Advanced Techniques in CBIR: Local Descriptors, Visual Dictionaries and Bags of Features

Local descriptors have been extensively used in CBIR systems, where their robustness to intense geometric and photometric transformations allows the identification of a target object/image with great reliability. However, due to their excessive discriminating power, their application to the retrieval of complex categories is challenging. The introduction of the technique of visual dictionaries (also known as dictionary of visual terms) is an important step towards the conciliation between the robustness of local descriptors and the flexibility of generalization needed by complex queries. As a bonus, we become able to employ advanced retrieval techniques which were so far available only for textual data.