Short Presentations 2005

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https://diglib.eg.org/handle/10.2312/250

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A 3D Perceptual Metric using Just-Noticeable-Difference
(The Eurographics Association, 2005) Cheng, Irene; Boulanger, Pierre; John Dingliana and Fabio Ganovelli
In multimedia applications, it is essential to distribute resources efficiently among different types of data in order to optimize overall quality. We propose a perceptual metric using Just-Noticeable-Difference (JND) to identify redundant mesh data so that available bandwidth can be allocated to improve texture resolution. Evaluation of perceptual impact during runtime is based on statistics in a lookup table generated during preprocessing. If the impact is less than the JND, no mesh refinement is performed. We apply Weber s fraction to compute the JND threshold, which is verified by perceptual evaluations. Experimental result shows that our JND model can accurately predict perceptual impact based on the human visual system.
Carving, Painting, and Printing with a Pen Tablet
(The Eurographics Association, 2005) Mizuno, Shinji; Kobayashi, Daigo; Okada, Minoru; Toriwaki, Junichiro; Yamamoto, Shinji; John Dingliana and Fabio Ganovelli
We discuss on an interactive CG system with a pressure sensitive pen tablet. This system is based on the virtual sculpting and printing method which are simulations of real sculpting and woodblock printing. In the sculpting process, the user operates virtual chisels with a pen to carve a virtual wooden object which has a 3D shape. The user can control the carving depth and the carving angle to the surface of the object with the pressure applied to the pen. In the painting process, the user paints ink with a pen on a 3D virtual sculpture created in the sculpting process. The painting result is determined by the surface shape of the sculpture and the pressure to the pen. In the printing process, a pen is used to operate a Japanese printing squeegee, Baren. The user can control the thickness of the print by changing the thickness of ink on the virtual woodblock and the pressure of printing operation.
Constriction Computation using Surface Curvature
(The Eurographics Association, 2005) Hétroy, F.; John Dingliana and Fabio Ganovelli
This paper provides a curvature-based algorithm to compute locally shortest geodesics on closed triangulated surfaces. These curves, which are called "constrictions", are useful for shape segmentation. The key idea of the algorithm is that constrictions are almost plane curves; it first finds well-located simple, plane, closed curves, and then slides them along the surface until a shortest geodesic is reached. An initial curve is defined as a connected component of the intersection between the surface and a plane going through an initial vertex. Initial vertices and planes are determined using approximations of surface curvature.
Differential Photon Mapping - Consistent Augmentation of Photographs with Correction of all Light Paths
(The Eurographics Association, 2005) Grosch, Thorsten; John Dingliana and Fabio Ganovelli
Augmenting images with consistent lighting is possible with differential rendering. This composition technique requires two lighting simulations, one simulation with only real geometry and another one with additional virtual objects. The difference of the two simulations can be used to modify the original pixel colors. The main drawback of differential rendering is that not all modified light paths can be displayed: The result of the lighting simulation is visible in a reflective object instead of the real environment, augmented with virtual objects. Moreover, many regions in the photograph remain unchanged and the same work is done twice without any visual effect. In this paper we present a new approach for augmenting a photograph with only a single photon mapping simulation. The changes in lighting introduced by a virtual object are directly simulated using a differential photon map. All light paths intersecting the virtual object are corrected. To demonstrate the correctness of our approach, we compare our simulation results with real photographs.
Efficient, Physically Plausible Finite Elements
(The Eurographics Association, 2005) Nesme, Matthieu; Payan, Yohan; Faure, François; John Dingliana and Fabio Ganovelli
This paper discusses FEM-based simulations of soft bodies in terms of speed and robustness. To be physically plausible, three fundamental laws must be respected: rotational invariance, Newton's law and Euler's law. We show that precomputed strain-displacement matrices generate nonphysical torques which can lead to visual artifacts. We then derive the fastest FEM-based method meeting our criteria of plausibility and robustness and discuss their limitations.
Estimating Mobile Memory Requirements and Rendering Time for Remote Execution of the Graphics Pipeline
(The Eurographics Association, 2005) Banerjee, Kutty; Wu, Fan; Agu, Emmanuel; John Dingliana and Fabio Ganovelli
Mobile devices have limited processing power, memory and battery power. Remote execution, wherein part or entire graphics pipeline is offloaded to a powerful surrogate server, is an attractive solution for low end mobile devices such as PDAs and cell phones that lack floating point units or GPUs. We have found that remote execution of floating-point-intensive pipeline stages such as transform and geometry operations can produce speedups of up to 10 times for a low-end mobile device. We introduce generalized pipeline-splitting, a paradigm whereby 15 sub-stages of the graphics pipeline are instrumented with networking code such that they can run either on a mobile client or a surrogate server. To validate our concepts, we create Remote Mesa (RMesa). As a foundation for deciding which stages of the pipeline would benefit from remote execution, this paper presents analytical models for the overall rendering time, memory requirements and roundtrip network delay incurred by RMesa.
