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Topic: speeding up assigning values to a matrix
Replies: 7   Last Post: Apr 8, 2013 3:52 AM

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Posts: 77
Registered: 6/6/12
Re: speeding up assigning values to a matrix
Posted: Apr 5, 2013 3:24 PM
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I think I've come to the ultimate optimization.
(now I'm at home with a 5 years old laptop, so the performance are way slower than on the verrifast office PC).
This time the quoted times are on this laptop, so definitely longer
I do this:
maskR= zeros(size(mask),'uint8'); %create 3 RGB separate masks of uint8, same size of the original
toc(ts); %less than 1 ms
toc(ts); %180ms
maskG(mask==1|mask==2) = 255;
maskB(mask==2|mask==3) = 255;
%180ms each
maskC = cat(4,maskR,maskG,maskB);
toc(ts); %140 ms

instead doing;
maskC = zeros (512,512,87,3,'uint8');
maskC(:,:,:,1)= uint8((mask==1))*255;
takes 800ms, 4 times more for each "color". And this is the second best optimization.

The original code
maskC(:,:,:,1) = (mask==1)*255,
takes, on this pc, 1.2 s.
Therefore I've sped up by a factor 10!
I don't think I can get any better. Anyway I think the problem in this "long" execution times are in the fact that I'm dealing with a 76MB matrix...

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