"Jaggies" is the informal name for artifacts in raster images, most frequently from aliasing

Aliasing

In signal processing and related disciplines, aliasing refers to an effect that causes different signals to become indistinguishable when sampled...

, which in turn is often caused by non-linear mixing effects producing high-frequency components and/or missing or poor anti-aliasing filter

Anti-aliasing filter

An anti-aliasing filter is a filter used before a signal sampler, to restrict the bandwidth of a signal to approximately satisfy the sampling theorem....

ing prior to sampling.

Jaggies are stairlike lines that appear where there should be smooth straight lines or curves. For example, when a nominally straight, un-aliased line steps across one pixel, a dogleg

Dogleg

Dogleg or dog-leg may refer to:Motor vehicles*Dog leg, an unusual manual transmission layout*Dog-leg, an offset 'zig-zag' plane of operation for a floor-mounted automatic transmission shift lever* The area behind the rear door on a four door car...

 occurs halfway through the line, where it crosses the threshold from one pixel to the other.

Jaggies should not be confused with most compression artifact

Compression artifact

A compression artifact is a noticeable distortion of media caused by the application of lossy data compression....

s, which are a different phenomenon.

Causes

Jaggies can occur for a variety of reasons, the most common being that the output device (display monitor

Computer display

A monitor or display is an electronic visual display for computers. The monitor comprises the display device, circuitry, and an enclosure...

 or printer

Computer printer

In computing, a printer is a peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a...

) does not have enough resolution

Display resolution

The display resolution of a digital television or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by all different factors in cathode ray tube , flat panel or projection...

 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

Vector graphics

Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon, which are all based on mathematical expressions, to represent images in computer graphics...

 has over bit-mapped graphics – the output looks the same regardless of the resolution of the output device.

Solutions

The effect of jaggies can be reduced somewhat by a graphics technique known as anti-aliasing

Anti-aliasing

In digital signal processing, spatial anti-aliasing is the technique of minimizing the distortion artifacts known as aliasing when representing a high-resolution image at a lower resolution...

. Anti-aliasing smooths out jagged lines by surrounding the jaggies with transparent pixel

Pixel

In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....

s to simulate the appearance of fractionally-filled pixels. The downside of anti-aliasing is that it reduces contrast – rather than sharp black/white transitions, there are shades of gray – and the resulting image is fuzzy. This is an inescapable trade-off: if the resolution is insufficient to display the desired detail, the output will either be jagged or fuzzy, or some combination thereof.

In realtime computer graphics, especially gaming, full screen anti-aliasing (FSAA) is used to remove jaggies created by the edges of polygons and other lines entirely. Some newer game consoles, such as the Xbox 360

Xbox 360

The Xbox 360 is the second video game console produced by Microsoft and the successor to the Xbox. The Xbox 360 competes with Sony's PlayStation 3 and Nintendo's Wii as part of the seventh generation of video game consoles...

 and PlayStation 3

PlayStation 3

The is the third home video game console produced by Sony Computer Entertainment and the successor to the PlayStation 2 as part of the PlayStation series. The PlayStation 3 competes with Microsoft's Xbox 360 and Nintendo's Wii as part of the seventh generation of video game consoles...

, had publishing policies which mandated the use of FSAA in all games released for them. Jaggies in bitmaps, such as sprites and surface materials, are most often dealt with by separate texture filtering

Texture filtering

In computer graphics, texture filtering or texture smoothing is the method used to determine the texture color for a texture mapped pixel, using the colors of nearby texels . Mathematically, texture filtering is a type of anti-aliasing, but it filters out high frequencies from the texture fill...

 routines, which are far easier to perform than FSAA. Texture filtering became ubiquitous on PCs after the introduction of 3Dfx

3dfx

3dfx Interactive was a company that specialized in the manufacturing of 3D graphics processing units and, later, graphics cards. It was a pioneer in the field for several years in the late 1990s until 2000 when it underwent one of the most high-profile demises in the history of the PC industry...

's Voodoo GPU, and on game consoles following the Nintendo 64

Nintendo 64

The , often referred to as N64, was Nintendo′s third home video game console for the international market. Named for its 64-bit CPU, it was released in June 1996 in Japan, September 1996 in North America, March 1997 in Europe and Australia, September 1997 in France and December 1997 in Brazil...

's debut.

Notable uses of the term

In the Atari 8-bit

Atari 8-bit family

The Atari 8-bit family is a series of 8-bit home computers manufactured from 1979 to 1992. All are based on the MOS Technology 6502 CPU and were the first home computers designed with custom coprocessor chips...

 game Rescue on Fractalus!, published by Lucasfilm Games

LucasArts

LucasArts Entertainment Company, LLC is an American video game developer and publisher. The company was once famous for its innovative line of graphic adventure games, the critical and commercial success of which peaked in the mid 1990s...

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 also initially titled the game Behind Jaggi Lines!. The latter idea was scrapped by the marketing department before release.