What is anti-aliasing?

Antialiasing is a technique used in computer graphics that reduce the visual defects that occur when high-resolution images are presented in a lower resolution. It occurs because of the output device, the monitor or printer, doesn't have a high enough resolution to represent a smooth line.

This is also an inherent problem on a computer. The pixels that make up the screen of the monitor are all shaped in rectangles or squares. Because lighting up only half of one of these square pixels is not possible, the result is roughness or jagged line.

The jagged line effect can be minimized by increasing the resolution of the monitor, making the pixels small enough that the human eye cannot distinguish them individually.

But, this is not a good solution. Because images are displayed based on their resolution and a single image pixel may take up many monitor pixels, making it impossible for a higher resolution monitor to mask the rough edges.

Here anti-aliasing is required. Anti-aliasing reduces the prominence of jaggies by adding additional pixels in-between the edges of an object and its background of gray or color. Tricking the human eye into thinking that the lines are not rough.

The slight changes in color around the edges of an image help the line blend around curves, giving the impression that the line is perfect. These pexel changes are made on a very small scale that the human eye cannot detect under normal circumstances. In order to be able to see that an graphic object or font has been antialiased, it would have to be magnified.

Different types of antialiasing techniques: 

Supersample Antialiasing - This process takes high-resolution images and downsamples to the necessary size. This results in a much smoother edge, but supersampling requires more hardware resources from a graphics card. That's why, it isn't used much anymore.

Multisample Antialiasing - In this process fewer resources being used compare to supersampling. It doesn't perform well with alpha/transparent textures, and because it doesn't sample the entire scene, image quality may be reduced.

Coverage Sampling Antialiasing - It was developed by NVIDIA to produce higher quality with only a slight performance cost over standard Multisample.

Adaptive Antialiasing - Adaptive Antialiasing is an extension of multisample that works better with alpha/transparent textures but it doesn't take up the bandwidth and resources of a graphics card.

Fast Approximate Antialiasing - It is much faster with less hardware performance cost. Also, it smooths out the edges on the entire image. But, appear a bit more blurry, which isn't useful if you're looking for sharp graphics.

Enhanced Quality Antialiasing - It was developed by AMD for their Radeon graphics cards, which is similar to coverage sampling and delivers higher quality antialiasing over multisample with minor impact on performance and no increased video memory requirements.

Temporal Antialiasing - It is a newer antialiasing process that produces improved results over fast approximate by incorporating several different smoothing techniques, but with a slightly higher performance cost. But, this method doesn't work on all graphics cards.