  We propose a new method for solving imaging inverse problems using
text-to-image latent diffusion models as general priors. Existing methods using
latent diffusion models for inverse problems typically rely on simple null text
prompts, which can lead to suboptimal performance. To address this limitation,
we introduce a method for prompt tuning, which jointly optimizes the text
embedding on-the-fly while running the reverse diffusion process. This allows
us to generate images that are more faithful to the diffusion prior. In
addition, we propose a method to keep the evolution of latent variables within
the range space of the encoder, by projection. This helps to reduce image
artifacts, a major problem when using latent diffusion models instead of
pixel-based diffusion models. Our combined method, called P2L, outperforms both
image- and latent-diffusion model-based inverse problem solvers on a variety of
tasks, such as super-resolution, deblurring, and inpainting.
