Robust Object Recognition in Images and the Related Database Problems

International audienceTraditional content-based image retrieval systems typically compute a single descriptor per image based for example on color histograms. The result of a query is in general the images from the database whose descriptors are the closest to the descriptor of the query image. Systems built this way are able to return images that are globally similar to the query image, but can not return images that contain some of the objects that are in the query. As opposed to this traditional coarse-grain recognition scheme, recent advances in image processing make fine-grain image recognition possible, notably by computing local descriptors that can detect similar objects in different images. Obviously powerful, fine-grain recognition in images also changes the retrieval process: instead of submitting a single query to retrieve similar images, multiple queries must be submitted and their partial results must be post-processed before delivering the answer. This paper first presents a family of local descriptors supporting fine-grain image recognition. These descriptors enforce robust recognition, despite image rotations and translations, illumination variations, and partial occlusions. Many multi-dimensional indexes have been proposed to speed-up the retrieval process. These indexes, however, have been mostly designed for and evaluated against databases where each image is described by a single descriptor. While this paper does not present any new indexing scheme, it shows that the three most efficient indexing techniques known today are still too slow to be used in practice with local descriptors because of the changes in the retrieval process