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An objective function based technique for devignetting fundus imagery using MST
摘要： Fundus photography is a powerful imaging modality that is utilized for detecting macular degeneration, retinal neoplasms, choroid disturbances, glaucoma and diabetic retinopathy. As the illumination source in fundus imaging is situated at the center of the fundus camera, the illumination at the peripheral regions of the images would be relatively less than the center, which is termed vignetting. Vignetting adversely affects the performance of computerized methods for analyzing fundus imagery. A devignetting method for fundus imagery based on the Modified Sigmoid Transform (MST) is proposed in this paper. Gain (A) and centering parameter (α) of MST have a crucial influence on its performance. For low values of the gain, local contrast is penalized, and the overall dynamic range is compressed. When the value of gain is very high, the images after the illumination correction will have a washed out appearance. The optimum value of gain is determined in this paper from an objective method based on two statistical indices, Average Gradient of Illumination Component (AGIC) and Error of Enhancement (EME). MST with gain value defined via objective methods is able to correct the uneven illumination in fundus images without penalizing the local contrast. The proposed method is compared with illumination equalization model, homomorphic filtering and Adaptive Gamma Correction (AGC) and was found to be superior in terms of ‘naturality’, uniformity of background illumination, and computational speed.
关键词： Devignetting,Objective function,Error of Enhancement,illumination correction,Average Gradient of Illumination Component,Modified Sigmoid Transform (MST),fundus imagery
更新于2025-09-09 09:28:46
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Quantum Illumination with Noiseless Linear Amplifier
摘要： Quantum illumination, that is, quantum target detection, is to detect the potential target with two-mode quantum entangled state. For a given transmitted energy, the quantum illumination can achieve a target-detection probability of error much lower than the illumination scheme without entanglement. We investigate the usefulness of noiseless linear amplification (NLA) for quantum illumination. Our result shows that NLA can help to substantially reduce the number of quantum entangled states collected for joint measurement of multi-copy quantum state. Our analysis on the NLA-assisted scheme could help to develop more efficient schemes for quantum illumination.
关键词： noiseless linear amplification,quantum target detection,quantum illumination
更新于2025-09-09 09:28:46
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Downlink resource allocation for dynamic TDMA-based VLC systems
摘要： Visible light communications (VLC) in general and resource allocation for VLC networks particularly have gained lots of attention recently. In this work, we consider the resource allocation problem of a VLC downlink transmission system employing dynamic time division multiple access where time and power variables are tuned to maximize spectral ef?ciency (SE). As for the operational conditions, we impose constraints on the average optical intensity, the energy budget and the quality-of-service. To solve the non-convex problem, we transform the objective function into a difference of concave functions by solving a second order differential inequality. Then, we propose a low-complexity algorithm to solve the resource allocation problem. Finally, we show by simulations the SE performance gains achieved by optimizing time and power allocation over the initial total power minimization solution for the considered system.
关键词： spectral ef?ciency,resource allocation,DC programming,illumination constraint,Visible light communication
更新于2025-09-09 09:28:46
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Faster, sharper, and deeper: structured illumination microscopy for biological imaging
摘要： Structured illumination microscopy (SIM) allows rapid, super-resolution (SR) imaging in live specimens. We review recent technical advances in SR-SIM, with emphasis on imaging speed, resolution, and depth. Since its introduction decades ago, the technique has grown to offer myriad implementations, each with its own strengths and weaknesses. We discuss these, aiming to provide a practical guide for biologists and to highlight which approach is best suited to a given application.
关键词： Structured illumination microscopy,resolution,biological imaging,super-resolution imaging,imaging speed,depth
更新于2025-09-09 09:28:46
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Theoretical Framework for Spatial Resolution in Edge-Illumination X-Ray Tomography
摘要： Edge-illumination tomography is a modality for performing x-ray phase-contrast imaging in 3D, based on structuring the primary beam into an array of beamlets and employing a dedicated incoherent sensing mechanism. In this article, we provide a theoretical framework for the spatial resolution of this method, based on the concept of the bowtie-shaped essential support of the Radon transform in frequency space, which is well known in conventional tomography. The additional complexity caused by the use of beamlets is added to the model, and its validity is confirmed by means of simulated and experimental results. In essence, we show that the precise location of non-negligible entries in the two-dimensional frequency spectrum of an edge-illumination sinogram can be predicted by only two parameters, the beamlet width and the sample thickness. This enables the derivation of sampling schemes tailored to avoid aliasing, thus maximizing spatial resolution.
关键词： beamlets,Radon transform,edge-illumination tomography,spatial resolution,x-ray phase-contrast imaging
更新于2025-09-09 09:28:46
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Single-sample face recognition under varying lighting conditions based on logarithmic total variation
摘要： The logarithmic total variation (LTV) algorithm is a classical algorithm that is proposed to address the illumination interference in face recognition. Some state-of-the-art techniques based on LTV assume that the illumination component mainly lies in the low-frequency features among face images. However, these techniques adopt unsuitable methods to process low-frequency features, resulting in ?nal unsatisfactory recognition rates. In this paper, we propose an improved illumination normalization method based on the LTV method, called the RETINA&TH-LTV algorithm. In this algorithm, the retina model is utilized to eliminate most of the illumination component in low-frequency features. Then, an advanced contrast-limited adaptive histogram equalization technique is proposed to remove the residual lighting component. At the same time, through realizing threshold-value ?ltering on high-frequency features, the enhancement of facial features is achieved. Finally, the processed frequency features are combined to form a robust holistic feature image, which is then utilized for recognition. Insuf?cient training images in face recognition are also taken into consideration in this research. Comparative experiments for single-sample face recognition are conducted on YALE B, CMU PIE and our self-built driver databases. The nearest neighbor classi?er and extended sparse representation classi?er are employed as classi?cation methods. The results indicate that the RETINA&TH-LTV algorithm has promising performance, especially in serious illumination and insuf?cient training sample conditions.
