HDR Test
Check in seconds whether your screen is running in HDR. Then use real HDR test patterns to compare HDR and SDR white, find roughly how many nits your display reaches and see if it shows wide gamut colors.
Last updated:
How to use the HDR Test
- Turn on HDR in your system display settings (Windows: Settings, Display, Use HDR; Mac: displays switch automatically), then open this page.
- Read the HDR status card: it shows whether the browser currently sees an HDR screen and its color gamut.
- Open HDR vs SDR: on a working HDR setup the 1000 nit square is clearly brighter than SDR white.
- Open Peak brightness and click the last tile where you can still see the inner square to get a nits estimate.
- Check Color gamut and Gradient, use View full screen in a dark room, then Copy result.
How the HDR patterns are encoded
HDR10 video and HDR images use the PQ transfer function from SMPTE ST 2084, which maps a signal value between 0 and 1 to an absolute brightness between 0 and 10,000 nits (cd/m²). The patterns on this page use the exact formula:
E = ((c1 + c2 × Ym1) ÷ (1 + c3 × Ym1))m2, where Y = nits ÷ 10,000, m1 = 0.1593, m2 = 78.84, c1 = 0.8359, c2 = 18.85 and c3 = 18.69.
| Brightness | PQ signal | 10-bit code | What it represents |
|---|---|---|---|
| 100 nits | 0.508 | 520 | Classic SDR peak white in a dim room |
| 203 nits | 0.581 | 594 | HDR reference white for graphics and text (ITU-R BT.2408) |
| 400 nits | 0.653 | 668 | DisplayHDR 400 minimum peak |
| 600 nits | 0.696 | 712 | DisplayHDR 600 minimum peak |
| 1,000 nits | 0.752 | 769 | Common mastering peak for HDR10 films |
| 4,000 nits | 0.903 | 923 | Peak of some Dolby Vision mastering monitors |
| 10,000 nits | 1.000 | 1023 | Maximum the PQ curve can describe |
The 10-bit codes are full range (0 to 1023). Each pattern is generated as a 16-bit PNG with a cICP chunk (primaries 9 = BT.2020, transfer 16 = PQ, matrix 0 = RGB, full range), so no video or download is needed.
Reading the results
- HDR vs SDR shows no difference: HDR is off in the operating system, the browser does not support HDR images, or the screen is SDR. Chrome and Edge on Windows and macOS support HDR images; other browsers may show the patterns as gray.
- Brightness steps stop changing early: the screen has reached its peak. Small differences between 1,000 nits and above are normal even on bright screens.
- All clipping tiles show the square: the screen tone maps highlights instead of clipping, which is common on TVs and on monitors with dynamic tone mapping. Turn tone mapping off in the monitor menu for a cleaner reading.
- Gradient bands in both versions: the signal is 8-bit somewhere along the way. Check that the cable and port support 10-bit at your refresh rate, for example HDMI 2.1 or DisplayPort 1.4.
Tips for a fair HDR check
- Use a dark room and look at the patterns in full screen; room light makes bright steps hard to tell apart.
- Small bright areas can get brighter than full-screen white on OLED and local-dimming screens, which is why the patterns use small patches on black.
- Laptops often limit HDR brightness on battery; plug in before testing.
- After changing the HDR setting in your system, reload the page so the browser re-reads the display.
Frequently asked questions
How does this page know if my screen is HDR?
It uses the CSS media query (dynamic-range: high), which browsers set when the current screen is in HDR mode and the browser can show HDR content. It also reads (video-dynamic-range: high), the color-gamut query and screen.colorDepth. If HDR is switched off in your operating system, the browser reports a standard screen even if the monitor supports HDR.
How are the HDR test patterns made without an HDR video?
The page generates 16-bit PNG images in your browser and tags them with a cICP chunk that marks them as Rec. 2020 colors with the PQ (SMPTE ST 2084) transfer function, the same encoding HDR10 uses. Each patch value is calculated from the PQ formula for an exact brightness in nits. Browsers that support HDR images, such as Chrome and Edge, display them as HDR.
How accurate is the peak brightness estimate?
It is a visual estimate, not a measurement. It works on screens that clip highlights above their peak. Many TVs and monitors tone map instead, compressing bright values so the squares stay visible longer, and the operating system's HDR brightness settings also change the result. A colorimeter is needed for exact nits.
What is the difference between HDR400, HDR600 and HDR1000?
VESA DisplayHDR levels name the minimum peak brightness the screen must reach in certification tests: 400, 600 or 1000 nits, along with rules for black level, color gamut and bit depth. DisplayHDR 400 screens often lack local dimming, so their HDR looks only slightly different from SDR.
Why does HDR look washed out or dim on my PC?
In Windows HDR mode, SDR content is mapped into the HDR signal using the SDR content brightness slider, and a screen with low peak brightness or no local dimming can look flat. Run the Windows HDR Calibration app, set the SDR brightness slider, and make sure the monitor's own HDR mode and full RGB range are enabled.
What does the color gamut test show?
It draws the most saturated red, green and blue that sRGB, Display P3 and Rec. 2020 can describe, using CSS color() functions. On a wide gamut screen the P3 and Rec. 2020 swatches look more vivid and a circle appears inside the last column. Most HDR monitors cover most of P3 but only part of Rec. 2020.
Is anything uploaded or recorded?
No. All patterns are generated and shown locally in your browser, and the only thing saved is your last peak brightness choice in local storage.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.