Contrast Degradation Research Articles

Monitoring ink disease epidemics in chestnut and cork oak forests in central Italy with remote sensing

Forests provide multiple ecosystem services including water and soil protection, biodiversity conservation, carbon sequestration, and recreation, which are crucial in sustaining human health and wellbeing. Global changes represent a serious threat to Mediterranean forests, and among known impacts, there is the spread of invasive pests and pathogens, often boosted by climate change and human pressure. Remote sensing can provide support to forest health monitoring, which is crucial to contrast degradation and adopt mitigation strategies. Here, different multispectral and SAR data are used to detect the incidence of ink disease driven by Phytophthora cinnamomi in forest sites in central Italy, dominated by chestnut and cork oak respectively. Sentinel 1, Sentinel 2, and PlanetScope data, together with ground information, served as input in Random Forests to model healthy and disease classes in the two sites. The results indicate that healthy and symptomatic trees are clearly distinguished, whereas the discrimination among disease classes of different severity (moderate and severe damage) is less accurate. Crown dimension and sampled spectral regions are a critical factors in the selection of the sensor; better results are obtained for the larger chestnut crowns with Sentinel 2 data. In both sites, the red and near infra-red bands from multispectral data resulted well suited to monitor the spread of the ink disease.

Harnessing forward multiple scattering for optical imaging deep inside an opaque medium

As light travels through a disordered medium such as biological tissues, it undergoes multiple scattering events. This phenomenon is detrimental to in-depth optical microscopy, as it causes a drastic degradation of contrast, resolution and brightness of the resulting image beyond a few scattering mean free paths. However, the information about the inner reflectivity of the sample is not lost; only scrambled. To recover this information, a matrix approach of optical imaging can be fruitful. Here, we report on a de-scanned measurement of a high-dimension reflection matrix R via low coherence interferometry. Then, we show how a set of independent focusing laws can be extracted for each medium voxel through an iterative multi-scale analysis of wave distortions contained in R. It enables an optimal and local compensation of forward multiple scattering paths and provides a three-dimensional confocal image of the sample as the latter one had become digitally transparent. The proof-of-concept experiment is performed on a human opaque cornea and an extension of the penetration depth by a factor five is demonstrated compared to the state-of-the-art.

Scatter estimation and correction using time-of-flight and deconvolution in x-ray medical imaging.

Objective Time-of-flight (TOF) scatter rejection requires a total timing jitter,
including the detector timing jitter and the X-ray source's pulses width, of 50 ps or less
to mitigate most of the effects of scattered photons in radiography and CT imaging.
However, since the total contribution of the source and detector to the timing jitter
can be retrieved during an acquisition with nothing between the source and detector,
it can be demonstrated that this contribution may be partially removed to improve
the image quality.
Approach A scatter correction method using iterative deconvolution of the measured
time point-spread function estimates the number of scattered photons detected in each
pixel. To evaluate the quality of the estimation, GATE was used to simulate the
radiography of a water cylinder with bone inserts, and a head and torso in a system
with total timing jitters from 100 ps up to 500 ps full-width-at-half-maximum.
Main results With a total timing jitter of 200 ps, 89% of the contrast degradation
caused by scattered photons was recovered in a head and torso radiography, compared
to 28% with a simple time threshold method. Corrected images using the estimation
have a percent root-mean square error between 2 and 14% in both phantoms with
timing jitters from 100 to 500 ps which is lower than the error achieved with scatter
rejection alone at 100 ps.
Significance TOF X-ray imaging has the potential to mitigate the effects of the
scattering contribution and offers an alternative to anti-scatter grids that avoids loss
of primary photons. Compare to simple TOF scatter rejection using only a threshold,
the deconvolution estimation approach has lower requirements on both the source and
detector. These requirements are now within reach of state-of-the-art systems.

Mesoporous chochleate particles doped liquid crystal as normally transparent smart window

