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Multi-Modal Synergistic Implicit Image Enhancement for Efficient Optical Flow Estimation
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Proposes a high-low frequency feature enhancement network for RAFT-based optical flow under low light, implicitly supervised during training by features from a pretrained 2D-3D RGB-depth fusion network.
Problem
Optical flow estimation degrades under adverse lighting (low texture, noise), and paired high-quality images from the same view are hard to obtain for image enhancement.
Approach
An enhancement network (high/low frequency decomposition with dense convs, channel self-attention, wavelet fusion) is trained end-to-end with optical flow loss plus a prior feature loss that aligns its encoder features with those of a pretrained RGB-point cloud 2D-3D fusion network, so depth-derived knowledge is distilled implicitly into RGB-only inference.
Key results
- On the noised FlyingThings3D val set, EPE improves from 4.18 (GMFlow) to 3.85 and ACC1px rises to 76.66%.
- On VBOF, EPE of 19.99 overall versus 20.11 for GMFlow; best on Sony and Fuji subsets.
- Ablation on RAFT: prior feature loss alone reduces EPE 4.41→4.06; enhancement network alone to 4.23; combined 3.85.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| use multi-modal synergistic implicit enhancement instead of GMFlow | optical flow estimation · Things(clean), C-trained | EPE2D: 3.21 -> 2.91 | Helped |
| use multi-modal synergistic implicit enhancement instead of GMFlow | optical flow estimation · Things(clean), C+N-trained | EPE2D: 3.50 -> 3.25 | Helped |
| use multi-modal synergistic implicit enhancement instead of GMFlow | optical flow estimation · Things(noise), C+N-trained | EPE2D: 4.18 -> 3.85 | Helped |
| use multi-modal synergistic implicit enhancement instead of GMFlow | optical flow estimation · VBOF Sony | EPE: 20.37 -> 20.05 | Helped |
| use multi-modal synergistic implicit enhancement instead of GMFlow | optical flow estimation · VBOF Fuji | EPE: 13.87 -> 13.72 | Helped |
| use multi-modal synergistic implicit enhancement instead of GMFlow | optical flow estimation · VBOF Canon | EPE: 19.48 -> 19.73 | Hurt |
| use multi-modal synergistic implicit enhancement instead of GMFlow | optical flow estimation · VBOF Nikon | EPE: 23.49 -> 23.68 | Hurt |
| use multi-modal synergistic implicit enhancement instead of GMFlow | optical flow estimation · VBOF All | EPE: 20.11 -> 19.99 | Helped |
| add the enhancement network (ablation) | RAFT · Things(noise) | EPE: 4.41 -> 4.23 | Helped |
| add implicit guidance (ablation) | RAFT · Things(noise) | EPE: 4.41 -> 4.06 | Helped |
| add both the enhancement network and implicit guidance (ablation) | RAFT · Things(noise) | EPE: 4.41 -> 3.85 | Helped |
Surprising findings
- Prior feature loss from depth-based fusion contributes more to the gain than the enhancement network itself in the ablation.
- On VBOF, the gain over GMFlow is small (about 1%) on several subsets, and the model is second-best on Canon and Nikon.
Limitations
- Gains on real low-light data (VBOF) are modest and uneven across camera subsets.
- Synthetic noise generalization depends on how noise is synthesized, as the authors note.
- Depends on point clouds derived from depth via unprojection, which is not available for all data.
Experimental setup
Datasets: FlyingThings3D FlyingThings3D noised subset VBOF
Benchmarks: FlyingThings3D Sintel VBOF
Metrics: EPE ACC1px parameters (M) memory (GB)
Baselines: RAFT GMA KPAFlow GMFlow CEDFlow
Builds on: RAFT FlowNet GMA CEDFlow
Closest papers by meaning
- Promoting Single-Modal Optical Flow Network for Diverse Cross-Modal Flow Estimation (AAAI 2022 · similarity 0.87)
- Injecting Frame-Event Complementary Fusion into Diffusion for Optical Flow in Challenging Scenes (NeurIPS 2025 · similarity 0.85)
- FlowAnyTime: Efficient Fine-tuning with Intra-Inter Frame Distillation for All-Weather Optical Flow Estimation (AAAI 2026 · similarity 0.85)
- Learning Optical Flow From Still Images (CVPR 2021 · similarity 0.85)
- DPFlow: Adaptive Optical Flow Estimation with a Dual-Pyramid Framework (CVPR 2025 · similarity 0.85)
- StreamFlow: Streamlined Multi-Frame Optical Flow Estimation for Video Sequences (NeurIPS 2024 · similarity 0.84)
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