1. A windowing system for use in windowing video displayed images, said system comprising: a source of digital data for use in providing the displayed images, means for supplying said digital data at substantially video raster rates, hardware means including a transfer function generator to provide an output that is an input transformed by a transfer function of said transfer function generator, said output effectively provided at said video raster rate, said transfer function being variable responsive to operator designated parameters including slope and threshold for transforming the said digital data to extend the data range of interest to substantially fill the entire intensity range of the displayed image, whereby windowing is accomplished on a non-look up table basis.