92 research outputs found
A survey of real-time crowd rendering
In this survey we review, classify and compare existing approaches for real-time crowd rendering. We first overview character animation techniques, as they are highly tied to crowd rendering performance, and then we analyze the state of the art in crowd rendering. We discuss different representations for level-of-detail (LoD) rendering of animated characters, including polygon-based, point-based, and image-based techniques, and review different criteria for runtime LoD selection. Besides LoD approaches, we review classic acceleration schemes, such as frustum culling and occlusion culling, and describe how they can be adapted to handle crowds of animated characters. We also discuss specific acceleration techniques for crowd rendering, such as primitive pseudo-instancing, palette skinning, and dynamic key-pose caching, which benefit from current graphics hardware. We also address other factors affecting performance and realism of crowds such as lighting, shadowing, clothing and variability. Finally we provide an exhaustive comparison of the most relevant approaches in the field.Peer ReviewedPostprint (author's final draft
Matrix-based Parameterizations of Skeletal Animated Appearance
Alors que le rendu réaliste gagne de l’ampleur dans l’industrie, les techniques à la
fois photoréalistes et basées sur la physique, complexes en terme de temps de calcul,
requièrent souvent une étape de précalcul hors-ligne. Les applications en temps réel,
comme les jeux vidéo et la réalité virtuelle, se basent sur des techniques d’approximation
et de précalcul pour atteindre des résultats réalistes. L’objectif de ce mémoire est l’investigation
de différentes paramétrisations animées pour concevoir une technique d’approximation
de rendu réaliste en temps réel.
Notre investigation se concentre sur le rendu d’effets visuels appliqués à des personnages
animés par modèle d’armature squelettique. Des paramétrisations combinant
des données de mouvement et d’apparence nous permettent l’extraction de paramètres
pour le processus en temps réel. Établir une dépendance linéaire entre le mouvement et
l’apparence est ainsi au coeur de notre méthode.
Nous nous concentrons sur l’occultation ambiante, où la simulation de l’occultation
est causée par des objets à proximité bloquant la lumière environnante, jugée uniforme.
L’occultation ambiante est une technique indépendante du point de vue, et elle est désormais
essentielle pour le réalisme en temps réel. Nous examinons plusieurs paramétrisations
qui traitent l’espace du maillage en fonction de l’information d’animation par
squelette et/ou du maillage géométrique.
Nous sommes capables d’approximer la réalité pour l’occultation ambiante avec une
faible erreur. Notre technique pourrait également être étendue à d’autres effets visuels
tels le rendu de la peau humaine (diffusion sous-surface), les changements de couleur
dépendant du point de vue, les déformations musculaires, la fourrure ou encore les vêtements.While realistic rendering gains more popularity in industry, photorealistic and physically-
based techniques often necessitate offline processing due to their computational
complexity. Real-time applications, such as video games and virtual reality, rely mostly
on approximation and precomputation techniques to achieve realistic results. The objective
of this thesis is to investigate different animated parameterizations in order to devise
a technique that can approximate realistic rendering results in real time.
Our investigation focuses on rendering visual effects applied to skinned skeletonbased
characters. Combined parameterizations of motion and appearance data are used
to extract parameters that can be used in a real-time approximation. Trying to establish
a linear dependency between motion and appearance is the basis of our method.
We focus on ambient occlusion, a simulation of shadowing caused by objects that
block ambient light. Ambient occlusion is a view-independent technique important for
realism. We consider different parameterization techniques that treat the mesh space
depending on skeletal animation information and/or mesh geometry.
