Decoding base64 from POST to use in PIL

Question

I'm making a simple API in Flask that accepts an image encoded in base64, then decodes it for further processing using Pillow.

I've looked at some examples (1, 2, 3), and I think I get the gist of the process, but I keep getting an error where Pillow can't read the string I gave it.

Here's what I've got so far:

import cStringIO from PIL import Image import base64  data = request.form image_string = cStringIO.StringIO(base64.b64decode(data['img'])) image = Image.open(image_string) 

which gives the error:

IOError: cannot identify image file <cStringIO.StringIO object at 0x10f84c7a0> 

Answer 1

You should try something like:

from PIL import Image from io import BytesIO import base64  data['img'] = '''R0lGODlhDwAPAKECAAAAzMzM/////wAAACwAAAAADwAPAAACIISPeQHsrZ5ModrLl N48CXF8m2iQ3YmmKqVlRtW4MLwWACH+H09wdGltaXplZCBieSBVbGVhZCBTbWFydFNhdmVyIQAAOw=='''   im = Image.open(BytesIO(base64.b64decode(data['img']))) 

Your data['img'] string should not include the HTML tags or the parameters data:image/jpeg;base64 that are in the example JSFiddle.

I've changed the image string for an example I took from Google just for readability purposes.

Answer 2

There is a metadata prefix of data:image/jpeg;base64, being included in the img field. Normally this metadata is used in a CSS or HTML data URI when embedding image data into the document or stylesheet. It is there to provide the MIME type and encoding of the embedded data to the rendering browser.

You can strip off the prefix before the base64 decode and this should result in valid image data that PIL can load (see below), but you really need to question how the metadata is being submitted to your server as normally it should not.

import re import cStringIO from PIL import Image  image_data = re.sub('^data:image/.+;base64,', '', data['img']).decode('base64') image = Image.open(cStringIO.StringIO(image_data))