de-gradient the stained glass filter

In my ongoing search to find a cobblestone pattern that I can use for my project I stubled upon the stained glass filter. I appears to give a perfect outline with only white stones (I need this to send a clean image to a laser), but when I looked closer, I saw a gradient going from white to black. I tried a grayscale and didn't get anywhere. I would love to have this in black and white (white stones) to be able to manipluate in size and thickness for bricks to be used in O scale.