We are able to approximate ground-truth ambient occlusion with low error. Our
technique can also be extended to different visual effects, such as rendering human skin
(subsurface scattering), changes in color due to the view orientation, deformation of
muscles, fur, or clothe
Implicit Skinning: Real-Time Skin Deformation with Contact Modeling
SIGGRAPH 2013 Conference ProceedingsInternational audienceGeometric skinning techniques, such as smooth blending or dualquaternions, are very popular in the industry for their high performances, but fail to mimic realistic deformations. Other methods make use of physical simulation or control volume to better capture the skin behavior, yet they cannot deliver real-time feedback. In this paper, we present the first purely geometric method handling skin contact effects and muscular bulges in real-time. The insight is to exploit the advanced composition mechanism of volumetric, implicit representations for correcting the results of geometric skinning techniques. The mesh is first approximated by a set of implicit surfaces. At each animation step, these surfaces are combined in real-time and used to adjust the position of mesh vertices, starting from their smooth skinning position. This deformation step is done without any loss of detail and seamlessly handles contacts between skin parts. As it acts as a post-process, our method fits well into the standard animation pipeline. Moreover, it requires no intensive computation step such as collision detection, and therefore provides real-time performances
Improving automatic rigging for 3D humanoid characters
In the field of computer animation the process of creating an animated character is usually a long and tedious task. An animation character is usually efined by a 3D mesh (a set of triangles in the space) that gives its external appearance or shape to the character. It also used to have an inner structure, the skeleton. When a skeleton is associated to a character mesh, this association is called skeleton binding, and a skeleton bound to a character mesh is an animation rig.
Rigging from scratch a character can be a very boring process. The definition and creation of a centered skeleton together with the ’painting’, by an artist,of the influence parameters between the skeleton and the mesh (the skinning) s the most demanding part to achieve an acceptable behavior for a character.
This rigging process can be simplified and accelerated using an automatic rigging method. Automatic rigging methods consist in taking as input a 3D mesh, generate a skeleton based in the shape of the original model, bound the input mesh to the generated skeleton, and finally to compute a set of parameters based in a chosen skinning method. The main objective of this thesis is to generate a method for rigging a 3D arbitrary model with minimum user interaction. This can be useful to people without experience in the animation field or to experienced people to accelerate the rigging process from days to hours or minutes depending the needed quality. Having in mind this situation we have designed our method as a set of tools that can be applied to general input models defined by an artist. The contributions made in the development of this thesis can be summarized as:
• Generation of an animation Rig: Having an arbitrary closed mesh we have implemented a thinning method to create first an unrefined geometry skeleton that captures the topology and pose of the input character. Using this geometric skeleton as starting point we use a refining method that creates an adjusted logic skeleton based in a template, or may be defined by the user, that is compatible with the current animation formats. The output logic skeleton is specific for each character, and it is bounded to the input mesh to create an animation rig.
• Skinning: Having defined an animation rig for an arbitrary mesh we have developed an improved skinning method; this method is based on the Linear Blend Skinning(LBS) algorithm. Our contributions in the skinning field can be sub-divided in:
– We propose a segmentation method that works as the core element in a weight assigning algorithm and a skinning lgorithm, we also have developed an automatic algorithm to compute the skin weights of the LBS Skinning of a rigged polygonal mesh.
– Our proposed skinning algorithm uses as base the features of the LBS Skinning. The main purpose of the developed algorithm is to solve the well-known ”candy wrap” artifact; that produces a substantial loss of volume when a link of an animation skeleton is rotated over its own axis. We have compared our results with the most important methods in the skinning field, such as Dual Quaternion Skinning (DQS) and LBS, achieving a better performance over DQS and an improvement in quality over LBS.
• Animation tools: We have developed a set of Autodesk Maya commands that works together as rig tool, using our previous proposed methods.
