summing along 3rd dimension every 10 frames

Hello,

I have a matrix of 32x32x2500.

I would like to sum it along the third dimension so to have a matrix of 32x32x250 so that along the third dimesion i have summed 10 paged together thus increasing my SNR.

I have tried with something like

sumby10 = zeros(32,32,2500);
for a = 1:11:2500
sumby10(:,:,a) = sum(micron_59frames(:,:,a:a+9),3);
end

but this does not work as it return a matrix of 32x32x2500.

Could someone help please?

Answer 1

[Philippe Lebel]

I would do:

sumby10 = zeros(32,32,250);

for a = 1:250

sumby10(:,:,a) = sum(micron_59frames(:,:,(a-1)*10+1:(a)*10),3);

end

Answer 2

[Stephan]

If A is your matrix:

B = sum(reshape(A,32,32,10,[]),3);

Answer 3

[the cyclist]

Stephan provided a slick one-liner, but I think it might also be useful for you to see what mistakes you made. Here is a corrected version of your original code:

sumby10 = zeros(32,32,250);
for a = 1:250
    idx = (a-1)*10+1:a*10;
    sumby10(:,:,a) = sum(micron_59frames(:,:,idx),3);
end

Note a couple things that are different:

• I preallocated sumby10 to be only length 250 in dimension 3. Your preallocation guaranteed that your result would be the full 2500 in length
• I re-did the loop index. You were using the loop index "a" to write into "slices" 1,11,22,33 etc of the sumby10 matrix. You were leaving the in-between rows equal to zero -- but they were there.
• You were confusing the indexing of the old matrix (needed to span all 2500 rows) with indexing of the new matrix (only needs to span 250 rows)

[Philippe Lebel]

HaHA, i got you!

[the cyclist]

¯\_(ツ)_/¯