This project consists of the following bits and pieces:

  * A proposed specification to add support for embedded color image
    glyphs in OpenType fonts,

  * A tool called emoji_builder.py, to embed a set of PNG images into
    an existing font,

  * Two sets of sample PNG images for ASCII characters and sample
    scripts to build them into test fonts: FruityGirl and Funkster.

  * Scripts to build a real color emoji font out of the Open Source
    PhantomOpenEmoji images.

Discussions about this work happen at:

  https://groups.google.com/forum/#!forum/color-emoji

Here is the version 1 of the spec:

  https://rawgit.com/behdad/color-emoji/master/specification/v1.html

Here is the announcement:

  http://google-opensource.blogspot.com/2013/05/open-standard-color-font-fun-for.html

Support for this format was included in FreeType in May 2013.  Support
has also been included in Fontconfig, as well Skia graphics library.
A proof-of-concept patchset for the Cairo graphics library to use
fallback software rendering for the Xlib backend with support for color
glyphs is at https://github.com/behdad/cairo/tree/color-emoji

Currently, Android, ChromeOS, Chrome Linux, as well as certain versions
of Firefox support rendering fonts built using this format.

This format is now part of OpenType specification, version 1.7:

  http://www.microsoft.com/typography/otspec/cbdt.htm
  http://www.microsoft.com/typography/otspec/cblc.htm