  Novel view synthesis aims to generate new view images of a given view image
collection. Recent attempts address this problem relying on 3D geometry priors
(e.g., shapes, sizes, and positions) learned from multi-view images. However,
such methods encounter the following limitations: 1) they require a set of
multi-view images as training data for a specific scene (e.g., face, car or
chair), which is often unavailable in many real-world scenarios; 2) they fail
to extract the geometry priors from single-view images due to the lack of
multi-view supervision. In this paper, we propose a Geometry-enhanced NeRF
(G-NeRF), which seeks to enhance the geometry priors by a geometry-guided
multi-view synthesis approach, followed by a depth-aware training. In the
synthesis process, inspired that existing 3D GAN models can unconditionally
synthesize high-fidelity multi-view images, we seek to adopt off-the-shelf 3D
GAN models, such as EG3D, as a free source to provide geometry priors through
synthesizing multi-view data. Simultaneously, to further improve the geometry
quality of the synthetic data, we introduce a truncation method to effectively
sample latent codes within 3D GAN models. To tackle the absence of multi-view
supervision for single-view images, we design the depth-aware training
approach, incorporating a depth-aware discriminator to guide geometry priors
through depth maps. Experiments demonstrate the effectiveness of our method in
terms of both qualitative and quantitative results.
