171 research outputs found
Interactive visual and graphical programming environments within three-dimensional computer animation domain
No full textOndanks succesvolle hedendaagse ontwikkelingen die bet aanwenden van computersystemen - vanuit bet standpunt van de programmeur alsook vanuit bet standpunt van de gebruiker - vergemakkelijken en verbeteren, blijkt toch dat het beheersen van deze computersystemen dikwijls nog steeds neerkomt op bet opbouwen van een mentaal beeld betreffende de toestand en/of functionaliteit van bet systeem in kwestie. Vaststellen waarom mensen dikwijls een probleem hebben in bet opbouwen van dit mentale beeld, condenseert vaak tot bet feit dat de componenten om dit beeld op te bouwen, niet toegankelijk zijn. Het "naar buiten brengen" van de interne structuren en functionaliteiten die de basisprocessen van bet programmeren en gebruiken van computersystemen regelen, kan naar onze mening het beheersen van computersystemen vereenvoudigen. Het toepassen van computer graphics elementen en technieken in programmeersystemen kan dit wezenlijk ondersteunen: Er moet warden gezocht nam geschikte grafische programmeeromgeving. Een probleem hierbij is dat een bepaalde gebruiker (aan programmeerzijde evenals aan toepassingszijde) een gegeven grafische programmeeromgeving als goed kan ervaren, terwijl een andere gebruiker diezelfde benadering eerder slecht vind. Het is zelf s z6 dat de mening van een gegeven persoon betreft ende de geschiktheid van een grafische representatie kan veranderen in de tijd, als bijv. het expertise-niveau van de persoon in kwestie veranderd: Er moet worden gezocht nam een gebruiker-aanpasbare programmeeromgeving. Aangezien de ruimte in dewelke men moet zoeken naar geschikte grafische entiteiten bovendien een enorme uitgestrektheid heeft, is bet beheersen van deze ruimte een verre van triviale aangelegenheid: Er moet warden gezocht nam een uniforme en modulaire programmeeromgeving
Interactive visual and graphical programming environments within three-dimensional computer animation domain
No full textOndanks succesvolle hedendaagse ontwikkelingen die bet aanwenden van computersystemen - vanuit bet standpunt van de programmeur alsook vanuit bet standpunt van de gebruiker - vergemakkelijken en verbeteren, blijkt toch dat het beheersen van deze computersystemen dikwijls nog steeds neerkomt op bet opbouwen van een mentaal beeld betreffende de toestand en/of functionaliteit van bet systeem in kwestie. Vaststellen waarom mensen dikwijls een probleem hebben in bet opbouwen van dit mentale beeld, condenseert vaak tot bet feit dat de componenten om dit beeld op te bouwen, niet toegankelijk zijn. Het "naar buiten brengen" van de interne structuren en functionaliteiten die de basisprocessen van bet programmeren en gebruiken van computersystemen regelen, kan naar onze mening het beheersen van computersystemen vereenvoudigen. Het toepassen van computer graphics elementen en technieken in programmeersystemen kan dit wezenlijk ondersteunen: Er moet warden gezocht nam geschikte grafische programmeeromgeving. Een probleem hierbij is dat een bepaalde gebruiker (aan programmeerzijde evenals aan toepassingszijde) een gegeven grafische programmeeromgeving als goed kan ervaren, terwijl een andere gebruiker diezelfde benadering eerder slecht vind. Het is zelf s z6 dat de mening van een gegeven persoon betreft ende de geschiktheid van een grafische representatie kan veranderen in de tijd, als bijv. het expertise-niveau van de persoon in kwestie veranderd: Er moet worden gezocht nam een gebruiker-aanpasbare programmeeromgeving. Aangezien de ruimte in dewelke men moet zoeken naar geschikte grafische entiteiten bovendien een enorme uitgestrektheid heeft, is bet beheersen van deze ruimte een verre van triviale aangelegenheid: Er moet warden gezocht nam een uniforme en modulaire programmeeromgeving
Differential Methods in Character Rigging
No full textMost 3D animation software comes with various mesh deformers for character
rigging, based on long known and widely used algorithms, like skeletal subspace
deformation or freeform deformation. We demonstrate how these methods can
be improved upon and made more flexible while still working interactively as
part of complicated character rigs, using the same workflow as before.
