Threshold Selection Techniques, 5.

Abstract : Some further methods of sharply localizing the valley between two peaks on a histogram of picture gray levels are investigated. These methods are based on histogramming the gray levels of just those picture points at which the value of some digital gradient operator lies in a high percentile range. The thresholds obtained are not the same as those found with an earlier, Laplacian-based method, but they appear to be equally satisfactory. Outlining of the objects can be accomplished by outputting a narrow range of near-threshold gray levels as black, and all gray levels outside this range as white.