Converts current color image to black/white (1 bit) with a Shen-Castan (ISEF) edge detection algorithm.

Shen-Castan algorithm convolves the image with the Infinite Symmetric Exponential Filter, computes the binary Laplacian image, suppresses false zero crossing, performs adaptive gradient thresholding, and, finally, also applies hysteresis thresholding. (Algorithms for Image Processing and Computer Vision J.R.Parker).