How to extract Exudates from retinal image

Hello everyone I am referring "Automated detection of diabetic retinopathy using SVM" this paper and I want to segment exudates from my input image. I followed the steps they have mentioned in paper, they wrote to mask the optoc disc on the image. But I am not getting how do I do that, I have tried to extract the optic disc but I am not getting the masking step. I am attaching the paper snap, and my segmented optic disc. Please help ,me with this I need it. This is the flow diagram.

And I am getting this optic disc