Frank Van Reeth

Interactive rendering of translucent deformable objects

Realistic rendering of materials such as milk, fruits, wax, marble, and so on, requires the simulation of subsurface scattering of light. This paper presents an algorithm for plausible reproduction of subsurface scattering effects. Unlike previously proposed work, our algorithm allows to interactively change lighting, viewpoint, subsurface scattering properties, as well as object geometry.The key idea of our approach is to use a hierarchical boundary element method to solve the integral describing subsurface scattering when using a recently proposed analytical BSSRDF model. Our approach is inspired by hierarchical radiosity with clustering. The success of our approach is in part due to a semi-analytical integration method that allows to compute needed point-to-patch form-factor like transport coefficients efficiently and accurately where other methods fail.Our experiments show that high-quality renderings of translucent objects consisting of tens of thousands of polygons can be obtained from scratch in fractions of a second. An incremental update algorithm further speeds up rendering after material or geometry changes.

Real-time simulation of watery paint

Existing work on applications for thin watery paint is mostly focused on automatic generation of painterly‐style images from input images, ignoring the fact that painting is a process that intuitively should be interactive. Efforts to create real‐time interactive systems are limited to a single paint medium and results often suffer from a trade‐off between real‐timeness and simulation complexity. We report on the design of a new system that allows the real‐time, interactive creation of images with thin watery paint. We mainly target the simulation of watercolor, but the system is also capable of simulating gouache and Oriental black ink. The motion of paint is governed by both physically based and heuristic rules in a layered canvas design. A final image is rendered by optically composing the layers using the Kubelka–Munk diffuse reflectance model. All algorithms that participate in the dynamics phase and the rendering phase of the simulation are implemented on graphics hardware. Images made with the system contain the typical effects that can be recognized in images produced with real thin paint, like the dark‐edge effect, watercolor glazing, wet‐on‐wet painting and the use of different pigment types. Copyright

Enhanced performance of polymer:fullerene bulk heterojunction solar cells upon graphene addition

Graphene has potential for applications in solar cells. We show that the short circuit current density of P3HT (Poly(3-hexylthiophene-2,5-diyl):PCBM((6,6)-Phenyl C61 butyric acid methyl ester) solar cells is enhanced by 10% upon the addition of graphene, with a 15% increase in the photon to electric conversion efficiency. We discuss the performance enhancement by studying the crystallization of P3HT, as well as the electrical transport properties. We show that graphene improves the balance between electron and hole mobilities with respect to a standard P3HT:PCBM solar cell.

FluidPaint: an interactive digital painting system using real wet brushes

This paper presents FluidPaint, a novel digital paint system using real wet brushes. A new interactive canvas, accurately registering brush footprints and paint strokes in high precision has been developed. It is based on the real-time imaging of brushes and other painting instruments as well as the real-time co-located rendering of the painting results. This new painting user interface enhances the user experience and the artists expressiveness. User tests demonstrate the intuitive nature of FluidPaint, naturally integrating interface elements of traditional painting in a digital paint system.

32.4: An Electronic Ink Low Latency Drawing Tablet

Using an electronic ink display and a touchpanel input device, a paper-like drawing tablet was created, closely mimicking the behaviour of normal paper. The tablet is initially intended to serve as an input-device for cartoon drawing and editing. However, its potential use goes far beyond that.

Designing a Virtual Environment for Large Audiences

In this paper we describe our approach in creating a truly scalable distributed virtual environment. The resulting system should not only support large amounts of users, but it should also be able to work with a general purpose network like the Internet and it is intended to work with typical personal computers or game consoles. To realize this, we propose a distributed client-server approach in which most of the responsibilities are concentrated at the client side. The servers will only be used for control purposes - e.g. access control. Direct communication between clients helps preventing servers from becoming bottlenecks and the network load is kept low by distributing only the actions of a client instead of continuously distributing position updates. Finally, we also address some security related issues which arise from this client-oriented approach.

