Image retrieval is an active area of research, which is growing very rapidly. Indeed, stimulated by the rapid growth in storage capacity and processing speed, the number of images in electronic collections and the World Wide Web has considerably increased over the last few years. However, with this abundance of information, people are continuously looking for tools that help them find the image(s) they are looking for within a reasonable amount of time. These tools are image retrieval engines. When using an image retrieval engine, the user is continuously interacting with the machine. First, he1 uses the system’s interface to formulate a query that expresses his needs. Second, he provides feedback about the retrieved results at each search iteration. This allows the engine to provide more accurate results by using relevance feedback (RF) techniques. Third, he may be asked to assign a goodness score or weight to each image retrieved, which helps evaluating the system’s performance. In this chapter, we will review the main interactions between human and the machine in the context of image retrieval. We will address several issues, including: Query formulation: • How the user expresses his needs and what he is looking for • The different ways the query can be formulated: keywords-based, sentence-based, query by example image, query by sketch, query by feature values, composite queries, etc. • Query by region of interest (ROI) vs. global query. • Queries with positive example only vs. queries with both positive and negative examples. • Page zero problem: finding a good image to initiate a retrieval session. Relevance feedback: we will try to answer questions like: • Why do systems use relevance feedback? • How can the user express his needs during the relevance feedback process • How this information is exploited by the system to perform operations like feature selection or the identification of the sought image. 1 Note that the masculine gender has been used strictly to facilitate reading, and is to be understood to include the feminine. Advances in Human-Computer Interaction 216 • The different families of RF techniques. • Relevance feedback with retrieval memory, i.e., taking into account the value of old iteration queries when constructing the new one. • Whether it is useful for the system to create user profiles, and the challenges it has to face. • The number of RF iterations required to obtain satisfactory results. Viewing retrieval results: • Existing viewing techniques: 2D linear presentation, 3D-based presentation, etc. • Different ways the resulting images may be ordered and presented to the user: similarity-ordered, time-ordered, event-ordered, etc. Evaluation of the retrieval performance by the user: • How the user can express his satisfaction/dissatisfaction about the retrieved images • What about the ground truth in image retrieval evaluation? • System response time and its influence on user satisfaction. • The ease of use of the system’s interface. Other issues: • User’s needs: He may be looking for a specific image, for images that meet a given need (e.g. illustrate a concept) or simply browsing the collection looking for potentially “good” images.
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