Floating-point and arbitrary channels
EXR stores pixels as floating-point numbers — typically 16-bit “half” floats, with 32-bit and integer options available — which lets it represent both the faint detail in shadows and the intensity of bright highlights without clipping. Crucially, an EXR is not limited to red, green, blue and alpha: it can hold an arbitrary set of named channels in the same file. Renderers exploit this to pack depth, motion vectors, surface normals, object IDs and dozens of other arbitrary output passes into one image, which compositors then recombine. This multi-channel design is what makes EXR central to a VFX pipeline rather than a mere picture container.
The format supports several compression schemes, both lossless options like PIZ and ZIP and lossy ones, so studios can balance fidelity against the very large file sizes that float imagery implies. It also supports tiling and multiple resolution levels for efficient access to huge renders.
Why VFX adopted it
Film compositing needs headroom: exposure, colour grading and relighting all push pixel values around aggressively, and an eight-bit image falls apart under that treatment. EXR’s float precision means a highlight that looks blown out can be pulled back, and a dark plate can be lifted, without banding. Combined with alpha and deep multi-channel data, it gives artists a single, lossless-capable working format from render through to final composite.
Strengths
- Floating-point precision preserves shadow and highlight detail.
- Holds many arbitrary named channels — depth, normals, IDs and more.
- Offers both lossless and lossy compression, plus tiling and mip levels.
Limitations
- Files are large, reflecting the float data they store.
- Overkill and unsupported for everyday photos and web use.
- Must be tonemapped to eight bits for display on ordinary screens.
When to use OpenEXR
Use OpenEXR throughout visual-effects and 3D rendering work, wherever you need float precision, alpha and multiple render passes carried losslessly in one file.
OpenEXR FAQ
- Why do VFX studios use EXR instead of TIFF or PNG?
- EXR stores floating-point values and many arbitrary channels, so highlights and shadows survive aggressive grading and a single file can carry depth, normals and other passes. TIFF and PNG are typically eight- or sixteen-bit integer and lack that headroom and channel flexibility.
- What does half-float mean in OpenEXR?
- Half-float is a 16-bit floating-point number that gives a wide dynamic range at half the storage of a 32-bit float. It is EXR’s usual default because it balances precision against file size well for imagery.
- Can I open an EXR without VFX software?
- Most everyday viewers cannot, since EXR is a specialist float format. Converting it to JPEG, PNG, WebP or TIFF — Morphr tonemaps the float data down to eight bits in the browser — gives you an image any program can open.