如何将PIL.Image对象转换为缓冲区字符串？

Question

sbuf = StringIO()
sbuf.write(decoded_file)
pimg = Image.open(sbuf)

print pimg.size

cimage = StringIO()
pimg.seek(0)
pimg.save(cimage,'jpeg')
contents = cimage.getvalue()
if contents == decoded_file:
   print '1------->> ok!'

＆＃39; decoded_file＆＃39;是一个图像缓冲区字符串。我想转换PIL.Image对象＆＃39; pimg＆＃39;到内容＆＃39;和＆＃39;内容＆＃39;应该等于＆＃39; decoding_file＆＃39;。