A composite layer of homogeneously aligned liquid crystal (LC) doped with nano or mesoporous microparticles (NMPs) has been shown to act as normally opaque smart window (SW) in what is called NMP-LC mode. The porosity of the particle plays two important roles: (i) When the LC infiltrates the particle, it brings its refractive index to be closer to that of its LC surrounding at a certain orientation of the LC molecules and creates a large index mismatch at the orthogonal orientation; (ii) the LC infiltration brings the porous particle density to be closer to the surrounding LC, thus preventing precipitation and floating. Here we demonstrate that LC doped with cochleate cigar-shaped hollow particles and using DMOAP as an alignment layer acts as a normally transparent smart window. Under voltage, the best scenario that explains the polarization-independent scattering is to have the cochleate particles inclined at an angle to balance the dielectric with the elastic forces effectively. The emergence of the scattering mode results from the symbiotic interplay of two distinct phenomena – the NMP effect and the electro-hydrodynamic instability effect. The synergy between these two effects manifests in lower operating voltage and frequency requirements for the device, hence less energy consumption. The scattering increases between 30 °C and 50 °C, thus it acts as a self-adjustable window giving more shade as the outside temperature rises. The threshold voltage is found to decrease with temperature. The SW exhibits high transparency in the OFF state, and high haze in the ON state, and the durability test shows that the SW switches for at least 6 days without degradation of optical contrast.

Temporal contrast degradation from mid-spatial-frequency surface error on stretcher mirrors

Temporal contrast degradation due to mid-spatial-frequency error in chirped-pulse amplification stretcher optics is studied. Third-order cross-correlation measurements reveal a temporal peak that appears when using two different mirrors processed by magnetorheological finishing, despite an improvement in rms roughness compared to a third unprocessed mirror. Simulations based on measured power spectral density show how the actual impact on contrast is different from measurements using a typical bandwidth-limited third-order cross correlator. Strategies are proposed to avoid this type of contrast degradation while exploiting computer numerically controlled polishing techniques for enhancement of surface figure and roughness.

Spectral degradation and carrier sentences increase age-related temporal processing deficits in a cue-specific manner.

Advancing age is associated with decreased sensitivity to temporal cues in word segments, particularly when target words follow non-informative carrier sentences or are spectrally degraded (e.g., vocoded to simulate cochlear-implant stimulation). This study investigated whether age, carrier sentences, and spectral degradation interacted to cause undue difficulty in processing speech temporal cues. Younger and older adults with normal hearing performed phonemic categorization tasks on two continua: a Buy/Pie contrast with voice onset time changes for the word-initial stop and a Dish/Ditch contrast with silent interval changes preceding the word-final fricative. Target words were presented in isolation or after non-informative carrier sentences, and were unprocessed or degraded via sinewave vocoding (2, 4, and 8 channels). Older listeners exhibited reduced sensitivity to both temporal cues compared to younger listeners. For the Buy/Pie contrast, age, carrier sentence, and spectral degradation interacted such that the largest age effects were seen for unprocessed words in the carrier sentence condition. This pattern differed from the Dish/Ditch contrast, where reducing spectral resolution exaggerated age effects, but introducing carrier sentences largely left the patterns unchanged. These results suggest that certain temporal cues are particularly susceptible to aging when placed in sentences, likely contributing to the difficulties of older cochlear-implant users in everyday environments.

Matter-wave interferometers with trapped strongly interacting Feshbach molecules

We implement two types of matter-wave interferometers using trapped Bose-condensed Feshbach molecules, from weak to strong interactions. In each case, we focus on investigating interaction effects and their implications for the performance. In the Ramsey-type interferometer where interference between the two motional quantum states in an optical lattice is observed, interparticle interactions are found to induce energy shifts in the states. Consequently, this results in a reduction of the interferometer frequency and introduces a phase shift during the lattice pulses used for state manipulation. Furthermore, nonuniformity leads to dephasing and collisional effects contribute to the degradation of contrast. In the Michelson-type interferometer, where matter waves are spatially split and recombined in a waveguide, interference is observed in the presence of significant interaction, however coherence degrades with increasing interaction strength. Notably, coherence is also observed in thermal clouds, indicating the white-light nature of the implemented Michelson-type interferometer. Published by the American Physical Society 2024

Reversible data hiding with automatic contrast enhancement for color images

Automatic contrast enhancement (ACE) is a technique that can automatically enhance the image contrast. Reversible data hiding (RDH) with ACE (ACERDH) can achieve ACE while hiding data. However, some methods with good performance for color images suffer from insufficient enhancement. Therefore, an ACERDH method based on the R, G, B, and V channels enhancement is proposed. First, histogram shifting with contrast control is proposed to enhance the R, G, and B channels. It can prevent contrast degradation and histogram shifting from stopping prematurely. Then, the V channel is enhanced. Since some RDH methods with non-ACE that can well enhance the V channel have a low automation level, histogram shifting with brightness control that can realize ACE very well is proposed. It can effectively avoid over-enhancement by controlling the brightness. Experimental results verify that the proposed method improves the image quality and embedding capability better than some state-of-the-art methods.

Degradation of temporal contrast from post-pedestal interference with a chirped pulse in an optical parametric amplifier.

