Add an extra column to the existing matrix (MAT file)

I have a mat file and its size is 1243x1182x3 . (please note that size of the Mat file is NOT consistent and there are about 50-60 MAT files in one folder). And i want to add an extra column to the Mat file? (columns in the matrix are x and y columns. And my requirement is to add a 3rd column which is z column to the matrix) I guess i can do two things:

1. Use save(filename, ..., '-append')But the class of my MAT file is uint8. But the examples i have seen were in the class Double.
2. Or else i have to write it in a cell array

for n=1:10  
A=rand(5);  
[i,j,vals]=find(A);  
data={[i,j,vals]};  
save('data','data','-append');  
end

As size of these MAT files are inconsistent and they are in RGB file formats hence i am not sure how to tackle this matter.

Can anyone kindly guide me to resolve this issue?

[Azzi Abdelmalek]

You mean the size and the class of the variable saved in a mat file. And what this example has to do with your problem?

[Walter Roberson]

1243x1182x3 sounds like it is an RGB image.

You speak of adding a third column, but that has 1182 columns, and 3 planes. After the additional column was added, what would you expect the size of the new matrix to be? Are you looking for something like,

[y, x] = find( any(data,3) );
z = f(x, y);
new_data = [x(:), y(:), z(:)];

The any(data,3) would return true for anywhere in the 1243 x 1182 array that at least one of the third dimension values was non-zero. Then the find() on that would return row and column pairs where that was true -- essentially it would return the locations of the non-black pixels. Then you process those indices (possibly ignoring the content of the data) to determine corresponding z; after that you create a something-by-3 array of x, y, and z values ?

[Chathu]

@ Azzi: i wasn't sure how to move forward, hence i added what i plan to do and expect that someone would shed some light to solve my issue. Sorry for the confusion and any inconvenience caused.

@ Walter: Thanks alot. you're right. This is an RGB image. Well, my goal is to build a 3D model(by employing above mention MAT files, as they are segmented images).

{i would have mentioned my goal beforehand, i totally forgot to mention it, i am sorry} The third column going to be the Slice thickness which i need to give it manually to the above said matrix. I guess i can extract x,y coordinates using find fun. But how to add the slice thickness as different files have different dimensions :(

[Chathu]

well, those MAT files(size:1243x1182x3, RGB )have different rows and columns from file to file. What i did so far:

load ('P3290190.mat') % load the MAT file in the workspace

[x, y] = find( any(Data,3) );

k=find(x) % Find non zero elements in X coordinate

l=find(y) % Find non zero elements in Y coordinate

Following are the results when i typed, k=find(x) and l=find(y), respectively:

x: 285447 285448 285449 285450 285451 285452

y: 285447 285448 285449 285450 285451 285452

How to go beyond this point, if i want to add another column (eg:z axis) to the MAT files (remember, MAT files are different sizes...). So my next step would be to convert these MAT files (x coordinates, y coordinates , z coordinates) and convert it to VTK.

Can anyone kindly help me to solve this issue. Thank you in advance.

[Walter Roberson]

The x and y values returned from the find(any(Data,3)) will never be 0.

[Chathu]

Alright:-)

Answer 1

[Walter Roberson]

xyz = [x, y];
xyz(:,3) = SliceThickness;
save('P3290190.mat', 'xyz', '-append')

[Chathu]

omg,that works like a charm.

Thanks a million, Walter. I am very much grateful to you for your kindest support,it's immeasurable. Thank you once again:)