Apply a mask to matrices stored in a cell array

Question

Aaron Smith 2017-7-21

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https://ww2.mathworks.cn/matlabcentral/answers/349729-apply-a-mask-to-matrices-stored-in-a-cell-array

评论： Aaron Smith 2017-7-26

I have a mask taken from an image. I need to apply this logical mask to a number of matrices that are the same dimensions as the image. The matrices are stored as the cells in a cell array. I have looked on mathworks at previous questions regarding masks but none appear to help with my particular

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Answer 1

Sayam Ganguly 2017-7-24

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Hi, I understand that you have a cell array of matrices and you have a mask of the same dimension as the the individual matrices. Now you want to apply these masks to all the matrices in your cell array. I would like to suggest an approach that should help you achieve this. Following is the code sample -

% X is a cell array of dimension 3*4 with matrices of 2*3 dimension
% cellmat is an NN-toolbox function
X = cellmat(3,4,2,3,10);
%mask is the mask to be applied
mask = [true false true ; false true false];
% Loop through the elements of the cell array
for i = 1 : numel(X)
  % Apply mask on each of the matrices and store the result back in the cell.
  % Here '.*' performs element wise multiplication between the matrices
  X{i} = X{i}.*mask;
end

Also you can achieve the same without iteration by using cellfun. Following is the sample code for the same -

X = cellfun(@(x) x.*mask,X,'UniformOutput', false)

Give either approach a try and see which suits your need better. Hope this helps!

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Aaron Smith 2017-7-26

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Thanks a million Sayam.

In you're sample code, the cellfun code without iteration, is the small x a typo? I can't tell what value this represents. I tried the first method, with the iteration. It generates an error once I added to my GUI stating that Cell contents reference from a non-cell array object.

The code is here:

handles = guidata(hObject);
Folder = uigetdir('C:\Users\c13459232\Documents\MATLAB'); % selecta folder from which to select files
File = uigetfile(Folder); % select a file
Image = imread(File); % Read image
[rows, columns, numberOfColorChannels] = size(Image);
imshow(Image); % generate the image in a figure
again = true; % again is true by default. the user must select stop to make it false
finalImage = false(rows, columns);
while again
    thisRegion = roipoly;
    % Add this in to the main one
    finalImage = finalImage | thisRegion;
      promptMessage = sprintf('Do you want to add another region?');
      titleBarCaption = 'Continue?';
      buttonText = questdlg(promptMessage, titleBarCaption, 'Yes', 'No', 'Yes');
      if strcmpi(buttonText, 'No')
          again = false;
      end
      labeledImage = logical(finalImage);
end 
X = handles.finishCell;
mask = labeledImage;
for i = 1 : numel(X)
    X{i} = X{i}.*mask;
end
handles.X = X{i};
guidata(hObject, handles);

Here, handles.finishCell is the cell array created previously in my GUI. it is a 1 x 120 cell array and each cell contains a 1024 x 1024 matrix. The Error:

Cell contents reference from a non-cell array object.
Error in hopefully_the_last_window>pushbutton3_Callback (line 185)
    X{i} = X{i}.*mask;
Error in gui_mainfcn (line 96)
        feval(varargin{:});
Error in hopefully_the_last_window (line 42)
    gui_mainfcn(gui_State, varargin{:});
Error in
@(hObject,eventdata)hopefully_the_last_window('pushbutton3_Callback',hObject,eventdata,guidata(hObject))
Error while evaluating uicontrol Call