Answer:
Monitor vignetting occurs due to the panel’s bad brightness uniformity, which makes the edges of the screen appear dimmer than the center.
Sadly, unless you have a professional-grade display with uniformity compensation technology, you won’t be able to fix it. You may be able to slightly reduce monitor vignetting by lowering the brightness setting.
Due to the complex process of constructing monitor panels, it’s impossible to create a display with perfect screen uniformity, which includes brightness, contrast and color uniformity.
Here’s an example of an image uniformity test performed with DisplayCAL from our KTC H24S17P review.
The picture above depicts brightness measured at 100%, 75%, 50%, and 25% white – 100% represents pure white, while 75%, 50%, and 25% are darker shades of gray.
The measurements from the other 24 zones are then compared to the center zone, which serves as the reference point, to show how much each area deviates from it.
As you can see, at 100% white, the monitor is darker around the edges of the screen (around 15% on average, and up to 25% in the upper-left corner). As a result, on a full-screen white background, you may notice a slight vignette effect.
DisplayCAL also calculates contrast deviation across the different zones, as well as color deviation expressed in Delta E (ΔE), which tells us whether there is any color tint, such as a region appearing slightly warmer, cooler, greener or more magenta than the rest.
A Delta E of 3 or below is generally considered good and is mostly unnoticeable to the human eye, while values above 3 start to become increasingly noticeable.
However, in our experience, even on this monitor with relatively poor uniformity results (a Delta E of up to 7 and brightness deviations of up to 25%), this wasn’t really noticeable in everyday use. It only becomes visible if you’re intentionally looking for it on solid-color backgrounds.
Of course, this would be an issue for professional color-critical work, where better uniformity is required.
That said, no display is perfect, but a good panel will keep these differences small enough that they are difficult to notice during normal use.
Different patterns are also possible. Sometimes only the top or bottom part of the screen may be darker than the rest, but a vignette pattern like this seems to be the most common.
Finally, brightness uniformity also varies between individual units. So, if your sample of a given monitor shows this kind of vignette effect, another unit of the same model may have better or worse uniformity.
How To Fix Screen Uniformity?
Unfortunately, on most monitors, you cannot fix brightness and color uniformity.
To somewhat reduce the effect, you can lower the brightness setting or use dark mode in your browser, which replaces bright backgrounds with darker ones and makes vignetting less noticeable.
Some professional displays offer features such as ‘brightness uniformity compensation’, but on entry-level models, it’s not very effective as it usually sacrifices too much contrast ratio.
For the best results, you’ll need a high-end professional display such as Eizo’s ColorEdge series with advanced digital uniformity equalizer (DUE) technology.
Luckily, in most cases, uniformity issues aren’t noticeable. Often, there would be only minor deviations visible, in which case the issue is tolerable, or even negligible. However, in extreme cases, you should RMA your monitor if you can.
Here’s an example from our BenQ EX321UX review – we tested brightness uniformity with BenQ’s Uniformity Technology disabled and enabled.