Pre-pedestal generation is observed in a 0.35-PW laser front end coming from a post-pedestal via instantaneous gain and pump depletion in an optical parametric amplifier during chirped-pulse amplification. Generalized simulations show how this effect arises from gain nonlinearity and applies to all optical parametric chirped-pulse-amplification systems with a post-pedestal. An experiment minimizing the effect of B-integral is used to isolate and study the newly observed conversion of a continuous post-pedestal into a continuous pre-pedestal. Matching numerical simulations confirm experimental results and additionally reveal how third-order dispersion largely controls the slope of the generated pre-pedestal.

Underwater Degraded Image Restoration by Joint Evaluation and Polarization Partition Fusion

Images of underwater environments suffer from contrast degradation, reduced clarity, and information attenuation. The traditional method is the global estimate of polarization. However, targets in water often have complex polarization properties. For low polarization regions, since the polarization is similar to the polarization of background, it is difficult to distinguish between target and non-targeted regions when using traditional methods. Therefore, this paper proposes a joint evaluation and partition fusion method. First, we use histogram stretching methods for preprocessing two polarized orthogonal images, which increases the image contrast and enhances the image detail information. Then, the target is partitioned according to the values of each pixel point of the polarization image, and the low and high polarization target regions are extracted based on polarization values. To address the practical problem, the low polarization region is recovered using the polarization difference method, and the high polarization region is recovered using the joint estimation of multiple optimization metrics. Finally, the low polarization and the high polarization regions are fused. Subjectively, the experimental results as a whole have been fully restored, and the information has been retained completely. Our method can fully recover the low polarization region, effectively remove the scattering effect and increase an image’s contrast. Objectively, the results of the experimental evaluation indexes, EME, Entropy, and Contrast, show that our method performs significantly better than the other methods, which confirms the feasibility of this paper’s algorithm for application in specific underwater scenarios.

Multiple Branch Deep Neural Network and Feature Fusion Model for Underwater Image Enhancement

Underwater imaging faces formidable challenges due to light absorption, scattering, and restricted visibility, demanding sophisticated enhancement methods. This research presents a novel Multiple Branch Deep Neural Network and Feature Fusion (MB-DNN-FF) Model tailored specifically for Underwater Images Enhancement (UWIE), with a focus on its application to the UFO120 dataset. Driven by the limitations of existing techniques, our model harnesses the potential of Deep Learning (DL) and Feature Fusion (FF) to effectively address the intricate complexities present in underwater environments. The innovative architecture incorporates multiple branches, each strategically designed to tackle distinct challenges such as contrast degradation, limited visibility, and color distortion. Central to our model is feature fusion, a critical aspect that harmoniously integrates information from diverse branches, thereby enhancing overall image quality. The training and optimization processes are thoroughly detailed, encompassing unique strategies and loss functions fine-tuned for the nuances of UWIE, with emphasis on the characteristics of the UFO120 dataset. Experimental evaluations leverage the comprehensive UFO120 dataset, employing established performance metrics to quantitatively assess the efficacy of our model. Results exhibit substantial improvements over baseline models and state-of-the-art methods, showcasing the effectiveness and versatility of the proposed multiple branch model, particularly on the UFO120 dataset. The discussion interprets these findings in the context of underwater imaging challenges, highlighting the model's effectiveness and outlining potential applications. This research contributes a valuable asset to the area of UWIE, offering a nuanced and potent solution through the integration of multiple branches and feature fusion, validated on the UFO120 dataset. The conclusions underscore the significance of the MB-DNN-FF in advancing the state-of-the-art in UWIE, opening avenues for future research and practical applications in marine sciences, surveillance, and exploration.

An introduction to double stain normalization technique for brain tumour histopathological images

Stain normalization is an image pre-processing method extensively used to standardize multiple variances of staining intensity in histopathology image analysis. Staining variations may occur for several reasons, such as unstandardized protocols while preparing the specimens, using dyes from different manufacturers, and varying parameters set while capturing the digital images. In this study, a double stain normalization technique based on immunohistochemical staining is developed to improve the performance of the conventional Reinhard’s algorithm. The proposed approach began with preparing a target image by applying the contrast-limited adaptive histogram equalization (CLAHE) technique to the targeted cells. Later, the colour distribution of the input image will be matched to the colour distribution of the target image through the linear transformation process. In this study, the power-law transformation was applied to address the over-enhancement and contrast degradation issues in the conventional method. Five quality metrics comprised of entropy, tenengrad criterion (TEN), mean square error (MSE), structural similarity index (SSIM) and correlation coefficient were used to measure the performance of the proposed system. The experimental results demonstrate that the proposed method outperformed all conventional techniques. The proposed method achieved the highest average values of 5.59, 3854.11 and 94.65 for entropy, TEN, and MSE analyses.

