Wednesday, February 10, 2021

“EDR” Brings HDR to Non-HDR Displays

Stu Maschwitz (via Hacker News):

When I watched the announcement of this display, I was curious how Apple would handle an HDR video monitor that was also tasked with the mundane duty of displaying your email and a web browser. Was Apple planning on rendering the 255-255-255 “white” of Google’s home page at one brightness level, and the HDR overbrights from a video clip at a much brighter level, right next to each other, on the same display? […] The answer is a resounding “yes,” and the effect is both impressive and a bit unnerving.


So Apple has a method of showing HDR and SDR content together on the same screen. It works on every display Apple bills as “HDR,” even though the phones are performing the stunt using a different underlying technology than the 32″ Mac display. The XDR uses “local dimming” to light up an array of LEDs brighter behind the HDR pixels, as needed. The OLED displays drive each pixel to the desired brightness individually.

Apple groups all this under one umbrella they call EDR, or Extended Dynamic Range. And even as they tout EDR as a selling point of their professional display and flagship iPhones, Apple has also quietly extended it to older Macs that were never advertised as being HDR-capable.

Michel Fortin:

My observations support that the display brightness and color mappings change dynamically when some HDR content appears on screen. Those are reverted back to normal once the HDR image disappears. So no compromise on battery life until you put HDR content on your screen: the display is only made brighter while HDR content is visible.


On macOS Big Sur, when in dark mode, I noticed some white text labels are sensitive to EDR. (This looks like a bug.) When the video becomes visible on screen and EDR activates, those white text labels will slowly brighten at the same time as the video. I’ve located two of those labels for now: Safari’s active tab text (while the window is frontmost), and Gamma Control’s text label below the tabs (when the palette is set to translucent dark appearance). There’s also the checkmark for checked items in menus that appears affected. […] Another Big Sur issue: running an app that tweaks the gamma curve can break this EDR system temporarily.


1 Comment RSS · Twitter

Of course, anyone who's been using Shady* has witnessed this as a potentiality, since with Shady the mouse cursor is not shaded, so ends up appearing whiter than white (very practical).

But with Shady, you're of course losing about one or two bits of color depths as a result (resulting in banding, etc.), so for basic fidelity this requires displays that suport more than 8 bits per channel; 10 ought to be enough, so that is probably the required criterion for the backport of this feature to e.g. P3 monitors. Enterprising third-party developers might have been able to pull off something of the sort themselves, though with Apple stepping in this is likely pointless now.

*site currently displays the nginx default page, so not linking to it

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