Having perceptual differences between scene colors is key in many computer vision applications such as image segmentation or visual salient region detection. Nevertheless, most of the times, we only have access to the rendered image colors, without any means to go back to the true scene colors. The main existing approaches propose either to compute a perceptual distance between the rendered image colors, or to estimate the scene colors from the rendered image colors and then to evaluate perceptual distances. However the first approach provides distances that can be far from the scene color differences while the second requires the knowledge of the acquisition conditions that are unavailable for most of the applications. In this paper, we design a new local Mahalanobis-like metric learning algorithm that aims at approximating a perceptual scene color difference that is invariant to the acquisition conditions and computed only from rendered image colors. Using the theoretical framework of uniform stability, we provide consistency guarantees on the learned model. Moreover, our experimental evaluation shows its great ability (i) to generalize to new colors and devices and (ii) to deal with segmentation tasks.
We consider the problem of classification in a comparison-based setting: given a set of objects, we only have access to triplet comparisons of the form object x i is closer to object x j than to object x k . In this paper we introduce TripletBoost, a new method that can learn a classifier just from such triplet comparisons. The main idea is to aggregate the triplets information into weak classifiers, which can subsequently be boosted to a strong classifier. Our method has two main advantages: (i) it is applicable to data from any metric space, and (ii) it can deal with large scale problems using only passively obtained and noisy triplets. We derive theoretical generalization guarantees and a lower bound on the number of necessary triplets, and we empirically show that our method is both competitive with state of the art approaches and resistant to noise.
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