# Spectral EXR format¶

OpenEXR is a versatile high dynamic-range (HDR) image file format developed by Industrial Light & Magic for use in computer imaging applications, with an open-source library for reading and writing EXR files.

It allows storing not only RGB data, but an unlimited number of named channels. The channels may be encoded in various binary number formats such as 32-bit float for high dynamic range and precision. It also offers compression, and allows setting meta-data in attributes.

Ocean uses a new spectral imaging format based on OpenEXR :

• The images have an arbitrary number of channels, with any valid channel name. Ocean uses wl0, wl1, wl2 but this is not required
• For each channel, an attribute named as the channel with .wavelength appended is defined, and its value is a Float or Double giving the channel central wavelength in meters.