关键词： Logarithmic total variation,Face recognition,Illumination normalization,Low- and high-frequency features
更新于2025-09-09 09:28:46
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[IEEE 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Atlanta, GA (2017.10.21-2017.10.28)] 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Comparing Different Preprocessing Methods in Automated Segmentation of Retinal Vasculature
摘要： Computer methods and image processing provide medical doctors assistance at any time and relieve their work load, especially for iterative processes like identifying objects of interest such as lesions and anatomical structures from the image. Vescular detection is considered to be a crucial step in some retinal image analysis algorithms to find other retinal landmarks and lesions, and their corresponding diameters, to use as a length reference to measure objects in the retina. The objective of this study is to compare effect of two preprocessing methods on retinal vessel segmentation methods, Laplacian-of-Gaussian edge detector (using second-order spatial differentiation), Canny edge detector (estimating the gradient intensity), and Matched filter edge detector either in the normal fundus images or in the presence of retinal lesions like diabetic retinopathy. The steps for the segmentation are as following: 1) Smoothing: suppress as much noise as possible, without destroying the true edges, 2) Enhancement: apply a filter to enhance the quality of the edges in the image (sharpening), 3) Detection: determine which edge pixels should be discarded as noise and which should be retained by thresholding the edge strength and edge size, 4) Localization: determine the exact location of an edge by edge thinning or linking. From the accuracy view point, comparing to manual segmentation performed by ophthalmologists for retinal images belonging to a test set of 120 images, by using first preprocessing method, Illumination equalization, and contrast enhancement , the accuracy of Canny, Laplacian-of-Gaussian, and Match filter vessel segmentation was more than 85% for all databases (MUMS-DB, DRIVE, MESSIDOR). The performance of the segmentation methods using top-hat preprocessing (the second method) was more than 80%. And lastly, using matched filter had maximum accuracy for the vessel segmentation for all preprocessing steps for all databases.
关键词： contrast Enhancement,image processing,Diabetic retinopathy,top hat transformation,Laplacian-of-Gaussian edge detector,Illumination Equalization,retinal blood vessel,Match filter,Canny edge detector
更新于2025-09-09 09:28:46
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Light-Assisted Room-Temperature NO2 Sensors Based on Black Sheet-Like NiO
摘要： In this study, we use two-dimensional black flake nickel oxide as the sensitive material which was synthesized by a facile hydrothermal route. The as-synthesized sheet-like NiO possessed a large specific surface area, as verified by BET characterization. The as-prepared NiO nanosheets had strong absorption in the range of 250–800 nm including UV and visible light. Upon exposure to ppb-level NO2, the presented sensors showed significant responses under light illumination at room temperature. In addition, the light wavelength also had a remarkable effect on the sensing performance in terms of sensitivity, response and recovery kinetics. Furthermore, the sensor showed a low humidity dependence.
关键词： NiO,light illumination,room temperature,NO2
更新于2025-09-09 09:28:46
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A Smart System for Low-Light Image Enhancement with Color Constancy and Detail Manipulation in Complex Light Environments
摘要： Images are an important medium to represent meaningful information. It may be difficult for computer vision techniques and humans to extract valuable information from images with low illumination. Currently, the enhancement of low-quality images is a challenging task in the domain of image processing and computer graphics. Although there are many algorithms for image enhancement, the existing techniques often produce defective results with respect to the portions of the image with intense or normal illumination, and such techniques also inevitably degrade certain visual artifacts of the image. The model use for image enhancement must perform the following tasks: preserving details, improving contrast, color correction, and noise suppression. In this paper, we have proposed a framework based on a camera response and weighted least squares strategies. First, the image exposure is adjusted using brightness transformation to obtain the correct model for the camera response, and an illumination estimation approach is used to extract a ratio map. Then, the proposed model adjusts every pixel according to the calculated exposure map and Retinex theory. Additionally, a dehazing algorithm is used to remove haze and improve the contrast of the image. The color constancy parameters set the true color for images of low to average quality. Finally, a details enhancement approach preserves the naturalness and extracts more details to enhance the visual quality of the image. The experimental evidence and a comparison with several, recent state-of-the-art algorithms demonstrated that our designed framework is effective and can efficiently enhance low-light images.
关键词： naturalness preservation,Retinex theory,image enhancement,color constancy,camera response framework,low illumination
更新于2025-09-09 09:28:46
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Advances in photonic quantum sensing
摘要： Quantum sensing has become a broad field. It is generally related with the idea of using quantum resources to boost the performance of a number of practical tasks, including the radar-like detection of faint objects, the readout of information from optical memories, and the optical resolution of extremely close point-like sources. Here, we first focus on the basic tools behind quantum sensing, discussing the most recent and general formulations for the problems of quantum parameter estimation and hypothesis testing. With this basic background in hand, we then review emerging applications of quantum sensing in the photonic regime both from a theoretical and experimental point of view. Besides the state of the art, we also discuss open problems and potential next steps.
关键词： quantum hypothesis testing,quantum parameter estimation,photonic quantum sensing,optical resolution,quantum reading,quantum sensing,quantum illumination
更新于2025-09-09 09:28:46