Copy object´s pixels to ones-matrix

Question

Mariana 2014-2-12

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https://ww2.mathworks.cn/matlabcentral/answers/115879-copy-object-s-pixels-to-ones-matrix

评论： Image Analyst 2014-2-16

Hello, I try following (for example):

[r, c] = find(bwlabel(BW)==2)

but I´ve found out that "r" and "c" vectors are the same length and they (probably) represent some sort of frame around an object rather then object itself. I wanted to use this function for replacing one-elements (pixel with value = 1) in ones matrix (matrix filled with ones (sorry for poor english) with pixel values of object copied... sth like: image2(r, c) = image1 (r, c) but the problem is that the background is "copied" also (and is unwanted, I want to have only the object copied)

Can you give an advice what is wrong (whether it is) or which better function I could use?

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Answer 1

Walter Roberson 2014-2-12

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https://ww2.mathworks.cn/matlabcentral/answers/115879-copy-object-s-pixels-to-ones-matrix#answer_124130

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idx = bwlabel(BW) == 2;
newmatrix = ones(size(originalmatrix));
newmatrix(idx) = originalmatrix(idx);

Or, following your existing code more closely,

[r, c] = find(bwlabel(BW)==2);
newmatrix = ones(size(originalmatrix));
nematrix(sub2ind(size(newmatrix),r,c)) = originalmatrix(sub2ind(size(newmatrix),r,c));

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Answer 2

Image Analyst 2014-2-12

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https://ww2.mathworks.cn/matlabcentral/answers/115879-copy-object-s-pixels-to-ones-matrix#answer_124144

在 MATLAB Online 中打开

Another way using ismember()

labeledImage = bwlabel(BW);
twoValuedPixels = ismember(labeledImage, 2) > 0;

This gives a logical matrix use int32(twoValuedPixels) if you want int32 or double(twoValuedPixels) if you want a double.

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Image Analyst 2014-2-16

Regarding your "Answer"...No problem. You almost never want a list of individual row and column numbers for every single binary pixel. See my Image Segmentation Tutorial, BlobsDemo: http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862

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