The X25 supports HDR10 signals by switching automatically when one is detected. Picture modes and color temp presets are still available, but you can’t change brightness or contrast values. Dynamic contrast is also employed through the Variable Backlight feature.
HDR Brightness and Contrast
The X25 meets its DisplayHDR 400 certification with a score over 444 nits. All the monitors are close in this test, with little visual difference in peak brightness (we omitted the BenQ monitor for this test because it doesn’t support HDR10. The black level test shows which screens use dynamic contrast. The X25 uses it to win this test by a nose. It also takes the HDR contrast crown with an excellent 8,292.8:1 ratio. That puts it ahead of many VA screens that do not use dynamic contrast. Acer’s Variable Backlight feature is very effective at adding pop without crushing highlight or shadow detail.
Grayscale, EOTF and Color
Though you can calibrate grayscale in HDR mode, the X25 uses the same RGB settings for both SDR and HDR. Rather than tweaking further, we stuck with our values from the SDR calibration. There were slight blue errors in the 55-65% brightness steps, near the transition to tone-mapping. This is a minor issue that was difficult to see in practice. The luminance curve, meanwhile, tracks very well. It’s slightly dark from 10-30% brightness, then a bit bright from 50-60%. The transition point is a little rounded off too. Again, we’re nitpicking.
HDR color suffers from a lack of saturation, but the targets track linearly until the X25 runs out of juice. At that point, the X25 varies hue to add a little extra punch. In practice, HDR and SDR color look about the same, but HDR’s greater contrast adds the effect of more color saturation.