MATLAB: Storing multiple value in array without overriding.


Below is the code snippet, where I am selecting images one by one, converting a image in 30*30 patch and calculating the standard deviation of patch and then storing that value in excel sheet. But the problem is only the standard deviation of last image is being saved to excel sheet others value are getting over ridden. How to avoid that?
Directory = 'With MA\';
%Imgs = dir(fullfile(Directory,'*.jpg'));
Imgs = dir(Directory);
nfiles = length(Imgs); % Number of files found
for z=1:nfiles
thisname = Imgs(z).name;
thisfile = fullfile(Directory, thisname);
Img = imread(thisfile);
%Img = imread(fullfile(Directory,Imgs(z).name));
imSz = size(I);
patchSz = [30 30];
xIdxs = [1:patchSz(2):imSz(2) imSz(2)+1];
yIdxs = [1:patchSz(1):imSz(1) imSz(1)+1];
patches = cell(length(yIdxs)-1,length(xIdxs)-1);%for patches
stan = cell(length(yIdxs)-1,length(xIdxs)-1);%for standard deviation
for i = 1:length(yIdxs)-1
Isub = I(yIdxs(i):yIdxs(i+1)-1,:);
for j = 1:length(xIdxs)-1
patches{i,j} = Isub(:,xIdxs(j):xIdxs(j+1)-1);%saving patches
stan{i,j} = std2(patches{i,j});%saving standard deviation
xlswrite('output.xlsx', stan);

Best Answer

  • "How to avoid that?"
    Simply by changing the Excel worksheet name on each iteration of the outer loop, e.g.:
    for z=1:nfiles
    F = sprintf('output_%d.xlsx',z);
    Or you could use fileparts to create a name based on the original image filenames, e.g.:
    [~,N] = fileparts(thisname);
    F = sprintf('%s.xlsx',N);
    Note that you should place the xlswrite inside the try section, otherwise your code will export the results from the last imported file, without any warning. Placing so much code inside try is not a good idea, as this hides any errors and bugs in that part of the code. Better code would simply use exist to test for the file (rather than try). I doubt that try does anything useful here anyway, as dir only lists existing files anyway, so most likely you should get rid of try entirely.
    Read this: