The blog post is from 10 years ago. I'm sure it's much faster on modern hardware. I'd say that the main difference is that JPEG XL can be rendered directly in many applications, while Lepton files will have to be processed into JPEG out of your archives.
Lepton guarantees that JPEG->Lepton->JPEG produces an identical file, not just identical pixels. Does JPEG XL achieve the same thing?
Yes, with all metadata preserved. The converted JXL even has checksum metadata for verification
That's actually the default behavior for libjxl cli: encoding and then decoding jpeg via jxl produces a file bit identical to the original jpeg file.
Try it: run cjxl › djxl and hash the output against the original.
Yes
yes
The blog post is from 10 years ago. I'm sure it's much faster on modern hardware. I'd say that the main difference is that JPEG XL can be rendered directly in many applications, while Lepton files will have to be processed into JPEG out of your archives.
If anything the gap is worse on modern hardware because Lepton is hostile to both SIMD and divide-and-conquer thread parallelism.
Microsoft's implementation claims to get a speedup using AVX2.