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AOC AG251FZ 240Hz FreeSync Monitor Review

Grayscale, Gamma & Color

The AG251FZ offers users a couple of viable options for image setup. In the Standard Eco mode, Game Mode off, and color temp set to Warm, you get decent performance that is not begging for a calibration. If you want that last 1%, select User and adjust the RGB sliders as we did. You’ll also need to make a gamma adjustment, which we’ll detail for you.

Grayscale Tracking

Our grayscale and gamma tests are described in detail here.

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If you compare the first and fourth charts, you’ll only see a tiny difference. Out of the box, the AG251FZ measures well but shows a slight purple tint at 100% brightness. That alone won’t take it off the “doesn’t need calibration” list. This display is a good performer. Selecting the sRGB color temp preset takes things to a warmer place with a reddish tint across the entire range. If you choose User, you’re committed to a calibration, because left unchanged, the picture becomes too blue. Grayscale isn’t an issue here, our main focus is on gamma, which we’ll talk about momentarily.


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Gaming monitors aren’t known for super accurate color, especially in an un-calibrated state. The AG251FZ manages to bypass that notion with an excellent 1.11dE default score. Our adjustments only yielded a tiny gain, so this display easily earns its way onto our “most accurate” list. We can think of a few professional screens that would benefit from this level of quality.

Gamma Response

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Gamma tracking is where the AG251FZ has a few issues. After measuring the many possible settings combinations, we concluded that there is no way to achieve ideal tracking at the 2.2 level. The first chart appears to show a need for reduction in the contrast slider. That served to tighten up the grayscale, but gamma was unaffected. Choosing the sRGB preset made most of the middle and brighter tones darker while increasing the darkest steps. The net effect was a reduction in perceived contrast.

In the User mode, our RGB changes had a positive impact when combined with the Gamma 2 preset. Shadow detail is still a little bright, but some gamers might consider that an asset. Most of the luminance values are close enough to the line to be considered visually correct. The last chart shows the Gamma 3 option. It’s clearly too dark, and in a monitor with 1000:1 contrast the image is murky and flat.


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The AG251FZ is last. Tracking is simply not as tight as the other screens. The difference is small but can be seen in a side-by-side comparison. The average value test has a better result as the AOC manages to keep its luminance values around the 2.2 mark.

Color Gamut & Luminance

For details on our color gamut testing and volume calculations, please click here.

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Luckily, our less-than-impressive gamma numbers do not impact gamut and luminance accuracy too much. The AG251FZ’s native color points match the sRGB spec very closely. In its default state, the average error is only 2.37dE, which puts it in very good company. The sRGB preset takes that error only a tad higher, to 2.75dE, so that result is a wash. In the User mode, we managed to reduce the number to 1.87dE. The only color that shows any issues is red, which has a few under-saturated targets. Our adjustments mainly served to bring luminance levels to a more neutral state. This makes a visual improvement in color quality.


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All the screens operate in a small window of good color accuracy. Only the Dell has any visible errors, and they will be hard to spot unless you’re looking for them. The AG251FZ takes a solid third place in the comparison. Had we left its settings at their defaults, the outcome would have been much the same. The gains are small, but when you pay good money for a display, you should wring every last drop of performance from it. Gamut volume exceeds 97% of the sRGB standard, which is about average for the category. The missing 3% is due to a tiny deficiency in green, which removes a sliver from the left side of the gamut triangle. It won’t affect gameplay in the slightest.

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Christian Eberle
Christian Eberle is a Contributing Editor for Tom's Hardware US. He's a veteran reviewer of A/V equipment, specializing in monitors.