Ilmbase are a set of utility libraries released by ilm, and used in their openexr implementation. included in this package you can find:

* libhalf: a class (half) for manipulating "half" values (16-bit
floating point format) as if they were a built-in c++ data type.
* libilmthread: a thread abstraction library on top of pthreads.
* libimath: a math library with support for matrices, 2d- and
3d-transformations, solvers for linear/quadratic/cubic equations,
and more.
* libiex: an exception handling library.