“Transform” Numpy Arrray: Move Dimension

I'm creating array a:

import numpy as np
a = np.zeros((3, 10, 10), np.uint8)
a[1,5,5] = 255


with a red dot in the center, where the RGB is the first dimension. Then I plot it using matplotlib:

import matplotlib.pyplot as plt
plt.imshow(a)


But of course this doesn't work because imshow expects an array with dimensions (10, 10, 3) and I am feeding it an array with dimensions (3, 10, 10). How could I 'flip' the array so that the RGB is the third dimension, instead of the first?

1 Answer
1

What you need is swapaxes.

swapaxes

import numpy as np
a = np.zeros((3, 10, 10), np.uint8)

print(a.shape) #(3,10,10)

print(np.swapaxes(a,0,2).shape) #(10,10,3)


See documentation.

np.swapaxes(a,0,2) equals to np.transpose(a, (2,1,0)).

np.swapaxes(a,0,2)

np.transpose(a, (2,1,0))

There is another option which is np.transpose(a, (1,2 0)).

np.transpose(a, (1,2 0))

As always, transpose matrix can have two versions which produce similar result but with different 3-dimensional rotational symmetry.

It depends on if the mirror matrix affect your result, you should carefully test if it makes difference.

np.transpose(a, (1,2 0))

np.transpose(a, (2,1,0))

np.moveaxis(a, 0, 2)

np.transpose(a, (1, 2, 0))

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