approach is known as photodynamic therapy (PDT), where a non-toxic photosensitizer (PS) produces oxidative stress via the formation of reactive oxygen species (ROS) after local illumination of the affected tissue. A very promising PS is 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (mTHPC, Temoporfin), which is approved for the treatment of head and neck cancer in Europe. In the present study, a combination of mTHPC-mediated PDT and either CBDCA, CDDP, or 1-OHP was applied to five human cancer cell lines from different tumour origins. Cytotoxicity was determined by the MTT assay and synergistic effects on cytotoxicity were evaluated by calculation of Combination Indices (CI). Synergy was identified in some of the combinations, for example, with 1-OHP in three of the tested cell lines but antagonism was also observed for a number of combinations in certain cell lines. In cases of synergy, elevated ROS levels were observed after combination but apoptosis induction was not necessarily increased compared to a treatment with a single compound. Cell cycle analysis revealed a formation of apoptotic subG1 populations and S phase as well as G2/M phase arrests after combination. In conclusion, pre-treatment with mTHPC-PDT has the potential to sensitize some types of tumour cells towards Pt(II) complexes, in particular 1-OHP but synergy is highly dependent on the type of cancer.

The evolution of gently sloping mantled deposits on Comet 67P/Churyumov-Gerasimenko

We investigated the role of local illumination and material parameters that can be important in determining evolution of a gently inclined slopes on the nucleus of comet. The considered material parameters are: size of ice grains, agglomerates and pores in-between, thermal conductivity of dust mantle, size of pores in the dust mantle, presence of organic admixtures in water ice, difference of bonds between agglomerates composing the dust mantle and bonds in the underlying ice-dust material, thickness of the layer of dust. The simulations were performed for the selected locations in the north part of the small lobe of the comet. We have found, that the rate of erosion is sensitive to the granulation of material, that is not the case in the region Hatmehit (Kossacki and Czechowski, 2018). The erosion may lead to the formation of small-scale pits.

High-speed ptychographic imaging based on multiple-beam illumination.

Ptychography is a lensless phase imaging technique that obtains an image by scanning a specimen at several points with respect to a localized illumination beam. For larger specimens, it takes a longer time to complete scanning and hence higher stability is required in the setup which is often not guaranteed. An alternative technique is proposed here that reduces the sequential scanning time for such applications. A pinhole array is used to generate multiple tiny spatially separated beams to scan an object simultaneously at various points. The resulting diffraction patterns are recorded and processed in the Fresnel regime to obtain the images. Unlike other ptychographic methods using multiple beams, the proposed method does not require the use of a multimode ptychography algorithm or autocorrelation filtering of the diffraction patterns. The effectiveness of the method is studied through simulations and experiments. In contrast to conventional single-beam ptychography, the proposed method has the ability to achieve a larger field of view while leaving the number of scanned positions unchanged.

An anisotropic heat diffusion model for enhancing the extraction of underground rail track fasteners under extremely low and uneven illumination conditions

During the past two decades, subway systems have become one of the most dominant infrastructural developments in China at an unprecedented pace and scale. More than 60 metro lines in 25 cities have been completed, transporting more than 70 million passengers daily. Operating the subway systems safely and efficiently is a continuously pressing demand from both the management companies and the public. Although many automated or semi-automated methods for extracting critical components of the rail track systems, e.g. rail, fastener, sleeper, etc., have significantly improved the productivity of routine inspection, the unique challenges posed by the subway systems have hindered these existing methods from successful implementation because of the extremely low illumination in the underground environment, whereas additional artificial lighting often poses extremely uneven illumination. In this study, a generalized local illumination adaptation model using an anisotropic heat equation is proposed to dynamically adjust the acquired rail track images with extremely low and uneven illumination conditions. An integration flow is then proposed to seamlessly incorporate the proposed model into the state-of-the-art automated fastener detection algorithms. The results show that the proposed local illumination adaptation model can significantly improve the performance of the tested state-of-the-art fastener detection algorithms when they are applied to the images collected in the environment with extremely low and uneven illumination conditions, e.g. subway systems.

From global radiance to an increased local political awareness of light pollution

We present a novel transparent method to analyze measurements of the Suomi NPP (Suomi National Polar-orbiting Partnership) satellite in night vision, into luminous intensity and luminance on the community level, with a special focus to address light planners and non-experts, and for the first time, to further address politicians, decision-makers and law-makers, and governmental agencies. We checked the propagated efficiency of road lighting and its impact on luminous flux, and identified a waste of light emissions in the largest city of Switzerland, Zurich. We looked at security (issues like criminal acts) and found no correlation with communities’ luminous intensity. We assessed road safety (accidents) against local luminance and found no evidence of darkness being more risky when the overall distribution of illuminance on roads is considered. We screened crayfish habitats in the Canton of Zurich against local illuminance and found clear evidence of preferred darkness for the living. Based on this finding, we propose an upper limit for light immissions in the crayfish habitats. These four analyses have been chosen to demonstrate the usefulness of Suomi NPP's coverage in combination with our approach. We could apply it to ecological, social and economical topics. We hope others will follow and we can draw more attention of governments to take action to reduce the light pollution on local levels, like Langnau am Albis of Switzerland has exemplified.

