A phone photo or a screenshot can easily land at 4-8MB — far more than any website, email attachment limit, or upload form actually needs. Compressing it trades some quality for a much smaller file, but "some" is doing a lot of work in that sentence. Here's how to keep that trade sensible instead of guessing.
Steps
- Open Image Compressor and add your JPG or PNG.
- Drag the quality slider — higher keeps the image sharper but shrinks it less; lower shrinks more but softens fine detail.
- Run it and compare the new size against the original, shown once it's done.
What's actually happening
The image is decoded onto a canvas in your browser and re-encoded as a JPEG at the quality level you chose — the same re-encoding step every image editor uses, just running locally instead of on a server. Because the output is always JPEG, this isn't the right tool if you need to keep a PNG's transparency; re-encoding to JPEG fills transparent areas in solid, since JPEG has no alpha channel at all.
Picking a quality setting
- Photos for the web or email: a lower-to-mid setting is usually fine — JPEG compression artifacts are much less noticeable on photographic content than on flat colors or text.
- Screenshots with text or sharp UI elements: stay closer to the higher end, or small text can start looking blurry or "smudged" at the edges.
- Not sure? Try the default 70%, check the result, and re-run at a different setting if it's not quite right — it takes a second since everything runs on your own device, not a queue on someone else's server.