Multi-focus image fusion (MFIF) enhances depth of field in photography by generating an all-in-focus image from multiple images captured at different focal lengths. While deep learning has shown promise in MFIF, most existing methods overlooked the physical properties of defocus blurring in their network design, limiting their interoperability and generalization. This paper introduces a novel framework that integrates explicit defocus blur modelling into the MFIF process, improving both interpretability and performance. Using an atom-based spatially-varying parameterized defocus blurring model, our approach calculates pixel-wise defocus descriptors and initial focused images from multi-focus source images in a scale-recurrent manner to estimate soft decision maps. Fusion is then performed using masks derived from these decision maps, with special treatment for pixels likely defocused in all source images or near boundaries of defocused/focused regions. The model is trained with a fusion loss and a cross-scale defocus estimation loss. Extensive experiments on benchmark datasets demonstrated the effectiveness of our approach.

Multi-focus image fusion (MFIF) aims at merging multiple images captured at different focal lengths to create an all-in-focus image. This paper introduces a fully unsupervised learning approach for MFIF that uses only pairs of defocused images for end-to-end training, bypassing the need for ground-truths in supervised learning. Unlike existing methods training via a similarity loss between fused and source images, we propose a dual-path learning framework comprising two networks: an image fuser and a mask predictor. The mask predictor is modeled as a self-supervised denoising network on imperfect fusion masks, trained with a masking-based unsupervised learning scheme. The image fuser, crafted with deep unrolling, leverages the output from the mask predictor to supervise its mask generation at each unrolled step. Moreover, we introduce a fusion consistency loss to ensure the alignment between the image fuser and the mask predictor. In extensive experiments, our proposed approach shows superiority over existing end-to-end unsupervised methods and competitive performance against the supervised ones.