Crowdsearching Training Sets for Image Classification

The success of an object classifier depends strongly on its training set, but this fact seems to be generally neglected in the computer vision community, which focuses primarily on the construction of descriptive features and the design of fast and effective learning mechanisms. Furthermore, collecting training sets is a very expensive step, which needs a considerable amount of manpower for selecting the most representative samples for an object class. In this paper, we face this problem, following the very recent trend of automatizing the collection of training images for image classification: in particular, here we exploit a source of information never considered so far for this purpose, that is the textual tags. Textual tags are usually attached by the crowd to the images of social platforms like Flickr, associating the visual content to explicit semantics, which unfortunately is noisy in many cases. Our approach leverages this shared knowledge, and collects images spanning the visual variance of an object class, removing at the same time the noise by different filtering query expansion techniques. Comparative results promote our method, which is capable to automatically generate in few minutes a training dataset leading to an 81.41% of average precision on the PASCAL VOC 2012 dataset.