Color Performance and Calibration
The AG251FZ uses a 24.5-inch TN LCD panel with a resolution of 1920 x 1080. It's most likely the exact same panel used in the Asus ROG PG258Q and other 240 Hz monitors of this type, considering this monitor features the exact same specifications as competing models on the market. In particular, the monitor is rated for 400 nits of brightness, a contrast ratio of 1000:1, 1ms response times, and 170/160-degree viewing angles.
As expected for a TN panel, the weak areas of this display are in viewing angles and contrast ratio. The AG251FZ is best viewed from directly in front; viewing from off angles results in luminance shifts, which are particularly noticeable in the vertical direction. Contrast ratio measured in at just 868:1 in its default mode, which is lower than AOC rates for this monitor, and lower than any IPS panel on the market.
I achieved 411 nits of peak brightness with the brightness level set to 100, although its default brightness level of 90 produces 336 nits of brightness. This is too bright for comfortable usage in most situations, and something we'll address later through calibration.
Here are the default settings and what we recommend for the best calibration:
| Setting | Default Value | Calibrated Value |
| Game Mode | Off | Off |
| Contrast | 50 | 45 |
| Brightness | 90 | 49 |
| Color Temp. | Warm | User: R=51, G=49, B=44 |
| Gamma | Gamma1 | Gamma1 |
| Shadow Control | 50 | 50 |
| Game Color | 10 | 10 |
| Low Blue Light | Off | Off |
| Overdrive | Off | Strong |
Default Performance
A default color temperature average of 6497K is decent, although the display is cooler at mid-gray levels, and warmer at pure white. This is reflected in a grayscale dE2000 average value of 2.39 and gamma of just 2.00, which is not as accurate as I'd like to see. As a note, a dE2000 value of under 1.0 is considered 'accurate', while a dE2000 value in the 2 to 3 range is considered good but not outstanding.
A saturation sweep average dE2000 value of 2.14 is again decent though not outstanding, with no noticeable outlier. In our custom ColorChecker test, the AG251FZ produced an average dE2000 value of 2.91. The AG251FZ is slightly less accurate than the PG258Q out of the box, but there's not much in it. This monitor is good for 97% sRGB gamut coverage.
Screen uniformity is similar to the PG258Q with no noticeable backlight bleed and only a small difference in brightness across the panel.
Performance After OSD Calibration
Adjusting the display using the above OSD values does improve the performance of this monitor, but not significantly. Grayscale dE2000 is improved to an average of 1.69, however gamma remains poor at around 2.0, and the CCT average of 6679K is decreased. Saturation and ColorChecker results are also improved, with average dE2000 values of 2.01 and 2.73.
Considering these results, you can't achieve a whole lot by simply messing around with the OSD settings, and this is partly due to a poor gamma value in all three of the display's gamma modes. In comparison, the PG258Q can be corrected to a greater degree using the OSD.
Fully-Calibrated Performance
The AG251Z can be calibrated to a decent extent. Using SpectraCAL's CALMAN 5 software, I was able to achieve a grayscale average dE2000 value of 0.75 and an average color temperature of 6506K, which are both extremely accurate. Unfortunately gamma couldn't be fully corrected and remains at 2.1, which is an improvement but isn't perfect.
Color accuracy has improved to an average dE2000 value of 1.53 in saturation sweeps and 1.87 in ColorChecker, both of which are good results. The monitor isn't as accurate as a professional IPS-level display, but it does a decent job for a TN gaming display.