Equalizing the histogram of an image is an operation on the pixel intensities aimed at enhancing the global contrast. The algorithm tries to transform the intensities so that they are uniformly distributed over the gray-scale range. It works by computing the cumulative intensity distribution of the image, and replace pixel intensities by their index in this distribution. The operation is nonlinear, so it can produce images that look unrealistic.
This plugin operates on a single channel of each single image of a sequence. Equalization of the luminance of a colored image is not possible yet.
This method has been generalized in various ways. See the Adaptative histogram equalization plugin for a context-dependant variant.