Cut region of interest images from 3D stack with known indices and without for loop

Question

Kevin Jansen 2023-3-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1921830-cut-region-of-interest-images-from-3d-stack-with-known-indices-and-without-for-loop

评论： Kevin Jansen 2023-3-2

采纳的回答： Matt J

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Hi! I am having trouble cutting region of interest from a 3D stack.

A small example, I have a 3x3x2 array of:

array = [1,2,3;4,5,6;7,8,9];
array(:,:,2) = [1,2,3;4,5,6;7,8,9];

mini image indices:

left = [1,2]
right = [2,3]
top = [1,2]
bottom = [2,3]

create mini images:

miniImages = array(top:bottom,left:right,:)

result:

miniImages(:,:,1) = [1,2;4,5]
miniImages(:,:,2) = [1,2;4,5]

However, I want the result to be:

miniImages(:,:,1) = [1,2;4,5]
miniImages(:,:,2) = [5,6;8,9]

It seems that it only uses the first indices in variables left, right, top, bottom to create all mini images.

Anyone know how to solve this? Currently I use a for loop over the indices, but I want to make it faster.

Thanks!

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Matt J 2023-3-2

miniImages(:,:,2) = [5,6;7,8]

Don't you mean [5 6;8;9] ?

Kevin Jansen 2023-3-2

Yes! That was a mistake, I will try to edit it.

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Answer 1

Matt J 2023-3-2

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https://ww2.mathworks.cn/matlabcentral/answers/1921830-cut-region-of-interest-images-from-3d-stack-with-known-indices-and-without-for-loop#answer_1183765

编辑：Matt J 2023-3-2

在 MATLAB Online 中打开

I doubt anything will be faster than a loop, but you can try this:

array = [1,2,3;4,5,6;7,8,9];
array(:,:,2) = [1,2,3;4,5,6;7,8,9]
array = 
array(:,:,1) =

     1     2     3
     4     5     6
     7     8     9


array(:,:,2) =

     1     2     3
     4     5     6
     7     8     9
left = [1,2];
top = [1,2];
bottom = [2,3];
right = [2,3];
args=cellfun(@(z)reshape(z,1,1,[])    , {left,top,bottom,right} ,'un' ,0);
[L,T,B,R]=deal(args{:});
[m,n,p]=size(array);
[I,J]=ndgrid(1:m,1:n);
lidx=T<=I & I<=B & L<=J & J<=R;
miniImages=reshape( array(lidx)  ,B(1)-T(1)+1,R(1)-L(1)+1,[])
miniImages = 
miniImages(:,:,1) =

     1     2
     4     5


miniImages(:,:,2) =

     5     6
     8     9

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Kevin Jansen 2023-3-2

Hey, awesome it worked! Much more difficult than I thought it would be. My code with larger arrays ran 380x faster without the for loop. Thank you so much!

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