OpenEXR is a high dynamic range imaging image file format, released as an open standard along with a set of software tools created by Industrial Light and Magic, released under a Free software license similar to the BSD license.
It is notable for supporting 16-bits-per-channel floating point values (half precision), with a sign bit, five bits of exponent, and a ten-bit mantissa. This allows a dynamic range of over thirty stops of exposure.
OpenEXR is directly supported by Artizen HDR, Combustion,Smoke 2008, Blender, CinePaint, Cinelerra, Houdini, Lightwave, modo, After Effects 7 Professional, Mental Ray, PRMan, Digital Fusion, Nuke, Toxik, Shake, Photoshop CS2, CINEMA 4D, Pixel Image Editor and Synfig. It is also supported by the Cg programming language and Mac OS X as of version 10.4.
Both lossless and lossy compression of high dynamic range data is also supported.
OpenEXR, or simply EXR for short, is a deep raster format developed by ILM and very broadly used in the CG industry, both visual effects and animation.
OpenEXR's multi-resolution and arbitrary channel format makes it appealing for compositing. OpenEXR alleviates several painful elements of the compositing process. Since it can store arbitrary channels, specular, diffuse, alpha, RGB, normals, and various other types of channels in one file, it takes away the need to store this information in separate files. The multi-channel concept also reduces the necessity to "bake" in the before mentioned data to the final image. If a compositer is not happy with the current level of specularity, he or she can adjust that specific channel.
OpenEXR's straightforward API also makes tools development a relative ease for developers. Since there are almost never two production pipelines that are the same, custom tools always need to be developed to address problems in the production process. Many times these tools are to address some type of image manipulation issue. OpenEXR's library reduces the pain of having to manage bulky header information and allows quick and easy access to the image's attributes such as tiles and channels.