What is image compression?
Image compression shrinks the file size of a photo or graphic so it loads faster, uploads quicker, and takes up less storage — ideally with no visible difference to the human eye. Every JPG, PNG, and WebP file already uses some compression, but images exported from cameras, phones, design tools, and screenshots are routinely two to ten times larger than they need to be for the web.
The reason is simple: those tools optimize for editing headroom and maximum fidelity, not for delivery. A 4MB photo straight off a phone might look identical at 600KB once it has been re-compressed with the right settings. Smaller images mean faster pages, lower bandwidth bills, better Core Web Vitals scores, and a smoother experience for everyone on a slow connection.
Lossy vs lossless: which should you pick?
There are two families of compression. Lossless compression — used by PNG and the lossless mode of WebP — reorganizes the data so the file is smaller but every pixel is reconstructed exactly. It is the right choice for logos, line art, screenshots of text, and anything where crisp edges and exact colors matter. The downside is that the savings are limited, often only 10–30%.
Lossy compression — used by JPEG, the default mode of WebP, and AVIF — throws away fine detail that the eye struggles to perceive, such as subtle gradients in a clear sky or texture in dark shadows. This is how a photo can lose 70% of its size while still looking the same at normal viewing distances. For photographs and complex images, lossy is almost always the better trade-off. The quality slider on this page controls exactly how aggressive that trade-off is.
When to use WebP and AVIF
If you only change one thing about how you save images, switch to WebP. It compresses 25–35% smaller than JPEG at the same visual quality, supports transparency like PNG, and is supported by every modern browser. Re-targeting your JPGs and PNGs to WebP with this tool is the single biggest easy win for page speed.
AVIF goes a step further, frequently reaching half the size of an equivalent JPEG, which makes it excellent for large hero images and image-heavy galleries. The trade-offs are slower encoding and slightly less universal support in older software, so it is best used where the bandwidth savings clearly justify it. On OpusImg, AVIF output is part of the Pro plan; WebP, JPEG, and PNG compression are free for everyone.
MozJPEG vs standard JPEG encoders
Not all JPEG encoders are equal. The encoders bundled into most operating systems and editing apps are tuned for speed, not for the smallest possible file. MozJPEG — the encoder behind this tool's JPEG output — uses smarter trellis quantization and progressive scan optimization to squeeze 5–15% more out of a JPEG at the same quality setting, with no change to how you work.
That is why re-compressing a JPEG here can save space even when the source was already a JPEG: you are swapping a generic encoder for a best-in-class one. Combined with the quality slider, it lets you dial in the exact balance of size and fidelity you want, and preview the result before you download anything.
Our privacy model: everything runs in your browser
Most online compressors upload your images to a server, process them in the cloud, and send the result back. That means your private photos and confidential documents pass through someone else's infrastructure, where they may be logged, cached, or retained. OpusImg works differently.
Compression here runs entirely on your device using WebAssembly ports of the Squoosh codecs. When you drop a file, it is decoded, re-encoded, and handed back to you without a single byte ever being uploaded. There is no server to trust, nothing to delete afterward, and the tool keeps working even if you go offline. It is the same fast, modern compression you would get from a desktop app — delivered through a web page that respects your privacy by design.