The goal of the lensfun library is to provide an open source database of
photographic lenses and their characteristics.  In the past there was an
effort in this direction (see http://www.epaperpress.com/ptlens/), but then
author decided to take the commercial route and the database froze at the
last public stage.  This database was used as the basement on which lensfun
database grew, thanks to PTLens author which gave his permission for this,
while the code was totally rewritten from scratch (and the database was
converted to a totally new, XML-based format).

The lensfun library not only provides a way to read the lens database and
search for specific things in it, but also offers a set of algorithms for
correcting images based on detailed knowledge of lens properties and
calibration data.  Right now lensfun is designed to correct distortion,
transversal (also known as lateral) chromatic aberrations, vignetting, and
colour contribution of the lens (e.g. when sometimes people says one lens
gives "yellowish" images and another, say, "bluish").