My god, thats complicated. Why not just create a new layer and fill it with the 25% dither pattern, much easier. I checked out that website. If your trying to accomplish the screen effect..

1. New Image-->Transparent-->500x500x16 million
2. Forground color-->White
3. Fill-->Pattern-->Dither 25%
4. Select all - Click the selection and it will select all the filled pixels.
5. Apply patterns or sculpture effects to suit.