How can I get the exact intensity change coordinates from graph automatically?

I am working on Eye-tracking thing i have to track the eye for open and close. for which I am using the concept of horizontal average intensity change. i have achieved the graph of average intensity change with following piece of code: I1=imread('open.jpg'); I2=rgb2gray(I1); x=(1:size(I2,1)); y=mean(I2,2); plot(x,y) after this plotting i want the intensity change coordinates which i want automatically retrieving from MATLAb in order to calculate the distance between those intensity changes to declare close or open eyes. In attached figure, red mark shows the intensity change points. I want their coordinates automatically from matlab. anybody have idea how to do it?