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

MonoPerfCap: Human Performance Capture from Monocular Video

We present the first marker-less approach for temporally coherent 3D performance capture of a human with general clothing from monocular video. Our approach reconstructs articulated human skeleton motion as well as medium-scale non-rigid surface deformations in general scenes. Human performance capture is a challenging problem due to the large range of articulation, potentially fast motion, and considerable non-rigid deformations, even from multi-view data. Reconstruction from monocular video alone is drastically more challenging, since strong occlusions and the inherent depth ambiguity lead to a highly ill-posed reconstruction problem. We tackle these challenges by a novel approach that employs sparse 2D and 3D human pose detections from a convolutional neural network using a batch-based pose estimation strategy. Joint recovery of per-batch motion allows to resolve the ambiguities of the monocular reconstruction problem based on a low dimensional trajectory subspace. In addition, we propose refinement of the surface geometry based on fully automatically extracted silhouettes to enable medium-scale non-rigid alignment. We demonstrate state-of-the-art performance capture results that enable exciting applications such as video editing and free viewpoint video, previously infeasible from monocular video. Our qualitative and quantitative evaluation demonstrates that our approach significantly outperforms previous monocular methods in terms of accuracy, robustness and scene complexity that can be handled.Comment: Accepted to ACM TOG 2018, to be presented on SIGGRAPH 201

Automatic skeletonization and skin attachment for realistic character animation.

The realism of character animation is associated with a number of tasks ranging from modelling, skin defonnation, motion generation to rendering. In this research we are concerned with two of them: skeletonization and weight assignment for skin deformation. The fonner is to generate a skeleton, which is placed within the character model and links the motion data to the skin shape of the character. The latter assists the modelling of realistic skin shape when a character is in motion. In the current animation production practice, the task of skeletonization is primarily undertaken by hand, i.e. the animator produces an appropriate skeleton and binds it with the skin model of a character. This is inevitably very time-consuming and costs a lot of labour. In order to improve this issue, in this thesis we present an automatic skeletonization framework. It aims at producing high-quality animatible skeletons without heavy human involvement while allowing the animator to maintain the overall control of the process. In the literature, the tenn skeletonization can have different meanings. Most existing research on skeletonization is in the remit of CAD (Computer Aided Design). Although existing research is of significant reference value to animation, their downside is the skeleton generated is either not appropriate for the particular needs of animation, or the methods are computationally expensive. Although some purpose-build animation skeleton generation techniques exist, unfortunately they rely on complicated post-processing procedures, such as thinning and pruning, which again can be undesirable. The proposed skeletonization framework makes use of a new geometric entity known as the 3D silhouette that is an ordinary silhouette with its depth information recorded. We extract a curve skeleton from two 3D silhouettes of a character detected from its two perpendicular projections. The skeletal joints are identified by down sampling the curve skeleton, leading to the generation of the final animation skeleton. The efficiency and quality are major performance indicators in animation skeleton generation. Our framework achieves the former by providing a 2D solution to the 3D skeletonization problem. Reducing in dimensions brings much faster performances. Experiments and comparisons are carried out to demonstrate the computational simplicity. Its accuracy is also verified via these experiments and comparisons. To link a skeleton to the skin, accordingly we present a skin attachment framework aiming at automatic and reasonable weight distribution. It differs from the conventional algorithms in taking topological information into account during weight computation. An effective range is defined for a joint. Skin vertices located outside the effective range will not be affected by this joint. By this means, we provide a solution to remove the influence of a topologically distant, hence highly likely irrelevant joint on a vertex. A user-defined parameter is also provided in this algorithm, which allows different deformation effects to be obtained according to user's needs. Experiments and comparisons prove that the presented framework results in weight distribution of good quality. Thus it frees animators from tedious manual weight editing. Furthermore, it is flexible to be used with various deformation algorithms

Non-Traditional Rig for virtual environment systems. Case study: Arm rig

Este trabajo presenta nuevas especificaciones de diseño para rigs de esqueleto basado en problemas encontrados en Entornos Virtuales, tomando en cuenta sus limitaciones y requerimientos, y la relación entre los usuarios y el avatar que encarnan. Este acercamiento es una alternativa al rig de esqueleto tradicionalmente usado en animación, que puede generar deformaciones indeseadas en el mesh, ya que suelen ser hechos con animación artesanal, y optimización de software, en mente. Este Trabajo incluye resultados prometedores en cuanto a una deformación más natural de la muñeca de un personaje digital, validado con la evaluación subjetiva de ocho expertos en el área de producción 3D.1- Introducción 2- Trabajos Previos 3- Nuestro Enfoque 4- Experimento y Resultados 5- ConclusiónThis paper presents new design specifications for skeleton rigs based on Virtual Environment problems, taking into account their limitations and requirements, and the relationship between users and the virtual avatar they embody. This approach is an alternative to traditional skeleton rigs used in animation, which may generate undesirable deformations in the mesh since they are usually made with handcrafted animation, and software optimization, in mind. This work includes promissory results in the naturalness of the deformation of the wrist of a digital character, validated with eight experts’ subjective evaluation in 3D production.Pregrad

