Real-Time Charcoal Rendering Using Contrast Enhancement Operators

Recent work in non-photorealistic rendering (NPR) has found methods to render various artistic effects like pen and ink illustrations, pencil sketching, water color, engraving, and silhouette rendering. In this paper, we present a new algorithm to achieve the effects of charcoal rendering in real-time using contrast enhancement operators. Charcoal is a medium that has limited dynamic range and tonal resolution. Hence it is difficult for artists to reproduce all the rich textures, colors and tonal variations existing in the physical world. One of the basic techniques that artists use to overcome this is to exaggerate the tonal contrast existing in the real world. In this paper we use contrast enhancement operators (CEO) on textures and/or colors of the model to achieve contrast enhanced textures (CET) and contrast enhanced model (CEM) respectively. We use the CEM and the CET to generate several effects characteristic of charcoal drawings like broad grainy strokes and the smooth tonal variations that are achieved by smudging the charcoal by hand. Further, we also generate the closure effect that is used by artists to avoid artistically and perceptually unpleasant hard silhouette edges. We present a single pass rendering technique that uses one CET to produce all the above charcoal rendering effects at interactive rates using the traditional graphics pipeline.