MATLAB: Making coarse matrix from fine resolution matrix

blockprocImage Processing Toolboxresize image

Hi, I am trying to make a coarse resolution matrix of 3600×1800 from a 8640×4320 matrix by summing up the elements of the matrix.
Hi am trying the following: However this doesnot work with fractions (here, 2.4)
%%%%Z1 is the  original 8640x4320 matrix
abc = blockproc(Z1,[2.4,2.4],@(x)sum(x.data));
abc1 = blockproc(abc,[1,2.4],@(x)sum(x.data));

Best Answer

A 3rd approach, more memory conserving and faster,.
Z1=randi(100,8640,4320);
u = 5;       %upsampling factor
d = 12;      %downsampling factor
t = d/u;     %reduction factor
[m,n]=size(Z1);
L1=speye(m); L2=speye(round(m/t))/u;
R1=speye(n); R2=speye(round(n/t))/u;
L=repelem(L2,1,d) * repelem(L1,u,1);
R=(repelem(R2,1,d) * repelem(R1,u,1)).';
tic
abc4= L*(Z1*R);
toc
Note as well that the matrices L and R are reusable on other Z1 of the same size that one might wish to downsample later on.
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