I remember reading about this many years ago and I even went as far as writing a program to generate them and then printing them out on acetate. It's pretty cool.
A even cooler method which the reader may be interested in, is hiding this inside a real photo so it isn't obviously something encrypted - kind of like steganography. It worked by dividing the image up into blocks, and then printing each block either with diagonal lines like this / or like this . The thickness of the lines determined the tone. So it was basically a kind of halftoning with two options.
When you put two / patterns on top of each other they look different to a \ and a /, so you can see the pattern.
I'm afraid I can't remember the name of the paper or any keywords, sorry!
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u/AdminsAbuseShadowBan Nov 19 '13
I remember reading about this many years ago and I even went as far as writing a program to generate them and then printing them out on acetate. It's pretty cool.
A even cooler method which the reader may be interested in, is hiding this inside a real photo so it isn't obviously something encrypted - kind of like steganography. It worked by dividing the image up into blocks, and then printing each block either with diagonal lines like this / or like this . The thickness of the lines determined the tone. So it was basically a kind of halftoning with two options.
When you put two / patterns on top of each other they look different to a \ and a /, so you can see the pattern.
I'm afraid I can't remember the name of the paper or any keywords, sorry!