====== Sharpie ======
Sharpie takes the difference between the red and blue separations of a pseudocolor image (see [[advanced_level:pseudocolor|Pseudocolor]]). The result is a black-and-white image that tends to suppress the overtext. The output is a floating-point monochrome image.

The technique is named for the late Robert Sharples, University College London, who preferred this rendition.