Learning Unsigned Distance Functions from Multi-view Images with Volume Rendering Priors (2407.16396v1)

Abstract: Unsigned distance functions (UDFs) have been a vital representation for open surfaces. With different differentiable renderers, current methods are able to train neural networks to infer a UDF by minimizing the rendering errors on the UDF to the multi-view ground truth. However, these differentiable renderers are mainly handcrafted, which makes them either biased on ray-surface intersections, or sensitive to unsigned distance outliers, or not scalable to large scale scenes. To resolve these issues, we present a novel differentiable renderer to infer UDFs more accurately. Instead of using handcrafted equations, our differentiable renderer is a neural network which is pre-trained in a data-driven manner. It learns how to render unsigned distances into depth images, leading to a prior knowledge, dubbed volume rendering priors. To infer a UDF for an unseen scene from multiple RGB images, we generalize the learned volume rendering priors to map inferred unsigned distances in alpha blending for RGB image rendering. Our results show that the learned volume rendering priors are unbiased, robust, scalable, 3D aware, and more importantly, easy to learn. We evaluate our method on both widely used benchmarks and real scenes, and report superior performance over the state-of-the-art methods.

• The paper introduces a novel neural network framework that learns volume rendering priors to improve unsigned distance function inference from multi-view images.
• The paper demonstrates substantial performance gains over traditional handcrafted renderers, achieving lower depth L1-error and Chamfer Distance on benchmarks like ShapeNet and DF3D.
• The paper validates its approach with rigorous experiments on diverse datasets, ensuring scalability and robust 3D reconstruction in real-world scenarios.

Learning Unsigned Distance Functions from Multi-view Images with Volume Rendering Priors

This paper introduces a novel approach for UDF inference from multi-view images, leveraging volume rendering priors learned via a neural network. Traditional methods, which rely on handcrafted differentiable renderers, often suffer from issues such as bias on ray-surface intersections, sensitivity to unsigned distance outliers, and poor scalability in large-scale scenes. The authors position their research as a significant improvement by addressing these limitations through the utilization of data-driven neural networks to learn volume rendering priors.

Research Contributions

The paper highlights several key contributions:

1. Volume Rendering Priors:
   • The authors propose a new differentiable renderer for UDFs that is a neural network, trained in a data-driven manner using ground truth depth images generated from 3D meshes.
   • The trained neural network learns to map unsigned distances to depths, forming a prior knowledge base termed as "volume rendering priors."
2. Robust & Scalable Renderer:
   • By using neural networks, the method mitigates the limitations of handcrafted equations, resulting in unbiased, robust, scalable, and 3D-aware differentiable renderers.
   • Extensive experiments demonstrate substantial improvements in multi-view image reconstruction, outperforming state-of-the-art methods both in widely used benchmarks and real-world scenes.
3. Evaluation on Diverse Datasets:
   • The proposed method is rigorously evaluated on several benchmarks, including DeepFashion3D (DF3D), DTU, and Replica datasets.
   • Significant improvements in metrics such as Chamfer Distance (CD), Normal Consistency (N.C.), and F1-score are reported.

Numerical and Empirical Results

The paper presents compelling numerical results showing superior performance over state-of-the-art methods. For instance, on the ShapeNet dataset, the proposed method achieves the lowest depth L1-error and Mask-L1 error, as shown in Table 1 of the paper. On the DF3D dataset, the method consistently outperforms NeuralUDF, NeUDF, and NeAT, reducing CD errors significantly.

Visual results, as illustrated in figures throughout the paper, underscore the efficacy of the method in recovering fine details and maintaining smooth surface reconstructions. This capability is notably demonstrated in the handling of geometrically complex and thin structures, further validating the robustness and accuracy of the learned volume rendering priors.

Theoretical and Practical Implications

Theoretically, the paper advances the state-of-the-art by shifting the paradigm from handcrafted rendering equations to neural network-based priors. This transition not only encapsulates more complex and extensive variations within the unsigned distance field but also brings in inherent 3D awareness due to the learning process involving large datasets.

Practically, the introduced method offers a scalable solution with substantial improvements in reconstruction accuracy. The robustness of their approach is particularly evident in multi-view settings and challenging real-world scenes, making it a practical tool for various applications in 3D computer vision, such as augmented reality, 3D modeling, and digital preservation.

Speculations on Future Developments

Future developments in this domain might focus on refining the progressive learning strategies and exploring even more sophisticated network architectures to further enhance scalability and generalization capabilities. Additionally, integrating monocular depth and normal priors could improve performance in low-texture regions, which remain a challenge.

In conclusion, "Learning Unsigned Distance Functions from Multi-view Images with Volume Rendering Priors" presents a significant academic contribution with practical implications, elevating the reliability and precision of UDF reconstruction from multi-view images. The promising results and the potential for future enhancements signify a meaningful step forward in the field of neural implicit 3D representations.