Computer-generated graphite pencil materials and rendering

During the past decades, photorealism has been the driving research effort in computer graphics and has become the method of choice for rendering 3D models. Despite much recent progress in efficiency and quality of photorealistic rendering methods, there is one very important open issue remaining: Photorealistic images are not always the best option for representing information in certain application domains (architecture design, technical and artistic illustration). Therefore, alternative display methods are necessary. The main thrust of research in Non-Photorealistic Rendering (NPR) is to devise such alternative display methods. Several approaches have been proposed, and they can be categorized in two main research directions: (1) simulation of natural media for drawing (pencil, charcoal, pen-and-ink) or painting (watercolor, oil), including their correspondent rendering tools and primitives (brush, boards, strokes); and (2) rendering methods applied to reference images and/or 3D models directly. This research contributes to both directions by presenting an automatic 3D pencil rendering system. We have broken the problem of simulating pencil drawing down into four basic parts: (1) simulating the drawing materials (graphite pencil and drawing paper, blenders and kneaded eraser), (2) modeling the drawing primitives (individual pencil strokes and mark-making to create tones and textures), (3) simulating the basic rendering techniques used by artists and illustrators familiar with pencil rendering, and (4) modeling the control of the drawing composition. Each part builds upon the others and is essential to developing the framework for higher-level rendering methods and tools. We demonstrate the capabilities of our approach with a variety of images generated from 3D models.