Digitized cell animations are typically composed of frames, which contain a small number of regions, which each contain pixels f the same color and exhibit a significant level of shape coherence through time. To exploit this coherence, we treat the stack of frames as a 3D volume and represent the evolution f each region by the bounding surface f the 3D volume V that it sweeps out. To reduce transmission costs, we triangulate and simplify the bounding surface and then encode it using the