Last updated 23 August 2026
Why the output is always a JPG
JPEG's quality setting is what gives you a real size-versus-quality trade-off — turn it down and the file shrinks, with more compression artifacts becoming visible the further you push it. PNG is lossless by design and doesn't have an equivalent slider, which is why any image you upload here comes back as a JPEG, with a white background filled in behind any transparency.
Lossy compression is a one-way trip
Compressing a JPG or WebP works by permanently discarding detail your eye is least likely to miss. The saving is real and usually invisible, but the discarded information is gone — you cannot recover the original by compressing less next time. Always keep the untouched file somewhere.
Repeated compression is the trap. Every save on an already-compressed image throws away a little more, and the damage accumulates: soft halos around text, blocky patches in skies and flat colour. If you need several sizes or formats, generate each one from the original rather than from a version you already compressed.
How much you can save depends on the picture. Photographs with lots of texture compress well. Screenshots, logos and images with large flat areas or sharp text compress badly as JPG and often look worse than they would as PNG, which stores that kind of content without loss.
Related guide: How to optimise images for a faster website
Common questions
Why does the output download as a JPG?
JPEG's quality setting is what actually makes a file smaller with a visible size/quality trade-off. PNG is lossless and doesn't compress the same way, so any input is converted to JPEG for compression, with a white background behind any transparency.
What quality setting should I use?
70-85% is a common sweet spot — meaningfully smaller than the original with little visible quality loss. Below about 50% starts to show visible blocky artifacts on most photos.
Does compressing lose image quality permanently?
Yes, JPEG compression is lossy — detail removed during compression can't be recovered. Keep your original file if you might need a higher-quality version later.