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DSR image quality in action
You can't capture screenshots of DSR's output using traditional software tools. You'll just end up with a high-res screenshot, not the native-resolution downscaled result. In order to grab DSR images, I fired up my FCAT rig and captured five-second-long snippets of completely uncompressed 1920x1200 video to a quad-SSD RAID 0 array. I was then able to choose an appropriate screenshot from each video clip. That's what you're seeing below.

There are lots of screenshots in these comparisons. You can click the buttons beneath the images in order to switch from one shot to the next. We'll start with a simple example from Guild Wars 2 showing some high-contrast edges. We have examples below from the display's native 1920x1200 resolution and several DSR modes, up to "3840 DSR" or (rendered internally) 3840x2400. I've also added examples using GW2's built-in "supersampling" option, its built-in FXAA post-process antialiasing filter, and the combination of 2560x1440 DSR with FXAA.

Flip through the screenshots, and you'll see the obvious jaggies in the first image start to become smoother as the internal DSR resolution rises. The dark, near-horizontal edge across the bottom of the frame is a nice litmus test. The fine geometry of the vines hanging down on the left side of the shot is better resolved by the higher-res DSR modes, too. Also, the silhouettes of the leaves on the right of the image become smoother and more organic in the higher DSR resolutions.

Now I'll ruin it for you. Look at the vine that shoots diagonally across the bottom right corner of the screenshot. Now look at it in 3840 DSR mode. You'll notice that there's kind of a dark halo effect around the vine in DSR. It's worst in the 3840 mode since the sky texture happened to be brighter, resulting in higher contrast, as I pulled that screenshot. That's one downside of DSR's gaussian downscaling filter. I don't think it's the end of the world, but it's not ideal, either.

I'm not quite sure what GW2's built-in supersampling option is doing—perhaps it's 2X supersampling?—but it's not very effective at eliminating jaggies.

FXAA is a different case. Created by Timothy Lottes while he worked at Nvidia, fast approximate antialiasing examines the frame after it's been completely rendered, detects edges in the image, and smooths along them. FXAA is very fast—the performance overhead is almost negligible on a high-end GPU—and can be quite effective, but it doesn't know anything about the underlying geometry in a frame; it only knows about objects at the pixel level. As a result, FXAA can lead to subtly shifting silhouettes from one frame to the next. I've noticed this effect in shooters where there's a gun positioned in front of the camera. The weapon's outline can subtly morph as it bobs around. I'll show you another one of FXAA's weaknesses shortly. That said, FXAA is quite effective in the static shot above.

FXAA is even more effective when combined with DSR at 2560x1600. The dark, near-horizontal edge in that shot is almost ridiculously soft and smooth. There's nothing wrong with layering on multiple AA methods that work differently. Doing so can produce stunning results.

This next example shows us how well the different AA modes resolve fine geometry. Look especially at the ropes stretching between the tips of the windmill's blades as you cycle through the images. Also concentrate on the arrow-like tops of the masts supporting those blades.

The reality becomes immediately obvious: without AA, the ropes are a blotchy, partial mess. Adding FXAA to the mix—with its ignorance of the underlying geometry—does nothing to help the situation.

With more internal samples, DSR is another story entirely. The ropes look a little better at DSR 2560x1600, and at DSR 3840x2400, they're vastly improved. Although the difference is apparent in screenshots, it's even more dramatic in motion. Without DSR, the ropes seem to sparkle, and portions of them disappear and reappear as the mill rotates. At 3840 DSR, the ropes appear properly as solid, fine silhouettes moving through the sky.

I've gotta say, though, I went back and looked at this same scene on a true 4K monitor. Yeah, uh, that's even better, to put it gently.