Weighted Low Rank Approximation for Background Estimation Problems

Classical principal component analysis (PCA) is not robust to the presence of sparse outliers in the data. The use of the $\ell_1$ norm in the Robust PCA (RPCA) method successfully eliminates the weakness of PCA in separating the sparse outliers. In this paper, by sticking a simple weight to the Frobenius norm, we propose a weighted low rank (WLR) method to avoid the often computationally expensive algorithms relying on the $\ell_1$ norm. As a proof of concept, a background estimation model has been presented and compared with two $\ell_1$ norm minimization algorithms. We illustrate that as long as a simple weight matrix is inferred from the data, one can use the weighted Frobenius norm and achieve the same or better performance

Characteristics of flight simulator visual systems

The physical parameters of the flight simulator visual system that characterize the system and determine its fidelity are identified and defined. The characteristics of visual simulation systems are discussed in terms of the basic categories of spatial, energy, and temporal properties corresponding to the three fundamental quantities of length, mass, and time. Each of these parameters are further addressed in relation to its effect, its appropriate units or descriptors, methods of measurement, and its use or importance to image quality

Análise da qualidade de medidas F-PIV 2D-2C e 2D-3C da velocidade da fase líquida em uma coluna de bolhas

Orientadores: Sávio Souza Venâncio Vianna, Guilherme José de CastilhoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: A análise da fluidodinâmica em reatores de coluna de bolha é importante na compreensão dos mecanismos relacionados à transferência de calor, transferência de massa e taxa de reação química. A precisão das medições experimentais depende diretamente do domínio de medição. A Velocimetria por imagem de partículas (PIV) é uma técnica não intrusiva utilizada para determinar o campo de velocidade 2D ou 3D. Um campo 2D-3C (bidimensional, três componentes) pode ser determinado por duas câmaras com projeções diferentes numa disposição estereoscópica (PIV 2D-3C). A perda de correlação devido ao movimento fora do plano de pares de imagens de partículas, que é comum em aplicações PIV, pode ser reduzida usando o sistema PIV 2D-3C. Um problema encontrado nas aplicações 2D-3C PIV está relacionado com o acesso óptico em algumas instalações. Para determinar a velocidade da fase líquida, não é interessante registrar as bolhas no escoamento multifásico. Por conseguinte, as partículas traçadoras fluorescentes combinadas com um filtro passa-alta na câmara são utilizadas nos sistemas Fluorescent PIV (F-PIV). Este trabalho tem como objetivo avaliar a qualidade das medidas 2D-2C e 2D-3C F-PIV da velocidade da fase líquida no regime de escoamento homogêneo e de transição homogêneo-heterogêneo de uma seção de coluna de bolha. As imagens 2D-2C e 2D-3C F-PIV foram processadas utilizando standard cross-correlation (SCC), ensemble correlation (EC) e sliding-average correlation (SAC) para comparar a qualidade das medições. O coeficiente de correlação cruzada, a relação sinal-ruído (SNR) e a quantificação de incerteza PIV estimada por estatísticas de correlação foram utilizados como indicadores de qualidade. A baixa concentração de imagem de partícula (baixa ppp) e a baixa faixa dinâmica de velocidade (baixa DVR) foram identificadas como fontes de ruído dominante nas medidas PIV. O efeito do baixo ppp foi relacionado diretamente com o comportamento dos indicadores de qualidade baseados na conectividade de vizinhança espacial, erro de reconstrução 3C e no diâmetro do pico de correlação. Quanto às condições de qualidade da abordagem SCC, foram obtidos cinco limites que garantem que os outliers (falsos vetores) podem ser corrigidos sem que o campo vetorial perca a representatividade do escoamento. No regime de escoamento homogêneo, os ruídos randômicos causados pela baixa ppp foram consideravelmente reduzidos utilizando a abordagem SACAbstract: The fluid dynamics analysis in bubble column reactors is important in understanding the mechanisms related to heat transfer, mass transfer and chemical reaction rate. The accuracy of the experimental measurements depends directly on the measurement domain. Particle image velocimetry (PIV) is a non-intrusive technique used to determine the 2D or 3D velocity field. A 2D-3C (two dimensional, three-component) field can be determined by two cameras with different projections in a stereoscopic arrangement (2D-3C PIV). The loss of correlation due to the out-of-plane motion of pairs of particle images, which is common in PIV applications, can be reduced using the 2D-3C PIV system. A problem encountered in 2D-3C PIV applications is related to optical access in some facilities. In order to determine the liquid phase velocity, it is not interesting to record bubbles in the multiphase flow. Therefore, fluorescent tracer particles combined with a high-pass filter on the camera are used in the Fluorescent PIV (F-PIV) systems. This work aims to evaluate the quality of the 2D-2C and 2D-3C F-PIV measurements of the liquid phase velocity in the homogeneous and homogeneous-heterogeneous transition flow regime of a bubble column. The 2D-2C and 2D-3C F-PIV images were processed using standard cross-correlation (SCC), ensemble correlation (EC), and sliding-average correlation (SAC) to compare the measurements quality. The cross-correlation coefficient, signal-to-noise ratio (SNR) and PIV uncertainty estimated by correlation statistics were used as quality indicators. The low particle image concentration (low ppp) and low dynamic velocity range (low DVR) were identified as dominant noise sources in the PIV measurements. The effect of the low ppp was directly related to the behavior of the quality indicators based on the spatial neighborhood connectivity, 3C reconstruction error, and correlation peak diameter. Regarding the quality conditions for SCC approach, five limits were obtained that guarantee that the outliers can be corrected without the vector field losing the representativeness of the flow. In the homogeneous flow regime, the random noise caused by low ppp was considerably reduced using the SAC approachDoutoradoEngenharia QuímicaDoutor em Engenharia Química2296/2013CAPE

