  We present a novel approach to leverage prior knowledge encapsulated in
pre-trained text-to-image diffusion models for blind super-resolution (SR).
Specifically, by employing our time-aware encoder, we can achieve promising
restoration results without altering the pre-trained synthesis model, thereby
preserving the generative prior and minimizing training cost. To remedy the
loss of fidelity caused by the inherent stochasticity of diffusion models, we
employ a controllable feature wrapping module that allows users to balance
quality and fidelity by simply adjusting a scalar value during the inference
process. Moreover, we develop a progressive aggregation sampling strategy to
overcome the fixed-size constraints of pre-trained diffusion models, enabling
adaptation to resolutions of any size. A comprehensive evaluation of our method
using both synthetic and real-world benchmarks demonstrates its superiority
over current state-of-the-art approaches. Code and models are available at
https://github.com/IceClear/StableSR.
