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

Enlarge / These jagged, colourful blocks are precisely what the idea of picture compression appears to be like like.

Benj Edwards / Ars Technica

Last week, Swiss software program engineer Matthias Bühlmann found that the favored picture synthesis mannequin Stable Diffusion may compress current bitmapped images with fewer visible artifacts than JPEG or WebP at excessive compression ratios, although there are important caveats.

Stable Diffusion is an AI picture synthesis mannequin that usually generates images primarily based on textual content descriptions (referred to as “prompts”). The AI mannequin discovered this skill by finding out thousands and thousands of images pulled from the Internet. During the coaching course of, the mannequin makes statistical associations between images and associated phrases, making a a lot smaller illustration of key details about every picture and storing them as “weights,” that are mathematical values that signify what the AI picture mannequin is aware of, so to talk.

When Stable Diffusion analyzes and “compresses” images into weight kind, they reside in what researchers name “latent space,” which is a approach of claiming that they exist as a type of fuzzy potential that can be realized into images as soon as they’re decoded. With Stable Diffusion 1.4, the weights file is roughly 4GB, but it surely represents information about a whole lot of thousands and thousands of images.

Examples of using Stable Diffusion to compress images.Enlarge / Examples of utilizing Stable Diffusion to compress images.

While most individuals use Stable Diffusion with textual content prompts, Bühlmann lower out the textual content encoder and as a substitute compelled his images by means of Stable Diffusion’s picture encoder course of, which takes a low-precision 512×512 picture and turns it right into a higher-precision 64×64 latent house illustration. At this level, the picture exists at a a lot smaller information measurement than the unique, but it surely can nonetheless be expanded (decoded) again right into a 512×512 picture with pretty good outcomes.


While working exams, Bühlmann discovered that a novel picture compressed with Stable Diffusion regarded subjectively higher at increased compression ratios (smaller file measurement) than JPEG or WebP. In one instance, he exhibits a photograph of a llama (initially 768KB) that has been compressed down to five.68KB utilizing JPEG, 5.71KB utilizing WebP, and 4.98KB utilizing Stable Diffusion. The Stable Diffusion picture seems to have extra resolved particulars and fewer apparent compression artifacts than these compressed within the different codecs.

Experimental examples of using Stable Diffusion to compress images. SD results are on the far right.Enlarge / Experimental examples of utilizing Stable Diffusion to compress images. SD outcomes are on the far proper.

Bühlmann’s technique at present comes with important limitations, nevertheless: It’s not good with faces or textual content, and in some circumstances, it can truly hallucinate detailed options within the decoded picture that weren’t current within the supply picture. (You most likely don’t desire your picture compressor inventing particulars in a picture that do not exist.) Also, decoding requires the 4GB Stable Diffusion weights file and additional decoding time.

While this use of Stable Diffusion is unconventional and extra of a enjoyable hack than a sensible answer, it may doubtlessly level to a novel future use of picture synthesis fashions. Bühlmann’s code can be discovered on Google Colab, and you will find extra technical particulars about his experiment in his publish on Towards AI.


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