AA/AF/VSync: What do they mean?

ZeGermans takes a look at certain terms always thrown around to describe the "eye candy" of a game, and explains what they all mean.

It can be seen in every single video benchmark from any reputable site: 1600×1200 speed mode, 1600×1200/4x AA/8x AF, 1600×1200/8x AA/16x AF. All are benchmarks showing pure performance, and then showing different levels of anti-aliasing and anisotropic filtering. But what in the world do these incredibly hard to pronounce words mean?

The number 8 image without any antialiasing appli

This article will examine the technology and theory behind AA and AF, as well as vsync, explaining how they make your game look better, and why using them will mean taking a hit to your frames per second.

a technology that has been around ever since the days of the Voodoo graphics cards. Obviously, since then, the technology has been streamlined; however, the basic theory remains the same. The purpose of AA, to put it simply, is to smooth out lines displayed by your computer. You see, your monitor has a certain amount of pixels on it that are arranged in an ordered pattern, which means that every time your computer draws any kind of line that is not totally vertical or totally horizontal, the line will start on one row of pixels and then jump up to the next row, as seen in the image. Now, obviously with a high-resolution monitor, this skip is hardly the most noticeable thing in the world. Still, though you may not register it visually, you will notice it subconsciously, making the gaming experience less ‘real’. This is where AA comes into play.

The same image of 8, this time with 8x antialiasing applied

AA is basically a program in the video card’s drivers that makes these lines smoother. How is this accomplished? It is actually fairly simple sounding. First, the program identifies a line on the 3D image. Then, it gathers data on a sample size of pixels around that line. Finally, it ‘averages’ out the pixels, so that whenever a row is skipped, the first row slowly dissolves into the background while the next row slowly fades in. The numbers designated to the different rankings of AA (on ATi it is 2x, 4x, or 6x, and for nVidia, 2x, 4x, and 8x) are a general indicator of what quality of algorithm you’re using to smooth the lines. The general idea is that the numbers indicate the kind of pixel sample size that the program takes around the line before smoothing it out. The reason there are so many options is to offer performance customizability, since the more complicated AA programs give you a bigger hit in performance. Generally, the performance hit between speed mode and max AA is about 10-15% of your FPS, so if you are an FPS junky, AA isn’t for you. However, if you are an image quality fan, it is a must-have.
{mospagebreak heading=Anti-Aliasing&title=Anisotropic Filtering, V-Sync}
Anisotropic filtering is a bit more complicated than AA. It deals with one of the most glaring and inherent flaws of 3D gaming: Painting a 3D image onto your 2D monitor screen. A little bit of background information here is needed. Every pixel on your computer screen has several X and Y texture elements, or ‘texels’, associated with it. Until the invention of AF, these textures where computed using an isotropic, or cubic, method.

A shallow plane of characters showing the distortions of purely isotropic filtering

Now, this method works best where you are looking at an object directly perpendicularly, from above. In other words, it works best on a 2D setting. If you start to change your angle of viewing until it is around 30 to 20 degrees, the video card needs to use a non-cubic texture filter to maintain proper clarity, because it is going to be processing much less information on the X or Y axis. That is where AF comes in to play. To put it simply, it is a non-isotropic filtering technique, or, An-isotropic filtering. This uses several different geometric shapes, depending on the angle, on each pixel to determine the clearest representation of the images. In fact, ATi’s 16x AF program uses 128 shapes per pixel to produce clarity at a low-angle perspective. The result, seen in this image courtesy of ATi, is quite staggering. ATi AF flavors come in 2x, 4x, 8x, and 16x, while nVidia offers 1x, 2x, 4x, and 8x. The numbers indicate how many different shapes are used in order to determine the proper pixel texture. This process sucks up a decent amount of ram bandwidth, so obviously turning it on gives you a performance hit. Once again, those who crave FPS ought to avoid AF, but for people like me, AF is where it’s at. The performance hit you could expect with AF and AA both at full blast is a bout 20-25%, slightly less if you have an ATi X800-series card, which have specially designed AA and AF pathways.

The same plane, now with 16x anistropic filtering applied

Well, it’s about time to take a break from the confusing realm of AA and AF and explain the (relatively) simple concept of vertical sync. Every monitor has a refresh rate on it, which goes down as your crank up the resolution. The best monitors have a refresh rate of about 100Hz at 1280×1024 resolution. This means it paints a new image on the screen 100 times in one second. However, video cards can generally produce much more than just 100 frames per second. This generates a bit of a problem where the next image starts getting drawn on the monitor before the first image is finished. Assuming you had a killer system and where running quake 3 at 800×600, you’d probably be getting 500 FPS. This means that at any given time, there are five different images being painted on your monitor. What vsync does is it binds your FPS to your monitor’s refresh rate, so that the highest FPS you can possible achieve is equal to the refresh rate your monitor is currently set at. Hence, it syncs the graphics card image with the monitor image.

Though I could go on and on all day long about the different video card settings, these appear to be the most major, at least with respect to image quality. So the next time you play your favorite games, and FPS isn’t an issue, try out these neat little video card tricks and find out if you like what you see. Believe me, sometimes the difference is like night and day. So give it a shot; see what you think.

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