Brightness Degradation Research Articles

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.

Исследование микроструктуры люминофоров для лазерных осветительных устройств

A brief description is given of phosphors from various manufacturers that can be used in lighting devices with laser injection in the range of 400–480 nm. An estimate of their energy output and inertia is given. The necessity of studying various types of luminescence to optimize the characteristics of phosphor lighting devices is described. It is known that the optical characteristics of laser lighting devices depend on the quality of the phosphor. However, at the moment there are no well-established methods for studying phosphors for compliance with the requirements for brightness, luminous flux, and thermal degradation. One of these methods can be microscopy, which allows you to study the microstructure of samples. The paper considers a method for determining the geometric and optical parameters of individual phosphor particles used for laser lighting devices using microscopy. On the example of a fine suspension of phosphors, images were obtained and some optical parameters of individual particles with diameters from 40 to 150 nm were determined. The conducted studies demonstrate the high resolution of the microscopy method, which can be used to visualize phosphor particles.

Time-Multiplexed PWM LED Driver With Grayscale Enhancement Techniques for Signage Display

In this article, a pulsewidth modulation (PWM) LED driver is proposed to overcome the challenges of time-multiplexed driving and to enhance the quality of displays sufficient for signage applications. First, adaptive duty cycle restoration (ADCR) compensates for the brightness degradation in low grayscale, where a simple analog timer circuit measures the limited charging time and compensates its effect to ensure the desired emission time. Second, amplitude-segmented PWM (ASPWM) improves the grayscale resolution without increasing the grayscale clock frequency; thus, the electromagnetic interference performance is not sacrificed. The proposed LED driver is fabricated in a 0.18-μm Bipolar-CMOS-DMOS (BCD) process. The measurement results show that the driver Integrated Circuit (IC) achieves a duty cycle restoration factor (DCRF) greater than 0.95 out of ten samples, whereas the DCRF is limited to 0.67 on average when the ADCR scheme is disabled. Resolution enhancement with the proposed ASPWM is verified, achieving 16-b grayscale resolution. The prototype driver IC occupies 3.56 × 3.00 mm of chip area, operated from a 4.5 V supply voltage.

CoSyR: A novel beam dynamics code for the modeling of synchrotron radiation effects

The self-consistent nonlinear dynamics of a relativistic charged particle beam interacting with its complete self-fields is a fundamental problem underpinning many of the accelerator design issues in high brightness beam applications, as well as the development of advanced accelerators. Particularly, synchrotron radiation induced effects in a magnetic dispersive beamline element can lead to collective beam instabilities and emittance growth. A novel beam dynamics code is developed based on a Lagrangian method for the calculation of the particles’ radiation near-fields using wavefront/wavelet meshes via the Green’s function of the Maxwell equations. These fields are then interpolated onto a moving mesh for dynamic update of the beam. This method allows radiation co-propagation and self-consistent interaction with the beam in 2D/3D simulations at greatly reduced numerical errors. Multiple levels of parallelisms are inherent in this method and implemented in our code CoSyR to enable at-scale simulations of nonlinear beam dynamics on modern computing platforms using MPI, multi-threading, and GPUs. The current 2D implementation of CoSyR has been used to evaluate the transverse and longitudinal coherent radiation effects on the beam and to investigate beam optics designs proposed for mitigation of beam brightness degradation in a magnetic bunch compressor. In this paper, the design of CoSyR, as well as the benchmark with other coherent synchrotron radiation models, are described and discussed. Extension of the core algorithms to 3D is possible and planned.

