Anti-aliasing isn't always there for us when we need it. Jaggies are the enemy, and PC gaming typically arms us with a few ways to beat them back, smoothing out those harsh lines and minimizing that unsightly simmer. But sometimes even minimal anti-aliasing hits performance hard. Sometimes AA options can cause graphical glitches; temporal anti-aliasing offers clean lines in exchange for unsightly ghosting. And, worst of all, some games don't offer anti-aliasing options at all. There are often ways to force anti-aliasing in games, but there's another solution: Downsampling.
It's a simple concept. Downsampling involves running a game at a custom resolution higher than the native output resolution of your monitor. For example, if your monitor outputs a 1920x1080 image, downsampling would require telling a game to run at, say, 2560x1440. That's a total increase of 1.6 million pixels! When that 2560x1440 image is rescaled, or downsampled, to 1080p, the extra pixels help smooth out those jagged edges and produces a sharper, cleaner picture.
Downsampling is performance intensive, of course. A guide on Guru 3D elaborates that "the performance impact will be proportional to the increase in resolution or total number of pixels; however, graphics card memory may also need to be considered." The upside, though, is that downsampling "should provide image quality comparable to full screen antialiasing but with far less compatibility issues and in many cases higher performance." And if your graphics card is especially powerful, you can combine anti-aliasing with downsampling for even better image quality.
Downsampling PC games starts with setting up a custom resolution through an Nvidia or AMD control panel. Finding the right resolution--high enough to improve image quality, but not too high for the GPU to handle--takes some tweaking. The type of monitor you have, the bandwidth of the cable used to connect to it (DVI, DisplayPort, etc.), and your graphics card drivers can all affect how well downsampling will work on your machine. That all sounds like bad news, but the good news is better: finding out if you can downsample will only take about 10 minutes, and the resulting custom resolution should work in just about any PC game you play.
We've worked up separate guides to downsampling for AMD and Nvidia graphics cards and thrown in some additional links to longer walkthroughs and more information on different types of anti-aliasing. If you're inspired by some of the amazing screenshots downsampling enables, give it a shot.