Composing matrix from small matrices

Hi all,

I have a random matrix generated by a rand function. The matrix size is 60x60 (a small array). I want to resize this matrix up to 600 x 600 (let's call it big array). I want that every 10x10 pixels from the 'big array' was filled by a corresponding pixel from a small array. For example pixels (1:10, 1:10) from a big array would have a '1' if the small_array(1,1) equals '1'.

How to do that? I tried to treat this array as an image and use imresize funtion, but it gives blurred image. I also tried following code, but there is something missing and I dont know what it is exactly.

size = 60;
Phi = rand(size,size)>0.5;
BigPhi = zeros(600,600);

for i=1:60
    n=(i-1)*10
    i
    if i==1
        BigPhi(i:(i*10),i:(i*10))=Phi(i,i);
    end;
    if i>1
        BigPhi((i-1)*10:(i*10),(i-1)*10:(i*10))=Phi(i,i);
    end
end

I will appreciate any help.

Answer 1

[Image Analyst]

One line of code:

BigPhi = imresize(Phi, [600 600], 'nearest');

By the way don't do this:

size = 60;

By doing so, you just blew away the very useful built in size() function!!!

[bikekowal Marcin Kowalski]

Oh, Why I didn't see this answer before? This is what I am talking about :) Thanks so much :)

Answer 2

[bikekowal Marcin Kowalski]

OK, I will remeber. Thanks for that.

Answer 3

[Ryan]

clear m n o p

% Generate matrices
 sizeA = 60;
 fill_size = 10;
 Phi = rand(size,size)>0.5;
 BigPhi = zeros(600,600); 

% Define BigPhi position counters
 o = 1;
 p = 1;

%Fill BigPhi
 for m = 1:sizeA
   for n = 1:sizeA
     BigPhi(p:m*fill_size,o:n*fill_size) = repmat(Phi(m,n),[fill_size fill_size]);
    p = p + fill_size;
  end
 o = o + fill_size;
 end

I don't have Matlab on this computer to test it, but I believe this should do what you're asking for. The m and n counters keep track of your position in Phi so you can pull out the appropriate data and also dictate the end range of where you will stop filling BigPhi with that value. The o and p counters provide a way to keep track of where to start filling (1,11,21, etc).

help for repmat http://www.mathworks.com/help/techdoc/ref/repmat.html.

B = repmat(A,[m n]) creates a larger m*n matrix, B, by repeating A.

[Ryan]

Go with Image Analyst answer. Much quicker than mine.

Answer 4

[bikekowal Marcin Kowalski]

Thank you for the code, but it doesn't work correctly. There is some mistake

"Subscripted assignment dimension mismatch." in this line:

BigPhi(p:m*fill_size,o:n*fill_size) = repmat(Phi(m,n),[fill_size fill_size]);

[Ryan]

Ahhh I believe that the code is trying to access "fill_size*m" extra members to fill BigPhi... have you tried Image Analyst's way? If you eliminate "BigPhi = Zeros(600,600)" then this should work.

perhaps try the loops set to 1:(sizeA-1) ? Maybe set it to BigPhi = Zeros(610,610) to preallocate?

I do not currently have Matlab at my disposal to test this.

[bikekowal Marcin Kowalski]

No, still the same error.

[Ryan]

I took a quick look at it and fixed the first bug, but ran into another. The skeleton is there if you'd like to debug and figure out where in the algebra it is getting screwed up, but I'd suggest trying what Image Analyst did. I don't have the time to try to fix it.

Answer 5

[Walter Roberson]

I would have to test to be sure this is exactly right, but I believe you can use

BigImage = kron(SmallImage, eye(10));

Be sure to test that this returns the correct class() for your purposes; you might need

BigImage = cast( kron(SmallImage, eye(10)), class(SmallImage) );

[bikekowal Marcin Kowalski]

Unfortunately this is not what I want to achieve. This code gives an array of diagonals.

[Andrei Bobrov]

BigImage = kron(SmallImage, ones(10));

[Walter Roberson]

That makes sense, andrei.

[bikekowal Marcin Kowalski]

Yes, this is it! Thanks a lot guys!