How to get the region shown in the image ?

Question

i want to get the red region as specified in the image below :

remember that the red region that is shown in the image is just for clarification , it is not present in original image , below is the original image attached :

i also have the iris point in this region, i already got that point , if that point can help me so i can share that image too.

can someone help me in this .....

Answer 1

For this specific image, let's call it BW, you can find the center region as:

BWnoBorder= imclearborder(BW); %# remove the white that touches the border
OnlyCenter = bwareaopen(BWnoBorder,1000); %# remove all small pixel areas

Answer 2

A robust method might be the snake region growing algorithm.

Answer 3

Seems like you thresholded the eye illuminated by IR or something. To answer your question or even to ask it correctly you have to show a number of images to evaluate the stability and noise in eye socket regions. Otherwise one can come up with a solution that works for the image above but not in general.

For example, I can invert your image, get the largest Connected Component (the dark region) and erode it till it becomes thin, see below. It is easy to get an ellipse from this binary mask but will it work in general case with your noisy input?

A good thing to start is to say what do you expect to find. Say you are looking for an eye, dark surrounding area and a bright skin tone - make it 3 Mixed models that settle simultaneously in the EM fashion. Provide some shape priors to increase accuracy. think about other visual cues such as specs on the iris, saccades, FA from blinks, etc.