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

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

Answer 1

[Matt J]

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

       Frames=Frames(I,J,:);

[Stephan]

Frames=Frames(J,I,:)

?

[Matt J]

Right you are!

[Nibras Abo Alzahab]

Works perfectly.

Thank you.

Answer 2

[Stephan]

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

[Nibras Abo Alzahab]

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]

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

Answer 3

[Luna]

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

[Stephan]

Hi Luna,

i think the result should be a 4×3×10 matrix. Your code seems to delete row 1, which appears to be wrong, since in slice 1 and in slice 7 there is row 1 different from zero. Due to this, the result has to have at least 4 rows.

[Luna]

There are 10 pages with 5x5. In each page there are 2 rows and 2 columns are completely zeros:

• for pages, 2,3,4,5,6,8,9,10 1st and 5th rows are zeros.
• for pages, 1 and 7 4th and 5th rows are zeros.
• for all pages, 4th and 5th columns are zeros.

so 2 rows and 2 colums will be deleted for each page and there left 3x3 pages.

That means 3x3x10 matrix, isn't it?

[Stephan]

i understand the question that way that all rows and columns shall be cropped, that are zeros on all slices, to get no information lost on the video the matrix represents. Maybe i understand it wrong - in this case you are right.

[Luna]

Ah, OK now I got what you mean. If all the pages have the common zero row/column that should be removed. In this case, you are right. The result will be 4x3x10 matrix.

[Stephan]

The questioner will let us know...

[Nibras Abo Alzahab]

Thank you for your intrest and ansewrs.

Luna is right

I souhld get 4x3x10 matrix.

But in your answer: 3x3x10 matrix