Kelly Ward

A Survey on Hair Modeling: Styling, Simulation, and Rendering

Realistic hair modeling is a fundamental part of creating virtual humans in computer graphics. This paper surveys the state of the art in the major topics of hair modeling: hairstyling, hair simulation, and hair rendering. Because of the difficult, often unsolved problems that arise in alt these areas, a broad diversity of approaches is used, each with strengths that make it appropriate for particular applications. We discuss each of these major topics in turn, presenting the unique challenges facing each area and describing solutions that have been presented over the years to handle these complex issues. Finally, we outline some of the remaining computational challenges in hair modeling

Modeling hair using level-of-detail representations

We present a novel approach for modeling hair using level-of-detail representations. The set of representations include individual strands, hair clusters, and hair strips. They are represented using subdivision curves or surfaces, and have the same underlying base skeleton to maintain consistent high-level physical behavior when a transition between different levels-of detail occurs. This framework supports automatic simplification of dynamic simulation, collision detection, and graphical rendering of animated hair. It also offers flexibility to balance between the overall performance and visual quality, and can be used to model and render different hairstyles. We have used these level-of-detail representations to animate various hairstyles and obtained noticeable performance improvement, with little loss in visual quality.

Adaptive grouping and subdivision for simulating hair dynamics

We present a novel approach for adaptively grouping and subdividing hair using discrete level-of-detail (LOD) representations. The set of discrete LODs include hair strands, clusters and strips. Their dynamic behavior is controlled by a base skeleton. The base skeletons are subdivided and grouped to form clustering hierarchies using a quad-tree data structure during the precomputation. At run time, our algorithm traverses the hierarchy to create continuous LODs on the fly and chooses both the appropriate discrete and continuous hair LOD representations based on the motion, the visibility, and the viewing distance of the hair from the viewer. Our collision detection for hair represented by the proposed LODs relies on a family of swept sphere volumes for fast and accurate intersection computations. We also use an implicit integration method to achieve simulation stability while allowing us to take large time steps. Together, these approaches for hair simulation and collision detection offer the flexibility to balance between the overall performance and visual quality of the animated hair. Furthermore, our approach is capable of modeling various styles, lengths, and motion of hair.

Detail preserving continuum simulation of straight hair

Hair simulation remains one of the most challenging aspects of creating virtual characters. Most research focuses on handling the massive geometric complexity of hundreds of thousands of interacting hairs. This is accomplished either by using brute force simulation or by reducing degrees of freedom with guide hairs. This paper presents a hybrid Eulerian/Lagrangian approach to handling both self and body collisions with hair efficiently while still maintaining detail. Bulk interactions and hair volume preservation is handled efficiently and effectively with a FLIP based fluid solver while intricate hair-hair interaction is handled with Lagrangian self-collisions. Thus the method has the efficiency of continuum/guide based hair models with the high detail of Lagrangian self-collision approaches.

Interactive Virtual Hair Salon

User interaction with animated hair is desirable for various applications but difficult because it requires real-time animation and rendering of hair. Hair modeling, in cluding styling, simulation, and rendering, is computationally challenging due to the enormous number of deformable hair strands on a human head, elevating the computational complexity of many essential steps, such as collision detection and self-shadowing for hair. Using simulation localization techniques, multi-resolution representations, and graphics hardware rendering acceleration, we have developed a physically-based virtual hair salon system that simulates and renders hair at accelerated rates, enabling users to interactively style virtual hair. With a 3D haptic interface, users can directly manipulate and position hair strands, as well as employ real-world styling applications (cutting, blow-drying, etc.) to create hairstyles more intuitively than previous techniques.

Strands and hair: modeling, animation, and rendering

The last six years has seen a renaissance in hair modeling, rendering and animation. This course covers the gamut of hair simulation problems and present working solutions, from recent and novel research ideas to time tested industrial practices that resulted in spectacular imagery.

A Simulation-based VR System for Interactive Hairstyling

We have developed a physically-based VR system that enables users to interactively style dynamic virtual hair by using multiresolution simulation techniques and graphics hardware rendering acceleration for simulating and rendering hair in real time. With a 3D haptic interface, users can directly manipulate and position hair strands, as well as employ real-world styling applications (cutting, blow-drying, etc.) to create hairstyles more intuitively than previous techniques.

Realistic hair simulation: animation and rendering

The last five years have seen a profusion of innovative solutions to one of the most challenging tasks in character synthesis: hair simulation. This class covers both recent and novel research ideas in hair animation and rendering, and presents time tested industrial practices that resulted in spectacular imagery.n The course is aimed at an intermediate level and addresses the special-effects developers and technical directors who are looking for innovation as well as proven methodologies in hair simulation. The audience will get a good grasp of the state of the art in hair simulation and will have plenty of working solutions that they can readily implement in their production pipelines. The course will also be a bootcamp for aspiring computer graphics researchers interested in physically based modeling in computer graphics.n The class addresses the special-effects developers and technical directors who are looking for innovation as well as proven methodologies in hair simulation. The audience will get a good grasp of the state of the art in hair simulation and will have plenty of working solutions that they can readily implement in their production pipelines. The class will also be a boot-camp for aspiring computer graphics researchers interested in physically based modeling.n The class covers two crucial tasks in hair simulation: animation and rendering. For hair animation, we first discuss recent successful models for simulating the dynamics of individual hair strands, before presenting viable solutions for complex hair-hair and hair-body interactions. For rendering, we address issues related to shading models, multiple scattering, and volumetric shadows. We finally demonstrate how hair simulation techniques are nowadays developed and applied in the feature films industry to produce outstanding visual effects.

Simulating Rapunzel's hair in Disney's Tangled

Hair simulation is known to be a complex problem in animation. In Tangled we have the extreme task of simulating 70 feet of hair for the films main character, Rapunzel. The excessive hair length in addition to the loose style and intricate structure of the hair present many unique challenges in simulation. Moreover, the specific art direction of the film adds to the complexity of the simulation.

Simulating and rendering wet hair

Simulating hair dynamics is one of the most challenging tasks in computer animation due to its complexity and required realism. The huge amount of hair make the computation and rendering very cumbersome, especially when influenced by visual effect elements such as water and fire. In this paper we propose a physically-based model to capture the characteristics of wet hair. Hair and fur in our system can interact with water particles and change the parameters such as weight and stiffness for physics simulation. A fast cohesion process is then applied to wet hair at each time step to achieve realistic clumping effects. We also introduces a shading model that produces convincing appearance for wet hair.