how to detect empty rows and columns from 3-D matrix and crop them?

Question

Nibras Abo Alzahab 2018-12-31

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评论： Nibras Abo Alzahab 2018-12-31

采纳的回答： Matt J

在 MATLAB Online 中打开

I have a 3-D matrix as a video. It contains empty (0) zero values along the tree dimentions.

The matrix is represented as a video. So I need to:

if the row along the frames is empty (==0), I want to crop it.
if the column along the frames is empty (==0), I want to crop it

I have an example 3-D dimention but I need a general method.

I have tried to write something but there is something wrong.

Please Help.

%% define the video (3-D matrix)
Frames         = [0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0;0 0 0 0 0];
Frames(:,:,2 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,3 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,4 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,5 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,6 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,7 ) = [0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0;0 0 0 0 0];
Frames(:,:,8 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,9 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,10) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
%% define some varibles
    %% n & m are zeros counters
    %% x,y,z are lengths along the three dimentions
n=0;
m=0;
x=length(Frames(:,1,1));
y=length(Frames(1,:,1));
z=length(Frames(1,1,:));
%% if the row along the frames is empty (==0),crop it.
    %% r for row
    % %% c for columns
    % %% f for frames
for c=1:y
    for r=1:x
        for f=1:z
            if Frames(r,c,f)==0     %detect
                m=m+1;
            end
        end
        if m==25
            Frames(:,c,:) = [];    %crop
        end
    end
end
%% %% if the column along the frames is empty (==0),crop it.
    %% r for row
    % %% c for columns
    % %% f for frames
for r=1:x
    for c=1:y
        for f=1:z
            if Frames(r,c,f)==0    %detect
                n=n+1;
            end
        end
        if m==25
            Frames(r,:,:) = [];    %crop
        end
    end
end

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Answer 1

Matt J 2018-12-31

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https://ww2.mathworks.cn/matlabcentral/answers/437760-how-to-detect-empty-rows-and-columns-from-3-d-matrix-and-crop-them#answer_354500

编辑：Matt J 2018-12-31

在 MATLAB Online 中打开

       
       tmp=any(Frames,3);
       I = any(tmp,2);
       J=  any(tmp,1);
       Frames=Frames(I,J,:);

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Matt J 2018-12-31

Right you are!

Nibras Abo Alzahab 2018-12-31

Works perfectly.

Thank you.

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Answer 2

Stephan 2018-12-31

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编辑：Stephan 2018-12-31

在 MATLAB Online 中打开

Hi,

two lines of code do the job:

Frames = zeros(5,5,10);
Frames(:,:,1 ) = [0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0;0 0 0 0 0];
Frames(:,:,2 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,3 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,4 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,5 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,6 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,7 ) = [0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0;0 0 0 0 0];
Frames(:,:,8 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,9 ) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
Frames(:,:,10) = [0 0 0 0 0;0 0 90 0 0; 0 0 90 0 0; 90 90 90 0 0;0 0 0 0 0];
% crop all empty rows and columns
Frames(:,find(sum(Frames,[1 3])==0),:)=[];
Frames(find(sum(Frames,[2 3])==0),:,:)=[]
disp('Please accept useful answers.')

Best regards

Stephan

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Nibras Abo Alzahab 2018-12-31

Thank you for your answer.

I got an error while using the

Error using sum

Dimension argument must be a positive integer scalar within indexing range.

Frames(:,find(sum(Frames,[1 3])==0),:)=[];

Stephan 2018-12-31

编辑：Stephan 2018-12-31

Hm, works for me. Which Release do you use? however - shortest answer from Matt is a nice one.

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Answer 3

Luna 2018-12-31

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编辑：Luna 2018-12-31

在 MATLAB Online 中打开

Hi,

Try this below:

%% delete zero rows
Frames = reshape(Frames(bsxfun(@times,any(Frames,2),ones(1,size(Frames,2)))>0),[],size(Frames,2),size(Frames,3));
%% delete zero columns
Frames = reshape(Frames(bsxfun(@times,any(Frames,1),ones(size(Frames,1),1))>0),size(Frames,1),[],size(Frames,3));

you will get 3x3x10 matrix