"Index exceeds matrix dimensions" error during performing RGB channel separation

Question

rakib mostafiz 2021-7-24

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https://ww2.mathworks.cn/matlabcentral/answers/885219-index-exceeds-matrix-dimensions-error-during-performing-rgb-channel-separation

评论： Simon Chan 2021-7-25

采纳的回答： Simon Chan

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The purpose of my code is -

scan all image from a folder
calculate entropy for each of RGB channel
export data to a xlsx file

my code :

folder = 'F:\images\';
filePattern = fullfile(folder, '*.png');
myFiles = dir(filePattern); % the folder inwhich ur images exists
for k = 1 : length(myFiles)
  fullFileName = fullfile(folder, myFiles(k).name);
  I= fullFileName;
Red = I(:,:,1);
Green = I(:,:,2);
Blue = I(:,:,3);
%I = I(:); % Vectorization of RGB values
p = imhist(Red); % Histogram
p(p == 0) = [ ];% remove zero entries in p
p = p ./ numel(I); % normalize p so that sum(p) is one.
Er(k) = round(-sum(p.*log2(p)),3);
p = imhist(Blue); % Histogram
p(p == 0) = [ ];% remove zero entries in p
p = p ./ numel(I); % normalize p so that sum(p) is one.
Eb(k) = round(-sum(p.*log2(p)),3);
xlswrite('myfile.xlsx', [Er(k),Eb(k)], 'Sheet 1');
end

But i am getting following error:

Index exceeds matrix dimensions.
Error in test1 (line 9)
Green = I(:,:,2);

I couldn't solve this problem. Can anyone help me please?

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Answer 1

Simon Chan 2021-7-25

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https://ww2.mathworks.cn/matlabcentral/answers/885219-index-exceeds-matrix-dimensions-error-during-performing-rgb-channel-separation#answer_753274

在 MATLAB Online 中打开

According to your code shown above, variable I is only a file name in the beginning of the for loop.

Have you do imread or some other command to read the images?

for k = 1 : length(myFiles)
  fullFileName = fullfile(folder, myFiles(k).name);
  I= imread(fullFileName);                                          % I added imread
Red = I(:,:,1);
Green = I(:,:,2);
Blue = I(:,:,3);

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rakib mostafiz 2021-7-25

All of the data are placed side by side column. Can it be done by two column only?

Simon Chan 2021-7-25

在 MATLAB Online 中打开

Doing transpose:

xlswrite('myfile.xlsx', [Er',Eb'], 'Sheet 1');

or

writematrix([Er',Eb'],'myfile.xlsx');

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Answer 2

Yongjian Feng 2021-7-24

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https://ww2.mathworks.cn/matlabcentral/answers/885219-index-exceeds-matrix-dimensions-error-during-performing-rgb-channel-separation#answer_753254

Most likely your image is just a grey scale one. Only one channel.

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rakib mostafiz 2021-7-24

Those image are colorful. Moreover, if i perform this operation on a single image rather than looping out all image from folder, it works just fine! But when i try to read each image and perform this operation, it showing that error. I really dont understand the problem here

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