Color Performance and Calibration
The ROG Swift PG258Q includes a 1920 x 1080 TN LCD panel, so some areas of color performance won't be as good as more popular VA or IPS displays. Viewing angles in particular are a weak spot for TN panels, and while they are respectable on the PG258Q, there is a noticeable luminance shift when viewing at off angles, especially in the vertical direction. This would be improved in an IPS panel, however you can only achieve 240 Hz on TN panels at this stage, so it's the best we can do.
Contrast is also limited on this display. Asus claims the PG258Q has a maximum contrast ratio of 1000:1, though I measured it to be around 850:1 by default, which is reasonably low for a modern display. Brightness, though, is impressive if you require a bright display, reaching around 460 nits at peak with default calibration. Through calibration it's easy to pull this back to around 200 nits, which is far more comfortable for typical indoor usage.
Leaving every setting at its default value, which I've listed in the table below, produces decent but not outstanding color performance. For most gamers and other people not interested in color accurate work, the performance in its default mode will be suitable, and in general the monitor looks good whether it's calibrated or not. Most of the limitations to the quality of this display are related to its TN panel, such as contrast, and can't be fixed through calibration. That said, you can achieve pretty accurate performance through OSD-level calibration, and even better performance with an external tool.
| Setting | Default Value | Calibrated Value |
| GameVisual Mode | Racing | Racing |
| Contrast | 50 | 50 |
| Brightness | 80 | 25 |
| Color Temp. | Normal | User: R=96, G=98, B=99 |
| Gamma | 2.2 | 2.2 |
| Blue Light Filter | Level 0 | Level 0 |
| Overdrive (OD) | Normal | Normal |
| Adaptive Contrast Control | Off | Off |
| Dark Boost | Off | Off |
Starting off with default performance, and the PG258Q produces decent grayscale performance, with a dE2000 value of 2.02 across CALMAN's grayscale sweeps, along with a temperature average of 6352. Gamma is disappointing, due to a dip at 90% white, resulting in a gamma reading of 2.09, less than the ideal 2.2. The monitor is slightly too warm by default, and reds are the dominant color.
Default Performance
Saturation performance is also decent thanks to an average dE2000 value of 2.13. Greens and blues are the worst performer here, but there weren't any significant outliers. This was also largely the case with our custom ColorChecker test, which is where the PG258Q reported an average dE2000 value of 2.287. 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.
I also took the time to measure screen uniformity, and the results were god, although the upper left corner is the weakest area of this display. The differences here are largely unnoticeable during regular use, and I didn't experience backlight bleed during dark scenes either, which was a positive.
OSD Calibrated Performance
Using the above calibrated settings, color performance improved noticeably without the need for an external calibration tool. Grayscale dE2000 reduced to under 1.0, which is an excellent result, while color balance improved. This lead to small improvements to saturation (dE2000 of 1.65) and general performance (dE2000 of 2.08). Gamma cannot be corrected without an external tool.
Fully Calibrated Performance
Using a basic X-Rite i1Display Pro and SpectraCal's CALMAN software, I was able to achieve great performance. A grayscale dE2000 value of 0.97 is still excellent, while color temperature and gamma are near accurate. Saturation performance improved to a dE2000 value of 1.03, and ColorChecker to 1.139. These aren't perfect results, but they're very solid for a gaming-oriented TN panel.