Check out this trick! By colouring in boxes, you can make a strange blobby picture that transforms when reflected in a curvy mirror!
When you copied your picture from the square grid to the anamorphic grid, you stretched it and flipped it until it looked very different. Reflected in the curved surface of the aluminium foil, the stretched shape looks normal.
When light hits a reflective surface, it bounces off at an angle. The angle between incoming light and the mirror’s surface is the same as the angle between mirror’s surface and the outgoing light. Think of a cricket ball bouncing off a pitch.
For a flat mirror, these bounces all line up, so the pattern of light heading towards the surface is the same as the pattern that leaves it. Curved mirrors have a changing surface, which means the pattern of light that leaves the mirror (and hits your eye) is not arranged in the same way as the light that hit it.
With a cylinder, the surface changes when you go around the cylinder, but not when you go up and down. Up and down lines in your picture stay straight in the anamorphic grid. Sideways lines have to curve on paper to look straight in the mirror.
Most surfaces around you are reflective. You can’t see your reflection in your shirt or the wall because its surface is like countless tiny curved mirrors, scattering light rather than reflecting the same incoming pattern.
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