Abstract

A technique for enhancing a displayed image originally stored at a density of 1 data bit per pel. The stored data is scanned to locate unit steps, one-row or one-column steps in binary values. Whenever a unit step is found, the distance from the step to the nearest transitions on both sides of the step are found. The distances are used to access lookup tables which assign 4 bit gray scale values to limited numbers of pels on both sides of the unit step. The assigned gray scale values produce a gradually-darkening string of pels extending through the step. When the entire image field has been scanned, a maximum 4 bit pel value is assigned to any unmodified pel having an original binary value of 1 and a minimum pel value is assigned to any unmodified pel having an original binary value of 0. The visual quality of the displayed image is enhanced by the selective introduction of intermediate gray scale values for pels adjacent unit steps.