Actually (:nerdface:) byte-accurate / DCT-coefficient-accurate, but using a JXL decoder to decode such a JXL to pixels directly (instead of roundtripping through JPEG) can produce better quality than a typical JPEG decoder, due to the use of higher precision in decoding.
Actually (:nerdface:) byte-accurate / DCT-coefficient-accurate, but using a JXL decoder to decode such a JXL to pixels directly (instead of roundtripping through JPEG) can produce better quality than a typical JPEG decoder, due to the use of higher precision in decoding.