Philip J. Willis

Modeling and generating moving trees from video

We present a probabilistic approach for the automatic production of tree models with convincing 3D appearance and motion. The only input is a video of a moving tree that provides us an initial dynamic tree model, which is used to generate new individual trees of the same type. Our approach combines global and local constraints to construct a dynamic 3D tree model from a 2D skeleton. Our modeling takes into account factors such as the shape of branches, the overall shape of the tree, and physically plausible motion. Furthermore, we provide a generative model that creates multiple trees in 3D, given a single example model. This means that users no longer have to make each tree individually, or specify rules to make new trees. Results with different species are presented and compared to both reference input data and state of the art alternatives.

The smart navigation of a ray through an oct-tree

Abstract Over the last few years, researchers have repeatedly proposed the use of oct-tree scene decompositions to accelerate ray-traced image synthesis by exploiting spatial object coherence. The computational load imposed by the solution of the scenes solid model may thereby be shifted from the calculation of many ray/object intersections to the simpler navigation of a ray through such a structure, so reducing the major portion of total synthesis cost. This article presents a particularly efficient navigation algorithm employing two decision vectors maintained by incremental integer arithmetic. Each vector is known as a Spatial Measure for Accelerated Ray Tracing (SMART).

Computer assisted animation: 2D or not 2D?

2D animation can only be automated to the extent that the computer acts as an interactive assistant to the animator. The key problem is that the 3D information which is implicit in the animated drawings is unavailable and this has encouraged the view of 2D animation being a subset of 3D animation in its fullest generality. However, introducing more than the absolute minimum of 3D information, essentially that contained in a hierarchy of drawing overlays, has matching advantages and disadvantages because animators, for aesthetic reasons, deliberately break the rules of geometry and physics as they apply to real-world objects. A software environment which only supports 2D functionality and drawing overlays is sufficient to promote cost-effectively the full range of effects that animators use while the state of the 3D animation art is as yet incapable of this. Essentially the same techniques can be used on live-capture images once they have had a structure similar to that required for animation imposed on them.

Water Surface Modeling from a Single Viewpoint Video

We introduce a video-based approach for producing water surface models. Recent advances in this field output high-quality results but require dedicated capturing devices and only work in limited conditions. In contrast, our method achieves a good tradeoff between the visual quality and the production cost: It automatically produces a visually plausible animation using a single viewpoint video as the input. Our approach is based on two discoveries: first, shape from shading (SFS) is adequate to capture the appearance and dynamic behavior of the example water; second, shallow water model can be used to estimate a velocity field that produces complex surface dynamics. We will provide qualitative evaluation of our method and demonstrate its good performance across a wide range of scenes.

A Dynamic Emotion Representation Model Within a Facial Animation System

This paper presents the Dynamic Emotion Representation (DER), and demonstrates how an instance of this model can be integrated into a facial animation system. The DER model has been implemented to enable users to create their own emotion representation. Developers can select which emotions they include and how these interact. The instance of the DER model described in this paper is composed of three layers, each representing states changing over different time scales: behavior activations, emotions and moods. The design of this DER is discussed with reference to emotion theories and to the needs of a facial animation system. The DER is used in our Emotionally Expressive Facial Animation System (EE-FAS) to produce emotional expressions, to select facial signals corresponding to communicative functions in relation to the emotional state of the agent and also in relation to the comparison between the emotional state and the intended meanings expressed through communicative functions.

Emotional posturing: a method towards achieving emotional figure animation

Putting emotion into figure animation is a difficult task. The paper describes a method towards solving this problem. An emotional model is proposed based on psychological theory and this is integrated into the posturing of the figure. The system is based on general posturing functions which are interpreted depending on the emotional state of the figure. These functions can affect individual joints but are typically used to modify the movement of areas of the body and general stance.

A survey of partial differential equations in geometric design

Computer-aided geometric design is an area where the improvement of surface generation techniques is an everlasting demand, since faster and more accurate geometric models are required. Traditional methods for generating surfaces were initially mainly based upon interpolation algorithms. Recently, partial differential equations (PDE) were introduced as a valuable tool for geometric modelling, since they offer a number of features from which these areas can benefit. This work summarizes the uses given to PDE surfaces as a surface generation technique together with some other applications to computer graphics.

Manipulating, Deforming and Animating Sampled Object Representations

A sampled object representation (SOR) defines a graphical model using data obtained from a sampling process, which takes a collection of samples at discrete positions in space in order to capture certain geometrical and physical properties of one or more objects of interest. Examples of SORs include images, videos, volume datasets and point datasets. Unlike many commonly used data representations in computer graphics, SORs lack in geometrical, topological and semantic information, which is much needed for controlling deformation and animation. Hence it poses a significant scientific and technical challenge to develop deformation and animation methods that operate upon SORs. Such methods can enable computer graphics and computer animation to benefit enormously from the advances of digital imaging technology.

A Physically Based Colour Model

We propose an intuitively simple way of representing colour which has the additional virtue that, it permits mixing and overlaying of transparent and opaque paints to an arbitrary degree. Our approach is related to the earlier alpha channel model used for compositing. It includes this as a special case but has applications in many other areas, especially animation, paint programs and graphics libraries.

Deforming and Animating Discretely Sampled Object Representations

A discretely sampled object representation (DSOR) denes a graphical model using data obtained by a sampling process, which takes a collection of samples at discrete positions in space in order to capture certain geometrical and physical properties of one or more objects of interest. Examples of DSORs include images, videos, volume datasets and point datasets. Unlike many commonly used data representations in computer graphics, DSORs lack in geometrical, topological and semantic information, which is much needed for controlling deformation and animation. Hence it poses a signicant scientic and technical challenge to develop deformation and animation methods that operate upon DSORs. Such methods can enable computer graphics and computer animation to benet enormously from the advances of digital imaging technology. In this state of the art report, we survey a wide-range of techniques that have been developed for manipulating, deforming and animating DSORs. We consider a collection of elementary operations for manipulating DSORs, which can serve as building blocks of deformation and animation techniques. We examine a collection of techniques that are designed to transform the geometry shape of deformable DSORs and pay particular attention to their deployment in surgical simulation. We review a collection of techniques for animating digital characters in DSORs, focusing on recent developments in volume animation.