Color constancy via multibranch deep probability network

A learning-based multibranch deep probability network is proposed to estimate the illuminated color of the light source in a scene, commonly referred to as color constancy. The method consists of two coupled subnetworks, which are the deep multibranch illumination estimating network (DMBEN) and deep probability computing network (DPN). The one branch of DMBEN estimates the global illuminant through pooling layer and fully connected layer, whereas the other branch is built as an end-to-end residuals network (Res-net) to evaluate the local illumination. The other adjoint subnetwork DPN separately computes the probabilities that results of DMBEN are similar to the ground truth, then determines the better estimation according to the two probabilities under a new criterion. The results of extensive experiments on Color Checker and NUS 8-Camera datasets show that the proposed approach is superior to the state-of-the-art methods both in efficiency and effectiveness.

Effectiveness of low level laser therapy for treating male infertility.

In half of the cases, the infertility of the couple is due to the disorder of the male fertility. The leading factors that cause male infertility are urogenital infections, disorders of the immune system, testicular and prostate pathology, as well as endocrine disorders.Low level laser therapy (LLLT) is a very effective physical therapy method, used in many areas of medicine, including obstetrics and gynaecology, andrology and urology; and it is recommended as an integral part of the complex treatment of infertility.The literature review showed that LLLT is beneficial in treating male infertility. Laser can significantly improve the survival, motility and speed of movement of spermatozoa. Laser therapy of patients with prostatitis and vesiculitis can eliminate infiltrative-exudative changes, improve reproductive and copulatory functions. Local illumination of red (635 nm) and infrared (904 nm) spectra should be combined with intravenous laser blood illumination (ILBI) of red (635 nm) and ultraviolet (UV) (365 nm) spectra.

Scanning photocurrent microscopy of electrons and holes in the pigment semiconductor epindolidione

Abstract Photocurrent microscopy is used to characterize the kinetics of electrons and holes in organic field-effect transistors (FETs) with the hydrogen-bonded pigment epindolidione as active layer. The method relies on electrons and holes, generated on local illumination, which are provided after exciton splitting, to probe charge trapping. In the dark, hole conduction is observed for negative gate voltage while no electron conduction is observed for positive gate voltage. However, under illumination, a fast displacement current with 60 μs onset time and 1 ms exponential decay occurs for positive gate voltage, which can be explained by exciton splitting underneath the semitransparent top contact followed by subsequent electron trapping and hole extraction. Afterward, trapped electrons hop via further trap states within the film to the insulator into interface traps (13 ms exponential decay) which induce a positive threshold voltage shift in the FET transfer curves for hole transport. Photocurrent microscopy confirms that the displacement current occurs only for illumination under and near the semitransparent source/drain contacts, which act here as metal-insulator-semiconductor (MIS) diodes. For negative gate voltage instead, the photocurrent comprises an enhanced hole current in the FET channel between the contacts. In the channel region, the detrapping of holes at the interface with the insulator (3 ms time constant) enhances the transistor current at low frequencies 10 kHz. Thus, we show here that photocurrent microscopy allows to identify the kinetics of electrons and holes in traps close to the contacts and in the FET channel of pigment transistors.

SEPARATE DETERMINATION OF THE PHOTOELECTRIC PARAMETERS OF THE BASE REGION OF N+−P(N)−P+ SILICON STRUCTURE BY NONCONTACT METHOD BASED ON QUANTUM EFfi CIENCY RELATION MEASUREMENTS AT TWO WAVELENGTHS

A noncontact method for the determination of recombination parameters of p(n) layer local ranges of silicon n+−p(n)−p+ structures is considered. The method is based on local illumination of the investigated structure by two different absorbed light beams. Initially both beams illuminate simultaneously one side of the local range of this structure and then another side. The intensities оf the light beams are modulated at one frequency so the alternative photo−voltage becomes equal to zero. In this case the short current regime is established for its alternating component. As a consequence the nonilluminated parts of the structure do not shunt its illuminated part. The ratios of the light beam intensities are measured under these conditions. In this work we calculated nomograms for separate determination of the nonequilibrium charge carrier lifetime of the illuminated p(n) local space and its surface recombination velocity using the measured intensity ratios. The calculations were performed at low injection level for one dimensional case. The nomograms were calculated at wave lengths of 1064 and 808 nm for various thicknesses of the n+−p(n)−p+ structures and various modulation frequencies. It was found that the nomograms almost do not depend on the modulation frequency if the live time of the nonequilibrium charge carriers is less than the modulation period. Furthermore, we observed that the nomograms shift substantially and change their shape for thin structures if the diffusion time of nonquilibrium charge carriers from the rear side of the structure to its face side becomes less than their lifetime. In this case the nomograms may be only used for the determination of the surface recombination velocity of the nonquilibrium charge carriers at the rear side of the structure.

