How to select a roi in greyscale image and put values to zero?

Hello, i have a 12bit greyscale image (tiff) which I want to be able to draw a rectangular roi and fill these values to zero (i.e. black)

This is my code, I cannot see where I am going wrong

Raw=getimage(handles.axes1);                % get image from axes component (im using GUIDE)    
h = imrect(handles.axes1);                  % User definable rectangle 
position=wait(h)                            
p = h.getPosition();
position=[p(1) p(2) p(3) p(4)];             % [xmin ymin width height]
delete(h);

Raw(p(2):(p(2)+p(4)),p(1):(p(1)+p(3)))==0;  % put user specified roi to 0 (black)
axes(handles.axes1); cla reset;             % Clear current axes
imshow(Raw)                                 % Draw modified image

NOTE:-

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Use = to assign, not == which is a comparison.

Raw(p(2):(p(2)+p(4)), p(1):(p(1)+p(3))) = 0;

mask = h.createmask();
Raw(mask) = 0;

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How to select a roi in greyscale image and put values to zero?

How to select a roi in greyscale image and put values to zero?