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Let’s start with AA (antialiasing). The name is sort of self-explanatory, as long as you know what aliasing is. Dictionary.com defines aliasing as a “jagged, stairstep effect on curved or diagonal lines that are reproduced in low resolution, as on a computer printout or display.” In truth, “aliasing” as a general term can often be applied to all sorts of sample-based situations, like digital audio. For graphics, the dictionary.com definition suits us just fine.
It’s an effect best explained in pictures. Ideally, any line on your computer monitor would have a perfectly smooth edge to it. In reality, the image is made up of a fixed number of pixels (usually square) that are of a certain size. So if you’re trying to reproduce a diagonal line like this:
The squares represent the pixels of your monitor, and we can see the diagonal line slices them in half (naturally). In fact, any line that isn’t perfectly horizontal or vertical will do this. Well, each pixel on your monitor can only display a single color at a time, so you get an “aliased” image that looks like this:
If our diagonal line covers 50% or more of the pixel, it colors that entire pixel. If it’s less than 50%, it doesn’t. Of course, in our example picture the pixels are huge, so it looks terrible. On your computer monitor, it’s not quite as bad. The higher the resolution, the better it looks. That’s a block of 8 pixels by 6 pixels above. If it were more like 80 by 60, it would look like this:
What you really want is a way to take all those pixels from the first image that are only partially filled by our black edge and partially color them. So if the pixel is 25% filled by the black edge, you make that pixel only 25% black—a light gray color. If it’s 80% covered by the black line, you make that pixel 80% black—dark grey. The result is an antialiased edge.
Let’s look at what that does when we’re not quite so up-close with giant pixels. On our higher-resolution 80×60 edge, it makes for a pretty smooth edge.
You can see how that’s a big improvement over the aliased image. Our example photo here is actually blown up quite large, with pixels the size of an old Atari 2600 game from the 1980s. At higher resolutions, those intermediate colors really trick your eye into seeing a perfectly smooth edge.
And that, in a nutshell, is antialiasing. It’s useful on literally every diagonal and curve of on your screen. In the world of 3D graphics, it gets quite complicated. We won’t describe every method and mode of antialiasing under the sun, but let’s discuss the most common AA methods for 3D graphics cards. Continued…