EXR (OpenEXR)

EXR is an image file format that stores the color and brightness information of each photo or frame in very fine detail, without rounding. If common photo formats save color as "roughly rounded numbers," EXR saves it as "numbers kept precise down to the decimal point." Because of this, even if you later push the brightness way up or heavily grade the color, the original information is still there, so you get less banding in the sky or crushed detail in dark areas.

Thanks to this trait, EXR is treated like the original camera footage in post-production work such as color grading and compositing for film and advertising. The final version shown to viewers is exported in a much lighter format, but during the intermediate stages of work, footage is kept in EXR so the image quality holds up through repeated editing. However, EXR is often handled not as a single video file but as a sequence — a stack of individual image files, one per frame.

In articles, you might see something like "Runway Ruby outputs 16-bit EXR image sequences or ProRes/HEVC files." What's easy to mix up here is that EXR isn't a single video but a sequence of per-frame image files, and it's not the final result viewers see directly, but an intermediate original meant for post-production work like color grading and compositing.