Rendering Silhouettes with Virtual Lights

We present a new method for obtaining non-photorealistic images. These images have two main visual components: silhouettes and non-realistic colouring. Silhouettes are lines that define the form of an object. They are used in classical animation and illustration as the main expressive components. In these applications, if it is necessary, colouring can be added once the drawings are made. For instance, generally, in illustration, colouring is flat and does not transmit volume information whilst silhouettes do it in an economical way. The proposed method is based on the Virtual Lights model, which allows us to use external components, the virtual lights, to define silhouettes. In this way, the designer is free to control where, when and how the silhouettes must appear. The method can be used with B-rep geometric models.