Lepton is a tool and file format for losslessly compressing JPEGs by an average of 22%.
This can be used to archive large photo collections, or to serve images live and save 22% bandwidth.
To roundtrip (compress and decompress) an image, original.jpg, do the following:
./lepton original.jpg compressed.lep
./lepton compressed.lep restored_original.jpg
Or all at once:
./lepton original.jpg compressed.lep && ./lepton compressed.lep restored_original.jpg && diff restored_original.jpg original.jpg && echo no differences
Lepton may also be used with pipes -- be sure to check the exit code when using pipes as if compression fails lepton will produce 0 bytes and return a nonzero exit code (failure). In this case do not assume the 0 byte file is representative of the original.
./lepton - < original.jpg > compressed.lep
./lepton - < compressed.lep > restored_original.jpg
You may specify higher memory limits than the default for lepton to handle bigger images:
./lepton -memory=1024M -threadmemory=128M input_file output_file
Additionally you can configure lepton to process progressive jpegs. Warning: these take more memory to decode than normal JPEGs since the entire framebuffer must be kept in memory for the duration of the decompression, instead if just 2 rows of blocks.
./lepton -allowprogressive -memory=1024M -threadmemory=128M progressive.jpg compressedprogressive.lep