• Animation loader: Moreover, an animation loader tool has been implemented, that allows the user to load animations from a skeleton with different structure to a rigged 3D model. The contributions previously described has been published in 3 research papers, the first two were presented in international congresses and the third one was acepted for its publication in an JCR indexed journal.En el campo de la animaciĂłn por computadora el proceso de crear un personaje de animaciĂłn es comĂşnmente una tarea larga y tediosa. Un personaje de animaciĂłn está definido usualmente por una malla tridimensional (un conjunto de triángulos en el espacio) que le dan su apariencia externa y forma al personaje. Es igualmente comĂşn que este tenga una estructura interna, un esqueleto de animaciĂłn. Cuando un esqueleto esta asociado con una malla tridimensional, a esta asociaciĂłn se le llama ligado de esqueleto, y un esqueleto ligado a la mallade un personaje es conocido en inglĂ©s como "animation rig" (el conjunto de elementos necesarios, que unidos sirven para animar un personaje). Hacer el rigging desde cero de un personaje puede ser un proceso muy tedioso. La definiciĂłn y creaciĂłn de un esqueleto centrado en la malla junto con el "pintado" por medio de un artista de los parámetros de influencia entre el esqueleto y la malla 3D (lo que se conoce como skinning) es la parte mas demandante para alcanzar un compartimiento aceptable al deformase (moverse) la malla de un personaje. Los mĂ©todos de rigging automáticos consisten en tomar una malla tridimensional como elemento de entrada, generar un esqueleto basado en la forma del modelo original, ligar la malla de entrada al esqueleto generado y finamente calcular el conjunto de parámetros utilizados por el mĂ©todo de skinning elegido. El principal objetivo de esta tesis es el generar un mĂ©todo de rigging para un modelo tridimensional arbitrario con una interacciĂłn mĂnima del usuario. Este mĂ©todo puede ser Ăştil para gente con poca experiencia en el campo de la animaciĂłn, o para gente experimentada que quiera acelerar el proceso de rigging de dĂas a horas o inclusive minutos, dependiendo de la calidad requerida. Teniendo en mente esta situaciĂłn, hemos diseñado nuestro mĂ©todo como un conjunto de herramientas las cuales pueden ser aplicadas a modelos de entrada generados por cualquier artista. Las contribuciones hechas en el desarrollo de esta tesis pueden resumirse a: -GeneraciĂłn de un rig de animaciĂłn: Teniendo una malla cerrada cualquiera, hemos implementado un mĂ©todo para crear primero un esqueleto geomĂ©trico sin refinar, el cual capture la pose y la topologĂa del personaje usado como elemento de entrada. Tomando este esqueleto geomĂ©trico como punto de partida usamos un mĂ©todo de refinado que crea un "esqueleto lĂłgico" adaptado a la forma del geomĂ©trico basándonos en una plantilla definida por el usuario o previamente definida, que sea compatible con los formatos actuales de animaciĂłn. El esqueleto lĂłgico generado será especifico para cada personaje, y esta ligado a la malla de entrada para asĂ crear un rig de animaciĂłn. - Skinning: Teniendo definido un rig de animaciĂłn para una malla de entrada arbitraria, hemos desarrollado un mĂ©todo mejorado de skinning, este mĂ©todo sera basado en el algoritmo "Linear Blending Skinnig" (algoritmo de skinning por combinaciĂłn lineal, LBS por sus siglas en inglĂ©s). Nuestras contribuciones en el campo del skinnig son: - Proponemos un nuevo mĂ©todo de segmentaciĂłn de mallas que sea la parte medular para algoritmos de asignaciĂłn automática de pesos y de skinning, tambiĂ©n hemos desarrollado un algoritmo automático que calcule los pesos utilizados por el algoritmo LBS para una malla poligonal que tenga un rig de animaciĂłn. - Nuestro algoritmo de skinning propuesto usará como base las caracterĂsticas del algoritmo LBS. El principal propĂłsito del algoritmo desarrollado es el solucionar el defecto conocido como "envoltura de caramelo" (candy wrapper artifact), que produce una substancial perdida de volumen al rotar una de las articulaciones del esqueleto de animaciĂłn sobre su propio eje. Nuestros resultados son comparados con los mĂ©todos mas importantes en el campo del skinning tal como Cuaterniones Duales (Dual Quaternions Skinning, DQS) y LBS, alcanzando un mejor desempeño que DQS y una mejora importante sobre LBSPostprint (published version
Investigating the Effect of Mixing Two Skinning Algorithms on Area Preservation
