Thresholding images of line drawings with hysteresis

Abstract

John Canny’s two-level thresholding with hysteresis is now a de facto standard in edge detection. The method consistently outperforms single threshold techniques and is simple to use, but relies on edge detection operators’ ability to produce thin input data. To date, thresholding with hysteresis has only been applicable to thick data such as line drawings by top-down systems using a priori knowledge of image content to specify the pixel tracks to be considered. We present, and discuss within the context of line drawing interpretation, a morphological implementation of thresholding with hysteresis that requires only simple thresholding and idempotent dilation and which is applicable to thick data. Initial experiments with the technique are described. A more complete evaluation and formal comparison of the performance of the proposed algorithm with alternative line drawing binarisation methods is underway and will be the subject of a future report.