Affective image classification via semi-supervised learning from web images

Affective image classification has drawn increasing research attentions in the affective computing and multimedia communities. Despite many solutions proposed in the literature, it remains a major challenge to bridge the semantic gap between visual features of images and their affective characteristics, partly due to the lack of adequate training samples, which can be largely ascribed to the all-consuming nature of affective image annotation. In this paper, we propose a novel affective image classification algorithm based on semi-supervised learning from web images (SSL-WI). This algorithm consists of four major steps, including color and texture feature extraction, baseline classifier construction, feature selection, and jointly using training images and retrieved web images to re-train the classifier. We have applied this algorithm, the baseline classifier that is not trained by web images, and two state-of-the-art algorithms to differentiating color images in a three-dimensional discrete emotional space. Our results suggest that, with the scheme of semi-supervised learning from web images, the proposed algorithm is able to produce more accurate affective image classification than other three approaches.