JPEG-LS (ISO/IEC 14495-1:1999 / ITU-T.87) is an image compression standard derived from the Hewlett Packard LOCO algorithm. JPEG-LS has low complexity (meaning fast compression) and high compression ratios, similar to the JPEG 2000 lossless ratios. JPEG-LS is more similar to the old Lossless JPEG than to JPEG 2000, but interestingly the two different techniques result in vastly different performance characteristics.
This project's goal is to provide a full implementation of the ISO/IEC 14495-1:1999, "Lossless and near-lossless compression of continuous-tone still images: Baseline" standard. This library is written from scratch in portable C++. The main branch uses C++17. The 2.x branch is maintained in C++14. All mainstream JPEG-LS features are implemented by this library.
According to preliminary test results published on <https://imagecompression.info/gralic,> CharLS is about *twice as fast* as the original HP code, and beats both JPEG-XR and JPEG 2000 by a factor 3.
After releasing the original baseline JPEG-LS standard ISO 14495-1:1999, ISO released an extension to the JPEG-LS standard called ISO/IEC 14495-2:2003: "Lossless and near-lossless compression of continuous-tone still images: Extensions". CharLS doesn't support this extension.
The code is regularly compiled/tested on Windows and 64 bit Linux. Additionally, the code has been successfully tested on Linux Intel/AMD 32/64 bit (slackware, debian, gentoo), Solaris SPARC systems, Intel based Macs and Windows CE (ARM CPU, emulated), where the less common compilers may require minor code edits. It leverages C++ language features (templates, traits) to create optimized code, which generally perform best with recent compilers.
For other platforms, more install options, how to build from source, and more, take a look at the [documentation](https://github.com/team-charls/charls/wiki).
Once you have the library, the sample folder provides some code samples to get you started.
## Release Management
This repository is provided as source code, and specifically does not offer binary releases. Instead, it is encouraged to either “live at head” (build from the latest version of or, if necessary, build against a known, supported branch, known as a Long Term Support (LTS) branch.
Support for older compiler versions will be phased out, 5 years from the moment that a newer version of that compiler has become available. The same applies to the minimal required C++ language version.
CharLS is being used by [GDCM DICOM toolkit](https://sourceforge.net/projects/gdcm/), thanks for [Mathieu Malaterre](https://sourceforge.net/users/malat) for getting CharLS started on Linux. Kato Kanryu wrote an initial version of the color transforms and the DIB output format code, for an [irfanview](https://www.irfanview.com) plugin using CharLS.
The code in this project is available through a BSD style license, allowing use of the code in commercial closed source applications if you wish. **All** the code in this project is written from scratch, and not based on other JPEG-LS implementations. Be aware that Hewlett Packard claims to own patents that apply to JPEG-LS implementations, but they license it for free for conformant JPEG-LS implementations. Some of these patents may already have expired in your country. Read more at <https://hpl.hp.com/loco/> before you use this if you use this code for commercial purposes.
