  Occlusion is a common issue in 3D reconstruction from RGB-D videos, often
blocking the complete reconstruction of objects and presenting an ongoing
problem. In this paper, we propose a novel framework, empowered by a 2D
diffusion-based in-painting model, to reconstruct complete surfaces for the
hidden parts of objects. Specifically, we utilize a pre-trained diffusion model
to fill in the hidden areas of 2D images. Then we use these in-painted images
to optimize a neural implicit surface representation for each instance for 3D
reconstruction. Since creating the in-painting masks needed for this process is
tricky, we adopt a human-in-the-loop strategy that involves very little human
engagement to generate high-quality masks. Moreover, some parts of objects can
be totally hidden because the videos are usually shot from limited
perspectives. To ensure recovering these invisible areas, we develop a cascaded
network architecture for predicting signed distance field, making use of
different frequency bands of positional encoding and maintaining overall
smoothness. Besides the commonly used rendering loss, Eikonal loss, and
silhouette loss, we adopt a CLIP-based semantic consistency loss to guide the
surface from unseen camera angles. Experiments on ScanNet scenes show that our
proposed framework achieves state-of-the-art accuracy and completeness in
object-level reconstruction from scene-level RGB-D videos. Code:
https://github.com/THU-LYJ-Lab/O2-Recon.
