How to downsample the 3D matrix in matlab??

Due to computational limitations, I need to downsample the 3D (1500x1500x1700) matrix by a factor of 2. The binning process should merg the 2x2x2 voxels and assign the mean intensity value of the group to the corresponding voxel in the reduced image.

Answer 1

[Jan]

X = rand(1500, 1500, 1700);   % 28.5 GB - does not run in the forum!
Y = reshape(X, 2, 750, 2, 750, 2, 850);
Z = squeeze(sum(Y, [1,3,5])) / 8;
size(Z)

[Rizwan Khan]

thanks Jan for your quick reply. I am getting an error if the dimension is odd.

One of my matrix is 1212x1212x1561 and the error is: "Size arguments must be real integers"

[Jan]

@Rizwan Khan: What do you wnt to do, if the dimension is odd? Omit the last vector or include it in the output without averaging? I cannot guess, what you need.

X = rand(1501, 1501, 1701);
s = size(X);
s = s - rem(s, 2);
XX = X(1:s(1), 1:s(2), 1:s(3));  % Crop, Needs a lot of memory...
Y = reshape(X, 2, s(1) / 2, 2, s(2) / 2, 2, s(3) / 2);
Z = squeeze(sum(Y, [1,3,5])) / 8;

[Rizwan Khan]

Yes, I omitted the last vector before downsampling.

thanks Jan

[Kristoffer Walker]

Brilliant Jan. Thank you.