Shading with Apparent Relief

SIGGRAPH '08: ACM SIGGRAPH 2008 talksInternational audienceShape depiction is an important dimension of image creation. For example, techniques are used to remove ambiguities in scientific illustrations, or to create more legible representations in paintings and drawings. Previous approaches focus on a set body of techniques: line-based rendering. Such techniques generate some shape cues to depict the object characteristics that correspond to discontinuities of shape features. Many artists rather depict an object's shape through shading. They have to use other kinds of shape cues that correspond to continuous variations of shape features to convey more subtle information about shape and integrate it seamlessly into conventional lighting. Instead of detecting sharp discontinuities as in line-based rendering, we thus seek a set of continuous cues that have to be defined for each pixel of an image. To this end, we introduce an intermediate representation that we call Apparent Relief to assist the user. It is a view-dependent shape descriptor, from which continuous shape cues are easily extracted, and which gives rise to stylized shading-based shape depictions. By construction, it is free of temporal coherence artifacts and naturally leads to automatic Levels-of-Detail (LOD) effects. Our approach is simple to implement, runs in real-time on modern graphics hardware, and allows a user selection of features. We illustrate its potential using several shading styles