from PIL import Image

try:
	im = Image.open(file)
except IOError:
	print "failed to identify", file
else:
	print "image format:", im.format
	print "image mode:", im.mode
	print "image size:", im.size
	if im.info.has_key("description"):
	print "image description:", im.info["description"]

MODEBITS = {
	# bits per pixel for common PIL image modes
	"1": 1, "P": 8, "L": 8, "RGB": 24, "RGBA": 32, "CMYK": 32
}

try:
	bits = MODEBITS[im.mode]
	imagebytes = ((im.size[0] * bits + 7) / 8) * im.size[1]
	filebytes = os.stat(file)[ST_SIZE]
except (IOError, KeyError):
	print "failed to determine compression ratio for", file
else:
	print "compression:", round(imagebytes / filebytes, 2), "times"

'''
The compression ratio is close to 1 for non-compressed formats 
like BMP and PPM, typically 2-10 for GIF and other lossless compression 
formats, and 10-20 for JPEG files.
'''