In the previous installments we’ve looked at Pupil Detection and Iris Detection. Now we’ll look at unwrapping the image of the iris from a circular pattern to a rectangular one. We will use this later for some other algorithms.
Iris detection is significantly more difficult than pupil. Mostly because it is not so well defined, pupil is just a black disk essentially as far as a grayscale image is concerned, but the outer edge of the iris is not nearly as sharp as the outer edge of the pupil is. Also, there is a much higher probability of glints and reflections in the iris, since it is larger than the pupil and this can complicate the detection further. And on top of all that the upper and lower eyelids often cover up portions of the iris, which means that detecting the iris as a circle is going to be either difficult or impossible.