I just finished putting all the books I want on my bookshelf back on my bookshelf, and I decided that I should take a picture of it. It’ll be cool to look at it in a few years and see which new books have showed up, and which old ones I’ve finally gotten rid of.
But, there’s a problem: you never look at a bookshelf from only one spot! You step back and stand on the tips of your toes to look at the high shelves, and you bend down to look at the low ones. It’s nicest to look at each book straight on.
So, how do you take one picture of a bookshelf? You could get very far away from it. But, my room isn’t nearly big enough — if you take a picture from the opposite wall, you’re still clearly looking up at the top shelf, and down at the bottom shelf.
A scanner has many image sensors across its width, and by moving (scanning!) the paper, or the sensors, down its length. As a result, a picture taken by a scanner has no perspective. It sees everything straight-on! But, I don’t have a giant flatbed scanner.
You could get the same effect by taking many pictures with one scanner and stitching them together — that would take a lot of work, and I wanted something a little bit quicker. So, instead, I took a few pictures of my bookshelf with a regular camera. I got as far away from it as I could, set my camera up on a tiny tripod, pointed straight at the bottom shelf, and took a picture. Then I switched to a bigger tripod, raised it up, and took a picture from slightly higher. I did this a few more times, raising the camera up all the way to the ceiling. Then I stitched them all together in my computer.
The result is pretty cool — a picture with normal perspective in the horizontal direction (you can see the inner sides of the left and right walls of the bookshelf) but with very little in the vertical direction (and the perspective is strange — you’re clearly looking up at some the books on the left side of the bottom shelf, but you can see the tops of the books on the top shelf!).