roipoly for multiple shapes

Question

Thomas Darwent 2018-8-17

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/415268-roipoly-for-multiple-shapes

评论： Image Analyst 2018-8-20

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);

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Answer 1

Image Analyst 2018-8-17

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/415268-roipoly-for-multiple-shapes#answer_333165

在 MATLAB Online 中打开

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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Thomas Darwent 2018-8-20

Hi, Thanks for your help. This method does build up an image of unconnected shapes but for the application we are using we need to build this image using roipoly.

Image Analyst 2018-8-20

Why do you say "but"? You still use roipoly(). You just also use poly2mask to create a mask from those vertices, and then OR in that mask with a cumulative mask you're building.

If you can't figure it out, attach 'Image0001.bmp' and I'll make a full demo.

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