Jaggies
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"Jaggies" is the informal name for artifacts in
raster image upright=1, The Smiley, smiley face in the top left corner is a raster image. When enlarged, individual pixels appear as squares. Enlarging further, each pixel can be analyzed, with their colors constructed through combination of the values for ...
s, most frequently from
aliasing In signal processing and related disciplines, aliasing is an effect that causes different signals to become indistinguishable (or ''aliases'' of one another) when sampled. It also often refers to the distortion or artifact that results when a ...
, which in turn is often caused by non-linear mixing effects producing high-frequency components, or missing or poor
anti-aliasing filter An anti-aliasing filter (AAF) is a filter used before a signal sampler to restrict the bandwidth of a signal to satisfy the Nyquist–Shannon sampling theorem over the band of interest. Since the theorem states that unambiguous reconstruction ...
ing prior to sampling. Jaggies are stair-like 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 either horizontally or vertically, a "dogleg" 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 A compression artifact (or artefact) is a noticeable distortion of media (including images, audio, and video) caused by the application of lossy compression. Lossy data compression involves discarding some of the media's data so that it beco ...
s, which are a different phenomenon.


Causes

Jaggies occur due to the "staircase effect". This is because a line represented in raster mode is approximated by a sequence of pixels. Jaggies can occur for a variety of reasons, the most common being that the output device (
display monitor A computer monitor is an output device that displays information in pictorial or textual form. A discrete monitor comprises a visual display, support electronics, power supply, housing, electrical connectors, and external user controls. The d ...
or
printer Printer may refer to: Technology * Printer (publishing), a person or a company * Printer (computing), a hardware device * Optical printer for motion picture films People * Nariman Printer (fl. c. 1940), Indian journalist and activist * James ...
) does not have enough
resolution Resolution(s) may refer to: Common meanings * Resolution (debate), the statement which is debated in policy debate * Resolution (law), a written motion adopted by a deliberative body * New Year's resolution, a commitment that an individual mak ...
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 is a form of computer graphics in which visual images are created directly from geometric shapes defined on a Cartesian plane, such as points, lines, curves and polygons. The associated mechanisms may include vector display a ...
have over
bitmapped graphics file:Rgb-raster-image.svg, upright=1, The Smiley, smiley face in the top left corner is a raster image. When enlarged, individual pixels appear as squares. Enlarging further, each pixel can be analyzed, with their colors constructed through comb ...
– 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
spatial anti-aliasing In digital signal processing, spatial anti-aliasing is a technique for minimizing the distortion artifacts (aliasing) when representing a high-resolution image at a lower resolution. Anti-aliasing is used in digital photography, computer graphics ...
. Anti-aliasing smooths out jagged lines by surrounding the jaggies with transparent
pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the smal ...
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 addition, jaggies often occur when a bit mapped image is converted to a different resolution. They can occur for 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 real-time computer graphics, especially gaming, anti-aliasing is used to remove jaggies created by the edges of polygons and other lines entirely. Some video game developers do not enable anti-aliasing by default for their games because the intended hardware is not powerful enough to run it at smooth
frames per second A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent. Frame and FRAME may also refer to: Physical objects In building construction *Framing (con ...
if anti-aliasing is enabled. On eighth-generation video game consoles, such as the
PlayStation 4 The PlayStation 4 (PS4) is a home video game console developed by Sony Interactive Entertainment. Announced as the successor to the PlayStation 3 in February 2013, it was launched on November 15, 2013, in North America, November 29, 2013 in ...
and
Xbox One The Xbox One is a home video game console developed by Microsoft. Announced in May 2013, it is the successor to Xbox 360 and the third base console in the Xbox series of video game consoles. It was first released in North America, parts of ...
, anti-aliasing and frame rate has been heavily improved. Jaggies in bitmaps, such as sprites and surface materials, are most often dealt with by separate
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 (pixels of the texture). There are two main categories of texture filtering ...
routines, which are far easier to perform than anti-aliasing filtering. Texture filtering became ubiquitous on PCs after the introduction of
3Dfx 3dfx Interactive was an American technology company headquartered in San Jose, California, founded in 1994, that specialized in the manufacturing of 3D graphics processing units, and later, video cards. It was a pioneer in the field from the l ...
's Voodoo GPU.


Notable uses of the term

In the
Atari 8-bit The Atari 8-bit family is a series of 8-bit home computers introduced by Atari, Inc. in 1979 as the Atari 400 and Atari 800. The series was successively upgraded to Atari 1200XL , Atari 600XL, Atari 800XL, Atari 65XE, Atari 130XE, Atari 800XE, ...
game ''
Rescue on Fractalus! ''Rescue On Fractalus!'' is a 1985 first-person shooter computer game created by Lucasfilm Games. It was originally released for the Atari 8-bit family and the Atari 5200 games console. It was also ported to other popular platforms of the day, ...
'', developed by
Lucasfilm Games Lucasfilm Games (known as LucasArts between 1990 and 2021) is an American video game licensor that is part of Lucasfilm. It was founded in May 1982 by George Lucas as a video game development group alongside his film company; as part of a large ...
and published 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.


See also

*
Posterization Posterization or posterisation of an image is the conversion of a continuous gradation of tone to several regions of fewer tones, causing abrupt changes from one tone to another. This was originally done with photographic processes to create p ...


References

{{reflist Computer graphic artifacts Image processing