A Reference-Free Quality Enhancement Framework for Low-quality Fundus Images

The progression of medical image analysis methodologies has significantly assisted fundus clinical decision-making, such as disease diagnosis and lesion segmentation. However, low-quality fundus images bring a series of challenges to the automatic screening of diseases and the segmentation of lesions. Most existing methods primarily concentrate on enhancing image quality by utilizing the supervision of paired fundus images, which are difficult to collect in real medical applications. High-quality reference images are essential for guiding quality enhancement. To this end, we propose an enhancement method for low-quality fundus images, called RF-IQE, to alleviate the requirement for paired training images and only requires low-quality fundus images. Specifically, we first construct the patch-level high-/low-quality domains by employing a rule-based quality assessment scheme. Then, to achieve the fundus image quality enhancement and unified illumination styles simultaneously, we formulate them as a patch quality domain adaptation and a multi-style domain adaptation, respectively. We qualitatively and quantitatively demonstrate that our reference-free image quality enhancement network outperforms the conventional methods and exhibits comparable performance than the deep learning-based image enhancement methods with paired images on both the EyeQ and Messidor datasets. Furthermore, we also investigate the influence of the RF-IQE method on various fundus imaging analysis tasks, including vessel segmentation, optic disc segmentation, lesion segmentation, and disease classification.