i wrote a node to subscribe to topic imagetopic2 which is publised by a node after using cv bridge to convert to illmage format then i run this node to detect blue color in the image. but i get the error. anyone can help to identify the problem?

Bad argument (Array should be CvMat or IplImage) in cvGetSize, file /tmp/buildd/ros-fuerte-opencv2-2.4.2-1precise-20130312-1308/modules/core/src/array.cpp, line 1238 Traceback (most recent call last): File "/home/wh07/fuerteworkspace/swri-ros-pkg2/OpenCV/src/Track.py", line 80, in colortracker.run() File "/home/wh07/fuerteworkspace/swri-ros-pkg2/OpenCV/src/Track.py", line 39, in run hsvimg = cv.CreateImage(cv.GetSize(img), 8, 3) cv2.error: Array should be CvMat or IplImage

!/usr/bin/env python

import roslib roslib.loadmanifest('OpenCV') import sys import rospy import cv from stdmsgs.msg import String from sensormsgs.msg import Image from cvbridge import CvBridge, CvBridgeError import cv2 import numpy as np

colortrackerwindow = "Color Tracker"

class ColorTracker:

def __init__(self):
    self.image_pub = rospy.Publisher("image_topic_3",Image)


    cv.NamedWindow( color_tracker_window, 1 )
    self.capture = cv.CaptureFromCAM(0)

    self.image_sub = rospy.Subscriber("image_topic_2",Image)

    cap = cv2.VideoCapture(0)

    while(1):

# Take each frame
      _, frame = cap.read()

# Convert BGR to HSV
      hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)

# define range of blue color in HSV
      lower_blue = np.array([110,50,50])
      upper_blue = np.array([130,255,255])

# Threshold the HSV image to get only blue colors
      mask = cv2.inRange(hsv, lower_green, upper_green)

# Bitwise-AND mask and original image
      res = cv2.bitwise_and(frame,frame, mask= mask)

      cv2.imshow('frame',frame)
      cv2.imshow('mask',mask)
      cv2.imshow('res',res)
      k = cv2.waitKey(5) & 0xFF
      if k == 27:
          break

    cv2.destroyAllWindows()

if name=="main": colortracker = ColorTracker() colortracker.run()

def main(args): ic = imageconverter() rospy.initnode('imageconverter', anonymous=True) try: rospy.spin() except KeyboardInterrupt: print "except shutting down" cv2.destroyAllWindows() if _name__ == 'main':