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Halliday, Colin George. "Aspects of photometric titration." Thesis, Queen's University Belfast, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329513.
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Powell, Christopher. "Mutual illumination photometric stereo." Thesis, University of East Anglia, 2018. https://ueaeprints.uea.ac.uk/67065/.
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Many techniques have been developed in computer vision to recover three-dimensional shape from two-dimensional images. These techniques impose various combinations of assumptions/restrictions of conditions to produce a representation of shape (e.g. surface normals or a height map). Although great progress has been made it is a problem which remains far from solved. In this thesis we propose a new approach to shape recovery - namely `mutual illumination photometric stereo'. We exploit the presence of colourful mutual illumination in an environment to recover the shape of objects from a single image.
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Pocino, Yuste Andrea. "Cosmology with photometric redshift." Doctoral thesis, Universitat Autònoma de Barcelona, 2020. http://hdl.handle.net/10803/671733.
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Els cartografiats de galàxies fotomètrics actuals i futurs observaran un gran volum de l’univers que ens permetrà acotar amb precisió el model cosmològic. Tanmateix, la capacitat de delimitar el model que tenen aquests cartografiats a través de les sondes cosmològiques depèn de la precisió i certesa amb les que es determina el redshift de les galàxies. Per tant, la determinació del redshift fotomètric i els seus efectes en les anàlisis cosmològiques han de ser tractats i estudiats curosament.
En la primera part de la tesi, transformem la fotometria de simulacions que ja existeixen per imitar les mesures fotomètriques del Dark Energy Survey (DES). D’aquesta manera, esperem recuperar la distribució real del redshift fotomètric en simulacions, i així crear una base encara més realista per comprovar els resultats de les anàlisis cosmològiques de DES que fan us del redshift fotomètric. Per transformar les simulacions utilitzem diversos mètodes que transfereixen les propietats estadístiques de la fotometria d’observacions real a les simulacions.
A la segona part de la tesi, utilitzem la tècnica del Self-Organizing Map per seleccionar galàxies per ser observades amb espectroscòpia, contribuint així al projecte C3R2 que vol establir un mapa correlacional entre l’espai de colors i redshift i omplir-ho amb informació espectroscòpica. En aquesta part també explorem l’espai de colors definit per la fotometria del Physics of the Accelerating Universe Survey (PAUS) per tal d’estudiar la cobertura del redshift espectroscòpic del seu espai de colors. Volem determinar la quantitat d’espai de color sense cobertura espectroscòpica perquè la falta de representació d’espectroscòpia pot ser una font de biaix quan la precisió dels redshifts fotomètrics és avaluada comparant-los amb redshifts espectroscòpics o quan els redshifts espectroscòpics s’utilitzen com a mostra d’entrenament per determinar els redshifts fotomètrics amb algoritmes d’entrenament.
Finalment, explorem com la variació en la profunditat de les observacions des de terra combinades amb les d’Euclid afecta la precisió dels redshifts fotomètrics i, per tant, la capacitat de determinar els paràmetres cosmològics d’Euclid sobretot quan utilitza galaxy clustering i galaxy-galaxy lensing com a sondes cosmològiques. També estudiem com la densitat de les mostres de galàxies afecta la capacitat de delimitar els paràmetres cosmològics i quina és la configuració de bins tomogràfics de redshift que permet extreure la màxima informació per delimitar els paràmetres cosmològics. Per tal de dur a terme aquesta anàlisi, creem diverses distribucions realistes de redshift fotomètric basades en la simulació Flagship d’Euclid i utilitzem el formalisme de Fisher per fer una estimació de la capacitat d’acotament dels paràmetres cosmològics de les diferents configuracions de les mostres de galàxies.Los cartografiados de galaxias fotométricos actuales y futuros observarán un gran volumen del universo que nos permitirá acotar con precisión el modelo cosmológico. Aun así, la capacidad de los cartografiados para delimitar el modelo a través de las sondas cosmológicas depende de la precisión y certeza con las que se determina el redshift de las galaxias. Por lo tanto, la determinación del redshift fotométrico y sus efectos en los análisis cosmológicos deben ser tratados y estudiados cuidadosamente. En la primera parte de la tesis, transformamos la fotometría de simulaciones que ya existen para imitar las mediciones fotométricas del Dark Energy Survey (DES). De esta forma, esperamos recuperar la distribución real del redshift fotométrico en simulaciones, y así crear una base aún más realista para comprobar los resultados de los análisis cosmológicos de DES que usan redshifts fotométricos. Para transformar las simulaciones utilizamos diversos métodos que transfieren las propiedades estadísticas de la fotometría de observaciones reales a las simulaciones. En la segunda parte de la tesis, utilizamos la técnica del Self-Organizing Map para seleccionar galaxias para ser observadas con espectroscopia, contribuyendo así al proyecto C3R2 que quiere establecer un mapa correlacional entre el espacio de colores y redshift y llenarlo con información espectroscópica. En esta parte también exploramos el espacio de colores definido por la fotometría del Physics of the Accelerating Universe Survey (PAUS) con tal de estudiar la cobertura del redshift espectroscópico de su espacio de colores. Queremos determinar la cantidad del espacio de color sin cobertura espectroscópica porque la falta de representación espectroscópica puede originar un sesgo cuando la precisión del redshift fotométrico se evalúa comparándolo con el redshift espectroscópico o cuando el redshift espectroscópico se utiliza como muestra de entrenamiento para determinar el redshift fotométrico con algoritmos de entrenamiento. Finalmente, exploramos como la variación en la profundidad de las observaciones desde tierra combinadas con las de Euclid afecta la precisión de los redshifts fotométricos y, por lo tanto, la capacidad de Euclid para determinar los parámetros cosmológicos sobre todo cuando se utilizan galaxy clustering y galaxy-galaxy lensing como sondas cosmológicas. También estudiamos como la densidad de las muestras de galaxias afecta la capacidad de acotar los parámetros cosmológicos y cuál es la configuración de bines tomográficos de redshift que permiten extraer la máxima información para delimitar los parámetros cosmológicos. Para llevar a cabo este análisis, creamos diversas distribuciones realistas de redshift fotométrico basadas en la simulación Flagship de Euclid y utilizamos el formalismo de Fisher para hacer una estimación de la capacidad de acotar los parámetros cosmológicos de las diferentes configuraciones de las muestras de galaxias.
Current and future photometric surveys will observe a large volume of the universe that will allow us to accurately constrain the cosmological model. However, the constraining power from cosmological probes of photometric surveys highly relies on the accuracy and precision with which we can determine the galaxies redshifts. Therefore, the determination of photometric redshifts (photo-zs) and their effect in cosmological analysis should be treated and studied carefully. In the first part of this thesis, we transform the photometry of existing simulations to mimic the photometric measurements of the Dark Energy Survey (DES). With this exercise, we expect to recover the real photo-z distribution in simulations, thus creating a more realistic environment to crosscheck the performance of DES in cosmological analyses that use photo-z. We transform the simulations using several method to transfer the statistical properties from the real observations photometry to the simulations. In the second part of the thesis, we use the Self-Organizing Map technique to select spectroscopic targets for the C3R2 program aimed at establishing the mapping between color and redshift space. We also explore the color space defined by the photometry of galaxies from the Physics of the Accelerating Universe Survey (PAUS) in order to study the spectroscopic redshift coverage of its color space. We want to quantify the regions of color space without spectroscopic redshifts because the lack of spectroscopic representation can be a source of bias when the accuracy of photo-zs is evaluated by comparing it to spectroscopic redshifts and when the spectroscopic redshifts are used to determine the photo- z with training-based algorithms. Lastly, we explore how the variation of the depth of ground-based observations combined with Euclid observations affects the accuracy and precision of the photo-z and thus the cosmological constraining power of Euclid focusing on photometric galaxy clustering and galaxy-galaxy lensing analyses. We also study how the number density of photometric galaxy samples affects the constraining power and which tomographic redshift binning configuration returns the maximum information to constrain the cosmological parameters. To perform such analyses, we create several realistic photo-z distributions based on the Euclid Flagship simulation and we use the Fisher forecast and the cosmological inference code, CosmoSIS, over the different configurations of the galaxy samples to determine the cosmological constraining power.
Universitat Autònoma de Barcelona. Programa de Doctorat en Física
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Bezanson, Rachel, David A. Wake, Gabriel B. Brammer, Pieter G. van Dokkum, Marijn Franx, Ivo Labbé, Joel Leja, et al. "LEVERAGING 3D-HST GRISM REDSHIFTS TO QUANTIFY PHOTOMETRIC REDSHIFT PERFORMANCE." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621218.
