Abstract
In the modern world, networked sensor technology makes it possible to capture the world around us in real-time. In the security domain cameras are an important source of information. Cameras in public places, bodycams, drones and recordings with smart phones are used for real time monitoring of the environment to prevent crime (monitoring case); and/or for investigation and retrieval of crimes, for example in evidence forensics (forensic case). In both cases it is required to quickly obtain the right information, without having to manually search through the data. Currently, many algorithms are available to index a video with some pre-trained concepts, such as people, objects and actions. These algorithms require a representative and large enough set of examples (training data) to recognize the concept. This training data is, however, not always present.
In this thesis, we aim to assist an analyst in their work on video stream data by providing a search capability that handles ad-hoc textual queries, i.e. queries that include concepts or events that are not pre-trained. We use the security domain as inspiration for our work, but the analyst can be working in any application domain that uses video stream data, or even indexed data. We focus on the retrieval of high-level events, such as birthday parties. In our aim to assist the analyst, we focus on the improvement of the visual search effectiveness (e.g. performance) by a semantic query-to-concept mapping: the mapping from the user query to the set of pre-trained concepts. We show that the main improvements can be achieved by using a combination of i) query-to-concept mapping based on semantic word embeddings (+12\%), ii) exploiting user feedback (+26\%) and iii) fusion of different modalities (data sources) (+17\%).
