subscribe sensor_message/Image without opencv

edit

I would like to print(or just read) the content(i.e. the 'data' field) of a ROS topic of type "sensor_message/Image", but without OpenCV(for performance consideration). Here is a snippet of some naive codes that I've tried:

#!/usr/bin/env python
PKG = 'numpy_tutorial'
import roslib; roslib.load_manifest(PKG)
import rospy 
from sensor_msgs.msg import Image 

def callback(Image):
    print (Image.data)

def listener():
    rospy.init_node('listener')
    rospy.Subscriber('/camera/color/image_raw', Image, callback)
    rospy.spin()

if __name__ == '__main__':
    listener()

But it just prints some unreadable characters in console, I anticipated that it's not just 'print(Image.data)', but how can I do it correctly in python? besides, my ultimate goal is to transform 'data' to numpy array format.

Many thanks in advance!