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We present a study of photometric redshift accuracy in the 3D-HST photometric catalogs, using 3D-HST grism redshifts to quantify and dissect trends in redshift accuracy for galaxies brighter than JH(IR) > 24 with an unprecedented and representative high-redshift galaxy sample. We find an average scatter of 0.0197 +/- 0.0003(1 + z) in the Skelton et al. photometric redshifts. Photometric redshift accuracy decreases with magnitude and redshift, but does not vary monotonically with color or stellar mass. The 1 sigma scatter lies between 0.01 and 0.03 (1 + z) for galaxies of all masses and colors below z. <. 2.5 (for JH(IR) < 24), with the exception of a population of very red (U - V > 2), dusty star-forming galaxies for which the scatter increases to similar to 0.1 (1+ z). We find that photometric redshifts depend significantly on galaxy size; the largest galaxies at fixed magnitude have photo-zs with up to similar to 30% more scatter and similar to 5 times the outlier rate. Although the overall photometric redshift accuracy for quiescent galaxies is better than that for star-forming galaxies, scatter depends more strongly on magnitude and redshift than on galaxy type. We verify these trends using the redshift distributions of close pairs and extend the analysis to fainter objects, where photometric redshift errors further increase to similar to 0.046 (1 + z) at H-F160W = 26. We demonstrate that photometric redshift accuracy is strongly filter dependent and quantify the contribution of multiple filter combinations. We evaluate the widths of redshift probability distribution functions and find that error estimates are underestimated by a factor of similar to 1.1 - 1.6, but that uniformly broadening the distribution does not adequately account for fitting outliers. Finally, we suggest possible applications of these data in planning for current and future surveys and simulate photometric redshift performance in the Large Synoptic Survey Telescope, Dark Energy Survey (DES), and combined DES and Vista Hemisphere surveys.
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Blake, R. Melvin. "Photometric decomposition of NGC 6166." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq22790.pdf.
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Silva, Fernández Simón Yeco. "Photometric Redshifts in the HDFS." Tesis, Universidad de Chile, 2015. http://repositorio.uchile.cl/handle/2250/133104.
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Magíster en Ciencias, Mención AstronomíaSe presenta fotometría óptica en 11 bandas medias a partir de observaciones realizadas con el telescopio de 2.2m en LSO (WFI) sobre un campo de ~30'×30' deg extendido en el Hubble Deep Field-South (EHDF-S), el cual es uno de los campos que contiene información en multibandas como parte del Multiwavelength Survey by Yale-Chile (MUSYC). Este campo tiene una gran cantidad de datos públicos y datos auxiliares en bandas UV, óptico, infrarrojo cercano e infrarrojo lejano. Se determinaron aperturas óptimas para fotometría de alta precisión para diversas fuentes y brillos. Se proporcionan incertezas en magnitud a través de una técnica mejorada que considera correlaciones a mayor y menor escala en el ruido. Se incluyen datos auxiliares en el óptico a partir del catálogo de MUSYC en bandas UBVRIz ' hasta una magnitud total de R=25 (AB), además de datos en infrarrojo cercano JHK de dos campos de 10 '× 10' deg con profundidades de J~22.5, H~21.5 y K~21 (5σ; Vega). Se creó un catálogo fotométrico de ~62.000 galaxias detectadas en la imagen BVR de MUSYC. Se miden redshifts fotométricos mediante el código EAzY y se compara con ~500 fuentes identificadas espectroscópicamente con la finalidad de probar la precisión y desempeño de los filtros en bandas medias. Los redshifts fotométricos resultaron más confiables para R<24 cuando la muestra contiene ~12.000 galaxias, particularmente en 0.1 < z < 1.2, región de sampleo en el óptico de características como el quiebre de Balmer. La precisión de los redshifts fotométricos en Δz/(1+z) es de 0.029, lo cual es comparable a estudios recientes con un mejoramiento del 20%. Estos valores se degradan en calidad para galaxias más débiles o cuando se utilizan menos bandas. Como demostración de la calidad de los resultados, se derivan tipos espectrales de las fuentes, luego se construyen funciones de luminosidad para comparar con trabajos similares, y así confirmar la fuerte dependencia de las SEDs con la densidad numérica de fuentes. Se incorporan datos observacionales en radio en el HDFS del Australia Telescopio Hubble Deep Field-South para estudiar en detalle su población. Este proyecto realizó observaciones en cuatro longitudes de onda, 20, 11, 6 y 3 cm y alcanza una sensibilidad en rms alrededor de 10 μJy para cada longitud de onda. Utilizando una muestra de 227 fuentes en radio seleccionadas, se realiza una clasificación detallada de la población en AGNs (-loud de radio (9%) y -quiet (46%)), galaxias con formación estelar (SFG; 39%), y galaxias normales (6%), usando los redshifts fotométricos, información en multibanda, un template combinado quasares, índices espectrales, las SEDs derivadas y la dependencia redshift luminosidad. Se confirman los resultados recientes sobre la disribución de AGNs y SFGs. Asimismo las LFs muestran consistencia para las fuentes en radio para z~1.0. Los resultados obtenidos siguen la tendencia de los trabajos previos de los últimos 4 a 5 años en la distribución de las fuentes de radio, y sugiere nuevas metodologías en torno a la caracterizacón la población en radio.
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Campisi, Andrea. "Development of a photometric stereo system." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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Photometric stereo is a method of estimating surface geometry by using a fixed-position camera and multiple light sources. The idea of photometric stereo is to vary the direction of incident illumination between successive images, while the viewing direction is constant; in this way, the correspondence of image points is known beforehand, as the position of the object is not changed, and surface orientation is determined by using the radiance values recorded with the different images. Photometric stereo has several applications: it is used to detect small surface defects, imperceptible to the human eye; it has also medical applications, i.e. to detect skin lesions and help in the diagnosis of melanoma. More recently, it has been used also to perform a non-invasive 3D scan of surfaces, and as a cheap method to get a real-time facial motion capture, widely used in computer graphics applications.
The goals of this thesis are to describe the main algorithms used to achieve a photometric stereo analysis of surfaces, and the realization of a hardware device capable of acquire the images.
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Botzler, Christine S. "Finding Structures in Photometric Redshift Surveys." Diss., lmu, 2004. http://nbn-resolving.de/urn:nbn:de:bvb:19-22187.
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Buyukatalay, Soner. "Photometric Stereo Considering Highlights And Shadows." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613749/index.pdf.
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Three dimensional (3D) shape reconstruction that aims to reconstruct 3D surface of objects
using acquired images, is one of the main problems in computer vision. There are many
applications of 3D shape reconstruction, from satellite imaging to material sciences, considering
a continent on earth or microscopic surface properties of a material. One of these
applications is the automated firearm identification that is an old, yet an unsolved problem in
forensic science. Firearm evidence matching algorithms rely on the fact that a firearm creates
characteristic marks on surfaces of the bullets and the cartridge cases. These marks should
be digitized unaffected from different surface material properties of evidences. Accuracy of
3D shape is one of the most important parameters affecting the overall identification performance.
A very high resolution, accurate 3D data have to be reconstructed in the order of
minutes. Photometric stereo (PS) method is capable of reconstructing high resolution surfaces
in a fast manner. But, the metallic material and the surface topology of the firearm evidences
generate highlights and shadows on their images that does not comply with the assumptions
of conventional PS. In the scope of this work, it is intended to design an accurate, fast and
robust 3D shape reconstruction scheme using PS considering highlights and shadows. These
new PS procedures to be developed here should not be limited only to the ballistic evidences
but they also could be used for a wider range of objects reflection properties and texture. For
this purpose, masked PS methods which are quite fast when compared to other approaches,
were classified and implemented. Simple additional masking methods are also proposed. A
novel weighted PS method, using weighted least square estimation, is presented to eliminate
false edges created by the masks. Concurrently, the calibration processes and the illumination
configuration were improved. The disturbances due to close light sources were removed
by image calibrations. From experimental tests to simulate the light positioning problem, it
is concluded that the double zenith illumination configuration have better performance than
the optimal single zenith illumination configuration, when the highlights and the shadows are
considered. Double zenith illumination configuration results were further improved by the
weighted normal PS with a small additional computation cost. All the implemented methods
were tested firstly on the controlled environment using synthetic images. Later the same tests
were conducted on real objects with varying characteristics as well as the firearm evidences.
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Samaddar, Debasmita. "Photometric variability of three brown dwarfs." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 2.24 Mb., 65 p, 2006. http://proquest.umi.com/pqdlink?did=1075713471&Fmt=7&clientId=8331&RQT=309&VName=PQD.