The nexus of research and development investment, financial development, energy use, and environmental degradation in Asian economies

AbstractThis study explores the impact of research and development () investment and financial development on environmental degradation measured by carbon emissions (CO2), and energy use along with some other variables in a panel of 12 Asian economies using balanced panel data from 1997 to 2020. The empirical estimates of and dynamic ordinary least squares reveal that spending, financial development, and globalization lower environmental degradation by reducing emissions. In contrast, economic growth, energy use, population, and industrialization increase environmental degradation (Model 1). Moreover, economic growth, R&D spending, financial development, environmental degradation, and industrialization have a positive direct effect on energy use, whereas population and globalization have an inverse relationship with energy use (Model 2). These empirical findings recommend that the management authorities of Asian economies need to develop thoughtful action plans to achieve a balance between economic growth, financial and industrial development, and the accomplishment of sustainable development goals by reducing carbon emissions and sustaining energy consumption.

Synthesis of novel fluorobenzene-thiophene hybrid polymer for high-performance electrochromic devices

Electrochromic devices based on high-performance polymer materials with exceptional optical contrast, superior cycling stability, and large coloration efficiency are critical for the advancement of electrochromics, and have the potential to innovate a broad range of applications, including flexible displays and wearable electronics. Here, we design and synthesize three precursors of fluorobenzene-3-methylthiophene D-A-D type polymers through one-step Stille coupling, and then prepare the corresponding polymer films with good electrochemical and electrochromic properties via low-potential electropolymerization at 0.52 V vs Ag/AgCl. Interestingly, such polymers exhibit overall high electrochromic performances during the electrochemical reaction with inversible color changes between yellow and dark blue, including high optical contrast (83% at 1050 nm), fast response time (1.4 s / 0.8 s), and long-term stability (< 2% reduction after 250 cycles). As-fabricated electrochromic devices display excellent cycling stability (< 3% optical contrast degradation after 1,000 cycles) at a low drive voltage (0.8 V). Due to these excellent electrochromic properties, d-A-D type polymers based on fluorobenzene-3-methylthiophene can be further developed for practical applications such as near-infrared camouflage and E-displays.

Maternal obesity alters the placental transcriptome in a fetal sex-dependent manner.

Infants born to obese mothers have an increased risk of developing obesity and metabolic diseases in childhood and adulthood. Although the molecular mechanisms linking maternal obesity during pregnancy to the development of metabolic diseases in offspring are poorly understood, evidence suggests that changes in the placental function may play a role. Using a mouse model of diet-induced obesity with fetal overgrowth, we performed RNA-seq analysis at embryonic day 18.5 to identify genes differentially expressed in the placentas of obese and normal-weight dams (controls). In male placentas, 511 genes were upregulated and 791 genes were downregulated in response to maternal obesity. In female placentas, 722 genes were downregulated and 474 genes were upregulated in response to maternal obesity. The top canonical pathway downregulated in maternal obesity in male placentas was oxidative phosphorylation. In contrast, sirtuin signaling, NF-kB signaling, phosphatidylinositol, and fatty acid degradation were upregulated. In female placentas, the top canonical pathways downregulated in maternal obesity were triacylglycerol biosynthesis, glycerophospholipid metabolism, and endocytosis. In contrast, bone morphogenetic protein, TNF, and MAPK signaling were upregulated in the female placentas of the obese group. In agreement with RNA-seq data, the expression of proteins associated with oxidative phosphorylation was downregulated in male but not female placentas of obese mice. Similarly, sex-specific changes in the protein expression of mitochondrial complexes were found in placentas collected from obese women delivering large-for-gestational-age (LGA) babies. In conclusion, maternal obesity with fetal overgrowth differentially regulates the placental transcriptome in male and female placentas, including genes involved in oxidative phosphorylation.

82‐1: Distinguished Paper: Radially Variant Contrast in Virtual Reality Headsets

Monocular image quality on virtual reality (VR) head‐mounted displays (HMDs) is radially variant on each eye piece. The virtual image is blurred at the periphery of display field of view primarily by thin lenses stacked on top of the VR display backplane, resulting in image resolution and contrast degradation. Conventional measurement methods adopted from flat‐panel display evaluation do not consider the spatially variant image artifacts by the additional optical components, and thus may not be adequate to assess the image quality in VR. We develop novel test patterns and a new method to measure the radially variant Michelson contrast on VR HMDs. The new method demonstrates efficient VR image quality evaluation using varied interpupillary distance settings.

