EXR file format (.exr)

What is an EXR file?

In short: An EXR file (.exr) is an image file in the EXR format. OpenEXR stores brightness as floating point numbers rather than a fixed 0 to 255 range, so a single image can hold both the detail in a shadow and the intensity of the sun without either being clipped. It can be converted to JPG, PNG or WEBP for free in a web browser with iHateFiles, without uploading it.

Created by Industrial Light & Magic and released as open source in 2003, after being used on their films.

OpenEXR stores brightness as floating point numbers rather than a fixed 0 to 255 range, so a single image can hold both the detail in a shadow and the intensity of the sun without either being clipped. It also holds arbitrary extra channels, such as depth or motion vectors, alongside the picture.

What EXR is good at

• High dynamic range with no clipping at either end
• Arbitrary named channels for compositing work
• Several lossless compressions to choose from

Where EXR falls short

• Large files
• Needs tone mapping before it looks right on a normal screen
• Not viewable in a browser

When to use EXR

Use EXR for visual effects, 3D rendering and compositing, where the extra range is the reason the format exists.

How to open a EXR file

Compositing and 3D software: Nuke, Blender, After Effects and their peers.

The thing that usually goes wrong

Converting an EXR to a normal format has to compress that huge range into 256 levels, so the result often looks flat or blown out. Tone map it deliberately rather than letting a converter guess.

Inside a EXR file

OpenEXR was developed at Industrial Light & Magic and released as open source in 2003, and it solved a specific problem: ordinary image formats cannot store a value brighter than white. An 8-bit PNG has 256 steps ending at pure white, so the sun and a sheet of paper are the same pixel. EXR stores floating point, so a highlight can be a hundred times brighter than white and stay recoverable.

That is what makes it the working format of visual effects. You can grade, relight and composite an EXR without the highlights clipping, because the information above white was never thrown away. It also carries arbitrary named channels, so a single file can hold colour alongside depth, motion vectors, object IDs and per-object mattes.

Nothing consumer-facing opens it. Windows Photos and macOS Preview both refuse, which is the usual reason people go looking for a converter — and converting to PNG or JPG necessarily discards the dynamic range that was the point of the file.