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Reverse video (or invert video or inverse video or 'reverse screen') is a computer display technique whereby the background and text color values are inverted. On older computers, displays were usually configured to display white text on a black background by default. 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 r - n, for r 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 errors, 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 colors such as blue, or to use a semi-transparent background to "highlight" the selected text.
On a terminal understanding ANSI escape sequences, the reverse video function is activated using the escape sequence CSI 7 m (which equals SGR 7).
Reverse video is also sometimes used for accessibility reasons. People with visual impairments such as ocular toxocariasis may find it 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.
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