Radially variant contrast measurement in virtual reality headsets using circular concentric ring patterns

AbstractImage quality on virtual reality (VR) head‐mounted displays (HMDs) is radially variant on each eyepiece from the visual center (optical axis of the HMD) towards the periphery. The virtual image is blurred at the periphery of display field of view (FOV) resulting in contrast and resolution degradation. Conventional measurement methods adopted from flat‐panel display evaluation do not consider the spatially dependent image artifacts by additional optical components such as HMD lenses and thus may not be adequate to assess the VR image quality. We develop a new method using circular concentric ring patterns to measure the radially variant Michelson contrast on multiple VR HMDs. The results show that measured image contrast reduces towards the periphery of display FOV especially at high‐spatial frequencies. In addition, image quality on VR HMDs can be affected by the 3D position of the eye (or the camera) within the eyebox. Specifically, contrast is further degraded if the interpupillary distance (IPD) setting of the HMD does not match that of the user. It also varies with the entrance pupil location of the light‐measuring device. We propose an efficient method for image quality evaluation that can facilitate the regulatory evaluation of VR headsets.

Large-Array Deep Abdominal Imaging in Fundamental and Harmonic Mode.

Deep abdominal images suffer from poor diffraction-limited lateral resolution. Extending the aperture size can improve resolution. However, phase distortion and clutter can limit the benefits of larger arrays. Previous studies have explored these effects using numerical simulations, multiple transducers, and mechanically swept arrays. In this work, we used an 8.8-cm linear array transducer to investigate the effects of aperture size when imaging through the abdominal wall. We acquired channel data in fundamental and harmonic modes using five aperture sizes. To avoid motion and increase the parameter sampling, we decoded the full-synthetic aperture data and retrospectively synthesized nine apertures (2.9-8.8 cm). We imaged a wire target and a phantom through ex vivo porcine abdominal samples and scanned the livers of 13 healthy subjects. We applied bulk sound speed correction to the wire target data. Although point resolution improved from 2.12 to 0.74 mm at 10.5 cm depth, contrast resolution often degraded with aperture size. In subjects, larger apertures resulted in an average maximum contrast degradation of 5.5 dB at 9-11 cm depth. However, larger apertures often led to visual detection of vascular targets unseen with conventional apertures. An average 3.7-dB contrast improvement over fundamental mode in subjects showed that the known benefits of tissue-harmonic imaging extend to larger arrays.

Shadowless Projection Mapping using Retrotransmissive Optics.

This paper presents a shadowless projection mapping system for interactive applications in which a target surface is frequently occluded from a projector with a user's body. We propose a delay-free optical solution for this critical problem. Specifically, as the primary technical contribution, we apply a large format retrotransmissive plate to project images onto the target surface from wide viewing angles. We also tackle technical issues unique to the proposed shadowless principle. First, the retrotransmissive optics inevitably suffer from stray light, which leads to significant contrast degradation of the projected result. We propose to block the stray light by covering the retrotransmissive plate with a spatial mask. Because the mask reduces not only the stray light but the achievable luminance of the projected result, we develop a computational algorithm that determines the shape of the mask to balance the image quality. Second, we propose a touch sensing technique by leveraging the optically bidirectional property of the retrotransmissive plate to support interaction between the user and the projected contents on the target object. We implement a proof-of-concept prototype and validate the above-mentioned techniques through experiments.

Wavefront Sensing by a Common-Path Interferometer for Wavefront Correction in Phase and Amplitude by a Liquid Crystal Spatial Light Modulator Aiming the Exoplanet Direct Imaging

We implemented the common-path achromatic interfero-coronagraph both for the wavefront sensing and the on-axis image component suppression, aiming for the stellar coronagraphy. A common-path achromatic interfero-coronagraph has its optical scheme based on a nulling rotational-shear interferometer. The angle of rotational shear can be chosen at a small angular extent of about 10 deg. Such a small angular shear maintains the coronagraphic contrast degradation known as the stellar leakage effect, caused by a finite stellar size. We study the phase and amplitude wavefront control by a liquid crystal spatial light modulator of reflection type which is used as the pixilated active adaptive optics unit. Therefore, adaptive optics perform a wavefront-correcting input toward a stellar interfero-coronagraph aiming at the direct exoplanet imaging. Presented here are both the numeric evaluations and the lab experiment stand to prove the declared functionality output.