Eric Paquette

Procedural and interactive icicle modeling

Icicle formation is a complex phenomenon which makes it difficult to model for computer graphics applications. The methods commonly used in computer graphics to model icicles provide only minimal control over the results and require several minutes or even hours of computation. This paper proposes a procedural approach allowing interactive modeling, which is broken down into four stages. The first computes the water motion on the surface; the second determines where the water drips; the third computes the trajectories of the icicles growth, and the fourth creates the surface. In addition, the approach allows the creation of glaze ice. The results are not only realistic but also rapidly computed. This approach provides a significant increase in control over results and computation speed.

Computer Graphics education in different curricula: analysis and proposal for courses

This paper studies how Computer Graphics (CG) is taught and proposes a course on 2D CG and Image Processing (IP) as an alternative to the traditional 3D CG course. This unconventional course is motivated by an analysis of more than 70 Computer Science curricula. This analysis considers many aspects: CG, IP, and Human-Computer Interaction courses; curricula such as Computer Engineering, Computer Science, Information Technology, and Software Engineering; the difference between introductory and advanced courses; and universities known for their leadership in CG as well as mainstream universities. The analysis suggests that, given the different types of universities and curricula, there should be more alternative courses tailored to the needs of particular curricula. Developing such courses can be difficult and time consuming, so a methodology is proposed to describe a course with information useful for others who could be selecting it or who could be putting it in practice. This methodology is put in practice with the description of a course on 2D CG and IP.

Efficient Visualization of Volume Data Sets with Region of Interest and Wavelets

The growing volume of medical images acquired with new imaging modalities poses big challenges to the radiologists interpretation process. Innovative image visualization techniques can play a major role in enabling efficient and accurate information presentation and navigation, by combining computational efficiency with diagnostic resolution. Efficiency and resolution, two opposing requirements, can be accomplished by focusing on full resolution regions of interest while maintaining sufficient contextual information. In fact, structures of interest typically occupy a small percentage of the data, but their analysis requires context information like locations within a specific organ or adjacency to sensitive structures. We propose a 3D visualization technique that is based on the multi-resolution property of the wavelet transform in order to display a full resolution region of interest while displaying a coarser context to achieve efficiency in rendering during the exploratory navigation phase. A full resolution context can also be rendered when needed for a specific view. In a preprocessing stage the data is decomposed with a three-dimensional wavelet transform. The interactive visualization process then uses the wavelet representation and a user-specified region to render a full resolution region of interest and a coarser context directly from the wavelet space through wavelet splatting, thus avoiding volume reconstruction. This efficient rendering approach is combined with lighting calculations, in the preprocessing stage. While greatly enhancing depth perception and objects shape, lighting does not add additional cost to the interactive visualization process, resulting in a good compromise between computational efficiency and image quality.

Region of Interest and Multiresolution for Volume Rendering

Medical image interpretation is facing an important challenge resulting from the continuously increasing amount of imaging data. Innovations in medical image visualization are necessary to assist the radiologist in interacting and navigating effectively large multidimensional imaging sets. We propose a novel wavelet splatting approach for multiresolution 3-D visualization. Our method renders the context with a low resolution at first, and then subsequently, refines it progressively to attain full resolution, while ensuring that a specific region of interest is rendered at full resolution at all times. It is based on the splatting approach for its computational efficiency and uses the localization property of the wavelet transform to simultaneously render a full-resolution region of interest with a coarser context. Lighting calculations are used in the preprocessing stage to enhance the quality of the visualization. A special data structure that is based on a zero-tree model is used to manipulate the region of interest more easily. The speed-up achieved reaches a factor of 30 compared to the time needed to display the full-resolution data. By achieving effective 3-D rendering, we bring an element of solution to the problem of the image overload.

Efficient editing of aged object textures

Real objects present an enormous amount of detail, including aging effects. Artists need an intuitive control when they iteratively review and redesign their work to achieve a specific aging effect pattern but physically based and empirical simulations rarely provide an appropriate control. Our motivation comes from simplifying the redesign step by providing appropriate tools. In our system the user interactively identifies aging effects in a source image or photograph. The user then designs a target aging mask presenting the wanted aging effects pattern. Our system then synthesizes the output texture within a few seconds using a texture synthesis approach adapted to aged object texture editing. Thus, the user can quickly redesign the aging mask to achieve better results or test new configurations.

