I've used the scanner method but I didn't get a distinct cut off point (where the pixels go white to black... there were lots of grey ones even when bumping the contrast during scanning. Maybe scanning as line-art would fix that but at the time I didn't think of that and was too eager to try the pinhole out anyway) so had to guess a bit, not that it really matters as you'll still need to experiment with the final exposure anyway.

Ummm, I don't think that paragraph would pass a grammer checker!