The technique of unsharp masking is described and its use as an image enhancement technique discussed. A mathematical model for the masking process is developed; experimental testing and MTF measurements of the masked and sharpened images are made to test the validity of the mathematical model as a predictor of the mask and final image characteristics. The effect of contrast, mask unsharpness, and source spread function size on the resulting MTF are presented. Subjective evaluations are used to determine the visually optimum image. It is shown that the visually best image is not necessarily the one with the largest MTF value or area; suggestions are made for adjusting existing image quality specifications to incorporate the results of unsharp masking techniques
