CNN2GNN: How to Bridge CNN with GNN.

Thanks to extracting the intra-sample representation, the convolution neural network (CNN) has achieved excellent performance in vision tasks. However, its numerous convolutional layers take a higher training expense. Recently, graph neural networks (GNN), a bilinear model, have succeeded in exploring the underlying topological relationship among the graph data with a few graph neural layers. Unfortunately, due to the lack of graph structure and high-cost inference on large-scale scenarios, it cannot be directly utilized on non-graph data. Inspired by these complementary strengths and weaknesses, we discuss a natural question, how to bridge these two heterogeneous networks? In this paper, we propose a novel CNN2GNN framework to unify CNN and GNN together via distillation. Firstly, to break the limitations of GNN, we design a differentiable sparse graph learning module as the head of the networks. It can dynamically learn the graph for inductive learning. Then, a response-based distillation is introduced to transfer the knowledge and bridge these two heterogeneous networks. Notably, due to extracting the intra-sample representation of a single instance and the topological relationship among the datasets simultaneously, the performance of the distilled "boosted" two-layer GNN on Mini-ImageNet is much higher than CNN containing dozens of layers, such as ResNet152.