We first consider the interpolation of affine transformations, and the solution
of differential equations, whose properties will be taken advantage of in the
algorithms we implemented. Next we consider the problem of shape interpolation,
and discuss a representation for mesh deformations that encodes them
in affine transformations per triangle, such that they can be interpolated and
edited in ways difficult to achieve otherwise. Then we discuss skeletal subspace
deformation and recent methods to get rid of its well known artifacts while still
being nearly as efficient. Additionally we demonstrate how t
Highly stylised drawn animation
No full textIn this paper we argue for our NPAR system as an effective 2D alternative to most of NPR research which is focused on frame coherent stylised rendering of 3D models. Our approach gives a highly stylised look to images without the support of 3D models, and yet they still behave as though animated by drawing, which they are.
First, a stylised brush tool is used to freely draw extreme poses of characters. Each character is built up of 2D drawn brush strokes which are manually grouped into layers. Each layer is assigned its place in a drawing hierarchy called a Hierarchical Display Model (HDM). Next, multiple HDMs are created for the same character, each corresponding to a specific view. A collection of HDMs essentially reintroduces some correspondence information to the 2D drawings needed for in-betweening and, in effect, eliminates the need for a true 3D model.
Once the models are composed the animator starts by defining keyframes from extreme poses in time. Next, brush stroke trajectories defined by the keyframe HDMs are in-betweened automatically across intermediate frames. Finally, each HDM of each generated in-between frame is traversed and all elements are drawn one on another from back to front.
Our techniques support highly rendered styles which are particularly difficult to animate by traditional means including the ‘airbrushed’, scraperboard, watercolour, Gouache, ‘ink-wash’, and the ‘crayon’ styles.
We believe our system offers a new fresh perspective on computer aided animation production and associated tools.
Keywords:Artist driven, stylised modelling, stylised animation, computer animation, computer-assisted animation, NPR, NPAR
Differential Methods in Character Rigging
No full textMost 3D animation software comes with various mesh deformers for character
rigging, based on long known and widely used algorithms, like skeletal subspace
deformation or freeform deformation. We demonstrate how these methods can
be improved upon and made more flexible while still working interactively as
part of complicated character rigs, using the same workflow as before.
We first consider the interpolation of affine transformations, and the solution
of differential equations, whose properties will be taken advantage of in the
algorithms we implemented. Next we consider the problem of shape interpolation,
and discuss a representation for mesh deformations that encodes them
in affine transformations per triangle, such that they can be interpolated and
edited in ways difficult to achieve otherwise. Then we discuss skeletal subspace
deformation and recent methods to get rid of its well known artifacts while still
being nearly as efficient. Additionally we demonstrate how t
Asteroseismic masses, ages, and core properties of γ Doradus stars using gravito-inertial dipole modes and spectroscopy
No full textContains fulltext :
204337.pdf (Publisher’s version ) (Open Access
Urban architecture, hybrid buildings: Studio Beveren
No full textMet als bijlage: A0 posterArchitectur
Design d'impulsions RF par contrôle optimal pour l'optimisation du contraste en IRM : applications in vivo
No full textNational audienceBut : Le design d’impulsions radio-fréquence (RF) par contrôle optimal pour l’optimisation du contraste a récemment été proposé [1]. Ces impulsions garantissent un certain degré d’optimalité sur le contraste obtenu, qui s’approche de la borne théorique. Jusqu’alors, leur utilisation a été validée sur IRM lors d’expériences in vitro uniquement [2]. Cette étude étend ces résultats in vivo sur cerveaux de rat et souris.Méthode : Le problème de contrôle optimal, via la résolution du Principe du Maximum de Pontryagin [3] (PMP), consiste à calculer le contrôle qui optimise une fonction de coût, connaissant la dynamique du système à optimiser. Appliqué à l’IRM, il s’agit de calculer les composantes réelles et imaginaires du champ RF qui amène l’aimantation, dont l’évolution est régie par les équations de Bloch, dans un état souhaité. Pour l’optimisation du contraste, l’état d’aimantation souhaité depend du contraste désiré. Soient Ma(t) et Mb(t) l’aimantation des spins a et b. L’optimisation du contraste (maximisation du signal du spin b et minimisation de a), revient à minimiser : C(w) = ||Ma(tf)||2 - ||Mb(tf)||2 avec w = (wx, wy) le champ RF et tf la durée du champ RF au bout de laquelle le contraste souhaité est atteint. Cette durée est généralement assez longue pour permettre la combinaison des phénomènes d’excitation et de relaxation (centaine de ms). La résolution numérique de ces équations est effectuée grâce à l’algorithme GRAPE [4], qui réduit itérativement la fonction de coût par descente de gradient tout en respectant les contraintes imposées par le PMP. Enfin, les inhomogénéités de champ sont prises en compte dans la dynamique du système, afin que le champ RF soit robuste aux déviations par rapport à la fréquence de Larmor.Résultats : Les acquisitions in vivo ont été réalisées sur cerveaux de rat et souris, sur un IRM Bruker petit animal 4.7T, avec des antennes en quadrature. Dans les deux expériences, le champ RF optimal est calculé de sorte à préparer le contraste sur l’axe longitudinal MZ (impulsion non sélective). L’aimantation est ensuite basculée dans le plan transverse en utilisant un schéma d’excitation classique, ici une séquence RARE. Le TE est fixé le plus court possible (8 ms) afin d’assurer la préservation du contraste au moment de l’acquisition. Le TR est fixé suffisamment long (5 s) pour assurer la repouse complète de l’aimantation, contrainte de l’implémentation actuelle de l’algorithme GRAPE. Le calcul des champs RF nécessite la connaissance des temps de relaxation des tissus à contraster. Ces derniers sont estimés à partir de régressions exponentielles du pic d’eau dans des voxels de spectroscopie acquis à plusieurs TE et TR. L’expérience sur souris consiste à saturer le signal du cerveau ([T1c T2c] = [920, 66] ms) et maximiser le signal des muscles pariétaux ([T mT2m] = [1011, 30] ms) situés de part et d’autre du cerveau. La Figure 1 montre l’amplitude du champ RF optimal calculé, ainsi que l’évolution de l’aimantation du cerveau et des muscles pendant l’application de ce champ. L’image acquise est montrée en Figure 2. L’expérience sur rat consiste à maximiser le signal de l’hippocampe ([T1h T2h] = [921, 68] ms) et minimiser celui du thalamus ([T1t T2t] = [832, 63] ms). La Figure 3 montre une comparaison entre l’image acquise au TE maximisant le contraste T2 (65.4 ms) et l’image obtenue grâce au champ optimal.Discussion : Notons tout d’abord que les images obtenues avec les champs RF calculés ne souffrent pas d’artefacts dus aux inhomogénéités de champ malgré la proximité des canaux auditifs. La Figure 2 illustre la flexibilité sur le contraste qu’offrent les champs calculés par contrôle optimal. Il est en effet difficile de reproduire ce contraste avec les pondérations classiques T1 ou T2 car (T2c > T2m) et (T1c ≈ T m). La Figure 3 montre que l’on peut obtenir un contraste meilleur que le simple contraste T2, et que la visualisation du lemnisque médian est nettement améliorée.Remerciements : ANR-DFG (14-CE35-0013-01), Labex PRIMES (ANR-11-LABX-0063/ANR-11-IDEX-0007).1. Lapert M, et al. Exploring the physical limits of saturation contrast in magnetic resonance imaging” Scientific Reports, Nature Publishing Group, 2012, 22. Van Reeth E, et al. Optimizing MRI Contrast with B1 pulses using optimal control theory, IEEE 12th International Symposium on Biomedical Imaging (ISBI), 20163. Pontryagin L S, Mathematical theory of optimal processes, CRC Press, 1987.4. Khaneja N, et al. “Optimal control of coupled spin dynamics: design of nmr pulse sequences by gradient ascent algorithms,” Journal of Magnetic Resonance, 172(2), 2005
Efficient rendering of translucent objects using the diffusion approximation
No full textIn translucent materials such as fruit and marble, light diffuses beneath the surface, creating a distinct appearance. I t is impossible to capture this using traditional reflection models, and requires computation of subsurface light transport. Full simulation has proven intractable, fueling the development of more efficient models, capable of retaining the most salient visual qualities. In this dissertation, we will explore the direction of approximating light transport as a diffusion process, in order to achieve efficient and practical simulation of subsurface light transport. In seminal work by .Jensen et al. [JMLHOla], a simplified diffusion model was introduced: the fast dipole approximation. It reduces the simulation of subsurface light transport to the computation of a surface integral over the object of interest. We show that the dipole approximation is simple enough to achieve the goal of interactive rendering. Two novel integration schemes are developed , which are fast and flexible enough to interactively account for varying viewpoint, illumination and geometry. In this context, we contribute to the dipole model in several ways: an efficient integration procedure over polygons, an importance sampling scheme for Monte Carlo quadrature, and an adjustment for ensuring reciprocity of light transport. The dipole approximation