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HDR Performance

Our HDR benchmarking uses Portrait Displays’ Calman software. To learn about our HDR testing, see our breakdown of how we test PC monitors.

Mini LED displays like the U27G4XM are great for HDR content thanks to their bright backlights and full array zone dimming (FALD). This monitor is rated for VESA DisplayHDR 1000, which is something rarely seen in the OLED category. The signal switch is automatic, and you get four additional picture modes.

HDR Brightness and Contrast

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AOC U27G4XM — (Image credit: Tom's Hardware)

It’s easy to identify which screens are Mini LED in the first chart above. The U27G4XM exceeds its HDR1000 rating, reaching a peak of 1,107 nits. I measured that from a 25% window pattern, and it is extremely bright. Only the TCL is brighter. Local dimming can be used to make the contrast ratio unmeasurable at its highest setting. On medium, the ratio is 13,061.4:1, which is excellent for an IPS panel. I noted that different local dimming settings did not change the peak value, only the black level.

Grayscale, EOTF and Color

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In the HDR grayscale test, the U27G4XM is slightly warm in tone from 70% brightness and higher. The error is hard to spot in content, but it would be nice to have RGB sliders available. Of the four HDR modes, Display HDR delivers the best EOTF with values a little below the reference until 60%, where it goes a bit light. These are small variations that will not negatively impact the image. The tone map transition is at 75%, which is correct for the measured white and black levels.

In the color test, the U27G4XM’s large gamut is used to full effect with general oversaturation in all colors. This gives HDR content some extra punch that isn’t strictly accurate, but it is pleasing. The BT.2020 test shows the same response with color running out at 90% red, 80% green and 95% blue. In both charts, hue targets are on point for all six colors.

Test Takeaway: The U27G4XM is a superb HDR display with bright highlights and deep shadows. The Mini LED backlight effectively increases contrast to over 13,000:1 with no penalty. Color is pleasingly oversaturated with vivid hues that deliver great impact to game and video content.

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Christian Eberle is a Contributing Editor for Tom's Hardware US. He's a veteran reviewer of A/V equipment, specializing in monitors. Christian began his obsession with tech when he built his first PC in 1991, a 286 running DOS 3.0 at a blazing 12MHz. In 2006, he undertook training from the Imaging Science Foundation in video calibration and testing and thus started a passion for precise imaging that persists to this day. He is also a professional musician with a degree from the New England Conservatory as a classical bassoonist which he used to good effect as a performer with the West Point Army Band from 1987 to 2013. He enjoys watching movies and listening to high-end audio in his custom-built home theater and can be seen riding trails near his home on a race-ready ICE VTX recumbent trike. Christian enjoys the endless summer in Florida where he lives with his wife and Chihuahua and plays with orchestras around the state.