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Howell, Steve Bruce. "Photometric observations of faint cataclysmic variables." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 1995. http://dare.uva.nl/document/92246.
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St, Germaine Michael Tyler. "Improving Photometric Redshift Measurements Using BPZ." Thesis, The University of Arizona, 2013. http://hdl.handle.net/10150/297785.
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Redshift measurements are used in astrophysics to measure distances and to constrain fundamental cosmological quantities. Although spectroscopic redshifts (spec-z) are much more reliable than photometric redshifts (photo-z), they are much more difficult or time-consuming to obtain. We seek to optimize photo-z measurements, i.e. bring their values closer to the "true" spec-z values, by using a tool called BPZ. We investigate the changes in photo-z resulting from modified galaxy templates using the SDSS catalogue of galaxies. We also consider the effect of adding artificial noise to galaxy spectra. The photo-z values were most improved when the templates contained emission lines, and noise of the same degree as in the catalogue.
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Hansen, Mark F. "3D face recognition using photometric stereo." Thesis, University of the West of England, Bristol, 2012. http://eprints.uwe.ac.uk/16754/.
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Automatic face recognition has been an active research area for the last four decades. This thesis explores innovative bio-inspired concepts aimed at improved face recognition using surface normals. New directions in salient data representation are explored using data captured via a photometric stereo method from the University of the West of England’s “Photoface” device. Accuracy assessments demonstrate the advantage of the capture format and the synergy offered by near infrared light sources in achieving more accurate results than under conventional visible light. Two 3D face databases have been created as part of the thesis – the publicly available Photoface database which contains 3187 images of 453 subjects and the 3DE-VISIR dataset which contains 363 images of 115 people with different expressions captured simultaneously under near infrared and visible light. The Photoface database is believed to be the ?rst to capture naturalistic 3D face models. Subsets of these databases are then used to show the results of experiments inspired by the human visual system. Experimental results show that optimal recognition rates are achieved using surprisingly low resolution of only 10x10 pixels on surface normal data, which corresponds to the spatial frequency range of optimal human performance. Motivated by the observed increase in recognition speed and accuracy that occurs in humans when faces are caricatured, novel interpretations of caricaturing using outlying data and pixel locations with high variance show that performance remains disproportionately high when up to 90% of the data has been discarded. These direct methods of dimensionality reduction have useful implications for the storage and processing requirements for commercial face recognition systems. The novel variance approach is extended to recognise positive expressions with 90% accuracy which has useful implications for human-computer interaction as well as ensuring that a subject has the correct expression prior to recognition. Furthermore, the subject recognition rate is improved by removing those pixels which encode expression. Finally, preliminary work into feature detection on surface normals by extending Haar-like features is presented which is also shown to be useful for correcting the pose of the head as part of a fully operational device. The system operates with an accuracy of 98.65% at a false acceptance rate of only 0.01 on front facing heads with neutral expressions. The work has shown how new avenues of enquiry inspired by our observation of the human visual system can offer useful advantages towards achieving more robust autonomous computer-based facial recognition.
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Regnault, Nicolas. "Photometric Calibration of Wide Field Imagers." Habilitation à diriger des recherches, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-01045107.
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Cette thèse d'habilitation consiste en trois petits articles de revue indépendants, couvrant mes activités passées au sein du groupe de cosmologie du LPNHE. Le premier chapitre est consacré à la mesure de l'histoire de l'expansion cosmique avec des supernovae de type Ia (SNe Ia). Les techniques de détermination de distance de luminosité mises en oeuvre au sein du Supernova Legacy Survey (SNLS) sont détaillées. Les résultats de l'analyse des trois premières années de données du SNLS sont présentés. Le second chapitre traite d'un ingrédient essentiel de ce type d'analyse, à savoir la calibration photométrique des imageurs grand-champ utilisés pour mesurer le flux des supernovae. Les techniques développées pour la calibration du survey SNLS (Regnault et al, 2009), puis quelques années plus tard pour l'intercalibration des surveys SNLS et SDSS-II (Betoule et al, 2013) sont présentées en détail. Enfin, le dernier chapitre présente les nouveaux projets de calibration instrumentale imaginés par plusieurs équipes dans le monde. Dans notre exposé, l'accent est mis sur le projet de calibration DICE, développé par le groupe du LPNHE. Au coeur de DICE est une source de calibration multi-longueur d'onde ultra-stable, réalisée au laboratoire, et testée notamment auprès du Canada-France-Hawaii Telescope (CFHT, Mauna Kea, Hawaii).
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Van, Heerden Hendrik Petrus. "Robotic control of a photometric telescope." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/11399.
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The objective of this project was to design and implement the telescope control software for the Alan Cousins Telescope (ACT), a robotic telescope at the Sutherland, South Africa, site of the South African Astronomical Observatory (SAAO). The approach adopted involved a high level of modularisation of the software and the use of software simulators in an effort to foster rapid software development and enable more rigorous software testing. Significant attention was also paid to new and emerging technologies and how these may be used within the specific context of robotic telescope control software. The software now acts as a demonstration platform for those technologies that were implemented.
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McMenemy, K. R. "Photometric evaluation of aerodrome ground lighting." Thesis, Queen's University Belfast, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273182.
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Berntsson, Robin. "Photometric stereo for eye tracking imagery." Thesis, Linköpings universitet, Medie- och Informationsteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-139019.
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The goal of this work is to examine the possibility of surface reconstruction from the images produced by the Tobii H5 eye tracker. It starts of by examining classic photometric stereo and its limitations under the illuminator configuration of the eye tracker. It then proceeds to investigate two alternative solutions: photometric stereo under the assumption that the albedo is known and a method that uses the images from the eye tracker as a guide to mold a reference model into the users face. In the second method the pose of the reference model is estimated by minimizing a photometric error under the assumption that the face is Lambertian, using particle swarm optimization. The position of the generic 3D model is then used in an attempt to mold its shape into the face of the user using shape-from-shading.
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Yang, Qian, Xue-Bing Wu, Xiaohui Fan, Linhua Jiang, Ian McGreer, Richard Green, Jinyi Yang, et al. "Quasar Photometric Redshifts and Candidate Selection: A New Algorithm Based on Optical and Mid-infrared Photometric Data." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/627092.
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We present a new algorithm to estimate quasar photometric redshifts (photo-zs), by considering the asymmetries in the relative flux distributions of quasars. The relative flux models are built with multivariate Skew-t distributions in the multidimensional space of relative fluxes as a function of redshift and magnitude. For 151,392 quasars in the SDSS, we achieve a photo-z accuracy, defined as the fraction of quasars with the difference between the photo-z z(p) and the spectroscopic redshift z(s), vertical bar Delta z vertical bar=vertical bar z(s)-z(p)vertical bar/(1 + z(s)) within 0.1, of 74%. Combining the WISE W1 and W2 infrared data with the SDSS data, the photo-z accuracy is enhanced to 87%. Using the Pan-STARRS1 or DECaLS photometry with WISE W1 and W2 data, the photo-z accuracies are 79% and 72%, respectively. The prior probabilities as a function of magnitude for quasars, stars, and galaxies are calculated, respectively, based on (1) the quasar luminosity function, (2) the Milky Way synthetic simulation with the Besancon model, and (3) the Bayesian Galaxy Photometric Redshift estimation. The relative fluxes of stars are obtained with the Padova isochrones, and the relative fluxes of galaxies are modeled through galaxy templates. We test our classification method to select quasars using the DECaLS g, r, z, and WISE W1 and W2 photometry. The quasar selection completeness is higher than 70% for a wide redshift range 0.5 < z < 4.5, and a wide magnitude range 18 < r < 21.5 mag. Our photo-z regression and classification method has the potential to extend to future surveys. The photo-z code will be publicly available.
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Domeniconi, Federico. "Deep Learning Techniques applied to Photometric Stereo." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20031/.
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La tesi si focalizza sullo studio dello stato dell’arte della fotometria stereo con deep learning: Self-calibrating Deep Photometric Stereo Networks. Il modello è composto è composto di due reti, la prima predice la direzione e l’intensità delle luci, la seconda predice le normali della superficie. L’obiettivo della tesi è individuare i limiti del modello e capire se possa essere modifcato per avere buone prestazioni anche in scenari reali. Il progetto di tesi è basato su fine-tuning, una tecnica supervisionata di transfer learning. Per questo scopo un nuovo dataset è stato creato acquisendo immagini in laboratorio. La ground-truth è ottenuta tramite una tecnica di distillazione. In particolare la direzione delle luci è ottenuta utilizzando due algoritmi di calibrazione delle luci e unendo i due risultati. Analogamente le normali delle superfici sono ottenute unendo i risultati di vari algoritmi di fotometria stereo. I risultati della tesi sono molto promettenti. L’errore nella predizione della direzione e dell’intensità delle luci è un terzo dell’errore del modello originale. Le predizioni delle normali delle superfici possono essere analizzate solo qualitativamente, ma i miglioramenti sono evidenti. Il lavoro di questa tesi ha mostrato che è possibile applicare transfer-learning alla fotometria stereo con deep learning. Perciò non è necessario allenare un nuovo modello da zero ma è possibile approfittare di modelli già esistenti per migliorare le prestazioni e ridurre il tempo di allenamento.
