General Tutorials-Anti aliasing

Anti-Aliasing

Before I explain what anti-aliasing is I'll cover aliasing. These two subjects are, of course, closely related. People almost never discuss aliasing, though. Before I discuss the two let me say that aliasing causes images to have a jagged staircase look to their edges while antialiasing smoothes out these jagged edges.

Aliasing

Aliasing is what happens when analog data is represented on a digital system. A curved line drawn on a grid, where the curved line represents the analog data and the grid represents the digital system, is a good example of analog data on a digital system.

When the analog data is converted to digital some problems arise. The digital system in this example is the grid. To convert the analog line to a digital line each point in the grid may either represent a point in the line, by being filled in, or represent an area where the line does not exist, by remaining white. There can't be a square that is only partly filled. Each square must be either filled in or not. In other words, to draw the line in digital format we need to completely fill in any square that a portion of the line passes through. That's all part

of it being digital.

Okay no problem, right? The line goes through the different squares so we'll fill in each square that the line goes through. Figure 2.2 shows what the line looks like when we do this. Not very smooth, is it? We no longer have curves; all we have is a choppy line made up of squares and rectangles.