Animation Setup Transfer for 3D Characters

We present a general method for transferring skeletons and skinning weights between characters with distinct mesh topologies. Our pipeline takes as inputs a source character rig (consisting of a mesh, a transformation hierarchy of joints, and skinning weights) and a target character mesh. From these inputs, we compute joint locations and orientations that embed the source skeleton in the target mesh, as well as skinning weights to bind the target geometry to the new skeleton. Our method consists of two key steps. We first compute the geometric correspondence between source and target meshes using a semi‐automatic method relying on a set of markers. The resulting geometric correspondence is then used to formulate attribute transfer as an energy minimization and filtering problem. We demonstrate our approach on a variety of source and target bipedal characters, varying in mesh topology and morphology. Several examples demonstrate that the target characters behave well when animated with either forward or inverse kinematics. Via these examples, we show that our method preserves subtle artistic variations; spatial relationships between geometry and joints, as well as skinning weight details, are accurately maintained. Our proposed pipeline opens up many exciting possibilities to quickly animate novel characters by reusing existing production assets.

Dynamic lapped texture for fluid simulations

We present a new approach for texturing fluids. Particle trackers are scattered on the surface of the fluid, and used to track deformations and topological changes. For every frame of the animation, the trackers are advected and rotated coherently with the flow of the fluid. Receiver polygons are identified on the fluid surface and are used to transfer uv coordinates, while ensuring a controllable amount of texture distortion. The density of the trackers is adjusted when constructing a texture atlas used for rendering. Trackers that remain unused when filling the atlas are safely removed, while texels of the atlas without any corresponding tracker identify areas where new trackers will be added. Together with our patch layering approach, this tracker creation and removal process reduces popping artifacts. Both the input (fluid surface mesh and velocity field) and the output (texture atlas) of our approach make it easy to integrate into a typical production pipeline. We tested our approach on several types of fluid simulation scenarios, including splashes, rotational flows, and viscous fluids. The resulting animations of textured fluids are free from temporal artifacts and popping, and show a limited amount of distortion, blurring, and discontinuity.

An efficient layered simulation workflow for snow imprints

This paper introduces a novel workflow to generate snow imprints, and model the interaction of snow with dynamic objects. We decoupled snow simulation into three components: a base layer, snow particles, and snow mist. The base layer consists of snow that has not been in contact with a dynamic object yet, and is stored as a level set. Snow particles model the interaction between the snow and the dynamic objects. They are added when the dynamic objects collide with the base layer, and are animated using an adapted granular material simulation. The very thin and powdery snow released by airborne snow particles is modeled by the snow mist. This component is greatly influenced by the surrounding air medium; thus, it is animated using a fluid simulation. This decomposition allows to focus memory expensive and time-consuming computations only where dynamic objects interact with the snow, which is much more efficient than relying on a full-scale simulation.

Joint planar parameterization of segmented parts and cage deformation for dense correspondence

Abstract In this paper, we present a robust and efficient approach for computing a dense registration between two surface meshes. The proposed approach exploits a user-provided sparse set of landmarks, positioned at semantic locations, along with closed paths connecting sequences of landmarks. The approach segments the mesh and then flattens the segmented parts using angle-based flattening and low distortion boundary constraints. It adjusts the segmented parts with a cage deformation to align the interior landmarks. As a last step, our approach extracts the dense registration from the flattened and deformed segmented parts. The approach is capable of handling a wide range of surfaces, and is not limited to genus-zero surfaces. It handles small features, such as fingers and facial attributes, as well as non-isometric pairs and pairs in different poses. The results show that the proposed approach is superior to current state-of-the-art methods.

Adaptable aging factory for multiple objects and colorations

The visual effects of synthetic objects and environments from modern video games and movies require an impressive amount of detail to properly duplicate their real world equivalents. Among these details, effects produced by aging are particularly hard to handle, and adding them is significantly time-consuming. Existing methods such as physically based and empirical simulations are not suitable for artists since they require the manipulation of complex physical parameters, and their results are difficult to control. Our approach offers a framework for quickly adding aging effects based on a simple example. By defining an aging recipe based on local properties, an artist can easily apply similar effects to different objects or to multiple occurrences of the same object. Also, when aging patterns consist of simple color variations, we propose a color-independent process capable of producing various colorations of the same effect from a single example. Graphical AbstractDisplay Omitted Research Highlights? A user-friendly semi-automatic framework for quickly adding aging effects based on a simple example. ? A property-based method to intuitively define aging patterns. It can also be used to similarly age objects of different shapes or to easily produce multiple aged occurrences of the same object. ? A color-independent synthesis process used to produce multiple colorations of aging effects from a single example. The process also takes advantage of bump mapping to increase realism without capturing complex BRDFs.