Drawing surfaces using hatching strokes simultaneously conveys material, tone, and form. We present a real-time system for nonphotorealistic rendering of hatching strokes over arbitrary surfaces. During an automatic preprocess, we construct a sequence of mipmapped hatch images corresponding to different tones, collectively called a tonal art map. Strokes within the hatch images are scaled to attain appropriate stroke size and density at all resolutions, and are organized to maintain coherence across scales and tones. At runtime, hardware multitexturing blends the hatch images over the rendered faces to locally vary tone while maintaining both spatial and temporal coherence. To render strokes over arbitrary surfaces, we build a lapped texture parametrization where the overlapping patches align to a curvature-based direction field. We demonstrate hatching strokes over complex surfaces in a variety of styles. Keywords: non-photorealistic rendering, line art, multitexturing, chicken-and-egg problem 1

In this paper we present a high-quality, image-space approach to illustration that preserves continuous tone by probabilistically distributing primitives while maintaining interactive rates. Our method allows for frame-to-frame coherence by matching movements of primitives with changes in the input image. It can be used to create a variety of drawing styles by varying the primitive type or direction. We show that our approach is able to both preserve tone and (depending on the drawing style) high-frequency detail. Finally, while our algorithm requires only an image as input, additional 3D information enables the creation of a larger variety of drawing styles.

maintaining even distributions as the viewpoint, illumination, and viewing distance change---or even as the model itself changes. Our contribution to this area is in integrating exist- We present an approach to produce animations of 3D models using stippling as a rendering style. Our technique ensures frame-toframe coherence as the model moves and changes over time. Oscar Meruvia Pastor, Bert Freudenberg, and Thomas Strothotte Otto-von-Guericke University of Magdeburg Real-Time Animated Stippling 62 July/August 2003 Published by the IEEE Computer Society 0272-1716/03/$17.00 2003 IEEE 1 Two stippling examples: (a) Ron C. Guthrie's Indian Pottery and (b) a closeup from the same image showing the individual stipples. 2 Stippling technique using Voronoi relaxation: (a) a stippled image of a grasshopper and (b) a detail of the grasshopper's head. 1-2 (b) Image courtesy of Ron C. Guthrie Image courtesy of Oliver Deussen ing work in point hierarchies

In this paper, we present simple rendering techniques implemented using traditional graphics hardware to achieve the effects of charcoal drawing. The effects include characteristics of charcoal drawings like broad grainy strokes and smooth tonal variations that are achieved by smudging the charcoal by hand. Further, we also generate the closure effect that is used by artists at times to avoid hard silhouette edges. All these effects are achieved using contrast enhancement operators on textures and/or colors of the 3D model.

In this paper, we show how many interactive 3D applications' visual styles can be changed to new, different, and interesting visual styles non-invasively. Our method lets a single stylized renderer be used with many applications. We implement this by intercepting the OpenGL graphics library and changing the drawing calls. Even though OpenGL only receives low-level information from an application, computation on this data and assumptions about the application can give us enough information to develop stylized renderers.

Actual graphic hardware becomes more and more powerful. Consequently, virtual scenes can be rendered in a very good quality integrating dynamic behavior, real-time shadows, bump mapped surfaces and other photorealistic rendering techniques. On the other hand, non-photorealistic rendering became popular as well, because of its artistic merits. An integration in an AR environment is the logical consequence. In this paper we present an AR framework that uses photorealistic rendering as well as non-photorealistic rendering techniques. The prototypes based on these techniques show the advantages and disadvantages of both technologies in combination with Augmented Reality.

Medical illustrations use simple drawing styles to demonstrate shapes and features of organs and organ systems, while omitting irrelevant details. In this contribution, we present a non-photorealistic rendering algorithm for illustrating anatomical data. Unlike other existing methods that rely on available triangulations of the organs to be rendered, our approach relies only on a subset of surface points, together with their normals. The advantage is that surface points and normals can be quite easily extracted from medical data, without an intermediate triangulation. 1

Simulation of a pen-and-ink illustration style in a realtime rendering system is a challenging computer graphics problem. Tonal art maps (TAMs) were recently suggested as a solution to this problem. Unfortunately, only the hatching aspect of pen-and-ink media was addressed thus far. We extend the TAM approach and enable representation of arbitrary textures. We generate TAM images by distributing stroke primitives according to a probability density function. This function is derived from the input image and varies depending on the TAM's scale and tone levels. The resulting depiction of textures approximates various styles of pen-and-ink illustrations such as outlining, stippling, and hatching.

We describe a multiresolution method for rendering curves that is based on exact reproduction of artistic silhouettes and line hand-gesture styles. Using analysis based on reverse subdivision, we extract examples from both scanned images of line-drawn artwork and interactively-sketched input and apply these styles to the arbitrary strokes of new illustrations. Our algorithms work directly with the extracted discrete point data using fast and simple local and global multiresolution filters, and we support the use of styles with gaps or discontinuities. Our results show how this technique can capture the complex contour drawings of landscape elements, allowing users without drawing skills to easily reproduce them. Keywords: Non-photorealistic rendering-by-example; multiresolutions; contour line drawings; reverse-subdivision. 1.

We present a method for frame coherent texturing and hatching of 3D models with a discrete set of colors. Our technique is inspired by various artistic styles that use a limited set of colors to convey surface shape and texture. In previous research discrete color shading was produced by modifying smooth shading with a threshold function. We extend this approach and specify threshold values with an image or a procedural texture. Texture values and mapping coordinates are adapted to surface orientation and scale. Aliasing artifacts are eliminated by the modified filtering technique. The threshold texturing approach enables an animator to control local shading and to display surface roughness and curvature with a limited set of colors.