Low-light image enhancement via deep Retinex decomposition and bilateral learning

Low-light images enhancement is a challenging task because enhancing image brightness and reducing image degradation should be considered simultaneously. Although existing deep learning-based methods improve the visibility of low-light images, many of them tend to lose details or sacrifice naturalness. To address these issues, we present a multi-stage network for low-light image enhancement, which consists of three sub-networks. More specifically, inspired by the Retinex theory and the bilateral grid technique, we first design a reflectance and illumination decomposition network to decompose an image into reflectance and illumination maps efficiently. To increase the brightness while preserving edge information, we then devise an attention-guided illumination adjustment network. The reflectance and the adjusted illumination maps are fused and refined by adversarial learning to reduce image degradation and improve image naturalness. Experiments are conducted on our rebuilt SICE low-light image dataset, which consists of 1380 real paired images and a public dataset LOL, which has 500 real paired images and 1000 synthetic paired images. Experimental results show that the proposed method outperforms state-of-the-art methods quantitatively and qualitatively.

Contrast Enhancement Using Inverted Gaussian Histogram Specification Technique

Contrast enhancement has become a vital process in improving the human perception as well as machine perception, due to the enormous application of digital imaging techniques in various fields like medical, aerospace, agriculture, machine vision, automation, surveillance, etc. During contrast enhancement by various existing techniques, the advent of adverse side effects like brightness degradation, intensity saturation and appearance of artifacts in the enhanced images is a critical issue, which needs more research attention. In this paper, an inverted Gaussian histogram specification technique for contrast enhancement of differently skewed images is proposed, in which the pixel concentration on either side of the histogram is increased to overcome the drawbacks in the existing methods. The proposed technique uses parameters like mean, standard deviation and inversion constant to generate various inverted Gaussian specified histograms. Further, transformation and objective functions are used to identify the best desired histogram so as to obtain the best enhanced image for the given image. The performance of the proposed method is compared with other existing techniques on the images taken from various standard databases. The experimental results show that the proposed technique is best suitable for contrast enhancement of images with differently skewed histograms.

Manipulating Ion Migration for Highly Stable Light-Emitting Diodes with Single-Crystalline Organometal Halide Perovskite Microplatelets.

Ion migration has been commonly observed as a detrimental phenomenon in organometal halide perovskite semiconductors, causing the measurement hysteresis in solar cells and ultrashort operation lifetimes in light-emitting diodes. In this work, ion migration is utilized for the formation of a p-i-n junction at ambient temperature in single-crystalline organometal halide perovskites. The junction is subsequently stabilized by quenching the ionic movement at a low temperature. Such a strategy of manipulating the ion migration has led to efficient single-crystalline light-emitting diodes that emit 2.3 eV photons starting at 1.8 V and sustain a continuous operation for 54 h at ∼5000 cd m-2 without degradation of brightness. In addition, a whispering-gallery-mode cavity and exciton-exciton interaction in the perovskite microplatelets have both been observed that can be potentially useful for achieving electrically driven laser diodes based on single-crystalline organometal halide perovskite semiconductors.

The photon pair source that survived a rocket explosion.

We report on the performance of a compact photon pair source that was recovered intact from a failed space launch. The source had been embedded in a nanosatellite and was designed to perform pathfinder experiments leading to global quantum communication networks using spacecraft. Despite the launch vehicle explosion soon after takeoff, the nanosatellite was successfully retrieved from the accident site and the source within it was found to be fully operational. We describe the assembly technique for the rugged source. Post-recovery data is compared to baseline measurements collected before the launch attempt and no degradation in brightness or polarization correlation was observed. The survival of the source through an extreme environment provides strong evidence that it is possible to engineer rugged quantum optical systems.

Study of Three-Dimensional Image Brightness Loss in Stereoscopy

When viewing three-dimensional (3D) images, whether in cinemas or on stereoscopic televisions, viewers experience the same problem of image brightness loss. This study aims to investigate image brightness loss in 3D displays, with the primary aim being to quantify the image brightness degradation in the 3D mode. A further aim is to determine the image brightness relationship to the corresponding two-dimensional (2D) images in order to adjust the 3D-image brightness values. In addition, the photographic principle is used in this study to measure metering values by capturing 2D and 3D images on television screens. By analyzing these images with statistical product and service solutions (SPSS) software, the image brightness values can be estimated using the statistical regression model, which can also indicate the impact of various environmental factors or hardware on the image brightness. In analysis of the experimental results, comparison of the image brightness between 2D and 3D images indicates 60.8% degradation in the 3D image brightness amplitude. The experimental values, from 52.4% to 69.2%, are within the 95% confidence interval

