Grayscale, Gamma & Color
The Z38c takes a unique approach to picture modes. By default, it runs in sRGB, which has fixed gamma and grayscale. You can adjust brightness, but that’s all. The enclosed calibration data sheet references that mode. Also available is Rec.709, which simply changes gamma to 2.4, but delivers the same color and grayscale performance.
Our grayscale and gamma tests are described in detail here.
The first two charts above are nearly identical. The slight blue tint we measured matches the data sheet included with our sample. The tint is barely visible from around 50% brightness and greater. The Custom RGB mode offers some relief, even without calibration. If you don’t want to tweak, we recommend that mode for all applications. With a few clicks of the RGB sliders, the HP Z38c delivers reference-level grayscale tracking. You can see the slight clip of green at 100%. That error can be reduced to under 1dE, but then output maxes at around 175 nits. If you’re willing to let that top level go a little blue, leave contrast set to 80 and dynamic range will be about 900:1.
The Z38c’s 3.96dE average grayscale error is a little high when compared to other premium displays, but it does match the certified results on our sample’s data sheet. And once calibration is complete, the numbers approach reference-level. This is what we expect from any professional or premium screen, and HP delivers excellent performance.
There is nothing to complain about regarding the HP Z38c’s gamma tracking. sRGB offers some of the best accuracy we’ve ever seen. You have to look closely to even see the white line in the first chart. That’s about as close to perfect as a monitor can get. Rec.709 tracks 2.4 well, and that darker presentation is suitable for video editing and movie-watching. In the Custom RGB mode, the contrast control affects the 90% level slightly. Without adjustment, it’s a little too dark, though you'll be hard-pressed to see that in actual content. After reducing the contrast control, the hump becomes a small dip, which is even harder to spot--impossible we’d say. This is excellent performance, and it’s the main reason behind the Z38c’s superb color tracking.
Without the dip at 90% brightness, the Z38c would easily win the gamma value range test. A .19 score is still higher than many monitors we’ve reviewed. It’s only in fifth place because this group is quite solid overall. With a small .9% deviation from 2.2, we’d rank this monitor in the top one percent in gamma tracking. That really helps make up for the display’s relatively low contrast.
Color Gamut & Luminance
For details on our color gamut testing and volume calculations, please click here.
There are no real faults to speak of in any of the color gamut or luminance tests. The Z38c delivers an on-target sRGB result, regardless of mode. sRGB and Rec.709 share the same primary and secondary coordinates. They differ only in gamma, which is reflected in our charts. Measurements that are not in the box are that way thanks to the slightly-blue grayscale tracking. That off-target white point pulls the entire gamut along with it. In all cases, luminance levels are perfectly neutral except for blue, which is pumped up to compensate for a slightly under-saturated primary. It’s a nit-picker’s detail for sure. Calibration pulls every measurement inside the box and every error under 3dE, the level at which you could see an issue. It doesn’t get much better than this.
Only a handful of monitors can achieve less than 1dE average color error. We’re glad to see three of them here, since all these screens sell for premium prices. Remember that this is an average of 30 measurements, not just the 100% saturation points. This is one of the hardest color tests we know of, and the HP Z38c aces it. In the gamut volume test, we observed a bit of extra red, which results in just over 103% sRGB coverage. We recommend a color profile for any critical work, and since there’s extra red, it’s a simple matter for software to compensate.
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