16-bit image format with unlimited layers and lossless compression — stores alpha, Z-depth, and multi-pass renders. Industry standard for VFX compositing and final DCP.
When working with VFX on set or in post-production, you can't avoid this format. OpenEXR stores image data with 16-bit color depth per channel — this means over 65,000 gradations per color value instead of the usual 256 in 8-bit formats like ProRes or H.264. This immense headroom isn't academic: in color grading, compositing, and complex effect layers, the difference is immediately apparent in the graduation resolution and in the ability to hold extreme light values without posterization.
The core feature that has made OpenEXR the standard is its support for unlimited layers and custom data channels — in addition to RGB and Alpha, you can store Z-Depth, object mattes, normals, velocity, emissive channels, and any number of other passes. A single EXR frame can thus hold the complete render data set of a 3D engine: beauty pass, shadow pass, AO pass, diffuse, specular — all in one file, losslessly, without you having to manage thousands of individual TIFFs or PNGs. In editing and compositing (Nuke, After Effects, Fusion), you load the EXR once and unpack the passes as needed.
Practically, this means a VFX supervisor can structure a complex composition much more intelligently. Instead of separate layer files for each pass, you work with an intelligent container — this saves storage space and massively reduces file handling errors. The compression is lossless (ZIP, PIZ, or uncompressed) and remains realistic in file size. For DCP mastering and archiving, OpenEXR has become the de facto industry standard because the bit depth and layering structure secure the entire grading and distribution pipeline.
A caveat: OpenEXR is not intended for fast proxies, nor for real-time playback — it is the format when quality and flexibility count, not speed. Those working with linear gamma (and every VFX compositor should), benefit additionally from OpenEXR's precise color space handling. Hardware requirements for reading large multi-layer EXRs can be significant, but that is the price for this control.