Performance Evaluation of Filters for Enhancement of Images in Different Application Areas

Contrast stretching is a method to enhance the image details. Histogram equalization is one of the most common spatial domain technique used for contrast enhancement. While stretching the contrast of an image , it results in the degradation of brightness of the image. To overcome this hurdle a method known as Bi- Histogram equalization was introduced to preserve the brightness level of the output image. As the contrast enhancement enhances the image , it also enhances the noise in the signal that causes the blurrness in the output image. The proposed BHEGF method reduces this drawback and provides more accurate and realistic results. In this paper we use four different types of filters i.e. median filter , gaussian filter , average filter & motion filter and various parameters such as processing time , MSE, brightness count and PSNR are used for performance evaluation. Keywords: Bi- Histogram Equalization , Tri- histogram equalization ,BHEGF , Contrast enhancement , Gaussian filter , brightness preserving , Spatial and frequency domain. I. Introduction The main purpose of image enhancement is to enhance or improve the quality of image with the minimum amount of MSE. Various enhancement techniques are used for this purpose both in spatial domain and frequency domain. This paper emphasizes mainly on spatial domain technique of image enhancement. The histogram equalization is the most commonly used technique for contrast enhancement and brightness preservation of the image. There are various techniques used to equalizes the given image's histogram such as BHE, DSHE, AHE, CHE, MHE, MMBEBHE, RMSHE. In all these technique the image have to first decomposed and then the histogram of each part generated from the decomposition is equalized . That is also known as the segmentation of an image into various sub-images. Segmentation of the image can be done in various ways such as amplitude thresholding, component labeling, boundary based approaches, region based approaches, template matching, texture based segmentation. In this paper, the image is segmentized on the bases of its component levels. Then the resultant histograms of the sub-images are equalized, while equalizing the histograms the impulse noises present in the images are also get enhanced along with the enhancement of the image (4) . Hence to overcome this drawback due to noise in the satellite imaging, this paper proposed the use of the Gaussian filter to filter out the noise from the enhanced image . The use of Gaussian filter shell reduced the MSE to a larger extent from the enhanced image . 1.1 Image Enhancement Image enhancement is a process of improving the quality of image by improving its features. The techniques used for image enhancement can be used to improve the image's contrast and brightness characteristics and reduces its noise contents or sharpen its details they can be classified as subjective enhancement and objective enhancement (9). Subjective enhancement techniques may be repeatedly applied in various forms until the observer feels that the image yields the details necessary for particular application. On the other hand objective image enhancement corrects an image for known degradation. This enhancement is not repeatedly applied but it is applied only once based on the measurement taken from the system. Image enhancement can also be categorized into two main and broad categories. They are as follows:

Viewing quality-enhanced reconstruction of 3-D object images by using a modified computational integral- imaging reconstruction technique

The conventional computational integral-imaging reconstruction (CIIR) method has some drawbacks of intensity irregularity and brightness degradation in the reconstructed pane object images (POIs) due to its insufficient and uneven overlapping of the projected elemental images. Thus, in this paper, a modified CIIR (M-CIIR) technique is proposed to dramatically enhance the viewing quality of the computationally reconstructed object images. For this, a pixel-count matrix (PCM) is introduced in the CIIR process to calculate the number of overlapped pixels of the projected elemental images in the reconstructed object plane. Each pixel value of the reconstructed POI, then, is determined as the average of all overlapped pixel values. As the pixel values of the reconstructed POI are regulated by the PCM, viewing quality of the reconstructed POIs can be dramatically improved in the proposed method. In order to show the feasibility of the proposed method, experiments are performed, and the results are compared and discussed with those of the conventional method.

