This paper describes a systematic method and an experimental software system for high-level transformations of designs specified at behavioral level. The goal is to transform the initial design specifications into an optimized data flow graph (DFG) better suited for high-level synthesis. The optimizing transformations are based on a canonical Taylor Expansion Diagram (TED) representation, followed by structural transformations of the resulting DFG network. The system is intended for data-flow and computation-intensive designs used in computer graphics and digital signal processing applications.