How to crop required ROI from an image?

 % code
   h = impoly(gca,[188,30; 189,142; 93,141; 13,41]);
   api = iptgetapi(h);
   fcn = makeConstrainToRectFcn('impoly',get(gca,'XLim'),get(gca,'YLim'));
   api.setPositionConstraintFcn(fcn);
   position = wait(h);
   a=imcrop(I,[250 91;251 203;155 202;75 102]]);
   imshow(I);

end
I am working on medical image processing.
I need to crop eye only from face & position is not constant for all images.
so i use polygonal ROI.
but it shows error.

[Image Analyst]

Read this link so you know how to format your code.

[Revathi S]

Ok. thanks Modified

Answer 1

[Image Analyst]

Call imcrop() with no arguments if the coordinates are not the same from image to image. This will let the user interactively select the box.

[Revathi S]

Imcrop() deals with rectangular boundary.

My ROI is not a rectangular shape (ie, Eye )

It contain some unwanted portion while cropping.

[Image Analyst]

Try this freehand masking demo.

Answer 2

[Revathi S]

 if true
   e = roipoly(I);
   ROI=zeros(size(I,1),size(I,2));
   NONROI=zeros(size(I,1),size(I,2));
   int16(i);
   int16(j);
   for i=1:size(I,1)
      for j=1:size(I,2)
           if e(i,j)==1  
              ROI(i,j)=I(i,j);
              ROI(i,j)=1;
           end
       end
    end

Code for Croping Required ROI