An Automated Build System for Articulated Characters

Rigging is the process of designing and implementing the manipulation architecture for an animated three-dimensional character. Rigs that give the animator the most control tend to be the most difficult to set up and maintain. Due to the linear nature of some elements of rigging, the more complicated a rig, the more time-intensive--and therefore more expensive--to achieve a high quality rig. A solution to complex rig iterability is to automate as much of the process as possible. The topic of this thesis is a framework for modular rigging automation, with a focus on quick and efficient rig iteration. A rigger is able to design a rig from predefined module elements (rig blocks) or quickly script new blocks. A rig is deconstructed into these elemental blocks and merged into a single rig script to regenerate the rig and attach a character\u27s geometry

Sketch-based skeleton-driven 2D animation and motion capture.

This research is concerned with the development of a set of novel sketch-based skeleton-driven 2D animation techniques, which allow the user to produce realistic 2D character animation efficiently. The technique consists of three parts: sketch-based skeleton-driven 2D animation production, 2D motion capture and a cartoon animation filter. For 2D animation production, the traditional way is drawing the key-frames by experienced animators manually. It is a laborious and time-consuming process. With the proposed techniques, the user only inputs one image ofa character and sketches a skeleton for each subsequent key-frame. The system then deforms the character according to the sketches and produces animation automatically. To perform 2D shape deformation, a variable-length needle model is developed, which divides the deformation into two stages: skeleton driven deformation and nonlinear deformation in joint areas. This approach preserves the local geometric features and global area during animation. Compared with existing 2D shape deformation algorithms, it reduces the computation complexity while still yielding plausible deformation results. To capture the motion of a character from exiting 2D image sequences, a 2D motion capture technique is presented. Since this technique is skeleton-driven, the motion of a 2D character is captured by tracking the joint positions. Using both geometric and visual features, this problem can be solved by ptimization, which prevents self-occlusion and feature disappearance. After tracking, the motion data are retargeted to a new character using the deformation algorithm proposed in the first part. This facilitates the reuse of the characteristics of motion contained in existing moving images, making the process of cartoon generation easy for artists and novices alike. Subsequent to the 2D animation production and motion capture,"Cartoon Animation Filter" is implemented and applied. Following the animation principles, this filter processes two types of cartoon input: a single frame of a cartoon character and motion capture data from an image sequence. It adds anticipation and follow-through to the motion with related squash and stretch effect

Dragon Slayer Short Film Modeling and Rigging a Quadruped Dragon

This thesis is a look at the design and implementation of a quadrupedal dragon, as specified by the needs of the short film Dragonslayer. It looks at the modeling of the three dimensional creature from artistic and technical points of view. The dragon is a worldwide fantasy and cultural icon, and this thesis focuses on the creation of one grounded in the western fantasy of the middle ages. The western dragons have four legs, a pair of wings, horns, and a relatively stout body in comparison to the eastern dragons, which more closely resemble serpents and possess antlers instead of horns. The distinction of the dragon as being quadrupedal is significant, since many rigs or models in industry use a wyvern, bipedal dragon, model instead. A wyvern is a much simpler design and very closely resembles the actual anatomy of a bat. Because the quadrupedal dragon is a creature that does not exist or have comparable anatomy to any known animals on Earth, its anatomy was based on a combination of real animal physiology and some educated inferences to fill in any anatomical weaknesses. Since the dragon is such a recognized character from mythos, it is important that this dragon be an anatomically sound creature that does little to damage the suspended disbelief of a viewer. The dragon is also rigged to be versatile, machine efficient, and intuitively manipulated by an animator for use in film, video games, television, or even academic exercises

