Object-aware semantics of attention for image captioning

In image captioning, exploring the advanced semantic concepts is very important for boosting captioning performance. Although much progress has been made in this regard, most existing image captioning models usually neglect the interrelationships between objects in an image, which is a key factor of accurately understanding image content. In this paper, we propose the object-aware semantic attention object-aware semantic attention (OSA) based captioning model to address this issue. Specifically, our attention model allows the explicit associations between the objects by coupling the attention mechanism with three types of semantic concepts, i.e., the category information, relative sizes of the objects, and relative distances between objects. In reality, they are easily built up and seamlessly coupled with the well-known encoder-decoder captioning framework. In our empirical analysis, these semantic concepts favor different aspects of the image content like the number of the objects belonging to each category, the main focus of an image, and the closeness between the objects. Importantly, they are cooperated with visual features to help the attention model effectively highlight the image regions of interest for significant performance gains. By leveraging three types of semantic concepts, we derive four semantic attention models for image captioning. Extensive experiments on MSCOCO dataset show our attention models within the encoder-decoder image captioning framework perform favorably as compared to representative captioning models.