OpenEXR Files

3ds Max 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.

OpenEXR files have a filename extension of .exr or .fxr.

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.

“OpenEXR's features include:

• “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, and so on) 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.

For example, you can output full-latitude 32-bit floating-point RGBA files. While the OpenEXR API itself fully supports this capability, and these files are written using the standard set of OpenEXR libraries, most applications read only the 16-bit “half” floating-point RGBA files: These are considered “standard” EXR files.

Tip: To take best advantage of the OpenEXR format’s 32-bit support, use the mental ray renderer with the Frame Buffer Type set to Floating-Point (32 bits per channel).

Note: When you render with floating-point, 32-bit output, bright areas such as self-illumination or reflections of light sources might appear to be jagged. See Frame Buffer Type for more information.

Configuration File

The OpenEXR plug-in stores configuration information in a binary CFG file named fopenexr.cfg. The file is generated automatically the first time you edit the OpenEXR configuration settings, and is updated each time you modify settings when you load or save an EXR file.