Concatenate the produced arrays from a for loop?

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iontrap
iontrap 2020-8-14
评论： Stephen23 2020-8-22
I am trying to calculate the mean and standard deviation of the R,G,B channels of 50 image files in sequence. I would like to write out the mean of these into a single column vector per color. This would result in 3 50x1 column vectors - one each for R, G, B. I am able to calculate the means, but they are being output separately. Thanks
for j = 1:50
fname = sprintf('test (%d).bmp',j);
image4d = imread(fname);
Mean = squeeze(mean(image4d, [1 2]));
MeanR = Mean(1,:)
MeanG = Mean(2,:)
MeanB = Mean(3,:)
end
My output looks like:
MeanR =
25.1629
MeanG =
3.1821
MeanB =
0
MeanR =
31.6650
MeanG =
3.6093
MeanB =
0
.
.
For all 50 images.
  2 个评论
Sara Boznik
Sara Boznik 2020-8-14
Maybe you can add one for loop and define k=0 and in each loop is k=k+1, and after you write the
MeanR(k,:) = Mean(1,:)
I am not sure but you can try it.
Wish you best of luck.
iontrap
iontrap 2020-8-14
Unfortunately, this yields a 50x1 column of duplicate results for one image.

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采纳的回答

Matt J
Matt J 2020-8-15
编辑：Matt J 2020-8-15
Mean=nan(50,3);
for j = 1:50
fname = sprintf('test (%d).bmp',j);
image4d = imread(fname);
Mean(j,:) = mean( image4d , [1 2]) ;
end
MeanR=Mean(:,1);
MeanG=Mean(:,2);
MeanB=Mean(:,3);
  3 个评论
显示 1更早的评论
Matt J
Matt J 2020-8-15
It just pre-allocates an array of NaNs so that you have somewhere to put the data generated by the loop, e.g.,
>> nan(5,3)
ans =
NaN NaN NaN
NaN NaN NaN
NaN NaN NaN
NaN NaN NaN
NaN NaN NaN

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