How can i extract a set of data if the corner points are known(not square) from a large matrix?

I have an image and using impoly image handle i can draw a polygon and get the x and y coordinates of the corner points.It is not a square or a rectangle. My aim is to extract the values coming within this region from a bigger matrix. I have attached an image from which a polygon is shown. i use polygon only to get the coordinates, but my matrix is another one.Please help me out.

Answer 1

[Image Analyst]

Create the mask with the .createMask method of the object returned by impoly(), then extract the values

pixelsInsidePoly = redChannel(mask);  % Repeat for green and blue channels.