Python PIL: Convert RGBA->P - ValueError: image has wrong mode

Question

Using the Python Imaging Library (PIL) I get a:

"ValueError: image has wrong mode"

when trying to convert an RGBA mode image to a P mode image. I couldn't find any evidence for the fact that it is possible. The material I found on the convert() method doesn't state that it isn't possible. I am wondering if I am doing something wrong or if this is just not possible.

Here is my code:

from PIL import Image

transImage = Image.open("transparent_8_bit.png")
print transImage.mode

transImageRGBA = transImage.convert("RGBA")
print transImageRGBA.mode

transImageP = transImageRGBA.convert('P', palette=Image.ADAPTIVE)
print transImageP.mode

Here is the image "transparent_8_bit.png": http://s24.postimg.org/4xqzu9n4h/transparent_8_bit.png

The output should be:

P
RGBA
P

However, I get this:

P
RGBA
Traceback (most recent call last):
  File "mode_test.py", line 7, in <module>
    transImageP = transImageRGBA.convert('P', palette=Image.ADAPTIVE)
  File "/Library/Python/2.7/site-packages/PIL/Image.py", line 689, in convert
    im = self.im.quantize(colors)
ValueError: image has wrong mode

Is PIL just not able to do this?

Thanks for your help!

PIL has lots of limitations. You've just run into one. You might try Pillow, I don't know if it's any better though. — Mark Ransom, Nov 12 '13 at 18:00
See http://stackoverflow.com/questions/6114534/converting-png32-to-png8-with-pil-while-preserving-transparency — Mark Ransom, Nov 12 '13 at 18:03
@Mark: Fantastic, thank you! I will try that. Sorry for duplicate question. — Kivak Wolf, Nov 12 '13 at 18:22

Python PIL: Convert RGBA->P - ValueError: image has wrong mode

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