python: convert base64 encoded png image to jpg

问题:

I want to convert some base64 encoded png images to jpg using python. I know how to decode from base64 back to raw:

import base64 
pngraw = base64.decodestring(png_b64text)

but how can I convert this now to jpg? Just writing pngraw to a file obviously only gives me a png file. I know I can use PIL, but HOW exactly would I do it? Thanks!

回答1:

You can use PIL:

data = b'''iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAYAAACNiR0NAAAAAXNSR0IArs4c6QAAAIBJRE
          FUOMvN08ENgCAMheG/TGniEo7iEiZuqTeiUkoLHORK++Ul8ODPZ92XS2ZiADITmwI+sWHwi
          w2BGtYN1jCAZF1GMYDkGfJix3ZK8g57sJywteTFClBbjmAq+ESiGIBEX9nCqgl7sfyxIykt
          7NUUD9rCiupZqAdTu6yhXgzgBtNFSXQ1+FPTAAAAAElFTkSuQmCC'''

import base64
from PIL import Image
from io import BytesIO

im = Image.open(BytesIO(base64.b64decode(data)))
im.save('accept.jpg', 'JPEG')

In very old Python versions (2.5 and older), replace b''' with ''' and from io import BytesIO with from StringIO import StringIO.

回答2:

Right from the PIL tutorial:

To save a file, use the save method of the Image class. When saving files, the name becomes important. Unless you specify the format, the library uses the filename extension to discover which file storage format to use.

Convert files to JPEG

import os, sys
import Image

for infile in sys.argv[1:]:
    f, e = os.path.splitext(infile)
    outfile = f + ".jpg"
    if infile != outfile:
        try:
            Image.open(infile).save(outfile)
        except IOError:
            print "cannot convert", infile

So all you have to do is set the file extension to .jpeg or .jpg and it will convert the image automatically.