Pop quiz: what’s the relation between the two images below? If you’re the first person to get it right (and do it before I get bored and tell you what it is), I’ll buy you a beer next time we chat.
EDIT: Erik the party pooper got it right, but I’ll not reveal it just yet.
visualization, etc. 
they’re 90 degrees out of phase; one is cos and the other is sin
before / after shaving mustache? 🙂
They second one is the inverse of the first?
“too clever by half”, as they say.
Robert got it. I think it’s pretty amazing that although they’re exact negatives of one another, both manage to look like reasonable faces (even eyebrows, bridge of nose, etc). Try finding a face image whose negative also looks like one.
Even more strangely, this is one of the principal components of an image set. The positive values are correlated with one person, while the negative values are correlated with another. This works because the faces are slightly misaligned.
At first, I though that only the part around the mouth had been inverted, but when I looked closer at the edges, it was pretty clear it’s all inverted.
Both kind of look like faces if you look close, but they don’t exactly pop out at you (Which Blair style – Gordon should know what that means ;). We’re also quite good at seeing faces where there really are none, see my article on Chernoff Faces
So do I get a beer? Or was Erik still ahead? And can I trade that beer for some other beverage?
Well, precisely the strange part about this is that I don’t think there will be a Which Blair effect: the negative image looks just as much like a face as the positive image. If you look at a smaller version of it (or just move ~10 feet away) it’s more stark.
I won’t claim you could recognize the two actors. But if I told you who they were, you’d probably agree.