Problem viewing images using python-opencv

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I have trouble viewing color images from R200 realsense camera using the python-opencv interface. The window is blank when I run this script. When I comment out'cv2.namedWindow("Image window", 1)', it shows the first image.

-P

import roslib
import sys
import rospy
import cv2
from std_msgs.msg import String
from geometry_msgs.msg import Twist
from sensor_msgs.msg import Image
from rospy.numpy_msg import numpy_msg
#from rospy_tutorials.msg import Floats
from cv_bridge import CvBridge, CvBridgeError
import numpy as np
import math;
import cv2;
#import matplotlib.pyplot as plt;
import sys;
#import caffe;
import socket;
#from sklearn import datasets;
import subprocess;

import message_filters
from rospy.numpy_msg import numpy_msg
import time
#####################

import os.path


class image_converter:

# Initializing variables, publishers and subscribers
  def __init__(self):
    print 'show window'
    cv2.namedWindow("Image window", 1)
#    print 'start bridge and subscribe'
    self.bridge = CvBridge()

    self.image_sub = rospy.Subscriber("/camera/rgb/image_color", Image, self.callback)


  # The main callback that processes the color and depth data.      
  def callback(self,color):


    start = time.time()
    # acquiring color and depth data (from ROS-python tutorial)
    try:

      frame = self.bridge.imgmsg_to_cv2(color, "bgr8")
    except CvBridgeError, e:
      print e

    frame = np.array(frame, dtype=np.uint8)

    cv2.imshow("Image window", frame)
    print 'test'
    cv2.waitKey(0)


def main(args):
  ic = image_converter()
  rospy.init_node('image_converter', anonymous=True)
  try:
    rospy.spin()
  except KeyboardInterrupt:
    print "Shutting down"
  cv2.destroyAllWindows()

if __name__ == '__main__':
    main(sys.argv)