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Spacetime Gaussian Feature Splatting for Efficient and Photorealistic Dynamic View Synthesis


Core Concepts
Our method proposes a novel Spacetime Gaussian representation that combines 3D Gaussians with temporal opacity, polynomial motion, and parametric rotation to efficiently model dynamic scenes. We further introduce splatted feature rendering to encode view- and time-dependent appearance in a compact manner, and leverage guided sampling of Gaussians to improve rendering quality.
Abstract

The paper presents a novel dynamic scene representation called Spacetime Gaussians (STG) that extends 3D Gaussians to the 4D spacetime domain. The key components of the STG representation are:

  1. Temporal Radial Basis Function: Each STG is equipped with a time-dependent opacity function modeled by a 1D Gaussian, which allows it to effectively capture emerging or vanishing content in the scene.

  2. Polynomial Motion Trajectory and Rotation: The position and rotation of each STG are represented by time-conditioned polynomial functions, enabling the modeling of complex motion and deformation.

  3. Splatted Feature Rendering: Instead of storing spherical harmonics coefficients, each STG stores a compact set of neural features that encode base color, view-dependent, and time-dependent information. These features are then splatted to the image plane and processed by a lightweight MLP to produce the final color.

  4. Guided Sampling of Gaussians: To improve rendering quality in sparsely covered regions, the method introduces a strategy to sample new Gaussians along rays with large training errors and leveraging coarse depth information.

Experiments on several real-world datasets demonstrate that the proposed method achieves state-of-the-art rendering quality and speed, while maintaining a compact model size. The key advantages include photorealistic quality, real-time high-resolution rendering, and efficient storage.

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Stats
Our method can render 8K 6-DoF video at 66 FPS on an Nvidia RTX 4090 GPU. The model size of our lite-version is 200 MB for 300 frames, which is significantly smaller than prior arts like NeRFPlayer (5130 MB) and StreamRF (5330 MB).
Quotes
"Our dynamic scene representation achieves photorealistic quality, real-time high-resolution rendering and compact model size." "Spacetime Gaussians are capable of faithfully modeling static, dynamic as well as transient (i.e., emerging or vanishing) content in a scene." "Splatted feature rendering enhances model compactness and facilitates the modeling of time-varying appearance."

Deeper Inquiries

How can the proposed Spacetime Gaussian representation be extended to handle occlusions and disocclusions more effectively?

The Spacetime Gaussian representation can be extended to handle occlusions and disocclusions more effectively by incorporating additional information about the scene geometry and dynamics. One approach could be to integrate depth information into the representation, allowing the model to understand the spatial relationships between objects in the scene. By incorporating depth cues, the model can better infer occlusions and disocclusions, leading to more accurate and realistic renderings. Additionally, the model could be trained on a wider variety of scenes with varying levels of occlusions to improve its ability to handle complex occlusion scenarios effectively.

What are the potential limitations of the polynomial motion and rotation models, and how could they be further improved to handle more complex dynamics?

The polynomial motion and rotation models may have limitations in capturing highly complex and non-linear motion patterns accurately. One potential limitation is the assumption of smooth and continuous motion, which may not always hold true in dynamic scenes with abrupt changes or irregular movements. To address this limitation, the models could be enhanced by incorporating higher-degree polynomials or more sophisticated motion representations, such as recurrent neural networks or attention mechanisms. These advanced models can better capture the nuances of complex dynamics and improve the fidelity of the rendered scenes.

Could the guided sampling strategy be combined with other scene representation techniques, such as neural radiance fields, to achieve even higher rendering quality and efficiency?

Yes, the guided sampling strategy can be combined with other scene representation techniques, such as neural radiance fields (NeRF), to enhance rendering quality and efficiency. By integrating guided sampling into NeRF models, the system can dynamically adapt the sampling strategy based on training errors and depth information, leading to more accurate and detailed renderings, especially in challenging areas with sparse coverage. This adaptive sampling approach can improve the overall quality of the rendered scenes while maintaining efficiency in the rendering process.
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