Envelope extraction for composite shapes for shape retrieval

Analysis of composite shapes recently receives increasing amount of research attention. Different from a silhouette, a composite shape rarely contains a complete envelope. In the paper, we propose a novel envelope extraction algorithm based on the Delaunay triangulation for composite shapes. By analyzing the spatial relationship among individual components of contours and their concavities, we establish new models to describe the envelope edges and their corresponding local enclosed regions. These new models are then used to extract accurate envelopes for composite shapes. We then apply the extracted envelopes to improve shape classification used in shape retrieval. The experimental results show that our algorithm effectively boosts existing shape retrieval algorithms.