Clean JPEG Compression Damage

How it works

Your image is scaled to about one and a half megapixels and repainted at a low denoise, with a fresh seed each run. The instruction names the three distinct symptoms rather than asking vaguely for a cleaner picture: square block edges, ringing around high contrast lines, and color banding across smooth gradients. The negative prompt argues against the usual overcorrection, which is waxy smoothing that takes the real texture out along with the artifacts.

Low denoise is deliberate. Compression damage is superficial in the literal sense — it sits on top of a picture that is otherwise correct — so the model is being asked to subtract something, not to rebuild anything.

Three symptoms, one cause

They look unrelated and they come from the same step.

Blocking is the visible grid. The format processes eight by eight squares independently, and when the quality setting forces it to describe each square coarsely, adjacent squares end up with slightly different average tones. In a clear sky, where nothing should change at all, those small disagreements are plainly visible as tiles.

Ringing is the halo along sharp edges. A hard black-to-white transition needs many high frequency terms to describe exactly, and those are the first things discarded. What remains overshoots on both sides, so you get a bright fringe outside dark text and a dark fringe inside it. This is why screenshots of text suffer more than photographs of faces.

Banding is the staircase in gradients. Subtle tonal steps get quantized onto a coarser ladder, so a smooth sunset becomes a set of visible steps with hard boundaries between them.

Because all three come from the same quantization, an image with one usually has all three, and treating them together works better than chasing them separately.

The save format is half the job

There is a failure mode here that has nothing to do with the model.

Run this page, get a clean file, open it in an editor, export at JPEG quality seventy, and you have re-run the exact process that caused the damage. Worse, you have run it on an image that now has larger flat areas — and flat areas are where blocking shows most. The output can end up looking no better than what you started with.

So the rule is simple and worth following even outside this page. PNG for anything being edited, archived, or passed to another tool. JPEG only at the very end, once, at high quality, for the specific place that needs a small file. Never JPEG in the middle of a chain.

Find the earlier copy first

Before running anything, spend a minute looking for a less damaged source.

Generation loss compounds. A photograph that has been through a chat app, then a screenshot, then a re-share, has been quantized several times over, and each pass degraded the output of the last. The camera roll original, the email attachment, the copy in the cloud backup — any of these is dramatically better than the file you are about to clean.

No amount of processing beats not having lost the information. This page is for when the damaged copy is genuinely the only one left.

Publication gate

This page ships once the workflow has been run against a heavily blocked sky, a screenshot of black text on white, a banded gradient, and a lightly compressed photograph that needs no work, confirming in the last case that fine texture survives the pass.