EDR and brightness headroom

Extended dynamic range (EDR) is Apple's rendering model for displaying values above ordinary standard dynamic range (SDR) white. Brightness headroom describes how much brighter those values can be than SDR white; it is a ratio rather than a brightness measurement in nits.

For example, headroom of 2 allows a peak twice as bright as the current SDR white. Available headroom can change with display brightness and system conditions. A display's potential maximum and its currently available headroom are different.

BetterDisplay uses available HDR/XDR headroom for software brightness upscaling. This can brighten SDR desktop content, but does not turn it into material mastered in HDR. See HDR, Brightness and Apple's EDR explanation.