  We present a novel method for 3D surface reconstruction from multiple images
where only a part of the object of interest is captured. Our approach builds on
two recent developments: surface reconstruction using neural radiance fields
for the reconstruction of the visible parts of the surface, and guidance of
pre-trained 2D diffusion models in the form of Score Distillation Sampling
(SDS) to complete the shape in unobserved regions in a plausible manner. We
introduce three components. First, we suggest employing normal maps as a pure
geometric representation for SDS instead of color renderings which are
entangled with the appearance information. Second, we introduce the freezing of
the SDS noise during training which results in more coherent gradients and
better convergence. Third, we propose Multi-View SDS as a way to condition the
generation of the non-observable part of the surface without fine-tuning or
making changes to the underlying 2D Stable Diffusion model. We evaluate our
approach on the BlendedMVS dataset demonstrating significant qualitative and
quantitative improvements over competing methods.
