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.

Using a single core

./autogen.sh ./configure make make check 

For multiprocessor machines:

./autogen.sh ./configure make -j8 make check -j8 

Using CMAKE:

mkdir -p build cd build cmake .. make -j8 

On Windows

mkdir -p build cd build "c:\Program Files\CMake\bin\cmake" .. start . REM Double click the Visual Studio project 

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 of just 2 rows of blocks.

./lepton -allowprogressive -memory=1024M -threadmemory=128M progressive.jpg compressedprogressive.lep 

Please begin by filling out the contributor form and asserting that

The code I'm contributing is mine, and I have the right to license it. I'm granting you a license to distribute said code under the terms of this agreement. 

at this page: https://opensource.dropbox.com/cla/

Then create a new pull request through the github interface

Lepton is designed to be easy to debug, but a command line requirement is necessary to prevent the standard forks that let it do a secure verification in a separate process.

To avoid setting follow fork flags, please pass -skipverify to the command line. This will stop verification and let you debug the app as a single process application. If the bug happens in single threaded mode, also you can pass -singlethread which makes it easier to step through the code without other threads hitting breakpoints.