create layers array and perform median python

Question

I've been struggling to create an array of layers, and each layer contains an image. Then perform median on this layer array to get one image.

Every added layer (from o[i,j]) is 2D with shape (460, 640) containing floats.

In matlab you could easily do:

r_n = cell(1, num_filters);

for i = 1:num_filters
    layers = o{i,1};
    for j = 2:num_faces
        layers = cat(3, layers, o{i,j});
    end
    r_n{i} = median(layers, 3);
end

The thing that I'm new to python, and maybe I'm still thinking in a Matlabish way

I tried:

k=0;
for i in range(0,num_filters):
    layers = o[i+k,0]
    for j in range(1,num_faces):
        layers = np.array([layers,o[i,j]]);  ### HERE IS MY PROBLEM
    print layers.shape;
    r_n[i] = np.median(layers, axis = 0);
    k = k + 65;        

my layers array is wrong... what is a proper way to do it ?

Answer 1

You could stack them with np.stack (creating a new axis) and then apply the median:

# just some random arrays
layers = [np.random.random((10, 10)), 
          np.random.random((10, 10)), 
          np.random.random((10, 10))]  
np.median(np.stack(layers, axis=0), axis=0)

Or with a for-loop:

layers = [o[i+k,0]]
for j in range(1,num_faces):
    layers.append(o[i,j])
np.median(np.stack(layers, axis=0), axis=0)