MATLAB: How to remove inside area from an ROI to analyse the outer area only

dicomdigital image processingimage processingimdilateimfreehandmedicalimagesradiomicsroi

I have recently started using MATLAB for image processing with MR images, and so far have found previously asked questions and examples to be a great help – but with this I am a little stuck! I have created an ROI on my dicom image using imfreehand() I have then dilated this ROI using the imdilate(I, strel('square',n)) function to create a new ROI. Ideally, I would now like to subtract the original ROI from the new ROI so that I am left with only the new area. Any help would be greatly appreciated!

Best Answer

I = imread('cameraman.tif') ;
imshow(I)
h = imfreehand ;
pos = wait(h); 
%%Extract the ROI 
[ny,nx] = size(I) ;
[X,Y] = meshgrid(1:nx,1:ny) ;
idx = inpolygon(X(:),Y(:),pos(:,1),pos(:,2)) ;
Z = I ;
Z(idx) = NaN ;
imshow(Z) ;
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