BIGPrior: Towards Decoupling Learned Prior Hallucination and Data Fidelity in Image Restoration

Image restoration encompasses fundamental image processing tasks that have been addressed with different algorithms and deep learning methods. Classical restoration algorithms leverage a variety of priors, either implicitly or explicitly. Their priors are hand-designed and their corresponding weights are heuristically assigned. Thus, deep learning methods often produce superior restoration quality. Deep networks are, however, capable of strong and hardly-predictable hallucinations. Networks jointly and implicitly learn to be faithful to the observed data while learning an image prior, and the separation of original and hallucinated data downstream is then not possible. This limits their wide-spread adoption in restoration applications. Furthermore, it is often the hallucinated part that is victim to degradation-model overfitting. We present an approach with decoupled network-prior hallucination and data fidelity. We refer to our framework as the Bayesian Integration of a Generative Prior (BIGPrior). Our BIGPrior method is rooted in a Bayesian restoration framework, and tightly connected to classical restoration methods. In fact, our approach can be viewed as a generalization of a large family of classical restoration algorithms. We leverage a recent network inversion method to extract image prior information from a generative network. We show on image colorization, inpainting, and denoising that our framework consistently improves the prior results through good integration of data fidelity. Our method, though partly reliant on the quality of the generative network inversion, is competitive with state-of-the-art supervised and task-specific restoration methods. It also provides an additional metric that sets forth the degree of prior reliance per pixel. Indeed, the per pixel contributions of the decoupled data fidelity and prior terms are readily available in our proposed framework.