That’s about a 50% reduction in size, lossless, zero reduction in quality or change to pixels from lossless PNG to lossless JXL.
So the browser tools i built basically serves you the tools to easily convert stuff without needing to know anything about libjxl.
The JPEG reconstruction is the most interesting thing, you’re taking a lossy JPEG, converting it to lossless JPEG XL, and you’re seeing a 20% reduction in size while preserving that compression data.
Indeed it’s a huge waste, and with all these data center hysteria, this is a genuine solution to reduce data storage/transfer costs.