Editing Visual comparison

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.<ref>{{Cite book |url=https://books.google.com/books?id=hMIOAAAAQAAJ&pg=PA188 |page=188 |title=Introductory spatial analysis |author=David John Unwin |date=January 1981 |publisher=Methuen |isbn=9780416721904 }}</ref>

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.<ref>{{cite book|title=The Child's Conception of Geometry|author1=Jean Piaget |author2=Bärbel Inhelder |author3=Alina Szeminska |pages=33|url=https://books.google.com/books?id=A-yQR6DxTkUC|isbn=0-415-20999-4|year=1999|publisher=Routledge}}</ref>

People with sufficient control over the [[parallax]] of their eyeballs (e.g. those who can easily view random-dot [[stereograms]]) can hold up two paper printouts and go [[cross-eyed]] to superimpose them. This invokes deep, fast, built-in image comparison [[wetware (brain)|wetware]] (the same machinery responsible for [[depth perception]]) 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.<ref name=jar/>

Visual comparison with a standard chart or reference is often used as a means of measuring complex phenomena such as the [[weather]], [[sea state]]s or the roughness of a river.<ref>{{cite book|title=Roughness Characteristics of New Zealand Rivers|author1=D. Murray Hicks |author2=Peter D. Mason |url=https://books.google.com/books?id=Oez427pUSB0C|isbn=4-7702-6087-3|year=1991|publisher=Water Resources Survey }}</ref>  A [[color chart|colour chart]] is used for this purpose in many contexts such as [[chemistry]], [[cosmetics]], [[medical test]]ing and [[photography]].

Comparison by eye may also be used as a source of amusement or [[intelligence testing]], as in the popular puzzle of [[spot the difference]].

In [[policing]], the technique is used for analysis of [[fingerprint]]s and [[identity parade]]s.

Visual comparison task can be simplified by using a computer software that automatically aligns a pair of images based on common visual features present in the two images.

==Computer jargon==
A '''visual diff''' or '''vdiff''' finds differences between two files by [[eyeball search]]. 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]] programs can make.<ref name=jar>''[[Jargon File]]'', version 4.4.6, 25 Oct 2003</ref>

==See also==
* [[Beaufort scale]]
* [[Blink comparator]]
* [[Hinman collator]]
* [[Image differencing]]
* [[Visual inspection]]
* [[Visual search]]

==References==
{{reflist}}

{{Improve categories|date=January 2024}}
[[Category:Vision]]
[[Category:Data differencing]]