CODEWITHSUNDEEP
pythonpython-3.xmatrix
Jame
Jame

Reputation: 3854

How to remove zero slice/images in a Nd matrix in Python?

I have a Nd matrix A with the dimension of (256,256,100). In which,256x256 are height and width, and 100 is the number of images/slice. In the 100 images, they have some images are zero (only background), other images are non-zero (including background and foreground). The background intensity is 0 and foreground intensity is 1. I want to delete/remove zero slices/images from the matrix A. How could I do it in python efficiently?

This is my implementation but I think we can do better

import numpy as np
h, w, c = A.shape
for i in range (c): 
   A_slice=A[:,:,i]
   sum_in= np.sum(A_slice)
   if (sum_in==0):
      np.delete(A,A_slice)

Update: Sorry I missing one requirement. I have a vector B with the shape of (100,). It contained the id of each slice from 1 to 100. When we remove the slice in the matrix A, I also want to remove its id/index in the vector B. Thanks

Upvotes: 0

Views: 234

Answers (1)

hilberts_drinking_problem
hilberts_drinking_problem

Reputation: 11602

We can compute a boolean mask for "zero" images as

zero_mask = A.sum((0,1)) == 0

To remove corresponding images, we can use

A = A[..., ~zero_mask]
B = B[~zero_mask]

Upvotes: 2

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