Light-induced formation of partially reduced oxygen species limits the lifetime of photosystem 1-based biocathodes

Interfacing photosynthetic proteins specifically photosystem 1 (PS1) with electrodes enables light-induced charge separation processes for powering semiartificial photobiodevices with, however, limited long-term stability. Here, we present the in-depth evaluation of a PS1/Os-complex-modified redox polymer-based biocathode by means of scanning photoelectrochemical microscopy. Focalized local illumination of the bioelectrode and concomitant collection of H2O2 at the closely positioned microelectrode provide evidence for the formation of partially reduced oxygen species under light conditions. Long-term evaluation of the photocathode at different O2 concentrations as well as after incorporating catalase and superoxide dismutase reveals the particularly challenging issue of avoiding the generation of reactive species. Moreover, the evaluation of films prepared with inactivated PS1 and free chlorophyll points out additional possible pathways for the generation of oxygen radicals. To avoid degradation of PS1 during illumination and hence to enhance the long-term stability, the operation of biophotocathodes under anaerobic conditions is indispensable.

Long-range interactions of Chara chloroplasts are sensitive to plasma-membrane H+ flows and comprise separate photo- and dark-operated pathways.

Local illumination of the characean internode with a 30-s pulse of white light was found to induce the delayed transient increase of modulated chlorophyll fluorescence in shaded cell parts, provided the analyzed region is located downstream in the cytoplasmic flow at millimeter distances from the light spot. The fluorescence response to photostimulation of a remote cell region indicates that the metabolites produced by source chloroplasts in an illuminated region are carried downstream with the cytoplasmic flow, thus ensuring long-distance communications between anchored plastids in giant internodal cells. The properties of individual stages of metabolite signaling are not yet well known. We show here that the export of assimilates and/or reducing equivalents from the source chloroplasts into the flowing cytoplasm is largely insensitive to the direction of plasma-membrane H+ flows, whereas the events in sink regions where these metabolites are delivered to the acceptor chloroplasts under dim light are controlled by H+ fluxes across the plasma membrane. The fluorescence response to local illumination of remote cell regions was best pronounced under weak background light and was also observed in a modified form within 1-2min after the transfer of cell to darkness. The fluorescence transients in darkened cells were suppressed by antimycin A, an inhibitor of electron transfer from ferredoxin to plastoquinone, whereas the fluorescence response under background light was insensitive to this inhibitor. We conclude that the accumulation of reduced metabolites in the stroma leads to the reduction of photosystem II primary quinone acceptor (QA) via two separate (photochemical and non-photochemical) pathways.

Structure‐based optics of centric diatom frustules: modulation of the in vivo light field for efficient diatom photosynthesis

The optical properties of diatom silicate frustules inspire photonics and nanotechnology research. Whether light interaction with the nano-structure of the frustule also affects diatom photosynthesis has remained unclear due to lack of information on frustule optical properties under more natural conditions. Here we demonstrate that the optical properties of the frustule valves in water affect light harvesting and photosynthesis in live cells of centric diatoms (Coscinodiscus granii). Microscale cellular mapping of photosynthesis around localized spot illumination demonstrated optical coupling of chloroplasts to the valve wall. Photonic structures of the three-layered C.granii valve facilitated light redistribution and efficient photosynthesis in cell regions distant from the directly illuminated area. The different porous structure of the two sides of the valve exhibited photon trapping and forward scattering of blue light enhancing photosynthetic active radiation inside the cell. Photonic structures of diatom frustules thus alter the cellular light field with implications on diatom photobiology.

Deformation of glassy nematic films due to local illumination

We studied photomechanical response of glassy nematic films to a single incident beam of light with circular spot. The effects of some typical director fields including homeotropic, uniaxial, splay-bend and twist distributions were examined. In all these cases, we showed that the mean of spontaneous bending moments in the exposed region arising from light attenuation is nonzero, and the deflection of the film scales logarithmically with the distance from the spot. The phenomenon implies that a local photo-excitation can induce large-scale deformation of glassy nematic films, and the mechanism may be inspiring in various applications of morphology manipulation.