A visual comparison is to compare two or more things by eye. This might be done by placing them side by side; by overlaying them; by alternating an image or by presenting each image to a separate eye. Such comparisons are the first stage in a child's development of an understanding of geometry and measurement, before they move to an understanding of measuring devices such as a ruler. People with sufficient control over the

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

of their eyeballs (e.g. those who can easily view random-dot

stereograms Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word ''stereoscopy'' derives . Any stereoscopic image is ...

) can hold up two paper printouts and go

cross-eyed Esotropia is a form of strabismus in which one or both eyes turns inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance. It is the opposite of exotropia and usual ...

to superimpose them. This invokes deep, fast, built-in image comparison wetware (the same machinery responsible for

depth perception Depth perception is the ability to perceive distance to objects in the world using the visual system and visual perception. It is a major factor in perceiving the world in three dimensions. Depth perception happens primarily due to stereopsis an ...

) and differences stand out almost immediately. This technique is good for finding edits in graphical images, or for comparing an image with a compressed version to spot artefacts. Visual comparison with a standard chart or reference is often used as a means of measuring complex phenomena such as the

weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the ...

sea state In oceanography, sea state is the general condition of the free surface on a large body of water—with respect to wind waves and swell—at a certain location and moment. A sea state is characterized by statistics, including the wave height, p ...

s or the roughness of a river. A

colour chart A color chart or color reference card is a flat, physical object that has many different color samples present. They can be available as a single-page chart, or in the form of swatchbooks or color-matching fans. Typically there are two diffe ...

is used for this purpose in many contexts such as

chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...

cosmetics Cosmetics are constituted mixtures of chemical compounds derived from either natural sources, or synthetically created ones. Cosmetics have various purposes. Those designed for personal care and skin care can be used to cleanse or protect ...

medical test A medical test is a medical procedure performed to detect, diagnose, or monitor diseases, disease processes, susceptibility, or to determine a course of treatment. Medical tests such as, physical and visual exams, diagnostic imaging, genetic te ...

ing and

photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employed ...

. Comparison by eye may also be used as a source of amusement or

intelligence testing An intelligence quotient (IQ) is a total score derived from a set of standardized tests or subtests designed to assess human intelligence. The abbreviation "IQ" was coined by the psychologist William Stern for the German term ''Intelligenzqu ...

, as in the popular puzzle of

spot the difference Globe and high court (Spot the difference)

policing The police are a constituted body of persons empowered by a state, with the aim to enforce the law, to ensure the safety, health and possessions of citizens, and to prevent crime and civil disorder. Their lawful powers include arrest and th ...

, the technique is used for analysis of

fingerprint A fingerprint is an impression left by the friction ridges of a human finger. The recovery of partial fingerprints from a crime scene is an important method of forensic science. Moisture and grease on a finger result in fingerprints on surfac ...

s and

identity parade A police lineup (in American English) or identity parade (in British English) is a process by which a crime victim or witness's putative identification of a suspect is confirmed to a level that can count as evidence at trial. The suspect, alo ...

s. Visual comparison task can be simplified by using a computer software (e.g
Image Compare
application) that automatically aligns a pair of images based on common visual features present in the two images. Such computer assisted visual comparison is being increasingly popular in Book history research.

Computer jargon

A visual diff finds differences between two files by

eyeball search Visual inspection is a common method of quality control, data acquisition, and data analysis. Visual Inspection, used in maintenance of facilities, mean inspection of equipment and structures using either or all of raw human senses such as vision, ...

. The term optical diff has also been reported, and is sometimes more specifically used for the act of superimposing two nearly identical printouts on one another and holding them up to a light to spot differences. Though this method is poor for detecting omissions in the ‘rear’ file, it can also be used with printouts of graphics, a claim few

diff In computing, the utility diff is a data comparison tool that computes and displays the differences between the contents of files. Unlike edit distance notions used for other purposes, diff is line-oriented rather than character-oriented, but it ...

programs can make.''

Jargon File The Jargon File is a glossary and usage dictionary of slang used by computer programmers. The original Jargon File was a collection of terms from technical cultures such as the MIT AI Lab, the Stanford AI Lab (SAIL) and others of the old ARPANET A ...

'', version 4.4.6, 25 Oct 2003

Software Applications for Visual Comparison

Image Compare
application automatically compares a pair of images and highlights their differences. This application runs in desktop and mobile phone browsers without requiring installation.

References

{{reflist Vision Computer jargon

Computer jargon

Software Applications for Visual Comparison

See also

References