LIQA: Lifelong Blind Image Quality Assessment

The image distortions are complex and dynamically changing in the real-world scenario, due to the fast development of the image processing system. The blind image quality assessment (BIQA) models may encounter the challenge of processing images with distortion types never seen before deployment. However, existing BIQA models generally cannot evolve with unseen distortion types adaptively, which greatly limits the deployment and application of BIQA models in real-world scenarios. To address this problem, we propose a novel Lifelong blind Image Quality Assessment (LIQA) approach, targeting to achieve the lifelong learning of BIQA. Without accessing to previous training data, our proposed LIQA can not only learn new knowledge, but also mitigate the catastrophic forgetting of learned knowledge. Specifically, we adopt the Split-and-Merge distillation strategy to train a single-head network that makes task-agnostic predictions. In the split stage, we first employ a distortion-specific generator to generate pseudo features of each previously seen distortion. Then, we utilize an auxiliary multi-head regression network to keep the response of each distortion. In the merge stage, we replay the pseudo features and use the pseudo labels generated by the auxiliary multi-head network to distill the knowledge of the multiple heads, which can build the final regression single head. Extensive experiments demonstrate that LIQA can perform well in handling both inner-dataset distortion shift and cross-dataset distortion shift. More importantly, our model can achieve stable performance even if the task sequences are long.