This work is about a realistic visualization technique called raytracing. It studies its original form, its extensions and optimizations. Raytracing casts rays through pixels and follows their propagation in the scene, according to the physical laws. It enables rendering of correct shadows, reflections and refractions. Distributed raytracing serves for better visualization and advanced effects. One ray is replaced with a beam of rays that allows soft shadows, fuzzy translucency, depth of field and antialiasing. With the increasing number of rays, the render time rises as well, so it is needed to use some optimization techniques and tools. A way of using this rendering method for visualization of alcoholic beverages is also described.

Masters thessis deals with the problematics of wireless signal propagation modeling inside buildings. The theoretical part of this thessis describes principles and methods of electromagnetic waves spreading in open areas and in indoor deployment. There are also described methods used for calculating the path of signal propagation ray-launching and ray-tracing. This part also includes description of an algorithm and equations used for simulating 5GHz WiFi signal propagation inside the Department of telecommunications corridors. Second part of this thessis includes a description of a NS-3 module mmWave, which was used for simulations of IEEE 802.11ad (WiGig) standard. There are also results of these simulations and their detailed description. At the end of this thessis comparison of these results with values gained by real environment measurements can be found.

The Scheimpflug principle was recommended as allowing distortion-free imaging; however, a detailed analysis reveals geometrical errors as well as distortions arising from absorption of light along the optical pathway. Correction formulas and factors will be presented and applied to the biometry of the eye. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

No description available.

Background. Rasterization of triangle geometry has been the dominating rendering technique in the real-time rendering industry for many years. However, triangles are not always easy to work with for content creators. With the introduction of hardware-accelerated ray tracing, rasterization-based lighting techniques have been steadily replaced by ray tracing techniques. This shift may signify the opportunity of exploring other, more easily manipulated, geometry-type alternatives compared to triangle geometry. One such geometry type is implicit surfaces. Objectives. This thesis investigates the rendering speed, editing speed, and image quality of different implicit surface rendering techniques using a state-of-the-art, hardware-accelerated, path tracing implementation. Furthermore, it investigates how implicit surfaces may be edited in real time and how editing affects rendering. Methods. A baseline direct sphere tracing algorithm is implemented to render implicit surfaces. Additionally, dense and narrow band discretization algorithms that sphere trace a discretization of the implicit surface are implemented. For each technique, two variations that provide potential benefits in rendering speed are also tested. Additionally, a real-time implicit surface editor that can utilize all the mentioned rendering techniques is created. Rendering speed, editing speed, and image quality metrics are captured for all techniques using different scenes created with the editor and an existing hardware-accelerated path tracing solution. Image quality differences are measured using mean squared error and the image difference evaluator FLIP. Results. Direct sphere tracing achieves the best image quality results but has the slowest rendering speed. Dense discretization achieves the best rendering speed in most tests and achieves better image quality results compared to narrow band discretization. Narrow band discretization achieves significantly better editing speed than both direct sphere tracing and dense discretization. All variations of each algorithm achieve better or equal rendering and editing speed compared to their standard implementation. All algorithms achieve real-time rendering and editing performance. However, only discretized methods display real-time rendering performance for all scenes, and only narrow band discretization displays real-time editing performance for a larger number of primitives. Conclusions. Implicit surfaces can be rendered and edited in real time while using a state-of-the-art, hardware-accelerated, path tracing algorithm. Direct sphere tracing degrades in performance when the implicit surface has an increased number of primitives, whereas discretization techniques perform independently of this. Furthermore, narrow band discretization is fast enough so that editing can be performed in real time even for implicit surfaces with a large number of primitives, which is not the case for direct sphere tracing or dense discretization. / Bakgrund. Triangelrastrering har varit den dominerande renderingstekniken inom realtidsgrafik i flera år. Trianglar är dock inte alltid lätta att jobba med för skapare av grafiska modeller. Med introduktionen av hårdvaruaccelererad strålspårning har rastreringsbaserade ljussättningstekniker stadigt ersatts av strålspårningstekniker. Detta skifte innebär att det kan finnas möjlighet för att utforska andra, mer lättredigerade geometrityper jämfört med triangelgeometri, exempelvis implicita ytor. Syfte. Detta examensarbete undersöker rendering- och redigeringshastigheten, samt bildkvaliteten av olika renderingstekniker för implicita ytor tillsammans med en spjutspetsalgoritm för hårdvaruaccelererad strålföljning. Den undersöker även hur implicita ytor kan redigeras i realtid och hur det påverkar rendering. Metod. En direkt sfärspårningsalgoritm implementeras som baslinje för att rendera implicita ytor. Även algoritmer som utför sfärstrålning över en kompakt- och smalbandsdiskretisering av den implicita ytan implementeras. För varje teknik implementeras även två variationer som potentiellt kan ge bättre prestanda. Utöver dessa renderingstekniker skapas även ett redigeringsverktyg för implicita ytor. Renderingshastighet, redigeringshastighet, och bildkvalité mäts för alla tekniker över flera olika scener som har skapats med redigeringsverktyget tillsammans med en hårdvaruaccelererad strålföljningsalgoritm. Skillnader i bildkvalité utvärderas med hjälp av mean squared error och evalueringsverktyget för bildskillnader som heter FLIP. Resultat. Direkt sfärspårning åstadkommer bäst bildkvalité, men har den långsammaste renderingshastigheten. Kompakt diskretisering renderar snabbast i de flesta tester och åstadkommer bättre bildkvalité än vad smalbandsdiskretisering gör. Smalbandsdiskretisering åstadkommer betydligt bättre redigeringshastighet än både direkt sfärspårning och kompakt diskretisering. Variationerna för respektive algoritm presterar alla lika bra eller bättre än standardvarianten för respektive algoritm. Alla algoritmer uppnår realtidsprestanda inom rendering och redigering. Endast diskretiseringsmetoderna uppnår dock realtidsprestanda för rendering med alla scener och endast smalbandsdiskretisering uppnår realtidsprestanda för redigering med ett större antal primitiver. Slutsatser. Implicita ytor kan renderas och redigeras i realtid tillsammans med en spjutspetsalgoritm för hårdvaruaccelererad strålföljning. Vid användning av direkt sfärstrålning minskar renderingshastigheten när den ytan består av ett stort antal primitiver. Diskretiseringstekniker har dock en renderingshastighet som är oberoende av antalet primitiver. Smalbandsdiskretisering är tillräckligt snabb för att redigering ska kunna ske i realtid även för implicita ytor som består stora antal primitiver.

