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A motion retargeting process is necessary as the body size and proportion of the actors are generally different from those of the target characters. However, the original spatial relationship between the multiple characters and the environment is easily broken when using previous motion retargeting methods, which are generally performed for each character independently. Therefore, time‐consuming manual adjustments by animators are usually required to obtain satisfactory results. To address these issues, we present a novel multicharacter motion retargeting method that preserves various types of spatial relationships between characters and environments. We establish a unified deformation‐based framework for the motion retargeting of multiple characters (more than two) or nonhuman characters with complex interactions. Also, an interactive motion editing interface with immediate feedback to the user is provided. We experimentally show that our method achieves a speedup when compared with previous motion retargeting methods. [ABSTRACT FROM AUTHOR]

Authoring an appealing animation for a virtual character is a challenging task. In computer‐aided keyframe animation artists define the key poses of a character by manipulating its underlying skeletons. To look plausible, a character pose must respect many ill‐defined constraints, and so the resulting realism greatly depends on the animator's skill and knowledge. Animation software provide tools to help in this matter, relying on various algorithms to automatically enforce some of these constraints. The increasing availability of motion capture data has raised interest in data‐driven approaches to pose design, with the potential of shifting more of the task of assessing realism from the artist to the computer, and to provide easier access to nonexperts. In this article, we propose such a method, relying on neural networks to automatically learn the constraints from the data. We describe an efficient tool for pose design, allowing Naïve users to intuitively manipulate a pose to create character animations. [ABSTRACT FROM AUTHOR]

We propose a design framework to assist with user‐generated content in facial animation — without requiring any animation experience or ground truth reference. Where conventional prototyping methods rely on handcrafting by experienced animators, our approach looks to encode the role of the animator as an Evolutionary Algorithm acting on animation controls, driven by visual feedback from a user. Presented as a simple interface, users sample control combinations and select favourable results to influence later sampling. Over multiple iterations of disregarding unfavourable control values, parameters converge towards the user's ideal. We demonstrate our framework through two non‐trivial applications: creating highly nuanced expressions by evolving control values of a face rig and non‐linear motion through evolving control point positions of animation curves. [ABSTRACT FROM AUTHOR]

Rig-space physics a finite element method(FEM) based simulation technique that aims at adding secondary motion on a character while maintaining seamless cooperation with traditional animation pipelines. We enhance the rig-space physics by introducing several techniques, including general field interaction, proportional-derivative control, and improved material control. This allows an animator to perform various interferences to the simulation process and create more abundant animation effects. Moreover, we also improve the numerical stability of the simulation algorithm by prepending a conjugate gradient procedure. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The crucial concept of modeling and synthesis/control of human motion (including face and body) for animation has been widely studied and explored in the literature. In this regard, the audience's perception of generated or recorded animation scenes is of critical importance. In this paper, we explore and conceptualize the general notions that need to be taken into account for human motion to maintain perceptual accuracy. We propose a paradigm called Perceptual Validity composed of four major components, which are discussed in detail. The model is concerned with different aspects of the scene such as correct illustration of the stimuli, context, and local/global relations of various visual cues present in human motion. Satisfying all the proposed principles, based on the literature, seems compulsory and vital for synthesis of perceptually valid animation scenes of human motion. We investigate the relative significance of the different components of the paradigm using feedback from expert animators and conduct a case study on one of the components of the paradigm. For further evaluation and exploration, Disney's principles of animation are discussed and compared against our proposed paradigm. We argue that while there are significant parallels and overlaps, our model is only focused on and more inclusive towards human motion and can therefore provide a valuable set of guidelines for animators in the field of character animation. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Timing plays a key role in expressing the qualitative aspects of a character's motion; that is, conveying emotional state, personality, and character role, all potentially without changing spatial positions. Temporal editing of locomotion style is particularly difficult for a novice animator since observers are not well attuned to the sense of weight and energy displayed through motion timing; and the interface for adjusting timing is far less intuitive to use than that for adjusting pose. In this paper, we propose an editing system that effectively captures the timing variations in an example locomotion set and utilizes them for style transfer from one motion to another via both global and upper-body timing transfers. The global timing transfer focuses on matching the input motion to the body speed of the selected example motion, while the upper-body timing transfer propagates the sense of movement flow -- succession -- through the torso and arms. Our transfer process is based on key times detected from the example set and transferring the relative changes of angle rotation in the upper body joints from a timing source to an input target motion. We demonstrate that our approach is practical in an interactive application such that a set of short locomotion cycles can be applied to generate a longer sequence with continuously varied timings. [ABSTRACT FROM AUTHOR]

