I used to write software for a living, and every once in a while I pick a fun project and mess around with it a bit. My current project is a program that will create a digital fore-edge image.
What's a fore-edge?
It's the surface of a book opposite the spine, where the red arrow is pointing.
What's a digital fore-edge?
Okay, so there are a couple ways to put a picture on the fore-edge. The most common way is to literally hold the pages closed and paint it. That gives you the best results, but it's expensive and only some printers offer it.
The other way is to print a slice of the image at the very edge of the page when you're printing the text of the book. When all the slices are put together, you have something like the original image.
For example, if I wanted to put this b&w dragon on my fore-edge (green background added for clarity):
First, I would slice the picture up sort of like this:
Then I would put one slice at the margin of each page of the book and when the book is held closed (or maybe with the pages slightly flexed), you would see the dragon.
That sounds easy
I mean, yeah, it's not that hard in concept. But the way they print books adds a few complications. Basically, they start with a larger page, print the words, and then chop off the edges.
Except...
There's a margin of error when cutting off the edges. So I need to account for that.
Anyhow, it's not really all that complicated. I'm using Python and I was able to quickly create a program that adds an image to a page on a pdf, so I know it can be done. (Then I changed a bunch of stuff in my program and broke it completely. This is how we code.)
How do you test it?
Yeah. This is one of the drawbacks. I won't know for sure if my program works until I load the paperback and buy a copy. (I'll probably use Barnes & Noble, because they allow authors to load a book and not make it public.)
If it works, great! If it doesn't... this could get expensive to debug.
Anyhow. This is what I do for fun.