How to resize a 3D matrix?

Hi, I want to reduce the size of a 3D image by averaging the values in 3D. For example if the image is 160*216*176. I wrote the code below to process the image to average the values in every 4*4*4 cube thereby creating a new matrix that is 40*54*44 in size.my code is below

X(1:40)=4;

Y(1:54)=4;

Z(1:44)=4;

A=mat2cell(imagestack_1,[X],[Y],[Z]);

average=cellfun(@mean2,A);

But this shows an error

Error using mat2cell (line 97)
Input arguments, D1 through D3, must sum to each dimension of the input matrix size, [160  216  176].'

Anyone who knows Please guide me!!

[KSSV]

What version you are using? Are you sure of size of imagestack_1 ? It worked for me without error on random data of size 160*216*176.

[Sandhiya Prakash]

I am using MatlabR2016a.

[Sandhiya Prakash]

I think i must give variable in which 3D image is stored instead of imagestack_1. Kindly guide me.I am new to matlab.

Answer 1

[Walter Roberson]

You probably had previous values in your X, Y, or Z, making them longer than what would be created with just the above code.

[Walter Roberson]

Example:

imagestack_1 = rand(160, 216,  176);

X = 4 * ones(1,40);
Y = 4 * ones(1,54);
Z = 4 * ones(1,44);

A = mat2cell(imagestack_1, X, Y, Z);
average = cellfun(@mean2, A);

[Sandhiya Prakash]

Thank you sir..its working.I hav anothe doubt.I am having a 160*216*176 input 3D image. For a given voxel i need to consider 26 neighbouring 3x3x3 patch.(now 27 scalar values)Then consider all 26 neighbouring conventional 3x3x3 patches and compute average intensity for all these neighbouring patches.(So totally i have 53 scalar intensity values).How to perform this?

[Walter Roberson]

What is the difference between a "neighbouring 3x3x3 patch" and a "conventional 3x3x3 patch" ?

Is that 53 scalar intensity values per voxel, or 53 total over the entire data?

It would help if you could give the calculation formula in terms of indexes. For example,

conventional = M(I-1:I+1, J-1:J+1, K-1:K+1);
mean_conventional = mean2(conventional);
unconventional = conventional;
unconventional(2,2,2) = [];            %center point not included in mean
mean_unconventional = mean2(unconventional);

[Sandhiya Prakash]

Thank U sir! I have a doubt in looping.

my code is

 for I=1:160
    for J=1:216
        for K=1:176
           conventional = data(I-1:I+1, J-1:J+1, K-1:K+1);
           mean_conventional = mean2(conventional);
           unconventional = conventional;
           unconventional(2,2,2) = [];            %center point not included in mean
           mean_unconventional = mean2(unconventional);
        end
    end
end

but it gives error like,

Subscript indices must either be real positive integers or logicals.

[Walter Roberson]

The boundary points do not have 27 neighbors. You should either calculate only on the interior, or you should define what you want the boundary calculation to be.

[SojM]

After the resize of the matrix, how to save new 3D matrix as stack of 2D images?