12 Jul
2016
12 Jul
'16
8:56 a.m.
Go to http://www.madandmoonly.com/doctormatt/mathematics/ulamSpirals/ulamSpirals.h... , hover your mouse over "modulo 2 (low res) <http://www.madandmoonly.com/doctormatt/mathematics/ulamSpirals/ulamSpirals.htm#nogo>", and step back. You should see a large "X" in the image. (With my glasses on, I see the "X" when I'm about five feet away from my laptop; with my glasss off, a foot will do.) What's happening here? That's really two questions. What is the image made of, on the pixel level? (I'm guessing that some of the "squares" are actually rectangles with aspect ratio close to 1.) And: What are my eyes and brain doing? (Why is the effect so salient from far away but invisible up close?) Jim Propp