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The CU34G3S supports HDR10 content with four HDR modes. The default is DisplayHDR, which follows the standard more closely than the others. The remaining ones are Movie, Game and Picture. However, they were a non-starter for me because they added edge enhancement. All this does is reduce resolution; it does not make the image sharper.
HDR Brightness and Contrast
The CU34G3S leaves some performance under the table in two areas. First, there is no more brightness available in HDR mode. It tops out at around the same 234-241 nits. Second, there is no dynamic dimming feature. SDR content gets a dynamic contrast option, but that setting is grayed out in HDR mode. Though the VA panel manages almost 3,400:1 contrast, it could be much better with a dimming option. Though I found that HDR content looked vivid and saturated, it didn’t look much different than SDR.
Grayscale, EOTF and Color
The CU34G3S retains its color accuracy in HDR mode. There are slight blue errors in the brighter steps, but these issues don’t impact actual content much at all. The EOTF curve shows a gradual transition to tone mapping, meaning some highlights will be a tad muted. Again, this is a minor error. The other HDR modes aren’t as precise with their luminance tracking which in practice, obscures some detail. DisplayHDR is the best choice.
HDR color tracking is quite good with just a slight under-saturation in red and magenta. The saturation points are arranged linearly so the picture is loaded with detail. For Rec.2020 mastered content, the CU34G3S tries to match the saturation points but comes up a bit short. This contributes to the observation that SDR and HDR look similar. There is some untapped potential here, but HDR performance is adequate.
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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.