Reverse video is a computer display technique whereby the background and text colour values are inverted. On older computers, displays were usually configured to display white text on a black background by default

Default (computer science)

A default, in computer science, refers to a setting or value automatically assigned to a software application, computer program or device, outside of user intervention. Such settings are also called presets, especially for electronic devices...

. For emphasis, one swapped the color scheme to bright background with dark text. Nowadays the two tend to be switched, since old reverse video is now the default format and the old default format reverse video/screen, using dark pen on white paper as a metaphor for the window area.

Video is usually reversed by inverting the brightness values of the pixels of the involved region of the display. If there are 256 levels of brightness, encoded as 0 to 255, the 255 value becomes 0 and vice versa. A value of 1 becomes 254, 2 of 253, and so on: n is swapped for 255 - n (if there are 256 levels of brightness). This is occasionally called a ones' complement. If the source image is of middle brightness, reverse video can be difficult to see, 127 becomes 128 for example, which is only one level of brightness different.

Reverse video is commonly used in software programs as a visual aid to highlight a selection that has been made as an aid in preventing description error

Description error

A description error is an error that occurs when a person performs an action on an object that is not the intended object. This error can be very disorienting and usually causes a brief loss of situation awareness or automation surprise if noticed right away. But much worse, if it goes unnoticed,...

s, where an intended action is performed on an object that is not the one intended. It is more common in modern desktop environments to change the background to other colours such as blue, or to use a semi-transparent background to "highlight" the selected text.

Accessibility

Reverse video is also sometimes used for accessibility

Accessibility

Accessibility is a general term used to describe the degree to which a product, device, service, or environment is available to as many people as possible. Accessibility can be viewed as the "ability to access" and benefit from some system or entity...

 reasons. People suffering from visual impairments such as ocular toxocariasis

Ocular larva migrans

Ocular larva migrans is the ocular form of the larva migrans syndrome that occurs when toxocara canis larvae invade the eye. They may be associated with visceral larva migrans...

may find it more comfortable and less tiring to the eyes to work with a predominantly black screen, since modern operating systems usually display a lot of white in a normal use. For the same, white-dominant reason, reverse video is an efficient way to read or write text in a dark environment, since the darkness of the screen may blend into the darkness of the environment.