PGMS: Pyramidal Gaussian Mixture Splatting for 3DGS Compression

3D Gaussian Splatting (3DGS) has become an established representation for real-time novel view synthesis. However, preserving fine geometric structures and appearance details typically requires millions of Gaussian primitives, resulting in substantial storage and transmission overhead. 3DGS compression has been extensively studied through attribute quantization, entropy coding, and lightweight reparameterization. However, existing methods often operate on a fixed backbone and therefore do not explicitly model the joint redundancy between geometry and appearance in the original dense Gaussian set. To address this limitation, we propose \textbf{Pyramidal Gaussian Mixture Splatting} (PGMS), a plug-and-play 3DGS compression framework that reformulates dense Gaussian primitives into a rate-controllable pyramidal representation with scale-dependent attributes. Specifically, PGMS first constructs a mixture pyramid by progressively partitioning dense Gaussians into hierarchical mixture centers, where different levels perform attribute-specific clustering to form shared prototypes. It then employs a rate-adaptive capacity allocator to determine the tiered budget under a target compression ratio. To further improve rendering quality, we introduce a compositing-aware parameter update rule that incorporates information from dense Gaussians into pyramid primitives according to their image-space contributions. Experiments on standard benchmarks show that our method delivers strong compression with high rendering fidelity and consistently outperforms state-of-the-art 3DGS compression methods.