In space exploration optical imaging is one of the key measurements conducted, with a vast majority of missions heavily relying on optical data acquisition to examine alien worlds. One such endeavor is ESA’s F-class mission Comet Interceptor, a multi-element spacecraft expected to be launched in 2028. It consists of a primary platform and two sub-spacecraft, one of which carrying the Optical Periscopic Imager for Comets (OPIC). An accurate prediction of the generated imagery is of undeniable importance as mission planning and instrument design strongly depend on the real-world output quality of the camera system. In the case of OPIC, the collected image data will be used to reconstruct three dimensional models of targeted celestial bodies. Furthermore, the sub-spacecraft faces a risk of high velocity dust impacts, leading to a limited number of data samples to be broadcasted back to the primary spacecraft before collision. Testing image prioritization algorithms and reconstruction methods prior to mission start requires accurate computer-generated images. Camera sensors and lens systems are subjected to various optical distortions and aberrations that degrade the final image. Popular render engines model those effects to a certain degree only and as a result produce content that is looking too perfect. While more sophisticated software products exist, they often come with compatibility limitations and other drawbacks. This report discusses the most important optical aberrations, as well as their relevance for optical instruments in space applications with a particular focus on the Comet Interceptor mission. The main part of this work is however the implementation of a dedicated software tool that simulates a variety of optical aberrations complementing the basic camera model of the Blender render engine. While its functionality is mostly demonstrated for OPIC, the software is designed with a broad range of usage scenarios in mind.

