CPFusion: A multi-focus image fusion method based on closed-loop regularization

The purpose of Multi-Focus Image Fusion (MFIF) is to extract the clear portions from multiple blurry images with complementary features to obtain a fully focused image, which is considered a prerequisite for other advanced visual tasks. With the development of deep learning technologies, significant breakthroughs have been achieved in multi-focus image fusion. However, most existing methods still face challenges related to detail information loss and misjudgment in boundary regions. In this paper, we propose a method called CPFusion for MFIF. On one hand, to fully preserve all detail information from the source images, we utilize an Invertible Neural Network (INN) for feature information transfer. The strong feature retention capability of INN allows for better preservation of the complementary features of the source images. On the other hand, to enhance the network’s performance in image fusion, we design a closed-loop structure to guide the fusion process. Specifically, during the training process, the forward operation of the network is used to learn the mapping from source images to fused images and decision maps, while the backward operation simulates the degradation of the focused image back to the source images. The backward operation serves as an additional constraint to guide the performance of the network’s forward operation. To achieve more natural fusion results, our network simultaneously generates an initial fused image and a decision map, utilizing the decision map to retain the details of the source images, while the initial fused image is employed to improve the visual effects of the decision map fusion method in boundary regions. Extensive experimental results demonstrate that the proposed method achieves excellent results in both subjective visual quality and objective metric assessments.