A Hybrid Method for Distance Metric Learning
  We consider the problem of learning a measure of distance among vectors in a feature space and propose a hybrid method that simultaneously learns from similarity ratings assigned to pairs of vectors and class labels assigned to individual vectors. Our method is based on a generative model in which class labels can provide information that is not encoded in feature vectors but yet relates to perceived similarity between objects. Experiments with synthetic data as well as a real medical image retrieval problem demonstrate that leveraging class labels through use of our method improves retrieval performance significantly. 
Yi-Hao Kao and Benjamin Van Roy and Daniel Rubin and Jiajing Xu and   Jessica Faruque and Sandy Napel
cs.LG cs.IR stat.ML