Reference: pmToGreyscale
pmToGreyscale(pm) returns a grey-scale representation of the pixmap pm. A pixel with coordinates (h, s, v) is replaced by (h, 0, v) in HSV coordinates.
pmToGreyscale(pm) returns a grey-scale representation of the pixmap pm. A pixel with coordinates (h, s, v) is replaced by (h, 0, v) in HSV coordinates.