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Borstad, Eriksen Martin. "Cross-correlating spectroscopic and photometric galaxy surveys." Doctoral thesis, Universitat Autònoma de Barcelona, 2014. http://hdl.handle.net/10803/133261.
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En esta tesis se estudia el acotamiento en los paraámetros cosmología al
combinar observaciones en catálogos de galaxias espectroscópicas y
fotométricos. Los catálogos fotométricos miden las distorsiones de lente
gravitacional débil (WL), mientras que los catalogos espectroscópicos, con más
alta precisión en la información de redshift (o corriento al rojo), son ideales
para el estudio de distorsiones espaciales de redshift (RSD). El análisis
combinado se realiza únicamente com funciones de correlación angular, lo que
simplifica el estudio, en particular en lo que respecta a la inclusión de la
covarianza entre observables.
El primer capítulo presenta un nuevo algoritmo para el cálculo eficaz de las
correlaciones cruzadas de varios marcadores, incluidos WL en correlaciones
cruzadas con bines estrechos. Estimar la función de correlación angular es
particularmente costoso dado que el número de correlaciones cruzadas aumenta
como O(n^2), donde $n$ es el número de bines en redshift.
Más adelante, el capítulo estudia el efecto de aproximación de Limber, y RSD en
el modelado de correlaciones auto y cruzadas. Para bines de redshift delgados,
la aproximación de Limber deja de funcionar y no permite incorporar las
correlaciones cruzadas. Al disminuir el ancho de los bines en redshift, crece
la amplitude de correlacion y el efecto de RSD, lo que redundará en beneficio
del acotamiento de parametros cosmológicos. Una tendencia interesante es la
contribución de las oscilaciones acústicas de bariones (BAO) en la correlacion
cruzadas entre bines de distitnto redshift. La separacion en redshift entre dos
bines reduce la amplitud de las correlaciones en escalas pequeñas, lo que
aumenta el contraste en el BAO. También estudiamos la relación señal-ruido de
diferentes correlaciones cruzadas.
El segundo Capítulo presenta un pronóstico de cotas en la historia de la
expansión y del crecimiento cósmico, usando un catalogo spectroscópico y otro
fotométrico ficticios de 14000 grados cuadrados cada uno. Cuando estos
catalogos se sobrelapan en la misma region del cielo, encontramos mejores cotas
en los parametros cosmológicos. Esto es debido a las correlaciones cruzadas
adicionales entre catálogos y la reducción de la varianza en el muestreo
(debida a la covarianza entre trazadores). En primer lugar mostramos un estudio
por separado de la dependencia en el ancho de bin en redshift, en RSD, en BAO y
en WL. Encontramos ganancias equivalentes a tener el 30% mas de área en los
catalogos cuando estos se superponen en el cielo. Por último, analizamos el
origen de esta moderada ganancia en el contexto de la literatura existente.
Diferentes grupos han reportado que al solapar los catalogos o bien no
encuentran ningún beneficio o bien encuentran grandes beneficios. Nosotros
sugerimos que la covarianza entre observables y el uso de diferentes
observables puede explicar estas diferencias.
El sesgo (bias) en galaxias, relaciona las sobredensidades de galaxias con las
del campo de fluctuaciones de materia, de manera que la incertidumbre en el
bias limita las predicciones. Por ello investigamos con detalle como las
correlaciones cruzadas, RSD, BAO y WL afectan las medidas del bias en galaxias.
En particular, cuando los catalogos sobrelapan disminuyen los errores en el
bias para la muestras fotométrica. La última seccion cuantifica los
beneficios de los "priors'' y los efectos de la estocasticidad en el bias. El
impacto de las incertidumbres en las estocasticidad es menor cuando hay
sobrelapamiento.In this thesis we study constraining cosmology when combining spectroscopic and photometric galaxy survey. The photometric survey measures galaxy shape distortions from Weak Lensing (WL), while high precision redshift information makes spectroscopic surveys ideal for redshift space distortions (RSD). The combined analysis is performed entirely in angular-correlation functions, which simplifies the joined analysis, in particular the inclusion of covariance between then. The first chapter introduce a novel algorithm for efficiently calculating the cross-correlations of multiple tracers (i.e. galaxy types/luminosities) and including WL in narrow redshift bin cross-correlations. Estimating the angular-correlations function is in particular demanding since the number for cross-correlations increase O(n^2) with $n$ being the number of redshift bins. Later the chapter study the effect of Limber approximation and RSD on the modeling of auto- and cross-correlations. For thin redshift bins, the Limber approximation completely breaks down and does not allow cross-correlations between redshift bins. Decreasing the bin width increases the amplitude of the galaxy correlations and the effect of RSD, which will benefit the cosmological constraints. One interesting trend is the baryon acoustic oscillation (BAO) contribution in the cross-correlations of redshift bins. The redshift separations between two bins reduce small-scale clustering, hence increasing the BAO contrast. We also study the signal-to-noise of different cross-correlations. The second chapter forecast the constraints on the cosmic expansion and growth history, using two fiducial 14000 sq deg. spectroscopic and photometric galaxy surveys. Overlapping surveys (same sky) has improved constraints from additional cross-correlations and sample variance cancellations (covariance in multiple tracers). We study first separate how redshift bin width, RSD, BAO and WL affect the forecast. We find gains equivalent to 30\% larger areas when using overlapping surveys. Last, we discuss the origen of this moderate gain in the context of existing literature. Different groups reports either none or high benefits for overlapping galaxy surveys. We suggest the covariance between surveys and different same-sky definitions (i.e. different observables) can explain the differences. Galaxy bias relate the galaxy overdensities to the underlying matter fluctuations, and the uncertainty in galaxy bias strongly affects the forecast. We therefore investigate in detail how cross-correlations, RSD, BAO and WL affects constraints on galaxy bias. Overlapping surveys in particular increase constraint on the bias from the photometric sample. Last section quantify the benefit of priors and the effect of bias stochasticity. The impact of uncertainties in bias stochasticity is less for overlapping surveys.
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Alarcon, Gonzalez Alex. "Higher resolution photometric redshifts for cosmological surveys." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/669762.
