Discriminative Soft Bag-of-Visual Phrase for Mobile Landmark Recognition

This paper proposes a new bag-of-visual phrase (BoP) approach for mobile landmark recognition based on discriminative learning of category-dependent visual phrases. Many previous landmark recognition works adopt a bag-of-words (BoW) method which ignores the co-occurrence relationship between neighboring visual words in an image. Although some works that focus on visual phrase learning have appeared, they mainly construct a generalized phrase dictionary from all categories for recognition, which lacks descriptive capability for a specific category. Another shortcoming of these works is the hard assignment of numerous feature sets to a limited number of phrases, which causes some useful feature sets to be discarded, and yields information loss. In view of this, this paper presents a discriminative soft BoP approach for mobile landmark recognition. The candidate phrases defined as adjacent pairwise codewords are first generated for each category. The important candidates are then selected through a proposed discriminative visual phrase (DVP) selection approach to form the BoP dictionary. Finally, a soft encoding method is developed to quantize each image into a BoP histogram. The context information such as location and direction captured by mobile devices is also integrated with the proposed BoP-based content analysis for landmark recognition. Experimental results on two datasets show that the proposed method is effective in mobile landmark recognition.