Jaggies

"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. Apparently the aliens in the videogame were called Jaggis because the characters in the game environment, due to lower graphic resolutions of the Atari, were blocky and jagged. This is believed to be the first time the term "jaggies" was used to refer to jagged computer graphics.

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.