HDR display test
This page draws real Rec.2100 PQ patches in your browser and tells you whether your screen can show them. Nothing is uploaded and there is nothing to install.
Make your own logo glow Free to test. Superwhite exports start at €3 one time for unlimited 400px logos.Checking your display
Running the test.
The live test
The card below is pure white, #ffffff, on purpose. The patches sitting on it are encoded as Rec.2100 PQ at real absolute luminance. On a display with headroom the brighter patches visibly out-shine the white card around them. On an ordinary display they all look like the same flat grey.
Each patch is generated in your browser as a PNG carrying a cICP chunk (9 16 0 1), which is how a still image declares itself as Rec.2100 PQ without an ICC profile. 203 nits is the reference white level, so that patch should look the same as the card. Anything above it is asking your display for extra light.
What your browser reports
These are CSS media queries the browser answers itself. The first one, dynamic-range: high, is the one that matters for still images: it is the browser telling you there is luminance available above the interface white level. Note that a browser can report headroom and still tone-map the result differently from another browser on the same panel, which is why no tool can promise a fixed brightness.
Why the patches might not glow
- Ordinary SDR monitor. Most desktop monitors have no headroom at all. Nothing to show.
- Windows with HDR off. The panel may be capable, but HDR has to be enabled in Display settings before the browser sees any headroom.
- Low power mode. On iPhone and some Macs, battery saver clamps peak brightness and the effect disappears until you turn it off.
- A screenshot. Screenshots are captured as SDR, which discards the luminance. This is why the effect cannot be demonstrated in a screenshot and has to be seen on a real file.
- DisplayHDR 400 class panels. Technically HDR, but only about one stop above reference white, so the effect is real yet subtle.
Where the glow shows up well
- Recent iPhone and iPad Pro. Peak around 1,200 to 2,000 nits on small highlights. The strongest case.
- MacBook Pro with Liquid Retina XDR. Up to 1,600 nits sustained on HDR content.
- Modern Android OLED. Strong, and also the platform where gain map images work.
- OLED TVs and monitors. Excellent, though rarely how anyone reads LinkedIn.
- Windows laptops with a real HDR panel. Good, conditional on HDR being switched on in the OS.
A note on formats, since this page uses one of them
The patches here are PNGs with a cICP chunk. That works because this page is served directly to your browser and nothing re-encodes the file on the way. Upload the same PNG to LinkedIn and the glow dies, because LinkedIn re-encodes uploads to JPEG and the chunk does not survive. The route that does survive is a JPEG carrying a Rec.2100 PQ ICC profile, which is what Superwhite exports. The full survival matrix is in LinkedIn HDR glow.
Frequently asked questions
How do I know if my screen supports HDR?
Look at the patches above. On a display with luminance headroom the 1,600 and 4,000 nit patches read clearly brighter than the pure white card behind them. If every patch looks like the same flat grey, your screen is showing SDR. The table also reports what your browser itself claims via the CSS dynamic-range media query.
Why does the 203 nit patch look the same as the white card?
Because it is meant to. ITU-R BT.2408 sets diffuse white at 203 nits, which is roughly the level your operating system paints ordinary interface white. That patch is the control: it shows the test is calibrated rather than just brightening everything.
My browser says HDR is supported but nothing looks brighter. Why?
Most often low power mode on a phone or laptop, which clamps peak brightness. On Windows it can also mean HDR is enabled but the browser is tone-mapping conservatively. A DisplayHDR 400 class monitor will also report support while only offering about one stop of headroom, which is real but subtle.
Does this test upload anything?
No. The patches are generated in your browser with JavaScript and never leave your device. There is no account and nothing is stored.
Will an HDR logo glow for everyone who sees my LinkedIn post?
No. Roughly half of a typical feed audience is on an HDR-capable screen with headroom available. Everyone else sees a completely normal image, which is why the design should still work without the glow.
Why does the test use a PNG when Superwhite exports JPEG?
Different jobs. A PNG with a cICP chunk is the cleanest way to signal HDR for a page you serve yourself, like this one. It does not survive a platform re-encode. For LinkedIn the file has to be a JPEG carrying a Rec.2100 PQ ICC profile, because that is the only HDR signalling LinkedIn preserves.