Estimating optical flow in occluded regions is a crucial challenge in unsupervised settings. In this work, we introduce M2Flow, a novel framework for unsupervised optical flow estimation that integrates motion information from multiple frames to address occlusions. By modeling inter-frame motion information and employing Motion Information Propagation (MIP) module, M2Flow effectively propagates and integrates motion information across frames, while concurrently estimating bidirectional optical flows for multiple frames. In addition, to handle occlusions across multiple frames, we provide two augmentation modules specifically designed for our multi-frame model to further refine optical flow. The experiments on KITTI and Sintel datasets demonstrate that M2Flow outperforms other state-of-the-art unsupervised approaches, especially in solving occlusions.

Extracting local features for accurate correspondences between image pairs is an essential basis for various computer vision tasks. Recent works have shown that deep neural networks (DNNs) have demonstrated promising performance in challenging environments. However, these state-of-the-art DNN-based approaches are not well suited for the scenario with geometry rotations due to their intrinsic deficiencies of square kernel structure. That is, square kernel structures in standard DNNs cannot fully identify the essentials of the rotations in geometry. To address this problem, we present RICNN, a novel deep learning framework that encodes invariance against the rotations in geometry explicitly into convolutional neural networks. Rather than using the square-shaped kernel structure, RICNN adopts sectorshaped convolutional kernels to achieve encoding invariance in all rotations. With the explicitness of such rotation encoding, RICNN enables the transfer of perspective DNN models to obtain rotation-invariant descriptions. Furthermore, we propose a novel multi-level hinge triplet loss function to strengthen the matching constraints against geometry rotations. Comprehensive experiments demonstrate the strong generalization ability of the RICNN descriptor on the HPatches dataset. Toward the rotation invariance evaluation, our method shows state-of-the-art results.