There are already quite a few Image Formats out there but the one that i feel is a lite one is WebP by Google. If you look at their page they mention a size reduction of around or more than 25% to the lossy (JPEG) and lossless (PNG) image formats. Less size means less transmission over the internet, faster page loading time. Google uses webp format in their chrome web store to load pages faster and richer way. Well only problem i feel with WebP is that it is no standard like JPEG and hence can only be rendered on a Google Chrome browser.
Further reading:
https://developers.google.com/speed/webp/
https://developers.google.com/speed/webp/gallery1
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