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Ghosting and persistence
Another bone of contention in the FreeSync-versus-G-Sync wars is the question of ghosting, those display after-images that you can sometimes see on LCDs. Turns out that the BenQ XL2730Z in particular has a ghosting issue in a very prominent scenario: AMD's own "Windmill" FreeSync demo. Below is a side-by-side slow-motion video that shows the Asus PG278Q versus the BenQ.

Watch the trailing edge of the windmill when the arm is moving the fastest—in the same direction as the base of the windmill—in order to see the ghost image. The problem is readily apparent on the BenQ display, but not on the Asus G-Sync monitor. For those who can't be bothered to watch the video, here's a single frame that tells the story.


The ROG Swift PG278Q (left) vs. the BenQ XL2730Z (right)

This isn't exactly the worst problem in the world, but some ghosting is apparent on the XL2730Z. That's true of the video, and if anything, the after-image is even easier to see in person. My first look at FreeSync in action was this demo, so seeing ghosting right away was a bit disappointing.

Here's the thing to realize: AMD's demo team has managed to concoct one heck of a scenario to bring out ghosting. The scene is high contrast, the blades sweep across the screen quickly, and the ghosts come out to play. I've spent some time with the XL2730Z, playing games and running the UFO tests and such, and this sort of ghosting isn't nearly as apparent on the XL2730Z in other cases.

There's a bit of after-image visible in the UFO ghosting test, but it's pretty minimal and wouldn't raise any red flags during our usual display testing routine.

Ghosting is almost entirely impossible to detect with the naked eye in this relatively high-contrast scene from Borderlands: The Pre-Sequel. I recorded this video at 240 FPS, and it plays back at half of game speed, so I was really sweeping the mouse around quickly. (60 FPS playback is available via YouTube.) Some small amount of ghosting is visible in this slow-mo video, but even at half speed, you have to watch carefully to see it.

The XP2730Z does have some ghosting issues that are perceptible in certain cases, but they are not especially common or distracting overall, in my view. I've seen much worse from cheaper monitors in the past. The ghosting issue has become a bit of a hot topic in part because, again, Nvidia has hinted that ghosting may be worse with FreeSync displays than with G-Sync displays.

I asked Nvidia's Tom Petersen about this issue, and he explained that maintaining the correct overdrive voltage needed to reduce ghosting on an LCD with variable refresh rates is a tricky challenge, one that Nvidia worked to overcome in the development of its G-Sync module. I think that's a credible claim.

When I asked AMD's Robert Hallock for his take, he responded with: "In our view, ghosting is one part firmware, one part panel, and zero parts FreeSync." I think that also is a credible statement.

The difference here is that with AMD's collaborative approach, the burden for ensuring the correct overdrive voltage falls to the makers of the monitor and the display logic chip. Since Nvidia has built its own display logic chip, the responsibility for tuning the panel voltage on G-Sync monitors falls mostly on Nvidia's shoulders.

The fact that we've seen some ghosting on BenQ's XL2730Z doesn't necessarily indicate there will be a general issue with ghosting on FreeSync displays. We'll have to wait and watch to see how other FreeSync monitors perform before we can generalize. It's up to the makers of FreeSync monitors and logic chips to tackle this problem.

Speaking of which, BenQ has built a blur-reduction feature into the XL2730Z that can be enabled via the monitor's settings menu. Turn it on, and you get low-persistence display mode that strobes the backlight very much like the ULMB mode built into the ROG Swift PG278Q. This feature does reduce ghosting and increase the clarity of objects in motion, but it also quite visibly lowers the screen brightness. Cranking up the brightness can offset that effect, to some extent. As with the ULMB mode on G-Sync displays, BenQ's blur-reduction mode is not compatible with variable refresh rates, so it's probably more of a curiosity than anything.