Facial Motion Cloning Using Global Shape Deformation
(The Eurographics Association, 2005) Fratarcangeli, Marco; Schaerf, Marco; John Dingliana and Fabio Ganovelli
We present a novel Facial Motion Cloning method relying on the combination of the radial basis functions (RBF) based scattered data interpolation with the encoding capabilities of the MPEG-4 Facial and Body Animation (FBA) international standard. Beside from an initial manual selection of feature points, our method works fully automatically without user interaction. The produced talking head is able to perform generic face animation which is stored in a MPEG-4 FBA data stream.
Fast and Controllable 3D Modelling From Silhouettes
(The Eurographics Association, 2005) Prasad, Mukta; Fitzgibbon, Andrew; Zisserman, Andrew; John Dingliana and Fabio Ganovelli
We show how a 3D model of a complex curved object can be easily extracted from a single 2D image. A userdefined silhouette is the key input; and we show that finding the smoothest 3D surface which projects exactly to this silhouette can be expressed as a quadratic optimization, a result which has not previously appeared in the large literature on the shape-from-silhouette problem. For simple models, this process can immediately yield a usable 3D model; but for more complex geometries the user will wish to further shape the surface. We show that a variety of editing operations which can be defined either in the image or in 3D can also be expressed as linear constraints on the 3D shape parameters. We extend the system to fit higher genus surfaces. Our method has several advantages over the system of Zhang et al. [ZDPSS01] and over systems such as SKETCH and Teddy.
Fast Body-Cloth simulation with moving humanoids
(The Eurographics Association, 2005) Rodriguez-Navarro, Javier; Sainz, Miguel; Susin, Antonio; John Dingliana and Fabio Ganovelli
In this paper we present a very fast method for body-cloth animation. The usual bottle-neck in cloth simulation performance is collision detection, which becomes more difficult to solve when a complex geometry, like a human body, is involved. Recent image based methods, that use depth images to detect collisions, usually relays on CPU for collision correction. In our work we implement a GPU based simulation that takes care both of cloth simulation and body-cloth collisions when the humanoid is moving. Our solution is based on a hierarchic depth map structure. A high frame rate is obtained with both structured and unstructured cloth meshes with thousands of particles.
Image Reconstruction Invariant to Relighting
(The Eurographics Association, 2005) Georgiev, Todor; John Dingliana and Fabio Ganovelli
This paper describes an improvement to the Poisson image editing method for seamless cloning. Our approach is based on minimizing an energy expression invariant to relighting. The improved method reconstructs seamlessly the selected region, matching both pixel values and texture contrast of the surrounding area, while previous algorithms matched pixel values only. Our algorithm solves a deeper problem: It performs reconstruction in terms of the internal working mechanisms of human visual system. Retinex-type effects of adaptation are built into the structure of the mathematical model, producing results that change covariantly with lighting.
Improving the Experience of Scenes with a Large Field of View using Shift Lens Perspective
(The Eurographics Association, 2005) Hoeben, Aldo; Stappers, Pieter Jan; John Dingliana and Fabio Ganovelli
In interactive computer graphics such as games and interactive panoramic photos, users are often presented a view with a larger field of view than would correspond to the distance to and size of the screen on which the graphics are viewed. This makes looking at the scene a less claustrophobic experience, showing more of the environment than that which is strictly ahead. In many applications however, where the goal is to get a sense of presence and ambiance of the depicted scene, the large field of view distracts the observer with extreme converging lines when looking up or down. Even though these converging lines are perspectively correct, the resulting image does not match the way we normally perceive the world around us. In this paper we discuss modifying the perspective to reduce the distortions caused by the large field of view, to enhance the experience of these scenes.
Interactive Manipulation Of Projections With a Curved Perspective
(The Eurographics Association, 2005) Sudarsanam, Nisha; Grimm, Cindy M; Singh, Karan; John Dingliana and Fabio Ganovelli
The concept of curved perspective has been used by artists such as M.C. Escher in order effectively convey a sense of three dimensional space while being restricted to a two dimensional canvas. We present an interactive system to create and manipulate projections with a curvilinear perspective. Our system presents the user with a set of intuitive screen-space perspective primitives that control the vanishing points of the scene. This allows the user to generate diverse projections having curved perspective.
Leaf Cluster Impostors for Tree Rendering with Parallax
(The Eurographics Association, 2005) Garcia, Ismael; Sbert, Mateu; Szirmay-Kalos, László; John Dingliana and Fabio Ganovelli
This paper presents a simple method to render complex trees on high frame rates while maintaining parallax effects. Based on the recognition that a planar impostor is accurate if the represented polygon is in its plane, we find an impostor for each of those groups of tree leaves that lie approximately in the same plane. The groups are built automatically by a clustering algorithm. Unlike billboards, these impostors are not rotated when the camera moves, thus the expected parallax effects are provided. On the other hand, clustering allows the replacement of a large number of leaves by a single semi-transparent quadrilateral, which improves rendering time considerably. Our impostors well represent the tree from any direction and provide accurate depth values, thus the method is also good for shadow computation.
