picture by RobotSkirts'
Tags (also known as markers) are the easiest way to augment the real world. Usually in the form of black and white squares, tags serve as an easily identified (from a computer vision point of view) visual queue. No wonder this method is so popular among amateurs and students. However, tags are ugly. Augmented reality cannot really hit mainstream if it keeps on using the computer-friendly but eye-sore inducing tags.
Thus, a lot of research was done on how we can make the tags less obtrusive or even on to get rid of them completely. Here's a collection of some of the methods developed by those smart Graz students:
Alas, having unobtrusive tags is computationally more expensive - it takes longer, and on mobile devices may drain your battery quicker. Is there a better option? How about tags that are clearly visible to the computer but nearly invisible to human eyes? Here's a fun experiment - take your camera phone and look through its camera while pressing a TV remote. You should then be able to see its IR signal - that is, your phone (or rather most camera phones) is able to see infra red light. On the other end of the spectrum (that is, the visible spectrum) is ultra violet. Here's a fluff story about a boy who made an invisible sticker (for humans) warning birds (apparently birds can see UV light) of birds. Can we adapt the same technology for augmented reality?