Full textAbstract:
Aquesta tesi doctoral està centrada en la mesura del desplaçament al vermell (redshift) fotomètric en cartografiats de galàxies fotogràfiques i en les seves aplicacions per a extreure informació cosmològica. En la primera part d'aquesta tesi fem un pronòstic amb la tècnica de matrius de Fisher per a un cartografiat de galàxies que tingui mesures molt precises del redshift fotomètric - que poden venir tant d'espectroscòpia com de múltiples fotografies amb filtre estret. Fem servir correlacions angulars de galàxies, és a dir, com es distribueixen espacialment les galàxies, dividint una mostra en dues submostres fent servir altres paràmetres observables. Fer servir dues mostres que es superposen redueix la variancia mostral en els observables, cosa que millora la precisió amb la qual es poden mesurar la història d'expansió i de creixement d'estructures en l'univers. En la segona part d'aquesta tesi mesurem redshifts fotomètrics de manera molt precisa fent servir dades d'un cartografiat de galàxies innovador anomenat PAUS que conté un conjunt únic de 40 filtres estrets. Desenvolupem dos algoritmes que fan servir estadística de màxima versemblança o d'integral Bayesiana per a deduir la probabilitat en redshift de cada galàxia, cosa que requereix modelar tant el flux del continu com el flux de les línies d'emissió de la galàxia. L'algoritme conté diverses correccions que tenen en compte els efectes sistemàtics que es troben en la calibració de les dades. Aquestes correccions s'examinen en simulacions que s'han desenvolupat per aquest motiu. Les mesures de redshifts fotomètrics a PAUS fan possible la ciència que es vol dur a terme i també es poden fer servir per a calibrar la distribució de redshifts de cartografiats de galàxies que mesuren l'efecte de lent dèbil. La darrera part d'aquesta tesi implementa per primer cop un model bayesià jeràrquic en una simulació de N cossos per a mesurar la distribució en redshift fotomètric d'un mapa de galàxies de lent dèbil fent servir tant informació de fotometria com de densitat. L'efecte de lent dèbil és un mètode molt poderós per extreure informació cosmològica, però és molt sensible a qualsevol esbiaix en la mitjana del redshift fotomètric d'una mostra de galàxies. Aquest mètode combina de manera consistent totes les fonts d'informació i fusiona les tècniques més típiques que es fan servir a la literatura per a estimar les distribucions en redshift.This PhD thesis is focused on the measurement of photometric redshifts in imaging galaxy surveys and its applications to extract cosmological information. In the first part of this thesis we forecast a galaxy survey with very precise redshift information, which can come either from spectroscopy or many narrow band images, using the Fisher matrix formalism. We use galaxy clustering, how galaxies group together in space, dividing a sample into two subsamples using other observable parameters. Using two overlapping subsamples reduces the sample variance in the observables, which improves the precision with which one can measure the expansion and growth history of the universe. In the second part of this thesis we measure highly precise photometric redshifts using the data from a novel imaging galaxy survey PAUS that contains a unique set of 40 narrow band filters. We develop two algorithms which use maximum likelihood or Bayesian evidence statistics to infer the redshift probability of each galaxy, which requires modeling both the continuum and emission line galaxy flux. The algorithm contains several corrections to account for systematic effects present in the data calibration which are tested in simulations developed for this purpose. The measurement of PAUS redshifts enables the science of the galaxy survey and can also be used to calibrate the redshift distribution of lensing surveys. The last part of this thesis implements for the first time a hierarchical Bayesian model in an N-body simulation to measure the redshift distribution of a lensing survey using both photometric and density information. Weak lensing is a very powerful tool to extract cosmological information, but it is very sensitive to any bias in the mean redshift of a sample of source galaxies. This method consistently combines all sources of information and merges the main techniques used in the literature to estimate redshift distributions.
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Lopéz-Cruz, Omar. "Photometric properties of low-redshift galaxy clusters." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ27999.pdf.
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Sethuram, Amrutha Shree. "Reconstruction of Lambertian Surfaces from Photometric Stereo." NCSU, 2005. http://www.lib.ncsu.edu/theses/available/etd-03142005-133624/.
Full textAbstract:
The objective of this thesis is to implement and compare two algorithms to reconstruct the shape of an object from photometric stereo. Photometric stereo is a practical technique for determining an object?s shape and surface reflectance properties at a distance. The implementation proposes the use of three images of an object, recorded from the same viewpoint but with different illumination. The first algorithm employs the Fourier transform method to solve the minimization problem. The gradient data is obtained by incorporating photometric stereo method on image triplets. The Fourier transform of the unknown surface is then expressed as a function of the Fourier transform of the gradients. The relative depth values are then obtained by applying an inverse Fourier transform of the function. The second algorithm is based on iterative reconstruction which minimizes the cost function by gradient descent and annealing. Both these algorithms are implemented to reconstruct both real and synthetic surfaces and the results are compared. It is also shown that better reconstruction results are obtained by adopting the second algorithm in the presence of discontinuities in the image. Noise sensitivity of the frequency-domain method is also evaluated. An experimental setup to obtain real world images is also presented.
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Stokman, Harro. "Robust photometric invariance in machine color vision." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2000. http://dare.uva.nl/document/56969.
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Babusiaux, Carine. "Photometric studies of the Milky Way Galaxy." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615732.
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Farooq, Abdul Rehman. "Dynamic photometric stereo for complex surface analysis." Thesis, University of the West of England, Bristol, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409451.
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McAllister, Martin J. "Photometric mass determinations of eclipsing cataclysmic variables." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/19647/.
Full textAbstract:
Cataclysmic variables (CVs) are a type of close, interacting binary system containing a white dwarf primary and a low-mass, Roche lobe-filling secondary/donor. Mass is commonly transferred from the donor to an accretion disc around the white dwarf, due to the conservation of angular momentum, before eventually reaching the surface of the white dwarf. A region of increased luminosity, termed the 'bright spot', exists at the intersection of accretion disc and mass transfer stream. The transfer of mass within the system is a turbulent process, giving rise to random photometric variations commonly referred to as 'flickering'. For high inclination systems, the donor eclipses all other components within the system, resulting in complex eclipse light curves that can be fit with a parameterised model to obtain system parameters. Eclipses of the white dwarf and bright spot occur in quick succession, and therefore precise eclipse modelling requires high-time-resolution photometry. Flickering is a hindrance to eclipse modelling, however, as it can obscure ingress/egress features of the component eclipses, and therefore existing studies use eclipse averaging to minimise its effects. In this thesis, a new approach to eclipse modelling is introduced, which involves modelling flickering through the utilisation of Gaussian processes (GPs). The new modelling approach is implemented on ULTRACAM/ULTRASPEC eclipse light curves of 18 eclipsing CVs, returning 18 sets of precise system parameters. Four of these systems have been modelled previously using the existing approach, while 14 are modelled for the first time. The 18 new/revised white dwarf and donor masses from this work are used alongside other CV component masses from the literature in an attempt to secure a better understanding of CVs and their evolution. One of the outcomes is a new estimate for the CV orbital period minimum, 79.57+-0.22 min, which is over 2 min shorter than previously thought.
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Cuesta, Contreras Angel. "Geometric and photometric affine invariant image registration." Thesis, Heriot-Watt University, 2009. http://hdl.handle.net/10399/2228.
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This thesis aims to present a solution to the correspondence problem for the registration of wide-baseline images taken from uncalibrated cameras. We propose an affine invariant descriptor that combines the geometry and photometry of the scene to find correspondences between both views. The geometric affine invariant component of the descriptor is based on the affine arc-length metric, whereas the photometry is analysed by invariant colour moments. A graph structure represents the spatial distribution of the primitive features; i.e. nodes correspond to detected high-curvature points, whereas arcs represent connectivities by extracted contours. After matching, we refine the search for correspondences by using a maximum likelihood robust algorithm. We have evaluated the system over synthetic and real data. The method is endemic to propagation of errors introduced by approximations in the system.
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Osborn, Hugh P. "Long-period exoplanets from photometric transit surveys." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/98252/.
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Photometric transit surveys on the ground & in space have detected thousands of transiting exoplanets, typically by analytically combining the signals from multiple transits. This technique of exoplanet detection was exploited in K2 to detect nearly 200 candidate planets, and extensive follow-up was able to confirm the planet K2-110b as a 2:6 0:1R , 16:7 3:2M planet on a 14d orbit around a K-dwarf. The ability to push beyond the time limit set by transit surveys to detect long-period transiting objects from a single eclipse was also studied. This was performed by developing a search technique to search for planets around bright stars in WASP and NGTS photometry, finding NGTS to be marginally better than WASP at detecting such planets with 4:14 0:16 per year compared to 1:43 0:15, and detecting many planet candidates for which follow-up is on-going. This search was then adapted to search for deep, long-duration eclipses in all WASP targets. The results of this survey are described in this thesis, as well as detailed results for the candidate PDS-110, a young T-Tauri star which exhibited 20d-long, 30%- deep eclipses in 2008 and 2011. Space-based photometers such as Kepler have the precision to identify small exoplanets and eclipsing binary candidates from only a single eclipse. K2, with its 75d campaign duration and high-precision photometry, is not only ideally suited to detect significant numbers of single-eclipsing objects, but also to characterise them from a single event. The Bayesian transit-fitting tool ("Namaste: An MCMC Analysis of Single Transit Exoplanets") was developed to extract planetary and orbital information from single transits, and was applied to 71 candidate events detected in K2 photometry. The techniques developed in this thesis are highly applicable to future transit surveys such as TESS & PLATO, which will be able to discover & characterise large numbers of long period planets in this way.
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Li, Boren. "Photometric stereo for micro-scale shape reconstruction." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/75021.
Full textAbstract:
This dissertation proposes an approach for 3D micro-scale shape reconstruction using photometric stereo (PS) with surface normal integration (SNI). Based on the proposed approach, a portable cost-effective stationary system is developed to capture 3D shapes in the order of micrometer scale. The PS with SNI technique is adopted to reconstruct 3D microtopology since this technique is highlighted for its capability to reproduce fine surface details at pixel resolution. Furthermore, since the primary hardware components are merely a camera and several typical LEDs, the system based on PS with SNI can be made portable at low cost.