We propose to investigate the effects of by mixing weights between two vertex skinning algorithms. The vertex skinning algorithms in discussion are Linear Blend Skinning (LBS) and Dual Quaternion Skinning (DQS), each of which is not perfect if used in isolation. With our proposed algorithm, a per-vertex mixing weight determines the linear combination with which LBS and DQS are employed to find a deformed mesh that is neither lacking in volume due to LBS, nor contains volume gain from DQS. Finding the best mixing weight will allow for more plausible deformations, with respect to shape and volume of models. We will investigate previous attempts to fix the flaws of LBS and DQS , which is important especially when many models are being skinned. This work extends the work by Yin, which was published in 2019, meaning this is still a very novel approach to skinning, without much other published material building off it yet. The expected outcome is an insight into the validity of Yin's approach in specific setups and how DQS and LBS can be combined at a per-vertex level to sustain mesh area and shape
MoDA: Modeling Deformable 3D Objects from Casual Videos
In this paper, we focus on the challenges of modeling deformable 3D objects
from casual videos. With the popularity of neural radiance fields (NeRF), many
works extend it to dynamic scenes with a canonical NeRF and a deformation model
that achieves 3D point transformation between the observation space and the
canonical space. Recent works rely on linear blend skinning (LBS) to achieve
the canonical-observation transformation. However, the linearly weighted
combination of rigid transformation matrices is not guaranteed to be rigid. As
a matter of fact, unexpected scale and shear factors often appear. In practice,
using LBS as the deformation model can always lead to skin-collapsing artifacts
for bending or twisting motions. To solve this problem, we propose neural dual
quaternion blend skinning (NeuDBS) to achieve 3D point deformation, which can
perform rigid transformation without skin-collapsing artifacts. In the endeavor
to register 2D pixels across different frames, we establish a correspondence
between canonical feature embeddings that encodes 3D points within the
canonical space, and 2D image features by solving an optimal transport problem.
Besides, we introduce a texture filtering approach for texture rendering that
effectively minimizes the impact of noisy colors outside target deformable
objects. Extensive experiments on real and synthetic datasets show that our
approach can reconstruct 3D models for humans and animals with better
qualitative and quantitative performance than state-of-the-art methods
LiveCap: Real-time Human Performance Capture from Monocular Video
We present the first real-time human performance capture approach that
reconstructs dense, space-time coherent deforming geometry of entire humans in
general everyday clothing from just a single RGB video. We propose a novel
two-stage analysis-by-synthesis optimization whose formulation and
implementation are designed for high performance. In the first stage, a skinned
template model is jointly fitted to background subtracted input video, 2D and
3D skeleton joint positions found using a deep neural network, and a set of
sparse facial landmark detections. In the second stage, dense non-rigid 3D
deformations of skin and even loose apparel are captured based on a novel
real-time capable algorithm for non-rigid tracking using dense photometric and
silhouette constraints. Our novel energy formulation leverages automatically
identified material regions on the template to model the differing non-rigid
deformation behavior of skin and apparel. The two resulting non-linear
optimization problems per-frame are solved with specially-tailored
data-parallel Gauss-Newton solvers. In order to achieve real-time performance
of over 25Hz, we design a pipelined parallel architecture using the CPU and two
commodity GPUs. Our method is the first real-time monocular approach for
full-body performance capture. Our method yields comparable accuracy with
off-line performance capture techniques, while being orders of magnitude
faster
Robust iso-surface tracking for interactive character skinning
International audienceWe present a novel approach to interactive character skinning, which is robust to extreme character movements, handles skin contacts and produces the effect of skin elasticity (sliding). Our approach builds on the idea of implicit skinning in which the character is approximated by a 3D scalar field and mesh-vertices are appropriately re-projected. Instead of being bound by an initial skinning solution used to initialize the shape at each time step, we use the skin mesh to directly track iso-surfaces of the field over time. Technical problems are two-fold: firstly, all contact surfaces generated between skin parts should be captured as iso-surfaces of the implicit field; secondly, the tracking method should capture elastic skin effects when the joints bend, and as the character returns to its rest shape, so the skin must follow. Our solutions include: new composition operators enabling blending effects and local self-contact between implicit surfaces, as well as a tangential relaxation scheme derived from the as-rigid-as possible energy to solve the tracking problem
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