How do I crop out an a circle image from an image after edge detection

I am trying to extract the annular portion from the image below. But am unable to find a function or code for this . Can somebody please help on how to proceed. I have the radius for the circles and the centre.

Answer 1

[Image Analyst]

Your first mistake was doing an edge detection. Just because you can see edges in an image does not mean that the first thing you do is edge detection, despite what other novices tell you. This is obviously an eye and you'd be better off doing color segmentation (to get everything not white or skin colored), or using imfindcircles().

There are lots of papers on this:

http://www.visionbib.com/bibliography/contentspeople.html#Face%20Recognition,%20Detection,%20Tracking,%20Gesture%20Recognition,%20Fingerprints,%20Biometrics

• 21.5.3 Biometrics, Iris Recognition Systems
• 21.5.3.1 Periocular Biometrics
• 21.5.3.2 Iris Based Biometrics, Biometrics Engineering Research Center, Dongguk University
• 21.5.3.3 Iris Recognition Systems, Infrared, Near-Infrared, NIR Based
• 21.5.3.4 Iris Recognition Systems, Spoofing, Liveness, Presentation Attack, Contact Lenses
• 21.5.3.5 Iris Recognition Systems, Wavelet Based
• 21.5.3.6 Iris Detection, Segmentation and Localization Systems
• 21.5.3.7 Iris Recognition Systems, Systems, Evaluation, Comparison, Surveys
• 21.5.3.8 Retinal Identification Systems and Tecniques

[Karthik Krishnan]

then what is the point of doing edge detection ?(here canny )

@Image Analyst

[Karthik Krishnan]

If i have a raw eye image from the dataset what all steps i need to do for extracting the iris for further processes?

Answer 2

[Yongjian Feng]

This be done by a brute-force approach, right? Read the bitmap, check the coordinates of each point. If it is outside the circle, set it to white (or black). If it is inside the circle, copy it over.

[Yongjian Feng]

Also found this existing answer:

How to crop circle from an image? - MATLAB Answers - MATLAB Central (mathworks.com)