Shadows, touch and digital puppeteering: a media archaeological approach

Aims The practical aim of this research project is to create a multi-touch digital puppetry system that simulates shadow theatre environments and translates gestural acts of touch into live and expressive control of virtual shadow figures. The research is focussed on the qualities of movement achievable through the haptics of single and multi-touch control of the digital puppets in the simulation. An associated aim is to create a collaborative environment where multiple performers can control dynamic animation and scenography, and create novel visualisations and narratives. The conceptual aim is to link traditional and new forms of puppetry seeking cultural significance in the ‘remediation’ of old forms that avail themselves of new haptic resources and collaborative interfaces. The thesis evaluates related prior art where traditional worlds of shadow performance meet new media, digital projection and 3D simulation, in order to investigate how changing technical contexts transform the potential of shadows as an expressive medium. Methodology The thesis uses cultural analysis of relevant documentary material to contextualise the practical work by relating the media archaeology of 2D puppetry—shadows, shadowgraphs and silhouettes—to landmark work in real-time computer graphics and performance animation. The survey considers the work of puppeteers, animators, computer graphics specialists and media artists. Through practice and an experimental approach to critical digital creativity, the study provides practical evidence of multiple iterations of controllable physics-based animation delivering expressive puppet motion through touch and multiuser interaction. Video sequences of puppet movement and written observational analysis document the intangible aspects of animation in performance. Through re-animation of archival shadow puppets, the study presents an emerging artistic media archaeological method. The major element of this method has been the restoration of a collection of Turkish Karagöz Shadow puppets from the Institut International de la Marionnette (Charleville, France) into a playable digital form. Results The thesis presents a developing creative and analytical framework for digital shadow puppetry. It proposes a media archaeological method for working creatively with puppet archives that unlock the kinetic and expressive potential of restored figures. The interaction design introduces novel approaches to puppetry control systems—using spring networks—with objects under physics-simulation that demonstrate emergent expressive qualities. The system facilitates a dance of agency¹ between puppeteer and digital instrument. The practical elements have produced several software iterations and a tool-kit for generating elegant, nuanced multi-touch shadow puppetry. The study presents accidental discoveries—serendipitous benefits of open-ended practical exploration. For instance: the extensible nature of the control system means novel input—other than touch—can provide exciting potential for accessible user interaction, e.g. with gaze duration and eye direction. The study also identifies limitations including the rate of software change and obsolescence, the scope of physics-based animation and failures of simulation. Originality/value The work has historical value in that it documents and begins a media archaeology of digital puppetry, an animated phenomenon of increasing academic and commercial interest. The work is of artistic value providing an interactive approach to making digital performance from archival material in the domain of shadow theatre. The work contributes to the electronic heritage of existing puppetry collections. The study establishes a survey of digital puppetry, setting a research agenda for future studies. Work may proceed to digitise, rig and create collaborative and web-mediated touch-based motion control systems for 2D and 3D puppets. The present study thus provides a solid platform to restore past performances and create new work from old, near forgotten-forms. ¹ Following Andrew Pickering, puppetry is ‘a temporally extended back-and-forth dance of human and non-human agency in which activity and passivity on both sides are reciprocally intertwined’ PICKERING, A. 2010. Material Culture and the Dance of Agency. In: BEAUDRY, M. C. & HICKS, D. (eds.) Oxford Handbook of Material Culture Studies. Oxford University Press.

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 animación por computadora el proceso de crear un personaje de animación es comúnmente una tarea larga y tediosa. Un personaje de animación 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 común que este tenga una estructura interna, un esqueleto de animación. Cuando un esqueleto esta asociado con una malla tridimensional, a esta asociación se le llama ligado de esqueleto, y un esqueleto ligado a la mallade un personaje es conocido en inglés 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 definición y creación 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 métodos 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 método de skinning elegido. El principal objetivo de esta tesis es el generar un método de rigging para un modelo tridimensional arbitrario con una interacción mínima del usuario. Este método puede ser útil para gente con poca experiencia en el campo de la animación, o para gente experimentada que quiera acelerar el proceso de rigging de días a horas o inclusive minutos, dependiendo de la calidad requerida. Teniendo en mente esta situación, hemos diseñado nuestro método 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: -Generación de un rig de animación: Teniendo una malla cerrada cualquiera, hemos implementado un método para crear primero un esqueleto geométrico sin refinar, el cual capture la pose y la topología del personaje usado como elemento de entrada. Tomando este esqueleto geométrico como punto de partida usamos un método de refinado que crea un "esqueleto lógico" adaptado a la forma del geométrico basándonos en una plantilla definida por el usuario o previamente definida, que sea compatible con los formatos actuales de animación. El esqueleto lógico generado será especifico para cada personaje, y esta ligado a la malla de entrada para así crear un rig de animación. - Skinning: Teniendo definido un rig de animación para una malla de entrada arbitraria, hemos desarrollado un método mejorado de skinning, este método sera basado en el algoritmo "Linear Blending Skinnig" (algoritmo de skinning por combinación lineal, LBS por sus siglas en inglés). Nuestras contribuciones en el campo del skinnig son: - Proponemos un nuevo método de segmentación de mallas que sea la parte medular para algoritmos de asignación automática de pesos y de skinning, también hemos desarrollado un algoritmo automático que calcule los pesos utilizados por el algoritmo LBS para una malla poligonal que tenga un rig de animación. - Nuestro algoritmo de skinning propuesto usará como base las características del algoritmo LBS. El principal propósito 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 animación sobre su propio eje. Nuestros resultados son comparados con los métodos 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