32.3: Invited Paper: Large‐Area, Ultraflexible Organic AMLED Pixel Circuits Driven by Printed Organic Floating‐Gate Transistors

AbstractWe have demonstrated an ultraflexible active matrix organic LED pixel circuit on 13‐μm thin‐film plastics for applications to medical sensors and treatments. The circuit that applies printed floating‐gate organic transistors can compensate LED brightness variations and degradation for more than 6 months. The 230times230 mm2 printed active matrix circuit comprises 64times64 screen‐printed organic 2‐transistor‐1‐capacitor cells.

Properties of single-walled carbon nanotube-based poly(phenylene vinylene) electroluminescent nanocomposites

Devices with varying concentrations of single-walled carbon nanotubes (SWNTs) dispersed in three derivatives of poly(p-phenylene vinylene) are prepared, and their electroluminescent properties evaluated. Increasing the concentration of SWNTs improves the electrical conductivity of the nanocomposites. However, an undesired increase in the electroluminescence (EL) turn-on voltage is observed for the hybrids, possibly due to photoluminescence quenching of excitons by the SWNTs. At relatively low concentrations of SWNTs, there is an increase in the EL lifetime; in contrast, at relatively high concentrations of SWNTs, due to photoluminescence quenching by the nanotubes, significant reduction in brightness and faster degradation of the EL performance of the devices is observed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

A novel 3-TFT voltage driving method of compensating V TH shift for a-Si:H TFT and OLED degradation for AMOLED

This work demonstrates the feasibility of a novel pixel circuit by using three a-Si:H TFTs. The proposed circuit can stabilize the OLED current and provide an additional driving current to ameliorate the brightness degradation of the AMOLED. Measurement results indicate that the current degradation of the proposed circuit, caused by V TH variations, is less than 5% over more than 50,000 s at 60 °C, whereas that of a conventional 2T1C pixel circuit is larger than 34%. Furthermore, to ameliorate the decrease in luminance owing to the OLED degradation, the OLED current can be increased by 10% by analyzing the current degradation and modulating the detected voltage appropriately.

Spectral properties of two frequency harmonic undulator radiations and effect of energy spread

Abstract The dynamics of complex spectral properties of two frequency harmonic undulator radiations along on and off axis has been analytically investigated using the techniques of generalized Bessel functions. The relativistic electron beams with non negligible energy spread results in degradation in brightness and gain. The effect of energy spread on two frequency harmonic undulator (TFHU) radiations and on axis gain has been analyzed. Maximum acceptable r.m.s. value of energy spread has been determined to support the complex spectral pattern of radiation and gain.

Reliability improvement of InGaN LED backlight module by accelerated life test (ALT) and screen policy of potential leakage LED

In this paper, to improve the reliability of InGaN white LED Backlight module, we have analyzed the module level accelerated life test (ALT) for LED which is used for the front display in the refrigerator. In addition, we have suggested a screen method that enables to screen out LEDs which have potential leakage problems. The stress factors and levels were decided based on the end user environment in the field. The acceleration factor (AF) was logically calculated according to the stress factor. After 12 h of ALT, we have found one brightness degradation in 6480 LEDs (98 modules). It was found from the failure analysis that the leakage was from the P-pad electrode failure and caused the brightness degradation. We have suggested a method that enables to screen the potential field failure LEDs in mass production which the failure can be occurred by external noise factor. We have added “turn on current level screen” on “operating current level screen”. As a result, we could make possible to screen leakage LEDs effectively which may fail in the end user side. This method was applied by 20 LED makers.

DESIGN OF A 2 kA, 30 fs RF-PHOTOINJECTOR FOR WATERBAG COMPRESSION

Because uniformly filled ellipsoidal ‘waterbag’ bunches have linear self-fields in all dimensions, they do not suffer from space-charge induced brightness degradation. This in turn allows very efficient longitudinal compression of high-brightness bunches at sub or mildly relativistic energies, a parameter regime inaccessible up to now due to detrimental effects of non-linear space-charge forces. To demonstrate the feasibility of this approach, we investigate ballistic bunching of 1 MeV, 100 pC waterbag electron bunches, created in a half-cell rf-photogun, by means of a two-cell booster-compressor. Detailed GPT simulations of this table-top set-up are presented, including realistic fields, 3D space-charge effects, path-length differences and image charges at the cathode. It is shown that with a single 10MW S-band klystron and fields of 100 MV/m, 2kA peak current is attainable with a pulse duration of only 30 fs at a transverse normalized emittance of 1.5 μm.