Multispectral photography for earth resources

A guide for producing accurate multispectral results for earth resource applications is presented along with theoretical and analytical concepts of color and multispectral photography. Topics discussed include: capabilities and limitations of color and color infrared films; image color measurements; methods of relating ground phenomena to film density and color measurement; sensitometry; considerations in the selection of multispectral cameras and components; and mission planning

Photogrammetric digital surface model reconstruction in extreme low-light environments

Digital surface models (DSM) have become one of the main sources of geometrical information for a broad range of applications. Image-based systems typically rely on passive sensors which can represent a strong limitation in several survey activities (e.g., night-time monitoring, underground survey and night surveillance). However, recent progresses in sensor technology allow very high sensitivity which drastically improves low-light image quality by applying innovative noise reduction techniques. This work focuses on the performances of night-time photogrammetric systems devoted to the monitoring of rock slopes. The study investigates the application of different camera settings and their reliability to produce accurate DSM. A total of 672 stereo-pairs acquired with high-sensitivity cameras (Nikon D800 and D810) at three different testing sites were considered. The dataset includes different camera configurations (ISO speed, shutter speed, aperture and image under-/over-exposure). The use of image quality assessment (IQA) methods to evaluate the quality of the images prior to the 3D reconstruction is investigated. The results show that modern high-sensitivity cameras allow the reconstruction of accurate DSM in an extreme low-light environment and, exploiting the correct camera setup, achieving comparable results to daylight acquisitions. This makes imaging sensors extremely versatile for monitoring applications at generally low costs

Development of optical methods for real-time whole-brain functional imaging of zebrafish neuronal activity

Each one of us in his life has, at least once, smelled the scent of roses, read one canto of Dante’s Commedia or listened to the sound of the sea from a shell. All of this is possible thanks to the astonishing capabilities of an organ, such as the brain, that allows us to collect and organize perceptions coming from sensory organs and to produce behavioural responses accordingly. Studying an operating brain in a non-invasive way is extremely difficult in mammals, and particularly in humans. In the last decade, a small teleost fish, zebrafish (Danio rerio), has been making its way into the field of neurosciences. The brain of a larval zebrafish is made up of 'only' 100000 neurons and it’s completely transparent, making it possible to optically access it. Here, taking advantage of the best of currently available technology, we devised optical solutions to investigate the dynamics of neuronal activity throughout the entire brain of zebrafish larvae

Pushing Light-Sheet Microscopy to Greater Depths

Light-sheet fluorescence microscopy (LSFM) has established itself as an irreplaceable imaging technique in developmental biology over the past two decades. With its emergence, the extended recording of in toto datasets of developing organisms across scales became possible. Remarkably, LSFM opened the door to new spatio-temporal domains in biology, offering cellular resolution on the one hand, and temporal resolution on the order of seconds on the other hand. As in any fluorescence microscopy technique, LSFM is also affected by image degradation at greater tissue depths. Thus far, this has been addressed by the suppression of scattered light, use of fluorophores emitting in the far red spectrum, multi-view detection and fusion, adaptive optics, as well as different illumination schemes. In this work, I investigate for the first time in vivo optical aberration reduction via refractive index matching in LSFM. Examples are shown on common model organisms as Arabidopsis thalina, Oryzias latipes, Mus musculus, as well as Drosophila. Additionally, I present a novel open-top light-sheet microscope, tailored for high-throughput imaging of mammalian samples, such as early stage mouse embryos. It is based on a three objective geometry, encompassing two opposing detection objective lenses with high light collection efficiency, and an invertedly mounted illumination lens. It bridges the spatial scale between samples by employing an extendible light-sheet illumination via a tunable acoustic gradient index lens. Both parts of this work improve the image quality across the 3D volume of specimens, paving the way for more quantitative recordings at greater tissue depths