MATLAB: Roipoly for multiple shapes

Image Processing Toolboxmaskingpoly2maskroipoly

I'm wanting to create multiple closed unconnected shapes using roipoly. I can do this fine for 2 shapes but when I add in the code for a 3rd shape it always connects the last coord of the 3rd shape to the first coord of the 1st shape.
if true
xmask_temp = [];
ymask_temp = [];
junk = [];
for i=1
  A=imread(['Image0001.bmp']);
  [junk,xmask_temp,ymask_temp]=roipoly(A);
  a = 1+size(xmask_temp,1);
  xmask(1:size(xmask_temp,1),i)=xmask_temp;
  ymask(1:size(ymask_temp,1),i)=ymask_temp;
  [junk,xmask_temp,ymask_temp]=roipoly(A);
  b = a-1+size(xmask_temp,1);
  xmask(a:b,i)=xmask_temp;
  ymask(a:b,i)=ymask_temp;
  b = b+1;
  [junk,xmask_temp,ymask_temp]=roipoly(A);    % where the problem starts
  c = b-1+size(xmask_temp,1);
  xmask(b:c,i)=xmask_temp;
  ymask(b:c,i)=ymask_temp;
end
B = roipoly(A,xmask,ymask);
imshow(B);

Best Answer

In the loop, call poly2mask() to get a new mask for the new polygon they draw. Then OR it in with the image.
Before the loop
mask = false(rows, columns); % Initialize final mask
Then in the loop
thisMask = poly2mask(xVertices, yVertices, rows, columns);
mask = mask | thisMask; % Combine this mask with the final mask.
That way you build up the final mask by ORing in each individual mask one at a time. Change variable names to whatever you're using, of course.
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