Journal of Intelligent & Robotic Systems manuscript No. (will be inserted by the editor) Watercolour robotic painting: a novel automatic system for artistic rendering Lorenzo Scalera · Stefano Seriani · Alessandro Gasparetto · Paolo Gallina Received: date / Accepted: date Abstract In this paper, we present a novel robotic system that produces watercolour paintings by means of a 6-degree-of-freedom collaborative robot. After an analysis of traditional watercolour, different non-photorealistic ren- dering techniques are applied in order to elaborate digital images into artworks. Several algorithms, aimed at processing both the backgrounds and the details, are implemented. Then, the resulting rendering is converted into a sequence of trajectories that the robot reproduces on paper. During the process, the artist controlling the system can change both the algorithm parameters and the hardware variables (e.g. brush type, colour dilution, etc.) in order to ob- tain a different artistic rendering. The challenge is indeed not to faithfully reproduce an image but to introduce a personal and original contribution to the artwork. The robotic painting system described in this paper was named “Busker Robot” and it is the first automatic system that uses the watercolour technique for artistic rendering. It was installed at the “Algorithmic Arts and Robotics” exhibition during the international event “Trieste Next” (Trieste, Italy, September 2017) and won an Honorable Mention at the 2018 Interna- tional Robotic Art Competition (RobotArt). Keywords robotic painting · watercolour · non-photorealistic rendering · artistic rendering · collaborative robotics. L. Scalera, A. Gasparetto University of Udine, via delle Scienze 206 33100, Udine, Italy E-mail: scalera.lorenzo@spes.uniud.it, alessandro.gasparetto@uniud.it S. Seriani, P. Gallina University of Trieste, via Valerio 10, 34127, Trieste, Italy E-mail: sseriani@units.it, pgallina@units.it