Patent US 4,885,605

A negative-positive microfilm discriminating system for use in a microfilm reader/printer apparatus, comprising a reflector mirror for projecting a beam of light bearing an image detected from a microfilm strip, a sensor disposed in the path of light from the reflector mirror for detecting the densities in each of a plurality of blocks of a patterned image zone of the microfilm strip, and a control circuit for selecting out of the blocks the blocks having acceptable degrees of contrast, determining whether the image zone within each of the selected blocks is a negative or is a positive and determining whether the micrifilm strip is a negative or is a positive.