Magic Mirror

By Alberto de la Torre

August 15, 2015

This guy (Michael Teeuw) has built something fantastic: A magic mirror. Like the one in Snowwhite, but without the face.

There was one approach prior to this one, thanks to Pierre Rafast but it was very slow. The system consisted in an Rpi connected to a webcam and a monitor. While the webcam registered what was in front, the Rpi could recognice the face, display sometring and talk. But due to the power needed, there was some lag between reality and the image displayed, so it is kind of weird.

Slow Magic Mirror

This new approach works differently, by using a one-way mirror (a.k.a. that mirror used by the police to watch the interrogations). This one-way mirror functions by having a hight reflection coeficient on one side, and a very low one on the other side.

Room A with low level light and a Blue observer. Room B with high level light and a Red observer. In the middle, a one-way mirror.

So imagine we have two rooms A & B, where A has low light (lets say “bright 1″) and B has high (lets say “bright 10″). Inside those rooms there are two observers, Blue and Red. Because of the different ilumination, Blue will emit not so many blue rays, while Red will emit a lot more. If we put a one-way mirror (of course, with the mirrowed-side on the right place), lots of red rays will be reflected, and some will be transmited (normally, a 9-1 ratio). With the brighness in room A, that means that 9 rays will return for 1 that goes through the mirror. On the other room, the blue rays don’t reflect, but get mostly transmitted (due to optics laws, in the opposite ratio: 1-9). Nevertheless, as there were so few blue rays, both the Blue and the Red guys can only see the red rays.

Of course, if Room A gets iluminated, more blue rays will reach the red observer, and the effect will no longer be.

So, what has Michael done? He has just added a one-way mirror to a monitor. When you look to the magic mirror, if the room is well iluminated and the screen is black you will only see your reflection. But when there screen is showing anything bright (some white text, for example), the one-way mirror will let that bright part show.

Add a camera and a computer, plus face recognition, and you can add whatever you want to your mirror. Or, with a text-to-speech software (such as espeak), it could talk to you.