Joint Augmented and Compressed Dictionaries for Robust Image Classification

Dictionary-based Classification (DC) has been a promising learning theory in multimedia computing. Previous studies focused on learning a discriminative dictionary as well as the sparsest representation based on the dictionary, to cope with the complex conditions in real-world applications. However, robustness by learning only one single dictionary is far from the optimal level. What is worse, it cannot take advantage of the available techniques proven in modern machine learning, like data augmentation, to mitigate the same problem. In this work, we propose a novel method that utilizes joint Augmented and Compressed Dictionaries for Robust Dictionary-based Classification (ACD-RDC). For optimization under the noise model introduced by real-world conditions, the objective function of ACD-RDC incorporates only two simple, but well-designed constraints, including one enhanced sparsity constraint by the general data augmentation, which requires less case-by-case and sophisticated tuning, and another discriminative constraint solved by a jointly learned dictionary. The optimization of the objective function is then deduced theoretically to an approximate linear problem. The sparsity and discrimination enhanced by data augmentation guarantees the robustness for image classification under various conditions, which constructs the first positive case using data augmentation to obtain robust dictionary-based classification. Numerous experiments have been conducted on popular facial and object image datasets. The results demonstrate that ACD-RDC obtains more promising classification on diversely collected images than the current dictionary-based classification methods. ACD-RDC is also confirmed to be a state-of-the-art classification method when using deep features as inputs.