AI

Self-Supervised Learning of Structure and Motion from Video

Abstract

We propose SfM-Net, a geometry-aware neural network for motion estimation in videos that decomposes frame-toframe pixel motion in terms of scene and object depth, camera motion and 3D object rotations and translations. Given a sequence of frames, SfM-Net predicts depth, segmentation, camera and rigid object motions, converts those into a dense frame-to-frame motion field (optical flow), differentiably warps frames in time to match pixels and backpropagates. The model can be trained with various degrees of supervision: 1) completely unsupervised, 2) supervised by ego-motion (camera motion), 3) supervised by depth (e.g., as provided by RGBD sensors), 4) supervised by ground-truth optical flow. We show that SfM-Net successfully estimates segmentation of the objects in the scene, even though such supervision is never provided. It extracts meaningful depth estimates or infills depth of RGBD sensors and successfully estimates frame-to-frame camera displacements. SfM-Net achieves state-of-the-art optical flow performance. Our work is inspired by the long history of research in geometry-aware motion estimation, Simultaneous Localization and Mapping (SLAM) and Structure from Motion (SfM). SfM-Net is an important first step towards providing a learning-based approach for such tasks. A major benefit over the existing optimization approaches is that our proposed method can improve itself by processing more videos, and by learning to explicitly model moving objects in dynamic scenes.