It does seem magical. The one thing I can answer is that multi-patterning does not shine light through two masks simultaneously. Instead, it consists of multip

It does seem magical. The one thing I can answer is that multi-patterning does not shine light through two masks simultaneously. Instead, it consists of multiple separate steps. I think for the rest, the point is that light arriving on the waver is not a binary thing, but due to refraction and self-interference light arrives in variable intensities. So within difficult constraints, this allows you to control the area in which the intensity is below our above certain thresholds. I assume that if you then manage to control the chemistry just right, you can then produce features that are smaller than the wavelength of the light -- under severe constraints of what shapes you can produce. You definitely do not get to produce an arbitrary bitmap of sub-wavelength pixel size.