Image Quality Assessment: From Mean Opinion Score to Opinion Score Distribution

Recently, many methods have been proposed to predict the image quality which is generally described by the mean opinion score (MOS) of all subjective ratings given to an image. However, few efforts focus on predicting the opinion score distribution of the image quality ratings. In fact, the opinion score distribution reflecting subjective diversity, uncertainty, etc., can provide more subjective information about the image quality than a single MOS, which is worthy of in-depth study. In this paper, we propose a convolutional neural network based on fuzzy theory to predict the opinion score distribution of image quality. The proposed method consists of three main steps: feature extraction, feature fuzzification and fuzzy transfer. Specifically, we first use the pre-trained VGG16 without fully-connected layers to extract image features. Then, the extracted features are fuzzified by fuzzy theory, which is used to model epistemic uncertainty in the process of feature extraction. Finally, a fuzzy transfer network is used to predict the opinion score distribution of image quality by learning the mapping from epistemic uncertainty to the uncertainty existing in the image quality ratings. In addition, a new loss function is designed based on the subjective uncertainty of the opinion score distribution. Extensive experimental results prove the superior prediction performance of our proposed method.