BytesIO replaces transparency in PNG files with black background

Question

I want to keep transparent background at my 'image' variable.

If I write into a file, image looks fine. I mean image has a transparent background.

with urllib.request.urlopen(request) as response:
     imgdata = response.read()
     with open("temp_png_file.png", "wb") as output:
         output.write(imgdata)

However, if I keep the image data in BytesIO, transparent background becomes a black background.

with urllib.request.urlopen(request) as response:
     imgdata = response.read()
ioFile = io.BytesIO(imgdata) 
img = Image.open(ioFile)
img.show()

(Above code piece, img.show line shows an image with black background.)

How can I keep a transparent image object in img variable ?

Answer 1

Two things...

---

Firstly, if you want and expect an RGBA image when opening a file with Pillow, it is best to convert whatever you get into that - else you may end up trying to display palette indices instead of RGB values:

So change this:

img = Image.open(ioFile)

to this:

img = Image.open(ioFile).convert('RGBA')

---

Secondly, OpenCV's imshow() can't handle transparency, so I tend to use Pillow's show() method instead. Like this:

from PIL import Image

# Do OpenCV stuff
...
...

# Now make OpenCV array into Pillow Image and display
Image.fromarray(numpyImage).show()