Better than JPEG? Researcher discovers that Stable Diffusion can compress images - Ars Technica

Last week, Swiss software engineer Matthias Bühlmann discovered that the popular image synthesis model Stable Diffusion could compress existing bitmapped images with fewer visual artifacts than JPEG or WebP at high compression ratios, though there are significant caveats.

Stable Diffusion is an AI image synthesis model that typically generates images based on text descriptions (called "prompts").

With Stable Diffusion 1.4, the weights file is roughly 4GB, but it represents knowledge about hundreds of millions of images.

While most people use Stable Diffusion with text prompts, Bühlmann cut out the text encoder and instead forced his images through Stable Diffusion's image encoder process, which takes a low-precision 512×512 image and turns it into a higher-precision 64×64 latent space representation.

The Stable Diffusion image appears to have more resolved details and fewer obvious compression artifacts than those compressed in the other formats.

(You probably don't want your image compressor inventing details in an image that don't exist.) Also, decoding requires the 4GB Stable Diffusion weights file and extra decoding time.