Composing matrix from small matrices

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bikekowal Marcin Kowalski
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.

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采纳的回答

Image Analyst
Image Analyst 2012-6-2
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!!!
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bikekowal Marcin Kowalski
bikekowal Marcin Kowalski 2012-6-4
Oh, Why I didn't see this answer before? This is what I am talking about :) Thanks so much :)

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更多回答（4 个）

bikekowal Marcin Kowalski
OK, I will remeber. Thanks for that.
Ryan
Ryan 2012-6-2
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.
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]);
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Ryan
Ryan 2012-6-4
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.

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Walter Roberson
Walter Roberson 2012-6-4
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) );
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