How to get alpha value of a PNG image with PIL?

Question

How to detect if a PNG image has transparent alpha channel or not using PIL?

img = Image.open(\'example.png\', \'r\')
has_alpha = img.mode == \'RGBA\'
         


        

Answer 1

I tried this:

from PIL import Image
import operator, itertools

def get_alpha_channel(image): 
   try: 
      alpha_index = image.getbands().index('A')
   except ValueError:
      # no alpha channel, so convert to RGBA
      image = image.convert('RGBA')
      alpha_index = image.getbands().index('A')
   alpha_getter = operator.itemgetter(alpha_index)
   return itertools.imap(alpha_getter, image.getdata())

This returned the result that I was expecting. However, I did some calculation to determine the mean and standard deviation, and the results came out slightly different from imagemagick's fx:mean function.

Perhaps the conversion changed some of the values? I'm unsure, but it seems relatively trivial.