How to Compress a JPG Without Artifacts
JPG compression is invisible until suddenly it isn't. Here's where the line sits and how to stay on the right side of it.
JPG is the format most photos live in, and it's the one most likely to be compressed badly. Drop a file into Compress JPG and it usually shrinks. The useful part is knowing how far you can push before it shows.
"Usually" is doing real work in that sentence. A JPG that was already saved at a low quality can come out bigger when re-encoded — so when you use the quality slider, the tool checks for that and hands you back your original untouched rather than a worse, larger file. If you compress a JPG and it reports no saving, that's not a failure: there was nothing left to win at that setting. (That check applies to the slider; give it a target size instead and it returns the smallest file it managed, which is the behaviour you want when a hard limit is the whole point.)
What an artifact actually is
JPG doesn't store your image pixel by pixel. It breaks the picture into small blocks and describes each one mathematically, discarding the finest detail on the theory that you won't miss it. At sensible settings, you don't.
Push too hard and the blocks stop hiding. You get blocking — visible squares in smooth areas like skies — and ringing, a faint halo around sharp edges and lettering. That's not the tool failing; it's JPG doing exactly what it was designed to do, past the point where the design still works.
This is also why JPG is the wrong format for screenshots of text, logos, and flat graphics: those are all sharp edges, which is precisely what it handles worst. For those, Compress PNG is the right tool — our PNG compression guide covers why it works completely differently.
Where the line sits
The quality slider runs from 0.3 to 1 and defaults to 0.75. Rough guide, judged on photographs:
- 0.9 and up — visually indistinguishable from the original, but you're leaving most of the savings on the table.
- 0.75–0.85 — the sweet spot. Large savings, and you'd need to pixel-peep to spot the difference.
- 0.5–0.7 — usable for thumbnails and previews; artifacts begin appearing in skies and gradients.
- Below 0.5 — visible damage on almost anything. Reserve it for when a hard size limit leaves no choice.
These are starting points, not laws. A busy, detailed photo hides compression far better than a portrait against a smooth backdrop, where a sky or a soft wall gives artifacts a blank canvas to show up on.
Every save costs you
The thing that catches people out: JPG loss compounds. Open a JPG, make a small edit, save it — the encoder re-analyses an image that has already been through the process and throws away another layer. Repeat that across a few rounds of editing and the damage accumulates into something you can see, even at a high quality setting each time.
So: don't edit in JPG. Work from the original, or convert to PNG with JPG to PNG before a long editing session, and export JPG once at the end. Our guide on what that conversion does and doesn't fix is worth reading first — it won't recover anything already lost.
Resize before you compress
The most effective compression isn't compression. A photo displayed at 800px wide but stored at 4000px is carrying five times the pixels anyone sees, and no quality setting fixes that — it just degrades detail you weren't showing. Resize Image first, compress second.
If you're aiming at a specific number rather than a look — an upload form with a hard cap — don't use the quality slider at all. Compress JPG has an optional target max size in MB field sitting right under the slider: fill that in and it works backward from your number instead, ignoring the quality setting. For the common KB limits, Compress Image to 100KB and its siblings are the same idea preset to the number you're most likely to need, and our guide to exact size limits explains what they do to get there — including that they'll reduce your dimensions if quality alone won't reach the target.
FAQ
What quality should I use for a JPG?
0.75–0.85 for photographs is a reliable balance. Go higher for images with sharp edges or text; go lower only when a size limit forces it.
Why does my photo look blocky?
The quality was pushed far enough that JPG's compression blocks became visible, most likely in a sky or another smooth area. Back the setting off, or resize the image down first.
Does compressing the same JPG twice make it worse?
Yes. Each lossy save discards a little more. Keep your original and compress a copy.