Interactive rigid body simulation is an important part of many modern computer tools, which no authoring tool nor game engine can do without. Such high-performance computer tools open up new possibilities for changing how designers, engineers, modelers and animators work with their design problems. This paper is a self contained state-of-the-art report on the physics, the models, the numerical methods and the algorithms used in interactive rigid body simulation all of which have evolved and matured over the past 20 years. Furthermore, the paper communicates the mathematical and theoretical details in a pedagogical manner. This paper is not only a stake in the sand on what has been done, it also seeks to give the reader deeper insights to help guide their future research. [ABSTRACT FROM AUTHOR]

Enabling animators to smoothly transform between animated meshes of differing topologies is a long-standing problem in geometric modelling and computer animation. In this paper, we propose a new hybrid approach built upon the advantages of scalar field-based models (often called implicit surfaces) which can easily change their topology by changing their defining scalar field. Given two meshes, animated by their rigging-skeletons, we associate each mesh with its own approximating implicit surface. This implicit surface moves synchronously with the mesh. The shape-metamorphosis process is performed in several steps: first, we collapse the two meshes to their corresponding approximating implicit surfaces, then we transform between the two implicit surfaces and finally we inverse transition from the resulting metamorphosed implicit surface to the target mesh. The examples presented in this paper demonstrating the results of the proposed technique were implemented using an in-house plug-in for Maya™. [ABSTRACT FROM AUTHOR]

ABSTRACT Content-based human motion retrieval is important for animators with the development of motion editing and synthesis, which need to search similar motions in large databases. Obtaining text-based representation from quantization of mocap data turned out to be efficient. It becomes a fundamental step of many researches in human motion analysis. Geometric features are one of these techniques, which involve much prior knowledge and reduce data redundancy of numerical data. We describe geometric features as basic unit to define human motions (also called mo-words) and view a human motion as a generative process. Therefore, we obtain topic motions, which possess more semantic information using latent Dirichlet allocation by learning from massive training examples in order to understand motions better. We combine probabilistic model with human motion retrieval and come up with a new representation of human motions and a new retrieval framework. Our experiments demonstrate its advantages, both for understanding motions and retrieval. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Rigging an arbitrary 3D character by creating an animation skeleton is a time-consuming process even for experienced animators. In this paper, we present an algorithm that automatically creates animation rigs for multi-component 3D models, as they are typically found in online shape databases. Our algorithm takes as input a multi-component model and an input animation skeleton with associated motion data. It then creates a target skeleton for the input model, calculates the rigid skinning weights, and a mapping between the joints of the target skeleton and the input animation skeleton. The automatic approach does not need additional semantic information, such as component labels or user-provided correspondences, and succeeds on a wide range of models where the number of components is significantly different. It implicitly handles large scale and proportional differences between input and target skeletons and can deal with certain morphological differences, e.g., if input and target have different numbers of limbs. The output of our algorithm can be directly used in a retargeting system to create a plausible animated character. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new method to index and retrieve animation scenes in which multiple characters closely interact with one another. Such a technique can be an important tool for animators when they want to automatically extract the desired scene from a large database of animation sequence. Existing methods for single character movements do not scale well for multiple characters as they do not take into account the interaction of different body parts. In this paper, we propose a new distance function that computes the similarity of two-character interations using the spatial relationship of the body parts. For each interaction, we produce a time-varying graph structure based on the proximity of different joints, and compute the similarity of interactions by comparing the topology and Laplacian coordinates of the time-varying graph. Experimental results show that the proposed method outperforms previous methods which are based on the kinematics of individual characters. The top retrieved samples are found similar in high level semantics while containing style variations. [ABSTRACT FROM AUTHOR]

Camera path planning for character motions is a fundamental and important research topic, benefiting many animation applications. Existing optimal-based approaches are generally computationally expensive and infeasible for interactive applications. In this paper, we propose an efficient approach that can take many constraints of finding the camera path into account and can potentially enable interactive camera control. Instead of solving a highly complicated camera optimization problem in a spatiotemporal four-dimensional space, we heuristically determine the camera path based on an efficient greedy-based tree traversal approach. The experimental results show that the proposed approach can efficiently generate a smooth, informative, and aesthetic camera path that can reveal the significant features of character motions. Moreover, the conducted user study also shows that the generated camera paths are comparable to those of a state-of-the-art approach and those made by professional animators. Copyright © 2011 John Wiley & Sons, Ltd. This paper proposes an efficient approach of finding the camera path for human motion and can potentially enable interactive camera control. Instead of solving a complicated camera optimization problem, we heuristically determine the camera path-based on an efficient greedy-based tree traversal approach. The experimental results show that the proposed approach generate a smooth, informative, and aesthetic motion over view efficiently. [ABSTRACT FROM AUTHOR]

