How to sum 20 images in a loop

Question

Ivan Shorokhov 2014-12-9

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/166053-how-to-sum-20-images-in-a-loop

编辑： Ivan Shorokhov 2015-1-14

采纳的回答： Geoff Hayes

在 MATLAB Online 中打开

Hello everybody I'm wondering how I can sum more than 15 images in a loop?

Here is the code:

imgs=<500x500x20 uint8> % 20 images
NI=size(imgs,3);                                % NI = Number of Images (i.e. = 20)
      for e=2:NI                                  % e = from 2 to 20 with step 1 (i.e 2,3,4....20)
          I1(:,:,e-1)= imgs(:,:,1)-imgs(:,:,e);   % subtract all other 19 images form the first image
          figure; imshow(I1(:,:,e-1),[]);         % plot results of each single subtractions 
      end

% Now I want to sum all subtracted images, how can I do it?

I have tried:

for i=1:size(I1,3)
        I2= sum(I1(:,:,i));
end
for i=2:size(I1,3)
    i3= imadd(I1(:,:,i),I1(:,:,i-1));
end

Can anyone give me line of code how to do it?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Geoff Hayes 2014-12-10

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/166053-how-to-sum-20-images-in-a-loop#answer_161866

在 MATLAB Online 中打开

Ivan - as all of your images are already of dimension 500x500, what is the imresize supposed to accomplish since the code seems to be trying to resize the images to the same dimension?

As for summing the 19 images, you want to just iterate over each one and add to the previous. Something like

 % initialize the image sum to the first image in the array
 I2 = I1(:,:,1);
 % now sum with the subsequent 18 images
 for k=2:size(I1,3)
     I2 = I2 + I1(:,:,k);
 end

Or, if you want to use imadd, then do

 % initialize the image sum to the first image in the array
 I2 = I1(:,:,1);
 % now sum with the subsequent 18 images
 for k=2:size(I1,3)
     I2 = imadd(I2,I1(:,:,k));
 end

The problem with your code, in both examples, is that you never re-use the I2 or i3 in subsequent additions, and so they are initialized with the last pair of matrices (or single matrix) only. As for using sum, this operation will sum the elements along one dimension which is not what you want.

Note that if you just use regular addition or imadd, if the summed value exceeds the range of the uint8 type, then it will be truncated to that maximum value. For example,

uint8(254) + uint8(42)

returns a value of

255

6 个评论
显示 4更早的评论隐藏 4更早的评论

Image Analyst 2015-1-8

And I'm still baffled, Ivan, as to why you even want to use a loop at all instead of just using the sum() function like I suggested. It's especially baffling since imadd will clip, like it says in the documentation "If X and Y are integer arrays, elements in the output that exceed the range of the integer type are truncated, and fractional values are rounded." Did you know that? sum() does not have that clipping problem, so tell me why you're using imadd() and not sum().

Ivan Shorokhov 2015-1-14

编辑：Ivan Shorokhov 2015-1-14

Dear Image Analyst, sorry for making you baffled, initially I wanted to use a loop to add extra functions inside the loop. But now I realised that you are right, and I will use the sum(), instead of inimadd(). Thank you to both of you for your help!

请先登录，再进行评论。

Answer 2

Image Analyst 2014-12-10

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/166053-how-to-sum-20-images-in-a-loop#answer_161865

编辑：Image Analyst 2014-12-10

在 MATLAB Online 中打开

Did you try not using a loop and simply using the sum function?

I2 = sum(double(I1), 3);

??? What you are doing is taking a slice, and summing the rows along the columns, so you have a row vector where each element is the sum along the columns.