Full Screen Anti-Aliasing (FSAA)

Most people today know what a pixel is, an abbreviation for "picture element," the small square dots that monitors use to display images (IBM once persisted in having its employees call them "pels" though the term never caught on). Because monitors use combinations of these small squares in image display, there are circumstances in which the pixels of the image are as or even more noticeable than the image itself. As people's standards for computer imagery have increased over they years, people have likewise become more aware of imperfections in computer display technologies. While "pixilated" has become a catchall term for this in the vernacular, "pixilation" actually refers to a variety of phenomena.

For example, one kind of "pixilation" (as it is commonly used) refers to imperfections in JPG pictures on the internet, which appear due to how they are compressed to make for shorter download times. These are known technically as "compression artifacts" and are actually often far larger than individual pixels in size, yet they are still described as pixilation by millions of users.

Another type is less well known. Aliasing, a term originally borrowed from sound and oscilloscope technology, occurs when high frequency data is sampled too slowly. There is one example of this which you see all the time: often on television when someone wears a shirt or tie with very thin stripes on it, a strange shimmer representing the full spectrum of colors will appear. This is called the moiré effect. It comes from the lines on your television being too thick to accurately display the thin detail of the tie--yet that detail must be displayed.

Likewise, pixels are often too large to accurately display many details in computer games--that is what happens when you try to represent curves, waves, diagonal lines, and all sorts of shapes using nothing but small squares (as pixels get smaller at high resolutions, this problem is diminished as well). These are referred to as "jaggies" or aliasing, but are often lumped under pixilation as well.

Jaggies most often occur when two distinct objects with different coloring intersect; for if their textures are similar, their boundaries will be camouflaged by it. That is why jaggies are especially noticeable in older games with often limited textures than in newer games with high definition textures, and in games with lighter color palates than those with dark.

But there is a way of getting around the limitations of square pixels. You might not be able to color only half a pixel, but you can simulate the same thing by giving a pixel half of the desired color. By using varied amounts of color (provided there is enough colors to pick from, in the days of 256 color displays, this was much harder to accomplish), nearly any fraction of a pixel can be represented. This is called anti-aliasing.

While at first glance, it might appear that anti-aliasing is simply blurring the line. It is not. Blurring would imply a lessening of detail, on the other hand, this is an increase in detail in that the line (if not magnified several times for clarity) would appear much more defined than it would otherwise.

There are two ways in which anti-aliasing is currently accomplished, depending on your video-card's manufacturer and settings.

Super-sampling anti-aliases by creating an image at a higher resolution than that which your game is set for, and then "samples" the image down to the desired size, using the extra information (in the above example, twice the resolution means four times as many pixels are rendered!) to eliminate the jaggies.

Multisampling, on the other hand, combines slightly different images that are rendered separately on the subpixel level, each adding more information to further anti-alias the image. Any number of samples can be used, though most video cards only support 2x or 4x multisampling, while some, such as nVidia cards, offer more complex forms of multisampling which purport to give added visual quality with less of a cost in speed.

Speed is the largest reason to not use anti-aliasing (though as it is a newer feature to video cards, typically only the fastest cards on the market have even supported it until very recently). As the video card is required to do more work--especially in super-sampling modes where it has to render four to eight times as many pixels--the FPS that it is capable of producing at a give resolution will be diminished proportionately.

However, newer cards are increasingly having anti-aliasing integrated as a key component rather than an afterthought, as well as using more innovative multisampling techniques, so the overhead for full screen anti-aliasing (FSAA) is diminishing.

Spidey with FSAA and without

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for FSAA Version

FSAA has a tendency to make everything look shiny and new--even older games that have been sitting on the shelf for a while. Not just in that they look better, still shots can be deceiving--the illusion of 3D is actually heightened by FSAA when you see it in motion, making a card capable of it a solid investment.