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Suppress and Rebalance: Towards Generalized Multi-Modal Face Anti-Spoofing
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Proposes MMDG, a ViT-based multi-modal face anti-spoofing framework with uncertainty-guided cross-adapters (U-Adapter) and gradient-modulation rebalancing (ReGrad), plus the first multi-source domain generalization benchmark for multi-modal FAS.
Problem
Multi-modal face anti-spoofing generalizes poorly to unseen attacks and deployment conditions because depth/infrared modalities cause unreliable cross-modal fusion under domain shift and training suffers from modality imbalance.
Approach
Use Monte Carlo dropout uncertainty to down-weight unreliable tokens in cross-modal attention fusion (U-Adapter), and adaptively modulate each modality's gradients based on gradient conflict and convergence speed, with a single-side prototypical loss to measure modality convergence (ReGrad).
Key results
- On Protocol 1 leave-one-out sub-protocols, MMDG reaches average HTER 19.25% and AUC 87.96%, versus 34.22% HTER for SSDG and 25.45% HTER for VP-FAS (best prior).
- On Protocol 2 with missing modalities, MMDG achieves average HTER 24.51% and AUC 82.69%, outperforming VP-FAS (29.74% HTER).
- Ablation on Protocol 1: ViT+U-Adapter with ReGrad reaches HTER 19.48% and AUC 87.48%, compared with 27.38% HTER without ReGrad.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Add MMDG with U-Adapter and ReGrad | ViT-B · Protocol 1 average (four cross-dataset sub-protocols) | HTER (%): 31.14 -> 19.25 | Helped |
| Add MMDG with U-Adapter and ReGrad | ViT-B · Protocol 2 average (missing-modality scenarios) | HTER (%): 37.67 -> 24.51 | Helped |
| Add MMDG with U-Adapter and ReGrad | ViT-B · Protocol 3 CW → PS | HTER (%): 42.66 -> 20.12 | Helped |
| Add MMDG with U-Adapter and ReGrad | ViT-B · Protocol 3 PS → CW | HTER (%): 42.75 -> 36.60 | Helped |
| Add U-Adapter (ablation) | ViT-B · Protocol 1 average (four cross-dataset sub-protocols) | HTER (%): 31.14 -> 27.38 | Helped |
| Add ReGrad (ablation) | ViT + U-Adapter · Protocol 1 average (four cross-dataset sub-protocols) | HTER (%): 27.38 -> 19.48 | Helped |
| Apply ReGrad only when modality gradients conflict (ablation) | ViT + U-Adapter · Protocol 1 average (four cross-dataset sub-protocols) | HTER (%): 27.38 -> 21.91 | Helped |
| Apply ReGrad only when modality gradients do not conflict (ablation) | ViT + U-Adapter · Protocol 1 average (four cross-dataset sub-protocols) | HTER (%): 27.38 -> 21.23 | Helped |
| Add ReGrad (ablation) | ViT-B without U-Adapter · Protocol 1 average (four cross-dataset sub-protocols) | HTER (%): 31.14 -> 30.59 | Helped |
| Use estimated uncertainty in U-Adapter and ReGrad (ablation) | MMDG · Protocol 1 average (four cross-dataset sub-protocols) | HTER (%): 28.40 -> 19.48 | Helped |
| Use estimated uncertainty in ReGrad (ablation) | MMDG without uncertainty in U-Adapter · Protocol 1 average (four cross-dataset sub-protocols) | HTER (%): 28.40 -> 26.13 | Helped |
| Use estimated uncertainty in U-Adapter (ablation) | MMDG without uncertainty in ReGrad · Protocol 1 average (four cross-dataset sub-protocols) | HTER (%): 28.40 -> 22.75 | Helped |
Surprising findings
- Multi-modal extensions of SSDG performed worse than its unimodal RGB version (AUC drop from 83.69 to 82.03), showing more modalities do not automatically improve generalization.
- Several methods (SSAN, IADG, ViT, ViT+AMA) performed better when both depth and infrared were missing than when only one was missing, suggesting unreliable modality information misleads detection.
Limitations
- Modality balance is not fully achieved; the authors note further enhancement of modality balance is needed.
- Uncertainty estimation via Monte Carlo dropout may not be the most efficient; the authors suggest more efficient uncertainty techniques.
- Performance on the benchmark remains far from perfect (average HTER around 19%), leaving room for improvement.
Experimental setup
Datasets: CASIA-CeFA PADISI-Face CASIA-SURF WMCA
Benchmarks: CASIA-CeFA PADISI-Face CASIA-SURF WMCA
Metrics: HTER AUC
Baselines: SSDG SSAN IADG ViTAF MM-CDCN CMFL ViT + AMA VP-FAS ViT PMR OGM-GE
Builds on: SSDG PMR OGM-GE Vision Transformer central difference convolution
Closest papers by meaning
- FaceShield: Explainable Face Anti-Spoofing with Multimodal Large Language Models (AAAI 2026 · similarity 0.84)
- mmFAS: Multimodal Face Anti-Spoofing Using Multi-Level Alignment and Switch-Attention Fusion (AAAI 2025 · similarity 0.83)
- Gradient Alignment for Cross-Domain Face Anti-Spoofing (CVPR 2024 · similarity 0.83)
- From Intuition to Investigation: A Tool-Augmented Reasoning MLLM Framework for Generalizable Face Anti-Spoofing (CVPR 2026 · similarity 0.82)
- Interpretable Face Anti-Spoofing: Enhancing Generalization with Multimodal Large Language Models (AAAI 2025 · similarity 0.82)
- Rethinking Generalizable Face Anti-spoofing via Hierarchical Prototype-guided Distribution Refinement in Hyperbolic Space (CVPR 2024 · similarity 0.82)
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