Android Java (OpenCV) function to detect which circles (OMR) are filled in mobile captured image

I need to develop an android app which can capture images of forms (OMR sheet) and can detect which circles are filled in the form. There will be exactly 6 fixed circles (bubbles) in the form & we need to accurately detect which one of them are filled. I have already developed the image capturing part & I'm getting the captured image in Bitmap format. So, the thing I want from you to do is to develop a function in java (OpenCV, etc.) which takes bitmap image as input & returns an array of 6 elements having values 0 or 1. If a circle is found to be filled then value would be 1 otherwise 0. Also, I need it in one day.