Invert

The Invert command in the Adjust section of the Image menu inverts all the pixel values in an image, that is changes them to their opposite value. More exactly, it calculates a new value for each pixel by taking the current value and subtracting it from 255. The new value then determines the brightness of the pixel, and therefore the brightness of all the colors in the whole image.

Note that the command is immediately applied once selected. If you would like to revert to the original brightness it is usually safe to do a reverse inverse by just selecting Invert again. However, in some circumstances it is often safer to select Undo from the Edit menu.

See:

Adjust Image