Abstract - This paper examines two varieties of super-sample anti-aliasing: Rotated Grid Super-Sampling (RGSS) and Ordered Grid Super-Sampling (OGSS). RGSS employs a sub-sampling grid that is rotated around the standard horizontal and vertical offset axes used in OGSS by (typically )20to 30 Â°. RGSS is seen to have one basic advantage over OGSS: More effective anti-aliasing near the horizontal and vertical axes, where the human eye can most easily detect screen aliasing (jaggies). This advantage also permits the use of fewer sub-samples to achieve approximately the same visual effect as OGSS.
In addition, this paper examines the fill-rate, memory, and bandwidth usage of both anti-aliasing techniques. Super-sampling anti-aliasing is found to be a costly process that inevitably reduces graphics processing performance, typically by a substantial margin. However, anti-aliasing's positive impact on image quality is significant and is seen to be very important to an improved gaming experience and worth the performance cost.
Computers have always strived to achieve a higher-level of quality in graphics, with the goal in mind of eventually being able to create an accurate representation of reality. Of course, to achieve reality itself is impossible, as reality is infinitely detailed. People deal with computer systems that have a finite, or set amount of memory, bandwidth and processing ability. Because of this, it is impossible to deal with infinite detail. The closer you look at something, the more you see and this remains true down to the sub-atomic level. So, computers (at least for the foreseeable future)must work around the problem of infinite detail by taking shortcuts. For instance, they can use sampling to approximate the character of extremely complex source data.
A sample is a measurement of a very specific point in time and/or a location in space. To understand this, consider sound waves. Sound is nothing more than a pressure wave:air compressing and decompressing. This physical event is infinite in detail and it moves through space, evolving with time. A CD is a digital medium of storing sound; it stores numbers equivalent to the amount of sound for specific points in time. This translation from a pressure wave to a number is done through a microphone and AD-converter. A microphone can trans- late the infinitely detailed pressure wave into an infinitely detailed electrical signal. The AD-converter then measures this electrical signal at specific points in time. Each such measurement is a sample. So an infinitely detailed event is translated into a discrete sample version that can be processed by a CPU, or stored on a digital medium like a CD. This translates to graphics in that a sample represents a specific moment as well as a specific area. A pixel represents each area and a frame represents each moment.
At our current level of consumer technology, it simply is not possible to render enough samples for anything close to an acceptable representation of reality. Because of this lack of samples, artifacts are introduced, artifacts known as "aliasing." Aliasing brings to the table a number of rendering problems that can seriously detract from the quality of an image. These problems are there every day in current 3D accelerators, taking away that immersiveness that computer games and 3D applications strive to deliver. Jagged, crawling edges and flickering objects are all symptoms of aliasing. Look at the edges of an object on a PC 3D accelerator and there you will find jagged edges. Now start moving away from the object and you'll see a "crawling "effect. These aliasing artifacts substantially reduce the overall quality of the rendered display.