This is a very nice function, but I need to increase resolution by different amounts in the x and y directions. For example I would like to be able to convert a 4:3 image to a 16:9 image. Is that possible with IIR?
Malcolm: Of course I'm not cheating (but I'm a bit offended, actually). Besides, it's not only the teeth, the whole image improves in definition (let's stay away from semantic subtleties). It can be appreciated best in all borders between light and dark areas (i.e. eye sockets). Anybody can try for himself: download the example image, crop the left part and use the function on it.
Cris: that's sort of true. You can't create information out of nowhere. However if I have a curve specified by several points, and the curve represents the true underlying data, I can improve the representation of the data by taking more points.
If you look at Fransisco's images, he's clearly improved the definition of the teeth. Unless he's cheating, the image quality has been improved.