UGD-IML: A Unified Generative Diffusion-based Framework for Constrained and Unconstrained Image Manipulation Localization

Yachun Mi1,Xingyang He1,Shixin Sun1,Yu Li1,Zhixuan Li2,Jian Jin3,Chen Hui3,Shaohui Liu1†
1Harbin Institute of Technology, 2Nanyang Technological University, 3Nanjing University of Information Science and Technology
Corresponding author.
Neurocomputing, 2026
Conditional diffusion architecture of UGD-IML.

UGD-IML formulates manipulation localization as conditional mask generation, using a shared diffusion model for both unconstrained localization and class-constrained localization.

Abstract

Image manipulation localization must handle both open-world forgeries and constrained settings where an original reference image is available. UGD-IML unifies these tasks with a generative diffusion framework that iteratively denoises a manipulation mask. A conditional control module extracts image guidance, while task-specific conditioning and noise embeddings allow one model to support both settings. Multi-step generation also exposes uncertainty around difficult boundaries and improves robustness across manipulation types.

Unified Task Conditioning

Different conditional-control processes for IML and CIML.

The same conditional control module processes forgery evidence in both tasks. Constrained localization additionally compares the manipulated image with its source image through shared feature extraction.

Localization Results

UGD-IML qualitative results for constrained and unconstrained manipulation localization.

UGD-IML localizes diverse edited regions with coherent masks in both unconstrained and source-guided scenarios.

Uncertainty Awareness

Uncertainty and error maps produced by UGD-IML.

Variation across diffusion samples provides an uncertainty estimate that concentrates near ambiguous manipulation boundaries and often aligns with localization errors.

BibTeX

@article{mi2026ugdiml,
  title={{UGD-IML}: A Unified Generative Diffusion-based Framework for Constrained and Unconstrained Image Manipulation Localization},
  author={Mi, Yachun and He, Xingyang and Sun, Shixin and Li, Yu and Li, Zhixuan and Jin, Jian and Hui, Chen and Liu, Shaohui},
  journal={Neurocomputing},
  year={2026},
  publisher={Elsevier}
}