To better understand aliasing, shown above are two sample images. In Part A of the Figure 1,we see what would potentially be the edge of a rendered image, mountains if you will. Now we see that this surface is on a grid, with each section of the grid representing a pixel. Because we generally render on a per-polygon and per-pixel basis, we either color the pixel or we don 't. It becomes like binary, either 1 (on) or 0 (off). There can be no partially filled pixels. On or off is decided based on the sampling of the center of the pixel zone (represented by a small circle in the image). So looking to Part B we see the result, a group of pixels that try and represent the surface we wanted to render. Unfortunately, this can result in something of a mess. These staircase edges are often referred to as "jaggies ".

Another example of aliasing in computer graphics is polygon "popping "(also referred to as pixel popping). This problem presents itself when dealing with thin polygons less than a pixel wide or tall. Sometimes, a thin polygon can be positioned in a spot where it cannot be sampled at all. From there, either all or part of the polygon disappears. Figure 2 illustrates various polygon popping effects. On the left we see the desired result, and on the right the rendered and sampled result, the latter suffering from polygon popping artifacts. Notice, for example, the green bar in (a). This bar covers the pixel centers in (a)and is thus visible, but now imagine a downward animation where the green bar ends up in position (b). In position (b) no pixel centers are covered by the green bar so nothing actually is rendered. Notice how the green bar went from full visibility to being completely invisible, all because of slight downward animation. If the animation continued downward, the bar would again cover pixel centers and become fully visible. Thus, as the bar moves down, the rendering would "flash" off and on -this is a perfect example of polygon popping aliasing. Furthermore, notice how the yellow shapes change between frame (a) and (b) of the animation. The yellow shapes are rendered differently from (a) to (b) due to the lack of sufficient rendering samples. The red, elongated triangles are exactly the same size but transposed, yet in both frames (a) and (b) they are shown covering a different amount of pixels. The blue square in frame (a) illustrates how a single equal polygon can end up looking very different when rendered just by changing its position or orientation. [1] All of these artifacts, characterized by different rendering of the same object as a function of different location or orientation, are symptoms of polygon popping aliasing.

To reduce the artifacts associated with aliasing, both jagged triangle edges and polygon popping, we utilize anti-aliasing algorithms. Anti-aliasing is basically the process of removing the unwanted artifacts. The problem with anti-aliasing algorithms and techniques has long been the required high bandwidth and fill-rates. This has caused AA to long be stuck in the CAD and high-end computer imagery markets. However, consumer level products are now reaching a point where real-time anti-aliasing is possible. In the next section we'll describe the working of several anti-aliasing methods.