I wanted to get the effect known as "Magic Eye Effect" (At least here in Germany). So here is how it works:
First we need a small image that forms the background. The Gimp wants it to have the same size as the map image, but the right parts of it don't matter, so I left them white. This one can be any type of image.
Then we need something to hide in this background. I took a word, written black on white, gaussian blurred at 2 and then inverted. The "whiter" the pixels are, the more they pop out of the background. This must be agrayscle image and the first n colums must be blank, where n is the number of colums you want to use from the background image.
Now we put them together. Click on the text and start the Magic Eye plugin. (If someone knows, why it gets an "unexpected message" when I click on the background image, please tell me.)
This uses the first 75 colums of fstrip.jpg as the background and ftext.gif as the map. And here, finally, the result of the effort:
If you stare at it long enough, the forest suddenly pops out of the image.
If you can make something usefull out of it, just send me a mail.
If you like, you can download the c source from here.
Alexander Schulz, 12. Januar 1997