Adaptive grey level assignment in CT scan display

The normal method of assigning grey levels to computed tomographic (CT) numbers in CT scan display involves interactive selection of an intensity window. This method often results in the inability to visualize different types of tissue in a single image and sometimes results in unnecessary loss of contrast sensitivity. A method is described that solves these problems by automatically adapting the assignment of displayable grey levels to CT numbers in a way that varies smoothly across the image according to local needs for the presentation of contrast. The adaptation is based on local histogram equalization implemented using interpolation so as to operate on a minicomputer in a few tens of seconds. This contrast enhancement is followed by a mapping that causes the viewer's perceptual response to be linear across the display scale.