Model-driven Virtual Mezzotint Techniques
(The Eurographics Association, 2005) Tasaki, Daisuke; Mizuno, Shinji; Okada, Minoru; John Dingliana and Fabio Ganovelli
Mezzotint is a traditional printing technique that is categorized into copperplate printing where an entire plate surface is roughened by some steel tools. In this paper the authors propose a method to realize two mezzotint techniques by replacing some physical models for the plate making process. The main characteristic of mezzotint is that roughening, scraping, and burnishing the plate will result on a gradation of color from black to white. The paraboloidal incising model and the sweeped paraboloidal model are applied to roughen the plate. Reducing and smoothing operations are introduced to scrape and burnish the plate. By some experiments the authors prove the proposed methods to synthesize copperplate print images.
Path Planning for Crowds: From Shared Goals to Individual Behaviors
(The Eurographics Association, 2005) Pettre, Julien; Thalmann, Daniel; John Dingliana and Fabio Ganovelli
This paper presents a novel approach for path planning in the context of crowds animation. The solution produces several paths joining each user-defined pair of locations in the environment. Pairs are possible initial/goal locations for the virtual characters. The obtained paths diversity enables individual behaviorial diversity, while ensuring the achievement of potentially complex goals. The solution is general, derives from the Probabilistic Roadmap motion planning technique developed in Robotics, and proceeds in two stages. First a dense roadmap is build from the 3D definition of the environment and individual s bounding box, then, given a specific problem, a set of feasible paths is extracted from the roadmap using a Diskstra s algorithm implementation and an edge deletion technique. Resulting paths are plausible, and covers widely the environment given that short paths are found as well as less optimal ones. The method is illustrated and demonstrated all along the paper with a generic example.
Perception-Based Rendering: Eyes Wide Bleached
(The Eurographics Association, 2005) Gutierrez, Diego; Anson, Oscar; Munoz, Adolfo; Seron, Francisco J.; John Dingliana and Fabio Ganovelli
Perception issues are a key factor in rendering Vision-Realistic images. This paper develops a novel spectral sensitive model of the Human Visual System (HVS) in order to simulate the bleaching effect in retinal photopigments. First, the Stiles-Crawford effect is taken into account to determine the pupil size of the adapted eye and to compute the directional sensitivity of the photoreceptors in the retina. After that, the percentage of bleached pigment based on the incident retinal illuminance is calculated to simulate the loss of spectral sensitivity of the human observer seeing the scene.
Photon Map Gathering on the GPU
(The Eurographics Association, 2005) Czuczor, Szabolcs; Szirmay-Kalos, László; Szécsi, László; Neumann, László; John Dingliana and Fabio Ganovelli
Photon mapping methods obtain the indirect illumination of a point by finding those photon hits that arrived at the neighborhood of the point on the object surface. This paper proposes a method that stores the photon hits in a texture of the graphics hardware and replaces the traditional kd-tree based neighborhood searches by the filtering of this texture. This step finds the irradiance of all points (i.e. all texels) simultaneously in a single step, thus the average irradiance of a point can be obtained by a single texture lookup. Using this approach we can port the final gathering step of photon mapping to the graphics hardware (GPU). The CPU is only responsible for generating new light paths and updating the unfiltered photon map. Thanks to the optimal subdivision of the computation work between the the CPU and the GPU, the proposed algorithm can render globally illuminated scenes interactively.
Predicting Natural Hair Shapes by Solving the Statics of Flexible Rods
(The Eurographics Association, 2005) Bertails, Florence; Audoly, Basile; Querleux, Bernard; Leroy, Frédéric; Lévêque, Jean-Luc; Cani, Marie-Paule; John Dingliana and Fabio Ganovelli
This paper presents a new physically-based method for predicting natural hairstyles in the presence of gravity and collisions. The method is based upon a mechanically accurate model for static elastic rods (Kirchhoff model), which accounts for the natural curliness of hair, as well as for hair ellipticity. The equilibrium shape is computed in a stable and easy way by energy minimization. This yields various typical hair configurations that can be observed in the real world, such as ringlets. As our results show, the method can generate different hair types with a very few input parameters, and perform virtual hairdressing operations such as wetting, cutting and drying hair.
Preface
(The Eurographics Association, 2005) -; John Dingliana and Fabio Ganovelli
Preface and Table of Contents
Proactive Steering Toward Oriented Targets
(The Eurographics Association, 2005) Boulic, Ronan; John Dingliana and Fabio Ganovelli
In this paper we introduce a real-time steering controller ensuring the reach of a (possible mobile) target position and orientation, without requiring to build/update the full trajectory to that target. We name it the funnelling control. The final orientation is achieved through the continuous adjustment of the heading direction. This control mode is proactive in the sense that it anticipates the success/failure of the reach and adjusts the desired speed accordingly. Both features rely on an heterogeneously sampled table of radial-tangential seek angles obtained when the controller reaches a desired position target without prescribed orientation. By construction, the control update has a constant computing cost, even with variable target characteristics. Its low update cost makes it particularly suited for controlling a large number of mobile entities in real-time. The present exposition is made for an obstacle-free context.

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