from PIL import Image
import numpy as np

#... get array s.t. arr.shape = (3,256, 256)
img = Image.fromarray(arr, 'RGB')
img.save('out.png')

>>> arr = np.random.uniform(size=(3,256,257))*255

>>> arr.T.shape
(257, 256, 3)

>>> arr.transpose(1, 2, 0).shape
(256, 257, 3)

>>> arr = np.random.uniform(size=(3,256,256))*255
>>> arr = np.ascontiguousarray(arr.transpose(1,2,0))
>>> img = Image.fromarray(arr, 'RGB')
>>> img.save('out.png')

arr = np.random.uniform(size=(3,256,256))*255
img = Image.fromarray(arr.T, 'RGB')
img.save('out.png')

arr = np.random.uniform(size=(3,256,256))*255
img = cv2.merge((arr[2], arr[1], arr[0]))  # b,g,r
cv2.imwrite('out.png', img)