Unsupervised learning of high-order structural semantics from images

Structural semantics are fundamental to understanding both natural and man-made objects from languages to buildings. They are manifested as repeated structures or patterns and are often captured in images. Finding repeated patterns in images, therefore, has important applications in scene understanding, 3D reconstruction, and image retrieval as well as image compression. Previous approaches in visual-pattern mining limited themselves by looking for frequently co-occurring features within a small neighborhood in an image. However, semantics of a visual pattern are typically defined by specific spatial relationships between features regardless of the spatial proximity. In this paper, semantics are represented as visual elements and geometric relationships between them. A novel unsupervised learning algorithm finds pair-wise associations of visual elements that have consistent geometric relationships sufficiently often. The algorithms are efficient - maximal matchings are determined without combinatorial search. High-order structural semantics are extracted by mining patterns that are composed of pairwise spatially consistent associations of visual elements. We demonstrate the effectiveness of our approach for discovering repeated visual patterns on a variety of image collections.