The last-linked "additional information" mentions rotated 1/2-circles with black & white halves to define greyscale images. There's an easier way, and it'll scale to as many layers and colors as you want:
pixel(r,g,b) = ((r1^r2), (g1^g2), (b1^b2)). (bit-level xoring) More layers just add in their values. Until you add all of them, there's no way to know what the final value for a pixel will be.
As for the "general access structures"... maybe this can be tweaked, haven't looked closely enough and my brain is tired.
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edit: fixed algorithm. wrote quick ruby script. first attempt at something like this, glad it works.
edit again: and for those interested, the last linked "additional info" article describes how to make multi-layer images like the one in the main article. It's kinda interesting.
The interesting thing about the original technique (to me) is that you can do the decryption without a computer. If you want to do this in color, I think you need to use the LCD approach of having red, green, and blue subpixels next to each other.
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[side topic]
The last-linked "additional information" mentions rotated 1/2-circles with black & white halves to define greyscale images. There's an easier way, and it'll scale to as many layers and colors as you want:
pixel(r,g,b) = ((r1^r2), (g1^g2), (b1^b2)). (bit-level xoring) More layers just add in their values. Until you add all of them, there's no way to know what the final value for a pixel will be.
As for the "general access structures"... maybe this can be tweaked, haven't looked closely enough and my brain is tired.
---
edit: fixed algorithm. wrote quick ruby script. first attempt at something like this, glad it works.
edit again: and for those interested, the last linked "additional info" article describes how to make multi-layer images like the one in the main article. It's kinda interesting.
You can avoid the waste of space implied by the circles by using ½×1 rectangles instead: http://lists.canonical.org/pipermail/kragen-hacks/2007-March...
The interesting thing about the original technique (to me) is that you can do the decryption without a computer. If you want to do this in color, I think you need to use the LCD approach of having red, green, and blue subpixels next to each other.