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Structural Pruning via Spatial-aware Information Redundancy for Semantic Segmentation
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Proposes SIRFP, a structured filter pruning method for semantic segmentation that scores channel redundancy with spatial-aware JS-divergence on full-resolution feature maps (EMA-accumulated), frames selection as a maximum edge weight clique problem, and solves it with a fast greedy algorithm (EHGP).
Problem
Existing filter pruning methods designed for image classification ignore spatial information, so they perform suboptimally when pruning location-sensitive segmentation (and detection) networks, and exact/heuristic solutions to the underlying clique formulation are too costly for network pruning.
Approach
Model channel selection as a maximum edge weight clique problem over a graph whose edge weights reflect spatial-aware (un-pooled feature map) redundancy measured via JS divergence and accumulated with EMA during training, then prune greedily by repeatedly removing the channel with the smallest total edge weight.
Key results
- On Cityscapes with DeepLabv3-ResNet50 at 60% FLOPs reduction, SIRFP reaches 81.3 mIoU vs 80.9 for DCFP and 81.6 unpruned.
- On ImageNet with ResNet-50 at 1.0G FLOPs, SIRFP achieves 74.67 top-1 vs 73.30 for CHIP.
- On COCO2017 SSD-ResNet50 at 50% FLOPs reduction, SIRFP reaches 26.6 AP vs 25.9 for CHEX-1.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use spatial-aware redundancy pruning rather than DCFP | Deeplabv3-ResNet50 · Cityscapes validation, 60% pruning | mIoU: 80.9 -> 81.3 | Helped |
| Use spatial-aware redundancy pruning rather than DCFP | Deeplabv3-ResNet50 · ADE20K, 60% FLOPs reduction | mIoU: 44.8 -> 44.9 | Helped |
| Use spatial-aware redundancy pruning rather than DCFP | Deeplabv3-ResNet50 · COCO stuff-10K, 60% FLOPs reduction | mIoU: 34.3 -> 34.8 | Helped |
| Use spatial-aware redundancy pruning rather than CHEX | SSD-ResNet50 · COCO2017 validation, 50% FLOPs reduction | AP: 25.9 -> 26.6 | Helped |
| Use spatial-aware redundancy pruning instead of CafeNet | ResNet-50 · ImageNet validation, 2.0G FLOPs | Top-1 accuracy: 76.90 -> 77.35 | Helped |
| Use full-resolution rather than 1×1 feature maps for redundancy (ablation) | SIRFP · Cityscapes, Deeplabv3-ResNet50 | mIoU: 80.4 -> 81.3 | Helped |
| Use full-resolution rather than quarter-resolution feature maps for redundancy (ablation) | SIRFP · Cityscapes, Deeplabv3-ResNet50 | mIoU: 80.6 -> 81.3 | Helped |
| Use full-resolution rather than half-resolution feature maps for redundancy (ablation) | SIRFP · Cityscapes, Deeplabv3-ResNet50 | mIoU: 80.8 -> 81.3 | Helped |
| Increase redundancy feature resolution from full to twice the input feature dimensions (ablation) | SIRFP · Cityscapes, Deeplabv3-ResNet50 | mIoU: 81.3 -> 81.3 | No clear effect |
| Use JS divergence instead of dot product for the redundancy metric (ablation) | SIRFP · Cityscapes, Deeplabv3-ResNet50 | mIoU: 80.5 -> 81.3 | Helped |
| Use JS divergence instead of KL divergence for the redundancy metric (ablation) | SIRFP · Cityscapes, Deeplabv3-ResNet50 | mIoU: 81.1 -> 81.3 | Helped |
| Use JS divergence instead of dice score for the redundancy metric (ablation) | SIRFP · Cityscapes, Deeplabv3-ResNet50 | mIoU: 81.0 -> 81.3 | Helped |
Surprising findings
- Dot-product redundancy metric performs notably worse (80.5 mIoU) than JS divergence (81.3), attributed to sign-related cancellation.
- Doubling the feature resolution (twice) gave no further mIoU gain over full resolution (both 81.3).
Limitations
- Requires forward inference over training samples to collect feature maps for pretrained networks, adding cost.
- Redundancy computation can be expensive for networks with very large feature map resolution.
- Gains over strong baselines are modest on some settings (e.g., ADE20K and COCO stuff-10K at 60% reduction vs DCFP: 44.9 vs 44.8).
Experimental setup
Datasets: Cityscapes ADE20K COCO stuff-10K ImageNet COCO2017
Benchmarks: Cityscapes ADE20K COCO stuff-10K COCO2017 ImageNet
Metrics: mIoU FLOPs reduction parameters AP Top-1 accuracy Top-5 accuracy FPS runtime
Baselines: Random NS Taylor DepGraph FPGM DCFP CAP CHEX DMCP
Builds on: FPGM DCFP HRank CHIP
Closest papers by meaning
- Structural Pruning via Latency-Saliency Knapsack (NeurIPS 2022 · similarity 0.87)
- Unsupervised Semantic Segmentation Through Depth-Guided Feature Correlation and Sampling (CVPR 2024 · similarity 0.86)
- Improving Semi-Supervised Semantic Segmentation with Sliced-Wasserstein Feature Alignment and Uniformity (CVPR 2025 · similarity 0.86)
- Hierarchy-Agnostic Unsupervised Segmentation: Parsing Semantic Image Structure (NeurIPS 2024 · similarity 0.85)
- Training-Free Dataset Pruning for Instance Segmentation (ICLR 2025 · similarity 0.85)
- VLM-Pruner: Buffering for Spatial Sparsity in an Efficient VLM Centrifugal Token Pruning Paradigm (CVPR 2026 · similarity 0.85)
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