The principal contributions are three folds. First, a PS method based on dichromatic reflectance model (DRM) using color input images is proposed to generalize PS applicable to a wider range of surfaces with non-Lambertian reflectances. The proposed method not only estimates surface orientations from diffuse reflection but also exploits information from specularities owing to the proposed diffuse-specular separation algorithm. Using the proposed PS method, material-dependent features can be simultaneously extracted in addition to surface orientations, which offers much richer information in understanding the 3D scene and poses more potential functionalities, such as specular removal, intrinsic image decomposition, digital relighting, material-based segmentation, material transfer and material classification.
The second contribution is the development of an SNI method dealing with perspective distortion. The proposed SNI is performed on the image plane instead of on the target surface as did by orthographic SNI owing to the newly derived representation of surface normals. The motivation behind the representation is from the observation that spatially uniform image points are simpler for integration than the non-uniform distribution of surface points under perspective projection. The new representation is then manipulated to the so-called log gradient space in analogy to the gradient space in orthographic SNI. With this analogy, the proposed method can inherit most past algorithms developed for orthographic SNI. By applying the proposed SNI, perspective distortion can be efficiently tackled with for smooth surfaces. In addition, the method is PS-independent, which can keep the image irradiance equation in a simple form during PS.
The third contribution is the design and calibration of a 3D micro-scale shape reconstruction system using the derived PS and SNI methods. This system is originally designed for on-site measurement of pavement microtexture, while its applicability can be generalized to a wider range of surfaces. Optimal illumination was investigated in theory and through numerical simulations. Five different calibrations regarding various aspects of the system were either newly proposed or modified from existing methods. The performances of these calibrations were individually evaluated. Efficacy of the developed system was finally demonstrated through comprehensive comparative studies with existing systems. Its capability for on-site measurement was also confirmed.Ph. D.
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Bakthavatchalam, Manikandan. "Utilisation of photometric moments in visual servoing." Thesis, Rennes 1, 2015. http://www.theses.fr/2015REN1S057/document.
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Cette thèse s'intéresse à l'asservissement visuel, une technique de commande à retour d'information visuelle permettant de contrôler le mouvement de systèmes équipées de caméras tels que des robots. Pour l'asservissement visuel, il est essentiel de synthétiser les informations obtenues via la caméra et ainsi établir la relation entre l'évolution de ces informations et le déplacement de la caméra dans l'espace. Celles-ci se basent généralement sur l'extraction et le suivi de primitives géométriques comme des points ou des lignes droites dans l'image. Il a été montré que le suivi visuel et les méthodes de traitement d'images restent encore un frein à l'expansion des techniques d'asservissement visuel. C'est pourquoi la distribution de l'intensité lumineuse de l'image a également été utilisée comme caractéristique visuelle. Finalement, les caractéristiques visuelles basée sur les moments de l'image ont permis de définir des lois de commande découplées. Cependant ces lois de commande sont conditionnées par l'obtention d'une région parfaitement segmentée ou d'un ensemble discret de points dans la scène. Ce travail propose donc une stratégie de capture de l'intensité lumineuse de façon indirecte, par le biais des moments calculés sur toute l'image. Ces caractéristiques globales sont dénommées moments photométriques. Les développements théoriques établis dans cette thèse tendent à définir une modélisation analytique de la matrice d'interaction relative aux moments photométriques. Ces derniers permettent de réaliser une tâche d'asservissement visuel dans des scènes complexes sans suivi visuel ni appariement. Un problème pratique rencontré par cette méthode dense d'asservissement visuel est l'apparition et la disparition de portions de l'image durant la réalisation de la tâche. Ce type de problème peut perturber la commande, voire dans le pire des cas conduire à l’échec de la réalisation de la tâche. Afin de résoudre ce problème, une modélisation incluant des poids spatiaux est proposée. Ainsi, la pondération spatiale, disposant d'une structure spécifique, est introduite de telle sorte qu'un modèle analytique de la matrice d'interaction peut être obtenue comme une simple fonction de la nouvelle formulation des moments photométriques. Une partie de ce travail apporte également une contribution au problème de la commande simultanée des mouvements de rotation autour des axes du plan image. Cette approche définit les caractéristiques visuelles de façon à ce que l'asservissement soit optimal en fonction de critères spécifiques. Quelques critères de sélection basées sur la matrice d'interaction ont été proposés. Ce travail ouvre donc sur d'intéressantes perspectives pour la sélection d'informations visuelles pour l'asservissement visuel basé sur les moments de l'imageThis thesis is concerned with visual servoing, a feedback control technique for controlling camera-equipped actuated systems like robots. For visual servoing, it is essential to synthesize visual information from the camera image in the form of visual features and establish the relationship between their variations and the spatial motion of the camera. The earliest visual features are dependent on the extraction and visual tracking of geometric primitives like points and straight lines in the image. It was shown that visual tracking and image processing procedures are a bottleneck to the expansion of visual servoing methods. That is why the image intensity distribution has also been used directly as a visual feature. Finally, visual features based on image moments allowed to design decoupled control laws but they are restricted by the availability of a well-segmented regions or a discrete set of points in the scene. This work proposes the strategy of capturing the image intensities not directly, but in the form of moments computed on the whole image plane. These global features have been termed photometric moments. Theoretical developments are made to derive the analytical model for the interaction matrix of the photometric moments. Photometric moments enable to perform visual servoing on complex scenes without visual tracking or image matching procedures, as long as there is no severe violation of the zero border assumption (ZBA). A practical issue encountered in such dense VS methods is the appearance and disappearance of portions of the scene during the visual servoing. Such unmodelled effects strongly violate the ZBA assumption and can disturb the control and in the worst case, result in complete failure to convergence. To handle this important practical problem, an improved modelling scheme for the moments that allows for inclusion of spatial weights is proposed. Then, spatial weighting functions with a specific structure are exploited such that an analytical model for the interaction matrix can be obtained as simple functions of the newly formulated moments. A part of this work provides an additional contribution towards the problem of simultaneous control of rotational motions around the image axes. The approach is based on connecting the design of the visual feature such that the visual servoing is optimal with respect to specific criteria. Few selection criteria based on the interaction matrix was proposed. This contribution opens interesting possibilities and finds immediate applications in the selection of visual features in image moments-based VS
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Wu, Tai-Pang. "From dense photometric stereo to interactive 3D markup /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?CSED%202007%20WU.
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Lawrie, Katherine Anne. "Photometric variability and rotation in magnetic white dwarfs." Thesis, University of Leicester, 2013. http://hdl.handle.net/2381/28179.
Full textAbstract:
This thesis explores the photometric variability in isolated magnetic white dwarfs (MWDs) to search for spin periods. Approximately 40% of MWDs exhibit photometric modulations as the star rotates due to the effects from a strong magnetic field or star spots. A sample of 77 MWDs is studied to discover periods on timescales of minutes to one week. Well-defined periods are determined in 12 MWDs, with periods of roughly an hour to a few days, and variability with poorly constrained periods is found in a further 13 stars. MWD spin periods can provide important constraints for their post main-sequence evolution and formation, and in particular, potential information on the influence magnetism plays on the mass and angular momentum loss of the evolving star. A correlation has emerged between the spin period and magnetic field strength and temperature, suggesting hotter MWDs spin faster and have higher field strengths, characteristics possibly associated with MWDs that might have formed in binary mergers. A similar investigation is carried out on longer timescales (months – years) for ten single MWDs, which are stable on short timescales but were previously found to display modulations between observing seasons. However, no significant variability is detected in the sample, although G240-72 may display variations over months. Finally, the spin period evolution over ∼ 20 years is studied in the hot, massive, highly magnetic, rapidly rotating MWD, RE J0317-853. A rate of period change is measured as Ṗ = (9.6 ± 1.4) × 10[superscript −14] s/s which is most likely due to the orbital motion of the wide binary pair of RE J0317-853 and LB9802. Spin-down from magnetic dipole radiation is ruled out as a possible mechanism. Periodic variations in the expected arrival times of maximum flux tentatively suggest a low-mass planetary companion may be orbiting RE J0317-853.
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Forne, Christopher Jes. "3-D Scene Reconstruction from Multiple Photometric Images." Thesis, University of Canterbury. Electrical and Computer Engineering, 2007. http://hdl.handle.net/10092/1227.