sacrifices accuracy to increase performance. We will analyze the underlying assumptions, and assess the impact for computer graphics. Most importantly, we find that conservation of energy is not guaranteed, and certain geometry-dependent visual cues are missing. When interactivity is not the main concern, a more accurate simulation is possible. We introduce a volumetric diffusion method for arbitrarily shaped objects, based on the multigrid method [Hac85, Sta95]. Two important issues are solved. First, accurate representation of interactions near the object's surface, which is realized by applying the so-called embedded boundary discretization [DCL +gs, JC98]. Second, the solution adaptively refines where required, in order to improve efficiency and keep memory requirements feasible [B084, DeZ93, BBSW94]. Although this approach may be slower than dipole-based methods, it is capable of dealing with both homogeneous and heterogeneous materials, and more accurately reproduces the general appearance of translucent objects. Contrary to previous methods for dealing with similar cases, computation time is only a few minutes. The dipole approximation makes no allowance for radiometric accuracy, but enjoys the attractive property of not requiring a volumetric representation. Inspired by the traditional boundary element method [HP02, HASS03] , we show that a general exact boundary diffusion model can be formulated. We point out the relationship to the well-known radiosity problem [CW93] and our novel polygon integration technique. As a practical application, the boundary diffusion model is employed for experimental validation of the dipole approximation, which confirms the findings of our analysis
Efficient rendering of translucent objects using the diffusion approximation
No full textIn translucent materials such as fruit and marble, light diffuses beneath the surface, creating a distinct appearance. I t is impossible to capture this using traditional reflection models, and requires computation of subsurface light transport. Full simulation has proven intractable, fueling the development of more efficient models, capable of retaining the most salient visual qualities. In this dissertation, we will explore the direction of approximating light transport as a diffusion process, in order to achieve efficient and practical simulation of subsurface light transport. In seminal work by .Jensen et al. [JMLHOla], a simplified diffusion model was introduced: the fast dipole approximation. It reduces the simulation of subsurface light transport to the computation of a surface integral over the object of interest. We show that the dipole approximation is simple enough to achieve the goal of interactive rendering. Two novel integration schemes are developed , which are fast and flexible enough to interactively account for varying viewpoint, illumination and geometry. In this context, we contribute to the dipole model in several ways: an efficient integration procedure over polygons, an importance sampling scheme for Monte Carlo quadrature, and an adjustment for ensuring reciprocity of light transport. The dipole approximation sacrifices accuracy to increase performance. We will analyze the underlying assumptions, and assess the impact for computer graphics. Most importantly, we find that conservation of energy is not guaranteed, and certain geometry-dependent visual cues are missing. When interactivity is not the main concern, a more accurate simulation is possible. We introduce a volumetric diffusion method for arbitrarily shaped objects, based on the multigrid method [Hac85, Sta95]. Two important issues are solved. First, accurate representation of interactions near the object's surface, which is realized by applying the so-called embedded boundary discretization [DCL +gs, JC98]. Second, the solution adaptively refines where required, in order to improve efficiency and keep memory requirements feasible [B084, DeZ93, BBSW94]. Although this approach may be slower than dipole-based methods, it is capable of dealing with both homogeneous and heterogeneous materials, and more accurately reproduces the general appearance of translucent objects. Contrary to previous methods for dealing with similar cases, computation time is only a few minutes. The dipole approximation makes no allowance for radiometric accuracy, but enjoys the attractive property of not requiring a volumetric representation. Inspired by the traditional boundary element method [HP02, HASS03] , we show that a general exact boundary diffusion model can be formulated. We point out the relationship to the well-known radiosity problem [CW93] and our novel polygon integration technique. As a practical application, the boundary diffusion model is employed for experimental validation of the dipole approximation, which confirms the findings of our analysis
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