In this paper, the authors provide details on the design of a new physically based system that allows for images to be created in real-time with thin, watery paint. The authors’ goal was to design a system that runs in real-time and yet is able to recreate the various effects specific to this medium.

In particular, the reported system mainly targets the simulation of watercolor, but also seems capable of simulating gouache and oriental black ink. The motion of paint is governed by both physically based and heuristic rules in a layered canvas design. A final image is rendered by optically composing the layers using the Kubelka-Munk diffuse reflectance model. All algorithms that participate in the dynamics and rendering phases of the simulation are implemented on graphics hardware. Images made with the system contain the typical effects that can be recognized in images produced with real thin paint, like the dark-edge effect, watercolor glazing, wet-on-wet painting, and the use of different pigment types.

A prototype was implemented on graphics hardware using several fragment programs that operate on simulation data stored in texture objects. In order to examine the prototype’s efficiency in creating a wide range of effects, it was evaluated by several users. The authors analyze both the weaknesses and strengths of the system, and present the experimental results obtained. They also provide a satisfactory literature review of the relevant research and a detailed description of their new system implementation. In general, the system seems quite promising.

This is an interesting research work that is well written and documented. It is intended for professionals in the field of real-time simulation.