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This thesis deals with the problem of three dimensional scene reconstruction from multiple camera images. This is a well established problem in computer vision and has been significantly researched. In recent years some excellent results have been achieved, however existing algorithms often fall short of many biological systems in terms of robustness and generality. The aim of this research was to develop improved algorithms for reconstructing 3D scenes, with a focus on accurate system modelling and correctly dealing with occlusions. With scene reconstruction the objective is to infer scene parameters describing the 3D structure of the scene from the data given by camera images. This is an illposed inverse problem, where an exact solution cannot be guaranteed. The use of a statistical approach to deal with the scene reconstruction problem is introduced and the differences between maximum a priori (MAP) and minimum mean square estimate (MMSE) considered. It is discussed how traditional stereo matching can be performed using a volumetric scene model. An improved model describing the relationship between the camera data and a discrete model of the scene is presented. This highlights some of the common causes of modelling errors, enabling them to be dealt with objectively. The problems posed by occlusions are considered. Using a greedy algorithm the scene is progressively reconstructed to account for visibility interactions between regions and the idea of a complete scene estimate is established. Some simple and improved techniques for reliably assigning opaque voxels are developed, making use of prior information. Problems with variations in the imaging convolution kernel between images motivate the development of a pixel dissimilarity measure. Belief propagation is then applied to better utilise prior information and obtain an improved global optimum. A new volumetric factor graph model is presented which represents the joint probability distribution of the scene and imaging system. By utilising the structure of the local compatibility functions, an efficient procedure for updating the messages is detailed. To help convergence, a novel approach of accentuating beliefs is shown. Results demonstrate the validity of this approach, however the reconstruction error is similar or slightly higher than from the Greedy algorithm. To simplify the volumetric model, a new approach to belief propagation is demonstrated by applying it to a dynamic model. This approach is developed as an alternative to the full volumetric model because it is less memory and computationally intensive. Using a factor graph, a volumetric known visibility model is presented which ensures the scene is complete with respect to all the camera images. Dynamic updating is also applied to a simpler single depth-map model. Results show this approach is unsuitable for the volumetric known visibility model, however, improved results are obtained with the simple depth-map model.
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Scott, Christopher John Piers. "Indirect photometric determination of polar solutes by HPLC." Thesis, University of Bristol, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327903.
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Tsiotsios, Chourmouzios. "Shape estimation in murky water using photometric stereo." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/57033.
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Photometric stereo offers the possibility of object shape reconstruction via reasoning about the amount of light reflected from oriented surfaces. However, in murky media such as sea water light interacts not only with the scene but also with the medium particles. The resulting image formation model is complex and hard to optimize directly for scene orientation and albedo. The effectiveness of previous solutions has been limited since they were based on unrealistic assumptions about the imaging conditions or on external hardware for estimating some of the unknown model variables. In this thesis we propose a complete Photometric Stereo framework that yields useful reconstructions within a wide range of conditions in murky water. First, we show how the problem can be simplified by taking account of the additive light component that is backscatterd by the particles. A backscatter compensation method is proposed, based on the observation that the respective light signal varies smoothly across the sensor according to the pixel position with respect to the light source but is scene-depth independent. This makes its approximation experimentally appropriate using only the captured images and results in shape reconstruction similar to that in clean water. Second, we propose an uncalibrated method for solving Photometric Stereo in the presence of near-field illumination within murky water. In this case, the incident illumination on the scene is non-uniform as it varies according to the scene depth and the attenuation coefficient of the medium. We propose an algorithm for optimizing the resulting complex system of equations without resorting to external equipment or calibration. Finally, we design a novel Photometric Stereo system with dynamic lighting that can predict the validity of different photometric models in uncontrolled imaging conditions. Both our and previous approaches have been based on simplifications of the original-complex image formation in murky water. The effectiveness of such simplified models differs according to the imaging conditions and it can not be easily estimated as both the scene and the environment are usually unknown. Our proposed system can predict the validity of such photometric models, based on the observation that the change in estimated surface normals as the light sources position is varied with respect to the camera is a direct estimate of a model's effectiveness. In this way, the system can approximate the true reconstruction error and adapt automatically some critical factors in order to maximize the reconstruction quality, such as the camera-scene distance, the light sources position and the photometric model. Our work is evaluated through extended numerical simulations and real experiments in a water tank and real port water, and yields detailed reconstructions over a wide range of distances and underwater visibilities.
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Collister, Adrian Ashley. "Galaxy clustering with spectroscopic and photometric redshift surveys." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613869.
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Fiedorowicz, Pier Alexander, and Pier Alexander Fiedorowicz. "Reducing Photometric Redshift Uncertainties Using Galaxy Clustering Information." Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/624981.
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In cosmology and astronomy, measuring the distances to galaxies is an important task. This is done by
measuring the redshift of the spectra from these sources. Photometric redshifts are a quick way of estimating
the true redshifts and are calculated using color band intensities. The errors on these measurements produce
an apparent anisotropy in the radial direction. One of our fundamental assumptions in cosmology is that
the universe is isotropic. The ultimate goal of this project is to recover isotropy in the photometric redshift
data. This is done using Bayesian statistical inference to update the probability distribution functions for
the galaxy redshifts. We also demonstrate a simplified method of estimating the underlying density field.
Ultimately, we found that this simplified method failed to generate significant improvements in photometric
redshift uncertainties. Work on this project is ongoing. When completed, we expect to find that we have
produced a robust system capable of complementing photometric redshift estimators and improving their
results. With these improved measurements it is possible to better constrain various cosmological parameters
important to dark-matter research.
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Davies, John Keith. "Photometric monitoring of early type emission line stars." Thesis, University of Central Lancashire, 1988. http://clok.uclan.ac.uk/20181/.
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A programme of simultaneous optical (UBVRI) and infrared (JHKL MNQ) photometry of early type, emission line, stars is described. Particular emphasis is placed on observations of suspected pre-main-sequence objects such as Herbig Ae/Be stars. The observations, together with data from the IRAS point source catalogue, are analysed to probe the circumstellar environments of these objects and to determine the extent and causes of optical variability in such stars. It was found that many of these stars are associated with warm circumstellar dust and that the mean temperature of that dust is higher than the characteristic temperature of dust associated with T Tauri stars. It is shown that many of the stars in the programme display variablity at optical and infrared wavelengths, but that no single mechanism can account for the variability. The main variability mechanisms found are obscuration by circumstellar dust and changes in the underlying star. In some cases more than one mechanism operates at different times in a single star. It is also shown that the class of objects described as Herbig Ae/Be stars is very heterogeneous and that trends of variability range with spectral type reported by other authors may be illusory. Some unusual stars, including V644 Cen and HD97048 are identified and examined in detail. Suggestions are made for future work A brief spectrophometric survey of similar stars is also reported.
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Etherington, James Daniel Lambert. "Measuring galaxy environment in large scale photometric surveys." Thesis, University of Portsmouth, 2016. https://researchportal.port.ac.uk/portal/en/theses/measuring-galaxy-environment-in-large-scale-photometric-surveys(acd86f3b-67cd-4684-8d88-e49bb54790c6).html.
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The properties of galaxies, such as the galaxy red fraction and galaxy stellar mass function, have been shown to depend upon their environment in the local Universe. Large scale photometric surveys such as the DES and in the future Euclid, will be vital to gain insight into the evolution of galaxy properties and the role of environment through cosmic time. Large samples come at the cost of redshift precision and this affects the measurement of galaxy environment. In this thesis an analysis pipeline is constructed to derive galaxy parameters including absolute magnitudes, stellar masses and galaxy environments. The analysis pipeline consists of well established components, such as HYPERZ, that performs SED fitting and components that I have developed and tested, including codes to compute galaxy environment. Five methods to compute galaxy environment are implemented, including three fixed aperture methods, based on spheres, cylinders and cones, the Nth nearest neighbour method and the adaptive Gaussian method. The codes are optimized and parallelized and are executed on Portsmouth’s high performance computer cluster. The codes are thoroughly tested using mock data. Further testing is conducted employing GAMA data, with an external collaborator. The pipeline is applied to two datasets and the results lead to two scientific papers: Etherington & Thomas (2015) and Etherington et al. (in DES collaboration review). The first study is based on a low redshift sample drawn from the SDSS. Spectroscopic and photometric redshifts and also simulated photometric redshifts with a range of uncertainties are employed to study the impact of photometric redshift uncertainty on measures of environment as a function of the aperture parameters. The photometric environments are found to have a smaller dynamic range compared to the spectroscopic measurements because uncertain redshifts scatter galaxies from dense environments into less dense environments. With the optimal aperture parameter values, even for large redshift uncertainties, ∼ 0.1, there is a Spearman Rank Correlation Coefficient of ∼ 0.4 between the photometric measurements and the spectroscopic benchmark environments. This is sufficient to extract an environment signal from large scale photometric surveys. The second study in this thesis is based on the science verification data from the DES. This is the first set of observations from the survey. This study uses ∼3.2 million galaxies from the SPT-East (South Pole Telescope) field that covers approximately 100 sq. deg. of the sky. From the grizY photometry the analysis pipeline is used to derive galaxy stellar masses and absolute magnitudes. The errors on these properties are assessed using Monte-Carlo simulations sampled from the full photometric redshift probability distributions. Galaxy environments are computed using a fixed conical aperture method, for a range of scales. Galaxy environment probability distribution functions are constructed and the dependence of the environment errors on the aperture parameters is investigated. The environment components of the galaxy stellar mass function for the redshift range: 0.15 < z < 1.05 are calculated. For z < 0.75 it is found that the fraction of massive galaxies is larger in high density environment than low density environments. The low and high density components converge with increasing redshift to z ∼ 1.0 where the shapes of the mass function components are indistinguishable. This redshift is important because it marks the transition between an earlier epoch where the mass distribution of galaxies is independent of environment and a later epoch where the mass distribution does depend on galaxy environment. This study shows the build up of high density structures around massive galaxies, through cosmic time. The results in this thesis demonstrate that large scale photometric surveys can produce competitive galaxy evolution science, enabling further investigations of the role of galaxy environment. This is hugely encouraging for current and future experiments.
