We report the design, implementation, and deployment of Lepton, a
fault-tolerant system that losslessly compresses JPEG images to 77% of their
original size on average. Lepton replaces the lowest layer of baseline JPEG
compression-a Huffman code-with a parallelized arithmetic code, so that the
exact bytes of the original JPEG file can be recovered quickly. Lepton matches
the compression efficiency of the best prior work, while decoding more than
nine times faster and in a streaming manner. Lepton has been released as
open-source software and has been deployed for a year on the Dropbox
file-storage backend. As of February 2017, it had compressed more than 203 PiB
of user JPEG files, saving more than 46 PiB.

Lepton 是一个开源的容错系统，它用算术编码替换了 JPEG 压缩的最底层 —— 霍夫曼码，使得原始 JPEG 文件的确切字节可以快速恢复，并且可以流式解码。它在压缩效率方面与最优先前的作品相匹配，而且解码速度更快九倍以上。