Hacker News Reader

JpegMini claims to be perceptually lossless, not mathematically lossless.

Besides offering lossless quality images, JPEGmini allows a much larger file size. Compressor.io only appears to allow 10MB files, which if you're trying to use it for photography, it won't be very useful because the jpeg's produced by a Canon 5D Mark III are about 20MB-30MB in size. It is also only web based, whereas JPEGmini has a native client. Compressor.io looks promising though.

Looks like it depends on the image.

Image1 reduction: Compressor.io 28.67% | JpegMini 34.35%

Image2 reduction: Compressor.io 69.55% | JpegMini 55.41%

If I had to choose, I'd say the visual quality of JpegMini is fractionally better, but it's hardly perceptible to my eye - they both produce incredible results.