LittleCMS 2 on github

So here you go:

http://github.com/mm2/Little-CMS

You can review all files in a nice web page and also that makes fair easy to send patches. Many thanks to Richard Hughes for this nice idea!

You can also review the documentation in such way. It is located on 'doc' folder. The tutorial is a good starting point.

Include files

Any application using LittleCMS 2 has to include just one header.

#include “lcms2.h”

The header has been renamed to lcms2.h in order to improve the adoption of version 2. In fact, both Little CMS 1.x and 2.0 can coexist installed in same machine. This is very important on platforms like linux, where LittleCMS is nested deep in the dependency tree. Little CMS 2 no longer relies on icc34.h or any file coming from ICC. All costants are now prefixed by “cms” and there is one license for all package.

Lcms2.h does expose the API, and only the API. Unlike 1.xx series, all internal functions are no longer accesible for client applications.

A special case are the LittleCMS plug-ins. Those constructs can access more functions that the API, just because they are supposed to access Little CMS internals to add new functionality. There is a specialized include file for that:

#include “lcms2_plugin.h”

This file should only be included when defining plug-ins. It defines some additional functions and is described in the LittleCMS2.0 Plugin API document.

Requeriments

In order to improve portability and minimize code complexity, LittleCMS 2.0 requires a C99 compliant compiler. This requirement has been relexed on Microsoft’s Visual Studio because its wide adoption by industry (VC is not fully C99 compliant). Borland C 5.5 (available for free) has been tested and found to work Ok. gcc and the Intel compiler does work ok.

Backwards compatibility

Little CMS 2 is almost a full rewrite of 1.x series, so there is no guarantee of backwards compatibility. Having said this, if your application doesn’t make use of advanced features, probably all what you need to do is to change the include file from lcms.h to lcms2.h and maybe to do some minor tweaks on your code. Profile opening and transform creation functions are kept the same, but there are some changes in the flags.  Little CMS 2 does offer more ways to access profiles, so it is certainly possible your code will get simplified.  The basic parts where Little CMS 2 differs from 1.x series are:

• ·    Transform flags
• ·    Error handling
• ·    Textual information retrieval
• ·    New non-ICC intents
• ·    Floating point modes
• ·    Pipelines

On internal advanced functions, the underlying implementation has changed significantly. You still can do all what lcms1 did, but in some cases by using a different approach. There are no longer gamma curves or matrix-shaper functions. Even the LUT functions are gone. All that has been superseded by:

• ·    Gamma functions -> Tone curves
• ·    Matrix Shaper, LUT -> Pipelines
• ·    LUT resampling -> Optimization engine

There is no one-to-one correspondence between old and new functions, but most old functionality can be implemented with new functions.

What is new from lcms 1.x

First obvious question is “why should I upgrade to Little CMS 2.0”. Here are some clues:

Little CMS 2.0 is a full v4 CMM, which can accept v2 profiles. Little CMS 1.xx was a v2 CMM which can deal with (some) V4 profiles. The difference is important, as 2.0 handling of PCS is different, definitively better and far more accurate.

• It does accept and understand floating point profiles (MPE) with DToBxx tags. (Yes, it works!) It has 32 bits precision. (lcms 1.xx was 16 bits)
• It handles float and double formats directly. MPE profiles are evaluated in floating point with no precision loss.
• It has plug-in architecture that allows you to change interpolation, add new proprietary tags, add new “smart CMM” intents, etc.
• Is faster. In some combinations, has a x 6 throughput boost.
• Some new algorithms, incomplete state of adaptation, Jan Morovic’s segment maxima gamut boundary descriptor, better K preservation…
• Historic issues, like faulty icc34.h, freeing profiles after creating transform, etc. All is solved.

Documentation!

Back from vacation. Lots of fun and some time devoted to LittleCMS. As a result, we have now some incipient documentation. There is a tutorial you can read to explore the differences between LittleCMS 1 and 2. The plug-in API is also documented, but the documentation lacks some explanations and is mostly unfinished. The API reference is a work in progress...