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Barsky, S. "Surface shape and colour reconstruction using photometric stereo." Thesis, University of Surrey, 2003. http://epubs.surrey.ac.uk/842858/.
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This thesis is on the use of a surface reconstruction method called Photometric Stereo in Machine Vision. In the first part we propose a modification of the method which allows one to reconstruct the shape and colour of the surface in the presence of highlights and shadows. We also provide an extensive error analysis of the algorithm, concentrating on design issues such as choice of thresholds. The second part of the thesis is on the subject of illumination direction invariant classification of 3-dimensional textures. Using Photometric Stereo, one can reconstruct the surface shape and infer its statistical properties. The learned statistics can be used to predict the behaviour of a class of texture features, which in its turn allows one to recognise a 3-dimensional texture under unknown illumination.
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Lee, Ki Won. "A photometric survey of the Small Magellanic Cloud." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1446424/.
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The initial mass function (IMF) is defined as the fraction or number of stars born per unit mass interval and is the one of key parameters in astronomy. Since Salpeter (1955)'s work, there have been many studies, and most of them show the universality of the IMF regardless of systems, mass ranges, and metallicity within observational errors, although recently there are some suggestions of its variation. The main aim of this thesis is to test the IMF universality, based on a photometric study of the SMC. In order to study the IMF of massive stars and the star formation history, we perform a BVR photometric survey of the Small Magellanic Cloud (SMC), chosen for its proximity and low metallicity. The observational data were acquired at Siding Spring Observatory, Australia during the 5 - 11 September and 26 - 31 October 2001 and 9-17 November 2002, covering essentially the whole SMC area. Details of the instruments, characteristics of each run, and the procedures of data reduction are presented. We catalogued 0.76 million SMC stars brighter than 18 magnitude in B from total 1.3 millions. Regarding to the accuracy, we found 0.1 arcsecond in astrometry and 0.1 magnitude at B and V and 0.2 at R in photometry. Together with spectroscopic data, we investigate the basic parameters of the SMC such as colour excess, reddening and distance modulus, and compare them with other studies. Based on these parameters, we study the IMF and star formation histories using population synthesis techniques. In contrast to other authors, we transform the theoretical quantities into observable ones, and use Bayesian inference in the comparison of the various IMF models. The procedures and background concepts for the generation of models incorporating the same constraints as observed samples, are also described. According to model calculations, a continuous star formation model with an IMF slope of 1.6 offers the best representation of the SMC stars. Therefore we suggest that our result is one of the implications for the variation of the IMF, at least for hot stars.
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Drory, Niv. "A near-infrared selected photometric survey of distant galaxies." Diss., lmu, 2002. http://nbn-resolving.de/urn:nbn:de:bvb:19-2849.
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Unger, Jonas, Stefan Gustavson, and Anders Ynnerman. "High Dynamic Range Video for Photometric Measurement of Illumination." Linköpings universitet, Visuell informationsteknologi och applikationer, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-40069.
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We describe the design and implementation of a high dynamic range (HDR) imaging system capable of capturing RGB color images with a dynamic range of 10,000,000 : 1 at 25 frames per second. We use a highly programmable camera unit with high throughput A/D conversion, data processing and data output. HDR acquisition is performed by multiple exposures in a continuous rolling shutter progression over the sensor. All the different exposures for one particular row of pixels are acquired head to tail within the frame time, which means that the time disparity between exposures is minimal, the entire frame time can be used for light integration and the longest expo- sure is almost the entire frame time. The system is highly configurable, and trade-offs are possible between dynamic range, precision, number of exposures, image resolution and frame rate.
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DeCocq, John D. "The impact of abundance variations on photometric luminosity indicators." Virtual Press, 1996. http://liblink.bsu.edu/uhtbin/catkey/1014853.
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Red dwarf stars are one proposed solution to the dark matter problem in the Milky Way Galaxy These cool, low luminosity stars are difficult to detect and segregate in surveys. This study utilizes photometric data obtained on the Kron-Cousins photometric system to develop criteria that classifies stars as red. Two of the color indices are then used to create a two-color diagram to allow separation of giant and dwarf stars. An algorithm based on calculated equations is provided to separate the giant and dwarf stars after detection. A third class of stars, subdwarfs, is addressed as a potential problem in future surveys. Some suggestions for detecting and removing these contaminating stars from the data are offered. Finally, a colormagnitude diagram is developed for red dwarf stars with KronCousins photometry. This curve allows for fairly accurate determination of photometric parallaxes for the red dwarf stars.An attempt was made to segregate the red dwarfs into velocity classes prior to calibrating the color-magnitude diagram. It was found that this approach offered no additional useful information.Department of Physics and Astronomy
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Spence, Andrew D. "Calibrated and uncalibrated photometric stereo for surface texture acquisition." Thesis, Heriot-Watt University, 2005. http://hdl.handle.net/10399/235.
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Allyn, M. Liz. "Indirect photometric chromatography of iodide ion in aqueous solutions /." Online version of thesis, 1987. http://hdl.handle.net/1850/8769.
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Soo, John Yue Han. "Enhancing photometric redshifts for the era of precision cosmology." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10055277/.
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Photometric redshifts (photo-z's) are vital for the success of current and forthcoming cosmological galaxy surveys. This work focuses on three different approaches to enhance photo-z's. Firstly, we study the extent to which galaxy morphology improves photo-z's. Using artificial neural networks, we compare the performances of several morphological parameters and find that galaxy size and surface brightness bring about the most improvement to photo-z's in bright samples. When multiple morphological parameters are used, the improvement in scatter reaches as high as 12% for the Main Galaxy Sample (MGS) of the Sloan Digital Sky Survey (SDSS). We also find that the improvement becomes significant under suboptimal conditions: when surveys have limited numbers of bands, low quality photometry, or an imperfect star-galaxy separator. Next we study aspects of photo-z probability density functions (PDFs) and the resulting redshift distributions of galaxy samples in the context of the Canada-France-Hawaii Telescope Stripe-82 (CS82) Survey. We discover that, while galaxy morphology brings marginal improvement to both, we are able to produce accurate redshift distributions using a single photometric band and multiple galaxy morphological parameters, and apply this to the CS82 survey. As part of the photo-z Working Group of the Large Synoptic Survey Telescope Dark Energy Science Collaboration (LSST-DESC), we use several metrics to assess the performances of two state-of-the-art photo-z codes, ANNz2 and Delight, and concluded that the photo-z's produced by both are close to the standard for the current photo-z requirements of LSST. Finally, we explore the performances of multiple photo-z codes on narrowband surveys. Using simulated and real data from the 40-narrowband Physics of the Accelerating Universe (PAU) Survey, we find that the hybrid spectral template-machine learning code Delight outperforms monolithic machine learning as well as template codes. Using the large suite of spectral templates and well-calibrated additional broadband fluxes, we are able to produce competitive photo-z's close to the nominal PAU requirement at 40% quality cut. We believe these method would be useful for the next generation of photometric surveys, like Euclid and LSST.
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Eminian, Celine. "Photometric redshifts and physical properties of low redshift galaxies." Thesis, University of Sussex, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496929.
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In this thesis we are interested in the properties of low redshift galaxies. In the first part, we look at the large-scale structure of the Sloan Digital Sky Survey galaxies using photometric redshifts. In the second part, we bring new insight into physical properties of galaxies, in particular into their dust content, and show how they are related to their near-infrared colours.
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D'Angelo, Paolo. "3D scene reconstruction by integration of photometric and geometric methods." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985352949.
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