How does anti-aliasing work?

[meglamaniac]

I've wondered this for a while.
Anti-aliasing, not so much realtime on graphics cards (but it's getting there), but in 3D modelling programs and landscape generation programs can remove the dreaded "jaggies" pretty much 100%.
But what is it that it actually does?
I'm assuming it does some kind of avereraging of colours (ie. looking at a pixel and seeing what colour the ones surrounding it are) and then writes the result, but there must be more to it than that, as you can get different levels of it and things.
Does it use any kind of edge detection?

[Raging.Retard]

Originally posted by meglamaniac
Anti-aliasing, not so much realtime on graphics cards (but it's getting there)

AA is supported in real time by most 3d cards, however I suspect its not the same technique use by 'slow' renders as you find in modelling programs.

Most of the methods for rendering anti-aliased primitives (in OpenGL at least) rely on blending the primitives in sorted order (either back to front or front to back). Anti-aliased points and lines typically use a lookup table technique to compute the fraction of each pixel covered by the primitive. The coverage value is then used to determined an alpha value to be used in the blending computation. This is done as part of standard scan-line rendering, which is how most (not all) current 3D cards render.

There are also some alternatives. One of these is called the accumulation buffer (which I dont really know about). Another method is using super-sampling.

In super-sampling additional subpixel storage is maintained as part of the color, depth and stencil buffers. Instead of using alpha for coverage, coverage masks are computed to help maintain sub-pixel coverage information for all pixels. The implementations available so far support tow, four, eight, and sixteen samples per pixel. These sample values are probably what you are refering to when you say 'levels'. These are normally found under your cards video options as 2x,4x,8x,16x AA.

[Structural Integrity]

Only thing I know is that it averages the color of edges to remove pixelated effect. I used it too in my Pong game.

[NEWSBOT3]

Originally posted by meglamaniac

http://www.lunaloca.com/tutorials/antialiasing/

How does it work? Well, if we zoom in a little bit, it should be apparent. On the left, the aliasing* (aka "staircasing" or "jaggies") is much more noticable. Antialiasing smooths out the discretization* of an image by padding pixels with intermediate colors. In this example, we have black lines on a white background, so to antialias, we pad with surrounding pixels of shades of gray.

Why gray? Well, because gray is between white and black. If we used red lines on a white background, we'd want to antialias with shades of pink.

also, check

http://www.visionengineer.com/comp/antialiasing.shtml

[Vaio]

So its nothing to do with the anti-aliasing pixies that live in the monitor then ?

Vaio

[NEWSBOT3]

Originally posted by Vaio
So its nothing to do with the anti-aliasing pixies that live in the monitor then ?

Vaio

shh, let him think its magical science stuff.