Cognitive and behavioral models have become popular methods for creating autonomous self-animating characters. Creating these models present the following challenges: (1) creating a cognitive or behavioral model is a time-intensive and complex process that must be done by an expert programmer and (2) the models are created to solve a specific problem in a given environment and because of their specific nature cannot be easily reused. Combining existing models together would allow an animator, without the need for a programmer, to create new characters in less time and to leverage each model's strengths, resulting in an increase in the character's performance and in the creation of new behaviors and animations. This article provides a framework that can aggregate existing behavioral and cognitive models into an ensemble. An animator has only to rate how appropriately a character performs in a set of scenarios and the system then uses machine learning to determine how the character should act given the current situation. Empirical results from multiple case studies validate the approach. [ABSTRACT FROM AUTHOR]

Traditionally, levels of detail (LOD) for animated characters are computed from a single pose. Later techniques refined this approach by considering a set of sample poses and evaluating a more representative error metric. A recent approach to the character animation problem, animation space, (AS) provides a framework for measuring error analytically. The work presented here uses the animation-space framework to derive two new techniques to improve the quality of LOD approximations. First, we use an animation-space distance metric within a progressive mesh-based LOD scheme, giving results that are reasonable across a range of poses, without requiring that the pose space be sampled. Second, we simplify individual vertices by reducing the number of bones that influence them, using a constrained least-squares optimization. This influence simplification is combined with the progressive mesh to form a single stream of simplifications. Influence simplification reduces the geometric error by up to an order of magnitude, and allows models to be simplified further than is possible with only a progressive mesh. Quantitative (geometric error metrics) and qualititative (user perceptual) experiments confirm that these new extensions provide significant improvements in quality over traditional, naïve simplification; and while there is naturally some impact on the speed of the off-line simplification process, it is not prohibitive. [ABSTRACT FROM AUTHOR]

We describe an animation creation system called PASCAL that supports sketch-based modeling and physics augmented locomotion simultaneously. The system uses sketches and reconfigurable space canvases as basic modeling primitives and uses physics to improve the expressiveness and efficiency of several animation techniques to obtain controllable and plausible locomotion animation. The usability evaluation of the system was conducted both with professional and novice animators. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel method for editing stylistic human motions. We represent styles as differences between stylistic and introduced neutral motions, including timing differences and spatial differences. Timing differences are defined as time alignment curves, while spatial differences are found by a machine learning technique: independent feature subspaces analysis, which is the combination of multidimensional independent component analysis and invariant feature subspaces. This technique is used to decompose two motions into several subspaces. One of these subspaces can be defined as style subspace that describes the style aspects of the stylistic motion. In order to find the style subspace, we compare norms of the projections of two motions on each subspace. Once the time alignment curves and style subspaces of several motion clips are obtained, animators can tune, transfer, and merge the style subspaces to synthesize new motion clips with various styles. Our method is easy to use since manual manipulations and large training data sets are not necessary. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We propose a simple framework for making elastic body animation with point constraints. In general, a physics-based approach for constraint animation offers a variety of animations with physically correct realism, which are achieved by solving the equations of motion. However, in the digital animation industry, solving the equations of motion is an indirect path to creating more art-directed animations that maintain a plausible realism. Our algorithms provide animators a practical way to make elastic body animation with plausible realism, while effectively using point-constraints to offer directatorial control. The animation examples illustrate that our framework creates a wide variety of point-constraint animations of elastic objects with greater directability than existing methods. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper we argue for the concept of brushes and pigments enhanced with behavioural intelligence as a complement to established 2D computer animation techniques. Our approach allows the user to enrich and animate interactively created images by semi-autonomously embedding procedural animation into them. This way, artistic skills of trained animators become within reach of everyone in the digital world, even to completely novice users. To exemplify this concept, we elaborate on several special-purpose brushes and animated pigment for painting with animation. These include a programmable semi-autonomous brush used to paint variations of strokes in successive frames (e.g. flames of fire), the moving-dab brush which enables dabs of paint to follow a user-defined path (e.g. smoke puffs) and animated pigment to produce secondary motion such as vibrant or waving paint textures. We believe our system offers a new fresh perspective on 2D computer aided animation production and associated tools. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article focuses on the treatment of time through animation technologies. It discusses the architectural use of parametric design and associative-geometry modeling tools to present an alternative reading of time in architectural presentation, form and technology. It also provides several works of early 20th-century experimental animators including Hans Richter, Alexander Alexeieff and Norman McLaren.

