Filtering 3D matrix above certain threshold?

Question

I have two 3D matrices of the same size. Say, A contain values ranging from 0 to 1 and B contains certain discrete values.

I want to extract values from B matrix which are above certain threshold values in A?

Can anyone help me out?

Answer 1

Like this? Have a look at logical indexing.

% Input.
B = reshape(1:18, 2, 3, 3)
A = rand(size(B))

% Threshold.
thr = 0.75

% Output.
output = B(A > thr)

B =
ans(:,:,1) =
   1   3   5
   2   4   6
ans(:,:,2) =
    7    9   11
    8   10   12
ans(:,:,3) =
   13   15   17
   14   16   18

A =
ans(:,:,1) =
   0.80533   0.24370   0.89180
   0.90358   0.22422   0.69243
ans(:,:,2) =
   0.119366   0.168337   0.771999
   0.206004   0.065481   0.979772
ans(:,:,3) =
   0.0057303   0.1469925   0.0556628
   0.0454038   0.4122576   0.9847027

thr =  0.75000

output =
    1
    2
    5
   11
   12
   18