Aliasing and Antialiasing ------------------------- Tell me more about aliasing & antialiasing. Sure. Aliasing is the effect that you get when you try to make an image too quickly. Actually, to be more precise, it's what happens when you don't use enough information to decide the color for a given pixel in the image. To generate a completely correct image, you must calculate, for each pixel, exactly what portions of the model are visible in that pixel. You should then take an appropriate color average of all the visible portions of the model (weighted according to what percentage of each part is visible in that pixel) and assign that to the pixel. However, doing that correctly takes a lot of work. To be quick, most images are drawn by taking only a single sample for each pixel. That is, you shoot a conceptual ray through a point in the middle of the pixel, and consider only the surface that is hit by that ray. (You don't actually trace rays like that for real-time image generation, but the effect is the same.) Taking just a single sample like that results in lots of aliasing. The usual effect that you see is a stair-stepping along diagonal edges. (There are many other kinds of aliasing effects, but all result from the sample fundamental problem.) Antialiasing is a set of different procedures that you can do to help eliminate aliasing. If you draw your image one surface at a time in front-to-back or back-to-front order, you can do something called A-buffer antialiasing, and use alpha values (transparency or blending mechanism) to do the appropriate averaging/weighting for each pixel. Alternatively, you can simply use more than one sample for each pixel (this is called supersampling). The basic idea is that you render an image of higher resolution than you really want to end up with, and then average together pixels in the larger image to produce the smaller one. Of course, if you use 4x supersampling, then you have 4x the amount of pixel work to do, possibly resulting in 1/4 of the speed you'd get otherwise. By the way, the various "filtering" techniques mentioned in conjunction with texture mapping are also various forms of antialiasing. The idea is the same, except that you are dealing with the drawing of a texture image on pixels in your desired image. Edge-antialiasing is a term used to refer to antialiasing as it is applied to the edges of objects. This is what people commonly think of when the term "antialiasing" is used. ---------------------------------------------------------------------- (c) 1997 Carl Mueller