how to apply the result of bwboundaries() output ?

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Piyum Rangana 2017-4-2

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https://ww2.mathworks.cn/matlabcentral/answers/333264-how-to-apply-the-result-of-bwboundaries-output

评论： Piyum Rangana 2017-4-4

This is the code.

%%%%%%Code begins %%%%
boundaries = bwboundaries(img);
NumOfBoundaries = size(boundaries, 1);
[x y t]= size(rgbImage);
ZeroPlate = redChannel == 0;
for k = 1 : NumOfBoundaries 
thisBoundary = boundaries{k};
%%%%%I want to set Value '1' to 'ZeroPlate' co-%%%ordination given in 'thisBoundary' %%%%%%%%
%%%%%---------------the code goes here------------------%%%%
%%%%%end %%%%%
end

I want to set value '1' to the ZeroPlate (which is red-channel of the given image in which the pixel values are all zeros) according to the co-ordination obtaining from the values of 'boundaries' variable. How to do this ?

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Answer 1

Image Analyst 2017-4-3

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https://ww2.mathworks.cn/matlabcentral/answers/333264-how-to-apply-the-result-of-bwboundaries-output#answer_261449

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Try this:

%%%%%%Code begins %%%%
boundaries = bwboundaries(img);
NumOfBoundaries = size(boundaries, 1);
% Get size.  
% Note: it is NOT NOT NOT [x,y,numColors] = size(rgbImage) as you had it.
% rows is y, NOT x.  But actually this line is not needed.
[rows, columns, numberOfColorChannels]= size(rgbImage);
ZeroPlate = redChannel == 0;
for k = 1 : NumOfBoundaries
  thisBoundary = boundaries{k};
  % Set Value '1' to 'ZeroPlate' 
  % coordinates given in 'thisBoundary'
  x = thisBoundary(:, 1);
  y = thisBoundary(:, 2);
  for index = 1 : length(x)
    % Get row and column.
    row = y(index);
    column = x(index);
    % Set that row and column = true = 1.
    ZeroPlate(row, column) = true;
  end
end

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Image Analyst 2017-4-4

在 MATLAB Online 中打开

I set it equal to true because ZeroPlate is a binary image and you said you want the value to be 1 (true).

Actually you're right sort of - I switched x and y. I thought bwboundaries returned (x,y) coordinates but it doesn't - it returns (row, column) which is (y, x). So the correct code should be:

for k = 1 : NumOfBoundaries
  thisBoundary = boundaries{k};
  % Set Value '1' to 'ZeroPlate' 
  % coordinates given in 'thisBoundary'
  x = thisBoundary(:, 2);
  y = thisBoundary(:, 1);
  for index = 1 : length(x)
    % Get row and column.
    row = y(index);
    column = x(index);
    % Set that row and column = true = 1.
    ZeroPlate(row, column) = true;
  end
end