Reverse video

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Reverse video (or invert video) is a computer display technique wherein the background and text colour values are swapped, like this. On older computers, it was sometimes used on specific letters, words or phrases to highlight them.

Usually this is done by inverting the brightness values of the pixels of the involved region of the display with an exclusive or. Since brightness values usually range from 0 to 255, a 255 value becomes 0 and vice versa. A 1 value becomes 254, etc. This is occasionally called a ones complement. If the source image is a neutral gray color, reverse video can be difficult to see.

Although reverse video can be used to indicate text the user has selected, it is more common in modern desktop environments to change the background to blue instead of black, since blue stands out even more in an otherwise monochrome block of text.

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 errors, where an intended action is performed on an object that is not the one intended.

[edit] Accessibility uses

Reverse video is also sometimes used for accessibility reasons. People suffering from eye problems (like ocular toxocarosis) find it more comfortable, less aggressive 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, invert video is an efficient way to read or write text in a dark environment, since the darkness of the screen may blend in the darkness of the environment

Under Mac OS X, whole screen reverse video is available from System Preferences/Universal Access/Display Black on White or with the keyboard shortcut ctrl + option + command + 8.

[edit] External links

• A definition of invert video
• Further information