Anti-Aliasing

Article : Anti-Aliasing
Date : 11/07/05
Page : 3

Contents

Multisampling

Multisampling is a more efficient but slightly less pretty form of Anti-Aliasing. Multisampling takes multiple samples for each pixel. In a fairly standard example the quincunx system takes 4 samples in the corners and 1 sample in the middle. Each of these samples is given a weight the corners are given a weight of 1/8 each and the centre sample is given a weight of 1/2. the colour of the pixel is then determined by similar calculations to Super sampling.

quincumx

With multisampling each cell on has two samples in it. Looking at the diagram below you can see that the other 3 samples are taken from neighbouring cells. So multisampling takes into account the colours around the pixel in question. This is how you get a blend of colour to achieve the desired result. It is important to note that Multisampling only happens when a cell is covered my more than one colour, otherwise a single colour is chosen and does not need to be calculated.

Levels of Anti-Aliasing

This refers to the amount of samples taken to determine the colour of the pixel. The higher the sample rate the better the quality of picture but the slower the image will be rendered. FSAA will be referred to as FSAA 2x or FSAA 4x, 6x and 8x are also available but have a larger performance hit and require more powerful graphics cards.

anti-alias 2 times anti-alias 4 times

The image on the left shows samples taken from a graphics card using FSAA 2x, two samples are taken in two corners and used to produce the pixels colour. With FSAA 4x on the right you simple double the amount of samples taken for each pixel from FSAA 2x. when this is done on every pixel along an edge, the blending is much smoother and even less noticeable. As always though the trick is to balance quality and performance for your individual machine.

Pro's and Cons - The Summery

There are pro's and cons for using anti-aliasing in both games and applications. We have been through them but here is a quick summery to help you make up your mind if using AA or FSAA is right for you and your PC

Pro's

Smoothes out screen fonts
Rounded edges look to have smooth curves
Type can be easier to read due to better quality fonts
Games look a lot prettier and more realistic

Cons

Small text can be too blurred to read
already sharp edges can be made fuzzier
You cant print out Anti-Aliased text as it blurs
Static image sizes are larger
Games are affected by lower frame rates

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