A tripture is a triple of pictures, where the last is the superimposition of the other two.

As an example, take a look at these three pictures A,B and C:

Our goal is to produce two new images A' and B' looking as A and B, such that their superimposition C' looks as C.

We get this result by producing the two images A' and B' in the next picture:

If A' and B' are printed on a transparency, the superimposition of A' and B' produces the image C'.

How to produce your own triptures

The procedure involves some steps:

How does this method work?

This method works because if we apply the previous rules we get that

In other words darker pixels in C correspond to darker 2x2 matrixes in C', while lighter pixels in C correspond to lighter 2x2 matrixes in C'. Let us examine this fact more carefully. In each 2x2 matrix of A' the information concerning A is represented by the pixel (1,1), while the pixel (1,2) is always black. Analogously, in each 2x2 matrix of B' the information regarding B is represented by the pixel (1,2), while the pixel (1,1) is always black. Therefore in the superimposition of A' and B' the pixel (1,2) of A' hides the pixel (1,2) of B', and the pixel (1,1) of B' hides the pixel (1,1) of A'. In other words the pictures A and B hide each other in C'. The information concerning C is contained in the second row of each 2x2 matrix in C'. Each white pixel in C corresponds to setting two different colors in that second row, while each black pixel in C produces two black pixels in that second row.

I hope you will have fun in making your own triptures!

P.S: I have developed this technique to produce my Christmas cards, but I have later discovered that it was already known in the scientific community. Please inform me if you know some similar or better procedure to get an image by superimposition of other two.

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