Apple is known to differentiate its technology with new names, but it often also ads a fresh perspective of its own. Apple calls its HDR technology EDR, primarily to differentiate from existing HDR standards like HDR10, HDR10+, HDR10+ Adaptive, HLG, Dolby Vision, and Dolby Vision IQ.
At WWDC 2021, Apple talked more about EDR and mentioned that this differentiation is important because HDR means different things to different people. It could refer to a display, HDR formats like Dolby Vision or HDR10, HDR transfer functions or HDR to SDR tone mapping. EDR, on the other hand, can be envisaged as a holistic approach that gives developers and content creators a clear-cut idea of how to achieve the best HDR results on Apple hardware, software and services.
To know EDR and Apple’s EDR implementation will help you make the most of high dynamic range content on Apple devices. So let’s get started.
To start with, EDR stands for Extended Dynamic Range and Apple uses the term in context with both HDR implementation and its HDR rendering technology.
HDR ecosystem is quite a mess without rigidly defined standards to uphold. As a result, HDR content, which is mastered for viewing in an almost dark environment, can look starkly different on two screens depending on their HDR rendering capabilities.
The end result also varies based on ambient conditions. For instance, the same display playing the same content might look vivid when viewed indoors and could be dull outdoors under natural sunlight. When in a dark room, your eyes adapt to the content being played and in a bright ambience, they adapt to the environment.
If you are watching SDR content on your TV in a dark room and someone turns on the light, all your TV needs to do is raise the display brightness to make the content suit your viewing environment. With HDR content, however, different elements within one scene are rendered at different brightness and simply bumping up the overall brightness would compromise shadow details.
With EDR, Apple tries to bring some order. EDR is adaptive technology and it’s about rendering HDR in a way best suited to a particular display and best suited to a particular viewing environment.
In fact, Apple also claims that EDR can bring ‘HDR response’ on conventional Standard Dynamic Range (SDR) displays - but only when displays are used in a dim environment with display brightness toggled towards the minimum (more on this later).
Of course, EDR is not the only adaptive HDR implementation. We have already heard of HDR10+ Adaptive and DolbyVision IQ that combine dynamic metadata with the inputs received from the light sensor to alter brightness while being as true to the creator intent as possible.
Since Apple makes its own HDR rendering displays, a properly defined EDR approach allows better consistency within its own ecosystem.
EDR does so by dynamically altering four parameters - White point, Black Point, Reference-white (as indicated by brightness slider) and EDR Headroom (dynamic range).
EDR headroom is how Apple quantifies the HDR capabilities of different displays. It represents how much bright a white pixel can be rendered as compared to the brightest SDR white. Note that the EDR headroom isn’t constant for a device and can vary based on whether you are sitting in a dark or bright room, what content you are watching, and what display you are watching it on.
To achieve the max dynamic range, your display brightness has to be toggled close to a minimum either automatically or manually.
EDR maps reference white of the content to the reference white in display and the reference white of the adapted vision (based on surrounding light). Apple says that EDR works similar to its colour management and a floating-point EDR value is assigned to every luminance value in the content to be rendered.
EDR 0.0 represents black, EDR 1.0 represents SDR white (100 nits). Values between EDR 0 and 1 represent the SDR range are never clipped. Values greater than 1 are bright and not all of these will be rendered.
To see the maximum dynamic range on your Apple devices, the brightness has to be set to a minimum (automatically or manually).
Yes, for instance, when the Pro Display XDR monitor is set to maximum 500Nits brightness. The display will map maximum SDR brightness EDR 1 to 500 Nits. The XDR Pro will render EDR values between 0.0 and 3.2. Values greater than EDR 3.2 will be clipped to 1600 Nits (the maximum brightness that Pro XDR can render).
When the Pro Display XDR is set to 4 Nits brightness, EDR values between 0 and 400 can be rendered. Elements with EDR greater than 400 will be clipped to 1600 Nits. So the brightest pixels that can be rendered are 400 times higher than SDR whites.
If you watch Dolby Vision, HLG or HDR10 content on Apple devices, the AVPlayer will automatically render it to EDR on all Apple devices (except those running WatchOS).
In conclusion, the idea is to take parameters like how bright or dark the room is, the content being watched, and display capabilities into consideration and enable only as much dynamic range as the user will be able to notice. Apple has designed EDR to be future proof (it can depict brightness levels that can be damaging to the human eye) and to seamlessly blend with SDR elements on all of its platforms. If you are a developer and want to check more on EDR best practices and how you can implement them in your App, go and check this detailed explainer from apple.