Cette thèse étudie la précision en vision stéréo, les méthodes de détection dites a contrario et en présente une application à l'imagerie satellitaire. La première partie a été réalisée dans le cadre du projet DGA-ANR-ASTRID "STÉRÉO". Son but est de définir les limites effectives des méthodes de reconstruction stéréo quand on contrôle toute la chaîne d’acquisition à la précision maximale, que l’on acquiert des paires stéréo en rapport B/H très faible et sans bruit. Pour valider ce concept, nous créons des vérités terrains très précises en utilisant un rendeur. En gardant les rayons calculés durant le rendu, nous avons une information très dense sur la scène 3D. Ainsi nous créons des cartes d'occultations, de disparités dont l'erreur de précision est inférieure à 10e-6. Nous avons mis à la disposition de la communauté de recherche des images de synthèse avec un SNR supérieur à 500 : un ensemble de 66 paires stéréo dont le B/H varie de1/2500 à 1/50. Pour évaluer les méthodes de stéréo sur ce nouveau type de données, nous proposons des métriques calculant la qualité des cartes de disparités estimées, combinant la précision et la densité des points dont l'erreur relative est inférieure à un certain seuil. Nous évaluons plusieurs algorithmes représentatifs de l'état de l'art, sur les paires créées ainsi sur les paires de Middlebury, jusqu'à leurs limites de fonctionnement. Nous confirmons par ces analyses, que les hypothèses théoriques sur le bien-fondé du faible B/H en fort SNR sont valides, jusqu'à une certaine limite que nous caractérisons. Nous découvrons ainsi que de simples méthodes de flux optique pour l'appariement stéréo deviennent plus performantes que des méthodes variationnelles discrètes plus élaborées. Cette conclusion n'est toutefois valide que pour des forts rapports signal à bruit. L'exploitation des données denses nous permet de compléter les vérités terrain par une détection très précise des bords d'occultation. Nous proposons une méthode de calcul de contours vectoriels subpixéliens à partir d'un nuage de points très dense, basée sur des méthodes a contrario de classification de pixels. La seconde partie de la thèse est dédiée à une application du flot optique subpixélien et des méthodes a contrario pour détecter des nuages en imagerie satellitaire. Nous proposons une méthode qui n'exploite que l'information visible optique. Elle repose sur la redondance temporelle obtenue grâce au passage répété des satellites au-dessus des mêmes zones géographiques. Nous définissons quatre indices pour séparer les nuages du paysage : le mouvement apparent inter-canaux, la texture locale, l'émergence temporelle et la luminance. Ces indices sont modélisés dans le cadre statistique des méthodes a contrario qui produisent un NFA (nombre de fausses alarmes pour chacun). Nous proposons une méthode pour combiner ces indices et calculer un NFA beaucoup plus discriminant. Nous comparons les cartes de nuages estimées à des vérités terrain annotées et aux cartes nuageuses produites par les algorithmes liés aux satellites Landsat-8 etSentinel-2. Nous montrons que les scores de détection et de fausses alarmes sont supérieurs à ceux obtenus avec ces algorithmes, qui pourtant utilisent une dizaine de bandes multi-spectrales. / This thesis studies the accuracy in stereo vision, detection methods calleda contrario and presents an application to satellite imagery. The first part was carried out within the framework of the project DGA-ANR-ASTRID"STEREO". His The aim is to define the effective limits of stereo reconstruction when controlling the entire acquisition chain at the maximum precision, that one acquires stereo pairs in very low baseline and noise-free. To validate thisconcept, we create very precise ground truths using a renderer. By keeping the rays computed during rendering, we have very dense information on the 3Dscene. Thus we create occultation and disparity maps whose precision error is less than 10e-6. We have made synthetic images available to the research community with an SNR greater than 500: a set of 66 stereo pairs whoseB/H varies from 1/2500 to 1/50. To evaluate stereo methods onthis new type of data, we propose metrics computing the quality of the estimated disparity maps, combining the precision and the density of the points whose relative error is less than a certain threshold. We evaluate several algorithmsrepresentative of the state of the art, on the pairs thus created and on theMiddlebury pairs, up to their operating limits. We confirm by these analyzesthat the theoretical assumptions about the merit of the low B/H in highSNR are valid, up to a certain limit that we characterize. We thus discover that simple optical flow methods for stereo matching become more efficient than more sophisticated discrete variational methods. This conclusion, however, is only valid for high signal-to-noise ratios. The use of the dense data allows us to complete the ground truths a subpixel detection of the occlusion edges. We propose a method to compute subpixel vector contours from a very dense cloud ofpoints, based on pixel classification a contrario methods. The second part of the thesis is devoted to an application of the subpixelian optical flowand a contrario methods to detect clouds in satellite imagery. We propose a method that exploits only visible optical information. It is based onthe temporal redundancy obtained by the repeated passages of the satellites overthe same geographical zones. We define four clues to separate the clouds fromthe landscape: the apparent inter-channel movement, Local texture, temporal emergence and luminance. These indices are modeled in the statistical framework of a contrario methods which produce an NFA (number of false alarms for each). We propose a method for combining these indices and computing a much more discriminating NFA. We compare the estimated cloud maps to annotated ground truths and the cloud maps produced by the algorithms related to the Landsat-8and Sentinel-2 satellites. We show that the detection and false alarms scores are higher than those obtained with these algorithms, which however use a dozen multi-spectral bands.

