Great comments. As co-creator of TinyPNG and TinyJPG I agree with you mostly; re-encoding images is not ideal. But it works for many people because a (too high

Great comments. As co-creator of TinyPNG and TinyJPG I agree with you mostly; re-encoding images is not ideal. But it works for many people because a (too high quality) JPEG file is what they have. There are going to be compression artefacts when compressing. The point is that is a fine line where they are unnoticeable for the casual observer but result in huge savings in file size. This fine line can indeed be found manually with a good JPEG encoder and a lot of time. Many people have neither. We made TinyJPG/TinyPNG for people who want to use images on websites (or in apps) that are of high enough quality for casual observers while having very small file sizes. The artefacts in your first comparison image won't be seen by most people from normal viewing distances. So we can mean a world of difference for people viewing your site with a mobile or poor internet connection. It can be the difference between a hero image that takes 4 seconds to load or 1 second to load. If you care about the highest quality possible without any sacrifices in file size at all, then TinyJPG is not for you. >> TinyJPG will actually quantize your PNGs first (like their TinyPNG service does) It's because you uploaded a PNG image – you also got a PNG image back but gave it a "jpg" extension yourself. It isn't actually a JPEG. TinyPNG/TinyJPG have the same back end service. They both accept PNG & JPEG, and currently won't convert between the formats.