Think of the numbers as percentages of Gray. 0 = White 0.1 = 10% Gray 0.5 = 50% Gray 0.9 = 90% Gray 1 = 100% Gray All negative numbers will give you white, all numbers greater 1 will give you black. The usefull range is 0 to 1. To invert a grayscale white must become black, 10% gray must become 90% gray. 50% gray should remain 50% gray. To do this use 1 - input. Stefan