La démarche « matériaux numériques », développée au CEA Le Ripaut, consiste à optimiser numériquement une structure, à l’aide de codes de calcul permettant de réaliser des expériences numériques, afin de répondre le plus précisément possible à un cahier des charges. La mise en œuvre de ces structures optimisées, aux formes pouvant être complexes, n’est parfois pas réalisable avec les procédés de fabrication actuels. Cependant, la progression rapide de l’impression 3D semble maintenant pouvoir concrétiser cette démarche. Le but de cette thèse est d’étudier cette faisabilité de fabrication, à travers une application concrète : l’optimisation des récepteurs volumétriques des Centrales Solaires Thermodynamiques (CST).Actuellement, la conception de ces récepteurs en Carbure de Silicium (SiC) est restreinte par les techniques existantes de fabrication, et leurs morphologies se limitent donc principalement à des mousses ou des canaux parallèles. Or, ce type de structure ne permet pas d’exploiter tout le caractère 3D proposé par les récepteurs, en raison notamment d’une absorption trop hétérogène du rayonnement solaire dans le volume. Dans ce travail de thèse, afin de rechercher la répartition de l’absorption la plus homogène possible dans l’ensemble du volume, de nombreuses structures aux formes variées sont générées virtuellement. Une simulation de l’éclairement solaire reçu est réalisée sur l’ensemble de ces structures, grâce à un code de calcul développé spécialement pour cette application, permettant ainsi d’en retenir trois répondants au mieux aux critères du cahier des charges. Ces structures potentiellement optimisées ont ensuite été fabriquées en SiC par impression 3D, par un procédé de projection de liant sur lit de poudre. Elles ont été ensuite testées sur un banc d’essai expérimental du laboratoire PROMES, reproduisant les conditions d’une CST. Les résultats ont montrés que ces structures, aux formes totalement différentes de mousses ou de canaux parallèles, sont capables de produire au maximum de l’air à 860°C en sortie de récepteur, et avec des rendements énergétiques proches de 0,65. Enfin, un code de calcul thermique couplé conducto-radiatif, amélioré durant ce travail, a permis d’analyser ces résultats expérimentaux et servira pour les futurs travaux d’optimisation de la géométrie d’un récepteur. / The "numerical materials" approach, developed at CEA Le Ripaut, consists to numerically optimize a structure, by using calculation codes that allow to realize numerical experiments, in order to answer, as precisely as possible, to a set of specifications. The manufacturing of these optimized structures, whose shapes can be complex, is sometimes not feasible with current manufacturing processes. However, the rapid progress of 3D printing now seems to be able to concretize this approach. The aim of this thesis is to study this manufacturing feasibility, through a concrete application: the optimization of the volumetric receivers of Concentrated Solar Power Plants (CSP). Currently, the design of these silicon carbide (SiC) receptors is restricted by the existing manufacturing techniques, and their morphologies are therefore mainly limited to foams or parallel channels. However, this type of structure does not allow to exploit all the 3D character proposed by the receivers, due in particular to a heterogeneous absorption of solar radiation in the volume. In this work, in order to find the distribution of the most homogeneous absorption possible in the whole volume, many structures with various shapes are generated virtually. A simulation of the solar irradiance received is carried out on all these structures, thanks to a calculation code developed especially for this application, thus allowing to choose three of them, respondents at best to the criteria of the specifications. These potentially optimized structures were then manufactured in SiC by 3D printing, by a binder jetting process. They were then tested on an experimental test bench of the PROMES laboratory, reproducing the conditions of a CSP. Results showed that these structures, where their shapes are totally different from foams or parallel channels, are able to produce a maximum air temperature of 860°C at the output of the receiver, and with efficiencies close to 0.65. Finally, a conducto-radiative coupled thermal computational code, improved during this work, made it possible to analyze these experimental results and will be used for the future work of optimization of the geometry of a receiver.

This thesis deals with practical implementation of photon mapping algorithm. To achieve better results some basic and some more advanced methods of global illumination has been examined. These time demanding algorithms are often practically unusable and their further optimization is necessary. Optimized ray tracer is essential for practical implementation. Computing diffuse interreflection by Monte Carlo sampling is also very time demanding operation. Therefore it is appropriate to use it along with proper interpolation.

In this master's thesis I'm engaged in problematic of texture mapping in ray tracing. Ray tracing is shortly described in the beginning. Texture mapping methods are described then, solid textures first and 2D textures follow. Implementation of MIP map method is deeply described in next chapters. The results are evaluated at the end.