UNIVERSAL THRESHOLDER/DISCRIMINATOR

Image processing system for reproducing on a bilevel medium documents having mixed formats (text, halftone, and continuous tone) by selective thresholding of scanned pel values based on detected characteristics of the material to be reproduced. The characteristics of interest for each pel include its reflectance (gray) level, a gradient value derived from surrounding pels, a hysteresis value based on the thresholding decisions for preceding pels, and a look-ahead value based on following pels. Depending on relationships among the characteristics of interest, the pel values are applied to one of a plurality of thresholders most suitable for thresholding the determined format. The determination (discrimination) process can be improved by including a novel defocused symmetry discriminator (or a high-frequency detector) in conjunction with an information homogeneity discriminator to eliminate local anomolies.