how to reduce the resolution of a matrix?

I have a matrix of dimension 140*140. i want to make it to dimension 35*35 by averaging grids. how can i do it in a simpler way? Actually i want to reduce the dimension by averaging the grids like [(1,1),(1,2),(2,1),(2,2)] and so on....

[Image Analyst]

It's like 1 or 2 lines if you use blockproc(), which is available in the Image Processing Toolbox. Do you have that toolbox? Or you can use mean2() in a for loop (also requires IPT).

Answer 1

[Star Strider]

This executes quickly on your small (140x140) matrix:

M = randn(140, 140);                    % Create Data
for k1 = 1:4:size(M,1)-3
    idxr = 1+fix(k1/4);
    for k2 = 1:4:size(M,2)-3
        idxc = 1+fix(k2/4);
        MF = M(k1:k1+3,k2:k2+3);        % Matrix Frame (4x4)
        MR(idxr,idxc) = mean(MF(:));
    end
end
Look = MR(1:5,1:5)                      % View Sample Results

[trailokya]

Thanks a lot :)

[Star Strider]

My pleasure!

[wesley lima]

hi, i have a similar problem that i am not able to solve, i have a matrix of 922x, 649x492 and i would like it to be 230x173x492.

Answer 2

[Orion]

There was the same problem here

Several solution have been proposed, pick the one you prefer, like

SEPBLOCKFUN

FEX: BlockMean.mex

[trailokya]

thanks