Highlighting gray scale video display terminal

In a CRT display of digitized gray scale information from a diagnostic scan, an operator-selectable area of the display can be highlighted to increase the contrast and brightness of a selected portion of the image while simultaneously viewing a wide range of information levels in the background portion of the image. The highlighted area and the background may encompass different operator-selectable information level windows. To accommodate the wide dynamic range necessary for such a display, and eliminate possible contouring effects when enhancing dark areas of the image, more gray scale display levels are used than are commonly used with diagnostic scanning systems, and full black on the CRT is set to correspond to a minimum digital display level sufficiently high so that no single display step results in more than a maximum predetermined contrast ratio in the display. Use of this minimum digital display level also improves the implementation of various non-linear transfer curves for image inversion and compensation of photographic film characteristics.