This Demonstration rasterizes an image in a triangular grid. The "resolution" slider controls the raster size and the "number of grays" slider controls the number of gray levels (in other words, posterization).
[1] M. Zawidzki and T. Nagakura, "Influence of Grid Type on Agents Behavior in Simulations Performed with Crowd-Z," in Proceedings of the Ninth International Conference on Engineering Computational Technology (ECT2014), Naples, Italy (P. Iványi and B.H.V. Topping, eds.), Cambrdige, MA: Department of Architecture, Massachusetts Institute of Technology, 2014. www.ctresources.info/ccp/paper.html?id=8505.