[Image-SIG] format is None after convert('RGB')

[Vitaliyi]

Hi

"""
from PIL import Image
img = Image.open('/tmp/tst.png')

#after following conversion format is unknown. is it correct ?
if img.mode != 'RGB':
    img = img.convert('RGB')

P.S. I'm using python-imaging 1.1.6-1 (from debian)

Thanks