Does Re-saving a JPEG Lower Its Quality? We Saved Photos 10 Times to Find Out

Photo by George Milton on Pexels.

A common piece of advice is that "every time you save a JPEG it loses quality". It is partly true, and the part that is true matters for how you edit. We tested it.

The experiment

We used eight camera photos, resized to 2000 px wide and kept as lossless PNG masters. All saves were JPEG quality 80, made with sharp 0.35. We compared each result against a lossless reference using SSIM, a similarity score where 1.0 means identical.

We ran three scenarios:

1. Saved once: apply five small edits losslessly (resizing in steps from 1800 px down to 1400 px, plus a 1% brightness increase each time), then save as JPEG once.
2. Re-saved 10 times: take that JPEG and open and re-save it nine more times, at the same quality, without changing anything.
3. Saved after every edit: make the same five edits, but save as JPEG after each one, the way many people work when they open, edit, save, and come back later.

Results

Re-saving without changes: almost nothing happened

Nine extra re-saves at the same quality left the median score exactly where it was. Once a JPEG has been compressed, compressing the same pixels again with the same settings and encoder mostly reproduces the same result. In practice, "Open, Save, Close" ten times is not what ruins photos.

Saving between edits: real, measurable damage

Saving after each of five edits dropped the median from 0.9753 to 0.9612. That is a bigger drop than we measured going from JPEG quality 80 down to 50 (0.976 to 0.965). For the most detailed photo, the score fell to 0.940.

The reason: an edit such as a resize, crop, rotation or colour change moves and recalculates pixels. The JPEG blocks from the last save no longer line up with the new image. The next save has to compress a slightly different picture, and it discards a new set of fine detail. The losses add up with every round.

Workflow that avoids it

1. Keep the original. Never overwrite the file that came from the camera or phone. Work on a copy.
2. Do all edits in one session, then export once. Crop, rotate, resize and adjust, and save as JPEG or WebP only at the end.
3. If you need to save midway, save losslessly. PNG (or lossless WebP) keeps every pixel. This is why the imgstools crop, resize, enhance and filters tools save as PNG: you can chain them without adding JPEG loss at every step.
4. Compress last. When the image is final, run it through the compress tool once and choose JPEG or WebP at the quality and size you need.
5. Go back to the original for new versions. For a smaller thumbnail or a different crop, start again from the original, not from an exported copy.

Things our test did not cover

• Different apps or settings between saves. We kept the encoder and quality fixed. Re-saving in a different program, or at a different quality, does not reproduce the same compression choices, and should cause more loss than our "no edits" scenario. Treat every save across apps like an edit.
• Messaging apps and social networks. These often resize and recompress uploads. A photo forwarded several times through chat apps can degrade noticeably. If quality matters, send the original file as a document or a link.
• Lossless edits. Some apps can rotate a JPEG in exact 90° steps without recompressing it. That is a special case and does not apply to crops, resizes or colour changes.

Summary

• Re-saving an unchanged JPEG at the same settings: practically harmless.
• Editing and re-saving as JPEG repeatedly: measurable loss, more than lowering quality from 80 to 50.
• Edit from the original, use lossless files in between, compress once at the end.