[Python] How to save an image with transparency

I start with an image that has transparent areas. I want to use perspective transform (see code below) and then save the result with imsave, savefig, or anything that works. I have no trouble saving the image, but I lose the transparency. How does one save the resultant image && retain transparency.

import os
import cv2 as cv
import numpy as np
import matplotlib.pyplot as plt

def PerspectiveTransform():
root = os.getcwd()

imgPath = os.path.join(root, 'images/circle_grid3.png') # source image has transparent area
img = cv.imread(imgPath)
img = cv.cvtColor(img,cv.COLOR_BGR2RGBA)

p1 = np.array([[0,0],[426,0],[0,426],[426,426]],dtype=np.float32)
p2 = np.array([[0,0],[506,0],[68,873],[438,873]],dtype=np.float32)
# array: topleft, topright, bottomleft, bottomright

T = cv.getPerspectiveTransform(p1,p2)
imgTrans = cv.warpPerspective(img,T,(506,873))

plt.figure()

plt.subplot(121)
plt.imshow(img)
plt.plot(p1[:,0],p1[:,1],'g.')

plt.subplot(122)
plt.imshow(imgTrans)
plt.plot(p2[:,0],p2[:,1],'r.')


plt.savefig('chart8.tiff', dpi=300, transparent=True)
plt.imsave('source8.png', img, dpi=300, format="png")
plt.imsave('destination8.tiff', imgTrans, dpi=300, format="tiff")
plt.imsave('destination8.png', imgTrans, dpi=300, format="png")


plt.show()

if __name__ == '__main__':
PerspectiveTransform()


imsave() does not expect keyword argument 'transparent'. savefig() gives a transparent background, but not in the figures/

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