Beyond homography: nonparametric image alignment via graph convolutional networks

We propose an image alignment algorithm based on weak supervision, which aims to identify the correspondence between a pair of reference and target images with no supervision of individual pixels. Since most existing methods have relied on a predefined geometric model such as homography, they often suffer from a lack of model flexibility and generalizability. To tackle the challenge, we propose a novel nonparametric transformation model based on graph convolutional networks without an explicit geometric constraint. The proposed method is generic and flexible in the sense that it is applicable to the image pairs undergoing diverse local and/or global transformations. To make the algorithm more suitable for real-world scenarios having potential noises from moving objects, we disregard those objects with an off-the-shelf semantic segmentation model. The proposed algorithm is evaluated on the Cityscapes dataset with annotated pixel-level correspondences and outperforms baseline methods relying on global parametric transformations.N