How to fix a blurry image after compression

Lossy compression discards information deliberately. The encoder decides certain fine detail is unlikely to be noticed, rounds those values to zero, and writes a file that does not contain them.

The file that reaches you has no record of what was removed. There is nothing to decode, nothing to undo and nothing to recover — which is why re-saving at quality 100 achieves precisely nothing except a larger file containing the same degraded image.

Any tool promising to restore a compressed image is either sharpening it or inventing new detail. Both can be useful; neither is recovery.

Sharpening finds edges and increases the contrast across them, making a light side lighter and a dark side darker. Your eye reads that heightened contrast as crispness.

No new information is created. And because compression artefacts are themselves edges — the boundaries of 8 × 8 blocks, the ringing beside a letter — sharpening amplifies them along with everything else. Applied heavily to a compressed image it makes the damage more visible, not less.

Use a light touch, view at display size, and stop as soon as it looks acceptable rather than pushing for how it used to look.

Modern upscalers are genuinely impressive. Trained on enormous numbers of images, they produce a plausible high-resolution version by generating detail consistent with what they have seen before.

That word — generating — is the whole point. The model is not recovering your image's lost detail; it is inventing detail that looks right. On landscapes and textures the result is often excellent. On faces it can subtly alter features, and on text it can produce letters that were never there.

This makes them useful for presentation and unsuitable for anything where accuracy matters: evidence, documentation, identification, or any image someone will rely on as a record of what was actually photographed.

• Keep originals. Compress copies, never the master.
• Compress once. Each lossy save compounds; three passes at 80 is worse than one at 70.
• Resize before compressing. Fewer pixels at good quality beats many pixels at poor quality, every time.
• Never enlarge. Upscaling cannot add detail; it only makes the softness bigger.
• Match format to content. Text and graphics in PNG or lossless WebP, photographs in JPEG or WebP.
• Send originals as documents through chat apps if quality matters, which bypasses their re-compression entirely.