From dust till drawn: A real-time bidirectional pastel simulation

We present a system for drawing pastel media in real-time as an effective alternative to most existing digital solutions that basically allow for drawing arbitrary strokes in a particular style. Our approach is focused on the simulation of the natural material itself and on its interaction with the drawing surface and the drawing tool.Upon free-form drawing, a bidirectional transfer of pigment takes place. In one direction, the paper surface is dusted with new pigment particles broken off the tip (i.e., the end of the drawing tool). A large part of these particles will be deposited or blended together with previously deposited ones whereas the remainder does not contribute to the drawing and is blown off. On the other hand, a certain amount of previously deposited pigment is scraped off and picked up again soiling the tip. This is noticeable in the next strokes to be drawn. Furthermore, both the tip and the paper surface are subject to weathering depending on the exerted pressure and friction of the drawing tool, and the bumpiness of the paper. As a result, the paper surface becomes slightly damaged, limiting the deposition of new pigment. The tip, on the other hand, becomes blunt making new strokes wider.From a stylistic point of view, similarly to traditional drawings our results convey the artists’ characteristics (e.g., the way of wielding the brush, skillfulness, feeling for the medium). Therefore, we believe that our system allows an artist to create realistically looking pastel images without losing his/her personal touch.We present a system for drawing pastel media in real-time as an effective alternative to most existing digital solutions that basically allow for drawing arbitrary strokes in a particular style. Our approach is focused on the simulation of the natural material itself and on its interaction with the drawing surface and the drawing tool. Upon free-form drawing, a bidirectional transfer of pigment takes place. In one direction, the paper surface is dusted with new pigment particles broken off the tip (i.e., the end of the drawing tool). A large part of these particles will be deposited or blended together with previously deposited ones whereas the remainder does not contribute to the drawing and is blown off. On the other hand, a certain amount of previously deposited pigment is scraped off and picked up again soiling the tip. This is noticeable in the next strokes to be drawn. Furthermore, both the tip and the paper surface are subject to weathering depending on the exerted pressure and friction of the drawing tool, and the bumpiness of the paper. As a result, the paper surface becomes slightly damaged, limiting the deposition of new pigment. The tip, on the other hand, becomes blunt making new strokes wider. From a stylistic point of view, similarly to traditional drawings our results convey the artists’ characteristics (e.g., the way of wielding the brush, skillfulness, feeling for the medium). Therefore, we believe that our system allows an artist to create realistically looking pastel images without losing his/her personal touch.

Sketching with a low-latency electronic ink drawing tablet

Drawing on paper is an experience which is still unmatched by any input device for drawing into a computer in terms of accuracy, dexterity and general pleasantness of use. This paper describes a paper-like drawing tablet which uses electronic ink as its output medium with stylus-based touchpanel input. The device mimics the experience of drawing in a manner which can be adjusted to approach the feel of different kinds of paper. We discuss further some basic issues which need to be addressed in managing interfacing to such a device, specifically the avoidance of the legacy of mouse-oriented point-and-click interfaces which have influenced GUI design for so long. We see a sketch-based model for interaction, based on free-form curve drawing, as being the way forward but new interaction models are required. The tablet is initially intended to serve as an input-device for cartoon drawing and editing, so the product of any sketching process has to be presented to the rest of the animation data-path in terms of a conventional curve model, here Bézier chains. We discuss models for achieving this without having to resort to legacy curve-editing techniques which have no counterpart in drawing on paper or in the repertoire of the traditional animator. Potential uses of these interaction techniques go well beyond supporting the cartoon drawing application.

Efficient Rendering of Local Subsurface Scattering.

A novel approach is presented to efficiently render local subsurface scattering effects. We introduce an importance sampling scheme for a practical subsurface scattering model. It leads to a simple and efficient rendering algorithm, which operates in image space, and which is even amenable for implementation on graphics hardware. We demonstrate the applicability of our technique to the problem of skin rendering, for which the subsurface transport of light typically remains local. Our implementation shows that plausible images can be rendered interactively using hardware acceleration.

Uniting cartoon textures with computer assisted animation

We present a novel method to create perpetual animations from a small set of given keyframes. Existing approaches either are limited to re-sequencing large amounts of existing image/video data, or to interpolating vector based drawings.Our approach benefits from several ideas and techniques from video textures, computer-assisted animation and motion graphs. It combines the re-sequencing of existing material with the automatic generation of new data. Furthermore, the animator can interfere with the animation process at each arbitrary moment.First, a given set of keyframes is used to automatically generate a set of in-betweens. The amount of in-betweens required, depends on a distance metric preventing possible visual discontinuities. Next, an optimised cost graph is derived from the generated frames, indicating for all keyframes how many steps are required to travel from one keyframe to another. Finally, by rearranging the generated sets of in-betweens according to the cost graph, new animations can be synthesised from the generated data.The resulting animations are smooth, broader than the input data and require no postprocessing.