Abstract. This article shows how the interactive segmentation tool termed “Active Paintbrush ” and a fully automatic region merging can both be based on the theoretical framework of contraction kernels within irregular pyramids instead of their own, specialized data structures. We introduce “continous pyramids ” in which we purposely drop the common requirement of a fixed reduction factor between successive levels, and we show how contraction kernels can be annotated for a fast navigation of such pyramids. Finally, we use these concepts for improving the integration of the automatic region merging and the interactive tool. 1