JPG Compressor

Compressing JPG is not the same job as compressing any other format, because JPG stores its data differently. Understanding what the encoder is actually doing is the difference between hitting a size target cleanly and mangling an image.

JPG compression works by discarding detail the eye is least likely to miss, then encoding what remains. The quality setting decides how much goes. Around 80 is usually indistinguishable from the original at normal viewing size, 60 starts to show on flat areas like skies, and below 40 the blocky artefacts become obvious.

This compressor uses MozJPEG rather than a stock encoder, which matters more than it sounds. MozJPEG applies trellis quantisation and smarter chroma subsampling, and typically produces files around ten percent smaller than a standard encoder at the same visual quality. On a large batch that adds up.

One thing to keep in mind: a JPG has already been compressed once. Compressing it again applies the process to an image that has already lost detail, so damage accumulates. Where you still have the camera original, start from that rather than from an already saved JPG.

Everything runs in this browser tab. Add one file or several hundred, set a target size or a quality level, and the results come back without anything being uploaded.

• Files never leave your device
• No size limits
• Free, no sign-up