Reading out values from one numpy array where there is true in another numpy array

Question

I have two numpy arrays of even size. One is the pixel values and another one is a "mask", where I have True or False, meaning if this is part of the cut out image or just "filled" up image to get an even size. So for example, if this is one column of the mask:

array([False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False,  True,  True,  True,  True,  True,
        True,  True,  True,  True,  True,  True,  True,  True,  True,
       False, False, False, False], dtype=bool)

Now I would like to (column by column) read out only the image values when there is a True in the mask array.

What is the best way to do this?

Thanks :)

(using python3 btw)

NumPy supports boolean indexing, so if I've understood your question you should just be able to write something like pixels[mask]. — Alex Riley
– Alex Riley, Commented Apr 20, 2016 at 20:30

Thomite · Accepted Answer · 2016-04-20 20:27:11Z

1

I think the function you're looking for is numpy.where. This will give you an array of indices where a condition is True.

answered Apr 20, 2016 at 20:27

Thomite

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