PortGS: Paired Opacity Reallocation for Transient-Free 3D Gaussian Splatting

Recovering static scenes from casually captured multi-view images with transient distractors remains challenging for 3D Gaussian Splatting (3DGS), as transient objects introduce cross-view inconsistencies while occluding static content, leaving the available static supervision incomplete. Existing transient-free 3DGS methods mainly suppress unreliable observations, disentangle scene components, or stabilize reconstruction. However, even after transient-aware training has established a reasonably reliable static representation, occlusion-induced missing evidence can leave it under-constrained, making further refinement from reliable but incomplete observations a distinct representation-level challenge. To address this problem, we propose PortGS, which coordinates representation retention and refinement through capacity-participation decoupling, expanding learnable capacity without automatically granting it independent rendering participation. PortGS organizes the scene into persistent base-plastic Gaussian pairs, with base primitives retaining established scene parameters and plastic primitives providing additional geometric and appearance capacity. We further introduce base-conditioned paired opacity reallocation, in which a trainable allocation variable partitions the base opacity reference between the paired primitives. This makes plastic rendering participation relative to the retained base rather than independently parameterized. Base and plastic are then jointly rasterized as a unified static representation under the inherited transient-aware supervision.