The availability of high-performance 3D workstations has increased the range of application for interactive real-time animation. In these applications the user can directly interact with the objects in the animation and direct the evolution of their motion, rather than simply watching a pre-computed animation sequence. Interactive real-time animation has fast-growing applications in virtual reality, scientific visualization, medical training and distant learning. Traditional approaches to computer animation have been based on the animator having complete control over all aspects of the motion. In interactive animation the user can interact with any of the objects, which changes the current motion path or behaviour in real time. The objects in the animation must be capable of reacting to the user's actions and not simply replay a canned motion sequence. This paper presents a framework for interactive animation that allows the animator to specify the reactions of objects to events generated by other objects and the user. This framework is based on the concept of relations that describe how an object reacts to the influence of a dynamic environment. Each relation specifies one motion primitive triggered by either its enabling condition or the state of the environment. A collection of the relations is structured through several hierarchical layers to produce responsive behaviours and their variations. This framework is illustrated by several room-based dancing examples that are modelled by relations. Copyright © 2000 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In most currently produced computer generated animation there is significant visual information that is literally never seen because of the characteristics of the human visual system. By tailoring the rendering of animation images to match the characteristics of human visual perception, significant computational and image storage savings can be obtained while retaining perceived animation quality. Vision research indicates that the human visual system processes two information channels. The transient channel rapidly processes low spatial resolution full colour information. The sustained channel processes high spatial resolution luminance information at a much slower rate. This paper discusses how the rendering of animation images can be accomplished to match these perception characteristics and achieve significant savings while maintaining animation quality. Computation and storage savings of up to 80 per cent are possible. Several animation segments have been produced to demonstrate the viability of this approach. [ABSTRACT FROM AUTHOR]

Today’s computer animators have access to many systems and techniques to author high-quality motion. Unfortunately, available techniques typically produce a particular motion for a specific character. In this paper we present a constraint-based approach to adapt previously created motions to new situations and characters. We combine constraint methods that compute changes to motion to meet specified needs with motion signal processing methods that modify signals yet preserve desired properties of the original motion. The combination allows the adaptation of motions to meet new goals while retaining much of the motion’s original quality. © 1998 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents a new image morphing method using a two-dimensional deformation technique which provides an intuitive model for a warp. The deformation technique derives a C¹-continuous and one-to-one warp from a set of point pairs overlaid on two images. The resulting in-between image precisely reflects the correspondence of features specified by an animator. We also control the transition behaviour in a metamorphosis sequence by taking another deformable surface model, which is simpler and thus more efficient than the deformation technique for a warp. The proposed method separates transition control from feature interpolation and is easier to use than the previous techniques. The multigrid relaxation method is employed to solve a linear system in deriving a warp or transition rates. This method makes our image morphing technique fast enough for an interactive environment. [ABSTRACT FROM AUTHOR]

This paper describes a method that facilitates the use of physically-based models by animators. The main point is to give the animator a familiar interface, while providing a simulation module which detects collisions, thus enhancing realism. The user gives a set of key-frames to guide motion, but does not have to address problems such as interpenetration avoidance, deformations due to collisions, or realism of motion. The simulator will correct the trajectories and compute deformations according to each object's physical properties (such as mass, inertia, stiffness) as well as the collisions and contacts automatically detected during motion. To achieve this, objects are provided with actuators capable of generating forces and torques computed via generalized proportional-derivative controllers. When deflected by external actions, actuated objects try to return to their initial path. Speed variations over time are computed during the simulation, and depend on the complexity of the paths, on the objects' models, and on the events such as collisions occurring during motion. In addition simulations are generated at interactive rates, even in the case of complex articulated objects. This facilitates the fine tuning of an animation sequence. [ABSTRACT FROM AUTHOR]

The dynamic constraints technique has been proposed for building geometrical models composed of rigid bodies, which are made to act naturally, according to Newtonian laws, by specifying constraints on their states. In computer animation, the dynamic constraints technique alleviates the work-load of animators who formerly had to plan animated sequences in detail by intuition alone. Nevertheless, for some real-world applications, it is desirable to have a mechanism that makes physically-based elements move according to a given scenario by providing some control states. The control states can be represented by transient constraints that are to be met and then released immediately. In this paper, a technique called the sequential-goal constraints technique is proposed to provide such a mechanism. With the sequential-goal constraints technique, it is easy to specify transient constraints according to a given scenario and derive proper forces and torques to drive an element to meet each transient constraint exactly at a specified time so that the whole motion of the element is continuous and integral. [ABSTRACT FROM AUTHOR]