Autodesk VIZ can both read and write image files in the OpenEXR format. OpenEXR is both an image file format and a general open-source API for reading and writing such files.
The best place to look for information on OpenEXR itself is the official Website. The following is taken directly from the OpenEXR home page:
OpenEXR is a high dynamic-range (HDR) image file format developed by Industrial Light & Magic for use in computer imaging applications.
OpenEXR is used by ILM on all motion pictures currently in production. The first movies to employ OpenEXR were Harry Potter and the Sorcerer's Stone, Men in Black II, Gangs of New York, and Signs. Since then, OpenEXR has become ILM's main image file format.
Higher dynamic range and color precision than existing 8- and 10-bit image file formats.
Support for 16-bit floating-point, 32-bit floating-point, and 32-bit integer pixels. The 16-bit floating-point format, called "half," is compatible with the half data type in NVIDIA's Cg graphics language and is supported natively on their new GeForce FX and Quadro FX 3D graphics solutions.
Multiple lossless image compression algorithms. Some of the included codecs can achieve 2:1 lossless compression ratios on images with film grain.
Extensibility. New compression codecs and image types can easily be added by extending the C++ classes included in the OpenEXR software distribution. New image attributes (strings, vectors, integers, etc.) can be added to OpenEXR image headers without affecting backward compatibility with existing OpenEXR applications.
The OpenEXR Bitmap I/O software goes beyond the “standard” OpenEXR format, taking advantage of the flexibility of the format itself. It can write channels and attributes as well as general RGBA data in formats that many OpenEXR file importers cannot understand, due to implementation limits as well as limits to the current set of standards. The full-latitude 32-bit floating point RGBA files that the output function can write is one example. While the OpenEXR API itself fully supports this capability, and these files are written using the standard set of OpenEXR libraries, most software only reads the 16-bit “half” floating point RGBA files that are considered standard EXR files.
Most bitmap I/O plug-ins, including those integrated into Autodesk VIZ, store their configuration information in a binary CFG file that cannot be edited. To allow external scripting support as well as ordinary preferences, the OpenEXR software uses a standard INI file format to store its configuration data. The file is named openexr.ini and is found in the plugcfg folder in the program directory. The file is generated automatically the first time you edit the OpenEXR configuration settings, and is updated each time you modify an EXR loader. It is a standard text file and can be modified with any text editor.
When the INI file is written, it automatically generates a companion “help” text file named openexr_ini_help.txt. This file contains the valid ranges for various INI settings, as well as the various text strings used to specify compression type and bit depth. This file is just a guide; editing it has no effect, and it is overwritten whenever the INI file is updated.
To restore the default settings after editing the INI file, simply delete the openexr.ini file and a new one with the original defaults will be generated the next time you edit the configuration settings.