bit-mapped image



"Jaggies" is the informal name for aliasing artifacts in raster images, often caused by non-linear mixing effects producing high-frequency components and/or missing or poor anti-aliasing filtering prior to sampling.

Jaggies are stairlike lines that appear where there should be smooth straight lines or curves. They can occur for a variety of reasons, the most common being that the output device (display monitor or printer) does not have enough resolution to portray a smooth line. In addition, jaggies often occur when a bit-mapped image is converted to a different resolution. This is one of the advantages that vector graphics has over bit-mapped graphics — the output looks the same regardless of the resolution of the output device. The effect of jaggies can be reduced somewhat by a graphics technique known as anti-aliasing. Anti-aliasing smooths out jagged lines by surrounding the jaggies with shaded pixels. This can be done in a computer or in a printer.

The origin of the term is believed to come from the Atari 8-bit game Rescue on Fractalus!, published by Lucasfilm Games in 1985. The graphics depicting the cockpit of the player's spacecraft contains two window struts, which are not anti-aliased and are therefore very "jagged". The developers made fun of this and named the in-game enemies "Jaggi", and the game itself in its prototype form bore the name Behind Jaggi Lines!. This is believed to be the first time the term "jaggies" was used to refer to jagged computer graphics.

In gaming, consoles that have jaggies are the sixth generation Playstation 2 in component mode, PSP, and most fifth generation 32-bit systems that are capable of rendering polygons. Sony's Playstation 2 has a unique system architecture which takes advantage of the high performance of its Emotion Engine and is capable of rendering vertex shaders but lacks anti-aliasing and bump mapping capabilities. Older consoles identify jaggies with texture mapped renditions instead of polygons. Current consoles such as the Xbox, Xbox 360, Playstation 3, Wii, Gamecube, and Dreamcast can render high quality graphics using separately custom graphics processing units (GPU]]). GPU manufactures of consoles such as ATI and Nvidia do not have jaggies, indicating the slow conformity in the market to PCs in general. In the future software problems are most likely going to be eliminated for the needs of the consumer.

Note: jaggies should not be confused with most compression artifacts, which are a different phenomenon.

A dogleg occurs when a nominally straight, un-aliased line steps across one pixel. The human eye is very perceptive of small irregular changes.


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