OpenEXR (also known as EXR or IlmImf) is a raster image file format developed by Industrial Light & Magic. It supports high dynamic range images. It usually uses 16-bit "half precision" floating point samples, though other sample formats are also supported.
Files start with bytes
76 2F 31 01.
The written documentation is unofficial. The format is defined as "whatever the IlmImf Library reads and writes."
- The IlmImf Library, a.k.a. The OpenEXR source distribution (C++): OpenEXR Downloads → openexr-x.x.x.tar.gz, ilmbase-x.x.x.tar.gz
The IlmImf Library includes some samples files for testing.