Production Ray Tracing of Feature Lines

Automated feature line drawing of virtual 3D objects helps artists depict shapes and allows for creating stylistic rendering effects. High-fidelity drawing of lines that are very thin or have varying thickness and color, or lines of recursively reflected and refracted objects, is a challenging task. In this paper we describe an image-based feature detection and line drawing method that integrates naturally into a ray tracing renderer and runs as a post-process, after the pixel sampling stage. Our method supports arbitrary camera projections and surface shaders, and its performance does not dependent on the geometric complexity of the scene but on the pixel sampling rate. By leveraging various attributes stored in every pixel sample, which are typically available in production renderers, e.g. for arbitrary output variables (AOVs), feature lines of reflected and refracted objects can be obtained with relative ease. The color and width of the lines can be driven by the surface shaders, which allows for achieving a wide variety of artistic styles.