CNN2Graph: Building Graphs for Image Classification

Neural Network classifiers generally operate via the i.i.d. assumption where examples are passed through independently during training. We propose CNN2GNN and CNN2Transformer which instead leverage inter-example information for classification. We use Graph Neural Networks (GNNs) to build a latent space bipartite graph and compute cross-attention scores between input images and a proxy set. Our approach addresses several challenges of existing methods. Firstly, it is end-to-end differentiable despite the generally discrete nature of graph construction. Secondly, it allows inductive inference at no extra cost. Thirdly, it presents a simple method to construct graphs from arbitrary datasets that captures both example level and class level information. Finally, it addresses the proxy collapse problem by combining contrastive and cross-entropy losses rather than separate clustering algorithms. Our results increase classification performance over baseline experiments and outperform other methods. We also conduct an empirical investigation showing that Transformer style attention scales better than GAT attention with dataset size.