Variance Reduction on the Camera Axis: Multi-View Score Distillation for 3D

Score distillation turns a pretrained 2D diffusion model into a 3D generator, but the per-step gradient is estimated from a single random view: this one-sample estimate has high variance (different views of the same partial scene disagree) and is blind to global shape consistency. Existing multi-view approaches address this by retraining the diffusion prior on multi-view data; this improves consistency but conflates the sampling contribution with the quality of the retrained prior. We instead isolate the sampling axis, leaving the prior frozen. We introduce Multi-View Aggregated Score Distillation (MV-SDI), a training-free sampler that replaces the single-view per-step gradient with an average over K views at a fixed UNet-call budget. Averaging K views lowers the per-step gradient variance toward 1/K of its single-view value. Drawing the K views as antithetic antipodal pairs adds no further variance reduction (measured antipodal correlation rho approximately 0) but stratifies angular coverage (every step covers both hemispheres) removing the same-hemisphere clustering of independent sampling. At a fixed 10,000-UNet-call budget on the 43-prompt SDI benchmark, K=2 halves the optimization steps and raises CLIP R-Precision from 74.8% to 83.8% and CLIP score from 0.297 to 0.312 over the single-view SDI baseline, with consistent gains on HPSv2 and ImageReward and a 0.0% divergence rate. K=4 gives a fourfold step reduction at R-Precision 86.9% and CLIP 0.307. The gains concentrate on hard prompts where single-view distillation collapses, at a measured cost in CLIP-IQA. MV-SDI is drop-in for gradient-based score-distillation pipelines, including Score Distillation via Inversion and plain SDS, and requires no retraining and no multi-view data. Code is available at: https://github.com/marianlupascu/MV-SDI