Cranio-Diff: Diffusion-based Cross-domain Craniofacial Reconstruction with 2D X-ray Skull

Abstract The identification of unknown human remains is a persistent humanitarian and forensic challenge. In forensic investigations, it becomes even more challenging when common biometric DNA identifications, such as soft-tissue or hair strands are not present, as they degrade with time. To narrow down the process of identification, few attempts have been made to identify an individual by reconstructing a face from the given skeletal remains ( i.e., skull) using generative AI models, such as CycleGAN, Pix2Pix, and diffusion models. However, they fail to effectively capture semantic information in craniofacial reconstruction, due to a mismatch in the alignment of structural information across modalities. To address this issue, we propose \textit{Cranio-Diff}, a diffusion-based framework for craniofacial reconstruction from 2D X-ray skull images. The proposed approach integrates skull-conditioned structural guidance through ControlNet with biometric text prompts to generate a face. The proposed \textit{Cranio-Diff} method is evaluated on skull-face dataset obtained from X-ray scans of 120 subjects in lateral and frontal views. To enable controlled evaluation, each face image is artificially synthesized across three age groups (25, 45, 65) and three BMI variations $\pm10\%$, yielding 4320 paired samples. This dataset is also curated across different facial modalities ( RGB and sketch) with different appearance conditions (hair and without hair). To the best of our knowledge, this is the only X-ray-face dataset with this magnitude. Extensive experiments showed that the proposed method achieves improved performance over the recent existing approaches in both generated image quality and retrieval task. Finally, to evaluate the performance of our proposed method, we have evaluated the quality of the generated image using FID, SSIM, LPIPS score. Additionally, retrieval performance is evaluated using recall@k, mAP@k and MRR@k. Obtained experimental results demonstrate that the proposed method can be used as an alternate tool in providing aid in forensic investigations.