Many work has been done in the field of computer graphics to simulate exactly the behavior of light in order to obtain images not distinguishable from reality. However, the field of Non Photo-realistic Rendering (NPR) takes interest in algorithmic techniques that could either imitate old pictorial styles or lead to developing new ones. We show in this paper how a Particle Swarm Optimization system has been found to be an effective solution to this problem. Furthermore, this work more generally explores how a metaheuristic based on cooperation and decentralized mechanisms can, through the process of emergence, lead to a given artistic rendering (expressionism) and mediate artistic exploration.