Image

==Characteristics==
[[File:TEIDE.JPG|thumb|right|A [[Synthetic aperture radar|synthetic-aperture radar]] [[radar imaging|image]] acquired by the SIR-C/X-SAR radar on board the [[Space Shuttle Endeavour|Space Shuttle ''Endeavour'']] shows the [[Teide]] volcano. The city of Santa Cruz de Tenerife is visible as the purple and white area on the lower right edge of the island. Lava flows at the summit crater appear in shades of green and brown, while vegetation zones appear as areas of purple, green, and yellow on the volcano's flanks.]]

=== Two-dimensional images ===
The word 'image' is also used in the broader sense of any two-dimensional figure such as a [[map]], [[Graph (data structure)|graph]], [[pie chart]], [[Painting (object)|painting]], or [[banner]].{{Clarify|date=November 2023|reason=This is contradictory to the previous assertion that images can represent non-real concepts, which includes all of the forms described in this sentence.}} In this wider sense, images can also be rendered manually, such as by [[drawing]], the art of painting, or the [[graphic arts]] (such as [[lithography]] or [[etching]]), rendered automatically by [[printing]] or [[Computer graphics workstation|computer graphics]] technology, or [[Image development (visual arts)|developed]] by a combination of methods.

A two-dimensional image does not have to use the entire visual system to be a visual representation. An example of this is a [[greyscale]] ("black and white") image, which uses the visual system's sensitivity to brightness across all wavelengths without taking into account different colors. A black-and-white visual representation of something is still an image, even though it does not fully use the visual system's capabilities.

On the other hand, some processes can be used to create visual representations of objects that are otherwise inaccessible to the human visual system. These include [[microscopy]] for the magnification of minute objects, [[telescope]]s that can observe objects at great distances, [[X-ray]]s that can visually represent interior structures of the human body (among other objects), [[Magnetic resonance imaging|magnetic resonance imaging (MRI)]], [[Positron emission tomography|positron emission tomography (PET scans)]], and others. Such processes often rely on the detection of [[electromagnetic radiation]] that occurs beyond the [[Electromagnetic spectrum|light spectrum]] visible to the human eye, converting such signals into recognizable images.

=== Three-dimensional images ===
Aside from sculpture and other physical activities that can create three-dimensional images from solid material, some modern techniques, such as [[holography]], can create three-dimensional images that are reproducible but intangible to human touch. Some photographic processes can now render the illusion of depth in an otherwise "flat" image, but "3-D photography" ([[stereoscopy]]) or "[[3D film|3-D film]]" are [[optical illusion]]s that require special devices such as eyeglasses to create that illusion of depth.

Copies of 3-dimensional images have traditionally had to be crafted one at a time, usually by an individual or team of [[artisan]]s.  In the modern age, the development of [[plastic]]s and other technologies made it possible to create multiple copies of a 3-dimensional object with less effort; the advent and development of "[[3D printing|3-D printing]]" have expanded that capability.

=== Moving images ===
{{See also|Film}}
"Moving" two-dimensional images are actually illusions of movement perceived when still images are displayed in sequence, each image lasting less, and sometimes much less, than a fraction of a second. The traditional standard for the display of individual [[Film frame|frames]] by a motion picture projector has been 24 frames per second (FPS) since at least the commercial introduction of "talking pictures" in the late 1920s, which necessitated a standard for the synchronization of images and sounds.{{citation needed|date=November 2023}} Even in electronic formats such as television and digital image displays, the apparent "motion" is actually the result of many individual lines giving the impression of continuous movement.

This phenomenon has often been described as "[[persistence of vision]]", a physiological effect of light impressions remaining on the retina of the eye for very brief periods. Even though the term is still sometimes used in popular discussions of movies, it is not a scientifically valid explanation.{{citation needed|date=November 2023}} Other terms emphasize the complex cognitive operations of the brain and the human visual system. "[[Flicker fusion threshold|Flicker fusion]]", the "[[phi phenomenon]]", and "[[beta movement]]" are among the terms that have replaced "persistence of vision", though no one term seems adequate to describe the process.