Create an empty array of size (MxN) for xlswrite.

Question

Abhilash Sukumari 2015-6-22

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回答： Image Analyst 2015-6-22

I have an Image which is 1944® x 2592 (C). I would like to take one column at a time; treating each column as an Image and calculate how many pixels among each row of that column contains value > half(max) value of that column. Those number of pixels are to be written to the excel sheet corresponding to it's respective column.

Image: Image

Here is what I have tried so far, I am not able to write it successfully.

 clc;
      sig = rgb2gray(imread('1.bmp')); % read in the image.
      % imshow(sig);
      ArraySize = size(sig); %1944(R) x 2592 (C)
      [maxval, maxloc] = max(sig(:)); % Gives the max and the location
      maxval; % max value
      [maxloc_row, maxloc_col] = ind2sub(size(sig), maxloc); % convert logical 
      %-------------------------------------------------------------------%
      % Count pixels through each column > half(max) value of that column
      %-------------------------------------------------------------------%
      newfilename = 'Results.csv'; % write new values to .csv files
      Array =  zeros(2592,2592);
      % % R = Array(:,1);
      % y = Array(:,2);
      for a = 1: 2592% maxloc_row =  635 maxloc_col = 1094 
         [a_maxval, a_maxloc] = max(sig(:,a)); % search max among every column.
         % maxloc is the row at which maxval is.
         newval = a_maxval/2; % averaged max value
      % New structure for find width
               x = 0; 
               x = Array(:, 1);
               for b = 1: 1944 % maxloc_row =  635 maxloc_col = 1094
      %                R = b;
                  if sig(b,a) > newval
                      x=x+1;
                  end      
               end % End row search
                x;
      % y = x*(2.2); % pixels into microns
                output = [num2cell(x)];
               xlswrite(newfilename, output);
      end % End column search

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Answer 1

James Tursa 2015-6-22

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编辑：James Tursa 2015-6-22

在 MATLAB Online 中打开

If an array has size 2592 x 2, then it is not empty. An empty array has at least one dimension that has size 0. If you mean create an array with zeros, then

Array = zeros(2592,2);

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Abhilash Sukumari 2015-6-22

No, I just want to initialize an array with dimensions: 2592 x 2

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Answer 2

Chad Greene 2015-6-22

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Try

Array = NaN(2592,2) ;

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Abhilash Sukumari 2015-6-22

I am later using xls write to write values into the array created by NaN, it would only write NaN. That is my problem. Let me edit the question to what I am trying to do.

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Answer 3

Jeremy 2015-6-22

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If you are writing to excel then you probably want to use a cell array,

Array = cell(2592,2);

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Abhilash Sukumari 2015-6-22

Please have a look at the script. I am trying to write the x values to the excel. However, the final out in excel seems to show wrong with only one constant value in all 2592 rows.

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Answer 4

Image Analyst 2015-6-22

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I'm surprised this even finished! You definitely don't want to call xlswrite 2592 times or it will take hours. Perhaps you opened up Excel to look at it after only a few of the calls to xlswrite had been executed.

You should create a 2D matrix for output and then put a single call to xlswrite after both "a" and "b" loops have finished.

Other problems: your (badly-named) x is just column 1 of Array every time. And you don't even need the loop over b because you can use the sum function: sum(x>newval) to count the number of pixels more than the half max value (which you chose the poor, non-descriptive name of newval for).