Heavy-ion-fusion-science: summary of US progress

Over the past two years noteworthy experimental and theoretical progress has been made towards the top-level scientific question for the US programme on heavy-ion-fusion-science and high energy density physics: ‘How can heavy-ion beams be compressed to the high intensity required to create high energy density matter and fusion conditions?’ New results in transverse and longitudinal beam compression, high-brightness transport and beam acceleration will be reported. Central to this campaign is final beam compression. With a neutralizing plasma, we demonstrated transverse beam compression by an areal factor of over 100 and longitudinal compression by a factor of > 50. We also report on the first demonstration of simultaneous transverse and longitudinal beam compression in plasma. High beam brightness is key to high intensity on target, and detailed experimental and theoretical studies on the effect of secondary electrons on beam brightness degradation are reported. A new accelerator concept for near-term low-cost target heating experiments was invented, and the predicted beam dynamics validated experimentally. We show how these scientific campaigns have created new opportunities for interesting target experiments in the warm dense matter regime. Finally, we summarize progress towards heavy-ion fusion, including the demonstration of a compact driver-size high-brightness ion injector. For all components of our high intensity campaign, the new results have been obtained via tightly coupled efforts in experiments, simulations and theory.

Semiconductor high-energy radiation scintillation detector

We propose a new scintillation-type detector in which high-energy radiation generates electron–hole pairs in a direct-gap semiconductor material that subsequently recombine producing infrared light to be registered by a photo-detector. The key issue is how to make the semiconductor essentially transparent to its own infrared light, so that photons generated deep inside the semiconductor could reach its surface without tangible attenuation. We discuss two ways to accomplish this, one based on doping the semiconductor with shallow impurities of one polarity type, preferably donors, the other by heterostructure bandgap engineering. The proposed semiconductor scintillator combines the best properties of currently existing radiation detectors and can be used for both simple radiation monitoring, like a Geiger counter, and for high-resolution spectrography of the high-energy radiation. An important advantage of the proposed detector is its fast response time, about 1 ns, essentially limited only by the recombination time of minority carriers. Notably, the fast response comes without any degradation in brightness. When the scintillator is implemented in a qualified semiconductor material (such as InP or GaAs), the photo-detector and associated circuits can be epitaxially integrated on the scintillator slab and the structure can be stacked-up to achieve virtually any desired absorption capability.

LED-backlight feedback control system with integrated amorphous-silicon color sensor on an LCD panel

— Thin-film-transistor liquid-crystal displays (TFT-LCDs) have the largest market share of all digital flat-panel displays. An LCD backlighting system employing a three-color red-green-blue light-emitting diode (RGB-LED) array is very attractive, considering its wide color gamut, tunable white point, high dimming ratio, long lifetime, and environmental compatibility. But the high-intensity LED has problems with thermal stability and degradation of brightness over time. Color and white luminance levels are not stable over a wide range of temperature due to inherent long-term aging characteristics. In order to minimize color point and brightness differences over time, optical feedback control is the key technology for any LED-backlight system. In this paper, the feasibility of an optical color-sensing feedback system for an LED backlight by integrating the amorphous-silicon (a-Si) color sensor onto the LCD panel will be presented. To minimize the photoconductivity degradation of a-Si, a new laser exposure treatment has been applied. The integrated color-sensor optical-feedback-controlled LED-backlight system minimized the color variation to less than 0.008 Δu'v' (CIE1976) compared to 0.025 for an open-loop system over the temperature range of 42–76°C.